Gradient- and Spin-Echo MR Imaging of the Brain

In their study comparing gradient- and spin-echo (GRASE) and T2-weighted fast spin-echo imaging of the brain, Rockwell et al (1) conclude that T2-weighted GRASE images are better at depicting lesions with paramagnetic susceptibility effects. Although this is likely true, as fast-spin-echo images have diminished susceptibility artifact, the authors fail to note previous reporting of hemosiderin-containing lesions from hemorrhage that were not visible on GRASE images but were seen on conventional spin-echo images (2). Therefore, neither GRASE nor fast spin-echo images should supplant gradient-echo images for the detection of hemosiderin.

Furthermore, we wish to caution readers that the contrast properties and sensitivity to detection of T2 hyperintense lesions on rapid, hybrid imaging sequences depend on the specific implementation of the pulse sequence, and particularly the k-space trajectory used for data acquisition (3–5). Two prior studies have shown that GRASE images have diminished sensitivity to T2 hyperintense lesions when compared with conventional spin-echo images (2, 6), although, admittedly, conventional spin-echo images may be more sensitive to small lesions than fast spin-echo images. Consequently, before reliance is placed on using rapid hybrid sequences in clinical practice, each site should develop its own experience and familiarity with these sequences.