Synthetic MRI of the Knee: Phantom Validation and Comparison with Conventional MRI

Abstract

Purpose To test the hypothesis that synthetic MRI of the knee generates accurate and repeatable quantitative maps and produces morphologic MR images with similar quality and detection rates of structural abnormalities than does conventional MRI. Materials and Methods Data were collected prospectively between January 2017 and April 2018 and were retrospectively analyzed. An International Society for Magnetic Resonance in Medicine-National Institute of Standards and Technology phantom was used to determine the accuracy of T1, T2, and proton density (PD) quantification. Statistical models were applied for correction. Fifty-four participants (24 men, 30 women; mean age, 40 years; range, 18-62 years) underwent synthetic and conventional 3-T MRI twice on the same day. Fifteen of 54 participants (28%) repeated the protocol within 9 days. The intra- and interday agreements of quantitative cartilage measurements were assessed. Contrast-to-noise (CNR) ratios, image quality, and structural abnormalities were assessed on corresponding synthetic and conventional images. Statistical analyses included the Wilcoxon test, χ test, and Cohen Kappa. P values less than or equal to .01 were considered to indicate a statistically significant difference. Results Synthetic MRI quantification of T1, T2, and PD values had an overall model-corrected error margin of 0.8%. The synthetic MRI interday repeatability of articular cartilage quantification had native and model-corrected error margins of 3.3% and 3.5%, respectively. The cartilage-to-fluid CNR and menisci-to-fluid CNR was higher on synthetic than conventional MR images (P ≤ .001, respectively). Synthetic MRI improved short-tau inversion recovery fat suppression (P ˂ .01). Intermethod agreements of structural abnormalities were good (kappa, 0.621-0.739). Conclusion Synthetic MRI of the knee is accurate for T1, T2, and proton density quantification, and simultaneously generated morphologic MR images have detection rates of structural abnormalities similar to those of conventional MR images, with similar acquisition time. © RSNA, 2018.

Rapid multicontrast brain imaging on a 0.35T MR‐linac

“…PD values measured in the ISMRM/NIST phantom by the STAGE sequence showed high correlation with the water concentration in the vials. Previously, Kumar et al quantified PD values in the same phantom on a 3 T system, using a synthetic MRI sequence 22 (QRAPMASTER). They obtained an RE of~5% through repeated measures (n = 8, over the course of 2 days) while the average RE for our experimental PD measurements was of similar magnitude (~8%).…”

“…Overall, good agreement was observed between STAGEbased T1 estimations and gold standard T1 values measured by IR at 0.35 T. The errors for these results are comparable to those reported in other studies that have been conducted using the ISMRM/NIST phantom for NMR relaxation time quantifications at higher field strengths. 16,22,26 Jiang et al performed a study using the ISMRM/NIST phantom to investigate the repeatability of T1 and T2 mapping using MR fingerprinting methods over 34 consecutive days 16 and showed < 5% CV over all measurements. Similarly, the majority of our intra/intersession STAGE T1 and intersession VFA measurements at 0.35 T yielded CVs < 5%.…”

“…Kumar et al used the QRAPMASTER sequence at 3.0 T and found that the RE of T1 measurements was 1.9%. 22 In one study across different MRI systems, T1 was assessed based on the IR and VFA methods using the same ISMRM/NIST phantom. 26 It was observed that both at 1.5 T and 3 T, while the IR measurements had good agreement with known T1 values, VFA measurements showed higher RE in all sites.…”

“…Similarly, the majority of our intra/intersession STAGE T1 and intersession VFA measurements at 0.35 T yielded CVs < 5%. Kumar et al used the QRAPMASTER sequence at 3.0 T and found that the RE of T1 measurements was 1.9% 22 . In one study across different MRI systems, T1 was assessed based on the IR and VFA methods using the same ISMRM/NIST phantom 26 .…”

Realistic head‐shaped phantom with brain‐mimicking metabolites for 7 T spectroscopy and spectroscopic imaging

“…However, the similarity between the images scanned in a phantom and in vivo can be crucial, for example, when a static magnetic field (B 0 ) distribution similar to that present in vivo is required. 5,6 For brain imaging, shaped phantoms are designed to mimic the B 0 distribution marking the susceptibility effects near nasal and ear areas. 7,8 When moving to ultra-high fields (≥7 T), the inhomogeneity of both the RF magnetic field (B 1 ) and B 0 increases, motivating further the design of a realistic head-shaped phantom, 9 especially for spectroscopic imaging.…”