Comparison between gated SPECT and echocardiography in evaluation of left ventricular ejection fraction

ABSTRACT

Gated SPECT myocardial perfusion imaging has be-come an established routine procedure in almost all nuclear medicine departments. It has many advantages it allows evaluation of myocardial wall motion, wall thickening, and calculation of left ventricular ejection fraction. This information helps to differentiate attenuation artifacts of breast tissue or diaphragm from true ischemic changes. The degree of wall thickening and increase in count density reflect myocardial viability. To test the validity of LVEF by Gated SPECT and correlate it with echocardiographic results. 63 patients [39 males 24 females] were imaged according to the following protocol. Detectors are 90 angle, cardiac leads and gated device activated, 64 x 64 x 16 matrix, 8 slices per cardiac cycle. 16 projections per detector for a total of 32 projections, covering from right anterior oblique to the left posterior oblique. Time of acquisition per projection is 40 seconds. We gated both early and delayed thallium studies. Early images began within 5-8 minutes of dose injection. Gated SPECT study, was usually completed in 20 minutes. The first part of the study was usually finished in less than 40 minutes from the time of injection. We correlated end diastolic volume, end systolic volume and LVEF calculated from gated thallium SPECT with echocardiography done immediately following thallium study. For gated SPECT, the mean LVEF was S 1.4 +/- 9, LV EDV of 96 +/- 22ml and ESV of 47.3 +/- 9m1. These were comparable to Echo result with correlation coefficient of 0.89 for LVEF. Gated SPECT changed the result of the test by 14% [from positive to negative] in 9/63 patients, 7 cases due to diaphragmatic attenuation and 2 due to breast artifact, and increasing the overall accuracy of the test. Gated SPECT is a good reproducible method to assess LVEF. Correlation of LVEF with 2D Echo is very high [0.89]. This proves the validity of GSPECT tecimique. Since thallium-201 chloride is preferred for myocardial imaging because it is more physiological and one injection is required in the presence of new true digital detectors gamma camera systems