Browsing by Author "Dimitrov, I. E."
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Item Accelerating Chemical Exchange Saturation Transfer MRI with Parallel Blind Compressed Sensing(John Wiley and Sons Inc.) She, H.; Greer, Joshua S.; Zhang, S.; Li, B.; Keupp, J.; Madhuranthakam, A. J.; Dimitrov, I. E.; Lenkinski, R. E.; Vinogradov, E.; Greer, Joshua S.Purpose: Chemical exchange saturation transfer is a novel and promising MRI contrast method, but it can be time-consuming. Common parallel imaging methods, like SENSE, can lead to reduced quality of CEST. Here, parallel blind compressed sensing (PBCS), combining blind compressed sensing (BCS) and parallel imaging, is evaluated for the acceleration of CEST in brain and breast. Methods: The CEST data were collected in phantoms, brain (N = 3), and breast (N = 2). Retrospective Cartesian undersampling was implemented and the reconstruction results of PBCS-CEST were compared with BCS-CEST and k-t sparse-SENSE CEST. The normalized RMSE and the high-frequency error norm were used for quantitative comparison. Results: In phantom and in vivo brain experiments, the acceleration factor of R = 10 (24 k-space lines) was achieved and in breast R = 5 (30 k-space lines), without compromising the quality of the PBCS-reconstructed magnetization transfer rate asymmetry maps and Z-spectra. Parallel BCS provides better reconstruction quality when compared with BCS, k-t sparse-SENSE, and SENSE methods using the same number of samples. Parallel BCS overperforms BCS, indicating that the inclusion of coil sensitivity improves the reconstruction of the CEST data. Conclusion: The PBCS method accelerates CEST without compromising its quality. Compressed sensing in combination with parallel imaging can provide a valuable alternative to parallel imaging alone for accelerating CEST experiments.Item Frequency Offset Corrected Inversion Pulse for B₀ and B₁ Insensitive Fat Suppression at 3T: Application to MR Neurography of Brachial Plexus(John Wiley and Sons Inc.) Wang, X.; Greer, Joshua S.; Dimitrov, I. E.; Pezeshk, P.; Chhabra, A.; Madhuranthakam, A. J.; Greer, Joshua S.BACKGROUND: The 3D short tau inversion recovery (STIR) sequence is routinely used in clinical MRI to achieve robust fat suppression. However, the performance of the commonly used adiabatic inversion pulse, hyperbolic secant (HS), is compromised in challenging areas with increased B₀ and B₁ inhomogeneities, such as brachial plexus at 3T. PURPOSE: To demonstrate the frequency offset corrected inversion (FOCI) pulse as an efficient fat suppression STIR pulse with increased robustness to B₀ and B₁ inhomogeneities at 3T, compared to the HS pulse. STUDY TYPE: Prospective. SUBJECTS/PHANTOM: Initial evaluation was performed in phantoms and one healthy volunteer by varying the B₁ field, while subsequent comparison was performed in three healthy volunteers and five patients without varying the B₁. FIELD STRENGTH/SEQUENCE: 3T; 3D TSE-STIR with HS and FOCI pulses. ASSESSMENT: Brachial plexus images were qualitatively evaluated by two musculoskeletal radiologists independently using a four-point grading scale for fat suppression, shading artifacts, and nerve visualization. STATISTICAL TEST: The Wilcoxon signed-rank test with P < 0.05 was considered statistically significant. RESULTS: Simulations and phantom experiments demonstrated broader bandwidth (2.5 kHz vs. 0.83 kHz, increased B₀ robustness) at the same adiabatic threshold and lower adiabatic threshold (5 μT vs. 7 μT at 3.5 ppm, increased B₁ robustness) at the same bandwidth with the FOCI pulse compared to the HS pulse. With increased bandwidth, the FOCI pulse achieved robust fat suppression even at 50% of maximum B₁ strength, while the HS pulse required > 75% of maximum B₁ strength. Compared to the standard 3D TSE-STIR with HS pulse, the FOCI pulse achieved uniform fat suppression (P < 0.05), better nerve visualization (P < 0.05), and minimal shading artifacts (P < 0.01) in brachial plexus at 3T. DATA CONCLUSION: The FOCI pulse has increased robustness to B₀ and B₁ inhomogeneities, compared to the HS LEVEL OF EVIDENCE: 1. TECHNICAL EFFICACY: Stage 1.