Fast T-2-weighted imaging by PSIF at 0.2 T for interventional MRI

Rapid T-2 weighted (T2W) images would facilitate physicians being able to d istinguish normal tissues, vessels, tumors, and thermal lesions from therap eutic devices throughout interventional MRI procedures commonly performed i n open low-field scanners (e.g., 0.2 T), Conventional diagnostic MRI techni ques have not been successful at low-field strength for fast T2W imaging du ring the guidance phase of interventional MRI (I-MRI) procedures. FISP and true-FISP methods yield T-1/T-2-weighted images and do not always provide s ufficient contrast for device guidance or lesion assessment. As such, a var iant of PSIF (a gradient reversed form of FISP) which collects the T-2-weig hted spin echo of the SSFP signal was developed and implemented at 0.2 T fo r use in I-MRI procedures. The sequence has a balanced readout gradient to reduce motion sensitivity. Asymmetric sampling toward the end of the TR cyc le reduces T-2* decay of the spin echo component in the SSFP signal. The se quence gives one image in 5-7 s in vivo with adequate SNR and T-2 contrast for interventional applications, Patient studies showed that the PSIF seque nce variant demarcates many tumors not detectable by either FISP or true-FI SP. Results from animal experiments suggested that it has potential to moni tor thermal lesions during interstitial thermal ablation procedures. Magn R eson Med 42: 335-344, 1999. (C) 1999 Wiley-Liss, Inc.