A single 1-min brain MRI scan for generating multiple synthetic image contrasts in awake children from quantitative relaxometry maps.

Background: Diagnostically adequate contrast and spatial resolution in brain MRI require prolonged scan times, leading to motion artifacts and image degradation in awake children. Rapid multi-parametric techniques can produce diagnostic images in awake children, which could help to avoid the need for sedation.

Objective: To evaluate the utility of a rapid echo-planar imaging (EPI)-based multi-inversion spin and gradient echo (MI-SAGE) technique for generating multi-parametric quantitative brain maps and synthetic contrast images in awake pediatric participants.

Materials and methods: In this prospective IRB-approved study, awake research participants 3-10 years old were scanned using MI-SAGE, MOLLI, GRASE, mGRE, and T1-, T2-, T2*-, and FLAIR-weighted sequences. The MI-SAGE T1, T2, and T2* maps and synthetic images were estimated offline. The MI-SAGE parametric values were compared to those from conventional mapping sequences including MOLLI, GRASE, and mGRE, with assessments of repeatability and reproducibility. Synthetic MI-SAGE images and conventional weighted images were reviewed by a neuroradiologist and scored using a 5-point Likert scale. Gray-to-white matter contrast ratios (GWRs) were compared between MI-SAGE synthetic and conventional weighted images. The results were analyzed using the Bland-Altman analysis and intra-class correlation coefficient (ICC).

Results: A total of 24 healthy participants aged 3 years to 10 years (mean ± SD, 6.5 ± 1.9; 12 males) completed full imaging exams including the 54-s MI-SAGE acquisition and were included in the analysis. The MI-SAGE T1, T2, and T2* had biases of 32%, -4%, and 23% compared to conventional mapping methods using MOLLI, GRASE, and mGRE, respectively, with moderate to very strong correlations (ICC=0.49-0.99). All MI-SAGE maps exhibited strong to very strong repeatability and reproducibility (ICC=0.80 to 0.99). The synthetic MI-SAGE had average Likert scores of 2.1, 2.1, 2.9, and 2.0 for T1-, T2-, T2*-, and FLAIR-weighted images, respectively, while conventional acquisitions had Likert scores of 3.5, 3.6, 4.6, and 3.8 for T1-, T2-, T2*-, and FLAIR-weighted images, respectively. The MI-SAGE synthetic T1w, T2w, T2*w, and FLAIR GWRs had biases of 17%, 3%, 7%, and 1% compared to the GWR of images from conventional T1w, T2w, T2*w, and FLAIR acquisitions respectively.

Conclusion: The derived T1, T2, and T2* maps were correlated with conventional mapping methods and showed strong repeatability and reproducibility. While synthetic MI-SAGE images had greater susceptibility artifacts and lower Likert scores than conventional images, the MI-SAGE technique produced synthetic weighted images with contrasts similar to conventional weighted images and achieved a ten-fold reduction in scan time.