Purpose or Case Report: Acquiring high-resolution diagnostic pediatric MR images is challenging due to patient movement during long scan times, resulting in spatial blurring and motion artifacts. Developing rapid acquisition methods is essential to obtaining diagnostic-quality MR images. Recently, an echo planar imaging (EPI)-based Multi-Inversion Spin and Gradient Echo (MI-SAGE) sequence was reported to acquire multiple tissue contrasts from adult brains with a single 1-minute scan. This study demonstrates the utility of a 1-minute MI-SAGE acquisition in pediatric subjects to generate clinically relevant synthetic image contrasts (T1w, T2w, T2*w) from quantitative relaxometry maps (T1, T2, and T2*).
Methods & Materials: In this IRB-approved study, 17 pediatric research participants underwent MI-SAGE scans (32 slices with 1.2mm resolution), MOLLI, GRASE, mFFE, and other standard weighted images on a 3T scanner (Elition; Philips Healthcare). The MI-SAGE T1, T2, and T2* parametric maps were estimated using in-house software (MATLAB). The T1, T2, and T2* values for grey matter (GM), white matter (WM), and cerebrospinal (CSF) were obtained by drawing matching regions of interest (ROIs) for both MI-SAGE maps and scanner-generated maps from conventional mapping sequences. Synthetic-weighted images were calculated from the MI-SAGE parametric maps and compared to standard weighted images using grey to white matter ratio (GWR).
Results: Study participants ranged from 3-10 years (mean age: 6.5 years; 10 males). The MI-SAGE method successfully estimated maps and synthetic images with minimal motion artifacts. The mean T1 and T2 values correlated to the values of conventional methods across subjects (p<0.05) and were comparable to values reported in the literature. The synthetic images showed similar grey and white matter contrast as standard images, with a mean (SD) GWR across subjects from synthetic images of 39 (4), -51 (13), and -20 (6)% for T1w, T2w, and T2*w respectively, and a GWR of 74 (5), -38 (6), and -23 (5)% for T1w, T2w, and T2*w from standard images.
Conclusions: A 1-minute MI-SAGE approach on awake pediatric subjects was shown to generate clinically relevant synthetic image contrasts that were not affected by motion artifacts. The relaxometry values obtained using MI-SAGE correlated with the values from conventional methods. The GWR of synthetic images was similar to standard images but acquired 5x faster.