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Objectives: The aims of this study were to observe the pattern of transient motion after gadoxetic acid administration including incidence, onset, and duration, and to evaluate the clinical feasibility of free-breathing gadoxetic acid-enhanced liver magnetic resonance imaging using golden-angle radial sparse parallel (GRASP) imaging with respiratory gating., Materials and Methods: In this institutional review board-approved prospective study, 59 patients who provided informed consents were analyzed. Free-breathing dynamic T1-weighted images (T1WIs) were obtained using GRASP at 3 T after a standard dose of gadoxetic acid (0.025 mmol/kg) administration at a rate of 1 mL/s, and development of transient motion was monitored, which is defined as a distinctive respiratory frequency alteration of the self-gating MR signals. Early arterial, late arterial, and portal venous phases retrospectively reconstructed with and without respiratory gating and with different temporal resolutions (nongated 13.3-second, gated 13.3-second, gated 6-second T1WI) were evaluated for image quality and motion artifacts. Diagnostic performance in detecting focal liver lesions was compared among the 3 data sets., Results: Transient motion (mean duration, 21.5 ± 13.0 seconds) was observed in 40.0% (23/59) of patients, 73.9% (17/23) of which developed within 15 seconds after gadoxetic acid administration. On late arterial phase, motion artifacts were significantly reduced on gated 13.3-second and 6-second T1WI (3.64 ± 0.34, 3.61 ± 0.36, respectively), compared with nongated 13.3-second T1WI (3.12 ± 0.51, P < 0.0001). Overall, image quality was the highest on gated 13.3-second T1WI (3.76 ± 0.39) followed by gated 6-second and nongated 13.3-second T1WI (3.39 ± 0.55, 2.57 ± 0.57, P < 0.0001). Only gated 6-second T1WI showed significantly higher detection performance than nongated 13.3-second T1WI (figure of merit, 0.69 [0.63-0.76]) vs 0.60 [0.56-0.65], P = 0.004)., Conclusions: Transient motion developed in 40% (23/59) of patients shortly after gadoxetic acid administration, and gated free-breathing T1WI using GRASP was able to consistently provide acceptable arterial phase imaging in patients who exhibited transient motion.

Purpose: This study aimed to determine whether an iterative model-based reconstruction (IMR) can improve lesion conspicuity and depiction on computed tomography (CT) compared with filtered back projection (FBP) and hybrid iterative reconstruction (iDose) using anthropomorphic phantoms., Materials and Methods: One small and one large anthropomorphic body phantoms, each containing 8 simulated focal liver lesions (FLLs), were scanned using a 256-channel CT scanner at 120 kVp with variable tube current-time products (10-200 mAs). Scans were divided into 3 groups based on radiation dose (RD) as follows: (a) full dose (FD), (b) low dose (FD50), and (c) ultralow dose (FD25 for the large phantom, FD15 for the small phantom). All images were reconstructed using FBP, iDose, and IMR. Image noise and lesion-to-liver contrast were assessed quantitatively and qualitatively. Thereafter, 6 radiologists independently evaluated conspicuity of FLLs, and then, compared the number of invisible FLLs on 3 image sets of each RD group., Results: Image noise was significantly lower with IMR than with FBP and iDose at the same RD. Iterative model-based reconstruction improved conspicuity of low-contrast FLLs in all RD groups compared to the others (P < 0.001). Furthermore, compared to FBP and iDose, the number of visible FLLs significantly increased on IMR images in the FD15 group of the small phantom 52.8% [38/72], 68.1% [49/72], and 84.8% [61/72], respectively; P < 0.001) and in the FD 25, FD50 groups of the large phantom (FD50: 56.9% [41/72], 76.4% [55/72], and 84.7% [61/72], respectively; P < 0.05)., Conclusions: Iterative model-based reconstruction reduced image noise and improved low-contrast FLL conspicuity, compared to FBP and iDose. Therefore, depiction of low-contrast FLLs on FBP could be improved using IMR.

Objective: The objective of this study was to evaluate the feasibility and accuracy of postcontrast, dual-energy computed tomography (DECT) using multimaterial decomposition (MMD) for quantification of the hepatic fat fraction (HFF)., Methods: Various degrees of fatty liver were produced in 16 rabbits divided into 4 groups, by feeding them a high-fat, high-cholesterol diet. After 6 weeks, precontrast, single-energy computed tomography (SECT) and postcontrast DECT were performed, and HFF maps were obtained from the DECT using MMD. T2*-corrected, multiecho, chemical-shift imaging for obtaining the proton density fat fraction (PDFF) map and histologic assessment of the hepatic steatosis were also performed. The Pearson correlations coefficients were calculated, and Bland-Altman analysis was performed of the fat fractions determined by DECT, magnetic resonance imaging (MRI), and pathology. Receiver operating characteristic curve analysis was performed to detect 5% hepatic steatosis or greater. The histologic HFF was used as the reference standard, and PDFFs determined by chemical-shift imaging as the technical standard., Results: The HFFs calculated by MMD of postcontrast DECT scans were strongly correlated with those of pathology as well as the PDFFs of MRI (P < 0.05), and the mean differences of the Bland-Altman plots between the HFFs of DECT with MMD and the PDFFs of MRI were close to zero. The diagnostic performance of postcontrast DECT with MMD for detecting 5% hepatic steatosis or greater was comparable to that of the attenuation value of precontrast SECT and the PDFFs of MRI (P = 0.17-0.82)., Conclusions: Quantification of the HFF using postcontrast DECT with MMD was feasible and showed comparable sensitivity and specificity to the precontrast SECT for the detection of hepatic steatosis.

Objective: The objective of this study was to investigate the image quality and diagnostic performance of model-based iterative reconstruction (MBIR) for hepatic vessel evaluation on low-tube-voltage (100 kilovolt [peak]) liver computed tomography (CT) for living donors., Methods: Fifty-one liver donor candidates (low-kilovolt group) underwent low-tube-voltage CT, which was reconstructed using filtered back projection, adaptive statistical iterative reconstruction, and MBIR. Additional 51 donor candidates who underwent 120-kilovolt (peak) CT using FBP were selected as matching control (standard group). The volume CT dose index, image noise, contrast-to-noise ratios, diagnostic accuracy, and confidence of hepatic vasculatures were evaluated., Results: Significant dose reduction was obtained with low-tube-voltage CT. The MBIR images of the low-kilovolt group showed significantly lower image noise and higher contrast-to-noise ratios than did the other image sets (P < 0.001). Regarding diagnostic accuracy and confidence of hepatic vessel anatomic variations with surgical correlation, the MBIR images provided results equivalent to those of other images (P > 0.05)., Conclusions: Low-tube-voltage liver CT using MBIR may increase image quality and preserve diagnostic performance of hepatic vessel evaluation at reduced radiation dose.