Validation of Compressed Sensing Accelerated Magnetization Prepared Rapid Acquisition Gradient Echo for Fast and Reliable Brain Volume Measurement

Dual-Echo bSSFP for Rapid T2-Sensitive Quantitative Contrast Imaging at Ultra-Low Field.

OBJECTIVE Rapid characterization of transverse-relaxation-sensitive MRI contrast is important for evaluating tissue-dependent signal behavior, but remains challenging in ultra-low-field (ULF) MRI because of limited signal-to-noise ratio (SNR) and acquisition-efficiency constraints. This study aims to develop a rapid, high-SNR, sequence-specific T2-sensitive quantitative contrast imaging method for ULF MRI. METHODS A balanced dual-echo steady-state (bDESS) sequence was developed to acquire two echoes at predefined echo times within each repetition of a balanced steady-state free precession acquisition. A logarithmic-ratio operator, based on a mono-exponential attenuation approximation, was used to derive a sequence-specific T2-sensitive contrast index, termed T2SDI, from the two echo magnitudes. The proposed method was implemented on a custom-built 6.5 mT MRI system and evaluated using numerical simulations, CuSO₄ phantom experiments, and in vivo brain imaging. RESULTS Numerical simulations showed that T2SDI exhibited a monotonic and approximately linear dependence on T2 under controlled field-inhomogeneity conditions. Phantom experiments confirmed that bDESS-derived T2SDI increased with CPMG-measured reference T2 and showed higher SNR than dual-echo SPGR. The method was further demonstrated in vivo by generating T2SDI maps of the human brain. CONCLUSION This study presents a sequence-specific, index-based method for rapid T2-sensitive quantitative contrast imaging in ULF MRI. SIGNIFICANCE The proposed dual-echo bSSFP/bDESS method provides a high-SNR and time-efficient strategy for sequence-specific T2-sensitive contrast characterization at ultra-low field.

Evaluation of k-Space Acquisition Strategies in Nonuniform B0 (NuBo) MRI.

PURPOSE To evaluate k-space acquisition strategies for magnetic resonance imaging (MRI) in a nonuniform B0 (NuBo) field-cycling system, focusing on image quality, scan-time efficiency, robustness to B0 inhomogeneity, and RF coil bandwidth constraints. METHODS Three acquisition strategies were compared: single-shot turbo spin echo (SS-TSE), multi-echo spin echo (MESE) with repeated phase encoding, and spin echo single-point imaging (SE-SPI) without applied readout (RO) gradients. Experiments were performed on an open, low-field, field-cycling MRI system using a nonuniform electromagnet. Imaging performance was assessed using a phantom and biological samples under matched total scan-time conditions. RF coils with wide- and narrow-bandwidth designs were evaluated to study sensitivity trade-offs. Retrospective k-space undersampling and compressed sensing reconstruction were applied to investigate potential scan-time reduction for all acquisition strategies. RESULTS SE-SPI consistently achieved larger full width at half maximum (FWHM) values than SS-TSE and MESE, indicating improved edge definition. Edge sharpness was higher along the RO (PE1) direction but comparable along the PE (PE2) direction. SS-TSE provided the fastest k-space acquisition and the highest central k-space SNR but exhibited increased blurring and bandwidth-related signal loss. MESE improved edge definition over SS-TSE while requiring additional polarization cycles. SE-SPI also showed greater robustness to compressed sensing undersampling. CONCLUSION SE-SPI provides a robust acquisition strategy for MRI in nonuniform B0 field-cycling systems by improving image fidelity, maintaining uniform signal intensity, enabling efficient use of high-Q RF coils, and supporting compressed sensing acceleration.

Evaluation of acquisition strategies in IVIM-DKI brain imaging: Effects on image quality, parameter stability, and comparison with DSC perfusion.

BACKGROUND Intravoxelincoherent motion (IVIM) and diffusion kurtosis imaging (DKI) provide complementary information on cerebral microstructure and microvascular perfusion without contrast agents. However, clinical translation of IVIM-DKI imaging is limited by variability in b-value selection and signal averaging, leading to inconsistent parameter estimates, and by limited validation against contrast-enhanced perfusion MRI. This study aimed to identify a robust IVIM-DKI acquisition strategy and evaluate its relationship with DSC (Dynamic Susceptibility Contrast)-derived perfusion metrics. METHODS This prospective study included 29 adults undergoing brain MRI on a 3T scanner (uMR 780). IVIM-DKI was acquired using four protocols (A1-A4) with varying b-value density and averaging strategies, including high b-value sampling (A1), optimized low b-value-weighted acquisition with targeted averaging (A2), and reduced sampling schemes (A3-A4). DSC perfusion imaging was subsequently performed. Parametric maps were generated using vendor-provided tools. Standardized gray matter (GM) and white matter (WM) ROIs were placed by two blinded radiologists. Image quality (SNR, CNR), stability (CV), and GM-WM contrast were compared using Friedman tests. Spearman correlation and regression-based analysis were used to assess IVIM-DSC relationships. RESULTS A2 demonstrated higher SNR and CNR and lower CV for most IVIM-derived perfusion parameters (p < 0.05), while certain diffusion and kurtosis metrics showed superior performance with alternative acquisitions (MK with A1 and MD with A3). A2 also achieved the highest GM-WM ratios for f (2.25), rBF (2.89), and D* (1.53), indicating improved tissue contrast. IVIM perfusion parameters showed moderate correlations with DSC-derived perfusion metrics, with f demonstrating the strongest association with rCBF (ρ = 0.67) and D* showing the highest correlation with rCBV (ρ = 0.51). Equation-based analysis demonstrated a strong relationship between rCBV and c_CBV (r = 0.77, p < 0.001), whereas no meaningful association was observed between MTT and c_MTT (r = 0.03, p = 0.84). CONCLUSION An optimized low b-value-weighted acquisition with targeted averaging (A2) provided the strongest overall balance between image quality, parameter stability, tissue contrast, and correspondence with DSC-derived perfusion measures. IVIM perfusion metrics demonstrate physiologically meaningful but non-equivalent relationships with DSC, supporting their complementary role in perfusion assessment. PLAIN LANGUAGE SUMMARY Brain MRI scans can provide information about brain tissue structure and blood flow, but finding the best scan settings remains a challenge. This study compared several acquistion strategies for IVIM-DKI MRI in adults to identify which approach produced the most reliable image measurements and how these measurements related to a standard blood flow imaging technique. This study found that one optimized scanning method provided the best balance of image quality, measurement stability, tissue contrast, and agreement with blood flow measurements. This matters because more reliable brain imaging may help clinicians better assess brain health without relying solely on contrast agents.

Usefulness of Adaptive Complex Signal Average Diffusion-weighted MR Imaging of the Abdomen.

PURPOSE To evaluate the clinical feasibility and quantitative performance of adaptive complex signal average (ACSA) diffusion-weighted imaging (DWI) in abdominal MRI and to compare ACSA DWI with conventional non-ACSA DWI in terms of signal intensity (SI), SNR, apparent diffusion coefficient (ADC), signal intensity difference ratio (SIDR), and lesion contrast across different numbers of excitations (NEX). METHODS This retrospective study included 82 patients who underwent free-breathing abdominal DWI on a 3T system between January and July 2025. ACSA DWI was reconstructed from the same raw data as non-ACSA DWI using a combination of adaptive averaging and complex-domain averaging. ROIs were placed in the liver, pancreas, left adrenal gland, and spinal muscles to measure SI, SNR, and ADC. SIDR and inter-lobar right-left (R-L) ratio in SI and ADC were calculated at NEX 2, 3, and 4. For 37 patients with non-cystic hepatic nodules, lesion SI, ADC, contrast ratio, and contrast-to-noise ratio (CNR) were assessed. RESULTS ACSA DWI significantly increased SI and SNR in motion-prone organs, including the lateral hepatic segment, pancreas, and left adrenal gland, at all NEX levels (P < 0.05). ADC values in abdominal parenchymal organs and hepatic nodules were lower with ACSA DWI, reflecting the noise-floor suppression and adaptive average effects. R-L SI and ADC ratios were significantly different and were closer to 1 in ACSA DWI, indicating improved hepatic signal homogeneity. Lesion SI, contrast ratio, and CNR were significantly higher with ACSA DWI, enhancing nodule conspicuity. CONCLUSION ACSA DWI improves signal uniformity, SNR, and lesion contrast while maintaining reasonable ADC quantification. Without prolonging scan time or modifying acquisition parameters, ACSA provides a robust, clinically feasible post-processing technique for enhancing both image quality and quantitative reliability in abdominal DWI.

Reproducibility of Volumetric Analysis using Ultra-Low-Field Portable Magnetic Resonance Imaging

Qualitative similarities between volume measurements in adults and the questions of reproducibility through test-retest reliability and external validity using recent software updates to the Hyperfine Swoop system constitute a crucial foundation for the clinical utility of 64 mT MRI in monitoring brain volume loss over time.

AI-based reconstruction from low-resolution acquisitions for diffusion MRI: evaluation of FOD similarity.