Evaluation of the increase in signal intensity from applying the fast recovery technique to fast spin echo images

The aim of the present study was to evaluate the increase in signal intensity caused by applying the fast recovery (FR) technique to fast spin echo (FSE) images, that is, the fast recovery fast spin echo (FR-FSE) method. All images of phantoms, whose T2 values were different, were acquired with a Signa 1.5 Tesla system (GE Medical Systems) using the three-dimensional (3D) FSE and 3D FR-FSE sequences. We assessed the increased signal intensity as follows: (signal intensity on the FR-FSE image-FSE image)/FSE image (%). Our results showed that the increased signal intensity became high when T2 of the phantom was prolonged, repetition time (TR) was shortened, and echo train length (ETL) was decreased. By utilizing the results of this study, the increased signal caused by the FR technique could be estimated quantitatively when the TR, ETL, and T2 of investigated substances were determined. For example, when TR, ETL, and T2 were 1500 msec, 16-64, and 1500 msec, respectively, the increase in signal intensity was estimated to be approximately 70%. In addition, when T2 was less than approximately 250 msec, signal intensity was not significantly increased by the FR pulses, that is, the FR-FSE image was the same as the FSE image. Accordingly, the FR-FSE method was confirmed to enhance the signal in substances with longer T2, while maintaining the same contrast of the image as that obtained by the conventional FSE method. Our results are useful for evaluating the increased signal intensity caused by employing the FR technique. (author)