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NCBI: db=pubmed; Term=Nishimura DG[Author] OR Pauly JM[Author] OR Macovski A[Author] OR Kerr AB[Author] OR greig scott mri OR John Pauly OR Dwight Nishimura
Updated: 5 hours 25 min ago

Technique development of 3D dynamic CS-EPSI for hyperpolarized 13 C pyruvate MR molecular imaging of human prostate cancer.

Wed, 03/28/2018 - 07:58
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Technique development of 3D dynamic CS-EPSI for hyperpolarized 13 C pyruvate MR molecular imaging of human prostate cancer.

Magn Reson Med. 2018 Mar 25;:

Authors: Chen HY, Larson PEZ, Gordon JW, Bok RA, Ferrone M, van Criekinge M, Carvajal L, Cao P, Pauly JM, Kerr AB, Park I, Slater JB, Nelson SJ, Munster PN, Aggarwal R, Kurhanewicz J, Vigneron DB

Abstract
PURPOSE: The purpose of this study was to develop a new 3D dynamic carbon-13 compressed sensing echoplanar spectroscopic imaging (EPSI) MR sequence and test it in phantoms, animal models, and then in prostate cancer patients to image the metabolic conversion of hyperpolarized [1-13 C]pyruvate to [1-13 C]lactate with whole gland coverage at high spatial and temporal resolution.
METHODS: A 3D dynamic compressed sensing (CS)-EPSI sequence with spectral-spatial excitation was designed to meet the required spatial coverage, time and spatial resolution, and RF limitations of the 3T MR scanner for its clinical translation for prostate cancer patient imaging. After phantom testing, animal studies were performed in rats and transgenic mice with prostate cancers. For patient studies, a GE SPINlab polarizer (GE Healthcare, Waukesha, WI) was used to produce hyperpolarized sterile GMP [1-13 C]pyruvate. 3D dynamic 13 C CS-EPSI data were acquired starting 5 s after injection throughout the gland with a spatial resolution of 0.5 cm3 , 18 time frames, 2-s temporal resolution, and 36 s total acquisition time.
RESULTS: Through preclinical testing, the 3D CS-EPSI sequence developed in this project was shown to provide the desired spectral, temporal, and spatial 5D HP 13 C MR data. In human studies, the 3D dynamic HP CS-EPSI approach provided first-ever simultaneously volumetric and dynamic images of the LDH-catalyzed conversion of [1-13 C]pyruvate to [1-13 C]lactate in a biopsy-proven prostate cancer patient with full gland coverage.
CONCLUSION: The results demonstrate the feasibility to characterize prostate cancer metabolism in animals, and now patients using this new 3D dynamic HP MR technique to measure kPL , the kinetic rate constant of [1-13 C]pyruvate to [1-13 C]lactate conversion.

PMID: 29575178 [PubMed - as supplied by publisher]

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Deep learning enables reduced gadolinium dose for contrast-enhanced brain MRI.

Wed, 02/14/2018 - 21:26
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Deep learning enables reduced gadolinium dose for contrast-enhanced brain MRI.

J Magn Reson Imaging. 2018 Feb 13;:

Authors: Gong E, Pauly JM, Wintermark M, Zaharchuk G

Abstract
BACKGROUND: There are concerns over gadolinium deposition from gadolinium-based contrast agents (GBCA) administration.
PURPOSE: To reduce gadolinium dose in contrast-enhanced brain MRI using a deep learning method.
STUDY TYPE: Retrospective, crossover.
POPULATION: Sixty patients receiving clinically indicated contrast-enhanced brain MRI.
SEQUENCE: 3D T1 -weighted inversion-recovery prepped fast-spoiled-gradient-echo (IR-FSPGR) imaging was acquired at both 1.5T and 3T. In 60 brain MRI exams, the IR-FSPGR sequence was obtained under three conditions: precontrast, postcontrast images with 10% low-dose (0.01mmol/kg) and 100% full-dose (0.1 mmol/kg) of gadobenate dimeglumine. We trained a deep learning model using the first 10 cases (with mixed indications) to approximate full-dose images from the precontrast and low-dose images. Synthesized full-dose images were created using the trained model in two test sets: 20 patients with mixed indications and 30 patients with glioma.
ASSESSMENT: For both test sets, low-dose, true full-dose, and the synthesized full-dose postcontrast image sets were compared quantitatively using peak-signal-to-noise-ratios (PSNR) and structural-similarity-index (SSIM). For the test set comprised of 20 patients with mixed indications, two neuroradiologists scored blindly and independently for the three postcontrast image sets, evaluating image quality, motion-artifact suppression, and contrast enhancement compared with precontrast images.
STATISTICAL ANALYSIS: Results were assessed using paired t-tests and noninferiority tests.
RESULTS: The proposed deep learning method yielded significant (n = 50, P < 0.001) improvements over the low-dose images (>5 dB PSNR gains and >11.0% SSIM). Ratings on image quality (n = 20, P = 0.003) and contrast enhancement (n = 20, P < 0.001) were significantly increased. Compared to true full-dose images, the synthesized full-dose images have a slight but not significant reduction in image quality (n = 20, P = 0.083) and contrast enhancement (n = 20, P = 0.068). Slightly better (n = 20, P = 0.039) motion-artifact suppression was noted in the synthesized images. The noninferiority test rejects the inferiority of the synthesized to true full-dose images for image quality (95% CI: -14-9%), artifacts suppression (95% CI: -5-20%), and contrast enhancement (95% CI: -13-6%).
DATA CONCLUSION: With the proposed deep learning method, gadolinium dose can be reduced 10-fold while preserving contrast information and avoiding significant image quality degradation.
LEVEL OF EVIDENCE: 3 Technical Efficacy: Stage 5 J. Magn. Reson. Imaging 2018.

PMID: 29437269 [PubMed - as supplied by publisher]

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Frequency shifting reduces but does not eliminate acoustic interference between echolocating bats: A theoretical analysis.

Sat, 11/04/2017 - 07:33
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Frequency shifting reduces but does not eliminate acoustic interference between echolocating bats: A theoretical analysis.

J Acoust Soc Am. 2017 Oct;142(4):2133

Authors: Perkins ML, Frank HK, Pauly JM, Hadly EA

Abstract
Bats have been observed to shift the frequency of their echolocation calls in the presence of other echolocating bats, ostensibly as a way to reduce acoustic interference. Few studies, however, have examined the theoretical efficacy of such jamming avoidance responses. The present study uses the wideband ambiguity function to analyze the effects of acoustic interference from conspecifics and congeneric heterospecifics on the target acquisition ability of Myotis californicus and Myotis yumanensis, specifically whether unilateral or bilateral frequency shifts reduce the effects of such interference. Model results suggest that in conspecific interactions, M. yumanensis recovers its target acquisition ability more completely and with less absolute frequency shift than does M. californicus, but that alternative methods of jamming avoidance may be easier to implement. The optimal strategy for reducing heterospecific interference is for M. californicus to downshift its call and M. yumanensis to upshift its call, which exaggerates a preexisting difference in mean frequency between the calls of the two species. Further empirical research would elucidate whether these species do in practice actively employ frequency shifting or other means for jamming avoidance, as well as illuminate the role of acoustic interference in niche partitioning.

PMID: 29092549 [PubMed - in process]

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Thermo-Acoustic Ultrasound for Detection of RF-Induced Device Lead Heating in MRI.

Sat, 10/21/2017 - 06:26
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Thermo-Acoustic Ultrasound for Detection of RF-Induced Device Lead Heating in MRI.

IEEE Trans Med Imaging. 2017 Oct 17;:1

Authors: Dixit N, Stang PP, Pauly JM, Scott GC

Abstract
Patients who have implanted medical devices with long conductive leads are often restricted from receiving MRI scans due to the danger of RF-induced heating near the lead tips. Phantom studies have shown that this heating varies significantly on a case-by-case basis, indicating that many patients with implanted devices can receive clinically useful MRI scans without harm. However, the difficulty of predicting RF-induced lead tip heating prior to scanning prevents numerous implant recipients from being scanned. Here, we demonstrate that thermo-acoustic ultrasound (TAUS) has the potential to be utilized for a prescan procedure assessing the risk of RF-induced lead tip heating in MRI. A system was developed to detect TAUS signals by four different TAUS acquisition methods. We then integrated this system with an MRI scanner and detected a peak in RF power absorption near the tip of a model lead when transmitting from the scanner's body coil. We also developed and experimentally validated simulations to characterize the thermo-acoustic signal generated near lead tips. These results indicate that TAUS is a promising method for assessing RF implant safety, and with further development, a TAUS pre-scan could allow many more patients to have access to MRI scans of significant clinical value.Patients who have implanted medical devices with long conductive leads are often restricted from receiving MRI scans due to the danger of RF-induced heating near the lead tips. Phantom studies have shown that this heating varies significantly on a case-by-case basis, indicating that many patients with implanted devices can receive clinically useful MRI scans without harm. However, the difficulty of predicting RF-induced lead tip heating prior to scanning prevents numerous implant recipients from being scanned. Here, we demonstrate that thermo-acoustic ultrasound (TAUS) has the potential to be utilized for a prescan procedure assessing the risk of RF-induced lead tip heating in MRI. A system was developed to detect TAUS signals by four different TAUS acquisition methods. We then integrated this system with an MRI scanner and detected a peak in RF power absorption near the tip of a model lead when transmitting from the scanner's body coil. We also developed and experimentally validated simulations to characterize the thermo-acoustic signal generated near lead tips. These results indicate that TAUS is a promising method for assessing RF implant safety, and with further development, a TAUS pre-scan could allow many more patients to have access to MRI scans of significant clinical value.

PMID: 29053449 [PubMed - as supplied by publisher]

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Body diffusion-weighted imaging using magnetization prepared single-shot fast spin echo and extended parallel imaging signal averaging.

Thu, 10/19/2017 - 21:23
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Body diffusion-weighted imaging using magnetization prepared single-shot fast spin echo and extended parallel imaging signal averaging.

Magn Reson Med. 2017 Oct 17;:

Authors: Gibbons EK, Vasanawala SS, Pauly JM, Kerr AB

Abstract
PURPOSE: This work demonstrates a magnetization prepared diffusion-weighted single-shot fast spin echo (SS-FSE) pulse sequence for the application of body imaging to improve robustness to geometric distortion. This work also proposes a scan averaging technique that is superior to magnitude averaging and is not subject to artifacts due to object phase.
THEORY AND METHODS: This single-shot sequence is robust against violation of the Carr-Purcell-Meiboom-Gill (CPMG) condition. This is achieved by dephasing the signal after diffusion weighting and tipping the MG component of the signal onto the longitudinal axis while the non-MG component is spoiled. The MG signal component is then excited and captured using a traditional SS-FSE sequence, although the echo needs to be recalled prior to each echo. Extended Parallel Imaging (ExtPI) averaging is used where coil sensitivities from the multiple acquisitions are concatenated into one large parallel imaging (PI) problem. The size of the PI problem is reduced by SVD-based coil compression which also provides background noise suppression. This sequence and reconstruction are evaluated in simulation, phantom scans, and in vivo abdominal clinical cases.
RESULTS: Simulations show that the sequence generates a stable signal throughout the echo train which leads to good image quality. This sequence is inherently low-SNR, but much of the SNR can be regained through scan averaging and the proposed ExtPI reconstruction. In vivo results show that the proposed method is able to provide diffusion encoded images while mitigating geometric distortion artifacts compared to EPI.
CONCLUSION: This work presents a diffusion-prepared SS-FSE sequence that is robust against the violation of the CPMG condition while providing diffusion contrast in clinical cases. Magn Reson Med, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

PMID: 29044721 [PubMed - as supplied by publisher]

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Mitigation of near-band balanced steady-state free precession through-plane flow artifacts using partial dephasing.

Wed, 10/11/2017 - 06:31

Mitigation of near-band balanced steady-state free precession through-plane flow artifacts using partial dephasing.

Magn Reson Med. 2017 Oct 10;:

Authors: Datta A, Cheng JY, Hargreaves BA, Baron CA, Nishimura DG

Abstract
PURPOSE: To mitigate artifacts from through-plane flow at the locations of steady-state stopbands in balanced steady-state free precession (SSFP) using partial dephasing.
METHODS: A 60° range in the phase accrual during a TR was created over the voxel by slightly unbalancing the slice-select dephaser. The spectral profiles of SSFP with partial dephasing for various constant flow rates and during pulsatile flow were simulated to determine if partial dephasing decreases through-plane flow artifacts originating near SSFP dark bands while maintaining on-resonant signal. Simulations were then validated in a flow phantom. Lastly, phase-cycled SSFP cardiac cine images were acquired with and without partial dephasing in six subjects.
RESULTS: Partial dephasing decreased the strength and non-linearity of the dependence of the signal at the stopbands on the through-plane flow rate. It thus mitigated hyper-enhancement from out-of-slice signal contributions and transient-related artifacts caused by variable flow both in the phantom and in vivo. In six volunteers, partial dephasing noticeably decreased artifacts in all of the phase-cycled cardiac cine datasets.
CONCLUSION: Partial dephasing can mitigate the flow artifacts seen at the stopbands in balanced SSFP while maintaining the sequence's desired signal. By mitigating hyper-enhancement and transient-related artifacts originating from the stopbands, partial dephasing facilitates robust multiple-acquisition phase-cycled SSFP in the heart. Magn Reson Med, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

PMID: 28994486 [PubMed - as supplied by publisher]

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Rapid compressed sensing reconstruction of 3D non-Cartesian MRI.

Tue, 09/26/2017 - 06:18

Rapid compressed sensing reconstruction of 3D non-Cartesian MRI.

Magn Reson Med. 2017 Sep 23;:

Authors: Baron CA, Dwork N, Pauly JM, Nishimura DG

Abstract
PURPOSE: Conventional non-Cartesian compressed sensing requires multiple nonuniform Fourier transforms every iteration, which is computationally expensive. Accordingly, time-consuming reconstructions have slowed the adoption of undersampled 3D non-Cartesian acquisitions into clinical protocols. In this work we investigate several approaches to minimize reconstruction times without sacrificing accuracy.
METHODS: The reconstruction problem can be reformatted to exploit the Toeplitz structure of matrices that are evaluated every iteration, but it requires larger oversampling than what is strictly required by nonuniform Fourier transforms. Accordingly, we investigate relative speeds of the two approaches for various nonuniform Fourier transform kernel sizes and oversampling for both GPU and CPU implementations. Second, we introduce a method to minimize matrix sizes by estimating the image support. Finally, density compensation weights have been used as a preconditioning matrix to improve convergence, but this increases noise. We propose a more general approach to preconditioning that allows a trade-off between accuracy and convergence speed.
RESULTS: When using a GPU, the Toeplitz approach was faster for all practical parameters. Second, it was found that properly accounting for image support can prevent aliasing errors with minimal impact on reconstruction time. Third, the proposed preconditioning scheme improved convergence rates by an order of magnitude with negligible impact on noise.
CONCLUSION: With the proposed methods, 3D non-Cartesian compressed sensing with clinically relevant reconstruction times (<2 min) is feasible using practical computer resources. Magn Reson Med, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

PMID: 28940748 [PubMed - as supplied by publisher]

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Self-Calibrating Wave-Encoded Variable-Density Single-Shot Fast Spin Echo Imaging.

Sat, 09/16/2017 - 06:13
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Self-Calibrating Wave-Encoded Variable-Density Single-Shot Fast Spin Echo Imaging.

J Magn Reson Imaging. 2017 Sep 14;:

Authors: Chen F, Taviani V, Tamir JI, Cheng JY, Zhang T, Song Q, Hargreaves BA, Pauly JM, Vasanawala SS

Abstract
BACKGROUND: It is highly desirable in clinical abdominal MR scans to accelerate single-shot fast spin echo (SSFSE) imaging and reduce blurring due to T2 decay and partial-Fourier acquisition.
PURPOSE: To develop and investigate the clinical feasibility of wave-encoded variable-density SSFSE imaging for improved image quality and scan time reduction.
STUDY TYPE: Prospective controlled clinical trial.
SUBJECTS: With Institutional Review Board approval and informed consent, the proposed method was assessed on 20 consecutive adult patients (10 male, 10 female, range, 24-84 years).
FIELD STRENGTH/SEQUENCE: A wave-encoded variable-density SSFSE sequence was developed for clinical 3.0T abdominal scans to enable high acceleration (3.5×) with full-Fourier acquisitions by: 1) introducing wave encoding with self-refocusing gradient waveforms to improve acquisition efficiency; 2) developing self-calibrated estimation of wave-encoding point-spread function and coil sensitivity to improve motion robustness; and 3) incorporating a parallel imaging and compressed sensing reconstruction to reconstruct highly accelerated datasets.
ASSESSMENT: Image quality was compared pairwise with standard Cartesian acquisition independently and blindly by two radiologists on a scale from -2 to 2 for noise, contrast, confidence, sharpness, and artifacts. The average ratio of scan time between these two approaches was also compared.
STATISTICAL TESTS: A Wilcoxon signed-rank tests with a P value under 0.05 considered statistically significant.
RESULTS: Wave-encoded variable-density SSFSE significantly reduced the perceived noise level and improved the sharpness of the abdominal wall and the kidneys compared with standard acquisition (mean scores 0.8, 1.2, and 0.8, respectively, P < 0.003). No significant difference was observed in relation to other features (P = 0.11). An average of 21% decrease in scan time was achieved using the proposed method.
DATA CONCLUSION: Wave-encoded variable-density sampling SSFSE achieves improved image quality with clinically relevant echo time and reduced scan time, thus providing a fast and robust approach for clinical SSFSE imaging.
LEVEL OF EVIDENCE: 1 TECHNICAL EFFICACY: Stage 6 J. Magn. Reson. Imaging 2017.

PMID: 28906567 [PubMed - as supplied by publisher]

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Robust Self-Calibrating nCPMG Acquisition: Application to Body Diffusion-Weighted Imaging.

Wed, 08/23/2017 - 21:43
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Robust Self-Calibrating nCPMG Acquisition: Application to Body Diffusion-Weighted Imaging.

IEEE Trans Med Imaging. 2017 Aug 17;:

Authors: Gibbons EK, Roux PL, Vasanawala SS, Pauly JM, Kerr AB

Abstract
This work demonstrates a robust diffusion-weighted single-shot FSE sequence in the presence of significant offresonance, which includes a variable-density acquisition and a self-calibrated reconstruction as improvements. An nCPMG SSFSE acquisition stabilizes both the main and parasitic echo families for each echo. This preserves both the in-phase and quadrature component of the magnetization throughout the echo train. However, nCPMG SS-FSE also promotes aliasing of the quadrature component, which complicates reconstruction. A new acquisition and reconstruction approach is presented here where the FOV is effectively doubled, but a partial k-space and variable density sampling is used to improve scan efficiency. The technique is presented in phantom scans to validate SNR and robustness against rapidly varying object phase. In vivo healthy volunteer examples and clinical cases are demonstrated in abdominal imaging. This new approach provides comparable SNR to previous nCPMG acquisition techniques as well as providing more uniform ADC maps in phantom scans. In vivo scans suggest that this method is more robust against motion than previous approaches. The proposed reconstruction is an improvement to the nCPMG sequence as it is auto-calibrating and is justified to accurately treat the signal model for the nCPMG SS-FSE sequence.

PMID: 28829307 [PubMed - as supplied by publisher]

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Comprehensive Multi-Dimensional MRI for the Simultaneous Assessment of Cardiopulmonary Anatomy and Physiology.

Sun, 07/16/2017 - 06:44

Comprehensive Multi-Dimensional MRI for the Simultaneous Assessment of Cardiopulmonary Anatomy and Physiology.

Sci Rep. 2017 Jul 13;7(1):5330

Authors: Cheng JY, Zhang T, Alley MT, Uecker M, Lustig M, Pauly JM, Vasanawala SS

Abstract
Diagnostic testing often assesses the cardiovascular or respiratory systems in isolation, ignoring the major pathophysiologic interactions between the systems in many diseases. When both systems are assessed currently, multiple modalities are utilized in costly fashion with burdensome logistics and decreased accessibility. Thus, we have developed a new acquisition and reconstruction paradigm using the flexibility of MRI to enable a comprehensive exam from a single 5-15 min scan. We constructed a compressive-sensing approach to pseudo-randomly acquire highly subsampled, multi-dimensionally-encoded and time-stamped data from which we reconstruct volumetric cardiac and respiratory motion phases, contrast-agent dynamics, and blood flow velocity fields. The proposed method, named XD flow, is demonstrated for (a) evaluating congenital heart disease, where the impact of bulk motion is reduced in a non-sedated neonatal patient and (b) where the observation of the impact of respiration on flow is necessary for diagnostics; (c) cardiopulmonary imaging, where cardiovascular flow, function, and anatomy information is needed along with pulmonary perfusion quantification; and in (d) renal function imaging, where blood velocities and glomerular filtration rates are simultaneously measured, which highlights the generality of the technique. XD flow has the ability to improve quantification and to provide additional data for patient diagnosis for comprehensive evaluations.

PMID: 28706270 [PubMed - in process]

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Slice profile effects on nCPMG SS-FSE.

Tue, 04/04/2017 - 08:00
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Slice profile effects on nCPMG SS-FSE.

Magn Reson Med. 2017 Mar 31;:

Authors: Gibbons EK, Le Roux P, Pauly JM, Kerr AB

Abstract
PURPOSE: To determine the effects of the RF refocusing pulse profile on the magnitude of the transverse signal smoothness throughout the echo train in non-Carr-Purcell-Meiboom-Gill (nCPMG) single-shot fast spin echo (SS-FSE) imaging and to design an RF refocusing pulse that provides improved signal stability. THEORY AND METHODS: nCPMG SS-FSE quadratic phase modulation requires sufficiently high and uniform refocusing flip angle to achieve a stable signal. Typically, refocusing pulses used in SS-FSE sequences are designed for minimum duration to minimize echo spacing and as a consequence have poor selectivity. However, delay-insensitive variable rate excitation Shinnar-Le Roux (DV-SLR) refocusing pulses can achieve both improved selectivity as well as a short duration. This class of RF pulse is compared against a traditional low time-bandwidth refocusing pulse in a nCPMG SS-FSE in simulation, phantom, and in vivo.
RESULTS: DV-SLR pulses achieve a more stable signal in simulation, phantom, and in vivo cases while maintaining an appropriately short duration as well as not dramatically increasing specific absorption rate (SAR) accumulation.
CONCLUSION: The nCPMG SS-FSE method demonstrates improved robustness when a more selective refocusing pulse is used. Refocusing pulses that use a time-varying excitation gradient can achieve this selectivity while maintaining short echo spacing. Magn Reson Med, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

PMID: 28370409 [PubMed - as supplied by publisher]

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Formulation of image fusion as a constrained least squares optimization problem.

Sat, 03/25/2017 - 07:40
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Formulation of image fusion as a constrained least squares optimization problem.

J Med Imaging (Bellingham). 2017 Jan;4(1):014003

Authors: Dwork N, Lasry EM, Pauly JM, Balbás J

Abstract
Fusing a lower resolution color image with a higher resolution monochrome image is a common practice in medical imaging. By incorporating spatial context and/or improving the signal-to-noise ratio, it provides clinicians with a single frame of the most complete information for diagnosis. In this paper, image fusion is formulated as a convex optimization problem that avoids image decomposition and permits operations at the pixel level. This results in a highly efficient and embarrassingly parallelizable algorithm based on widely available robust and simple numerical methods that realizes the fused image as the global minimizer of the convex optimization problem.

PMID: 28331885 [PubMed - in process]

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Autocalibrating motion-corrected wave-encoding for highly accelerated free-breathing abdominal MRI.

Wed, 12/14/2016 - 06:37
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Autocalibrating motion-corrected wave-encoding for highly accelerated free-breathing abdominal MRI.

Magn Reson Med. 2016 Dec 09;:

Authors: Chen F, Zhang T, Cheng JY, Shi X, Pauly JM, Vasanawala SS

Abstract
PURPOSE: To develop a motion-robust wave-encoding technique for highly accelerated free-breathing abdominal MRI.
METHODS: A comprehensive 3D wave-encoding-based method was developed to enable fast free-breathing abdominal imaging: (a) auto-calibration for wave-encoding was designed to avoid extra scan for coil sensitivity measurement; (b) intrinsic butterfly navigators were used to track respiratory motion; (c) variable-density sampling was included to enable compressed sensing; (d) golden-angle radial-Cartesian hybrid view-ordering was incorporated to improve motion robustness; and (e) localized rigid motion correction was combined with parallel imaging compressed sensing reconstruction to reconstruct the highly accelerated wave-encoded datasets. The proposed method was tested on six subjects and image quality was compared with standard accelerated Cartesian acquisition both with and without respiratory triggering. Inverse gradient entropy and normalized gradient squared metrics were calculated, testing whether image quality was improved using paired t-tests.
RESULTS: For respiratory-triggered scans, wave-encoding significantly reduced residual aliasing and blurring compared with standard Cartesian acquisition (metrics suggesting P < 0.05). For non-respiratory-triggered scans, the proposed method yielded significantly better motion correction compared with standard motion-corrected Cartesian acquisition (metrics suggesting P < 0.01).
CONCLUSION: The proposed methods can reduce motion artifacts and improve overall image quality of highly accelerated free-breathing abdominal MRI. Magn Reson Med, 2016. © 2016 International Society for Magnetic Resonance in Medicine.

PMID: 27943402 [PubMed - as supplied by publisher]

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A Millimeter-Wave Digital Link for Wireless MRI.

Wed, 11/09/2016 - 13:11
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A Millimeter-Wave Digital Link for Wireless MRI.

IEEE Trans Med Imaging. 2016 Oct 27;

Authors: Aggarwal K, Joshi K, Rajavi Y, Taghivand M, Pauly J, Poon A, Scott G

Abstract
A millimeter (mm) wave radio is presented in this work to support wireless MRI data transmission. High path loss and availability of wide bandwidth make mm-waves an ideal candidate for short range, high data rata communication required for wireless MRI. The proposed system uses a custom designed integrated chip (IC) mm-wave radio with 60 GHz as radio frequency carrier. In this work, we assess performance in a 1.5 T MRI field, with the addition of optical links between the console room and magnet. The system uses ON-OFF keying (OOK) modulation for data transmission and supports data rates from 200 Mb/s to 2.5 Gb/s for distances up-to 65 cm. The presence of highly directional, linearly polarized, on-chip dipole antennas on the mm-wave radio along with the time division multiplexing (TDM) circuitry allows multiple wireless links to be created simultaneously with minimal inter-channel interference. This leads to a highly scalable solution for wireless MRI.

PMID: 27810803 [PubMed - as supplied by publisher]

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Body diffusion weighted imaging using non-CPMG fast spin echo.

Wed, 11/09/2016 - 13:11
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Body diffusion weighted imaging using non-CPMG fast spin echo.

IEEE Trans Med Imaging. 2016 Oct 27;

Authors: Gibbons E, Le Roux P, Vasanawala S, Pauly J, Kerr A

Abstract
SS-FSE is a fast technique that does not suffer from off-resonance distortions to the degree that EPI does. Unlike EPI, SS-FSE is ill-suited to diffusion weighted imaging (DWI) due to the Carr-Purcell-Meiboom-Geill (CPMG) condition. Non- CPMG phase cycling does accommodate SS-FSE and DWI but places constraints on reconstruction, which are resolved here through parallel imaging. Additionally, improved echo stability can be achieved by using short duration and highly selective DIVERSE radiofrequency pulses. Here, signal-to-noise ratio (SNR) comparisons between EPI and nCPMG SS-FSE acquisitions and reconstruction techniques give similar values. Diffusion imaging with nCPMG SS-FSE gives similar SNR to an EPI acquisition, though apparent diffusion coefficient values are higher than seen with EPI. In vivo images have good image quality with little distortion. This method has the ability to capture distortionfree DWI images near areas of significant off-resonance as well as preserve adequate SNR. Parallel imaging and DIVERSE refocusing RF pulses allow shorter ETL compared to previous implementations and thus reduces phase encode direction blur and SAR accumulation.

PMID: 27810802 [PubMed - as supplied by publisher]

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Spectrally selective three-dimensional dynamic balanced steady-state free precession for hyperpolarized C-13 metabolic imaging with spectrally selective radiofrequency pulses.

Wed, 11/09/2016 - 13:11
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Spectrally selective three-dimensional dynamic balanced steady-state free precession for hyperpolarized C-13 metabolic imaging with spectrally selective radiofrequency pulses.

Magn Reson Med. 2016 Oct 21;:

Authors: Shang H, Sukumar S, von Morze C, Bok RA, Marco-Rius I, Kerr A, Reed GD, Milshteyn E, Ohliger MA, Kurhanewicz J, Larson PE, Pauly JM, Vigneron DB

Abstract
PURPOSE: Balanced steady-state free precession (bSSFP) sequences can provide superior signal-to-noise ratio efficiency for hyperpolarized (HP) carbon-13 ((13) C) magnetic resonance imaging by efficiently utilizing the nonrecoverable magnetization, but managing their spectral response is challenging in the context of metabolic imaging. A new spectrally selective bSSFP sequence was developed for fast imaging of multiple HP (13) C metabolites with high spatiotemporal resolution.
THEORY AND METHODS: This novel approach for bSSFP spectral selectivity incorporates optimized short-duration spectrally selective radiofrequency pulses within a bSSFP pulse train and a carefully chosen repetition time to avoid banding artifacts.
RESULTS: The sequence enabled subsecond 3D dynamic spectrally selective imaging of (13) C metabolites of copolarized [1-(13) C]pyruvate and [(13) C]urea at 2-mm isotropic resolution, with excellent spectral selectivity (∼100:1). The sequence was successfully tested in phantom studies and in vivo studies with normal mice.
CONCLUSION: This sequence is expected to benefit applications requiring dynamic volumetric imaging of metabolically active (13) C compounds at high spatiotemporal resolution, including preclinical studies at high field and, potentially, clinical studies.Magn Reson Med, 2016. © 2016 International Society for Magnetic Resonance in Medicine.

PMID: 27770458 [PubMed - as supplied by publisher]

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Reduced field-of-view DWI with robust fat suppression and unrestricted slice coverage using tilted 2D RF excitation.

Wed, 11/09/2016 - 13:11
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Reduced field-of-view DWI with robust fat suppression and unrestricted slice coverage using tilted 2D RF excitation.

Magn Reson Med. 2016 Sep 21;:

Authors: Banerjee S, Nishimura DG, Shankaranarayanan A, Saritas EU

Abstract
PURPOSE: Reduced field-of-view (rFOV) diffusion-weighted imaging (DWI) using 2D echo-planar radiofrequency (2DRF) excitation has been widely and successfully applied in clinical settings. The purpose of this work is to further improve its clinical utility by overcoming slice coverage limitations without any scan time penalty while providing robust fat suppression.
THEORY AND METHODS: During multislice imaging with 2DRF pulses, periodic sidelobes in the slice direction cause partial saturation, limiting the slice coverage. In this work, a tilting of the excitation plane is proposed to push the sidelobes out of the imaging section while preserving robust fat suppression. The 2DRF pulse is designed using Shinnar-Le Roux algorithm on a rotated excitation k-space. The performance of the method is validated via simulations, phantom experiments, and high in-plane resolution in vivo DWI of the spinal cord.
RESULTS: Results show that rFOV DWI using the tilted 2DRF pulse provides increased signal-to-noise ratio, extended coverage, and robust fat suppression, without any scan time penalty.
CONCLUSION: Using a tilted 2DRF excitation, a high-resolution rFOV DWI method with robust fat suppression and unrestricted slice coverage is presented. This method will be beneficial in clinical applications needing large slice coverage, for example, axial imaging of the spine, prostate, or breast. Magn Reson Med, 2016. © 2016 International Society for Magnetic Resonance in Medicine.

PMID: 27654126 [PubMed - as supplied by publisher]

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B0 mapping using rewinding trajectories (BMART).

Wed, 11/09/2016 - 13:11
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B0 mapping using rewinding trajectories (BMART).

Magn Reson Med. 2016 Aug 24;:

Authors: Baron CA, Nishimura DG

Abstract
PURPOSE: To create a B0 map and correct for off-resonance with minimal scan time increase for two-dimensional (2D) or 3D non-Cartesian acquisitions.
METHODS: Rewinding trajectories that bring the zeroth gradient moment to zero every repetition time (TR) were used to estimate the off-resonance with a center-out 3D cones trajectory, which required an increase in the minimum TR by 5%. The off-resonance estimation and correction was implemented using an algorithm based on binning and object-domain phase correction. B0 maps using BMART (B0 mapping using rewinding trajectories) were compared to maps obtained using separate scans with multiple echo time (TE) in a phantom and human brain.
RESULTS: Excellent agreement between BMART and the multiple-TE method were observed, and images corrected with BMART were deblurred.
CONCLUSION: BMART can correct for off-resonance without requiring an additional scan, and can be easily applied to center-out or projection trajectories (2D or 3D). Magn Reson Med, 2016. © 2016 International Society for Magnetic Resonance in Medicine.

PMID: 27555219 [PubMed - as supplied by publisher]

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Depletion-Mode GaN HEMT Q-Spoil Switches for MRI Coils.

Wed, 11/09/2016 - 13:11
Related Articles

Depletion-Mode GaN HEMT Q-Spoil Switches for MRI Coils.

IEEE Trans Med Imaging. 2016 Jun 28;

Authors: Lu J, Grafendorfer T, Zhang T, Vasanawala S, Robb F, Pauly J, Scott G

Abstract
Q-spoiling is the process of decoupling an MRI receive coil to protect the equipment and patient. Conventionally, Q-spoiling is performed using a PIN diode switch that draws significant current. In this work, a Q-spoiling technique using a depletion-mode Gallium Nitride HEMT device was developed for coil detuning at both 1.5 T and 3 T MRI. The circuits with conventional PIN diode Q-spoiling and the GaN HEMT device were implemented on surface coils. SNR was measured and compared for all surfaces coils. At both 1.5 T and 3 T, comparable SNR was achieved for all coils with the proposed technique and conventional Qspoiling. The GaN HEMT device has significantly reduced the required power for Q-spoiling. The GaN HEMT device also provides useful safety features by detuning the coil when unpowered.

PMID: 27362895 [PubMed - as supplied by publisher]

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Resolving phase ambiguity in dual-echo dixon imaging using a projected power method.

Wed, 11/09/2016 - 13:11
Related Articles

Resolving phase ambiguity in dual-echo dixon imaging using a projected power method.

Magn Reson Med. 2016 May 25;:

Authors: Zhang T, Chen Y, Bao S, Alley MT, Pauly JM, Hargreaves BA, Vasanawala SS

Abstract
PURPOSE: To develop a fast and robust method to resolve phase ambiguity in dual-echo Dixon imaging.
METHODS: A major challenge in dual-echo Dixon imaging is to estimate the phase error resulting from field inhomogeneity. In this work, a binary quadratic optimization program was formulated to resolve the phase ambiguity. A projected power method was developed to efficiently solve the optimization problem. Both the 1-peak fat model and 6-peak fat model were applied to three-dimensional (3D) datasets. Additionally, the proposed method was extended to dynamic magnetic resonance imaging (MRI) applications using the 6-peak fat model. With institutional review board (IRB) approval and patient consent/assent, the proposed method was evaluated and compared with region growing on 29 consecutive 3D high-resolution patient datasets.
RESULTS: Fast and robust water/fat separation was achieved by the proposed method in different representative 3D datasets and dynamic 3D datasets. Superior water/fat separation was achieved using the 6-peak fat model compared with the 1-peak fat model. Compared to region growing, the proposed method reduced water/fat swaps from 76 to 7% of the patient cohort.
CONCLUSION: The proposed method can achieve fast and robust phase error estimation in dual-echo Dixon imaging. Magn Reson Med, 2016. © 2016 Wiley Periodicals, Inc.

PMID: 27221766 [PubMed - as supplied by publisher]

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