Free‐Breathing Volumetric Liver and Proton Density Fat Fraction Quantification in Pediatric Patients Using Stack‐of‐Radial MRI With Self‐Gating Motion Compensation

Abstract

Background: Stack-of-radial multiecho gradient-echo MRI is promising for free-breathing liver R * 2 quantification and may benefit children. Purpose: To validate stack-of-radial MRI with self-gating motion compensation in phantoms, and to evaluate it in children. Study Type: Prospective. Phantoms: Four vials with different R * 2 driven by a motion stage. Subjects: Sixteen pediatric patients with suspected nonalcoholic fatty liver disease or steatohepatitis (five females, 13 ± 4 years, body mass index 29.2 ± 8.6 kg/m 2). Field Strength/Sequences: Stack-of-radial, and 2D and 3D Cartesian multiecho gradient-echo sequences at 3T. Assessment: Ungated and gated stack-of-radial proton density fat fraction (PDFF) and R * 2 maps were reconstructed without and with self-gating motion compensation. Stack-of-radial R * 2 measurements of phantoms without and with motion were validated against reference 2D Cartesian results of phantoms without motion. In subjects, free-breathing stack-ofradial and reference breath-hold 3D Cartesian were acquired. Subject inclusion for statistical analysis and region of interest placement were determined independently by two observers. Statistical Tests: Phantom results were fitted with a weighted linear model. Demographic differences between excluded and included subjects were tested by multivariate analysis of variance. PDFF and R * 2 measurements were compared using Bland-Altman analysis. Interobserver agreement was assessed by the intraclass correlation coefficient (ICC). Results: Ungated stack-of-radial R * 2 inside moving phantom vials showed a significant positive bias of 64.3 s −1 (P < 0.00001), unlike gated results (P > 0.31). Subject inclusion decisions for statistical analysis from two observers were consistent. No significant differences were found between four excluded and 12 included subjects (P = 0.14). Compared to breath-hold Cartesian, ungated and gated free-breathing stack-of-radial exhibited mean R * 2 differences of 18.5 s −1 and 3.6 s −1. Mean PDFF differences were 1.1% and 1.0% for ungated and gated measurements, respectively. Interobserver agreement was excellent (ICC for PDFF = 0.99, ICC for R * 2 = 0.90; P < 0.0003).

Accelerated k‐space shift calibration for free‐breathing stack‐of‐radial MRI quantification of liver fat and

“…A multi-echo GRE stack-of-radial prototype sequence [24][25][26] with the baseline k-space shift calibration to sample all partitions was employed. Raw data were saved for offline retrospective reconstruction with different Acc values by discarding and calculating calibration data for the corresponding partitions and different Ave values for averaging (see the previous section).…”

Free-Breathing Liver Fat, $R_2^*$ and $B_0$ Field Mapping Using Multi-Echo Radial FLASH and Regularized Model-based Reconstruction

“…First, radial sampling is motion robust and well suited for dynamic imaging [14][15][16][17][18]. Second, self-gating techniques have been introduced for liver fat and R * 2 quantification to correct for motion during free-breathing volumetric acquisition [19][20][21]. For a multi-echo stack-of-stars volumetric acquisition, the long echo-train and volume coverage require long scan times of about 5 min.…”

“…Therefore, real-time acquisition becomes infeasible and self-gating is required to resolve respiration phases in free-breathing scans. These techniques, however, require about 800 radial spokes per echo and per partition to balance volumetric spatial resolution and temporal resolution [19,21].…”

Hepatic Iron Quantification Using a Free‐Breathing 3D Radial Gradient Echo Technique and Validation With a 2D Biopsy‐Calibrated R2* Relaxometry Method

“…Recently, 3D stack‐of‐radial multi‐echo GRE sequences have been investigated for R 2 * and FF quantification and were found to be promising alternatives to Cartesian sequences in patients unable to breath‐hold 19,20 . To further reduce the influence of respiratory motion on radial acquisitions, self‐gating motion compensation techniques have been proposed for stack‐of‐radial GRE scans to correct for the respiratory motion bias and produce accurate R 2 * quantification similar to that of breath‐hold 3D Cartesian GRE 21–23 . These studies, however, tested their techniques only in patients with normal to mild iron concentrations (HIC < 4 mg/g Fe dry weight tissue) at 3 T (R 2 * < 250 s −1 ), and the performance of these techniques still needs to be validated in patients with a wider range of hepatic iron overload.…”