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Vidya Shankar R, Huang L, Neji R, Kowalik G, Neofytou AP, Mooiweer R, Moon T, Mellor N, Razavi R, Pushparajah K, Roujol S. Real-time automatic image-based slice tracking of gadolinium-filled balloon wedge catheter during MR-guided cardiac catheterization: A proof-of-concept study. Magn Reson Med 2024; 91:388-397. [PMID: 37676923 PMCID: PMC10952810 DOI: 10.1002/mrm.29822] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2023] [Revised: 06/28/2023] [Accepted: 07/17/2023] [Indexed: 09/09/2023]
Abstract
PURPOSE MR-guided cardiac catheterization procedures currently use passive tracking approaches to follow a gadolinium-filled catheter balloon during catheter navigation. This requires frequent manual tracking and repositioning of the imaging slice during navigation. In this study, a novel framework for automatic real-time catheter tracking during MR-guided cardiac catheterization is presented. METHODS The proposed framework includes two imaging modes (Calibration and Runtime). The sequence starts in Calibration mode, in which the 3D catheter coordinates are determined using a stack of 10-20 contiguous saturated slices combined with real-time image processing. The sequence then automatically switches to Runtime mode, where three contiguous slices (acquired with partial saturation), initially centered on the catheter balloon using the Calibration feedback, are acquired continuously. The 3D catheter balloon coordinates are estimated in real time from each Runtime slice stack using image processing. Each Runtime stack is repositioned to maintain the catheter balloon in the central slice based on the prior Runtime feedback. The sequence switches back to Calibration mode if the catheter is not detected. This framework was evaluated in a heart phantom and 3 patients undergoing MR-guided cardiac catheterization. Catheter detection accuracy and rate of catheter visibility were evaluated. RESULTS The automatic detection accuracy for the catheter balloon during the Calibration/Runtime mode was 100%/95% in phantom and 100%/97 ± 3% in patients. During Runtime, the catheter was visible in 82% and 98 ± 2% of the real-time measurements in the phantom and patients, respectively. CONCLUSION The proposed framework enabled real-time continuous automatic tracking of a gadolinium-filled catheter balloon during MR-guided cardiac catheterization.
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Affiliation(s)
- Rohini Vidya Shankar
- Biomedical Engineering Department, School of Biomedical Engineering and Imaging SciencesKing's College LondonLondonUK
| | - Li Huang
- Biomedical Engineering Department, School of Biomedical Engineering and Imaging SciencesKing's College LondonLondonUK
| | - Radhouene Neji
- Biomedical Engineering Department, School of Biomedical Engineering and Imaging SciencesKing's College LondonLondonUK
- MR Research Collaborations, Siemens Healthcare LimitedCamberleyUK
| | - Grzegorz Kowalik
- Biomedical Engineering Department, School of Biomedical Engineering and Imaging SciencesKing's College LondonLondonUK
| | - Alexander Paul Neofytou
- Biomedical Engineering Department, School of Biomedical Engineering and Imaging SciencesKing's College LondonLondonUK
| | - Ronald Mooiweer
- Biomedical Engineering Department, School of Biomedical Engineering and Imaging SciencesKing's College LondonLondonUK
- MR Research Collaborations, Siemens Healthcare LimitedCamberleyUK
| | - Tracy Moon
- Guy's and St Thomas' NHS Foundation TrustLondonUK
| | - Nina Mellor
- Guy's and St Thomas' NHS Foundation TrustLondonUK
| | - Reza Razavi
- Biomedical Engineering Department, School of Biomedical Engineering and Imaging SciencesKing's College LondonLondonUK
| | - Kuberan Pushparajah
- Biomedical Engineering Department, School of Biomedical Engineering and Imaging SciencesKing's College LondonLondonUK
| | - Sébastien Roujol
- Biomedical Engineering Department, School of Biomedical Engineering and Imaging SciencesKing's College LondonLondonUK
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Mooiweer R, Rogers C, Vidya Shankar R, Razavi R, Neji R, Roujol S. Feasibility of cardiac MR thermometry at 0.55 T. Front Cardiovasc Med 2023; 10:1233065. [PMID: 37859681 PMCID: PMC10584305 DOI: 10.3389/fcvm.2023.1233065] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2023] [Accepted: 09/22/2023] [Indexed: 10/21/2023] Open
Abstract
Radiofrequency catheter ablation is an established treatment strategy for ventricular tachycardia, but remains associated with a low success rate. MR guidance of ventricular tachycardia shows promises to improve the success rate of these procedures, especially due to its potential to provide real-time information on lesion formation using cardiac MR thermometry. Modern low field MRI scanners (<1 T) are of major interest for MR-guided ablations as the potential benefits include lower costs, increased patient access and device compatibility through reduced device-induced imaging artefacts and safety constraints. However, the feasibility of cardiac MR thermometry at low field remains unknown. In this study, we demonstrate the feasibility of cardiac MR thermometry at 0.55 T and characterized its in vivo stability (i.e., precision) using state-of-the-art techniques based on the proton resonance frequency shift method. Nine healthy volunteers were scanned using a cardiac MR thermometry protocol based on single-shot EPI imaging (3 slices in the left ventricle, 150 dynamics, TE = 41 ms). The reconstruction pipeline included image registration to align all the images, multi-baseline approach (look-up-table length = 30) to correct for respiration-induced phase variations, and temporal filtering to reduce noise in temperature maps. The stability of thermometry was defined as the pixel-wise standard deviation of temperature changes over time. Cardiac MR thermometry was successfully acquired in all subjects and the stability averaged across all subjects was 1.8 ± 1.0°C. Without multi-baseline correction, the overall stability was 2.8 ± 1.6°C. In conclusion, cardiac MR thermometry is feasible at 0.55 T and further studies on MR-guided catheter ablations at low field are warranted.
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Affiliation(s)
- Ronald Mooiweer
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and Medicine, King’s College London, London, United Kingdom
- MR Research Collaborations, Siemens Healthcare Limited, Camberley, United Kingdom
| | - Charlotte Rogers
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and Medicine, King’s College London, London, United Kingdom
| | - Rohini Vidya Shankar
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and Medicine, King’s College London, London, United Kingdom
| | - Reza Razavi
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and Medicine, King’s College London, London, United Kingdom
| | - Radhouene Neji
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and Medicine, King’s College London, London, United Kingdom
- MR Research Collaborations, Siemens Healthcare Limited, Camberley, United Kingdom
| | - Sébastien Roujol
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and Medicine, King’s College London, London, United Kingdom
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Neofytou AP, Neji R, Kowalik GT, Mooiweer R, Wong J, Fotaki A, Ferreira J, Evans C, Bosio F, Mughal N, Razavi R, Pushparajah K, Roujol S. Retrospective motion correction through multi-average k-space data elimination (REMAKE) for free-breathing cardiac cine imaging. Magn Reson Med 2023; 89:2242-2254. [PMID: 36763898 PMCID: PMC10952356 DOI: 10.1002/mrm.29613] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2022] [Revised: 01/06/2023] [Accepted: 01/20/2023] [Indexed: 02/12/2023]
Abstract
PURPOSE To develop a motion-robust reconstruction technique for free-breathing cine imaging with multiple averages. METHOD Retrospective motion correction through multiple average k-space data elimination (REMAKE) was developed using iterative removal of k-space segments (from individual k-space samples) that contribute most to motion corruption while combining any remaining segments across multiple signal averages. A variant of REMAKE, termed REMAKE+, was developed to address any losses in SNR due to k-space information removal. With REMAKE+, multiple reconstructions using different initial conditions were performed, co-registered, and averaged. Both techniques were validated against clinical "standard" signal averaging reconstruction in a static phantom (with simulated motion) and 15 patients undergoing free-breathing cine imaging with multiple averages. Quantitative analysis of myocardial sharpness, blood/myocardial SNR, myocardial-blood contrast-to-noise ratio (CNR), as well as subjective assessment of image quality and rate of diagnostic quality images were performed. RESULTS In phantom, motion artifacts using "standard" (RMS error [RMSE]: 2.2 ± 0.5) were substantially reduced using REMAKE/REMAKE+ (RMSE: 1.5 ± 0.4/1.0 ± 0.4, p < 0.01). In patients, REMAKE/REMAKE+ led to higher myocardial sharpness (0.79 ± 0.09/0.79 ± 0.1 vs. 0.74 ± 0.12 for "standard", p = 0.004/0.04), higher image quality (1.8 ± 0.2/1.9 ± 0.2 vs. 1.6 ± 0.4 for "standard", p = 0.02/0.008), and a higher rate of diagnostic quality images (99%/100% vs. 94% for "standard"). Blood/myocardial SNR for "standard" (94 ± 30/33 ± 10) was higher vs. REMAKE (80 ± 25/28 ± 8, p = 0.002/0.005) and tended to be lower vs. REMAKE+ (105 ± 33/36 ± 12, p = 0.02/0.06). Myocardial-blood CNR for "standard" (61 ± 22) was higher vs. REMAKE (53 ± 19, p = 0.003) and lower vs. REMAKE+ (69 ± 24, p = 0.007). CONCLUSIONS Compared to "standard" signal averaging reconstruction, REMAKE and REMAKE+ provide improved myocardial sharpness, image quality, and rate of diagnostic quality images.
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Affiliation(s)
- Alexander Paul Neofytou
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and MedicineKing's College LondonLondonUK
| | - Radhouene Neji
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and MedicineKing's College LondonLondonUK
- MR Research CollaborationsSiemens Healthcare LimitedNewton House, Sir William Siemens Square, Frimley, CamberleySurreyUK
| | - Grzegorz Tomasz Kowalik
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and MedicineKing's College LondonLondonUK
| | - Ronald Mooiweer
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and MedicineKing's College LondonLondonUK
- MR Research CollaborationsSiemens Healthcare LimitedNewton House, Sir William Siemens Square, Frimley, CamberleySurreyUK
| | - James Wong
- Department of Paediatric CardiologyEvelina London Children's HospitalLondonUK
| | - Anastasia Fotaki
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and MedicineKing's College LondonLondonUK
| | - Joana Ferreira
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and MedicineKing's College LondonLondonUK
| | - Carl Evans
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and MedicineKing's College LondonLondonUK
| | - Filippo Bosio
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and MedicineKing's College LondonLondonUK
| | - Nabila Mughal
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and MedicineKing's College LondonLondonUK
| | - Reza Razavi
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and MedicineKing's College LondonLondonUK
| | - Kuberan Pushparajah
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and MedicineKing's College LondonLondonUK
- Department of Paediatric CardiologyEvelina London Children's HospitalLondonUK
| | - Sébastien Roujol
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and MedicineKing's College LondonLondonUK
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Dokumacı AS, Aitken FR, Sedlacik J, Bridgen P, Tomi‐Tricot R, Mooiweer R, Vecchiato K, Wilkinson T, Casella C, Giles S, Hajnal JV, Malik SJ, O'Muircheartaigh J, Carmichael DW. Simultaneous Optimization of MP2RAGE T 1 -weighted (UNI) and FLuid And White matter Suppression (FLAWS) brain images at 7T using Extended Phase Graph (EPG) Simulations. Magn Reson Med 2023; 89:937-950. [PMID: 36352772 PMCID: PMC10100108 DOI: 10.1002/mrm.29479] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2022] [Revised: 09/16/2022] [Accepted: 09/16/2022] [Indexed: 11/11/2022]
Abstract
PURPOSE The MP2RAGE sequence is typically optimized for either T1 -weighted uniform image (UNI) or gray matter-dominant fluid and white matter suppression (FLAWS) contrast images. Here, the purpose was to optimize an MP2RAGE protocol at 7 Tesla to provide UNI and FLAWS images simultaneously in a clinically applicable acquisition time at <0.7 mm isotropic resolution. METHODS Using the extended phase graph formalism, the signal evolution of the MP2RAGE sequence was simulated incorporating T2 relaxation, diffusion, RF spoiling, and B1 + variability. Flip angles and TI were optimized at different TRs (TRMP2RAGE ) to produce an optimal contrast-to-noise ratio for UNI and FLAWS images. Simulation results were validated by comparison to MP2RAGE brain scans of 5 healthy subjects, and a final protocol at TRMP2RAGE = 4000 ms was applied in 19 subjects aged 8-62 years with and without epilepsy. RESULTS FLAWS contrast images could be obtained while maintaining >85% of the optimal UNI contrast-to-noise ratio. Using TI1 /TI2 /TRMP2RAGE of 650/2280/4000 ms, 6/8 partial Fourier in the inner phase-encoding direction, and GRAPPA factor = 4 in the other, images with 0.65 mm isotropic resolution were produced in <7.5 min. The contrast-to-noise ratio was around 20% smaller at TRMP2RAGE = 4000 ms compared to that at TRMP2RAGE = 5000 ms; however, the 20% shorter duration makes TRMP2RAGE = 4000 ms a good candidate for clinical applications example, pediatrics. CONCLUSION FLAWS and UNI images could be obtained in a single scan with 0.65 mm isotropic resolution, providing a set of high-contrast images and full brain coverage in a clinically applicable scan time. Images with excellent anatomical detail were demonstrated over a wide age range using the optimized parameter set.
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Affiliation(s)
- Ayşe Sıla Dokumacı
- Biomedical Engineering DepartmentSchool of Biomedical Engineering and Imaging Sciences, King's College London
LondonUnited Kingdom
- London Collaborative Ultra high field System (LoCUS)LondonUnited Kingdom
| | - Fraser R. Aitken
- Biomedical Engineering DepartmentSchool of Biomedical Engineering and Imaging Sciences, King's College London
LondonUnited Kingdom
- London Collaborative Ultra high field System (LoCUS)LondonUnited Kingdom
| | - Jan Sedlacik
- London Collaborative Ultra high field System (LoCUS)LondonUnited Kingdom
- Radiology DepartmentGreat Ormond Street Hospital for ChildrenLondonUnited Kingdom
| | - Pip Bridgen
- Biomedical Engineering DepartmentSchool of Biomedical Engineering and Imaging Sciences, King's College London
LondonUnited Kingdom
- London Collaborative Ultra high field System (LoCUS)LondonUnited Kingdom
| | - Raphael Tomi‐Tricot
- Biomedical Engineering DepartmentSchool of Biomedical Engineering and Imaging Sciences, King's College London
LondonUnited Kingdom
- London Collaborative Ultra high field System (LoCUS)LondonUnited Kingdom
- MR Research CollaborationsSiemens Healthcare LimitedCamberleyUnited Kingdom
| | - Ronald Mooiweer
- Biomedical Engineering DepartmentSchool of Biomedical Engineering and Imaging Sciences, King's College London
LondonUnited Kingdom
- MR Research CollaborationsSiemens Healthcare LimitedCamberleyUnited Kingdom
| | - Katy Vecchiato
- London Collaborative Ultra high field System (LoCUS)LondonUnited Kingdom
- Department of Forensic and Neurodevelopmental SciencesInstitute of Psychiatry, Psychology and Neuroscience, King's College LondonLondonUnited Kingdom
- Centre for the Developing BrainSchool of Biomedical Engineering and Imaging Sciences, King's College LondonLondonUnited Kingdom
| | - Tom Wilkinson
- Biomedical Engineering DepartmentSchool of Biomedical Engineering and Imaging Sciences, King's College London
LondonUnited Kingdom
- London Collaborative Ultra high field System (LoCUS)LondonUnited Kingdom
| | - Chiara Casella
- London Collaborative Ultra high field System (LoCUS)LondonUnited Kingdom
- Centre for the Developing BrainSchool of Biomedical Engineering and Imaging Sciences, King's College LondonLondonUnited Kingdom
| | - Sharon Giles
- Biomedical Engineering DepartmentSchool of Biomedical Engineering and Imaging Sciences, King's College London
LondonUnited Kingdom
- London Collaborative Ultra high field System (LoCUS)LondonUnited Kingdom
| | - Joseph V. Hajnal
- Biomedical Engineering DepartmentSchool of Biomedical Engineering and Imaging Sciences, King's College London
LondonUnited Kingdom
- London Collaborative Ultra high field System (LoCUS)LondonUnited Kingdom
| | - Shaihan J. Malik
- Biomedical Engineering DepartmentSchool of Biomedical Engineering and Imaging Sciences, King's College London
LondonUnited Kingdom
- London Collaborative Ultra high field System (LoCUS)LondonUnited Kingdom
| | - Jonathan O'Muircheartaigh
- London Collaborative Ultra high field System (LoCUS)LondonUnited Kingdom
- Department of Forensic and Neurodevelopmental SciencesInstitute of Psychiatry, Psychology and Neuroscience, King's College LondonLondonUnited Kingdom
- Centre for the Developing BrainSchool of Biomedical Engineering and Imaging Sciences, King's College LondonLondonUnited Kingdom
- MRC Centre for Neurodevelopmental Disorders, King's College LondonLondonUnited Kingdom
| | - David W. Carmichael
- Biomedical Engineering DepartmentSchool of Biomedical Engineering and Imaging Sciences, King's College London
LondonUnited Kingdom
- London Collaborative Ultra high field System (LoCUS)LondonUnited Kingdom
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Mooiweer R, Clark IA, Maguire EA, Callaghan MF, Hajnal JV, Malik SJ. Universal pulses for homogeneous excitation using single channel coils. Magn Reson Imaging 2022; 92:180-186. [PMID: 35820546 DOI: 10.1016/j.mri.2022.07.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2021] [Revised: 06/24/2022] [Accepted: 07/07/2022] [Indexed: 11/29/2022]
Abstract
PURPOSE Universal Pulses (UPs) are excitation pulses that reduce the flip angle inhomogeneity in high field MRI systems without subject-specific optimization, originally developed for parallel transmit (PTX) systems at 7 T. We investigated the potential benefits of UPs for single channel (SC) transmit systems at 3 T, which are widely used for clinical and research imaging, and for which flip angle inhomogeneity can still be problematic. METHODS SC-UPs were designed using a spiral nonselective k-space trajectory for brain imaging at 3 T using transmit field maps (B1+) and off-resonance maps (B0) acquired on two different scanner types: a 'standard' single channel transmit system and a system with a PTX body coil. The effect of training group size was investigated using data (200 subjects) from the standard system. The PTX system was used to compare SC-UPs to PTX-UPs (15 subjects). In two additional subjects, prospective imaging using SC-UP was studied. RESULTS Average flip angle homogeneity error fell from 9.5 ± 0.5 % for 'default' excitation to 3.0 ± 0.6 % using SC-UPs trained over 50 subjects. Performance of the UPs was found to steadily improve as training group size increased, but stabilized after ~15 subjects. On the PTX-enabled system, SC-UPs again outperformed default excitation in simulations (4.8 ± 0.6 % error versus 10.6 ± 0.8 % respectively) though greater homogenization could be achieved with PTX-UPs (3.9 ± 0.6 %) and personalized pulses (SC-PP 3.6 ± 1.0 %, PTX-PP 2.9 ± 0.6 %). MP-RAGE imaging using SC-UP resulted in greater separation between grey and white matter signal intensities than default excitation. CONCLUSIONS SC-UPs can improve excitation homogeneity in standard 3 T systems without further calibration and could be used instead of a default excitation pulse for nonselective neuroimaging at 3 T.
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Affiliation(s)
- Ronald Mooiweer
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and Medicine, King's College London, London, United Kingdom; Center for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King's College London, St. Thomas' Hospital, London, United Kingdom; MR Research Collaborations, Siemens Healthcare Limited, Camberley, United Kingdom
| | - Ian A Clark
- Wellcome Centre for Human Neuroimaging, UCL Queen Square Institute of Neurology, University College London, London, United Kingdom
| | - Eleanor A Maguire
- Wellcome Centre for Human Neuroimaging, UCL Queen Square Institute of Neurology, University College London, London, United Kingdom
| | - Martina F Callaghan
- Wellcome Centre for Human Neuroimaging, UCL Queen Square Institute of Neurology, University College London, London, United Kingdom
| | - Joseph V Hajnal
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and Medicine, King's College London, London, United Kingdom; Center for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King's College London, St. Thomas' Hospital, London, United Kingdom
| | - Shaihan J Malik
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and Medicine, King's College London, London, United Kingdom; Center for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King's College London, St. Thomas' Hospital, London, United Kingdom.
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Mooiweer R, Schneider R, Krafft AJ, Empanger K, Stroup J, Neofytou AP, Mukherjee RK, Williams SE, Lloyd T, O'Neill M, Razavi R, Schaeffter T, Neji R, Roujol S. Active Tracking-based cardiac triggering for MR-thermometry during radiofrequency ablation therapy in the left ventricle. Front Cardiovasc Med 2022; 9:971869. [PMID: 36093156 PMCID: PMC9453599 DOI: 10.3389/fcvm.2022.971869] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2022] [Accepted: 07/29/2022] [Indexed: 11/13/2022] Open
Abstract
Cardiac MR thermometry shows promise for real-time guidance of radiofrequency ablation of cardiac arrhythmias. This technique uses ECG triggering, which can be unreliable in this situation. A prospective cardiac triggering method was developed for MR thermometry using the active tracking (AT) signal measured from catheter microcoils. In the proposed AT-based cardiac triggering (AT-trig) sequence, AT modules were repeatedly acquired to measure the catheter motion until a cardiac trigger was identified to start cardiac MR thermometry using single-shot echo-planar imaging. The AT signal was bandpass filtered to extract the motion induced by the beating heart, and cardiac triggers were defined as the extremum (peak or valley) of the filtered AT signal. AT-trig was evaluated in a beating heart phantom and in vivo in the left ventricle of a swine during temperature stability experiments (6 locations) and during one ablation. Stability was defined as the standard deviation over time. In the phantom, AT-trig enabled triggering of MR thermometry and resulted in higher temperature stability than an untriggered sequence. In all in vivo experiments, AT-trig intervals matched ECG-derived RR intervals. Mis-triggers were observed in 1/12 AT-trig stability experiments. Comparable stability of MR thermometry was achieved using peak AT-trig (1.0 ± 0.4°C), valley AT-trig (1.1 ± 0.5°C), and ECG triggering (0.9 ± 0.4°C). These experiments show that continuously acquired AT signal for prospective cardiac triggering is feasible. MR thermometry with AT-trig leads to comparable temperature stability as with conventional ECG triggering. AT-trig could serve as an alternative cardiac triggering strategy in situations where ECG triggering is not effective.
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Affiliation(s)
- Ronald Mooiweer
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and Medicine, King's College London, London, United Kingdom
- MR Research Collaborations, Siemens Healthcare Limited, Camberley, United Kingdom
| | | | | | - Katy Empanger
- Imricor Medical Systems, Burnsville, MN, United States
| | - Jason Stroup
- Imricor Medical Systems, Burnsville, MN, United States
| | - Alexander Paul Neofytou
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and Medicine, King's College London, London, United Kingdom
| | - Rahul K. Mukherjee
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and Medicine, King's College London, London, United Kingdom
| | - Steven E. Williams
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and Medicine, King's College London, London, United Kingdom
- Centre for Cardiovascular Science, The University of Edinburgh, Edinburgh, United Kingdom
| | - Tom Lloyd
- Imricor Medical Systems, Burnsville, MN, United States
| | - Mark O'Neill
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and Medicine, King's College London, London, United Kingdom
| | - Reza Razavi
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and Medicine, King's College London, London, United Kingdom
| | - Tobias Schaeffter
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and Medicine, King's College London, London, United Kingdom
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany
| | - Radhouene Neji
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and Medicine, King's College London, London, United Kingdom
- MR Research Collaborations, Siemens Healthcare Limited, Camberley, United Kingdom
| | - Sébastien Roujol
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and Medicine, King's College London, London, United Kingdom
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Godinez F, Tomi-Tricot R, Delcey M, Williams SE, Mooiweer R, Quesson B, Razavi R, Hajnal JV, Malik SJ. Interventional cardiac MRI using an add-on parallel transmit MR system: In vivo experience in sheep. Magn Reson Med 2021; 86:3360-3372. [PMID: 34286866 DOI: 10.1002/mrm.28931] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2021] [Revised: 06/15/2021] [Accepted: 06/28/2021] [Indexed: 12/19/2022]
Abstract
PURPOSE We present in vivo testing of a parallel transmit system intended for interventional MR-guided cardiac procedures. METHODS The parallel transmit system was connected in-line with a conventional 1.5 Tesla MRI system to transmit and receive on an 8-coil array. The system used a current sensor for real-time feedback to achieve real-time current control by determining coupling and null modes. Experiments were conducted on 4 Charmoise sheep weighing 33.9-45.0 kg with nitinol guidewires placed under X-ray fluoroscopy in the atrium or ventricle of the heart via the femoral vein. Heating tests were done in vivo and post-mortem with a high RF power imaging sequence using the coupling mode. Anatomical imaging was done using a combination of null modes optimized to produce a useable B1 field in the heart. RESULTS Anatomical imaging produced cine images of the heart comparable in quality to imaging with the quad mode (all channels with the same amplitude and phase). Maximum observed temperature increases occurred when insulation was stripped from the wire tip. These were 4.1℃ and 0.4℃ for the coupling mode and null modes, respectively for the in vivo case; increasing to 6.0℃ and 1.3℃, respectively for the ex vivo case, because cooling from blood flow is removed. Heating < 0.1℃ was observed when insulation was not stripped from guidewire tips. In all tests, the parallel transmit system managed to reduce the temperature at the guidewire tip. CONCLUSION We have demonstrated the first in vivo usage of an auxiliary parallel transmit system employing active feedback-based current control for interventional MRI with a conventional MRI scanner.
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Affiliation(s)
- Felipe Godinez
- School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom.,Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom
| | - Raphael Tomi-Tricot
- MR Research Collaborations, Siemens Healthcare Limited, Frimley, United Kingdom
| | - Marylène Delcey
- Centre de Recherche Cardio, Thoracique de Bordeaux/IHU Liryc, INSERM U1045-University of Bordeaux, Pessac, France.,Siemens Healthcare, Saint-Denis, France
| | - Steven E Williams
- School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom
| | - Ronald Mooiweer
- School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom
| | - Bruno Quesson
- Centre de Recherche Cardio, Thoracique de Bordeaux/IHU Liryc, INSERM U1045-University of Bordeaux, Pessac, France
| | - Reza Razavi
- School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom
| | - Joseph V Hajnal
- School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom.,Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom
| | - Shaihan J Malik
- School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom.,Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom
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8
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Mooiweer R, Neji R, McElroy S, Nazir MS, Razavi R, Chiribiri A, Roujol S. A fast navigator (fastNAV) for prospective respiratory motion correction in first-pass myocardial perfusion imaging. Magn Reson Med 2020; 85:2661-2671. [PMID: 33270946 PMCID: PMC7898590 DOI: 10.1002/mrm.28617] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2020] [Revised: 11/05/2020] [Accepted: 11/05/2020] [Indexed: 11/10/2022]
Abstract
PURPOSE To develop and evaluate a fast respiratory navigator (fastNAV) for cardiac MR perfusion imaging with subject-specific prospective slice tracking. METHODS A fastNAV was developed for dynamic contrast-enhanced cardiac MR perfusion imaging by combining spatially nonselective saturation with slice-selective tip-up and slice-selective excitation pulses. The excitation slice was angulated from the tip-up slice in the transverse plane to overlap only in the right hemidiaphragm for suppression of signal outside the right hemidiaphragm. A calibration scan was developed to enable the estimation of subject-specific tracking factors. Perfusion imaging using subject-specific fastNAV-based slice tracking was then compared to a conventional sequence (ie, without slice tracking) in 10 patients under free-breathing conditions. Respiratory motion in perfusion images was quantitatively assessed by measuring the average overlap of the left ventricle across images (avDice, 0:no overlap/1:perfect overlap) and the average displacement of the center of mass of the left ventricle (avCoM). Image quality was subjectively assessed using a 4-point scoring system (1: poor, 4: excellent). RESULTS The fastNAV calibration was successfully performed in all subjects (average tracking factor of 0.46 ± 0.13, R = 0.94 ± 0.03). Prospective motion correction using fastNAV led to higher avDice (0.94 ± 0.02 vs. 0.90 ± 0.03, P < .001) and reduced avCoM (4.03 ± 0.84 vs. 5.22 ± 1.22, P < .001). There were no statistically significant differences between the 2 sequences in terms of image quality (both sequences: median = 3 and interquartile range = 3-4, P = 1). CONCLUSION fastNAV enables fast and robust right hemidiaphragm motion tracking in a perfusion sequence. In combination with subject-specific slice tracking, fastNAV reduces the effect of respiratory motion during free-breathing cardiac MR perfusion imaging.
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Affiliation(s)
- Ronald Mooiweer
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and Medicine, King's College London, London, United Kingdom
| | - Radhouene Neji
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and Medicine, King's College London, London, United Kingdom.,MR Research Collaborations, Siemens Healthcare Limited, Frimley, United Kingdom
| | - Sarah McElroy
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and Medicine, King's College London, London, United Kingdom
| | - Muhummad Sohaib Nazir
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and Medicine, King's College London, London, United Kingdom
| | - Reza Razavi
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and Medicine, King's College London, London, United Kingdom
| | - Amedeo Chiribiri
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and Medicine, King's College London, London, United Kingdom
| | - Sébastien Roujol
- School of Biomedical Engineering and Imaging Sciences, Faculty of Life Sciences and Medicine, King's College London, London, United Kingdom
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9
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Mooiweer R, Sbrizzi A, Raaijmakers AJ, van den Berg CA, Luijten PR, Hoogduin H. Combining a reduced field of excitation with SENSE-based parallel imaging for maximum imaging efficiency. Magn Reson Med 2017; 78:88-96. [PMID: 27633931 PMCID: PMC5484283 DOI: 10.1002/mrm.26346] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2016] [Revised: 06/23/2016] [Accepted: 06/24/2016] [Indexed: 12/27/2022]
Abstract
PURPOSE To show that a combination of parallel imaging using sensitivity encoding (SENSE) and inner volume imaging (IVI) combines the known benefits of both techniques. SENSE with a reduced field of excitation (rFOX) is termed rSENSE. THEORY AND METHODS The noise level in SENSE reconstructions is reduced by removing voxels from the unfolding process that are rendered silent by using rFOX. The silent voxels need to be identified beforehand, this is done by using rFOX in the coil sensitivity maps. In vivo experiments were performed at 7 Tesla using a 32-channel receive coil. RESULTS Good image quality could be obtained in vivo with rSENSE at acceleration factors that are higher than could be obtained using SENSE or IVI alone. With rSENSE we were also able to accelerate scans using an rFOX that was purposely designed to be imperfect or incompatible at all with IVI. CONCLUSION rSENSE has been demonstrated in vivo with two-dimensionally selective radiofrequency pulses. Besides allowing additional scan acceleration, it offers a greater robustness and flexibility than IVI. The proposed method can be used with other field strengths, anatomies and other rFOX techniques. Magn Reson Med 78:88-96, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution Non Commercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.
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Affiliation(s)
- Ronald Mooiweer
- Center for Image Sciences, University Medical Center UtrechtUtrechtThe Netherlands
| | - Alessandro Sbrizzi
- Center for Image Sciences, University Medical Center UtrechtUtrechtThe Netherlands
| | | | | | - Peter R. Luijten
- Center for Image Sciences, University Medical Center UtrechtUtrechtThe Netherlands
| | - Hans Hoogduin
- Center for Image Sciences, University Medical Center UtrechtUtrechtThe Netherlands
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10
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Çavuşoğlu M, Mooiweer R, Pruessmann KP, Malik SJ. VERSE-guided parallel RF excitations using dynamic field correction. NMR Biomed 2017; 30:e3697. [PMID: 28211968 PMCID: PMC5484370 DOI: 10.1002/nbm.3697] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/05/2016] [Revised: 11/24/2016] [Accepted: 12/29/2016] [Indexed: 06/06/2023]
Abstract
In parallel RF pulse design, peak RF magnitudes and specific absorption rate levels are critical concerns in the hardware and safety limits. The variable rate selective excitation (VERSE) method is an efficient technique to limit the peak RF power by applying a local-only RF and gradient waveform reshaping while retaining the on-resonance profile. The accuracy of the excitation performed by the VERSEd RF and gradient waveforms strictly depends on the performance of the employed hardware. Any deviation from the nominal gradient fields as a result of frequency dependent system imperfections violates the VERSE condition similarly to off-resonance effects, leading to significant excitation errors and the RF pulse not converging to the targeted peak RF power. Moreover, for iterative VERSE-guided RF pulse design (i.e. reVERSE), the k-space trajectory actually changes at every iteration, which is assumed to be constant. In this work, we show both theoretically and experimentally the effect of gradient system imperfections on iteratively VERSEd parallel RF excitations. In order to improve the excitation accuracy besides limiting the RF power below certain thresholds, we propose to integrate gradient field monitoring or gradient impulse response function (GIRF) estimations of the actual gradient fields into the RF pulse design problem. A third-order dynamic field camera comprising a set of NMR field sensors and GIRFs was used to measure or estimate the actual gradient waveforms that are involved in the VERSE algorithm respectively. The deviating and variable k-space is counteracted at each iteration of the VERSE-guided iterative RF pulse design. The proposed approaches are demonstrated for accelerated multiple-channel spatially selective RF pulses, and highly improved experimental performance was achieved at both 3 T and 7 T.
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Affiliation(s)
- Mustafa Çavuşoğlu
- Institute for Biomedical EngineeringUniversity and ETH ZürichZürichSwitzerland
| | - Ronald Mooiweer
- Division of Imaging Sciences and Biomedical Engineering, King's College LondonSt. Thomas' HospitalLondonUK
- Center for Image SciencesUniversity Medical Center UtrechtUtrechtThe Netherlands
| | - Klaas P. Pruessmann
- Institute for Biomedical EngineeringUniversity and ETH ZürichZürichSwitzerland
| | - Shaihan J. Malik
- Division of Imaging Sciences and Biomedical Engineering, King's College LondonSt. Thomas' HospitalLondonUK
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11
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Mooiweer R, Sbrizzi A, El Aidi H, Eikendal ALM, Raaijmakers A, Visser F, van den Berg CAT, Leiner T, Luijten PR, Hoogduin H. Fast 3D isotropic imaging of the aortic vessel wall by application of 2D spatially selective excitation and a new way of inversion recovery for black blood imaging. Magn Reson Med 2015; 75:547-55. [PMID: 25761646 DOI: 10.1002/mrm.25599] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2014] [Revised: 12/09/2014] [Accepted: 12/09/2014] [Indexed: 11/06/2022]
Abstract
PURPOSE Aortic vessel wall imaging requires large coverage and a high spatial resolution, which makes it prohibitively time-consuming for clinical use. This work explores the feasibility of imaging the descending aorta in acceptable scan time, using two-dimensional (2D) spatially selective excitation and a new way of inversion recovery for black blood imaging. METHODS The excitation pattern and field of view in a 3D gradient echo sequence are reduced in two dimensions, following the aorta's anisotropic geometry. Black blood contrast is obtained by partially inverting the blood's magnetization in the heart at the start of the cardiac cycle. Imaging is delayed until the inverted blood has filled the desired part of the aorta. The flip angle and delay are determined such that the blood signal is nulled upon arrival in the aorta. RESULTS Experiments on eight volunteers showed that the descending aortic vessel wall could be imaged over more than 15 cm at a maximal resolution of 1.5 × 1.5 × 1.5 mm(3) in less than 5 min minimal scan time. CONCLUSION This feasibility study demonstrates that time-efficient isotropic imaging of the descending aorta is possible by using 2D spatially selective excitation for motion artifact reduction and a new way of inversion recovery for black blood imaging.
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Affiliation(s)
- Ronald Mooiweer
- Department of Radiology, University Medical Center Utrecht, The Netherlands
| | - Alessandro Sbrizzi
- Department of Radiology, University Medical Center Utrecht, The Netherlands
| | - Hamza El Aidi
- Department of Radiology, University Medical Center Utrecht, The Netherlands.,Department of Cardiology, University Medical Center Utrecht, The Netherlands
| | - Anouk L M Eikendal
- Department of Radiology, University Medical Center Utrecht, The Netherlands
| | - Alexander Raaijmakers
- Department of Radiology, University Medical Center Utrecht, The Netherlands.,Department of Radiotherapy, University Medical Center Utrecht, The Netherlands
| | - Fredy Visser
- Department of Radiology, University Medical Center Utrecht, The Netherlands.,Philips Healthcare, Best, The Netherlands
| | | | - Tim Leiner
- Department of Radiology, University Medical Center Utrecht, The Netherlands
| | - Peter R Luijten
- Department of Radiology, University Medical Center Utrecht, The Netherlands
| | - Hans Hoogduin
- Department of Radiology, University Medical Center Utrecht, The Netherlands
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