Influence of myocardial count on phase dyssynchrony analysis of gated myocardial perfusion single-photon emission computed tomography

Abstract

Drugs and acquisition times for gated myocardial perfusion single-photon emission computed tomography scintigraphy vary depending on the facility. Even if the same examination is performed in the same facility, the acquisition count differs for each examination because factors such as the patient's age, stress protocol of the patient, the biological half-life of the stress agent, and the patient's response are different. We aimed to evaluate the differences in acquisition counts on the effect of left ventricular function and phase analysis indices. A gated myocardial perfusion phantom was used. The acquisition times acquired were varied (nine steps from 3 to 51 s per view). The myocardial average count per pixel of the left anterior oblique (LAO) of 45° of projection data were 9.4, 17.8, 28.7, 47.1, 67.1, 97.7, 122.7, 174.4, and 254.0 counts per view. We used the count value of LAO of 45° of projection data to find the lowest count that the left ventricular function and phase analysis indices can accurately calculate. The left ventricular function indices evaluated were the left ventricular ejection fraction (LVEF), end-diastolic volume (EDV), and end-systolic volume (ESV). The bandwidth, phase SD, and entropy were evaluated as phase analysis indices. Functional analysis: LVEF and EDV showed constant values even when the collection count changed (%coefficient of variation (CV) of LVEF=2.1%, %CV of EDV=3.9%). The ESV value was large when the lowest count was obtained (9.4 counts per pixel per view), which caused %CV of ESV to be greater than that of LVEF and EDV (%CV of EDV=7.8%). Phase analysis indices: The difference between the highest and lowest values was that the bandwidth was 100.0%, phase SD was 62.0%, and entropy was 58.3%. Phase analysis indices declined as a function of increasing acquisition time. To accurately calculate left ventricular function, the myocardial counts of LAO of 45° of projection data should be at least 17.8 average counts per pixel per view. To accurately calculate the phase analysis index, the myocardial counts of LAO of 45° of projection data should be at least 67.1 average counts per pixel per view.