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Whiting ME, Mettenburg J, Novelli EM, Santini T, Martins T, Ibrahim TS, LeDuc PR, Cagan J. Inducing Vascular Grammars for Anomaly Classification in Brain Angiograms. JOURNAL OF ENGINEERING AND SCIENCE IN MEDICAL DIAGNOSTICS AND THERAPY 2022; 5:021002. [PMID: 35833206 PMCID: PMC8932082 DOI: 10.1115/1.4053424] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2021] [Revised: 12/23/2021] [Indexed: 11/08/2022]
Abstract
Abstract
As machine learning is used to make strides in medical diagnostics, few methods provide heuristics from which human doctors can learn directly. This work introduces a method for leveraging human observable structures, such as macroscale vascular formations, for producing assessments of medical conditions with relatively few training cases, and uncovering patterns that are potential diagnostic aids. The approach draws on shape grammars, a rule-based technique, pioneered in design and architecture, and accelerated through a recursive subgraph mining algorithm. The distribution of rule instances in the data from which they are induced is then used as an intermediary representation enabling common classification and anomaly detection approaches to identify indicative rules with relatively small data sets. The method is applied to seven-tesla time-of-flight angiography MRI (n = 54) of human brain vasculature. The data were segmented and induced to generate representative grammar rules. Ensembles of rules were isolated to implicate vascular conditions reliably. This application demonstrates the power of automated structured intermediary representations for assessing nuanced biological form relationships, and the strength of shape grammars, in particular for identifying indicative patterns in complex vascular networks.
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Affiliation(s)
- Mark E. Whiting
- Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213
| | - Joseph Mettenburg
- Department of Radiology, University of Pittsburgh, Pittsburgh, PA 15213
| | - Enrico M. Novelli
- Department of Medicine, University of Pittsburgh, Pittsburgh, PA 15213
| | - Tales Santini
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA 15260
| | - Tiago Martins
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA 15260
| | - Tamer S. Ibrahim
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA 15260
| | - Philip R. LeDuc
- Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213
| | - Jonathan Cagan
- Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213
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2
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Improved 7 Tesla transmit field homogeneity with reduced electromagnetic power deposition using coupled Tic Tac Toe antennas. Sci Rep 2021; 11:3370. [PMID: 33564013 PMCID: PMC7873125 DOI: 10.1038/s41598-020-79807-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2020] [Accepted: 11/26/2020] [Indexed: 12/28/2022] Open
Abstract
Recently cleared by the FDA, 7 Tesla (7 T) MRI is a rapidly growing technology that can provide higher resolution and enhanced contrast in human MRI images. However, the increased operational frequency (~ 297 MHz) hinders its full potential since it causes inhomogeneities in the images and increases the power deposition in the tissues. This work describes the optimization of an innovative radiofrequency (RF) head coil coupled design, named Tic Tac Toe, currently used in large scale human MRI scanning at 7 T; to date, this device was used in more than 1,300 neuro 7 T MRI scans. Electromagnetic simulations of the coil were performed using the finite-difference time-domain method. Numerical optimizations were used to combine the calculated electromagnetic fields produced by these antennas, based on the superposition principle, resulting in homogeneous magnetic field distributions at low levels of power deposition in the tissues. The simulations were validated in-vivo using the Tic Tac Toe RF head coil system on a 7 T MRI scanner.
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Del Bosque R, Cui J, Ogier S, Cheshkov S, Dimitrov IE, Malloy C, Wright SM, McDougall M. A 32-channel receive array coil for bilateral breast imaging and spectroscopy at 7T. Magn Reson Med 2020; 85:551-559. [PMID: 32820540 DOI: 10.1002/mrm.28425] [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: 12/12/2019] [Revised: 06/19/2020] [Accepted: 06/22/2020] [Indexed: 11/09/2022]
Abstract
PURPOSE This work describes the construction and evaluation of a bilateral 32-channel receive array for breast imaging at 7T. METHODS The receive array consisted of 32 receive coils, placed on two 3D-printed hemispherical formers. Each side of the receive array consisted of 16 receive loops, each loop having a corresponding detachable board with match/tune capacitors, active detuning circuitry, and a balun. Coil performance was evaluated on homogeneous canola oil phantoms using a Philips Achieva 7T system. Array coil performance was compared with a bilateral forced current excitation volume coil in transmit/receive mode and with a previously reported 16-channel unilateral coil with a similar design. RESULTS The 32-channel array had an increase in average SNR throughout both phantoms by a factor of five as compared with the volume coil, with SNR increases up to 10 times along the periphery and three times in the center. Noise measurements showed low interelement noise correlation (average: 5.4%; maximum: 16.8%). Geometry factor maps were acquired for various acceleration factors and showed mean geometry factors <1.2, for combined acceleration factors of up to six. CONCLUSIONS The improvements achieved demonstrate the clear potential for use in dynamic contrast-enhanced or diffusion-weighted MR studies, while maintaining diagnostically relevant spatial and temporal resolutions.
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Affiliation(s)
- Romina Del Bosque
- Department of Biomedical Engineering, Texas A&M University, College Station, Texas, USA
| | - Jiaming Cui
- Department of Electrical and Computer Engineering, Texas A&M University, College Station, Texas, USA
| | - Stephen Ogier
- Department of Electrical and Computer Engineering, Texas A&M University, College Station, Texas, USA
| | - Sergey Cheshkov
- Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, Texas, USA.,Department of Radiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA.,Center for Brain Health, University of Texas at Dallas, Dallas, Texas, USA
| | - Ivan E Dimitrov
- Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, Texas, USA.,Philips Healthcare, Gainesville, Florida, USA
| | - Craig Malloy
- Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, Texas, USA.,Department of Radiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA.,Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Steven M Wright
- Department of Biomedical Engineering, Texas A&M University, College Station, Texas, USA.,Department of Electrical and Computer Engineering, Texas A&M University, College Station, Texas, USA
| | - Mary McDougall
- Department of Biomedical Engineering, Texas A&M University, College Station, Texas, USA.,Department of Electrical and Computer Engineering, Texas A&M University, College Station, Texas, USA
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Chhetri A, Li X, Rispoli JV. Current and Emerging Magnetic Resonance-Based Techniques for Breast Cancer. Front Med (Lausanne) 2020; 7:175. [PMID: 32478083 PMCID: PMC7235971 DOI: 10.3389/fmed.2020.00175] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2019] [Accepted: 04/15/2020] [Indexed: 01/10/2023] Open
Abstract
Breast cancer is the most commonly diagnosed cancer among women worldwide, and early detection remains a principal factor for improved patient outcomes and reduced mortality. Clinically, magnetic resonance imaging (MRI) techniques are routinely used in determining benign and malignant tumor phenotypes and for monitoring treatment outcomes. Static MRI techniques enable superior structural contrast between adipose and fibroglandular tissues, while dynamic MRI techniques can elucidate functional characteristics of malignant tumors. The preferred clinical procedure-dynamic contrast-enhanced MRI-illuminates the hypervascularity of breast tumors through a gadolinium-based contrast agent; however, accumulation of the potentially toxic contrast agent remains a major limitation of the technique, propelling MRI research toward finding an alternative, noninvasive method. Three such techniques are magnetic resonance spectroscopy, chemical exchange saturation transfer, and non-contrast diffusion weighted imaging. These methods shed light on underlying chemical composition, provide snapshots of tissue metabolism, and more pronouncedly characterize microstructural heterogeneity. This review article outlines the present state of clinical MRI for breast cancer and examines several research techniques that demonstrate capacity for clinical translation. Ultimately, multi-parametric MRI-incorporating one or more of these emerging methods-presently holds the best potential to afford improved specificity and deliver excellent accuracy to clinics for the prediction, detection, and monitoring of breast cancer.
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Affiliation(s)
- Apekshya Chhetri
- Magnetic Resonance Biomedical Engineering Laboratory, Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN, United States
- Basic Medical Sciences, College of Veterinary Medicine, Purdue University, West Lafayette, IN, United States
| | - Xin Li
- Magnetic Resonance Biomedical Engineering Laboratory, Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN, United States
| | - Joseph V. Rispoli
- Magnetic Resonance Biomedical Engineering Laboratory, Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN, United States
- Center for Cancer Research, Purdue University, West Lafayette, IN, United States
- School of Electrical & Computer Engineering, Purdue University, West Lafayette, IN, United States
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5
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Sharma U, Jagannathan NR. In vivo MR spectroscopy for breast cancer diagnosis. BJR Open 2019; 1:20180040. [PMID: 33178927 PMCID: PMC7592438 DOI: 10.1259/bjro.20180040] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2018] [Revised: 05/02/2019] [Accepted: 06/14/2019] [Indexed: 12/23/2022] Open
Abstract
Breast cancer is a significant health concern in females, worldwide. In vivo proton (1H) MR spectroscopy (MRS) has evolved as a non-invasive tool for diagnosis and for biochemical characterization of breast cancer. Water-to-fat ratio, fat and water fractions and choline containing compounds (tCho) have been identified as diagnostic biomarkers of malignancy. Detection of tCho in normal breast tissue of volunteers and in lactating females limits the use of tCho as a diagnostic marker. Technological developments like high-field scanners, multi channel coils, pulse sequences with water and fat suppression facilitated easy detection of tCho. Also, quantification of tCho and its cut-off for objective assessment of malignancy have been reported. Meta-analysis of in vivo 1H MRS studies have documented the pooled sensitivities and the specificities in the range of 71-74% and 78-88%, respectively. Inclusion of MRS has been shown to enhance the diagnostic specificity of MRI, however, detection of tCho in small sized lesions (≤1 cm) is challenging even at high magnetic fields. Potential of MRS in monitoring the effect of chemotherapy in breast cancer has also been reported. This review briefly presents the potential clinical role of in vivo 1H MRS in the diagnosis of breast cancer, its current status and future developments.
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Affiliation(s)
- Uma Sharma
- Department of NMR & MRI Facility, All India Institute of Medical Sciences , New Delhi, India
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Abstract
Radiofrequency (RF) coils are an essential part of the magnetic resonance (MR) system. To exploit the inherently higher signal-to-noise ratio at ultrahigh magnetic fields (UHF), research sites were forced to build up expertise in RF coil development, as the number of commercially available RF coils were limited. In addition, an integrated transmit body RF coil, which is well-established at MR systems of lower field strength, is still missing at UHF due to technical and physical constraints. This review article provides a brief recapitulation of RF characteristics and RF coils in general to introduce terminology and RF-related parameters, and will then provide an extensive overview of current state-of-the-art RF coils used for MRI from head to toe at 7 Tesla. Finally, a section on RF safety will briefly discuss challenges in performing a safety assessment for custom-designed RF coils, and issues arising from the interaction of the RF field and potentially implanted medical devices.
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Affiliation(s)
- Oliver Kraff
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen, Germany
| | - Harald H Quick
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen, Germany
- High-Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
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7
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Zaric O, Farr A, Poblador Rodriguez E, Mlynarik V, Bogner W, Gruber S, Asseryanis E, Singer CF, Trattnig S. 7T CEST MRI: A potential imaging tool for the assessment of tumor grade and cell proliferation in breast cancer. Magn Reson Imaging 2019; 59:77-87. [PMID: 30880110 DOI: 10.1016/j.mri.2019.03.004] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2019] [Revised: 03/03/2019] [Accepted: 03/04/2019] [Indexed: 12/16/2022]
Abstract
OBJECTIVES To investigate the feasibility of chemical exchange saturation transfer (CEST) MRI in patients with breast carcinomas and possible correlations between magnetization transfer asymmetry (MTRasym) values and histological features, such as tumor grade and the Ki-67 proliferation index. MATERIALS AND METHODS Nine healthy subjects and 18 female patients were enrolled for this study. The imaging protocol for the patients consisted of diffusion-weighted imaging (DWI), CEST imaging, and T1-weighted, contrast-enhanced (CE)-MRI. CEST was performed using a 3D gradient echo (GRE) sequence, employing eight pre-saturation pulses of a duration of 50 ms and a duty cycle (DC) of 80%, with a mean amplitude of the saturation pulse train of 1 μT. The Z-spectrum was plotted and MTRasym values calculated for the frequency of the maximum of MTRasym curve, were correlated with the Ki-67 proliferation index and apparent diffusion coefficient (ADC). Patient data were statistically assessed using the Games-Howell post-hoc and Pearson's correlation test. RESULTS Different tumor types had asymmetry peaks at different positions of Z-spectrum. MTRasym (mean ± SD) (%) calculated for G1 (3.0 ± 0.3; range: 2.70-3.50) was not significantly lower than for G2 (4.50 ± 1.30; range: 3.20-6.50; p = 0.066). In contrast, the increase in MTRasym between G1 and G3 (6.40 ± 1.70; range: 4.80-9.80) lesions was significant (p = 0.007). No significant difference was observed between G2 and G3 with regard to MTRasym (p = 0.089). There was a strong positive correlation between the MTRasym, and Ki-67 proliferation index (r = 0.890; p = 0.001), while there was a moderate negative correlation between MTRasym and ADC values (r = -0.506; p = 0.027). CONCLUSIONS Calculated MTRasym demonstrates a strong positive correlation with tumor proliferation and has the potential to become a valuable biomarker for breast tumor characterization.
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Affiliation(s)
- Olgica Zaric
- High Field MR Centre, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna, Austria
| | - Alex Farr
- Breast Health Centre, Department of Obstetrics and Gynecology, Medical University of Vienna, Vienna, Austria.
| | - Esau Poblador Rodriguez
- High Field MR Centre, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna, Austria
| | - Vladimir Mlynarik
- High Field MR Centre, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna, Austria; Karl Landsteiner Gesellschaft, St. Pölten, Austria
| | - Wolfgang Bogner
- High Field MR Centre, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna, Austria
| | - Stephan Gruber
- High Field MR Centre, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna, Austria
| | - Ella Asseryanis
- Breast Health Centre, Department of Obstetrics and Gynecology, Medical University of Vienna, Vienna, Austria
| | - Christian F Singer
- Breast Health Centre, Department of Obstetrics and Gynecology, Medical University of Vienna, Vienna, Austria
| | - Siegfried Trattnig
- High Field MR Centre, Department of Biomedical Imaging and Image-guided Therapy, Medical University of Vienna, Vienna, Austria; Christian Doppler Laboratory for Clinical Molecular MRI, Christian Doppler Forschungsgesellschaft, Vienna, Austria
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8
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Krikken E, Steensma BR, Voogt IJ, Luijten PR, Klomp DW, Raaijmakers AJ, Wijnen JP. Homogeneous B 1+ for bilateral breast imaging at 7 T using a five dipole transmit array merged with a high density receive loop array. NMR IN BIOMEDICINE 2019; 32:e4039. [PMID: 30489661 PMCID: PMC6587506 DOI: 10.1002/nbm.4039] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/26/2018] [Revised: 09/24/2018] [Accepted: 10/12/2018] [Indexed: 06/09/2023]
Abstract
To explore the use of five meandering dipole antennas in a multi-transmit setup, combined with a high density receive array for breast imaging at 7 T for improved penetration depth and more homogeneous B1 field. Five meandering dipole antennas and 30 receiver loops were positioned on two cups around the breasts. Finite difference time domain simulations were performed to evaluate RF safety limits of the transmit setup. Scattering parameters of the transmit setup and coupling between the antennas and the detuned loops were measured. In vivo parallel imaging performance was investigated for various acceleration factors. After RF shimming, a B1 map, a T1 -weighted image, and a T2 -weighted image were acquired to assess B1 efficiency, uniformity in contrast weighting, and imaging performance in clinical applications. The maximum achievable local SAR10g value was 7.0 W/kg for 5 × 1 W accepted power. The dipoles were tuned and matched to a maximum reflection of -11.8 dB, and a maximum inter-element coupling of -14.2 dB. The maximum coupling between the antennas and the receive loops was -18.2 dB and the mean noise correlation for the 30 receive loops 7.83 ± 8.69%. In vivo measurements showed an increased field of view, which reached to the axilla, and a high transmit efficiency. This coil enabled the acquisition of T1 -weighted images with a high spatial resolution of 0.7 mm3 isotropic and T2 -weighted spin echo images with uniformly weighted contrast.
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Affiliation(s)
- Erwin Krikken
- Department of RadiologyUniversity Medical Center UtrechtUtrechtThe Netherlands
| | - Bart R. Steensma
- Department of RadiologyUniversity Medical Center UtrechtUtrechtThe Netherlands
| | - Ingmar J. Voogt
- Department of RadiologyUniversity Medical Center UtrechtUtrechtThe Netherlands
| | - Peter R. Luijten
- Department of RadiologyUniversity Medical Center UtrechtUtrechtThe Netherlands
| | - Dennis W.J. Klomp
- Department of RadiologyUniversity Medical Center UtrechtUtrechtThe Netherlands
| | - Alexander J.E. Raaijmakers
- Department of RadiologyUniversity Medical Center UtrechtUtrechtThe Netherlands
- Department of Biomedical EngineeringEindhoven University of TechnologyEindhovenThe Netherlands
| | - Jannie P. Wijnen
- Department of RadiologyUniversity Medical Center UtrechtUtrechtThe Netherlands
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Krishnamurthy N, Santini T, Wood S, Kim J, Zhao T, Aizenstein HJ, Ibrahim TS. Computational and experimental evaluation of the Tic-Tac-Toe RF coil for 7 Tesla MRI. PLoS One 2019; 14:e0209663. [PMID: 30629618 PMCID: PMC6328242 DOI: 10.1371/journal.pone.0209663] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2018] [Accepted: 12/10/2018] [Indexed: 01/18/2023] Open
Abstract
A variety of 7 Tesla RF coil systems have been proposed to produce spin excitation (B1+ field) and MR image acquisition. Different groups have attempted to mitigate the challenges at high and ultra-high field MRI by proposing novel hardware and software solutions to obtain uniformly high spin excitation at acceptable RF absorption levels. In this study, we extensively compare the designs of two distributed-circuit based RF coils: the Tic-Tac-Toe (TTT) head coil and TEM head coil on multiple anatomically detailed head models and in-vivo. Bench measurements of s-parameters and experimental B1+ field distribution were obtained in volunteers and compared with numerical simulations. RF absorption, quantified by both average and peak SAR, and B1+ field intensity and homogeneity, calculated/measured in terms of maximum over minimum and coefficient of variation (CV) in the region of interest (ROI), are presented for both coils. A study of the RF consistency of both coils across multiple head models for different RF excitation strategies is also presented.
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Affiliation(s)
- Narayanan Krishnamurthy
- University of Pittsburgh, Department of Bioengineering, Pittsburgh, PA, United States of America
| | - Tales Santini
- University of Pittsburgh, Department of Bioengineering, Pittsburgh, PA, United States of America
| | - Sossena Wood
- University of Pittsburgh, Department of Bioengineering, Pittsburgh, PA, United States of America
| | - Junghwan Kim
- University of Pittsburgh, Department of Bioengineering, Pittsburgh, PA, United States of America
| | - Tiejun Zhao
- Siemens Medical Solutions, New York, NY, United States of America
| | - Howard J. Aizenstein
- University of Pittsburgh, Department of Bioengineering, Pittsburgh, PA, United States of America
- University of Pittsburgh, Department of Psychiatry, Pittsburgh, PA, United States of America
| | - Tamer S. Ibrahim
- University of Pittsburgh, Department of Bioengineering, Pittsburgh, PA, United States of America
- University of Pittsburgh, Department of Psychiatry, Pittsburgh, PA, United States of America
- University of Pittsburgh, Department of Radiology, Pittsburgh, PA, United States of America
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10
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Santini T, Zhao Y, Wood S, Krishnamurthy N, Kim J, Farhat N, Alkhateeb S, Martins T, Koo M, Zhao T, Aizenstein HJ, Ibrahim TS. In-vivo and numerical analysis of the eigenmodes produced by a multi-level Tic-Tac-Toe head transmit array for 7 Tesla MRI. PLoS One 2018; 13:e0206127. [PMID: 30481187 PMCID: PMC6258503 DOI: 10.1371/journal.pone.0206127] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2018] [Accepted: 10/08/2018] [Indexed: 11/18/2022] Open
Abstract
Radio-frequency (RF) field inhomogeneities and higher levels of specific absorption rate (SAR) still present great challenges in ultrahigh-field (UHF) MRI. In this study, an in-depth analysis of the eigenmodes of a 20-channel transmit Tic-Tac-Toe (TTT) RF array for 7T neuro MRI is presented. The eigenmodes were calculated for five different Z levels (along the static magnetic field direction) of the coil. Four eigenmodes were obtained for each Z level (composed of 4 excitation ports), and they were named based on the characteristics of their field distributions: quadrature, opposite-phase, anti-quadrature, and zero-phase. Corresponding finite-difference time-domain (FDTD) simulations were performed and experimental B1+ field maps were acquired using a homogeneous spherical phantom and human head (in-vivo). The quadrature mode is the most efficient and it excites the central brain regions; the opposite-phase mode excites the brain peripheral regions; anti-quadrature mode excites the head periphery; and the zero-phase mode excites cerebellum and temporal lobes. Using this RF array, up to five eigenmodes (from five different Z levels) can be simultaneously excited. The superposition of these modes has the potential to produce homogeneous excitation with full brain coverage and low levels of SAR at 7T MRI.
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Affiliation(s)
- Tales Santini
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States of America
| | - Yujuan Zhao
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States of America
| | - Sossena Wood
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States of America
| | - Narayanan Krishnamurthy
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States of America
| | - Junghwan Kim
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States of America
| | - Nadim Farhat
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States of America
| | - Salem Alkhateeb
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States of America
| | - Tiago Martins
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States of America
| | - Minseok Koo
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States of America
| | - Tiejun Zhao
- Siemens Medical Solutions, Pittsburgh, PA, United States of America
| | - Howard J. Aizenstein
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States of America
- Department of Psychiatry, University of Pittsburgh Medical Center, Pittsburgh, PA, United States of America
| | - Tamer S. Ibrahim
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States of America
- Department of Psychiatry, University of Pittsburgh Medical Center, Pittsburgh, PA, United States of America
- * E-mail:
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11
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Smagula SF, Karim HT, Rangarajan A, Santos FP, Wood SC, Santini T, Jakicic JM, Reynolds CF, Cameron JL, Vallejo AN, Butters MA, Rosano C, Ibrahim TS, Erickson KI, Aizenstein HJ. Association of Hippocampal Substructure Resting-State Functional Connectivity with Memory Performance in Older Adults. Am J Geriatr Psychiatry 2018; 26:690-699. [PMID: 29628321 PMCID: PMC5993618 DOI: 10.1016/j.jagp.2018.03.003] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/16/2018] [Revised: 02/28/2018] [Accepted: 03/06/2018] [Indexed: 11/17/2022]
Abstract
OBJECTIVES Hippocampal hyperactivation marks preclinical dementia pathophysiology, potentially due to differences in the connectivity of specific medial temporal lobe structures. Our aims were to characterize the resting-state functional connectivity of medial temporal lobe sub-structures in older adults, and evaluate whether specific substructural (rather than global) functional connectivity relates to memory function. METHODS In 15 adults (mean age: 69 years), we evaluated the resting state functional connectivity of medial temporal lobe substructures: dentate/Cornu Ammonis (CA) 4, CA1, CA2/3, subiculum, the molecular layer, entorhinal cortex, and parahippocampus. We used 7-Tesla susceptibility weighted imaging and magnetization-prepared rapid gradient echo sequences to segment substructures of the hippocampus, which were used as structural seeds for examining functional connectivity in a resting BOLD sequence. We then assessed correlations between functional connectivity with memory performance (short and long delay free recall on the California Verbal Learning Test [CVLT]). RESULTS All the seed regions had significant connectivity within the temporal lobe (including the fusiform, temporal, and lingual gyri). The left CA1 was the only seed with significant functional connectivity to the amygdala. The left entorhinal cortex was the only seed to have significant functional connectivity with frontal cortex (anterior cingulate and superior frontal gyrus). Only higher left dentate-left lingual connectivity was associated with poorer CVLT performance (Spearman r = -0.81, p = 0.0003, Benjamini-Hochberg false discovery rate: 0.01) after multiple comparison correction. CONCLUSIONS Rather than global hyper-connectivity of the medial temporal lobe, left dentate-lingual connectivity may provide a specific assay of medial temporal lobe hyper-connectivity relevant to memory in aging.
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Affiliation(s)
- Stephen F Smagula
- Department of Psychiatry, Western Psychiatric Institute and Clinic of University of Pittsburgh Medical Center, Pittsburgh, PA; Department of Epidemiology, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, PA.
| | - Helmet T Karim
- Department of Psychiatry, Western Psychiatric Institute and Clinic of University of Pittsburgh Medical Center, Pittsburgh, PA
| | - Anusha Rangarajan
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA
| | | | - Sossena C Wood
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA
| | - Tales Santini
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA
| | - John M Jakicic
- Department of Health and Physical Activity, University of Pittsburgh, Pittsburgh, PA
| | - Charles F Reynolds
- Department of Psychiatry, Western Psychiatric Institute and Clinic of University of Pittsburgh Medical Center, Pittsburgh, PA
| | - Judy L Cameron
- Department of Psychiatry, Western Psychiatric Institute and Clinic of University of Pittsburgh Medical Center, Pittsburgh, PA
| | - Abbe N Vallejo
- Department of Pediatrics and Immunology, University of Pittsburgh, Pittsburgh, PA
| | - Meryl A Butters
- Department of Psychiatry, Western Psychiatric Institute and Clinic of University of Pittsburgh Medical Center, Pittsburgh, PA
| | - Caterina Rosano
- Department of Epidemiology, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, PA
| | - Tamer S Ibrahim
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA
| | - Kirk I Erickson
- Department of Psychology, University of Pittsburgh, Pittsburgh, PA
| | - Howard J Aizenstein
- Department of Psychiatry, Western Psychiatric Institute and Clinic of University of Pittsburgh Medical Center, Pittsburgh, PA
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12
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Santini T, Kim J, Wood S, Krishnamurthy N, Farhat N, Maciel C, Raval SB, Zhao T, Ibrahim TS. A new RF transmit coil for foot and ankle imaging at 7T MRI. Magn Reson Imaging 2018; 45:1-6. [PMID: 28893660 PMCID: PMC5935253 DOI: 10.1016/j.mri.2017.09.005] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2017] [Revised: 09/05/2017] [Accepted: 09/05/2017] [Indexed: 12/31/2022]
Abstract
A four-channel Tic-Tac-Toe (TTT) transmit RF coil was designed and constructed for foot and ankle imaging at 7T MRI. Numerical simulations using an in-house developed FDTD package and experimental analyses using a homogenous phantom show an excellent agreement in terms of B1+ field distribution and s-parameters. Simulations performed on an anatomically detailed human lower leg model demonstrated an B1+ field distribution with a coefficient of variation (CV) of 23.9%/15.6%/28.8% and average B1+ of 0.33μT/0.56μT/0.43μT for 1W input power (i.e., 0.25W per channel) in the ankle/calcaneus/mid foot respectively. In-vivo B1+ mapping shows an average B1+ of 0.29μT over the entire foot/ankle. This newly developed RF coil also presents acceptable levels of average SAR (0.07W/kg for 10g per 1W of input power) and peak SAR (0.34W/kg for 10g per 1W of input power) over the whole lower leg. Preliminary in-vivo images in the foot/ankle were acquired using the T2-DESS MRI sequence without the use of a dedicated receive-only array.
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Affiliation(s)
- Tales Santini
- University of Pittsburgh, Department of Bioengineering, United States
| | - Junghwan Kim
- University of Pittsburgh, Department of Bioengineering, United States
| | - Sossena Wood
- University of Pittsburgh, Department of Bioengineering, United States
| | | | - Nadim Farhat
- University of Pittsburgh, Department of Bioengineering, United States
| | - Carlos Maciel
- University of Sao Paulo, Department of Electrical and Computer Engineering, Brazil
| | | | | | - Tamer S Ibrahim
- University of Pittsburgh, Department of Bioengineering, United States; University of Pittsburgh, Department of Radiology, United States.
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van der Velden TA, Luijten PR, Klomp DW. Improved fat suppression of the breast using discretized frequency shimming. Magn Reson Med 2017; 79:593-599. [DOI: 10.1002/mrm.26651] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2016] [Revised: 01/24/2017] [Accepted: 01/27/2017] [Indexed: 11/12/2022]
Affiliation(s)
- Tijl A. van der Velden
- Department of Radiology; University Medical Centre Utrecht; 3584CX Utrecht the Netherlands
| | - Peter R. Luijten
- Department of Radiology; University Medical Centre Utrecht; 3584CX Utrecht the Netherlands
| | - Dennis W.J. Klomp
- Department of Radiology; University Medical Centre Utrecht; 3584CX Utrecht the Netherlands
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