[en] ¹²³I Produced by ¹²⁴Te(p, 2n)¹²³I reaction is contaminated with ¹²⁴I (< 5 %) and ¹²⁶I (< 0.3 %). High energy photons from these mixed radioiodine compromise seriously image quality due to scattered photons and to septal penetration in the collimator. Four collimators of LEAP (for) low energy all purpose), LEHR (for low energy high resolution), MESI (for medium energy made by Siemens) and MENU (for medium energy made by nuclear technology) mounted on a rotating gamma camera (Siemens, ZLC-7500), were examined in order to select a suitable collimator for ¹²³I SPECT (singel photon emission computed tomography) imaging. Sensitivities were measured with a plane source (5 x 5 x 0.5 cm) at the collimator face and distances from 2 to 30 cm in air. And, spatial resolutions in FWHM (full width at half maximum) and FWTM (full width at tenth maximum) were determined from line spread functions with planar and SPECT imaging. From the comparison of collimator performances with ^99mTc and ¹²³I, both collimators for low energy were not useful for ¹²³I imaging. In other two collimators for medium energy, however, apparently the effect of septal penetration by the higher energy photons were also recognized, MENU with high geometrical resolution was more suitable for ¹²³I SPECT imaging compared with MESI. And, it is important to perform the SPECT imaging with radius as short as possible. (author)