Comparison of chemical shift-encoded water-fat MRI and MR spectroscopy in quantification of marrow fat in postmenopausal females.

PURPOSE: To validate a chemical shift-encoded (CSE) water-fat imaging for quantifying marrow fat fraction (FF), using proton magnetic resonance spectroscopy (MRS) as reference. MATERIALS AND METHODS: Multiecho T2 -corrected MRS and CSE imaging with eight-echo gradient-echo acquisitions at 3T were performed to calculate marrow FF in 83 subjects, including 41 with normal bone mineral density (BMD), 26 with osteopenia, and 16 with osteoporosis (based on DXA). Eight participants were scanned three times with repositioning to assess the repeatability of CSE FF map measurements. Pearson correlation coefficient, Bland-Altman 95% limit of agreement, and Lin's concordance correlation coefficient were calculated. RESULTS: The Pearson correlation coefficient was 0.979 and Lin's concordance correlation coefficient was 0.962 between CSE-based FF and MRS-based FF. All data points, calculated using the Bland-Altman method, were within the limits of agreement. The intra- and interrater agreement for average CSE-based FF was excellent (intrarater, intraclass correlation coefficient [ICC] = 0.993; interrater, ICC = 0.976-0.982 for different BMD groups). In the subgroups of varying BMD, inverse correlations were observed to be very similar between BMD (r = -0.560 to -0.710), T-score (r = -0.526 to -0.747), and CSE-based FF, and between BMD (r = -0.539 to -0.706), T-score (r = -0.501 to -0.742), and MRS-based FF even controlling for age, years since menopause, and body mass index. The repeatability for CSE FF map measurements expressed as absolute precision error was 1.45%. CONCLUSION: CSE imaging is equally accurate in characterizing marrow fat content as MRS. Given its excellent correlation and concordance with MRS, the CSE sequence could be used as a potential replacement technique for marrow fat quantification. LEVEL OF EVIDENCE: 1 J. Magn. Reson. Imaging 2017;45:66-73.

To assess differential features of marrow adiposity between postmenopausal women with osteoarthritis and osteoporosis using water/fat MRI.

OBJECTIVE: To assess the differential features of marrow adiposity between osteoarthritis (OA) and osteoporosis (OP) in postmenopausal women using water/fat MRI. METHODS: This cross-sectional study included 97 postmenopausal women (OA [n = 25], OA + osteopenia [n = 27], OA + OP [n = 23], and OP groups [n = 22]). Water/fat MRI, dual-energy x-ray absorptiometry and biochemical analysis were performed to assess vertebral marrow fat fraction, bone mineral density, and bone biomarkers, respectively. Harris Hip Score was recorded to evaluate hip function. RESULTS: There were significant differences in marrow fat content among the OA, OA + osteopenia, and OA + OP groups, between OP and OA participants with normal bone mass or osteopenia (all P < 0.05); no significant difference was observed between OA + OP and OP groups. Serum levels of leptin and ß-Crosslaps in OA with normal bone mass and osteopenic OA groups were higher than in OP group. Marrow fat fraction was inversely correlated with Harris Hip Score (r = -0.371, P = 0.013), bone mineral density (r = -0.554, P = 0.009) and leptin levels (r = -0.610, P < 0.001). In multivariate regression analysis, marrow fat fraction was found to have a consistent and unchanged inverse association with leptin levels (Sß = -0.311, P = 0.002) and bone mineral density (Sß =  -0.265, P = 0.006) after adjusting for age, years since menopause, and body mass index. CONCLUSIONS: Postmenopausal OA with OP have a phenotype with higher marrow adiposity. OA and OP could coexist, for the presence of a specific subgroup of OA with increased marrow fat accumulation and high risk of developing OP.

Short- and midterm reproducibility of marrow fat measurements using mDixon imaging in healthy postmenopausal women.

OBJECTIVE: We tested the short- and midterm reproducibility of vertebral marrow fat fraction (FF) measurements using mDixon imaging. MATERIALS AND METHODS: Thirty postmenopausal women underwent mDixon scans to obtain L1-4 FF from three slices per vertebra by two independent observers (session 1). Measurements were repeated after 6 weeks (session 2) and 6 months (session 3). The mean FF for three regions of interest per vertebra was calculated. The coefficients of variation (CVs) were calculated for each participant and imaging session, and the intraclass correlation coefficients (ICCs) were calculated to assess interobserver and intersession agreements. RESULTS: There were no significant differences in FF measurements among the three slices, imaging sessions or observers. The mean intrasubject CV for FF measurement reproducibility was 1.94 %. The interobserver agreement for the average FF value was excellent (ICC ≥0.945 for each session). The ICC for intersession agreement was excellent (ICC ≥0.955 between sessions). The mean intersession CV was lower within a short-term interval (2.97 %) than within sessions 1 and 3 (4.80 %) or sessions 3 and 2 (4.44 %). The overall mean CV for the reproducibility of FF measured with mDixon imaging over the short- and midterm was 4.09 % (95 % CI, 3.79-4.40 %). CONCLUSION: mDixon is a reproducible method for FF quantification over short- and midterm intervals up to 6 months in healthy postmenopausal women. Our results also provide data by which a power analysis can be optimized when designing studies involving the use of FF derived from similar mDixon sequences.

Longitudinal assessment of marrow fat content using three-point Dixon technique in osteoporotic rabbits.

OBJECTIVE: In this longitudinal pilot study, we aimed to investigate the intra-, interobserver, and scan-rescan reproducibility of marrow fat fraction (FF) measurements using three-point Dixon imaging in osteoporotic rabbits: comparison with histopathology. METHODS: Twenty female rabbits were randomly assigned to sham-operation and ovariectomy in combination with daily methylprednisolone hemisuccinate groups (n = 10 per group). Marrow FF by three-point Dixon technique and bone density by dual-energy x-ray absorptiometry were assessed at baseline, 6 and 12 weeks after operation. Intra-, inter-reader, and scan-rescan reliability of FF measurements were evaluated using intraclass correlation coefficient (ICC) and Bland-Altman 95% limit of agreement. Histomorphometry was performed to quantify marrow adipocyte parameters. RESULTS: Intra- and inter-reader reproducibility of FF measurements was "substantial" (ICC = 0.984 and 0.978, respectively). Although the ICC for scan-rescan reliability was excellent (ICC = 0.962), increased measurement variability was observed using Bland-Altman plot. Relative to the sham-operated rabbits, the adipocytes mean diameter, density, and percent adipocytes area in the osteoporotic rabbits increased by 23.4%, 68.9%, and 117.0%, respectively. Marrow FF was positively correlated with the quantitative parameters of adipocytes, particularly with percent adipocyte area, but inversely associated with bone density. At the relatively early stage, the percentage of bone loss was similar to that of elevated fatty marrow in the osteoporotic rabbits; at the later stage, the change for the latter outweighed that of the former. CONCLUSIONS: Results of three-point Dixon technique demonstrated a very reproducible manner within and between observers and acceptable scan-rescan performance in the assessment of marrow fat in rabbits.

Preliminary Study of MR Diffusion Tensor Imaging of the Liver for the Diagnosis of Hepatocellular Carcinoma.

OBJECTIVES: To evaluate the feasibility of differentiating between hepatocellular carcinomas (HCC) and healthy liver using diffusion tensor imaging (DTI). MATERIAL AND METHODS: All subjects underwent an abdominal examination on a 3.0T MRI scanner. Two radiologists independently scored the image quality (IQ). An optimal set of DTI parameters was obtained from a group of fifteen volunteers with multiple b-values (100, 300, 500, and 800 s/mm2) and various diffusion-encoding directions (NED = 6, 9, and 12)using two way ANOVA analysis. Eighteen Patients with HCC underwent DTI scans with the optimized parameters. Fractional anisotropy(FA) and average apparent diffusion coefficient (ADC) values were measured. The differences of FA and ADC values between liver healthy region and HCC lesion were compared through paired t tests. RESULTS: There were no significant changes in liver IQ and FA/ADC values with increased NED(P >0.05), whereas the liver IQ and FA/ADC values decreased significantly with increased b-values(P <0.05). Good IQ, acceptable scan time and reasonable FA/ADC values were acquired using NED = 9 with b-value of (0,300) s/mm2. Using the optimized DTI sequence, ADC value of the tumor lesion was significantly lower than that of the healthy liver region (1.30 ± 0.34×10-3 vs 1.52 ± 0.27×10-3 mm2/s, P = 0.013), whereas the mean FA value of the tumor lesion (0.42 ± 0.11) was significantly higher than the normal liver region (0.32 ± 0.10) (P = 0.004). CONCLUSION: Either FA or ADC value from DTI can be used to differentiate HCC from healthy liver. HCC lead to higher FA value and lower ADC value on DTI than healthy liver.