BACKGROUND AND PURPOSE: Parathyroid 4-dimensional CT (4DCT) involves repeated noncontrast and multiphase contrast-enhanced acquisitions, leading to increased radiation exposure. Because the examination targets the anatomically complex structures of the neck, maintaining high image quality is particularly important. Photon-counting CT (PCCT) is a novel technology reported to improve dose efficiency and image quality compared with conventional energy-integrating detector CT (EIDCT). This study provides a systematic, quantitative comparison of CT scanner radiation output (volume CT dose index [CTDIvol] and dose-length product [DLP]) and image quality, assessed by SNR and contrast-to-noise ratio (CNR), between PCCT and EIDCT for multiphase parathyroid 4DCT examinations. MATERIALS AND METHODS: In this institutional review board–approved retrospective study, 96 patients who underwent a 4DCT for the work-up of hyperparathyroidism (PCCT, n =32; EIDCT, n =64) were reviewed. ROIs were placed on the noncontrast, arterial, and venous phase images in the sternocleidomastoid muscles at the upper thyroid level, the anterior scalene muscles at the lower thyroid level, and in the extracorporeal air. Mean attenuation, SNR, and CNR were measured. Statistical analyses included unpaired t tests and 2-way ANOVA. RESULTS: PCCT had significantly lower radiation output across all 4DCT phases (total CTDIvol 30.6 ± 3.3 vs 60.8 ± 15.7 mGy; DLP 859 ± 178 vs 1523 ± 519 mGy·cm; P < .001). SNR and CNR were significantly higher on PCCT across all evaluated ROIs, with lower background noise (all P < .05). Two-way ANOVA confirmed the advantages of PCCT regardless of contrast injection side, with no significant interactions. CONCLUSIONS: PCCT substantially reduces CT scanner radiation output while improving quantitative image quality in multiphase parathyroid 4DCT, including technically challenging arterial-phase acquisitions at the lower thyroid level, supporting its technical advantage over conventional EIDCT. AP : arterial phase CNR : contrast to noise ratio CTDIvol : volume CT dose index DLP : dose-length product EIDCT : energy-integrating detector CT LT : lower thyroid NC : noncontrast phase PCCT : photon-counting CT UT : upper thyroid VP : venous phase