JNM: SPECT/CT misregistration of cardiac perfusion greatly affects image quality
SPECT/CT misregistration of attenuation-corrected (AC) myocardial perfusion imaging (MPI) can significantly affect imaging quality, particularly along the dorsal/ventral axis, according to a study in this month's Journal of Nuclear Medicine.

According to John A. Kennedy, PhD, of the department of nuclear medicine at Rambam Health Care Campus in Haifa, Israel, and colleagues, while previous research has demonstrated the value of software tools in allowing operator realignment of misregistered SPECT/CT for avoiding artifacts, the routine availability of this software “raises . . . the question of which directions of misalignment between SPECT and CT most severely affect AC myocardial perfusion image quality."

Their study included a retrospective analysis of MPI studies performed on 144 patients in two groups. The first group included 248 consecutive stress–rest MPI studies performed on 124 patients (60 men, mean age 62) to assess the incidence, magnitude, and direction of misregistration. In a second study group, cardiac SPECT/CT registration was artificially modified to determine the effect of misregistration on AC myocardial perfusion image quality.

SPECT/CT misregistration of greater than one pixel was found in 181 of the 248 studies, for a frequency of 73 percent. Misregistrations of more than one pixel along more than one axis, or misregistrations of more than three pixels, were found in 28 percent of the studies. Differences in misregistration of more than one pixel along at least one axis between the stress and the rest study of the same patient were found in 36 percent of patients.

“Clinically significant SPECT/CT misregisration of severe magnitude (greater than two pixels) occurred in 23 percent of studies and specifically in the direction leading to the most severe artifacts in 16 percent of the studies,” the authors found, and severe misregistration along the dorsal/ventral significantly effected AC-MPI quality.

“Results of the present study provide guidance before the performance of manual realignment using registration software tools, demonstrating that priority should be given to cases showing overlay of the myocardium on SPECT with lung tissue on the CT component of AC-MPI studies,” the authors concluded.