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Abstract
Alterations in cerebral blood flow are common in several neurological diseases among the elderly including stroke, cerebral small vessel disease, vascular dementia, and Alzheimer's disease. 4D flow magnetic resonance imaging (MRI) is a relatively new technique to investigate cerebrovascular disease, and makes it possible to obtain time-resolved blood flow measurements of the entire cerebral arterial venous vasculature and can be used to derive a repertoire of hemodynamic biomarkers indicative of cerebrovascular health. The information that can be obtained from one single 4D flow MRI scan allows both the investigation of aberrant flow patterns at a focal location in the vasculature as well as estimations of brain-wide disturbances in blood flow. Such focal and global hemodynamic biomarkers show the potential of being sensitive to impending cerebrovascular disease and disease progression and can also become useful during planning and follow-up of interventions aiming to restore a normal cerebral circulation. Here, we describe 4D flow MRI approaches for analyzing the cerebral vasculature. We then survey key hemodynamic biomarkers that can be reliably assessed using the technique. Finally, we highlight cerebrovascular diseases where one or multiple hemodynamic biomarkers are of central interest.
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Affiliation(s)
- Anders Wåhlin
- Department of Radiation Sciences, Umeå University, Umeå, Sweden.,Department of Applied Physics and Electronics, Umeå University, Umeå, Sweden.,Umeå Center for Functional Brain Imaging (UFBI), Umeå University, Umeå, Sweden
| | - Anders Eklund
- Department of Radiation Sciences, Umeå University, Umeå, Sweden.,Umeå Center for Functional Brain Imaging (UFBI), Umeå University, Umeå, Sweden
| | - Jan Malm
- Department of Clinical Science and Neurosciences, Umeå University, Umeå, Sweden
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2
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Kim D, Eisenmenger L, Turski P, Johnson KM. Simultaneous 3D-TOF angiography and 4D-flow MRI with enhanced flow signal using multiple overlapping thin slab acquisition and magnetization transfer. Magn Reson Med 2021; 87:1401-1417. [PMID: 34708445 DOI: 10.1002/mrm.29060] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2021] [Revised: 10/03/2021] [Accepted: 10/08/2021] [Indexed: 12/29/2022]
Abstract
PURPOSE To investigate the fusion of 3D time-of-flight principles into 4D-flow MRI to enhance vessel contrast and signal without an exogenous contrast agent, enabling simultaneous in-flow based angiograms. METHODS A 4D-flow MRI technique was developed consisting of multiple overlapping slabs with intermittent magnetization transfer preparation. The scan time penalty associated with multiple slab acquisitions was mitigated by using undersampled distributed spiral trajectories and compressed sensing reconstruction. A flow phantom was used to characterize in-flow enhancement, velocity noise improvement, and flow rate measurements against the single-slab 4D-flow MRI. In a patient-volunteer cohort (n = 15), magnitude-based angiograms were radiologically evaluated against 3D time-of-flight, and velocity measurements were compared pixel-wise against single-slab and contrast-enhanced 4D-flow MRI. RESULTS Multiple-slab acquisitions, together with magnetization transfer preparation, substantially improved vessel signal, contrast, and vessel conspicuity in magnitude angiograms. Both clinical 3D time-of-flight and the proposed technique produced equivalent vessel depictions with no statistically significant difference (p < .1). Both techniques also produced clear depictions of brain aneurysms in all patients; however, very small vessels tended to show reduced conspicuity in the proposed technique. Velocity measurements agreed with contrast-enhanced and single-slab scans with high correlations (R2 = 0.941-0.974) and agreements (slopes = 0.994-1.071). Slab boundary and magnetization transfer-related artifacts were not observed in velocity measurements, and velocity noise was reduced with in-flow enhancement over single-slab scans (phantom). CONCLUSION The vessel signal and contrast can be improved in 4D-flow MRI without exogenous contrast agents by utilizing in-flow enhancement, efficient sampling, and compressed sensing. The in-flow enhancement also enables simultaneous 3D time-of-flight angiograms useful for flow quantification and diagnosis.
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Affiliation(s)
- Dahan Kim
- Department of Physics, University of Wisconsin, Madison, Wisconsin, USA.,Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
| | - Laura Eisenmenger
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
| | - Patrick Turski
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
| | - Kevin M Johnson
- Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA.,Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
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3
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Eisenmenger LB, Rivera-Rivera LA, Johnson KM, Drolet BA. Utilisation of advanced MRI techniques to understand neurovascular complications of PHACE syndrome: a case of arterial stenosis and dissection. BMJ Case Rep 2020; 13:13/9/e235992. [PMID: 32928832 PMCID: PMC7490943 DOI: 10.1136/bcr-2020-235992] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
PHACE syndrome is a rare disorder with posterior fossa brain malformations, segmental infantile haemangiomas, arterial anomalies, cardiac defects and eye anomalies. Cerebral and cervical arterial abnormalities occur commonly in these patients, predisposing subjects with PHACE syndrome to neurovascular complications including migraine-like headaches, moyamoya vasculopathy, arterial dissection and arterial ischaemia stroke. We leveraged institutional MRI protocols developed for adult neurovascular disease to better elucidate the pathogenesis of the arterial alternations observed in PHACE. Using high-resolution vessel wall and 4D flow MRI, we demonstrated enhancement, focal dissection and altered blood flow in a 7-year-old girl with PHACE syndrome. This is the first-time vessel wall imaging has been used to detail the known arterial changes in PHACE, and these findings may indicate that progressive vascular narrowing and vessel wall changes/inflammation are a factor in chronic headaches and other arterial complications seen in subjects with PHACE syndrome.
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Affiliation(s)
| | | | - Kevin M Johnson
- Radiology, University of Wisconsin, Madison, Wisconsin, USA.,Medical Physics, University of Wisconsin, Madison, Wisconsin, USA
| | - Beth A Drolet
- Dermatology, University of Wisconsin, Madison, Wisconsin, USA
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4
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Castle-Kirszbaum M, Maingard J, Lim RP, Barras CD, Kok HK, Chandra RV, Chong W, Asadi H. Four-Dimensional Magnetic Resonance Imaging Assessment of Intracranial Aneurysms: A State-of-the-Art Review. Neurosurgery 2020; 87:453-465. [PMID: 32140714 DOI: 10.1093/neuros/nyaa021] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2019] [Accepted: 12/15/2019] [Indexed: 11/14/2022] Open
Abstract
Treatment of unruptured intracranial aneurysms can reduce the risk of subarachnoid hemorrhage and its associated morbidity and mortality. However, current methods to predict the risk of rupture and optimize treatment strategies for intracranial aneurysms are limited. Assessment of intra-aneurysmal flow using 4-dimensional magnetic resonance imaging (4D MRI) is a novel tool that could be used to guide therapy. A systematic search of the literature was performed to provide a state-of-the-art review on 4D MRI assessment of unruptured intracranial aneurysms. A total of 18 studies were available for review. Eccentric flow on 4D MRI is associated with a greater aspect ratio and peak wall shear stress (WSS). WSS, vorticity, and peak velocity are greater in saccular than fusiform aneurysms. Unstable aneurysms are associated with greater WSS, peak wall stress, and flow jet angle and may exhibit wall enhancement. In comparison to computational fluid dynamics (CFD), 4D MRI has a lower spatial resolution and reports lower WSS and velocity magnitudes, but these parameters equalize when spatial resolution is matched. 4D MRI demonstrates the intra-aneurysmal hemodynamic changes associated with flow diversion, including significantly decreased flow velocity. Thus, 4D MRI is a novel, noninvasive imaging tool used for the evaluation of hemodynamics within intracranial aneurysms. Hemodynamic indices derived from 4D MRI appear to correlate well with the simulated (CFD) values and may be used to measure the success of endovascular therapies and risk factors for aneurysm growth and rupture.
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Affiliation(s)
- Mendel Castle-Kirszbaum
- NeuroInterventional Radiology Unit, Monash Health, Melbourne, Australia.,Department of Neurosurgery, Monash Health, Melbourne, Australia
| | - Julian Maingard
- NeuroInterventional Radiology Unit, Monash Health, Melbourne, Australia.,Department of Imaging, Monash Health, Melbourne, Australia.,School of Medicine, Deakin University, Victoria, Australia
| | - Ruth P Lim
- Austin Health, Melbourne, Australia.,The University of Melbourne, Melbourne, Australia
| | - Christen D Barras
- Department of Radiology, Royal Adelaide Hospital, The University of Adelaide, Australia.,South Australian Health and Medical Research Institute, Adelaide, Australia
| | - Hong Kuan Kok
- School of Medicine, Deakin University, Victoria, Australia.,Department of Radiology Northern Health, Melbourne, Australia
| | - Ronil V Chandra
- NeuroInterventional Radiology Unit, Monash Health, Melbourne, Australia.,Department of Imaging, Monash Health, Melbourne, Australia.,Monash University, Melbourne, Australia
| | - Winston Chong
- NeuroInterventional Radiology Unit, Monash Health, Melbourne, Australia.,Department of Imaging, Monash Health, Melbourne, Australia.,Monash University, Melbourne, Australia
| | - Hamed Asadi
- NeuroInterventional Radiology Unit, Monash Health, Melbourne, Australia.,Department of Imaging, Monash Health, Melbourne, Australia.,School of Medicine, Deakin University, Victoria, Australia.,Austin Health, Melbourne, Australia
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5
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Sugiyama M, Takehara Y, Kawate M, Ooishi N, Terada M, Isoda H, Sakahara H, Naganawa S, Johnson KM, Wieben O, Wakayama T, Nozaki A, Kabasawa H. Optimal Plane Selection for Measuring Post-prandial Blood Flow Increase within the Superior Mesenteric Artery: Analysis Using 4D Flow and Computational Fluid Dynamics. Magn Reson Med Sci 2020; 19:366-374. [PMID: 32009062 PMCID: PMC7809144 DOI: 10.2463/mrms.mp.2019-0089] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
PURPOSE 2D cine phase contrast (PC)-MRI is a standard velocimetry for the superior mesenteric artery (SMA); however, the optimal localization of the measurement plane has never been fully discussed previously. The purpose of this Institutional Review Board approved prospective and single arm study is to test whether flow velocimetry of the SMA with combined use of 2D cine PC-MRI and meal challenge is dependent on the localizations of the measurement planes and to seek optimal section for velocimetry. METHODS Seven healthy volunteers underwent cardiac phase resolved ECG gated 2D cine PC-MRI pre- and 30 min post-meal challenge at three measurement planes: proximal, curved mid section and distal straight section of the SMA at 3T. 4D Flow using 3D cine PC-MRI with vastly undersampled isotropic projection imaging (PC VIPR) was also performed right after 2D cine PC-MRI to delineate the flow dynamics within the SMA using streamline analysis. Two radiologists measured flow velocities, and rated the appearances of the abnormal flow in the SMA on streamlines derived from the 4D Flow and the computational fluid dynamics (CFD). RESULTS 2D cine PC-MRI measured increased temporally averaged flow velocity (mm/s) after the meal challenge only in the proximal (129.3 vs. 97.8, P = 0.0313) and distal section (166.9 vs. 96.2, P = 0.0313), not in the curved mid section (113.1 vs. 85.5, P = 0.0625). The average velocities were highest and their standard errors (8.5-26.5) were smallest at the distal straight section both before and after the meal challenge as compared with other sections. The streamline analysis depicted more frequent appearances of vertical or helical flow in the curved mid section both on 4D Flow and CFD (κ: 0.27-0.68). CONCLUSION SMA velocimetry with 2D cine PC-MRI was dependent on the localization of the measurement planes. Distal straight section, not in the curved mid section is recommended for MR velocimetry.
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Affiliation(s)
- Masataka Sugiyama
- Department of Fundamental Development for Advanced Low Invasive Diagnostic Imaging, Nagoya University Graduate School of Medicine
| | - Yasuo Takehara
- Department of Fundamental Development for Advanced Low Invasive Diagnostic Imaging, Nagoya University Graduate School of Medicine
| | - Masanori Kawate
- Department of Radiological Technology, Hamamatsu University Hospital
| | - Naoki Ooishi
- Department of Radiological Technology, Hamamatsu University Hospital
| | - Masaki Terada
- Department of Radiological Technology, Iwata Municipal Hospital
| | - Haruo Isoda
- Brain & Mind Research Center, Nagoya University
| | - Harumi Sakahara
- Department of Diagnostic Radiology & Nuclear Medicine, Hamamatsu University School of Medicine
| | - Shinji Naganawa
- Department of Radiology, Nagoya University Graduate School of Medicine
| | - Kevin M Johnson
- Department of Medical Physics, University of Wisconsin.,Department of Radiology, University of Wisconsin
| | - Oliver Wieben
- Department of Medical Physics, University of Wisconsin.,Department of Radiology, University of Wisconsin
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6
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Li Y, Ahmed R, Rivera-Rivera LA, Stadler JA, Turski P, Aagaard-Kienitz B. Serial Quantitative and Qualitative Measurements of Flow in Vein of Galen Malformations Using 4-Dimensional Flow Magnetic Resonance Imaging (Phase Contrast Vastly undersampled Isotropic PRojection). World Neurosurg 2019; 126:405-412. [PMID: 30849554 PMCID: PMC6924166 DOI: 10.1016/j.wneu.2019.02.131] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2018] [Revised: 02/20/2019] [Accepted: 02/21/2019] [Indexed: 11/19/2022]
Abstract
BACKGROUND Vein of Galen malformations (VoGMs) induce cerebrovascular dysfunction through arterial steal and venous hypertension resulting, if untreated, in severe neurologic morbidity and mortality. Noninvasive techniques for quantitative, serial evaluation of cerebrovascular hemodynamics in VoGMs are lacking. This proof of concept study using quantitative blood flow measurements from 4-dimensional flow magnetic resonance imaging may be useful as a noninvasive biomarker to guide timing of intervention and assess disease progression and treatment outcomes. CASE DESCRIPTION Between July 2016 and July 2018, 4 patients harboring VoGMs underwent Phase Contrast Vastly undersampled Isotropic PRojection (PCVIPR) imaging at the University of Wisconsin Hospitals and Clinics. We applied PCVIPR imaging to assess its potential for obtaining anatomic and physiologic flow data before and after surgical embolization of VoGMs. Hemodynamic pressure parameters obtained from PCVIPR imaging were compared with stump pressures recorded in vivo. We found a decrease in mean arterial pressure from 97 mm Hg pretreatment to 65 mm Hg post treatment. These findings corroborate the decrement in venous pressure gradients documented on PCVIPR imaging. For all patients, pressure gradient changes on PCVIPR imaging correlated with in vivo arterial pressures and aided in clinical decision related to cerebrovascular evaluation, treatment planning, and clinical course. CONCLUSIONS Four-dimensional flow magnetic resonance imaging/PCVIPR imaging has a potential role in determining endovascular embolization and therapeutic outcomes on the basis of objective and reproducible hemodynamic characteristics of the vascular lesion. It represents a novel, noninvasive approach that may guide the extent and timing of therapeutic intervention and treatment of cerebrovascular diseases in pediatric patients.
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Affiliation(s)
- Yiping Li
- Department of Neurological Surgery, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
| | - Raheel Ahmed
- Department of Neurological Surgery, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
| | - Leonardo A Rivera-Rivera
- Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
| | - James A Stadler
- Department of Neurological Surgery, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
| | - Patrick Turski
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
| | - Beverly Aagaard-Kienitz
- Department of Neurological Surgery, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA; Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA.
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7
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Nguyen TQ, Hansen KL, Bechsgaard T, Lönn L, Jensen JA, Nielsen MB. Non-Invasive Assessment of Intravascular Pressure Gradients: A Review of Current and Proposed Novel Methods. Diagnostics (Basel) 2018; 9:diagnostics9010005. [PMID: 30597993 PMCID: PMC6468662 DOI: 10.3390/diagnostics9010005] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2018] [Revised: 12/21/2018] [Accepted: 12/26/2018] [Indexed: 11/16/2022] Open
Abstract
Invasive catheterization is associated with a low risk of serious complications. However, although it is the gold standard for measuring pressure gradients, it induces changes to blood flow and requires significant resources. Therefore, non-invasive alternatives are urgently needed. Pressure gradients are routinely estimated non-invasively in clinical settings using ultrasound and calculated with the simplified Bernoulli equation, a method with several limitations. A PubMed literature search on validation of non-invasive techniques was conducted, and studies were included if non-invasively estimated pressure gradients were compared with invasively measured pressure gradients in vivo. Pressure gradients were mainly estimated from velocities obtained with Doppler ultrasound or magnetic resonance imaging. Most studies used the simplified Bernoulli equation, but more recent studies have employed the expanded Bernoulli and Navier⁻Stokes equations. Overall, the studies reported good correlation between non-invasive estimation of pressure gradients and catheterization. Despite having strong correlations, several studies reported the non-invasive techniques to either overestimate or underestimate the invasive measurements, thus questioning the accuracy of the non-invasive methods. In conclusion, more advanced imaging techniques may be needed to overcome the shortcomings of current methods.
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Affiliation(s)
- Tin-Quoc Nguyen
- Department of Diagnostic Radiology, Copenhagen University Hospital, Blegdamsvej 9, 2100 Copenhagen, Denmark.
- Department of Clinical Medicine, University of Copenhagen, Blegdamsvej 3B, 2200 Copenhagen, Denmark.
| | - Kristoffer Lindskov Hansen
- Department of Diagnostic Radiology, Copenhagen University Hospital, Blegdamsvej 9, 2100 Copenhagen, Denmark.
- Department of Clinical Medicine, University of Copenhagen, Blegdamsvej 3B, 2200 Copenhagen, Denmark.
| | - Thor Bechsgaard
- Department of Radiology, Odense University Hospital Svendborg Hospital, Baagøes Alle 31, 5700 Svendborg, Denmark.
| | - Lars Lönn
- Department of Diagnostic Radiology, Copenhagen University Hospital, Blegdamsvej 9, 2100 Copenhagen, Denmark.
- Department of Clinical Medicine, University of Copenhagen, Blegdamsvej 3B, 2200 Copenhagen, Denmark.
| | - Jørgen Arendt Jensen
- Center for Fast Ultrasound Imaging, DTU Elektro, Technical University of Denmark, Ørsteds Plads Building 349, 2800 Lyngby, Denmark.
| | - Michael Bachmann Nielsen
- Department of Diagnostic Radiology, Copenhagen University Hospital, Blegdamsvej 9, 2100 Copenhagen, Denmark.
- Department of Clinical Medicine, University of Copenhagen, Blegdamsvej 3B, 2200 Copenhagen, Denmark.
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8
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Rivera-Rivera LA, Johnson KM, Turski PA, Wieben O. Pressure Mapping and Hemodynamic Assessment of Intracranial Dural Sinuses and Dural Arteriovenous Fistulas with 4D Flow MRI. AJNR Am J Neuroradiol 2017; 39:485-487. [PMID: 29269408 DOI: 10.3174/ajnr.a5494] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2017] [Accepted: 10/26/2017] [Indexed: 11/07/2022]
Abstract
The feasibility of 4D flow MR imaging to visualize flow patterns and generate relative pressure maps in the dural venous sinus in healthy subjects (n = 60) and patients with dural arteriovenous fistulas (n = 7) was investigated. Dural venous drainage was classified based on torcular Herophili anatomy by using 4D flow MR imaging-derived angiograms and magnitude images. Subjects were scanned in a 3T clinical MR imaging system. 4D flow MR imaging enabled noninvasive characterization of dural sinus anatomy and mapping of relative pressure differences.
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Affiliation(s)
- L A Rivera-Rivera
- From the Departments of Medical Physics (L.A.R.-R., K.M.J., P.A.T., O.W.)
| | - K M Johnson
- From the Departments of Medical Physics (L.A.R.-R., K.M.J., P.A.T., O.W.).,Radiology (K.M.J., P.A.T., O.W.), University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin
| | - P A Turski
- From the Departments of Medical Physics (L.A.R.-R., K.M.J., P.A.T., O.W.).,Radiology (K.M.J., P.A.T., O.W.), University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin
| | - O Wieben
- From the Departments of Medical Physics (L.A.R.-R., K.M.J., P.A.T., O.W.) .,Radiology (K.M.J., P.A.T., O.W.), University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin
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9
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Fatehi Hassanabad A, Barker AJ, Guzzardi D, Markl M, Malaisrie C, McCarthy PM, Fedak PWM. Evolution of Precision Medicine and Surgical Strategies for Bicuspid Aortic Valve-Associated Aortopathy. Front Physiol 2017; 8:475. [PMID: 28740468 PMCID: PMC5502281 DOI: 10.3389/fphys.2017.00475] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2017] [Accepted: 06/21/2017] [Indexed: 12/15/2022] Open
Abstract
Bicuspid aortic valve (BAV) is a common congenital cardiac malformation affecting 1–2% of people. BAV results from fusion of two adjacent aortic valve cusps, and is associated with dilatation of the aorta, known as bicuspid valve associated aortopathy. Bicuspid valve aortopathy is progressive and associated with catastrophic clinical events, such as aortic dissection and rupture. Therefore, frequent monitoring and early intervention with prophylactic surgical resection of the proximal aorta is often recommended. However, the specific pattern of aortopathy is highly variable among patients, with different segments of the ascending aorta being affected. Individual patient risks are sometimes difficult to predict. Resection strategies are informed by current surgical guidelines which are primarily based on aortic size and growth criteria. These criteria may not optimally reflect the risk of important aortic events. To address these issues in the care of patients with bicuspid valve aortopathy, our translational research group has focused on validating use of novel imaging techniques to establish non-invasive hemodynamic biomarkers for risk-stratifying BAV patients. In this article, we review recent efforts, successes, and ongoing challenges in the development of more precise and individualized surgical approaches for patients with bicuspid aortic valves and associated aortic disease.
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Affiliation(s)
- Ali Fatehi Hassanabad
- Section of Cardiac Surgery, Department of Cardiac Sciences, Cumming School of Medicine, Libin Cardiovascular Institute of Alberta, University of CalgaryCalgary, AB, Canada
| | - Alex J Barker
- Department of Radiology, Feinberg School of Medicine, Northwestern UniversityChicago, IL, United States
| | - David Guzzardi
- Section of Cardiac Surgery, Department of Cardiac Sciences, Cumming School of Medicine, Libin Cardiovascular Institute of Alberta, University of CalgaryCalgary, AB, Canada
| | - Michael Markl
- Department of Radiology, Feinberg School of Medicine, Northwestern UniversityChicago, IL, United States.,Department of Bioengineering, Feinberg School of Medicine, Northwestern UniversityChicago, IL, United States
| | - Chris Malaisrie
- Martha and Richard Melman Family Bicuspid Aortic Valve Program, Division of Cardiothoracic Surgery, Bluhm Cardiovascular Institute, Northwestern UniversityChicago, IL, United States
| | - Patrick M McCarthy
- Martha and Richard Melman Family Bicuspid Aortic Valve Program, Division of Cardiothoracic Surgery, Bluhm Cardiovascular Institute, Northwestern UniversityChicago, IL, United States
| | - Paul W M Fedak
- Section of Cardiac Surgery, Department of Cardiac Sciences, Cumming School of Medicine, Libin Cardiovascular Institute of Alberta, University of CalgaryCalgary, AB, Canada.,Martha and Richard Melman Family Bicuspid Aortic Valve Program, Division of Cardiothoracic Surgery, Bluhm Cardiovascular Institute, Northwestern UniversityChicago, IL, United States
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10
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Mikhail Kellawan J, Harrell JW, Roldan-Alzate A, Wieben O, Schrage WG. Regional hypoxic cerebral vasodilation facilitated by diameter changes primarily in anterior versus posterior circulation. J Cereb Blood Flow Metab 2017; 37:2025-2034. [PMID: 27406213 PMCID: PMC5464698 DOI: 10.1177/0271678x16659497] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The inability to quantify cerebral blood flow and changes in macrocirculation cross-sectional area in all brain regions impedes robust insight into hypoxic cerebral blood flow control. We applied four-dimensional flow magnetic resonance imaging to quantify cerebral blood flow (ml • min-1) and cross-sectional area (mm2) simultaneously in 11 arteries. In healthy adults, blood pressure, O2 Saturation (SpO2), and end-tidal CO2 were measured at baseline and steady-state hypoxia (FiO2 = 0.11). We investigated left and right: internal carotid, vertebral, middle, anterior, posterior cerebral arteries, and basilar artery. Hypoxia (SpO2 = 80±2%) increased total cerebral blood flow from 621±38 to 742±50 ml • min-1 ( p < 0.05). Hypoxia increased cerebral blood flow, except in the right posterior cerebral arteries. Hypoxia increased cross-sectional area in the anterior arteries (left and right internal carotid arteries, left and right middle, p < 0.05; left and right anterior p = 0.08) but only the right vertebral artery of the posterior circulation. Nonetheless, relative cerebral blood flow distribution and vascular reactivity (Δ%cerebral blood flow • ΔSpO2-1) were not different between arteries. Collectively, moderate hypoxia: (1) increased cerebral blood flow, but relative distribution remains similar to normoxia, (2) evokes similar vascular reactivity between 11 arteries, and (3) increased cross-sectional area primarily in the anterior arteries. This study provides the first wide-ranging, quantitative, functional and structural data regarding intracranial arteries during hypoxia in humans, highlighting cerebral blood flow regulation of microcirculation and macrocirculation differs between anterior and posterior circulation.
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Affiliation(s)
- J Mikhail Kellawan
- 1 Departments of Kinesiology, University of Wisconsin - Madison, WI, USA
| | - John W Harrell
- 1 Departments of Kinesiology, University of Wisconsin - Madison, WI, USA
| | - Alejandro Roldan-Alzate
- 2 Departments of Medical Physics, University of Wisconsin - Madison, WI, USA.,3 Departments of Radiology, University of Wisconsin - Madison, WI, USA
| | - Oliver Wieben
- 2 Departments of Medical Physics, University of Wisconsin - Madison, WI, USA.,3 Departments of Radiology, University of Wisconsin - Madison, WI, USA
| | - William G Schrage
- 1 Departments of Kinesiology, University of Wisconsin - Madison, WI, USA
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11
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Motoyama D, Ishii Y, Takehara Y, Sugiyama M, Yang W, Nasu H, Ushio T, Hirose Y, Ohishi N, Wakayama T, Kabasawa H, Johnson K, Wieben O, Sakahara H, Ozono S. Four-dimensional phase-contrast vastly undersampled isotropic projection reconstruction (4D PC-VIPR) MR evaluation of the renal arteries in transplant recipients: Preliminary results. J Magn Reson Imaging 2017; 46:595-603. [DOI: 10.1002/jmri.25607] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2016] [Accepted: 12/05/2016] [Indexed: 11/11/2022] Open
Affiliation(s)
- Daisuke Motoyama
- Department of Urology; Hamamatsu University School of Medicine; Shizuoka Japan
| | - Yasuo Ishii
- Department of Surgery; Kidney Center, Toranomon Hospital; Tokyo Japan
| | - Yasuo Takehara
- Department of Fundamental Development for Advanced Low Invasive Diagnostic Imaging; Nagoya University, Graduate School of Medicine; Nagoya Japan
| | - Masataka Sugiyama
- Department of Diagnostic Radiology & Nuclear Medicine; Hamamatsu University School of Medicine; Shizuoka Japan
| | - Wang Yang
- Department of Diagnostic Radiology & Nuclear Medicine; Hamamatsu University School of Medicine; Shizuoka Japan
| | - Hatsuko Nasu
- Department of Diagnostic Radiology & Nuclear Medicine; Hamamatsu University School of Medicine; Shizuoka Japan
| | - Takasuke Ushio
- Department of Diagnostic Radiology & Nuclear Medicine; Hamamatsu University School of Medicine; Shizuoka Japan
| | - Yuko Hirose
- Department of Diagnostic Radiology & Nuclear Medicine; Hamamatsu University School of Medicine; Shizuoka Japan
| | - Naoki Ohishi
- Department of Radiology; Hamamatsu University Hospital; Shizuoka Japan
| | - Tetsuya Wakayama
- Applied Science Laboratory Asia Pacific, GE Healthcare Japan; Tokyo Japan
| | - Hiroyuki Kabasawa
- Department of Medical Physics and Radiology; University of Wisconsin School of Medicine and Public Health; Madison Wisconsin USA
| | - Kevin Johnson
- Department of Medical Physics and Radiology; University of Wisconsin School of Medicine and Public Health; Madison Wisconsin USA
| | - Oliver Wieben
- Department of Medical Physics and Radiology; University of Wisconsin School of Medicine and Public Health; Madison Wisconsin USA
| | - Harumi Sakahara
- Department of Diagnostic Radiology & Nuclear Medicine; Hamamatsu University School of Medicine; Shizuoka Japan
| | - Seiichiro Ozono
- Department of Urology; Hamamatsu University School of Medicine; Shizuoka Japan
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12
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Deng Z, Fan Z, Lee SE, Nguyen C, Xie Y, Pang J, Bi X, Yang Q, Choi BW, Kim JS, Berman D, Chang HJ, Li D. Noninvasive measurement of pressure gradient across a coronary stenosis using phase contrast (PC)-MRI: A feasibility study. Magn Reson Med 2016; 77:529-537. [PMID: 28019028 DOI: 10.1002/mrm.26579] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2016] [Revised: 10/24/2016] [Accepted: 11/21/2016] [Indexed: 01/10/2023]
Abstract
PURPOSE To investigate the feasibility of blood pressure difference measurement, ΔP, across the coronary artery using phase contrast (PC)-MRI for potential noninvasive assessment of the functional significance of coronary artery stenosis. METHODS Three-directional velocities in the coronary arteries acquired using 2D-PC-MRI were used with the Navier-Stokes equations to derive ΔP. Repeat phantom studies were performed to assess the reproducibility of flow velocity and ΔP. ΔP derived using PC-MRI (ΔPMR ) and that obtained using pressure transducer (ΔPPT ) were compared. Reproducibility of coronary flow velocity was assessed in healthy controls (n = 11). Patients with suspected coronary artery disease (n = 6) were studied to evaluate the feasibility of ΔPMR measurement across a coronary stenosis. RESULTS Phantom: Good overall reproducibility of flow velocity and ΔP measurements and excellent correlation (ΔPMR vs ΔPPT ) was observed: intraclass correlation (ICC) of 0.95(Vz ), 0.72(Vx ), 0.73(Vy ), and 0.87(ΔPMR ) and R2 = 0.94, respectively. Human: Good reproducibility of coronary flow velocity was observed: ICC of 0.94/0.95(Vz ), 0.76/0.74(Vx ), and 0.80/0.77(Vy ) at cardiac phase 1/2. Significant (p = 0.025) increase in ΔPMR was observed in patients (6.40 ± 4.43 mmHg) versus controls (0.70 ± 0.57 mmHg). CONCLUSION ΔPMR in the coronary arteries is feasible. Upon further validation using the invasive measure, ΔPMR has the potential for noninvasive assessment of coronary artery stenosis. Magn Reson Med 77:529-537, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Zixin Deng
- Biomedical Imaging Research Institute, Department of Biomedical Sciences, Cedars-Sinai Medical Center, Los Angeles, California, USA.,Department of Bioengineering, University of California, Los Angeles, California, USA
| | - Zhaoyang Fan
- Biomedical Imaging Research Institute, Department of Biomedical Sciences, Cedars-Sinai Medical Center, Los Angeles, California, USA
| | - Sang-Eun Lee
- Division of Cardiology, Severance Cardiovascular Hospital, Seoul, South Korea
| | - Christopher Nguyen
- Biomedical Imaging Research Institute, Department of Biomedical Sciences, Cedars-Sinai Medical Center, Los Angeles, California, USA
| | - Yibin Xie
- Biomedical Imaging Research Institute, Department of Biomedical Sciences, Cedars-Sinai Medical Center, Los Angeles, California, USA
| | - Jianing Pang
- Biomedical Imaging Research Institute, Department of Biomedical Sciences, Cedars-Sinai Medical Center, Los Angeles, California, USA
| | | | - Qi Yang
- Biomedical Imaging Research Institute, Department of Biomedical Sciences, Cedars-Sinai Medical Center, Los Angeles, California, USA
| | | | - Jung-Sun Kim
- Division of Cardiology, Severance Cardiovascular Hospital, Seoul, South Korea
| | - Daniel Berman
- Biomedical Imaging Research Institute, Department of Biomedical Sciences, Cedars-Sinai Medical Center, Los Angeles, California, USA
| | - Hyuk-Jae Chang
- Division of Cardiology, Severance Cardiovascular Hospital, Seoul, South Korea
| | - Debiao Li
- Biomedical Imaging Research Institute, Department of Biomedical Sciences, Cedars-Sinai Medical Center, Los Angeles, California, USA.,Department of Bioengineering, University of California, Los Angeles, California, USA.,Department of Medicine, University of California, Los Angeles, California, USA
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13
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MacDonald ME, Dolati P, Mitha AP, Wong JH, Frayne R. Flow and pressure measurements in aneurysms and arteriovenous malformations with phase contrast MR imaging. Magn Reson Imaging 2016; 34:1322-1328. [PMID: 27469312 DOI: 10.1016/j.mri.2016.07.007] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2015] [Revised: 06/27/2016] [Accepted: 07/18/2016] [Indexed: 10/21/2022]
Abstract
PURPOSE To explore phase contrast (PC) magnetic resonance imaging of aneurysms and arteriovenous malformations (AVM). PC imaging obtains a vector field of the velocity and can yield additional hemodynamic information, including: volume flow rate (VFR) and intravascular pressure. We expect to find lower VFR distal to aneurysms and higher VFR in vessels of the AVM. MATERIALS AND METHODS Five cerebral aneurysm and three AVM patients were imaged with PC techniques and compared to VFR of a healthy cohort. VFR was calculated in vessel segments in each patient and compared statistically to the healthy cohort by computing the z-score. Intravascular pressure was calculated in the aneurysms and in the nidus of each AVM. RESULTS We found that patients with aneurysm had z<-0.48 in vessels distal to the aneurysm (reduced flow), while AVM patients had z>6 in some vessels supplying and draining the nidus (increased flow). Pressures in aneurysms were highly variable between subjects and location, while in the nidus of the AVM patients; pressure trended higher in larger AVMs. CONCLUSION The study findings confirm the expectation of lower distal flow in aneurysm and higher arterial and venous flow in AVM patients.
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Affiliation(s)
- M Ethan MacDonald
- Biomedical Engineering, University of Calgary, Calgary, AB, Canada; Radiology, University of Calgary, Calgary, AB, Canada; Clinical Neuroscience, University of Calgary, Calgary, AB, Canada; Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada; Seaman Family Magnetic Resonance Research Centre, Foothills Medical Centre, Calgary, AB, Canada.
| | - Parviz Dolati
- Radiology, University of Calgary, Calgary, AB, Canada; Clinical Neuroscience, University of Calgary, Calgary, AB, Canada; Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada; Seaman Family Magnetic Resonance Research Centre, Foothills Medical Centre, Calgary, AB, Canada
| | - Alim P Mitha
- Radiology, University of Calgary, Calgary, AB, Canada; Clinical Neuroscience, University of Calgary, Calgary, AB, Canada; Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada; Seaman Family Magnetic Resonance Research Centre, Foothills Medical Centre, Calgary, AB, Canada
| | - John H Wong
- Radiology, University of Calgary, Calgary, AB, Canada; Clinical Neuroscience, University of Calgary, Calgary, AB, Canada; Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada; Seaman Family Magnetic Resonance Research Centre, Foothills Medical Centre, Calgary, AB, Canada
| | - Richard Frayne
- Biomedical Engineering, University of Calgary, Calgary, AB, Canada; Radiology, University of Calgary, Calgary, AB, Canada; Clinical Neuroscience, University of Calgary, Calgary, AB, Canada; Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada; Seaman Family Magnetic Resonance Research Centre, Foothills Medical Centre, Calgary, AB, Canada.
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14
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Ha H, Kim GB, Kweon J, Lee SJ, Kim YH, Lee DH, Yang DH, Kim N. Hemodynamic Measurement Using Four-Dimensional Phase-Contrast MRI: Quantification of Hemodynamic Parameters and Clinical Applications. Korean J Radiol 2016; 17:445-62. [PMID: 27390537 PMCID: PMC4936168 DOI: 10.3348/kjr.2016.17.4.445] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2016] [Accepted: 04/22/2016] [Indexed: 11/21/2022] Open
Abstract
Recent improvements have been made to the use of time-resolved, three-dimensional phase-contrast (PC) magnetic resonance imaging (MRI), which is also named four-dimensional (4D) PC-MRI or 4D flow MRI, in the investigation of spatial and temporal variations in hemodynamic features in cardiovascular blood flow. The present article reviews the principle and analytical procedures of 4D PC-MRI. Various fluid dynamic biomarkers for possible clinical usage are also described, including wall shear stress, turbulent kinetic energy, and relative pressure. Lastly, this article provides an overview of the clinical applications of 4D PC-MRI in various cardiovascular regions.
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Affiliation(s)
- Hojin Ha
- POSTECH Biotech Center, Pohang University of Science and Technology, Pohang 37673, Korea
| | - Guk Bae Kim
- Asan Institute of Life Science, Asan Medical Center, University of Ulsan College of Medicine, Seoul 05505, Korea
| | - Jihoon Kweon
- Department of Cardiology, Asan Medical Center, University of Ulsan College of Medicine, Seoul 05505, Korea
| | - Sang Joon Lee
- POSTECH Biotech Center, Pohang University of Science and Technology, Pohang 37673, Korea.; Department of Mechanical Engineering, Pohang University of Science and Technology, Pohang 37673, Korea
| | - Young-Hak Kim
- Department of Cardiology, Asan Medical Center, University of Ulsan College of Medicine, Seoul 05505, Korea
| | - Deok Hee Lee
- Department of Radiology, Asan Medical Center, University of Ulsan College of Medicine, Seoul 05505, Korea
| | - Dong Hyun Yang
- Department of Radiology, Asan Medical Center, University of Ulsan College of Medicine, Seoul 05505, Korea
| | - Namkug Kim
- Department of Radiology, Asan Medical Center, University of Ulsan College of Medicine, Seoul 05505, Korea.; Department of Convergence Medicine, Asan Medical Center, University of Ulsan College of Medicine, Seoul 05505, Korea
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15
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Advanced flow MRI: emerging techniques and applications. Clin Radiol 2016; 71:779-95. [PMID: 26944696 DOI: 10.1016/j.crad.2016.01.011] [Citation(s) in RCA: 85] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2015] [Revised: 12/10/2015] [Accepted: 01/10/2016] [Indexed: 12/12/2022]
Abstract
Magnetic resonance imaging (MRI) techniques provide non-invasive and non-ionising methods for the highly accurate anatomical depiction of the heart and vessels throughout the cardiac cycle. In addition, the intrinsic sensitivity of MRI to motion offers the unique ability to acquire spatially registered blood flow simultaneously with the morphological data, within a single measurement. In clinical routine, flow MRI is typically accomplished using methods that resolve two spatial dimensions in individual planes and encode the time-resolved velocity in one principal direction, typically oriented perpendicular to the two-dimensional (2D) section. This review describes recently developed advanced MRI flow techniques, which allow for more comprehensive evaluation of blood flow characteristics, such as real-time flow imaging, 2D multiple-venc phase contrast MRI, four-dimensional (4D) flow MRI, quantification of complex haemodynamic properties, and highly accelerated flow imaging. Emerging techniques and novel applications are explored. In addition, applications of these new techniques for the improved evaluation of cardiovascular (aorta, pulmonary arteries, congenital heart disease, atrial fibrillation, coronary arteries) as well as cerebrovascular disease (intra-cranial arteries and veins) are presented.
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16
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Nayak KS, Nielsen JF, Bernstein MA, Markl M, D Gatehouse P, M Botnar R, Saloner D, Lorenz C, Wen H, S Hu B, Epstein FH, N Oshinski J, Raman SV. Cardiovascular magnetic resonance phase contrast imaging. J Cardiovasc Magn Reson 2015; 17:71. [PMID: 26254979 PMCID: PMC4529988 DOI: 10.1186/s12968-015-0172-7] [Citation(s) in RCA: 149] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2015] [Accepted: 07/16/2015] [Indexed: 11/10/2022] Open
Abstract
Cardiovascular magnetic resonance (CMR) phase contrast imaging has undergone a wide range of changes with the development and availability of improved calibration procedures, visualization tools, and analysis methods. This article provides a comprehensive review of the current state-of-the-art in CMR phase contrast imaging methodology, clinical applications including summaries of past clinical performance, and emerging research and clinical applications that utilize today's latest technology.
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Affiliation(s)
- Krishna S Nayak
- Ming Hsieh Department of Electrical Engineering, University of Southern California, 3740 McClintock Ave, EEB 406, Los Angeles, California, 90089-2564, USA.
| | - Jon-Fredrik Nielsen
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA.
| | | | - Michael Markl
- Department of Radiology, Northwestern University, Chicago, IL, USA.
| | - Peter D Gatehouse
- Cardiovascular Biomedical Research Unit, Royal Brompton Hospital, London, UK.
| | - Rene M Botnar
- Cardiovascular Imaging, Imaging Sciences Division, Kings's College London, London, UK.
| | - David Saloner
- Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, USA.
| | - Christine Lorenz
- Center for Applied Medical Imaging, Siemens Corporation, Baltimore, MD, USA.
| | - Han Wen
- Imaging Physics Laboratory, National Heart Lung and Blood Institute, Bethesda, MD, USA.
| | - Bob S Hu
- Palo Alto Medical Foundation, Palo Alto, CA, USA.
| | - Frederick H Epstein
- Departments of Radiology and Biomedical Engineering, University of Virginia, Charlottesville, VA, USA.
| | - John N Oshinski
- Departments of Radiology and Biomedical Engineering, Emory University School of Medicine, Atlanta, GA, USA.
| | - Subha V Raman
- Division of Cardiovascular Medicine, The Ohio State University, Columbus, OH, USA.
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17
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Abstract
Tremendous advances have been made in abdominopelvic MR imaging, which continue to improve image quality, and make acquisitions faster and robust. We briefly discuss the role of non-Cartesian acquisition schemes as well as dual parallel radiofrequency (RF) transmit systems in the article to further improve image quality of the abdominal MR imaging. Furthermore, the use of hybrid PET/MR systems has the potential to synergistically combine MR imaging with PET acquisition, and the evolving role of hybrid PET/MR imaging is discussed.
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Affiliation(s)
- Andrea Kierans
- Department of Radiology, New York University Langone Medical Center, 660 First Avenue, New York, NY 10016, USA
| | - Nainesh Parikh
- Department of Radiology, New York University Langone Medical Center, 660 First Avenue, New York, NY 10016, USA
| | - Hersh Chandarana
- Department of Radiology, New York University Langone Medical Center, 660 First Avenue, New York, NY 10016, USA.
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18
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MacDonald ME, Frayne R. Cerebrovascular MRI: a review of state-of-the-art approaches, methods and techniques. NMR IN BIOMEDICINE 2015; 28:767-791. [PMID: 26010775 DOI: 10.1002/nbm.3322] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/10/2014] [Revised: 04/08/2015] [Accepted: 04/09/2015] [Indexed: 06/04/2023]
Abstract
Cerebrovascular imaging is of great interest in the understanding of neurological disease. MRI is a non-invasive technology that can visualize and provide information on: (i) the structure of major blood vessels; (ii) the blood flow velocity in these vessels; and (iii) the microcirculation, including the assessment of brain perfusion. Although other medical imaging modalities can also interrogate the cerebrovascular system, MR provides a comprehensive assessment, as it can acquire many different structural and functional image contrasts whilst maintaining a high level of patient comfort and acceptance. The extent of examination is limited only by the practicalities of patient tolerance or clinical scheduling limitations. Currently, MRI methods can provide a range of metrics related to the cerebral vasculature, including: (i) major vessel anatomy via time-of-flight and contrast-enhanced imaging; (ii) blood flow velocity via phase contrast imaging; (iii) major vessel anatomy and tissue perfusion via arterial spin labeling and dynamic bolus passage approaches; and (iv) venography via susceptibility-based imaging. When designing an MRI protocol for patients with suspected cerebral vascular abnormalities, it is appropriate to have a complete understanding of when to use each of the available techniques in the 'MR angiography toolkit'. In this review article, we: (i) overview the relevant anatomy, common pathologies and alternative imaging modalities; (ii) describe the physical principles and implementations of the above listed methods; (iii) provide guidance on the selection of acquisition parameters; and (iv) describe the existing and potential applications of MRI to the cerebral vasculature and diseases. The focus of this review is on obtaining an understanding through the application of advanced MRI methodology of both normal and abnormal blood flow in the cerebrovascular arteries, capillaries and veins.
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Affiliation(s)
- Matthew Ethan MacDonald
- Biomedical Engineering, Radiology, and Clinical Neuroscience, Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada
| | - Richard Frayne
- Biomedical Engineering, Radiology, and Clinical Neuroscience, Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada
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19
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Chang W, Wu Y, Johnson K, Loecher M, Wieben O, Edjlali M, Oppenheim C, Roca P, Hald J, Aagaard-Kienitz B, Niemann D, Mistretta C, Turski P. Fast contrast-enhanced 4D MRA and 4D flow MRI using constrained reconstruction (HYPRFlow): potential applications for brain arteriovenous malformations. AJNR Am J Neuroradiol 2015; 36:1049-55. [PMID: 25698624 DOI: 10.3174/ajnr.a4245] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2014] [Accepted: 09/29/2014] [Indexed: 11/07/2022]
Abstract
BACKGROUND AND PURPOSE HYPRFlow is a novel imaging strategy that provides fast, high-resolution contrast-enhanced time-resolved images and measurement of the velocity of the entire cerebrovascular system. Our hypothesis was that the images obtained with this strategy are of adequate diagnostic image quality to delineate the major components of AVMs. MATERIALS AND METHODS HYPRFlow and 3D TOF scans were obtained in 21 patients with AVMs with correlative DSA examinations in 14 patients. The examinations were scored for image quality and graded by using the Spetzler-Martin criteria. Mean arterial transit time and overlap integrals were calculated from the dynamic image data. Volume flow rates in normal arteries and AVM feeding arteries were measured from the phase contrast data. RESULTS HYPRFlow was equivalent to 3D-TOF in delineating normal arterial anatomy, arterial feeders, and nidus size and was concordant with DSA for AVM grading and venous drainage in 13 of the 14 examinations. Mean arterial transit time on the AVM side was 0.49 seconds, and on the normal contralateral side, 2.53 seconds with P < .001. Across all 21 subjects, the mean arterial volume flow rate in the M1 segment ipsilateral to the AVM was 4.07 ± 3.04 mL/s; on the contralateral M1 segment, it was 2.09 ± 0.64 mL/s. The mean volume flow rate in the largest feeding artery to the AVM was 3.86 ± 2.74 mL/s. CONCLUSIONS HYPRFlow provides an alternative approach to the MRA evaluation of AVMs, with the advantages of increased coverage, 0.75-second temporal resolution, 0.68-mm isotropic spatial resolution, and quantitative measurement of flow in 6 minutes.
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Affiliation(s)
- W Chang
- From the Department of Radiology (W.C.), University of California, Los Angeles, Los Angeles, California
| | - Y Wu
- Medical Physics (Y.W., K.J., M.L., O.W., C.M.), University of Wisconsin School of Medicine, Madison, Wisconsin
| | - K Johnson
- Medical Physics (Y.W., K.J., M.L., O.W., C.M.), University of Wisconsin School of Medicine, Madison, Wisconsin
| | - M Loecher
- Medical Physics (Y.W., K.J., M.L., O.W., C.M.), University of Wisconsin School of Medicine, Madison, Wisconsin
| | - O Wieben
- Medical Physics (Y.W., K.J., M.L., O.W., C.M.), University of Wisconsin School of Medicine, Madison, Wisconsin
| | - M Edjlali
- Department of Radiology (M.E., C.O., P.R.), Université Paris-Descartes, Paris, France
| | - C Oppenheim
- Department of Radiology (M.E., C.O., P.R.), Université Paris-Descartes, Paris, France
| | - P Roca
- Department of Radiology (M.E., C.O., P.R.), Université Paris-Descartes, Paris, France
| | - J Hald
- Department of Radiology (J.H.), Rikshospitalet, Oslo, Norway
| | | | | | - C Mistretta
- Medical Physics (Y.W., K.J., M.L., O.W., C.M.), University of Wisconsin School of Medicine, Madison, Wisconsin
| | - P Turski
- Departments of Radiology (B.A.-K., P.T.)
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Hemodynamic alterations measured with phase-contrast MRI in a giant cerebral aneurysm treated with a flow-diverting stent. Radiol Case Rep 2015; 10:1109. [PMID: 27398123 PMCID: PMC4921189 DOI: 10.2484/rcr.v10i2.1109] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Many risk factors have been proposed in the development of the cerebral aneurysms. Hemodynamics including blood velocity, volume flow rate (VFR), and intravascular pressure are thought to be prognostic indicators of aneurysm development. We hypothesize that treatment of cerebral aneurysm using a flow-diverting stent will bring these hemodynamic parameters closer to those observed on the contralateral side. In the current study, a patient with a giant cerebral aneurysm was studied pre- and postoperatively using phase contrast MRI (PC-MRI) to measure the hemodynamic changes resulting from the deployment of a flow-diverting stent. PC-MRI was used to calculate intravascular pressure, which was compared to more invasive endovascular catheter-derived measurements. After stent placement, the measured VFRs in vessels of the treated hemisphere approached those measured on the contralateral side, and flow symmetry changed from a laterality index of -0.153 to 0.116 in the middle cerebral artery. Pressure estimates derived from the PC-MRI velocity data had an average difference of 6.1% as compared to invasive catheter transducer measurements. PC-MRI can measure the hemodynamic parameters with the same accuracy as invasive methods pre- and postoperatively.
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21
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Abstract
4D flow MRI permits a comprehensive in-vivo assessment of three-directional blood flow within 3-dimensional vascular structures throughout the cardiac cycle. Given the large coverage permitted from a 4D flow acquisition, the distribution of vessel wall and flow parameters along an entire vessel of interest can thus be derived from a single measurement without being dependent on multiple predefined 2D acquisitions. In addition to qualitative 3D visualizations of complex cardiac and vascular flow patterns, quantitative flow analysis can be performed and is complemented by the ability to compute sophisticated hemodynamic parameters, such as wall shear stress or 3D pressure difference maps. These metrics can provide information previously unavailable with conventional modalities regarding the impact of cardiovascular disease or therapy on global and regional changes in hemodynamics. This review provides an introduction to the methodological aspects of 4D flow MRI to assess vascular hemodynamics and describes its potential for the assessment and understanding of altered hemodynamics in the presence of cardiovascular disease.
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22
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Stankovic Z, Allen BD, Garcia J, Jarvis KB, Markl M. 4D flow imaging with MRI. Cardiovasc Diagn Ther 2014; 4:173-92. [PMID: 24834414 DOI: 10.3978/j.issn.2223-3652.2014.01.02] [Citation(s) in RCA: 102] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2013] [Accepted: 10/21/2013] [Indexed: 12/22/2022]
Abstract
Magnetic resonance imaging (MRI) has become an important tool for the clinical evaluation of patients with cardiovascular disease. Since its introduction in the late 1980s, 2-dimensional phase contrast MRI (2D PC-MRI) has become a routine part of standard-of-care cardiac MRI for the assessment of regional blood flow in the heart and great vessels. More recently, time-resolved PC-MRI with velocity encoding along all three flow directions and three-dimensional (3D) anatomic coverage (also termed '4D flow MRI') has been developed and applied for the evaluation of cardiovascular hemodynamics in multiple regions of the human body. 4D flow MRI allows for the comprehensive evaluation of complex blood flow patterns by 3D blood flow visualization and flexible retrospective quantification of flow parameters. Recent technical developments, including the utilization of advanced parallel imaging techniques such as k-t GRAPPA, have resulted in reasonable overall scan times, e.g., 8-12 minutes for 4D flow MRI of the aorta and 10-20 minutes for whole heart coverage. As a result, the application of 4D flow MRI in a clinical setting has become more feasible, as documented by an increased number of recent reports on the utility of the technique for the assessment of cardiac and vascular hemodynamics in patient studies. A number of studies have demonstrated the potential of 4D flow MRI to provide an improved assessment of hemodynamics which might aid in the diagnosis and therapeutic management of cardiovascular diseases. The purpose of this review is to describe the methods used for 4D flow MRI acquisition, post-processing and data analysis. In addition, the article provides an overview of the clinical applications of 4D flow MRI and includes a review of applications in the heart, thoracic aorta and hepatic system.
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Affiliation(s)
- Zoran Stankovic
- 1 Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, USA ; 2 Department Biomedical Engineering, McCormick School of Engineering, Northwestern University, Chicago, USA
| | - Bradley D Allen
- 1 Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, USA ; 2 Department Biomedical Engineering, McCormick School of Engineering, Northwestern University, Chicago, USA
| | - Julio Garcia
- 1 Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, USA ; 2 Department Biomedical Engineering, McCormick School of Engineering, Northwestern University, Chicago, USA
| | - Kelly B Jarvis
- 1 Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, USA ; 2 Department Biomedical Engineering, McCormick School of Engineering, Northwestern University, Chicago, USA
| | - Michael Markl
- 1 Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, USA ; 2 Department Biomedical Engineering, McCormick School of Engineering, Northwestern University, Chicago, USA
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23
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Edjlali M, Roca P, Gentric JC, Trystram D, Rodriguez-Régent C, Nataf F, Chrétien F, Wieben O, Turski P, Meder JF, Naggara O, Oppenheim C. Advanced technologies applied to physiopathological analysis of central nervous system aneurysms and vascular malformations. Diagn Interv Imaging 2014; 95:1187-93. [PMID: 24933269 DOI: 10.1016/j.diii.2014.05.003] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
While depiction and definition of morphological and architectural characteristics of CNS vascular disorders remains the first step of an MR analysis, emerging imaging techniques offer new functional information that might help to characterize rupture risk of CNS vascular disorders. Two main orientations are suggested by recent studies: inflammation of the vessel wall and analysis of physical constraints of blood flow using 4D flow imaging (shear parietal). This paper will focus on radiological application of 4D flow imaging and inflammation imaging, in the characterization of potential prognostic markers of CNS vascular disorders. We will review the basic technical considerations of 4D flow MRA, inflammation imaging and discuss their applications in CNS vascular disorders: aneurysms, arteriovenous malformation, dural arteriovenous fistulas. We will illustrate their potential in the development of individual rupture risk criteria in brain vascular disorders.
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Affiliation(s)
- M Edjlali
- Département de neuroradiologie, hôpital Sainte-Anne, 1, rue Cabanis, 75014 Paris, France.
| | - P Roca
- Département de neuroradiologie, hôpital Sainte-Anne, 1, rue Cabanis, 75014 Paris, France
| | - J-C Gentric
- Département de neuroradiologie, hôpital universitaire de Montréal, Québec, Canada
| | - D Trystram
- Département de neuroradiologie, hôpital Sainte-Anne, 1, rue Cabanis, 75014 Paris, France
| | - C Rodriguez-Régent
- Département de neuroradiologie, hôpital Sainte-Anne, 1, rue Cabanis, 75014 Paris, France
| | - F Nataf
- Département de neurochirurgie, hôpital Sainte-Anne, 1, rue Cabanis, 75014 Paris, France
| | - F Chrétien
- Département d'anatomopathologie, hôpital Sainte-Anne, 1, rue Cabanis, 75014 Paris, France
| | - O Wieben
- Département de physique médicale (O.W.) et de radiologie (P.T.), université du Wisconsin, Madison, Wisconsin, United States
| | - P Turski
- Département de physique médicale (O.W.) et de radiologie (P.T.), université du Wisconsin, Madison, Wisconsin, United States
| | - J-F Meder
- Département de neuroradiologie, hôpital Sainte-Anne, 1, rue Cabanis, 75014 Paris, France
| | - O Naggara
- Département de neuroradiologie, hôpital Sainte-Anne, 1, rue Cabanis, 75014 Paris, France; Département de neuroradiologie (O.N.), hôpital Necker, AP-HP, 149, rue de Sèvres, 75015 Paris, France
| | - C Oppenheim
- Département de neuroradiologie, hôpital Sainte-Anne, 1, rue Cabanis, 75014 Paris, France
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24
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Abstract
Traditionally, magnetic resonance imaging (MRI) of flow using phase contrast (PC) methods is accomplished using methods that resolve single-directional flow in two spatial dimensions (2D) of an individual slice. More recently, three-dimensional (3D) spatial encoding combined with three-directional velocity-encoded phase contrast MRI (here termed 4D flow MRI) has drawn increased attention. 4D flow MRI offers the ability to measure and to visualize the temporal evolution of complex blood flow patterns within an acquired 3D volume. Various methodological improvements permit the acquisition of 4D flow MRI data encompassing individual vascular structures and entire vascular territories such as the heart, the adjacent aorta, the carotid arteries, abdominal, or peripheral vessels within reasonable scan times. To subsequently analyze the flow data by quantitative means and visualization of complex, three-directional blood flow patterns, various tools have been proposed. This review intends to introduce currently used 4D flow MRI methods, including Cartesian and radial data acquisition, approaches for accelerated data acquisition, cardiac gating, and respiration control. Based on these developments, an overview is provided over the potential this new imaging technique has in different parts of the body from the head to the peripheral arteries.
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Affiliation(s)
- Michael Markl
- Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611, USA.
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Jiang J, Strother CM. Interactive decomposition and mapping of saccular cerebral aneurysms using harmonic functions: its first application with "patient-specific" computational fluid dynamics (CFD) simulations. IEEE TRANSACTIONS ON MEDICAL IMAGING 2013; 32:153-64. [PMID: 22955892 DOI: 10.1109/tmi.2012.2216542] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Recent developments in medical imaging and advanced computer modeling simulations) now enable studies designed to correlate either simulated or measured "patient-specific" parameters with the natural history of intracranial aneurysm i.e., ruptured or unruptured. To achieve significance, however, these studies require rigorous comparison of large amounts of data from large numbers of aneurysms, many of which are quite dissimilar anatomically. In this study, we present a method that can likely facilitate such studies as its application could potentially simplify an objective comparison of surface-based parameters of interest such as wall shear stress and blood pressure using large multi-patient, multi-institutional data sets. Based on the concept of harmonic function/field, we present a unified and simple approach for mapping the surface of an aneurysm onto a unit disc. Requiring minimal human interactions the algorithm first decomposes the vessel geometry into 1) target aneurysm and 2) parent artery and any adjacent branches; it, then, maps the segmented aneurysm surface onto a unit disk. In particular, the decomposition of the vessel geometry quantitatively exploits the unique combination of three sets of information regarding the shape of the relevant vasculature: 1) a distance metric defining the spatially varying deviation from a tubular characteristic (i.e., cylindrical structure) of a normal parent artery, 2) local curvatures and 3) local concavities at the junction/interface between an aneurysm and its parent artery. These three sets of resultant shape/geometrical data are then combined to construct a linear system of the Laplacian equation with a novel shape-sensitive weighting scheme. The solution to such a linear system is a shape-sensitive harmonic function/field whose iso-lines will densely gather at the border between the normal parent artery and the aneurysm. Finally, a simple ranking system is utilized to select the best candidate among all possible iso-lines. Quantitative analysis using “patient-specific” aneurysm geometries taken from our internal database demonstrated that the technique is robust. Similar results were obtained from aneurysms having widely different geometries (bifurcation, terminal and lateral aneurysms). Application of our method should allow for meaningful, reliable and reproducible model-to-model comparisons of surface-based physiological and hemodynamic parameters.
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Affiliation(s)
- Jingfeng Jiang
- Medical Physics Department, University of Wisconsin, Madison, WI 53705, USA.
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Grist TM, Mistretta CA, Strother CM, Turski PA. Time‐resolved angiography: Past, present, and future. J Magn Reson Imaging 2012; 36:1273-86. [DOI: 10.1002/jmri.23646] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2011] [Accepted: 02/17/2012] [Indexed: 11/08/2022] Open
Affiliation(s)
- Thomas M. Grist
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
| | - Charles A. Mistretta
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
- Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
| | - Charles M. Strother
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
| | - Patrick A. Turski
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA
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Chang W, Loecher MW, Wu Y, Niemann DB, Ciske B, Aagaard-Kienitz B, Kecskemeti S, Johnson KM, Wieben O, Mistretta C, Turski P. Hemodynamic changes in patients with arteriovenous malformations assessed using high-resolution 3D radial phase-contrast MR angiography. AJNR Am J Neuroradiol 2012; 33:1565-72. [PMID: 22499844 DOI: 10.3174/ajnr.a3010] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
BACKGROUND AND PURPOSE Arteriovenous malformations have a high lifetime risk of hemorrhage; however, treatment carries a significant risk of morbidity and mortality, including permanent neurologic sequelae. WSS and other hemodynamic parameters are altered in patients with symptomatic AVMs, and analysis of hemodynamics may have value in stratifying patients into different risk groups. In this study, we examined hemodynamic data from patients with stable symptoms and those who presented with acute symptoms to identify trends which may help in risk stratification. MATERIALS AND METHODS Phase-contrast MRA using a radial readout (PC-VIPR) is a fast, high-resolution technique that can acquire whole-brain velocity-encoded angiograms with scan times of approximately 5 minutes. Ten patients with AVMs were scanned using PC-VIPR; velocity, area, flow, and WSS in vessels feeding the AVMs and normal contralateral vessels were calculated using velocity data from the phase-contrast acquisition. RESULTS Patients with an asymptomatic presentation or mild symptoms (n = 4) had no significant difference in WSS in feeding vessels compared with normal contralateral vessels, whereas patients presenting with hemorrhage, severe headaches/seizures, or focal neurologic deficits (n = 6) had significantly higher WSS in feeding vessels compared with contralateral vessels. CONCLUSIONS In this study, we demonstrate that estimates of WSS and other hemodynamic parameters can be obtained noninvasively in patients with AVMs in clinically useful imaging times. Variation in WSS between feeders and normal vessels appears to relate to the clinical presentation of the patient. Further analysis of hemodynamic changes may improve characterization and staging of AVM patients, when combined with existing risk factors.
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Affiliation(s)
- W Chang
- Department of Medical Physics, University of Wisconsin, Madison, WI 53705, USA.
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Jiang J, Johnson K, Valen-Sendstad K, Mardal KA, Wieben O, Strother C. Flow characteristics in a canine aneurysm model: a comparison of 4D accelerated phase-contrast MR measurements and computational fluid dynamics simulations. Med Phys 2012; 38:6300-12. [PMID: 22047395 DOI: 10.1118/1.3652917] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE Our purpose was to compare quantitatively velocity fields in and around experimental canine aneurysms as measured using an accelerated 4D PC-MR angiography (MRA) method and calculated based on animal-specific CFD simulations. METHODS Two animals with a surgically created bifurcation aneurysm were imaged using an accelerated 4D PC-MRA method. Meshes were created based on the geometries obtained from the PC-MRA and simulations using "subject-specific" pulsatile velocity waveforms and geometries were then solved using a commercial CFD solver. Qualitative visual assessments and quantitative comparisons of the time-resolved velocity fields obtained from the PC-MRA measurements and the CFD simulations were performed using a defined similarity metric combining both angular and magnitude differences of vector fields. RESULTS PC-MRA and image-based CFD not only yielded visually consistent representations of 3D streamlines in and around both aneurysms, but also showed good agreement with regard to the spatial velocity distributions. The estimated similarity between time-resolved velocity fields from both techniques was reasonably high (mean value >0.60; one being the highest and zero being the lowest). Relative differences in inflow and outflow zones among selected planes were also reasonable (on the order of 10%-20%). The correlation between CFD-calculated and PC-MRA-measured time-averaged wall shear stresses was low (0.22 and 0.31, p < 0.001). CONCLUSIONS In two experimental canine aneurysms, PC-MRA and image-based CFD showed favorable agreement in intra-aneurismal velocity fields. Combining these two complementary techniques likely will further improve the ability to characterize and interpret the complex flow that occurs in human intracranial aneurysms.
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Affiliation(s)
- Jingfeng Jiang
- Medical Physics Department, University of Wisconsin-Madison School of Medicine and Public Health, Madison, WI 53705, USA.
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Penn DL, Komotar RJ, Sander Connolly E. Hemodynamic mechanisms underlying cerebral aneurysm pathogenesis. J Clin Neurosci 2011; 18:1435-8. [PMID: 21917457 DOI: 10.1016/j.jocn.2011.05.001] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2011] [Accepted: 05/10/2011] [Indexed: 11/15/2022]
Abstract
Intracranial aneurysms and associated subarachnoid hemorrhage (SAH) are predominant cerebrovascular disorders that present a significant public health risk through high rates of morbidity and mortality. Unruptured aneurysms that become large enough compress cerebral tissue and manifest various neurological signs. But the largest danger presented by these cerebrovascular lesions is from the increased likelihood that the vessel will rupture, causing a SAH, a condition that creates higher risk of cerebral ischemia through reduced cerebral blood flow and vasospasm. The specific pathophysiological mechanisms that cause these lesions are not fully understood. The current literature focuses on understanding the effects of and links between hemodynamic forces, vascular remodeling and inflammation, and genetics in aneurysm formation, development, and rupture. The present study represents a survey of the complete hemodynamic pathogenesis of aneurysmal SAH detailing the many factors and their connections that contribute to the pathophysiology of this disorder.
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Affiliation(s)
- David L Penn
- Department of Neurological Surgery, Columbia University, New York, NY, USA.
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Calderon-Arnulphi M, Amin-Hanjani S, Alaraj A, Zhao M, Du X, Ruland S, Zhou XJ, Thulborn KR, Charbel FT. In vivo evaluation of quantitative MR angiography in a canine carotid artery stenosis model. AJNR Am J Neuroradiol 2011; 32:1552-9. [PMID: 21835941 DOI: 10.3174/ajnr.a2546] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
BACKGROUND AND PURPOSE Large-vessel cerebral blood flow quantification has emerged as a potential predictor of stroke risk. QMRA uses phase-contrast techniques to noninvasively measure vessel flows. To evaluate the in vivo accuracy of QMRA for measuring the effects of progressive arterial stenosis, we compared this technique with invasive flow measurements from a sonographic transit-time flow probe in a canine model. MATERIALS AND METHODS A sonographic flow probe was implanted around the CCA of hound dogs (n = 4) under general anesthesia. Pulsatile blood flow and arterial pressure were continuously recorded during CCA flow measurements with QMRA. A vascular tourniquet was applied around the CCA to produce progressive stenosis and varying flow rates. Statistical comparisons were made by using the Pearson product moment correlation coefficient. RESULTS A total of 60 paired CCA flow measurements were compared. Mean blood flows ranged between 21 and 691 mL/min during QMRA acquisition as measured by the flow probe. The correlation coefficients between flow probe and QMRA measurements for mean, maximum, and minimum volume flow rates were 0.99 (P < .0001), 0.98 (P < .0001), and 0.96 (P < .0001), respectively. The overall proportional difference between the 2 techniques was 7.8 ± 1%. Measurements at higher flow rates and in the absence of arterial stenosis had the lowest PD. CONCLUSIONS Noninvasive CCA flow measurements by using QMRA are accurate compared with invasive flow-probe measurements in a canine arterial flow model with stenosis and may be useful for the evaluation of the hemodynamic effects of stenosis caused by cerebrovascular atherosclerosis.
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Bley TA, Johnson KM, François CJ, Reeder SB, Schiebler ML, R Landgraf B, Consigny D, Grist TM, Wieben O. Noninvasive assessment of transstenotic pressure gradients in porcine renal artery stenoses by using vastly undersampled phase-contrast MR angiography. Radiology 2011; 261:266-73. [PMID: 21813739 DOI: 10.1148/radiol.11101175] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
PURPOSE To compare noninvasive transstenotic pressure gradient (TSPG) measurements derived from high-spatial- and temporal-resolution four-dimensional magnetic resonance (MR) flow measurements with invasive measurements obtained from endovascular pressure wires with digital subtraction angiographic guidance. MATERIALS AND METHODS After Animal Care and Use Committee approval, bilateral renal artery stenosis (RAS) was created surgically in 12 swine. Respiratory-gated phase-contrast vastly undersampled isotropic projection (VIPR) MR angiography of the renal arteries was performed with a 1.5-T clinical MR system (repetition time, 11.4 msec; echo time [first echo], 3.7 msec; 18,000 projection angles; imaging volume, 260 × 260 × 200 mm; acquired isotropic spatial resolution, 1.0 × 1.0 × 1.0 mm; velocity encoding, 150 cm/sec). Velocities measured with phase-contrast VIPR were used to calculate TSPGs by using Navier-Stokes equations. These were compared with endovascular pressure measurements (mean and peak) performed by using fluoroscopic guidance with regression analysis. RESULTS In 19 renal arteries with an average stenosis of 62% (range, 0%-87%), there was excellent correlation between the noninvasive TSPG measurement with phase-contrast VIPR and invasive TSPG measurement for mean TSPG (R² = 95.4%) and strong correlation between noninvasive TSPG and invasive TSPG for the peak TSPG measures (R² = 82.6%). The phase-contrast VIPR-derived TSPG measures were slightly lower than the endovascular measurements. In four arteries with severe stenoses and one occlusion (mean, 86%; range, 75%-100%), the residual lumen within the stenosis was too small to determine TSPG with phase-contrast VIPR. CONCLUSION The unenhanced MR angiographic technique with phase-contrast VIPR allows for accurate noninvasive assessment of hemodynamic significance in a porcine model of RAS with highly accurate TSPG measurements.
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Affiliation(s)
- Thorsten A Bley
- Department of Radiology, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705-2275, USA
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Mistretta CA. Sub-Nyquist acquisition and constrained reconstruction in time resolved angiography. Med Phys 2011; 38:2975-85. [PMID: 21815371 PMCID: PMC3125079 DOI: 10.1118/1.3589132] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2011] [Revised: 04/13/2011] [Accepted: 04/13/2011] [Indexed: 11/07/2022] Open
Abstract
In 1980 DSA provided a real time series of digitally processed angiographic images that facilitated and reduced the risk of angiographic procedures. This technique has become an enabling technology for interventional radiology. Initially it was hoped that intravenous DSA could eliminate the need for arterial injections. However the 2D nature of the images resulted in overlap of vessels and repeat injections were often required. Ultimately the use of smaller arterial catheters and reduced iodine injections resulted in significant reduction in complications. During the next two decades time resolved MR DSA angiographic methods were developed that produced time series of 3D images. These 4D displays were initially limited by tradeoffs in temporal and spatial resolution when acquisitions obeying the Nyquist criteria were employed. Then substantial progress was made in the implementation of undersampled non-Cartesian acquisitions such as VIPR and constrained reconstruction methods such as HYPR, which removed this tradeoff and restored SNR usually lost by accelerated techniques. Recently, undersampled acquisition and constrained reconstruction have been applied to generate time series of 3D x-ray DSA volumes reconstructed using rotational C-arm acquisition completing a 30 year evolution from DSA to 4D DSA. These 4D DSA volumes provide a flexible series of roadmaps for interventional procedures and solve the problem of vessel overlap for intravenous angiography. Full time-dependent behavior can be visualized in three dimensions. When a biplane system is used, 4D fluoroscopy is also possible, enabling the interventionalist to track devices in vascular structures from any angle without moving the C-arm gantrys. Constrained reconstruction methods have proved useful in a broad range of medical imaging applications, where substantial acquisition accelerations and dose reductions have been reported.
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Affiliation(s)
- Charles A Mistretta
- University of Wisconsin International Center for Accelerated Medical Imaging, Department of Medical Physics, The University of Wisconsin, Madison, Wisconsin 53704, USA.
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Bock J, Frydrychowicz A, Lorenz R, Hirtler D, Barker AJ, Johnson KM, Arnold R, Burkhardt H, Hennig J, Markl M. In vivo noninvasive 4D pressure difference mapping in the human aorta: phantom comparison and application in healthy volunteers and patients. Magn Reson Med 2011; 66:1079-88. [PMID: 21437978 DOI: 10.1002/mrm.22907] [Citation(s) in RCA: 85] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2010] [Revised: 02/14/2011] [Accepted: 02/15/2011] [Indexed: 12/21/2022]
Abstract
In this work, we present a systematic phantom comparison and clinical application of noninvasive pressure difference mapping in the human aorta based on time-resolved 3D phase contrast data. Relative pressure differences were calculated based on integration and iterative refinement of pressure gradients derived from MR-based three-directional velocity vector fields (flow-sensitive 4D MRI with spatial/temporal resolution ∼ 2.1 mm(3)/40 ms) using the Navier-Stokes equation. After in vitro study using a stenosis phantom, time-resolved 3D pressure gradients were systematically evaluated in the thoracic aorta in a group of 12 healthy subjects and 6 patients after repair for aortic coarctation. Results from the phantom study showed good agreement with expected values and standard methods (Bernoulli). Data of healthy subjects showed good intersubject consistency and good agreement with the literature. In patients, pressure waveforms showed elevated peak values. Pressure gradients across the stenosis were compared with reference measurements from Doppler ultrasound. The MRI findings demonstrated a significant correlation (r = 0.96, P < 0.05) but moderate underestimation (14.7% ± 15.5%) compared with ultrasound when the maximum pressure difference for all possible paths connecting proximal and distal locations of the stenosis were used. This study demonstrates the potential of the applied approach to derive additional quantitative information such as pressure gradients from time-resolved 3D phase contrast MRI.
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Affiliation(s)
- Jelena Bock
- Department of Radiology, Medical Physics, University Medical Center Freiburg, Freiburg, Germany.
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Markl M, Kilner PJ, Ebbers T. Comprehensive 4D velocity mapping of the heart and great vessels by cardiovascular magnetic resonance. J Cardiovasc Magn Reson 2011; 13:7. [PMID: 21235751 PMCID: PMC3025879 DOI: 10.1186/1532-429x-13-7] [Citation(s) in RCA: 285] [Impact Index Per Article: 21.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2010] [Accepted: 01/14/2011] [Indexed: 01/20/2023] Open
Abstract
BACKGROUND Phase contrast cardiovascular magnetic resonance (CMR) is able to measure all three directional components of the velocities of blood flow relative to the three spatial dimensions and the time course of the heart cycle. In this article, methods used for the acquisition, visualization, and quantification of such datasets are reviewed and illustrated. METHODS Currently, the acquisition of 3D cine (4D) phase contrast velocity data, synchronized relative to both cardiac and respiratory movements takes about ten minutes or more, even when using parallel imaging and optimized pulse sequence design. The large resulting datasets need appropriate post processing for the visualization of multidirectional flow, for example as vector fields, pathlines or streamlines, or for retrospective volumetric quantification. APPLICATIONS Multidirectional velocity acquisitions have provided 3D visualization of large scale flow features of the healthy heart and great vessels, and have shown altered patterns of flow in abnormal chambers and vessels. Clinically relevant examples include retrograde streams in atheromatous descending aortas as potential thrombo-embolic pathways in patients with cryptogenic stroke and marked variations of flow visualized in common aortic pathologies. Compared to standard clinical tools, 4D velocity mapping offers the potential for retrospective quantification of flow and other hemodynamic parameters. CONCLUSIONS Multidirectional, 3D cine velocity acquisitions are contributing to the understanding of normal and pathologically altered blood flow features. Although more rapid and user-friendly strategies for acquisition and analysis may be needed before 4D velocity acquisitions come to be adopted in routine clinical CMR, their capacity to measure multidirectional flows throughout a study volume has contributed novel insights into cardiovascular fluid dynamics in health and disease.
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Affiliation(s)
- Michael Markl
- Department of Radiology, Medical Physics, University Hospital Freiburg, Germany
| | - Philip J Kilner
- CMR Unit, Royal Brompton Hospital and Imperial College, London, UK
| | - Tino Ebbers
- Center for Medical Image Science and Visualization, Linköping University, Sweden
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Chang W, Landgraf B, Johnson KM, Kecskemeti S, Wu Y, Velikina J, Rowley H, Wieben O, Mistretta C, Turski P. Velocity measurements in the middle cerebral arteries of healthy volunteers using 3D radial phase-contrast HYPRFlow: comparison with transcranial Doppler sonography and 2D phase-contrast MR imaging. AJNR Am J Neuroradiol 2011; 32:54-9. [PMID: 20947642 DOI: 10.3174/ajnr.a2240] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
BACKGROUND AND PURPOSE We have developed PC HYPRFlow, a comprehensive MRA technique that includes a whole-brain CE dynamic series followed by PC velocity-encoding, yielding a time series of high-resolution morphologic angiograms with associated velocity information. In this study, we present velocity data acquired by using the PC component of PC HYPRFlow (PC-VIPR). MATERIALS AND METHODS Ten healthy volunteers (6 women, 4 men) were scanned by using PC HYPRFlow and 2D-PC imaging, immediately followed by velocity measurements by using TCD. Velocity measurements were made in the M1 segments of the MCAs from the PC-VIPR, 2D-PC, and TCD examinations. RESULTS PC-VIPR showed approximately 30% lower mean velocity compared with TCD, consistent with other comparisons of TCD with PC-MRA. The correlation with TCD was r = 0.793, and the correlation of PC-VIPR with 2D-PC was r = 0.723. CONCLUSIONS PC-VIPR is a technique capable of acquiring high-resolution MRA of diagnostic quality with velocity data comparable with TCD and 2D-PC. The combination of velocity information and fast high-resolution whole-brain morphologic angiograms makes PC HYPRFlow an attractive alternative to current MRA methods.
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Affiliation(s)
- W Chang
- Department of Medical Physics, University of Wisconsin, Madison, Wisconsin, USA.
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Delles M, Rengier F, Ley S, von Tengg-Kobligk H, Kauczor HU, Dillmann R, Unterhinninghofen R. Polynomial regularization for robust MRI-based estimation of blood flow velocities and pressure gradients. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2011; 2011:6829-6832. [PMID: 22255907 DOI: 10.1109/iembs.2011.6091684] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
In cardiovascular diagnostics, phase-contrast MRI is a valuable technique for measuring blood flow velocities and computing blood pressure values. Unfortunately, both velocity and pressure data typically suffer from the strong image noise of velocity-encoded MRI. In the past, separate approaches of regularization with physical a-priori knowledge and data representation with continuous functions have been proposed to overcome these drawbacks. In this article, we investigate polynomial regularization as an exemplary specification of combining these two techniques. We perform time-resolved three-dimensional velocity measurements and pressure gradient computations on MRI acquisitions of steady flow in a physical phantom. Results based on the higher quality temporal mean data are used as a reference. Thereby, we investigate the performance of our approach of polynomial regularization, which reduces the root mean squared errors to the reference data by 45% for velocities and 60% for pressure gradients.
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Affiliation(s)
- Michael Delles
- Department of Diagnostic and Interventional Radiology, University Hospital Heidelberg, 69120 Heidelberg, Germany.
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Wu Y, Chang W, Johnson KM, Velikina J, Rowley H, Mistretta C, Turski P. Fast whole-brain 4D contrast-enhanced MR angiography with velocity encoding using undersampled radial acquisition and highly constrained projection reconstruction: image-quality assessment in volunteer subjects. AJNR Am J Neuroradiol 2010; 32:E47-50. [PMID: 20223884 DOI: 10.3174/ajnr.a2048] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
We report on the image quality obtained by using fast contrast-enhanced whole-brain 4D radial MRA with 0.75-second temporal resolution, isotropic submillimeter spatial resolution, and velocity encoding (HYPRFlow). Images generated by HYPR-LR by using the velocity-encoded data as the constraining image were of diagnostic quality. In addition, we demonstrate that measurements of shear stress within the middle cerebral artery can be derived from the high-resolution 3D velocity data.
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Affiliation(s)
- Y Wu
- Department of Medical Physics, University of Wisconsin, Madison, 53705, USA.
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Isoda H, Ohkura Y, Kosugi T, Hirano M, Takeda H, Hiramatsu H, Yamashita S, Takehara Y, Alley MT, Bammer R, Pelc NJ, Namba H, Sakahara H. In vivo hemodynamic analysis of intracranial aneurysms obtained by magnetic resonance fluid dynamics (MRFD) based on time-resolved three-dimensional phase-contrast MRI. Neuroradiology 2009; 52:921-8. [PMID: 20012431 DOI: 10.1007/s00234-009-0635-3] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2009] [Accepted: 11/16/2009] [Indexed: 10/20/2022]
Abstract
INTRODUCTION Hemodynamics is thought to play a very important role in the initiation, growth, and rupture of intracranial aneurysms. The purpose of our study was to perform in vivo hemodynamic analysis of unruptured intracranial aneurysms of magnetic resonance fluid dynamics using time-resolved three-dimensional phase-contrast MRI (4D-Flow) at 1.5 T and to analyze relationships between hemodynamics and wall shear stress (WSS) and oscillatory shear index (OSI). METHODS This study included nine subjects with 14 unruptured aneurysms. 4D-Flow was performed by a 1.5-T magnetic resonance scanner with a head coil. We calculated in vivo streamlines, WSS, and OSI of intracranial aneurysms based on 4D-Flow with our software. We evaluated the number of spiral flows in the aneurysms and compared the differences in WSS or OSI between the vessel and aneurysm and between whole aneurysm and the apex of the spiral flow. RESULTS 3D streamlines, WSS, and OSI distribution maps in arbitrary direction during the cardiac phase were obtained for all intracranial aneurysms. Twelve aneurysms had one spiral flow each, and two aneurysms had two spiral flows each. The WSS was lower and the OSI was higher in the aneurysm compared to the vessel. The apex of the spiral flow had a lower WSS and higher OSI relative to the whole aneurysm. CONCLUSION Each intracranial aneurysm in this study had at least one spiral flow. The WSS was lower and OSI was higher at the apex of the spiral flow than the whole aneurysmal wall.
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Affiliation(s)
- Haruo Isoda
- Department of Radiology, Hamamatsu University School of Medicine, 1-20-1 Handayama Higashiku, Hamamatsu, Shizuoka, 431-3192, Japan.
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Huang BY, Castillo M. Neurovascular imaging at 1.5 tesla versus 3.0 tesla. Magn Reson Imaging Clin N Am 2009; 17:29-46. [PMID: 19364598 DOI: 10.1016/j.mric.2008.12.005] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
The primary advantage of high field strength MR imaging over imaging on modern 1.5 Tesla (T) systems is increased signal-to-noise ratio, which can be used to improve image quality or shorten scan acquisition time. In the years since 3.0T scanners were first approved for clinical use, one of the areas which has benefited greatly from its introduction is neurovascular MR angiography (MRA). Early experience has shown significant improvements in resolution and image quality. Whether high field strength MRA is robust or accurate enough to replace digital subtraction angiography in the foreseeable future remains to be seen. This article discusses the current state of neurovascular MRA at 3.0T, basic physical differences between MR imaging at 1.5T and 3.0T, and their effects on MRA sequences. The literature regarding the efficacy of 3.0T MRA techniques for diagnosing specific neurovascular pathologies and carotid steno occlusive disease is reviewed.
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Affiliation(s)
- Benjamin Y Huang
- Department of Radiology, University of North Carolina School of Medicine, CB#7510, 101 Manning Drive, Chapel Hill, NC 27599, USA.
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Hope TA, Hope MD, Purcell DD, von Morze C, Vigneron DB, Alley MT, Dillon WP. Evaluation of intracranial stenoses and aneurysms with accelerated 4D flow. Magn Reson Imaging 2009; 28:41-6. [PMID: 19577400 DOI: 10.1016/j.mri.2009.05.042] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2009] [Revised: 03/07/2009] [Accepted: 05/10/2009] [Indexed: 10/20/2022]
Abstract
The aim of this study was to evaluate intracranial arterial stenoses and aneurysms with accelerated time-resolved three-dimensional (3D) phase-contrast MRI or 4D flow. The 4D flow technique was utilized to image four normal volunteers, two patients with intracranial stenoses and two patients with intracranial aneurysms. In order to reduce scan time, parallel imaging was combined with an acquisition strategy that eliminates the corners of k-space. In the two patients with intracranial stenoses, 4D flow velocity measurements showed that one patient had normal velocity profiles in agreement with a previous magnetic resonance angiogram (MRA), while the second showed increased velocities that indicated a less significant narrowing than suspected on a previous MRA, as confirmed by catheter angiography. This result may have prevented an invasive angiogram. In the two patients with 4-mm intracranial aneurysm, one had a stable helical flow pattern with a large jet, while the other had a temporally unstable flow pattern with a more focal jet possibly indicating that the second aneurysm may have a higher likelihood of rupture. Accelerated 4D flow provides time-resolved 3D velocity data in an 8- to 10-min scan. In the stenosis patients, the addition of 4D flow to a traditional MRA adds the velocity data provided from transcranial Doppler ultrasound (TCD) possibly allowing for more accurate grading of stenoses. In the aneurysm patients, visualization of flow patterns may help to provide prognostic information about future risk of rupture.
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Affiliation(s)
- Thomas A Hope
- Department of Radiology, University of California San Francisco, San Francisco, CA 94143-0628, USA.
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Funamoto K, Suzuki Y, Hayase T, Kosugi T, Isoda H. Numerical validation of MR-measurement-integrated simulation of blood flow in a cerebral aneurysm. Ann Biomed Eng 2009; 37:1105-16. [PMID: 19350390 DOI: 10.1007/s10439-009-9689-y] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2008] [Accepted: 03/27/2009] [Indexed: 12/01/2022]
Abstract
This study proposes magnetic resonance (MR)-measurement-integrated (MR-MI) simulation, in which the difference between the computed velocity field and the phase-contrast MRI measurement data is fed back to the numerical simulation. The computational accuracy and the fundamental characteristics, such as steady characteristics and transient characteristics, of the MR-MI simulation were investigated by a numerical experiment. We dealt with reproduction of three-dimensional steady and unsteady blood flow fields in a realistic cerebral aneurysm developed at a bifurcation. The MR-MI simulation reduced the error derived from the incorrect boundary conditions in the blood flow in the cerebral aneurysm. For the reproduction of steady and unsteady standard solutions, the error of velocity decreased to 13% and to 22% in one cardiac cycle, respectively, compared with the ordinary simulation without feedback. Moreover, the application of feedback shortened the computational convergence, and thus the convergent solution and periodic solution were obtained within less computational time in the MR-MI simulation than that in the ordinary simulation. The dividing flow ratio toward the two outlets after bifurcation was well estimated owing to the improvement of computational accuracy. Furthermore, the MR-MI simulation yielded wall shear stress distribution on the cerebral aneurysm of the standard solution accurately and in detail.
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Affiliation(s)
- Kenichi Funamoto
- Institute of Fluid Science, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577, Japan.
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Nett EJ, Johnson KM, Francois CJ, Wieben O. Analysis platform for hemodynamic function in congenital heart disease. J Cardiovasc Magn Reson 2009. [PMCID: PMC7860837 DOI: 10.1186/1532-429x-11-s1-p126] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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Hemodynamics and cerebrovascular disease. ACTA ACUST UNITED AC 2008; 70:447-53. [DOI: 10.1016/j.surneu.2008.07.010] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2008] [Accepted: 07/16/2008] [Indexed: 11/20/2022]
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