In vivo validation of gated myocardial SPECT imaging for quantification of small hearts: comparison with cardiac MRI

BACKGROUND: In patients with small hearts, the Quantitative Gated single-photon emission computed tomography (SPECT) (QGS) program frequently underestimates the left ventricular (LV) end-systolic volume (ESV) and overestimates the ejection fraction (EF). A newly developed cardiac software program, cardioREPO/EXINI heart (cREPO), has been proposed to more accurately quantify small hearts using active shape modeling and a volume-dependent edge correction algorithm for LV delineation. The aim of this study was to validate cREPO in vivo for measuring the LV volumes and EF of both small and non-small hearts, in comparison with values obtained via cardiac MRI (CMR). METHODS: We performed stress (99m)Tc-MIBI SPECT and CMR within a 30-day interval for 44 patients (mean age, 66 years; 27 men). Resting EF, end-diastolic volume (EDV), and ESV with QGS and cREPO were compared with values obtained via CMR. RESULTS: The subjects consisted of 17 small and 27 non-small hearts. CMR yielded EDV, ESV, and EF values of 135 ± 31 ml (mean ± SD, range 85–217 ml), 57 ± 21 ml (27–105 ml), and 60 ± 6 % (45–70 %), respectively. Compared with CMR, both QGS and cREPO systematically underestimated both EDV and ESV and overestimated EF. The magnitude of the overestimation of EF by QGS, compared with CMR, correlated strongly with the given EF values (r = 0.71, P < 0.0001). In contrast, no significant correlation was seen with cREPO (r = 0.18, P = 0.24). In addition, no significant correlation was found between the magnitude of the underestimation of ESV and heart size with cREPO (r = 0.03, P = 0.83). Thus, cREPO provided a relatively constant 9 % overestimation of EF values relative to CMR, for the studied EF range for both small and non-small hearts. CONCLUSIONS: The use of the new algorithm of cREPO ameliorated exaggerated EF in small hearts but not resolved completely. The program provided a constant 9 % overestimation for both small and non-small hearts, which should be carefully taken into account for clinical assessment of LV function.