Comparative study of quantitative blood pool SPECT imaging with 180° and 360° acquisition orbits on accuracy of cardiac function

Background Quantitative blood pool single photon emission computed tomography (SPECT) (QBS) can measure ejection fraction (EF) and volumes from gated blood pool single photon emission tomography (GBPS) working in fully automatic mode in 3-dimensional space. The effects of 180° and 360° data acquisition in GBPS have not been fully evaluated. This study compares the accuracy of 360° and 180° data acquisition for left ventricular (LV) systolic function in a clinical study and measures LV volume by GBPS compared with ultrasound echocardiography. Methods and Results The study population comprised 9 normal volunteers and 34 patients. GBPS data were acquired by use of 360° rotation and 60 stops per head. All 60 (360°) and 30 (45° right anterior oblique to 45° left posterior oblique) pieces of projection data that were selected for reconstructing the 180° data were reconstructed and both ventricular functional parameters were automatically obtained by QBS software. The contour of the LV septal wall was concave in 6 patients (14%) when processed at 180°, whereas a concave septum at 360° processing was observed in only 1 patient (2%). The coefficients of correlation between 180° and 360° were 0.467 for the end-diastolic volume (EDV) and 0.648 for the end-systolic volume (ESV). The mean 180° EDV value (152.9 ± 46.1 mL) was significantly smaller than that of the 360° EDV (191 ± 70.8 mL) (P <.001). However, there was no significant difference between the 360° EDV (0.623) and 180° EDV (0.407) as compared by echocardiography (P =.218). The agreement of the EF between both methods was close (r = 0.894, P <.0001). The agreement of the right ventricular volumes between the 180° and 360° orbits was close (r = 0.800 for EDV and 0.706 for ESV). The EF was relatively dispersed between the 180° and 360° methods (r = 0.642). Conclusion This study showed that SPECT image acquisition by use of both the 180° method and the 360° method considerably underestimated LV volume quantification. In addition, the LV volume with the 180° method was significantly smaller than that with the 360° method. Thus a 360° acquisition orbit may be suitable for more quantitatively accurate results when blood pool imaging is performed with gated SPECT.