Liver diffusion-weighted MR imaging with L1-regularized iterative sensitivity encoding reconstruction based on single-shot echo-planar imaging: initial clinical experience.

To investigate whether combining L1-regularized iterative sensitivity encoding (SENSE) reconstruction and single-shot echo planar imaging (EPI) is useful in hepatic DWI. Single-shot EPI-DWI with L1-regularized iterative SENSE reconstruction (L1-DWI) and conventional parallel imaging-based reconstruction (conv-DWI) in liver MRI were compared in volunteers and patients. For the patient cohort, 75 subjects (60 ± 13 years) with 349 focal liver lesions (FLL) were included. Patient groups A and B were used to reduce acquisition time or improve spatial resolution, respectively. Image parameters were rated on a 5-point scale. The number of FLLs was recorded; in case of discrepancy, the reason for non-detectability was analyzed. In volunteers, higher signal-to-noise ratio (24.4 ± 5.6 vs. 12.2 ± 2.3, p < 0.001 at b = 0; 19.3 ± 2.8 vs. 9.8 ± 1.6, p < 0.001 at b = 800) and lower standard deviation of the apparent diffusion coefficient-values (0.17 vs. 0.20 mm2/s, p < 0.05) were found on L1-DWI compared to conv-DWI. In patients, image ratings were similar for all parameters except for "conspicuity of FLLs" which was rated significantly lower on L1-DWI vs. conv-DWI (4.7 ± 0.6 vs. 4.2 ± 0.9, p < 0.05) in group A. In five patients, 11/349 FLLs were not detectable on L1-DWI, but on conv-DWI. L1-regularized iterative reconstruction of single-shot EPI DWI can accelerate image acquisition or improve spatial resolution. However, our finding that FLLs were non-detectable on L1-DWI warrants further research.

Relaxation-Enhanced Angiography without Contrast and Triggering (REACT) for pelvic MR venography in comparison to balanced gradient-echo and T2-weighted spin-echo techniques.

RATIONALE AND OBJECTIVES: To evaluate the imaging capabilities of the REACT pulse sequence in pelvic venous vessels compared to conventional non-contrast pulse sequences. MATERIALS AND METHODS: In addition to routine MRI venography, non-contrast enhanced REACT pulse sequence was performed in 4 healthy volunteers and 21 patients with suspected or known deep venous thrombosis and post thrombotic syndrome. Acquired images were independently interpreted by two MRI radiologists. The sequence performance was subjectively evaluated on a four-point scale regarding the delineation of small peripheral, midsize and large proximal venous vessels, the imaging of vascular pathologies, and the degradation due to artifacts. To evaluate statistical differences in diagnostic accuracy Friedman's test with Dunn's correction was used. RESULTS: REACT depicted the peripheral veins superior to bTFE and T2-TSE with an average score of 3.39 compared to 2.33 in bTFE and 1.77 in T2-TSE. In midsize vessels REACT performed significantly better than T2-TSE (1.94) and bTFE (2.68) with a score of 3.64. For the large proximal vessels REACT (3.39), bTFE (3.33) and T2-TSE (3.56) performed equally without statistical difference. Visibility of venous pathologies was found to be equal between REACT (3.62), bTFE (3.51) and T2-TSE (3.52). The image degradation due to artifacts was rated best in T2-TSE (3.56), followed by REACT (3.39) and bTFE (3.33). CONCLUSIONS: REACT is a promising tool for the visualization of the pelvic venous system using magnetic resonance imaging.