In the case of 123I from the 124Te(p,2n)reaction, the radionuclidic impurity is the high-energy gamma- emitting 124I, which interferes greatly with nuclear medicine images. The choice of a collimator can affect the quality of clinical SPECT images of [I-123]MIBG, [I-123]β-CIT, or [I-123]IPT. The tradeoffs that two different collimators make among spatial resolution, sensitivity, and scatter were studied by imaging a line source at 5cm, 10cm, 15cm distance using a number of plexiglass sheets between source and collimator, petridish, two-dimensional Hoffman brain phantom, Jaszczak phantom, and three-dimensional Hoffman brain phantom after filling with 123I. (FWHM, FWTM, Sensitivity) for low-energy ultrahigh-resolution parallel-hole(LEUHRP) collimator and medium-energy general-purpose(MEGP) collimator were measured as (9.27mm, 61.27mm, 129 CPM/ μCi) and (10.53mm, 23.17mm, 105CPM/μ/Ci), respectively. The image quality of two- dimensional Hoffman brain phantom with LEUHRP looked better than the one with MEGP. However, the image quality of Jaszczak phantom and three-dimensional Hoffman brain phantom with LEUHRP looked much worse than the one with MEGP because of scatter contributions in three-dimensional imaging situation. The results suggest that the MEGP is preferable to LEUHRP for three-dimensional imaging studies of [I-123]MIBG, [I- 123] β-CIT, or [I-123] IPT.