OBJECTIVE The purpose of this study was to evaluate the reproducibility (interreviewer agreement) and repeatability (intrareviewer agreement) of ROI sampling strategies to measure chemical shift–encoded (CSE) MRI-based liver proton density fat fraction (PDFF) and R2* (1 / T2*). A secondary purpose was to standardize ROI-based liver PDFF and R2* measurements by providing a compromise between measurement reproducibility and repeatability and time burden for image analysts. MATERIALS AND METHODS CSE data from two cohorts were retrospectively analyzed. Cohort A included 53 patients referred for abdominal MRI and healthy subjects recruited for a comparison study of CT and MRI. Cohort B included 37 patients with suspected liver iron overload. Three reviewers measured liver PDFF and R2* using previously reported ROI sampling strategies. Inter- and intrareviewer agreement of liver PDFF and R2* were evaluated using Bland-Altman analysis. RESULTS Averaging largest-fit ROIs over the nine Couinaud segments resulted in the narrowest limits of agreement (LOA) for liver PDFF and R2* measurements in both cohorts. For PDFF, interreviewer agreement had mean LOA of ± 0.8% for cohort A and ± 1.7% for cohort B. Intrareviewer agreement was ± 0.5% for cohort A and ± 0.9% for cohort B. For R2* interreviewer agreement had mean LOA of ± 3.0 s−1 for cohort A and ± 17.9 s−1 for cohort B. Intrareviewer agreement was ± 2.6 s−1 for cohort A and ± 14.6 s−1 for cohort B. This approach was the most time-burdensome, requiring a mean ± SD of 149.7 ± 8.6 s per dataset. CONCLUSION For improved reproducibility and repeatability of liver PDFF and R2* measurements, clinicians and researchers should sample as much area of the liver as possible using multiple large ROIs.

Objectives Objectives of this study were to compare radial time-resolved phase contrast magnetic resonance imaging (4D Flow-MRI) with perivascular ultrasound (pvUS) and to explore a porcine model of acute pre-hepatic portal hypertension (PHTN). Methods Abdominal 4D Flow-MRI and pvUS in portal and splenic vein, hepatic and both renal arteries were performed in 13 pigs of approximately 60 kg. In six pigs, measurements were repeated after partial portal vein (PV) ligature. Inter-and intra-reader comparisons and statistical analysis including Bland–Altman (BA) comparison, paired Student’s t tests and linear regression were performed. Results PvUS and 4D Flow-MRI measurements agreed well; flow before partial PV ligature was 322 ± 30 ml/min in pvUS and 297 ± 27 ml/min in MRI (p = 0.294), and average BA difference was 25 ml/min [−322; 372]. Inter- and intra-reader results differed very little, revealed excellent correlation (R2 = 0.98 and 0.99, respectively) and resulted in BA differences of −5 ml/min [−161; 150] and −2 ml/min [−28; 25], respectively. After PV ligature, PV flow decreased from 356 ± 50 to 298 ± 61 ml/min (p = 0.02), and hepatic arterial flow increased from 277 ± 36 to 331 ± 65 ml/min (p = n.s.). Conclusion The successful in vivo comparison of radial 4D Flow-MRI to perivascular ultrasound revealed good agreement of abdominal blood flow although with considerable spread of results. A model of pre-hepatic PHTN was successfully introduced and acute responses monitored.

Background The off-label use of ferumoxytol (FE), an intravenous iron preparation for iron deficiency anemia, as a contrast agent for MRI is increasing; therefore, it is critical to understand its pharmacokinetics. Purpose To evaluate the pharmacokinetics of FE in the abdomen and pelvis, as assessed with quantitative 1.5-and 3.0-T MRI relaxometry. Materials and Methods R2*, an MRI technique used to estimate tissue iron content in the abdomen and pelvis, was performed at 1.5 and 3.0 T in 12 healthy volunteers between April 2015 and January 2016. Volunteers were randomly assigned to receive an FE dose of 2 mg per kilogram of body weight (FE 2mg ) or 4 mg/kg (FE 4mg ). MRI was repeated at 1.5 and 3.0 T for each volunteer at five time points: days 1, 2, 4, 7, and 30. A radiologist experienced in MRI relaxometry measured R2* in organs of the mononuclear phagocyte system (MPS) (ie, liver, spleen, and bone marrow), non-MPS anatomy (kidney, pancreas, and muscle), inguinal lymph nodes (LNs), and blood pool. A paired Student t test was used to compare changes in tissue R2*. Results Volunteers (six female; mean age, 44.3 years ± 12.2 [standard deviation]) received either FE 2mg (n = 5) or FE 4mg (n = 6). Overall R2* trend analysis was temporally significant (P < .001). Time to peak R2* in the MPS occurred on day 1 for FE 2mg and between days 1 and 4 for FE 4mg (P < .001 to P < .002). Time to peak R2* in non-MPS anatomy, LNs, and blood pool occurred on day 1 for both doses (P < .001 to P < .09). Except for the spleen (at 1.5 T) and liver, MPS R2* remained elevated through day 30 for both doses (P = .02 to P = .03). Except for the kidney and pancreas, non-MPS, LN, and blood pool R2* returned to baseline levels between days 2 and 4 at FE 2mg (P = .06 to P = .49) and between days 4 and 7 at FE 4mg (P = .06 to P = .63). There was no difference in R2* change between non-MPS and LN R2* at any time (range, 1-71 sec −1 vs 0-50 sec −1 ; P = .06 to P = .97). Conclusion The pharmacokinetics of ferumoxytol in lymph nodes are distinct from those in mononuclear phagocyte system (MPS) organs, parallel non-MPS anatomy, and the blood pool.

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