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Abstract
Parallel imaging has been the single biggest innovation in magnetic resonance imaging in the last decade. The use of multiple receiver coils to augment the time consuming Fourier encoding has reduced acquisition times significantly. This increase in speed comes at a time when other approaches to acquisition time reduction were reaching engineering and human limits. A brief summary of spatial encoding in MRI is followed by an introduction to the problem parallel imaging is designed to solve. There are a large number of parallel reconstruction algorithms; this article reviews a cross-section, SENSE, SMASH, g-SMASH and GRAPPA, selected to demonstrate the different approaches. Theoretical (the g-factor) and practical (coil design) limits to acquisition speed are reviewed. The practical implementation of parallel imaging is also discussed, in particular coil calibration. How to recognize potential failure modes and their associated artefacts are shown. Well-established applications including angiography, cardiac imaging and applications using echo planar imaging are reviewed and we discuss what makes a good application for parallel imaging. Finally, active research areas where parallel imaging is being used to improve data quality by repairing artefacted images are also reviewed.
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Affiliation(s)
- David J Larkman
- The Imaging Sciences Department, Clinical Sciences Centre, Faculty of Medicine, Imperial College London, Hammersmith Hospital Campus, Du Cane Road, London W12 0NN, UK.
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Bammer R, Hope TA, Aksoy M, Alley MT. Time-resolved 3D quantitative flow MRI of the major intracranial vessels: initial experience and comparative evaluation at 1.5T and 3.0T in combination with parallel imaging. Magn Reson Med 2007; 57:127-40. [PMID: 17195166 PMCID: PMC3985842 DOI: 10.1002/mrm.21109] [Citation(s) in RCA: 133] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Exact knowledge of blood flow characteristics in the major cerebral vessels is of great relevance for diagnosing cerebrovascular abnormalities. This involves the assessment of hemodynamically critical areas as well as the derivation of biomechanical parameters such as wall shear stress and pressure gradients. A time-resolved, 3D phase-contrast (PC) MRI method using parallel imaging was implemented to measure blood flow in three dimensions at multiple instances over the cardiac cycle. The 4D velocity data obtained from 14 healthy volunteers were used to investigate dynamic blood flow with the use of multiplanar reformatting, 3D streamlines, and 4D particle tracing. In addition, the effects of magnetic field strength, parallel imaging, and temporal resolution on the data were investigated in a comparative evaluation at 1.5T and 3T using three different parallel imaging reduction factors and three different temporal resolutions in eight of the 14 subjects. Studies were consistently performed faster at 3T than at 1.5T because of better parallel imaging performance. A high temporal resolution (65 ms) was required to follow dynamic processes in the intracranial vessels. The 4D flow measurements provided a high degree of vascular conspicuity. Time-resolved streamline analysis provided features that have not been reported previously for the intracranial vasculature.
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Affiliation(s)
- Roland Bammer
- Lucas Center, Department of Radiology, Stanford University, Stanford, California 94305-5488, USA.
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Lew CD, Alley MT, Bammer R, Spielman DM, Chan FP. Peak velocity and flow quantification validation for sensitivity-encoded phase-contrast MR imaging. Acad Radiol 2007; 14:258-69. [PMID: 17307658 PMCID: PMC1993829 DOI: 10.1016/j.acra.2006.11.008] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2006] [Revised: 11/17/2006] [Accepted: 11/17/2006] [Indexed: 11/22/2022]
Abstract
RATIONALE AND OBJECTIVES Phase-contrast (PC) magnetic resonance imaging (MRI) technique has important clinical applications in blood flow quantification and pressure gradient estimation by velocity measurement. Parallel imaging using sensitivity encoding (SENSE) may substantially reduce scan time. We demonstrate the utility of PC-MRI measurements accelerated by SENSE under clinical conditions. MATERIALS AND METHODS Accuracy and repeatability of a SENSE-PC implementation was evaluated by comparison with a commercial PC sequence with five normal volunteers. Twenty-six patients were then scanned with SENSE-PC at reduction factors (R = 1, 2, and 3). Blood flow and peak velocity were measured in the aorta and pulmonary trunk in 16 patients and peak velocity was measured at the coarctation of 10 patients. Quantitative flow, shunt ratio, and peak velocity measurements obtained with different reduction factors were compared using correlation, linear regression, and Bland-Altman statistics. All studies were approved by an Institutional Review Board, and informed consent was acquired from all subjects. RESULTS The correlation coefficients for all comparisons were >0.962 and with high statistical significance (P < .01). Linear regression slopes ranged between 0.96 and 1.11 for flow and 0.88 to 1.05 for peak velocity. For flow, the Bland-Altman statistics yielded a total mean difference ranging from -0.02 to 0.05) L/minute with 2 standard of deviation limits ranging from -0.52 to 0.75 L/minute. For peak velocity, the total mean difference ranged from -0.10 to -0.004) milliseconds with 2-SD limits ranging from -0.062 to 0.46 milliseconds. R = 3 to R = 1 comparisons had greater 2-SD limits than R = 2 to R = 1 comparisons. CONCLUSION SENSE PC-MRI measurements for flow and pressure gradient estimation were comparable to conventional PC-MRI.
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Affiliation(s)
- Calvin D Lew
- Lucas MRS/I Center, Stanford University, 1201 Welch Road, Stanford, CA 94305.
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Blaimer M, Breuer FA, Mueller M, Seiberlich N, Ebel D, Heidemann RM, Griswold MA, Jakob PM. 2D-GRAPPA-operator for faster 3D parallel MRI. Magn Reson Med 2007; 56:1359-64. [PMID: 17058204 DOI: 10.1002/mrm.21071] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
When using parallel MRI (pMRI) methods in combination with three-dimensional (3D) imaging, it is beneficial to subsample the k-space along both phase-encoding directions because one can then take advantage of coil sensitivity variations along two spatial dimensions. This results in an improved reconstruction quality and therefore allows greater scan time reductions as compared to subsampling along one dimension. In this work we present a new approach based on the generalized autocalibrating partially parallel acquisitions (GRAPPA) technique that allows Fourier-domain reconstructions of data sets that are subsampled along two dimensions. The method works by splitting the 2D reconstruction process into two separate 1D reconstructions. This approach is compared with an extension of the conventional GRAPPA method that directly regenerates missing data points of a 2D subsampled k-space by performing a linear combination of acquired data points. In this paper we describe the theoretical background and present computer simulations and in vivo experiments.
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Affiliation(s)
- Martin Blaimer
- Department of Experimental Physics 5, University of Würzburg, Würzburg, Germany.
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Zuo J, Li X, Banerjee S, Han E, Majumdar S. Parallel imaging of knee cartilage at 3 Tesla. J Magn Reson Imaging 2007; 26:1001-9. [PMID: 17896394 DOI: 10.1002/jmri.21122] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
PURPOSE To evaluate the feasibility and reproducibility of quantitative cartilage imaging with parallel imaging at 3T and to determine the impact of the acceleration factor (AF) on morphological and relaxation measurements. MATERIALS AND METHODS An eight-channel phased-array knee coil was employed for conventional and parallel imaging on a 3T scanner. The imaging protocol consisted of a T2-weighted fast spin echo (FSE), a 3D-spoiled gradient echo (SPGR), a custom 3D-SPGR T1rho, and a 3D-SPGR T2 sequence. Parallel imaging was performed with an array spatial sensitivity technique (ASSET). The left knees of six healthy volunteers were scanned with both conventional and parallel imaging (AF = 2). RESULTS Morphological parameters and relaxation maps from parallel imaging methods (AF = 2) showed comparable results with conventional method. The intraclass correlation coefficient (ICC) of the two methods for cartilage volume, mean cartilage thickness, T1rho, and T2 were 0.999, 0.977, 0.964, and 0.969, respectively, while demonstrating excellent reproducibility. No significant measurement differences were found when AF reached 3 despite the low signal-to-noise ratio (SNR). CONCLUSION The study demonstrated that parallel imaging can be applied to current knee cartilage quantification at AF = 2 without degrading measurement accuracy with good reproducibility while effectively reducing scan time. Shorter imaging times can be achieved with higher AF at the cost of SNR.
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Affiliation(s)
- Jin Zuo
- Musculoskeletal and Quantitative Imaging Research (MQIR), Department of Radiology, University of California, San Francisco, San Francisco, California, USA
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56
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Müller S, Umathum R, Speier P, Zühlsdorff S, Ley S, Semmler W, Bock M. Dynamic coil selection for real-time imaging in interventional MRI. Magn Reson Med 2006; 56:1156-62. [PMID: 17029224 DOI: 10.1002/mrm.21028] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
MR-guided intravascular interventions require image update rates of up to 10 images per second, which can be achieved using parallel imaging. However, parallel imaging requires many coil elements, which increases reconstruction times and thus compromises real-time image reconstruction. In this study a dynamic coil selection (DCS) algorithm is presented that selects a subset of receive coils to reduce image reconstruction times. The center-of-sensitivity coordinates and the relative signal intensities are determined for each coil in a prescan. During the intervention m coils are selected for reconstruction using a coil ranking based on the distance to the current slice or catheter position. In a phantom experiment for m = 6, an optimal signal-to-background ratio (SBR) was achieved and foldover artifacts were avoided. In three animal experiments involving catheter manipulation in the aorta and the right heart chamber, the anatomy was successfully visualized at frame rates of about 5 Hz using active catheter tracking.
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Affiliation(s)
- Sven Müller
- Deutsches Krebsforschungszentrum, Heidelberg, Germany
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57
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Banerjee S, Choudhury S, Han ET, Brau ACS, Morze CV, Vigneron DB, Majumdar S. Autocalibrating parallel imaging of in vivo trabecular bone microarchitecture at 3 Tesla. Magn Reson Med 2006; 56:1075-84. [PMID: 17041879 DOI: 10.1002/mrm.21059] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
In this work the generalized autocalibrating partially parallel acquisition (GRAPPA) technique was implemented with modified reconstruction and applied to in vivo high-resolution (HR) magnetic resonance imaging (MRI) of the trabecular bone microarchitecture at 3 Tesla (T) with a multiple-acquisition balanced steady-state free precession (b-SSFP) sequence. Trabecular bone is made up of a network of microstructures (80-140 microm), and its structural deterioration is associated with the skeletal metabolic disorder osteoporosis. HR-MRI is a promising noninvasive tool for assessing the trabecular microarchitecture in vivo, but it involves long acquisition times. Using partially parallel imaging (PPI) to accelerate the acquisition may help mitigate this shortcoming and allow more flexibility in protocol design. In this study the effects of GRAPPA-based reconstruction on image characteristics and the measurement of trabecular bone structural parameters were evaluated. Initial studies showed that image quality and depiction of microstructure were preserved in the GRAPPA-based reconstruction, indicating the feasibility of PPI in HR-MRI of trabecular bone. The results also demonstrated the potential of PPI for increasing the signal-to-noise ratio (SNR) efficiency of multiple-acquisition b-SSFP imaging protocols.
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Affiliation(s)
- S Banerjee
- Department of Radiology, University of California-San Francisco, San Francisco, California 94158, USA.
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Ozturk-Isik E, Crane JC, Cha S, Chang SM, Berger MS, Nelson SJ. Unaliasing lipid contamination for MR spectroscopic imaging of gliomas at 3T using sensitivity encoding (SENSE). Magn Reson Med 2006; 55:1164-9. [PMID: 16596629 DOI: 10.1002/mrm.20860] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
3D magnetic resonance spectroscopic imaging (MRSI) has been successfully employed to extract information about brain tumor metabolism, such as cell membrane breakdown, cellular energetics, and neuronal integrity, through its ability to differentiate signals coming from choline (Cho), creatine (Cr), and N-acetyl aspartate (NAA) molecules. The additional presence of lipids within subregions of the tumor may indicate cellular membrane breakdown due to cell death. Another potential source of lipids is subcutaneous fat, which may be excited with point-resolved spectroscopy (PRESS) volume selection and aliased into the spectral field of view (FOV) due to the chemical shift artifact and the low bandwidth of the selection pulses. The purpose of our study was to employ a postprocessing method for unaliasing lipid resonances originating from in-slice subcutaneous lipids from the 3D MRSI of gliomas at 3T, using an eight-channel phased-array coil and sensitivity encoding (SENSE).
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Affiliation(s)
- Esin Ozturk-Isik
- UCSF/UCB Joint Graduate Group in Bioengineering, University of California-San Francisco, San Francisco, California 94143-2532, USA.
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Michaely HJ, Dietrich O, Nael K, Weckbach S, Reiser MF, Schoenberg SO. MRA of abdominal vessels: technical advances. Eur Radiol 2006; 16:1637-50. [PMID: 16721552 DOI: 10.1007/s00330-006-0240-3] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2005] [Revised: 02/20/2006] [Accepted: 03/06/2006] [Indexed: 11/26/2022]
Abstract
Magnetic resonance angiography (MRA) in general and MRA of the abdominal vessels in particular have undergone substantial improvements in the past 5 years triggered by the introduction and application of parallel imaging (PI), new sequence techniques such as centric k-space trajectories and undersampling, dedicated contrast agents and clinical high-field scanners. All of these techniques have the potential to improve image quality and resolution or decrease the image acquisition time. However, each of them has its own specific advantages and drawbacks. This review describes the main technical innovations and focuses on the impact these developments may have on abdominal MRA. Special consideration is given to the interaction of these various technical advances. The clinical value of advanced MRA techniques is discussed and illustrated by characteristic cases.
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Affiliation(s)
- Henrik J Michaely
- Department of Clinical Radiology, University Hospitals - Grosshadern, Ludwig-Maximilians-University Munich, Marchioninistr.15, 81377 Munich, Germany.
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Wintersperger BJ, Reeder SB, Nikolaou K, Dietrich O, Huber A, Greiser A, Lanz T, Reiser MF, Schoenberg SO. Cardiac CINE MR imaging with a 32-channel cardiac coil and parallel imaging: impact of acceleration factors on image quality and volumetric accuracy. J Magn Reson Imaging 2006; 23:222-7. [PMID: 16374875 DOI: 10.1002/jmri.20484] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
PURPOSE To assess the impact of parallel imaging algorithms on image quality and volumetric accuracy of CINE magnetic resonance imaging (MRI) with high temporal and spatial resolution using a new 32-channel dedicated cardiac phased array coil. MATERIALS AND METHODS Fourteen individuals underwent steady-state free precession (SSFP) CINE MRI using a 32-element phased-array coil and parallel imaging acceleration using spatiotemporal sensitivity encoding (TSENSE). Acquisition acceleration ranged from R = 2 to 7. In conjunction with data extracted from phantom measurements, contrast-to-noise ratio (CNR) performance was evaluated for each acceleration factor and subjective image quality was evaluated by two independent readers. In addition, volumetric assessment was performed for each acceleration factor based on a single breath-hold multi-slice data acquisition. Results were compared to nonTSENSE measurements. RESULTS CNR for non-accelerated CINE (R = 1) was 45.7 +/- 12.8 and showed a constant decrease with increase in acceleration of 51% at R = 4 and 86% at R = 7. CNR losses accompanied reductions in subjective image quality. Volumetric evaluation was accurate for R <or= 4, with significant underestimation of ejection fraction (EF) at higher accelerations. CONCLUSION This study shows that one-dimensional acceleration factors up to R = 4 allow accurate SSFP CINE MRI even though CNR is significantly reduced. This allows for a marked reduction in scan time and allows for multi-slice CINE imaging with high spatial and temporal resolution.
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Affiliation(s)
- Bernd J Wintersperger
- Department of Clinical Radiology, University Hospitals Grosshadern, Ludwig-Maximilians-University, Munich, Germany.
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Niendorf T, Sodickson DK. Parallel imaging in cardiovascular MRI: methods and applications. NMR IN BIOMEDICINE 2006; 19:325-41. [PMID: 16705633 DOI: 10.1002/nbm.1051] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Cardiovascular MR imaging (CVMR) has become a valuable modality for the non-invasive detection and characterization of cardiovascular diseases. CVMR requires high imaging speed and efficiency, which is fundamentally limited in conventional cardiovascular MRI studies. With the introduction of parallel imaging, alternative means for increasing acquisition speed beyond these limits have become available. In parallel imaging some image data are acquired simultaneously, using RF detector coil sensitivities to encode simultaneous spatial information that complements the information gleaned from sequential application of magnetic field gradients. The resulting improvements in imaging speed can be used in various ways, including shortening long examinations, improving spatial resolution and/or anatomic coverage, improving temporal resolution, enhancing image quality, overcoming physiological constraints, detecting and correcting for physiologic motion, and streamlining work flow. Examples of each of these strategies will be provided in this review. First, basic principles and key concepts of parallel MR are described. Second, practical considerations such as coil array design, coil sensitivity calibrations, customized pulse sequences and tailored imaging parameters are outlined. Next, cardiovascular applications of parallel MR are reviewed, ranging from cardiac anatomical and functional assessment to myocardial perfusion and viability to MR angiography of the coronary arteries and the large vessels. Finally, current trends and future directions in parallel CVMR are considered.
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Affiliation(s)
- Thoralf Niendorf
- Department of Diagnostic Radiology, University Hospital, RWTH Aachen, Pauwelsstrasse 30, 52057 Aachen, Germany
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62
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Griswold MA, Breuer F, Blaimer M, Kannengiesser S, Heidemann RM, Mueller M, Nittka M, Jellus V, Kiefer B, Jakob PM. Autocalibrated coil sensitivity estimation for parallel imaging. NMR IN BIOMEDICINE 2006; 19:316-24. [PMID: 16705632 DOI: 10.1002/nbm.1048] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Parallel imaging has proven to be a robust solution to the problem of acquisition speed in MRI. These methods are based on extracting spatial information from an array of multiple surface coils in order to speed up image acquisition. One of the most essential elements of any parallel imaging method is the information describing the coil sensitivity distribution throughout the sample. This paper covers some of the advanced methods to obtain coil sensitivity-related information, focusing particularly on the class of methods referred to as autocalibrating. These methods all acquire the data for coil sensitivity estimation directly before, during or directly after the reduced data acquisition. After a review of standard methods for coil sensitivity estimation, some of the basic and advanced autocalibrating methods are reviewed, and some example applications shown.
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Affiliation(s)
- Mark A Griswold
- University of Würzburg, Department of Physics, EP5, Am Hubland, 97074 Würzburg, Germany.
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63
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Wintersperger BJ, Bauner K, Reeder SB, Friedrich D, Dietrich O, Sprung KC, Picciolo M, Nikolaou K, Reiser MF, Schoenberg SO. Cardiac Steady-State Free Precession CINE Magnetic Resonance Imaging at 3.0 Tesla. Invest Radiol 2006; 41:141-7. [PMID: 16428985 DOI: 10.1097/01.rli.0000192419.08733.37] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
OBJECTIVES We sought to evaluate the impact of 3.0 T on accelerated CINE steady-state free precession (SSFP) regarding signal parameters and its volumetric accuracy. MATERIAL AND METHODS Ten individuals underwent cardiac CINE imaging at 1.5 T and 3.0 T using standard single-slice CINE and multislice TSENSE-accelerated CINE (5 slices/breath-hold) with 4-fold acceleration. Data were evaluated for left ventricular volumetric parameters (EDV, ESV, and EF) as well as for SNR and CNR. Phantom based data allowed for g-factor evaluation for estimation of noise levels for accelerated data sets. Volumetric results and signal parameters were compared with results of single-slice CINE SSFP at 1.5 T as standard of reference (SOR). RESULTS Single-slice CINE at 3.0 T showed a approximately 90% increase in CNR compared with the SOR (P < 0.001). At 3.0 T, TSENSE CINE showed a less pronounced estimated loss in CNR (-58 +/- 6%) compared with single-slice CINE than at 1.5 T (-71 +/- 2%). 3.0 T TSENSE CINE showed a 21 +/- 18% lower CNR than the nonaccelerated 1.5 T CINE (P < 0.05). EF results for all data sets did not show any significant error while for EDV some errors have been encountered. CONCLUSION 3.0 T permits compensation for the high CNR loss, which accompanies the 4-fold TSENSE acceleration at 1.5 T and shows volumetric accuracy. The use of parallel imaging may help to alleviate SAR limitations at higher field strength.
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Affiliation(s)
- Bernd J Wintersperger
- Department of Clinical Radiology, University Hospitals, Grosshadern, Ludwig-Maximilians-University, Munich, Germany.
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Hu HH, Madhuranthakam AJ, Kruger DG, Glockner JF, Riederer SJ. Continuously moving table MRI with SENSE: application in peripheral contrast enhanced MR angiography. Magn Reson Med 2006; 54:1025-31. [PMID: 16149061 PMCID: PMC2716116 DOI: 10.1002/mrm.20639] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
An integration of SENSitivity Encoding (SENSE) with continuously moving table (CMT) MRI for extended field-of-view (FOV) acquisitions is described. In this work, the approach in which receiver coils are attached to the object and move in synchrony with the scanner table is considered. Technical issues dealing with the implementation of SENSE-CMT are addressed, including coil calibration, correction for non-uniform magnetic gradients, and specific reconstruction steps. An explanation of combining SENSE with gradient non-linearity correction is given, as the latter becomes necessary in CMT acquisitions where a large sampling FOV is used. It is hypothesized that SENSE can provide at least a 2-fold improvement in lateral spatial resolution compared to non-accelerated CMT acquisitions. The hypothesis is tested in phantoms, where the effectiveness of both SENSE and gradient non-linearity correction to improve spatial resolution is shown. The SENSE-CMT technique is further demonstrated in vivo with contrast-enhanced MR angiography of the peripheral vasculature.
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Affiliation(s)
| | | | | | | | - Stephen J. Riederer
- Correspondence to: Stephen J. Riederer, Ph.D., Magnetic Resonance Laboratory, Mayo Clinic College of Medicine, 200 First Street S.W., Rochester, MN 55905, USA. E-mail:
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Schoenberg SO, Rieger J, Weber CH, Michaely HJ, Waggershauser T, Ittrich C, Dietrich O, Reiser MF. High-Spatial-Resolution MR Angiography of Renal Arteries with Integrated Parallel Acquisitions: Comparison with Digital Subtraction Angiography and US. Radiology 2005; 235:687-98. [PMID: 15770035 DOI: 10.1148/radiol.2352031693] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
PURPOSE To retrospectively compare three-dimensional gadolinium-enhanced magnetic resonance (MR) angiography, performed with an integrated parallel acquisition technique for high isotropic spatial resolution, with selective digital subtraction angiography (DSA) and intravascular ultrasonography (US) for accuracy of diameter and area measurements in renal artery stenosis. MATERIALS AND METHODS The study was approved by the institutional review board, and consent was obtained from all patients. Forty-five patients (17 women, 28 men; mean age, 62.2 years) were evaluated for suspected renal artery stenosis. Three-dimensional gadolinium-enhanced MR angiograms were acquired with isotropic spatial resolution of 0.8 x 0.8 x 0.9 mm in 23-second breath-hold with an integrated parallel acquisition technique. In-plane diameter of stenosis was measured along vessel axis, and perpendicular diameter and area of stenosis were assessed in cross sections orthogonal to vessel axis, on multiplanar reformations. Interobserver agreement between two radiologists in measurements of in-plane and perpendicular diameters of stenosis and perpendicular area of stenosis was assessed with mean percentage of difference. In a subset of patients, degree of stenosis at MR angiography was compared with that at DSA (n = 20) and intravascular US (n = 11) by using Bland-Altman plots and correlation analyses. RESULTS Mean percentage of difference in stenosis measurement was reduced from 39.3% +/- 78.4 (standard deviation) with use of in-plane views to 12.6% +/- 9.5 with use of cross-sectional views (P < .05). Interobserver agreement for stenosis grading based on perpendicular area of stenosis was significantly better than that for stenosis grading based on in-plane diameter of stenosis (mean percentage of difference, 15.2% +/- 24.2 vs 54.9% +/- 186.9; P < .001). Measurements of perpendicular area of stenosis on MR angiograms correlated well with those on intravascular US images (r(2) = 0.90). CONCLUSION Evaluation of cross-sectional images reconstructed from high-spatial-resolution three-dimensional gadolinium-enhanced MR renal angiographic data increases the accuracy of the technique and decreases interobserver variability.
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Affiliation(s)
- Stefan O Schoenberg
- Institute of Clinical Radiology, Ludwig-Maximilians-University of Munich, Marchioninistrasse 15, 81377 Munich, Germany.
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Current awareness in NMR in biomedicine. NMR IN BIOMEDICINE 2005; 18:205-12. [PMID: 15920785 DOI: 10.1002/nbm.964] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
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67
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Gizewski ER, Maderwald S, Wanke I, Goehde S, Forsting M, Ladd ME. Comparison of volume, four- and eight-channel head coils using standard and parallel imaging. Eur Radiol 2005; 15:1555-62. [PMID: 15856247 DOI: 10.1007/s00330-005-2730-0] [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: 10/26/2004] [Revised: 02/04/2005] [Accepted: 02/25/2005] [Indexed: 10/25/2022]
Abstract
Array coils can potentially offer increased signal-to-noise ratio (SNR) over standard coils adjacent to the array elements, while preserving the SNR at the center of the volume. The SNR advantage should theoretically increase with the number of array elements. Parallel acquisition techniques (PAT), on the other hand, can benefit acquisition times or spatial resolution at a cost to SNR as well as image quality. This study examines the question of whether SNR and image quality are still acceptable with two different array coils (four and eight channels) in conjunction with PAT when compared to standard imaging with a volume coil. All imaging was on a 1.5 T MR scanner. T2-weighted, FLAIR, diffusion-weighted, and time of flight (TOF) angiography images were performed with and without PAT in a phantom and in ten healthy volunteers. The phantom measurements demonstrated superior SNR for the eight-channel coil versus the four-channel and standard head coils. Using the eight-channel head coil for in vivo imaging, image quality with PAT (acceleration factor=2) was scored similar to images without PAT using the volume coil. The four-channel head coil suffered from inhomogeneity, lower SNR and poorer image quality when using PAT compared to standard imaging with the volume head coil. Both the in vivo and the phantom results indicate that the eight-channel head coil should be used for the highest quality brain images; this coil can be combined with PAT sequences for shorter acquisition time without a significant decrease in image quality relative to a volume coil without PAT.
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Affiliation(s)
- Elke R Gizewski
- Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Essen, Germany.
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