Image construction methods for phased array magnetic resonance imaging

Erdoğmuş, Deni̇z; Yan, Rui; Larsson, Erik G.; Prı́ncipe, José C.; Fitzsimmons, Jeffrey R.

doi:10.1002/jmri.20115

Cited by 20 publications

(16 citation statements)

References 34 publications

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“…The code also reconstructed the complex images from the k-space data extracted from the raw data files and calculated the composite image from the individual coil images using a spatial-matched filter as described in Walsh et al (21). The noise covariance matrix was assumed to be the identity matrix, and coil sensitivities were estimated from the coil images following the procedure of Erdogmus et al (22).…”

Section: Mri and Postprocessingmentioning

confidence: 99%

MRI Measurement of Bone Marrow Cellularity for Radiation Dosimetry

Pichardo

Milner²,

Bolch³

2011

J Nucl Med

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The current gold standard for measuring marrow cellularity is the bone marrow (BM) biopsy of the iliac crest. This measure is not predictive of total marrow cellularity, because the biopsy volume is typically small and fat fraction varies across the skeleton. MRI and localized MR spectroscopy have been demonstrated as noninvasive means for measuring BM cellularity in patients. The accuracy of these methods has been well established in phantom studies and in the determination of in vivo hepatic fat fractions but not for in vivo measurement of BM cellularity. Methods: Spoiled gradient-echo in vivo images of the femur, humerus, upper spine, and lower spine were acquired for 2 dogs using a clinical 3-T MRI scanner. Single-peak iterative decomposition of water and fat with echo asymmetry and least squares (SP-IDEAL) was used to derive BM fat fractions. Stimulated-echo acquisition mode spectra were acquired in order to perform multipeak IDEAL with precalibration (MP-IDEAL). In vivo accuracy was validated by comparison with histology measurements. Histologic fat fractions were derived from adipocyte segmentation. Results: Bland-Altman plots demonstrated excellent agreement between SP-IDEAL and histology, with a mean difference of 20.52% cellularity and most differences within 62% cellularity, but agreement between MP-IDEAL and histology was not as good (mean difference, 27% cellularity, and differences between 5% and 220%). Conclusion: Adipocyte segmentation of histology slides provides a measure of volumetric fat fraction (i.e., adipocyte volume fraction [AVF]) and not chemical fat fraction, because fat fraction measured from histology is invariant to the relative abundances of lipid chemical species. In contrast, MP-IDEAL provides a measure of chemical fat fraction, thus explaining the poor agreement of this method with histology. SP-IDEAL measures the relative abundance of methylene lipids, and this measure is shown to be equivalent to AVF. AVF provides the appropriate parameter to account for patient-specific cellularity in BM mass predictive equations and is consistent with current micro-CTbased models of skeletal dosimetry.

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Section: Mri and Postprocessingmentioning

confidence: 99%

MRI Measurement of Bone Marrow Cellularity for Radiation Dosimetry

Pichardo

Milner²,

Bolch³

2011

J Nucl Med

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“…With different reasoning, others have suggested using the SVD to combine images (27,28) and spectra (9) from receive arrays without accounting for noise correlations. Figure 4 demonstrates the importance of noise whitening: with the exact noise covariance matrix, the WSVD algorithm is significantly less biased at all amplitudes and for all sizes of receive array than the SVD alone.…”

Section: Noise Whiteningmentioning

confidence: 99%

Receive array magnetic resonance spectroscopy: Whitened singular value decomposition (WSVD) gives optimal Bayesian solution

2010

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Receive array coils play a pivotal role in modern MRI. MR spectroscopy can also benefit from the enhanced signal-tonoise ratio and field of view provided by a receive array. In any experiment using an n-element array, n different complex spectra will be recorded and each spectrum unavoidably contains an undesired noise contribution. Previous algorithms for combining spectra have ignored the fact that the noise detected by different array elements is correlated. We introduce here an algorithm for efficiently, robustly, and automatically combining these n spectra using noise whitening and the singular value decomposition to provide the single combined spectrum that has maximum likelihood in the presence of this correlated noise. Simulations are performed that demonstrate the superiority of this approach to previous methods. Experiments in phantoms and in vivo on the brain, heart, and liver of normal volunteers, at 1.5 T and 3 T, using array coils from eight to 32 elements and with 1 H and 31 P nuclei, validate our approach, which provides signal-to-noise ratio improvements of up to 60% in our tests. The whitening and the singular value decomposition algorithm become most advantageous for large arrays, when the noise is markedly correlated, and when the signal-to-noise ratio is low. Key words: MR spectroscopy; array; coil combination; WSVD; SVD; noise whitening MR spectroscopy provides unique insights into the chemical composition of a subject in a completely noninvasive manner. For example, chemical shift imaging (CSI) and single voxel spectroscopy allow measurement of the concentrations of metabolites containing nuclei such as 1 H and 31 P, offering a window into biochemical processes occurring in vivo. Nevertheless, constraints on the signalto-noise ratio (SNR) obtainable with current technology are one of the primary factors limiting clinical applications of MR spectroscopy. We report our recent work to alleviate this SNR limitation through an improved method for combining the data gathered from receive array coils.Receive array coils have a long history in the MRI community following the work of Hyde et al. (1) and Roemer et al. (2). By replacing the single radiofrequency receive coil in an MR scanner with an array of smaller coils (''array elements''), improvements in SNR are obtained. The smaller size of each of these elements makes them couple more strongly with the magnetization in the subject under examination, giving stronger signals and hence a larger SNR than with a single element coil. Furthermore, although each element has a smaller field of view, the field of view covered by at least one coil may be very large. Thus, when the signals from each element are combined appropriately, a receive array provides data of significantly enhanced SNR that cover a wider field of view. The Roemer et al. (2) founding paper on receive array MRI introduced a widely accepted model of the array detection process, which we use here to allow a unified description of existing methods for receive array combination in MR sp...

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“…Other strategies include Local Look (LoLo), reduced FOV imaging, segmented k ‐space, wavelet encoding, and non‐Cartesian k ‐space sampling using spiral or radial trajectories (67, 70, 73–76). Parallel acquisition of image data using techniques such as SMASH and SENSE can reduce scan time by using the local spatial information that can be acquired from each coil within a phased array to reduce the number of phase‐encoding steps without reducing in‐plane resolution (68, 77–84). Using parallel processing imaging, speed generally increases by approximately a factor of 2–3, but as the number of coils within phased array increases, so does the imaging speed.…”

Section: Supplemental Technical Developmentsmentioning

confidence: 99%

MR‐guided biopsy: A review of current techniques and applications

Weiss

Nour

Lewin

2008

Magnetic Resonance Imaging

104

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Biopsy has become a cornerstone of modern medicine and most modern biopsies are performed percutaneously using image guidance, typically computed tomography or ultrasound. MR-guided biopsy offers many advantages over these more traditional modalities, and the recent development of interventional MR imaging techniques has made MR-guided percutaneous biopsies and aspirations a clinical reality. As the field of MR-guided procedures continues to expand and to attract more attention from radiologists, it is important to understand the concepts, techniques, applications, advantages, and limitations of MR-guided biopsy/percutaneous procedures. Radiologists should also recognize the need for their significant involvement in the technical aspects of MR-guided procedures, since several user-defined parameters can alter device visualization in the MR imaging environment and affect procedure safety. This article reviews the prerequisites, systems, and applications of MR-guided biopsy.

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Image construction methods for phased array magnetic resonance imaging

Cited by 20 publications

References 34 publications

MRI Measurement of Bone Marrow Cellularity for Radiation Dosimetry

MRI Measurement of Bone Marrow Cellularity for Radiation Dosimetry

Receive array magnetic resonance spectroscopy: Whitened singular value decomposition (WSVD) gives optimal Bayesian solution

MR‐guided biopsy: A review of current techniques and applications

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