Evaluation of a Modified Stejskal-Tanner Diffusion Encoding Scheme, Permitting a Marked Reduction in TE, in Diffusion-Weighted Imaging of Stroke Patients at 3 T

Purpose: To evaluate a modified Stejskal-Tanner diffusion gradient pulsing scheme that applies diffusion encoding during the entire time between the 2 requisite radiofrequency pulses, shortening TE. Materials and Methods: Seventeen healthy volunteers and 15 patients with acute and early subacute infarcts were evaluated at 3 T utilizing: a conventional bipolar gradient double spin echo planar imaging diffusion weighted imaging with a parallel imaging factor of 2 (p2) and a modified Stejskal-Tanner short TE (sTE) SE echo planar imaging diffusion weighted imaging with parallel imaging factors of 2, 3, and 4. Signal-to-noise ratio (SNR) and susceptibility-induced spatial distortions were quantified, and a blinded reader ranked scans in terms of susceptibility artifact and overall preference. Results: The sTE sequence allowed a shortening in TE of 18 to 28 milliseconds versus the standard bipolar gradient sequence. SNRs were generally not significantly different among the sTE scans because of compensation by number of scan averages. By using twice the number of averages, the SNR with the bipolar gradient sequence was not significantly different from that of the sTE sequences in patients. sTE scans with higher parallel imaging factors demonstrated less susceptibility-related artifact. The blinded reader ranked the p3 or p4 sTE scans most preferred and the bipolar gradient scans least or tied for least preferred in every case. Conclusions: Utilization of the sTE modified Stejskal-Tanner sequence markedly improves SNR—an increase that may be used with parallel imaging to improve overall scan quality whereas maintaining reasonable scan times and SNR.