Effect of the Relationship between Respiratory Interval and Temporal Resolution on Image Quality in Free-breathing Abdominal MR Imaging.

PURPOSE: To evaluate how the relationship between respiratory interval (RI) and temporal resolution (TR) impacts image quality in free-breathing abdominal MRI (FB-aMRI) using golden-angle radial sparse parallel (GRASP). METHODS: Ten healthy volunteers (25.9 ± 2.5 years, four women) underwent 2 mins free-breathing fat-suppression T1-weighted imaging using GRASP at RIs of 3 and 5s (RI3 and RI5, respectively) and retrospectively reconstructed at TR of 1.8, 2.9, 4.8, and 7.7s (TR1.8, TR2.9, TR4.8, and TR7.7, respectively) in each patient. The standard deviation (SD) under the diaphragm was measured using SD maps showing the discrepancy for each horizontal section at all TRs. Two radiologists evaluated image quality (visualization of the right hepatic vein at the confluence of the inferior vena cava, posterior segment branch of portal vein, pancreas, left kidney, and artifacts) at all TRs using a 5-point scale. RESULTS: The SD was significantly higher at TR1.8 compared to TR4.8 (P < 0.01) and TR7.7 (P < 0.001), as well as at TR2.9 compared to TR7.7 (P < 0.01) for both RIs. The SD between TR4.8 and TR7.7 did not differ for both RIs. For all visual assessment metrics, the TR1.8 scores were significantly lower than the TR4.8 and TR7.7 scores for both RIs. The pancreas and left kidney scores at TR2.9 were significantly lower than those at TR7.7 (P < 0.05) for RI5. Additionally, the left kidney score at TR1.8 was lower than that at TR2.9 (P < 0.05) for RI3. All scores at TR2.9, TR4.8, and TR7.7 were similar for RI3, while those at TR4.8 and TR7.7 were similar for RI5. CONCLUSION: Prolonging the TRs compared to RIs enhances image quality in FB-aMRI using GRASP.

Usefulness of Breath-Hold Fat-Suppressed T2-Weighted Images With Deep Learning-Based Reconstruction of the Liver: Comparison to Conventional Free-Breathing Turbo Spin Echo.

OBJECTIVES: The aim of this study was to evaluate the usefulness of breath-hold turbo spin echo with deep learning-based reconstruction (BH-DL-TSE) in acquiring fat-suppressed T2-weighted images (FS-T2WI) of the liver by comparing this method with conventional free-breathing turbo spin echo (FB-TSE) and breath-hold half Fourier single-shot turbo spin echo with deep learning-based reconstruction (BH-DL-HASTE). MATERIALS AND METHODS: The study cohort comprised 111 patients with suspected liver disease who underwent 3 T magnetic resonance imaging. Fifty-eight focal solid liver lesions ≥10 mm were also evaluated. Three sets of FS-T2WI were acquired using FB-TSE, prototypical BH-DL-TSE, and prototypical BH-DL-HASTE, respectively. In the qualitative analysis, 2 radiologists evaluated the image quality using a 5-point scale. In the quantitative analysis, we calculated the lesion-to-liver signal intensity ratio (LEL-SIR). Friedman test and Dunn multiple comparison test were performed to assess differences among 3 types of FS-T2WI with respect to image quality and LEL-SIR. RESULTS: The mean acquisition time was 4 minutes and 43 seconds ± 1 minute and 21 seconds (95% confidence interval, 4 minutes and 28 seconds to 4 minutes and 58 seconds) for FB-TSE, 40 seconds for BH-DL-TSE, and 20 seconds for BH-DL-HASTE. In the qualitative analysis, BH-DL-HASTE resulted in the fewest respiratory motion artifacts ( P < 0.0001). BH-DL-TSE and FB-TSE exhibited significantly less motion-related signal loss and clearer intrahepatic vessels than BH-DL-HASTE ( P < 0.0001). Regarding the edge sharpness of the left lobe, BH-DL-HASTE scored the highest ( P < 0.0001), and BH-DL-TSE scored higher than FB-TSE ( P = 0.0290). There were no significant differences among 3 types of FS-T2WI with respect to the edge sharpness of the right lobe ( P = 0.1290), lesion conspicuity ( P = 0.5292), and LEL-SIR ( P = 0.6026). CONCLUSIONS: BH-DL-TSE provides a shorter acquisition time and comparable or better image quality than FB-TSE, and could replace FB-TSE in acquiring FS-T2WI of the liver. BH-DL-TSE and BH-DL-HASTE have their own advantages and may be used complementarily.

Optimal Temporal Resolution to Achieve Good Image Quality and Perform Pharmacokinetic Analysis in Free-breathing Dynamic Contrast-enhanced MR Imaging of the Pancreas.

PURPOSE: The optimal temporal resolution for free-breathing dynamic contrast-enhanced MRI (FBDCE-MRI) of the pancreas has not been determined. This study aimed to evaluate the appropriate temporal resolution to achieve good image quality and to perform pharmacokinetic analysis in FBDCE-MRI of the pancreas using golden-angle radial sparse parallel (GRASP). METHODS: Sixteen participants (53 ± 15 years, eight females) undergoing FBDCE-MRI were included in this prospective study. Images were retrospectively reconstructed at four temporal resolutions (1.8, 3.0, 4.8, and 7.8s). Two radiologists (5 years of experience) evaluated the image quality of each reconstructed image by assessing the visualization of the celiac artery (CEA), the common hepatic artery, the splenic artery, each area of the pancreas, and artifacts using a 5-point scale. Using Tissue-4D, pharmacokinetic parameters were calculated for each area in the reconstructed images at each temporal resolution for 16 examinations, excluding two with errors in the pharmacokinetic modeling analysis. Friedman and Bonferroni tests were used for analysis. A P value < 0.05 was considered statistically significant. RESULTS: During vascular assessment, only scores for the CEA at 7.8s were significantly lower than the other temporal resolutions. Scores of all pancreatic regions and artifacts were significantly lower at 1.8s than at 4.8s and 7.8s. In the pharmacokinetic analysis, all volume transfer coefficients (Ktrans), rate constants (Kep), and the initial area under the concentration curve (iAUC) in the pancreatic head and tail were significantly lower at 4.8s and 7.8s than at 1.8s. iAUC in the pancreatic body and extracellular extravascular volume fraction (Ve) in the pancreatic head were significantly lower at 7.8s than at 1.8s. CONCLUSION: A temporal resolution of 3.0s is appropriate to achieve image quality and perform pharmacokinetic analysis in FBDCE-MRI of the pancreas using GRASP.

Optimization of scan protocol for high temporal resolution magnetic resonance imaging of the liver under single breath-holding using compressed sensing and parallel imaging techniques in a 1.5-T magnetic resonance system.

OBJECTIVE: To optimize the scan protocol for high temporal resolution magnetic resonance (MR) imaging of the liver under single breath-holding, using compressed sensing (CS) and parallel imaging (PI) techniques in a 1.5 T MR system. METHODS: 31 healthy volunteers who underwent fat-suppressed gradient-echo T 1 weighted imaging using a 1.5 T MR system were included. Image quality was evaluated on altering various imaging parameters in CS and PI so that the scan time was adjusted to 10 and 6 s within a single breath-holding. Normalized standard deviation (nSD = SD/mean value) and signal-to-noise ratio (SNR = mean value/SD) of liver signal intensity were measured. Visual scores for the outline of the liver and inferior right hepatic vein (IRHV) were evaluated using a 4-point scale and compared with that of the reference standard (20 s scan without CS). RESULTS: The nSD and SNR were not significantly different when the 10 s scan with CS factor 2.0 and the 6 s scan with CS factor 2.0 and 2.5 were compared to the 20 s scan. Overall visual score (mean score of the outline of the liver and IRHV) was significantly better (p < 0.05) with the 10 s scan with CS factor 2.0 compared to the other scan protocols. CONCLUSION: The 10 s scan with CS factor 2.0 should be recommended for high temporal resolution MR imaging of the liver using CS and PI in a 1.5 T MR system. ADVANCES IN KNOWLEDGE: This study conducts a novel MR imaging of the liver using CS and PI in a 1.5 T MR system.

High-resolution three-dimensional T1-weighted hepatobiliary MR cholangiography using Gd-EOB-DTPA for assessment of biliary tree anatomy: Parallel imaging versus compressed sensing.

PURPOSE: To compare the quality of images obtained by T1-weighted hepatobiliary MR cholangiography using Gd-EOB-DTPA with 1-mm isovoxel acquisition and compressed sensing (T1-MRCCS) or parallel imaging (T1-MRCPI) for assessment of biliary tree anatomy. METHOD: We prospectively reviewed T1-MRCCS, T1-MRCPI, and respiratory-triggered 3D T2-weighted MR cholangiography (T2-MRC) images in 58 patients. Two radiologists independently assessed the three sets of images and scored the biliary tree visualization and overall image quality in all cases using a 5-point Likert scale. The resulting scores were compared among T1-MRCCS, T1-MRCPI, and T2-MRC images using a Friedman test followed by a Scheffe test. The inter-reader agreement in scoring was assessed using κ statistics. RESULTS: The image quality scores for the gallbladder on both T1-MRCCS and T1-MRCPI were significantly lower than those on T2-MRC (p < 0.01) for both readers. Meanwhile, the image quality scores for the right and left hepatic ducts and the anterior and posterior branches of the right hepatic duct on both T1-MRCCS and T1-MRCPI were significantly higher than those on T2-MRC (p < 0.05) for both readers. For Reader 2, the overall image quality scores on T1-MRCCS and T1-MRCPI were both significantly higher than those on T2-MRC (p < 0.05). There were no significant differences between the image quality scores on T1-MRCCS and T1-MRCPI for visualization of each bile duct (p < 0.05). CONCLUSIONS: There may be no significant difference in quality between T1-MRCCS images and T1-MRCPI images for assessment of biliary tree anatomy, and both types of images may be better than T2-MRC images, although clinical indication is limited compared with T2-MRC.

Usefulness of breath-hold compressed sensing accelerated three-dimensional magnetic resonance cholangiopancreatography (MRCP) added to respiratory-gating conventional MRCP.

PURPOSE: To clarify the clinical usefulness of breath-hold compressed sensing three-dimensional magnetic resonance cholangiopancreatography (BH-MRCP) added to conventional respiratory-gating MRCP (RG-MRCP), we prospectively evaluated the image quality of BH-MRCP and compared it with that of RG-MRCP. We also evaluated to what extent the overall image quality was improved by adding BH-MRCP to RG-MRCP. MATERIALS AND METHODS: A total of 113 patients who underwent RG-MRCP and BH-MRCP at a 3-T MR unit were enrolled. We set a scan time of approximately 180 s for RG-MRCP and 20 s for BH-MRCP before examination, and measured actual scan time and assessed image quality using a 5-point scale (5, good; 1, poor). Image quality scores of 1, 2 and 3 were considered clinically inadequate. Image quality scores of RG-MRCP and BH-MRCP were compared. In addition, we compared "RG-MRCP alone" and "hybrid MRCP" (the best-scoring image was picked from RG-MRCP and BH-MRCP when the RG-MRCP score was clinically inadequate). RESULTS: The mean actual scan time of RG-MRCP/BH-MRCP was 191/20 s. The mean scores of RG-MRCP, BH-MRCP and hybrid MRCP were 3.67, 3.35 and 3.92, respectively. The score of hybrid MRCP was significantly better than that of RG-MRCP (P <  0.05). The image quality of RG-MRCP was clinically inadequate in 43/113 (38 %) cases and the inadequate image quality was improved to be clinically adequate in 13/43 (30 %) cases by adding BH-MRCP. CONCLUSION: BH-MRCP brings added value to RG-MRCP because an additional examination of BH-MRCP could compensate for the image deterioration of RG-MRCP caused by motion artifacts.