Radial fast spin‐echo method for T2‐weighted imaging and T2 mapping of the liver

Abstract

Purpose: To evaluate a multishot radial fast-spin echo (RAD-FSE) method developed to improve the quality of abdominal T2-weighted imaging as well as the characterization of focal liver lesions. Materials and Methods:The RAD-FSE sequence used in this work consisted of a preparatory period followed by a short echo train (ETL ϭ 16). A novel radial k-space trajectory was used to minimize streaking artifacts due to T2 variations and motion. Small diffusion gradients (b ϭ 1.2 mm/s 2 ) were used to improve flow suppression. The quality of images obtained with RAD-FSE was compared to multishot 2DFT fast spin-echo (2DFT-FSE) and half-Fourier acquisition single-shot turbo-spin-echo (HASTE) images using data from 16 patients. A postprocessing algorithm was used to generate multiple high-resolution images (at different effective TE values) as well as a T2 map from a single RAD-FSE data set. The T2 maps were used to differentiate malignant from benign lesions for a set of 33 lesions ranging from 0.8 -194 cm 3 .Results: RAD-FSE produces high-resolution images of the liver in a breath-hold without the motion artifacts of 2DFT-FSE methods, and without the blurriness and loss of small lesion detectability of HASTE. The inclusion of diffusion weighting in RAD-FSE decreases the signal from blood in hepatic vessels, which improves lesion visualization. The T2 values obtained by postprocessing a single RAD-FSE data set can differentiate malignant from benign lesions. The mean T2 values obtained for malignancies, hemangiomas, and cysts are 108 Ϯ 30 msec, 240 Ϯ 14 msec, and 572 Ϯ 334 msec, respectively. Conclusion:These results indicate that RAD-FSE produces abdominal images of higher quality than 2DFT-FSE and HASTE. In addition, lesions can be characterized using T2 maps generated from a single RAD-FSE data set.

Processing of radial fast spin‐echo data for obtaining T2 estimates from a single k‐space data set

“…The method is fast (in the case of body applications, data can be acquired in a breath hold) and since the TE images are generated from a single k-space data set, misregistration problems are minimized. We have shown that this methodology can be used to measure T 2 s in patients with focal liver lesions and successfully characterize lesions as benign or malignant (13). However, as was pointed out in our initial work, there are artifacts in the T 2 maps due to the mixing of TE data in the reconstruction process.…”

“…Recently it was shown that high resolution images at various effective TE (TE eff ) values can be generated from a single radial fast spin-echo k-space data set (12,13). This is achieved by using data acquired at a specific TE (or narrow TE range) at the center of k-space and all the radial data in the outer part of k-space.…”

Diffusion-weighted Imaging of the Liver: Technical Challenges and Prospects for the Future

“…7). Two-dimensional prospective acquisition correction (PACE) [13][14][15][16][17][18] is the other solution. It is important to select the most suitable method for the patient depending on his W her status.…”

Simultaneous imaging and R2* mapping using a radial multi‐gradient‐echo (rMGE) sequence

“…The coarsely sampled k-space periphery is filled by all other single-echo data sets. In addition, motion-induced ar-tifacts can by minimized by an appropriate view-ordering scheme that distributes sequentially acquired echotrains over radians (20) so that adjacent views experience different motion kinetics. However, this would hamper an appropriate phase correction that presupposes that the difference in the linear phases of adjacent projections evolves solely from system latencies.…”