Synthetic MRI in the Detection of Multiple Sclerosis Plaques

Abstract

Background and purpose: Synthetic MR imaging enables the creation of various contrast-weighted images including double inversion recovery and phase-sensitive inversion recovery from a single MR imaging quantification scan. Here, we assessed whether synthetic MR imaging is suitable for detecting MS plaques.

Materials and methods: Quantitative and conventional MR imaging data on 12 patients with MS were retrospectively analyzed. Synthetic T2-weighted, FLAIR, double inversion recovery, and phase-sensitive inversion recovery images were produced after quantification of T1 and T2 values and proton density. Double inversion recovery images were optimized for each patient by adjusting the TI. The number of visible plaques was determined by a radiologist for a set of these 4 types of synthetic MR images and a set of conventional T1-weighted inversion recovery, T2-weighted, and FLAIR images. Conventional 3D double inversion recovery and other available images were used as the criterion standard. The total acquisition time of synthetic MR imaging was 7 minutes 12 seconds and that of conventional MR imaging was 6 minutes 29 seconds The lesion-to-WM contrast and lesion-to-WM contrast-to-noise ratio were calculated and compared between synthetic and conventional double inversion recovery images.

Results: The total plaques detected by synthetic and conventional MR images were 157 and 139, respectively (P = .014). The lesion-to-WM contrast and contrast-to-noise ratio on synthetic double inversion recovery images were superior to those on conventional double inversion recovery images (P = .001 and < 0.001, respectively).

Conclusions: Synthetic MR imaging enabled detection of more MS plaques than conventional MR imaging in a comparable acquisition time. The contrast for MS plaques on synthetic double inversion recovery images was better than on conventional double inversion recovery images.

Fig 1.

An example of DIR optimization. A DIR image with a second TI of 460 ms (A) (as determined according to the equations in the main text) shows better delineation of MS plaques than a DIR image with a second TI of 360 ms (B) or 560 ms (C).

Fig 2.

Representative sections of synthetic T2-weighted (A), FLAIR (B), PSIR (C), and DIR (D) images, along with conventional T2-weighted (E), FLAIR (F), and T1IR (G) images.

Fig 3.

An example of ROI placement. A plaque (arrow) is shown on the synthetic DIR image (A). A circular ROI (arrow) that covers almost the entire lesion is placed in B. The ROI was copied and pasted on the contralateral normal-appearing WM (arrowhead).

Fig 4.

An MS plaque readily detected on PSIR and DIR images. This plaque (arrows) is difficult to identify on synthetic T2-weighted (A) and FLAIR (B) images and on conventional T2-weighted (E), FLAIR (F), and T1IR (G) images, but it is clearly delineated on synthetic PSIR (C) and DIR (D) images. The plaque was detected by a neuroradiologist (K.K.) on synthetic but not conventional MR images.

Fig 5.

An example of a false-positive lesion. The surface of the brain tends to become hyperintense on synthetic FLAIR and DIR images. Note the hyperintense focus (arrow) in the inferior horn of the right lateral ventricle on synthetic FLAIR (A) and DIR (B) images; this focus was identified as an MS plaque by a neuroradiologist (K.K.). No hyperintense focus is seen in the same place on a conventional FLAIR image (C).

Fig 6.

Sample sections of synthetic (A) and conventional (B) DIR images. Note the better suppression of WM on the synthetic DIR image.