Objective:To investigate the effect of ultra-low dose (ULD) computed tomography (CT) scanning on the diagnosis of ankle fractures and the quality of a three-dimensional printing (3DP) model.Methods:This study was a prospective study. A total of 61 patients with clinical ankle fractures treated conservatively in Zhuhai Hospital of Guangdong Hospital of Traditional Chinese Medicine from November 2019 to January 2022 were included in this study. Patients underwent standard dose (SD) CT scan and ultra-low dose (ULD) CT scan, respectively. The tube voltage/tube current of SD and ULD were 120 kV/100 mAs and 80 kV/10 mAs, respectively. Two senior radiologists evaluated the presence of ankle fractures. The effective radiation dose ( E), noise, signal-to-noise ratio (SNR), contrast signal-to-noise ratio (CNR), and CT value of bone cortex minus CT value of peripheral fat (CTc) were compared. The radiologists also evaluated the discoverability, diagnosability, and overall image quality of the fracture line according to Likert′s 5-point scoring method. Two senior orthopedists subjectively evaluated the quality of each 3DP model (model clarity and operation guidance). A score ≥ 3 indicated that the quality of the CT diagnostic image and 3DP model were acceptable. Results:The interval between the two CT scans was (9.23 ± 1.92) d. A total of 94 fracture sites were found. There were no missed diagnosis or misdiagnosis based on the SD and ULD scans.Noise, SNR, and CNR were better on the SD CT scanning ( F=5.92, 9.70, 8.32, P=0.00), however, CTc was higher on the ULD scans ( F=27.55, P<0.01). The image scores of the SD and ULD scans were (4.97 ± 0.18) and (4.21 ± 0.71), and the quality scores of the 3DP model (4.99 ± 0.01) and (4.87 ± 0.34), respectively. The SD scans were better than the ULD scans with respect to CT image quality and 3DP model quality ( Z=-6.88, -2.91, P<0.01), but both were considered suitable to meet clinical needs (all ≥ 3 points). The E associated with SD and ULD scannings were (34.68 ± 4.96) μSV and (1.04 ± 0.10) μSV, respectively. The latter was thus significantly better than the former ( F=38.77, P =0.00). Conclusions:The E value of ULD scanning is about 3.00% of SD scanning E, which can meet the needs of clinical diagnosis of ankle fracture and 3DP model printing diagnosis.