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.