Andrew Scott Nencka1, Daniel L. Shefchik1, Eric S. Paulson2, Andrzej Jesmanowicz1, James S. Hyde1
1Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI, United States; 2Department of Radiation Oncology, Medical College of Wisconsin, Milwaukee, WI, United States
Pulse sequences which acquire trains of echoes face an inherent limit in resolution due to intra-acquisition decay. In gradient echo sequences, often used in functional studies, T2* decay leads to an increased point spread function in the phase encoding direction due to the lower effective bandwidth in that direction during data acquisition. In this abstract, we illustrate that the desirable T2 weighting associated with gradient echo sequences may be preserved with an asymmetric spin echo, and that acquisitions on the ascending edge of the spin echo yield point spread functions which are reduced in the phase encoding direction. This effect comes from the competing T2 rephrasing and T2 decay leading up to the formation of the spin echo. Matching the effective echo time on the ascending and descending sides of the spin echo can yield varying image contrast in vivo due to true T2 decay, thereby affecting the perceived smoothness of the reconstructed image.