Accuracy of PDFF estimation by magnitude‐based and complex‐based MRI in children with MR spectroscopy as a reference

Abstract

Purpose To assess and compare the accuracy of magnitude-based MRI (MRI-M) and complex-based MRI (MRI-C) for estimating hepatic proton density fat fraction (PDFF) in children, using magnetic resonance spectroscopy (MRS) as the reference standard. A secondary aim was to assess the agreement between MRI-M and MRI-C. Methods This was a HIPAA-compliant, retrospective analysis of data collected in children enrolled in prospective, IRB-approved studies between 2012 and 2014. Informed consent was obtained from 200 children (ages 8–19 years) who subsequently underwent 3T MR exams that included MRI-M, MRI-C, and T1-independent, T2-corrected, single-voxel STEAM MRS. Both MRI methods acquired 6 echoes at low flip angles. T2*-corrected PDFF parametric maps were generated. PDFF values were recorded from regions of interest (ROIs) drawn on the maps in each of the 9 Couinaud segments and 3 ROIs co-localized to the MRS voxel location. Regression analyses assessing agreement with MRS were performed to evaluate accuracy of each MRI method, and Bland-Altman and ICC analyses were performed to assess agreement between the MRI methods. Results MRI-M and MRI-C PDFF were accurate relative to the co-localized MRS reference standard, with regression intercepts of 0.63% and −0.07%, slopes of 0.998 and 0.975, and proportion-of-explained-variance values (R2) of 0.982 and 0.979, respectively. For individual Couinaud segments and for the whole liver averages, Bland-Altman biases between MRI-M and MRI-C were small (ranging from 0.04 to 1.11%) and ICCs were high (≥0.978). Conclusions Both MRI-M and MRI-C accurately estimated hepatic PDFF in children, and high inter-method agreement was observed.

Cross‐sectional correlation between hepatic R2* and proton density fat fraction (PDFF) in children with hepatic steatosis

“…Further research is needed to confirm and explain the discrepancy in R2* estimation by MRI‐M and MRI‐C in the low R2* range. The slight underestimation of PDFF by MRI‐M is consistent with previous studies …”

“…We selected children because they rarely have excess hepatic iron and are an ideal population to determine the relationship between PDFF and R2* unconfounded by iron content. A secondary purpose of the study was to evaluate the agreement between MRI‐M and MRI‐C for estimating R2* values in human subjects, and to validate the high agreement between these techniques reported in prior studies for estimating PDFF …”

Accuracy and precision of proton density fat fraction measurement across field strengths and scan intervals: A phantom and human study

“…In our study, although small, there was an overestimation in CSE‐PDFF compared with MRS‐PDFF as indicated by an intercept of 1.74 and a mean bias of 3.4 PDFF%. Several studies have described minimal overestimation by CSE‐MRI, more so in the 1.5 T, than by MRS, while in a meta‐analysis CSE‐MRI slightly underestimated the MRS . Overestimation by CSE‐MRI could reflect residual T 1 bias, particularly as the parameters used in our study (TR = 8.9 msec and flip angle = 5° at 1.5 T) can induce ~2% of fat fraction measurement error .…”

“…Several studies have described minimal overestimation by CSE-MRI, more so in the 1.5 T, than by MRS, 30,31 while in a meta-analysis CSE-MRI slightly underestimated the MRS. 22 Overestimation by CSE-MRI could reflect residual T 1 bias, particularly as the parameters used in our study (TR = 8.9 msec and flip angle = 5 at 1.5 T) can inducẽ 2% of fat fraction measurement error. 30,32 Also, including all measurements from different field strengths/2-week interscan period and using a phased array coil identical to the one used in the clinical scan might have contributed to field inhomogeneity in the non-anthromorphologic phantom, resulting in greater measurement bias. 33 Additionally, because the CSE-MRI technique in the current study employed spectral models of fat based on body temperature, CSE-PDFF of the phantom with lower temperature (16-20 C) could deviate from MRS-PDFF.…”

Clinical strategy of diagnosing and following patients with nonalcoholic fatty liver disease based on invasive and noninvasive methods

“…An increasing number of studies have shown MRE to be an accurate method for diagnosing and staging hepatic fibrosis in patients with NAFLD (Table 4 ). Among the studies using MRE, the AUROC for diagnosis of stages > 1, > 2, > 3, and 4 ranged from 0.772 to 0.860, 0.856 to 890, 0.870 to 0.981, and 0.882 to 0.993, respectively [ 62 , 63 , 81 , 93 – 98 ]. The corresponding MRE liver stiffness cut-offs for mild fibrosis (stage > 1) or advanced fibrosis (stage > 3) ranged from 2.50 to 3.02 kPa or 2.99 to 4.80 kPa with a sensitivity of 44–75% or 33–91% and specificity of 77–91% or 80–94%, respectively.…”