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.

Graphical Abstract