Purpose: This study aims to evaluate the clinical utility and applicability of volume of interest based quantitative analysis by comparing region of interest based ejection fraction analysis in two dimensional planar imaging with volume of interest based quantitative analysis in three dimensional SPECT/CT. Materials and Methods: A 99mTcO4- solution with a uniform radioactivity concentration of 1.48 M㏃/㎖ was injected into each of the six spheres of the NEMA IEC Body phantom according to their respective volumes. After acquiring planar images and SPECT/CT scans with different acquisition times, count-based quantitative analysis was performed using Syngo.via and the results were compared with the preset volume change values of the phantom. Results: In planar imaging, region of interest based EF (EFR) showed percentage errors ranging from -3.89% to 0.19% across all sphere sizes. In 3D SPECT/CT, volume of interest based EF (EFV) consistently demonstrated higher values than ejection fraction phantom (EFP). The percentage error ranged from 1.36% to 7.56%, and the magnitude of error decreased as sphere volume increased. When the time per view was varied from 1 to 15 seconds, EFV values remained relatively stable. The difference between the maximum and minimum error across acquisition times (ΔE) ranged from 0.07% to 2.96%. Larger sphere volumes showed smaller variability in error across acquisition durations. Conclusion: As the volumetric difference between the spheres of the phantom increased, changes in counts on both planar and volumetric images could be evaluated more accurately. Furthermore, the error in the ejection fraction associated with variations in acquisition time for SPECT/CT imaging was observed to be at a comparable level. These results suggest that quantitative analysis of volumes of interest can be performed in SPECT/CT with reduced acquisition times without significant loss of accuracy, as in planar imaging.