Fig. 4.

Quantitative comparison of lesion visibility and image blurring at 3T and 64mT. (A) Lesion conspicuity measures the intensity of a lesion relative to background tissue. Lesion conspicuity for the largest lesion was measured on 3T (light blue) and 64mT (dark blue) T2-FLAIR images for 10 patients. There was no significant difference in conspicuity between the scanners (paired t-test, t = 0.14, p = 0.89). (B) SNR compares mean lesion intensity to background noise. SNR was significantly higher in 3T images in the subset of 10 patients (paired t-test, t = 4.36, p = 0.00184). (C) Similarly, CNR, which compares the contrast between lesion and white matter to background noise, was also significantly higher in 3T imaging (paired t-test, t = 4.89, p < 0.001). (D-F) The variance of the Laplacian is a measure of image focus, with larger values indicating clearer images. We registered and resliced 3T to 64mT images and calculated this focus feature for both images. This process was carried out for (D) T2-FLAIR, (E) T1w, and (F) T2w sequences. Four subjects without T2w sequence pairs were excluded from panel D. For all sequences, low-field images were significantly more blurred than their resliced 3T counterparts (paired t-tests, T2-FLAIR: t = 11.6, p < 0.001, T1w: t = 9.5, p < 0.001, T2w: t = 19.5, p < 0.001). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)