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Complete Restitution of the Ischemic Penumbra after Successful Thrombectomy : A Pilot Study Using Quantitative MRI. Clin Neuroradiol 2018; 29:415-423. [PMID: 29460141 DOI: 10.1007/s00062-018-0675-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2017] [Accepted: 01/25/2018] [Indexed: 12/26/2022]
Abstract
PURPOSE Endovascular thrombectomy is highly effective in patients with proximal large artery occlusion but the relevance of reperfusion injury after recanalization is a matter of debate. The aim of this study was to investigate potential residual metabolic distress and microstructural tissue damage or edema after reperfusion using quantitative oxygen-sensitive T2' and T2-mapping in patients successfully treated by thrombectomy. METHODS Included in this study were 11 patients (mean age 70 ± 11.4 years) with acute ischemic stroke due to internal carotid artery and/or middle cerebral artery occlusion. Quantitative T2 and T2' (1/T2' = 1/T2* - 1/T2) were determined within the ischemic core and hypoperfused but salvaged tissue with delayed time-to-peak (TTP) in patients before and after successful thrombectomy and compared to a control region within the unaffected hemisphere. RESULTS Decreased T2' values within hypoperfused tissue before thrombectomy showed a normalization after recanalization (p < 0.01). In formerly hypoperfused but salvaged tissue, T2 values increased significantly after thrombectomy (p < 0.05) but did not differ from reference values in the control region. In salvaged tissue, increases of quantitative T2' and T2 to follow-up were more pronounced in areas with severe TTP delay. CONCLUSION After successful recanalization, T2' re-increased back to normal in formerly hypoperfused areas as a sign of prompt normalization of oxygen metabolism. Furthermore, quantitative T2 in the formerly hypoperfused tissue did not differ from reference values in unaffected tissue. These results indicate complete restitution of salvaged tissue after reperfusion and support the overall safety of endovascular thrombectomy with respect to microstructural tissue integrity.
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Mashhood A, Kim P, Almaguel F, McWilliams G, Jacobson JP. Cerebral Misery Perfusion on Susceptibility Weighted Imaging in Acute Carotid Dissection. J Radiol Case Rep 2016; 10:1-6. [PMID: 28580051 PMCID: PMC5443581 DOI: 10.3941/jrcr.v10i10.2653] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
The cerebral vasculature incorporates several fail-safes that must be breached before an irreversible ischemic event takes place. In particular, when autoregulatory vasodilatation fails secondary to falling cerebral perfusion pressure (CPP; stage I hemodynamic failure), increases in the oxygen extraction fraction work to maintain the cerebral metabolic rate of oxygen. Previously, failure of this mechanism, stage II hemodynamic failure, or misery perfusion, has been imaged via positron emission tomography/computed tomography (PET/CT). Current susceptibility-weighted sequences (SWI) allow for more efficient imaging of this physiology. In this case, we identify an incident of reversible ischemia caused by spontaneous carotid artery dissection using a combination of diffusion weighted imaging (DWI) and SWI. The level of hemodynamic failure identified by the imaging sequences elevated the urgency of neurointervention, expediting the patient's arrival to the neurointerventional table and thus avoiding impending irreversible ischemia.
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Affiliation(s)
- Arian Mashhood
- Department of Radiology, Loma Linda University Hospital, Loma Linda, USA
| | - Paggie Kim
- Department of Radiology, Loma Linda University Hospital, Loma Linda, USA
| | - Frankis Almaguel
- Department of Radiology, Loma Linda University Hospital, Loma Linda, USA
| | - Geoffery McWilliams
- Department of Radiology, University of California, Davis, Medical Center, Sacramento, USA
| | - J Paul Jacobson
- Department of Radiology, Loma Linda University Hospital, Loma Linda, USA
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Krishnamurthy U, Szalai G, Shen Y, Xu Z, Yadav BK, Tarca AL, Chaiworapongsa T, Hernandez-Andrade E, Than NG, Haacke EM, Romero R, Neelavalli J. Longitudinal Changes in Placental Magnetic Resonance Imaging Relaxation Parameter in Murine Pregnancy: Compartmental Analysis. Gynecol Obstet Invest 2015; 81:193-201. [PMID: 26336923 PMCID: PMC4769121 DOI: 10.1159/000431223] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2015] [Accepted: 05/06/2015] [Indexed: 01/17/2023]
Abstract
OBJECTIVE To quantify gestation-dependent longitudinal changes in the magnetic resonance transverse relaxation time (T2) parameter of the major constituent regions of the mouse placenta and to evaluate their relative contributions to changes in overall placental T2. METHODS Timed-pregnant CD-1 mice underwent magnetic resonance imaging at 7.0 T field strength, on gestational day 13 (GD13), GD15 and GD17. T2 of the placenta and its constituent high and low blood perfusion regions were quantified. A linear mixed-effects model was used to fit the T2 across gestation, and the significance of coefficients was tested. RESULTS A decrease in the T2 values of the placenta and its constituent regions was observed across gestation. The temporal change in T2 was estimated to be -1.85 ms/GD (p < 0.0001) for the placenta, -1.00 ms/GD (p < 0.001) for the high-perfusion zones (HPZs) and -1.66 ms/GD (p < 0.0001) for the low-perfusion zones (LPZs). CONCLUSION T2 of the constituent zones of the murine placenta decreases with advancing gestation. While the T2 of the LPZ is smaller than that of the HPZ, there is no difference in their decrease rate relative to that of the whole placenta (p = 0.24). The results suggest an increased role of constituent volume fractions in affecting overall gestation-dependent placental T2 decrease in mice.
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Affiliation(s)
- Uday Krishnamurthy
- Department of Radiology, Wayne State University School of Medicine, Detroit, Michigan, USA
- Department of Biomedical Engineering, Wayne State University College of Engineering, Detroit, Michigan, USA
| | - Gabor Szalai
- Perinatology Research Branch, NICHD/NIH/DHHS, Bethesda, Maryland, and Detroit, Michigan, USA
| | - Yimin Shen
- Department of Radiology, Wayne State University School of Medicine, Detroit, Michigan, USA
| | - Zhonghui Xu
- Perinatology Research Branch, NICHD/NIH/DHHS, Bethesda, Maryland, and Detroit, Michigan, USA
| | - Brijesh Kumar Yadav
- Department of Radiology, Wayne State University School of Medicine, Detroit, Michigan, USA
- Department of Biomedical Engineering, Wayne State University College of Engineering, Detroit, Michigan, USA
| | - Adi Laurentiu Tarca
- Perinatology Research Branch, NICHD/NIH/DHHS, Bethesda, Maryland, and Detroit, Michigan, USA
- Department of Computer Science, Wayne State University, Detroit, Michigan, USA
| | - Tinnakorn Chaiworapongsa
- Perinatology Research Branch, NICHD/NIH/DHHS, Bethesda, Maryland, and Detroit, Michigan, USA
- Department of Obstetrics and Gynecology, Wayne State University School of Medicine, Detroit, Michigan, USA
| | - Edgar Hernandez-Andrade
- Perinatology Research Branch, NICHD/NIH/DHHS, Bethesda, Maryland, and Detroit, Michigan, USA
- Department of Obstetrics and Gynecology, Wayne State University School of Medicine, Detroit, Michigan, USA
| | - Nandor Gabor Than
- Perinatology Research Branch, NICHD/NIH/DHHS, Bethesda, Maryland, and Detroit, Michigan, USA
- Department of Obstetrics and Gynecology, Wayne State University School of Medicine, Detroit, Michigan, USA
- Institute of Enzymology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Budapest, Hungary
| | - Ewart Mark Haacke
- Department of Radiology, Wayne State University School of Medicine, Detroit, Michigan, USA
- Department of Biomedical Engineering, Wayne State University College of Engineering, Detroit, Michigan, USA
| | | | - D Med Sci
- Perinatology Research Branch, NICHD/NIH/DHHS, Bethesda, Maryland, and Detroit, Michigan, USA
- Department of Obstetrics and Gynecology, University of Michigan, Ann Arbor, Michigan, USA
- Department of Epidemiology and Biostatistics, Michigan State University, East Lansing, Michigan, USA
| | - Jaladhar Neelavalli
- Department of Radiology, Wayne State University School of Medicine, Detroit, Michigan, USA
- Department of Biomedical Engineering, Wayne State University College of Engineering, Detroit, Michigan, USA
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Kauppinen RA. Multiparametric magnetic resonance imaging of acute experimental brain ischaemia. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2014; 80:12-25. [PMID: 24924265 DOI: 10.1016/j.pnmrs.2014.05.002] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/03/2014] [Revised: 05/07/2014] [Accepted: 05/07/2014] [Indexed: 06/03/2023]
Abstract
Ischaemia is a condition in which blood flow either drops to zero or proceeds at severely decreased levels that cannot supply sufficient oxidizable substrates to maintain energy metabolism in vivo. Brain, a highly oxidative organ, is particularly susceptible to ischaemia. Ischaemia leads to loss of consciousness in seconds and, if prolonged, permanent tissue damage is inevitable. Ischaemia primarily results in a collapse of cerebral energy state, followed by a series of subtle changes in anaerobic metabolism, ion and water homeostasis that eventually initiate destructive internal and external processes in brain tissue. (31)P and (1)H NMR spectroscopy were initially used to evaluate anaerobic metabolism in brain. However, since the early 1990s (1)H Magnetic Resonance Imaging (MRI), exploiting the nuclear magnetism of tissue water, has become the key method for assessment of ischaemic brain tissue. This article summarises multi-parametric (1)H MRI work that has exploited diffusion, relaxation and magnetisation transfer as 'contrasts' to image ischaemic brain in preclinical models for the first few hours, with a view to assessing evolution of ischaemia and tissue viability in a non-invasive manner.
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Affiliation(s)
- Risto A Kauppinen
- School of Experimental Psychology and Clinical Research and Imaging Centre, University of Bristol, 12a Priory Road, Bristol BS8 1TU, UK.
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Meoded A, Poretti A, Benson JE, Tekes A, Huisman TA. Evaluation of the ischemic penumbra focusing on the venous drainage: The role of susceptibility weighted imaging (SWI) in pediatric ischemic cerebral stroke. J Neuroradiol 2014; 41:108-16. [DOI: 10.1016/j.neurad.2013.04.002] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2012] [Revised: 03/31/2013] [Accepted: 04/04/2013] [Indexed: 11/30/2022]
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Abstract
The ability to image the ischemic penumbra during hyper-acute stroke promises to identify patients who may benefit from treatment intervention beyond population-defined therapeutic time windows. MR blood oxygenation level dependent (BOLD) contrast imaging has been explored in ischemic stroke. This review provides an overview of several BOLD-based methods, including susceptibility weighted imaging (SWI), R2, R2*, R2', R2* under oxygen challenge, MR_OEF and MROMI approaches to assess cerebral oxygen metabolism in ischemic stroke. We will review the underlying pathophysiological basis of the imaging approaches, followed by a brief introduction of BOLD contrast. Finally, we will discuss the applications of the BOLD approaches in patients with ischemic stroke. BOLD-based methods hold promise for imaging tissue oxygenation during acute ischemia. Further technical refinement and validation studies in stroke patients against positron emission tomography (PET) measurements are needed.
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Jensen-Kondering U, Baron JC. Oxygen imaging by MRI: can blood oxygen level-dependent imaging depict the ischemic penumbra? Stroke 2012; 43:2264-9. [PMID: 22588263 DOI: 10.1161/strokeaha.111.632455] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- Ulf Jensen-Kondering
- Stroke Research Group, University of Cambridge, Department of Clinical Neurosciences, Addenbrooke's Hospital, Cambridge, UK
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Metabolic Imaging in Translational Stroke Research. Transl Stroke Res 2012. [DOI: 10.1007/978-1-4419-9530-8_41] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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An H, Liu Q, Chen Y, Vo KD, Ford AL, Lee JM, Lin W. Oxygen metabolism in ischemic stroke using magnetic resonance imaging. Transl Stroke Res 2011; 3:65-75. [PMID: 24323755 DOI: 10.1007/s12975-011-0141-x] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2011] [Revised: 12/01/2011] [Accepted: 12/05/2011] [Indexed: 12/22/2022]
Abstract
Detecting "at-risk" but potentially salvageable brain tissue, known as the ischemic penumbra, is of importance for identifying patients who may benefit from thrombolytic or other treatments beyond the currently FDA-approved short therapeutic window for tissue plasminogen activator. Since the magnetic resonance blood oxygenation level-dependent (BOLD) contrast may provide information concerning tissue oxygen metabolism, its utilization in ischemic stroke has been explored. The focus of this review is to provide an introduction of several BOLD-based methods, including susceptibility-weighted imaging, R2 BOLD, R2*, R2', MR_OEF, and MR_OMI approaches to assess cerebral oxygenation changes induced by ischemia. Specifically, we will review the underlying pathophysiological basis of the imaging approaches, followed by a brief introduction of BOLD contrast, and finally the applications of BOLD approaches in ischemic stroke. The advantages and disadvantages of each method are addressed. In summary, the BOLD-based methods are promising for imaging oxygenation in ischemic tissue. Future steps would include technical refinement and vigorous validation against another independent method, such as positron emission tomography.
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Affiliation(s)
- Hongyu An
- Department of Radiology and Biomedical Research Imaging Center, CB#7513, University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA,
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Shen Q, Huang S, Du F, Duong TQ. Probing ischemic tissue fate with BOLD fMRI of brief oxygen challenge. Brain Res 2011; 1425:132-41. [PMID: 22032876 DOI: 10.1016/j.brainres.2011.09.052] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2011] [Revised: 09/20/2011] [Accepted: 09/23/2011] [Indexed: 11/17/2022]
Abstract
It has been recently shown that at-risk tissue exhibits exaggerated T(2)⁎-weighted MRI signal increases during transient oxygen challenge (OC), suggesting that the tissue is still metabolically active. This study further characterized the effects of transient OC on T(2)⁎-weighted MRI in permanent focal stroke rats (N=8) using additional quantitative measures. The major findings were: i) the ischemic core cluster showed no significant response, whereas the mismatch cluster showed markedly higher percent changes relative to normal tissue in the acute phase. ii) Many of the mismatch pixels showed exaggerated OC responses which became hyperintense on T(2)-weighted MRI at 24h. The area with exaggerated OC responses was larger than the mismatch, suggesting that some tissue with reduced diffusion were potentially at risk. iii) Basal T(2)⁎-weighted intensities on the perfusion-diffusion contourplot were high in normal tissue and low in the core, with a sharp transition in the mismatch. iv) OC-induced changes on the perfusion-diffusion contourplot dropped as perfusion and diffusion values fell below their respective viability thresholds. v) Basal T(1) increased slightly in the ischemic core (P<0.05). OC decreased T(1) in normal (P<0.05) but not in mismatch and core pixels. vi) OC decreased CBF in normal (P<0.05) but not in mismatch and core pixels. T(2)⁎-weighted MRI of OC has the potential to offer unique clinically relevant data.
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Affiliation(s)
- Qiang Shen
- Research Imaging Institute, Department of Ophthalmology, Radiology and Physiology University of Texas Health Science Center, San Antonio, TX, USA
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11
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Robertson CA, McCabe C, Gallagher L, Lopez-Gonzalez MDR, Holmes WM, Condon B, Muir KW, Santosh C, Macrae IM. Stroke penumbra defined by an MRI-based oxygen challenge technique: 1. Validation using [14C]2-deoxyglucose autoradiography. J Cereb Blood Flow Metab 2011; 31:1778-87. [PMID: 21559032 PMCID: PMC3154682 DOI: 10.1038/jcbfm.2011.66] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Accurate identification of ischemic penumbra will improve stroke patient selection for reperfusion therapies and clinical trials. Current magnetic resonance imaging (MRI) techniques have limitations and lack validation. Oxygen challenge T(2)(*) MRI (T(2)(*) OC) uses oxygen as a biotracer to detect tissue metabolism, with penumbra displaying the greatest T(2)(*) signal change during OC. [(14)C]2-deoxyglucose (2-DG) autoradiography was combined with T(2)(*) OC to determine metabolic status of T(2)(*)-defined penumbra. Permanent middle cerebral artery occlusion was induced in anesthetized male Sprague-Dawley rats (n=6). Ischemic injury and perfusion deficit were determined by diffusion- and perfusion-weighted imaging, respectively. At 147 ± 32 minutes after stroke, T(2)(*) signal change was measured during a 5-minute 100% OC, immediately followed by 125 μCi/kg 2-DG, intravenously. Magnetic resonance images were coregistered with the corresponding autoradiograms. Regions of interest were located within ischemic core, T(2)(*)-defined penumbra, equivalent contralateral structures, and a region of hyperglycolysis. A T(2)(*) signal increase of 9.22% ± 3.9% (mean ± s.d.) was recorded in presumed penumbra, which displayed local cerebral glucose utilization values equivalent to contralateral cortex. T(2)(*) signal change was negligible in ischemic core, 3.2% ± 0.78% in contralateral regions, and 1.41% ± 0.62% in hyperglycolytic tissue, located outside OC-defined penumbra and within the diffusion abnormality. The results support the utility of OC-MRI to detect viable penumbral tissue following stroke.
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Affiliation(s)
- Craig A Robertson
- Glasgow Experimental MRI Centre, Institute of Neuroscience and Psychology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, UK.
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Blood-oxygenation-level-dependent-(BOLD-) based R2' MRI study in monkey model of reversible middle cerebral artery occlusion. J Biomed Biotechnol 2011; 2011:318346. [PMID: 21331339 PMCID: PMC3038692 DOI: 10.1155/2011/318346] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2010] [Revised: 11/25/2010] [Accepted: 12/30/2010] [Indexed: 11/17/2022] Open
Abstract
Objective. To investigate the value of BOLD-based reversible transverse relaxation rate (R2′) MRI in detecting ischemic penumbra (IP) in a monkey model of reversible middle cerebral artery occlusion (MCAO) and time evolution of relative R2′ (rR2′) in infarcted core, IP, and oligemia. Materials and Methods. 6 monkeys were used to make MCAO by the microcatheter method. MR scans were performed at 0 h (1 h after MCAO), 1 h, 3 h, 6 h, 12 h, 24 h, and 48 h after reperfusion. R2′ was calculated using quantitative T2 and T2* maps. Ischemic area was subdivided into infracted core, IP and oligemia. rR2′ was calculated respectively. Results. Reversible MCAO model for 4/6 monkeys was made successfully. rR2′ values were significantly different at each time point, being highest in oligemia followed by IP and infarcted core (P < .05). With reperfusion time evolution, rR2′ in infarcted core showed a decreased trend: sharply decreased within 6 hours and maintained at 0 during 6–48 hours (P < .05). rR2′ values in IP and oligemia showed similar increased trend: sharply increased within 6 hours, maintained a plateau during 6–24 hours, and slightly increased until 48 hours. Conclusion. BOLD-based R2′ MRI can be used to describe changes of cerebral oxygen extract in acute ischemic stroke, and it can provide additional information in detecting IP. The time evolution rR2′ in infarcted core, IP, and oligemia is in accordance with the underlying pathophysiology.
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Imaging in Acute Stroke – a Personal View*. Clin Neuroradiol 2009; 19:20-30. [DOI: 10.1007/s00062-009-8030-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2008] [Accepted: 10/26/2008] [Indexed: 11/27/2022]
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Potential use of oxygen as a metabolic biosensor in combination with T2*-weighted MRI to define the ischemic penumbra. J Cereb Blood Flow Metab 2008; 28:1742-53. [PMID: 18545262 PMCID: PMC3119432 DOI: 10.1038/jcbfm.2008.56] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
We describe a novel magnetic resonance imaging technique for detecting metabolism indirectly through changes in oxyhemoglobin:deoxyhemoglobin ratios and T2(*) signal change during 'oxygen challenge' (OC, 5 mins 100% O(2)). During OC, T2(*) increase reflects O(2) binding to deoxyhemoglobin, which is formed when metabolizing tissues take up oxygen. Here OC has been applied to identify tissue metabolism within the ischemic brain. Permanent middle cerebral artery occlusion was induced in rats. In series 1 scanning (n=5), diffusion-weighted imaging (DWI) was performed, followed by echo-planar T2(*) acquired during OC and perfusion-weighted imaging (PWI, arterial spin labeling). Oxygen challenge induced a T2(*) signal increase of 1.8%, 3.7%, and 0.24% in the contralateral cortex, ipsilateral cortex within the PWI/DWI mismatch zone, and ischemic core, respectively. T2(*) and apparent diffusion coefficient (ADC) map coregistration revealed that the T2(*) signal increase extended into the ADC lesion (3.4%). In series 2 (n=5), FLASH T2(*) and ADC maps coregistered with histology revealed a T2(*) signal increase of 4.9% in the histologically defined border zone (55% normal neuronal morphology, located within the ADC lesion boundary) compared with a 0.7% increase in the cortical ischemic core (92% neuronal ischemic cell change, core ADC lesion). Oxygen challenge has potential clinical utility and, by distinguishing metabolically active and inactive tissues within hypoperfused regions, could provide a more precise assessment of penumbra.
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Brockmann MA, Kemmling A, Groden C. Current issues and perspectives in small rodent magnetic resonance imaging using clinical MRI scanners. Methods 2007; 43:79-87. [PMID: 17720566 DOI: 10.1016/j.ymeth.2007.07.001] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2007] [Accepted: 07/10/2007] [Indexed: 12/16/2022] Open
Abstract
Small rodents such as mice and rats are frequently used in animal experiments for several reasons. In the past, animal experiments were frequently associated with invasive methods and groups of animals had to be killed to perform longitudinal studies. Today's modern imaging techniques such as magnetic resonance imaging (MRI) allow non-invasive longitudinal monitoring of multiple parameters. Although only a few institutions have access to dedicated small animal MR scanners, most institutions carrying out animal experiments have access to clinical MR scanners. Technological advances and the increasing field strength of clinical scanners make MRI a broadly available and viable technique in preclinical in vivo research. This review provides an overview of current concepts, limitations, and recent studies dealing with small animal imaging using clinical MR scanners.
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Affiliation(s)
- Marc A Brockmann
- Department of Neuroradiology, Medical Faculty Mannheim, University of Heidelberg, Theodor-Kutzer-Ufer 1-3, 61867 Mannheim, Germany.
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Bartsch AJ, Homola G, Biller A, Solymosi L, Bendszus M. Diagnostic functional MRI: illustrated clinical applications and decision-making. J Magn Reson Imaging 2006; 23:921-32. [PMID: 16649199 DOI: 10.1002/jmri.20579] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Abstract
Functional magnetic resonance imaging (fMRI) has become a popular research tool, yet its use for diagnostic purposes and actual treatment planning has remained less widespread. The literature yields rather sparse evidence-based data on clinical fMRI applications and accordant decision-making. Notwithstanding, blood oxygenation level dependent (BOLD)- and arterial spin labeling (ASL)-fMRI can be judiciously combined with perfusion measurements, electroencephalographic (EEG) recordings, diffusion-weighted imaging (DWI), and fiber tractographies to assist clinical decisions. In this article we provide an overview of clinical fMRI applications based on illustrative examples. Assessment of cochlear implant candidates by fMRI is covered in some detail, and distinct reference is made to particular challenges imposed by brain tumors, other space-occupying lesions, cortical dysplasias, seizure disorders, and vascular malformations. Specific strategies, merits, and pitfalls of analyzing and interpreting diagnostic fMRI studies in individual patients are highlighted.
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Geisler BS, Brandhoff F, Fiehler J, Saager C, Speck O, Röther J, Zeumer H, Kucinski T. Blood-oxygen-level-dependent MRI allows metabolic description of tissue at risk in acute stroke patients. Stroke 2006; 37:1778-84. [PMID: 16741186 DOI: 10.1161/01.str.0000226738.97426.6f] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND AND PURPOSE The delineation of the "penumbra" is of particular interest in acute stroke imaging. The "mismatch concept" applying perfusion-weighted imaging (PWI) and diffusion-weighted imaging (DWI) appears to be an oversimplification of the underlying electrophysiological tissue status. An additional parameter reflecting the metabolic state of the threatened brain tissue would improve our ability to describe the penumbra. One candidate is deoxyhemoglobin (deoxy-Hb) as an indicator of the oxygen extraction fraction that can be visualized by T2*-based blood oxygen level-dependent (BOLD) imaging. METHODS We analyzed data from 32 patients with acute stroke in the territory of the middle cerebral artery. MRI included fluid-attenuated inversion recovery, DWI, PWI, time-of-flight angiography, and quantitative T2 and T2* (qT2, qT2*) imaging. Follow-up was performed on day 1 and days 5 to 8. We calculated 1/T2'=1/qT2*-1/qT2. Changes of T2', representing the deoxy-Hb effect, were analyzed by 3D regions of interest (ROIs): apparent diffusion coefficient lesion day 0 (L0), time-to-peak-lesion day 0 (T0), final infarct size days 5 to 8 (F5-8), lesion growth (LG; F5-8-L0), and surviving tissue (ST; T0-F5-8). RESULTS We observed a clear decrease of T2' in the infarcted hemisphere compared with the unaffected control ROIs. The mean value showed the most pronounced loss of T2' signal intensity in L0 (-15.7%), followed by LG (-10.5%) and ST (-8.0%). CONCLUSIONS The implementation of BOLD imaging in acute stroke MRI offers a noninvasive estimation of the O2 utilization and is able to add additional information concerning the present metabolic state of the threatened brain tissue. The changes in T2' intensity are visually noticeable in the reconstructed T2' images and provide a better estimation of the real penumbra.
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Affiliation(s)
- Benjamin S Geisler
- Department of Neuroradiology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
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Bodo M, Pearce FJ, Baranyi L, Armonda RA. Changes in the intracranial rheoencephalogram at lower limit of cerebral blood flow autoregulation. Physiol Meas 2005; 26:S1-17. [PMID: 15798222 DOI: 10.1088/0967-3334/26/2/001] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Cerebral blood flow (CBF) reactivity monitoring is an appropriate primary parameter to evaluate cerebral resuscitation due to a systemic or regional cerebral injury leading to possible irreversible brain injury. Use of the electrical impedance method to estimate CBF is rare, as the method's anatomical background is not well understood. Use of intracranial rheoencephalography (iREG) during hemorrhage and comparison of iREG to other CBF measurements have not been previously reported. Our hypothesis was that iREG would reflect early cerebrovascular alteration (CBF autoregulation). Studies comparing iREG, laser Doppler flowmetry and ultrasound were undertaken on anesthetized rats to define CBF changes during hemorrhage. Blood was removed at a rate required to achieve a mean arterial blood pressure (MABP) of 40 mm Hg over 15 min. Estimation of CBF was taken with intracranial, bipolar REG (REG I; n=14), laser Doppler flowmetry (LDF; n=3) and carotid flow by ultrasound (n=11). Data were processed off-line. During the initial phase of hemorrhage, when MABP was close to 40 mm Hg, intracranial REG amplitude transiently increased (80.94%); LDF (77.92%) and carotid flow (52.04%) decreased and changed with systemic arterial pressure. Intracranial REG amplitude change suggests classical CBF autoregulation, demonstrating its close relationship to arteriolar changes. The studies indicate that iREG might reflect cerebrovascular responses more accurately than changes in local CBF measured by LDF and carotid flow. REG may indicate promise as a continuous, non-invasive life-sign monitoring tool with potential advantages over ultrasound, the CBF measurement technique normally applied in clinical practice. REG has particular advantages in non-hospital settings such as military and emergency medicine.
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Affiliation(s)
- M Bodo
- Department of Resuscitative Medicine, Walter Reed Army Institute of Research, Silver Spring, MD 20910, USA.
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Kavec M, Gröhn OHJ, Kettunen MI, Silvennoinen MJ, Garwood M, Kauppinen RA. Acute cerebral ischemia in rats studied by Carr-Purcell spin-echo magnetic resonance imaging: assessment of blood oxygenation level-dependent and tissue effects on the transverse relaxation. Magn Reson Med 2004; 51:1138-46. [PMID: 15170833 DOI: 10.1002/mrm.20089] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Acute cerebral ischemia has been shown to be associated with an enhanced transverse relaxation rate in rat brain parenchyma, chiefly due to the blood oxygenation level-dependent (BOLD) effect. In this study, Carr-Purcell R(2) (CP R(2)), acquired both with short and long time intervals between centers of adiabatic pi-pulses (tau(CP)), was used to assess the contributions of BOLD and tissue effects to the transverse relaxation in two brain ischemia models of rat at 4.7 T. R(1rho) and diffusion MR images were also acquired in the same animals. During the first minutes of global ischemia, the long tau(CP) R(2) in brain parenchyma increased, whereas the short tau(CP) R(2) was unchanged. Based on the simulations, and using constraints of intravascular BOLD effect on parenchymal R(2), the former observation was ascribed to be due to susceptibility changes arising in the extravascular compartment. R(1rho) declined almost immediately after the onset of focal cerebral ischemia, and further declined during the evolution of ischemic damage. Interestingly, short tau(CP) CP R(2) started to decline after some 20 min of focal ischemia and declined over a time course similar to that of R(1rho), indicating that it may be an MRI marker for irreversible tissue changes in cerebral ischemia. The present results show that CP R(2) MRI can reveal both tissue- and blood-derived contrast changes in acute cerebral ischemia.
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Affiliation(s)
- Martin Kavec
- Department of Biomedical NMR and National Bio-NMR Facility, A.I. Virtanen Institute, University of Kuopio, Kuopio, Finland
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Abstract
BACKGROUND Susceptibility-weighted (SW) MRI provides insight into the pathophysiology of acute stroke. We report on the use of SW imaging (SWI) sequences in clinical practice and highlight the future applications. SUMMARY OF REVIEW SWI exploits the magnetic susceptibility effects generated by local inhomogeneities of the magnetic field. The paramagnetic properties of deoxyhemoglobin support signal changes related to acute hemorrhage and the intravascular spontaneous blood oxygen level dependent (BOLD) effect. SWI allows the early detection of acute hemorrhage within 6 hours after symptom onset. SWI may also identify previous microbleeds in acute ischemia; however, the impact of these findings on thrombolytic therapy safety has not been definitely established. The diagnosis of arterial occlusion is usually performed by magnetic resonance angiography. SWI allows intravascular clot detection at the acute stage.Substantial experimental data suggest that spontaneous BOLD contrast may improve tissue viability assessment. The ratio of oxyhemoglobin to deoxyhemoglobin, measured by MRI in the capillary and venous compartments, reflects the oxygen extraction fraction (OEF) and the cerebral metabolic rate of oxygen. The combination of magnetic resonance (MR)-measured OEF and cerebral blood flow, via perfusion studies, may provide information about tissue viability. CONCLUSIONS SWI offers a spectrum of current clinical applications and may improve our knowledge of the pathophysiology of acute stroke.
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Affiliation(s)
- Marc Hermier
- Department of Neuroradiology and MRI, and the Cerebrovascular Disease Center, CREATIS, CNRS UMR 5515, INSERM U630 Hôpital Neurologique P. Wertheimer, Claude-Bernard Lyon-I University, Lyon, France
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Kavec M, Usenius JP, Tuunanen PI, Rissanen A, Kauppinen RA. Assessment of cerebral hemodynamics and oxygen extraction using dynamic susceptibility contrast and spin echo blood oxygenation level-dependent magnetic resonance imaging: applications to carotid stenosis patients. Neuroimage 2004; 22:258-67. [PMID: 15110016 DOI: 10.1016/j.neuroimage.2004.01.009] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2003] [Revised: 01/05/2004] [Accepted: 01/05/2004] [Indexed: 11/23/2022] Open
Abstract
Blood oxygenation level-dependent (BOLD) magnetic resonance imaging (MRI) has been recently used to quantify cerebral blood volume (CBV) and oxygen extraction ratio (OER). In the present study, we have exploited the intravascular BOLD model to assess gray matter (GM) OER at hemispheric level using parenchymal T(2) and CBV data at 1.5 T, obtained by single spin echo and dynamic susceptibility contrast (DSC) perfusion MRI, respectively. An OER of 0.40 +/- 0.07 was determined in gray matter for control subjects. A group of carotid stenosis (CS) patients (n = 22) was examined by multiparametric MRI. The degree of CS was determined by contrast agent-enhanced magnetic resonance angiography. Within the group, eight cases with <70% narrowing of a carotid lumen, nine cases with 70-99%, and five cases with complete occlusion of either carotid arteries were found. DSC MRI revealed abnormalities in 14 patients in dynamic parameters of perfusion images. These included four cases with elevated hemispheric gray matter CBV ipsilateral to the stenosis, above 2 SD of the level determined in control subjects. These four patients showed large variation in the degree of stenosis. We also found three cases with ipsilateral gray matter CBV below 2 SD of the control value, two of these with >70% stenosis. Gray matter OER ipsilateral to the stenosis was above 2 SD of the control range in eight CS patients, three of these showing also high CBV. Use of the present approach to determine OER for the assessment of hemodynamic adaptations in CS patients is discussed in the light of documented hemodynamic adaptations to carotid stenosis.
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Affiliation(s)
- Martin Kavec
- Department of Biomedical NMR and National Bio-NMR Facility, A.I. Virtanen Institute, University of Kuopio, Kuopio, Finland
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Norris DG, Zysset S, Mildner T, Wiggins CJ. An investigation of the value of spin-echo-based fMRI using a Stroop color-word matching task and EPI at 3 T. Neuroimage 2002; 15:719-26. [PMID: 11848715 DOI: 10.1006/nimg.2001.1005] [Citation(s) in RCA: 111] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
This study examines the value of spin-echo-based fMRI for cognitive studies at the main magnetic field strength of 3 T using a spin-echo EPI (SE-EPI) sequence and a Stroop color-word matching task. SE-EPI has the potential advantage over conventional gradient-echo EPI (GE-EPI) that signal losses caused by dephasing through the slice are not present, and hence although image distortion will be the same as for an equivalent GE-EPI sequence, signal voids will be eliminated. The functional contrast in SE-EPI will be lower than for GE-EPI, as static dephasing effects do not contribute. As an auxiliary experiment interleaved diffusion-weighted and non-diffusion-weighted SE-EPI was performed in the visual cortex to further elucidate the mechanims of functional contrast. In the Stroop experiment activation was detected in all areas previously found using GE-EPI. Additional frontopolar and ventral frontomedian activations were also found, which could not be detected using GE-EPI. The experiments from visual cortex indicated that at 3 T the BOLD signal change has contributions from the extravascular space and larger blood vessels in roughly equal amounts. In comparison with GE-EPI the absence of static dephasing effects would seem to result in a superior intrinsic spatial resolution. In conclusion the sensitivity of SE-EPI at 3 T is sufficient to make it the method of choice for fMR studies that require a high degree of spatial localization or where the requirement is to detect activation in regions affected by strong susceptibility gradients.
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Affiliation(s)
- David G Norris
- Max-Planck-Institute for Cognitive Neuroscience, Stephanstrasse 1a, D-04103 Leipzig, Germany
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Kettunen MI, Gröhn OHJ, Silvennoinen MJ, Penttonen M, Kauppinen RA. Quantitative assessment of the balance between oxygen delivery and consumption in the rat brain after transient ischemia with T2 -BOLD magnetic resonance imaging. J Cereb Blood Flow Metab 2002; 22:262-70. [PMID: 11891431 DOI: 10.1097/00004647-200203000-00003] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The balance between oxygen consumption and delivery in the rat brain after exposure to transient ischemia was quantitatively studied with single-spin echo T2-BOLD (blood oxygenation level-dependent) magnetic resonance imaging at 4.7 T. The rats were exposed to graded common carotid artery occlusions using a modification of the four-vessel model of Pulsinelli. T2, diffusion, and cerebral blood volume were quantified with magnetic resonance imaging, and CBF was measured with the hydrogen clearance method. A transient common carotid artery occlusion below the CBF value of approximately 20 mL x 100 g(-1) x min(-1) was needed to yield a T2 increase of 4.6 +/- 1.2 milliseconds (approximately 9% of cerebral T2) and 6.8 +/- 1.7 milliseconds (approximately 13% of cerebral T2) after 7 and 15 minutes of ischemia, respectively. Increases in CBF of 103 +/- 75% and in cerebral blood volume of 29 +/- 20% were detected in the reperfusion phase. These hemodynamic changes alone could account for only approximately one third of the T2 increase in luxury perfusion, suggesting that a substantial increase in blood oxygen saturation (resulting from reduced oxygen extraction by the brain) is needed to explain the magnetic resonance imaging observation.
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Affiliation(s)
- Mikko I Kettunen
- National Bio-NMR Facility and Cognitive Neurobiology Laboratory, A. I. Virtanen Institute for Molecular Sciences, University of Kuopio, Kuopio, Finland
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Gröhn OH, Kauppinen RA. Assessment of brain tissue viability in acute ischemic stroke by BOLD MRI. NMR IN BIOMEDICINE 2001; 14:432-440. [PMID: 11746935 DOI: 10.1002/nbm.739] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The introduction of new neuroprotective treatment strategies for acute stroke patients has provided a requirement for neuroimaging methods capable of identifying salvageable tissue in acute stroke patients. Substantial positron emission tomography evidence points to the fact that a peri-infarct zone with blood flow of 20-45% of normal, metabolic rate of oxygen of >35% of normal and oxygen extraction ratio (OER) of >0.7 are indices of tissue at risk of infarction, yet with potential for recovery. The sensitivity of T(2) to blood oxygen level dependent (BOLD) effects allows the mismatch between oxygen delivery and consumption in the brain to be imaged. Previous evidence from animal models of cerebral hypoperfusion and ischemic stroke strongly suggest that T(2) BOLD MRI highlights viable and salvageable brain regions. The Hahn-echo T(2) and diffusion show distinct flow thresholds in the rat brain so that the former parameter probes areas with high OER and the latter genuine ischemia. In the flow-compromised tissue showing negative T(2) BOLD, substantial residual perfusion is evident as revealed by bolus-tracking perfusion MRI, in agreement with the idea that tissue metabolic viability must be preserved for expression of BOLD. It is concluded that BOLD MRI may have potential for the assessment of tissue viability in acute ischemic stroke.
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Affiliation(s)
- O H Gröhn
- National Bio-NMR Facility, A.I. Virtanen Institute for Molecular Sciences, University of Kuopio, Kuopio, Finland
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