BACKGROUND: It is necessary to improve image contrast of hepatic arterial-dominant phase CT (HAP) images because the sensitivity of hypervascular hepatic lesions (HHL) with HAP is insufficient. OBJECTIVE: To investigate the efficacy of newly-developed downslope injection method (DIM)) of contrast material (CM) for improving the image contrast and the lesion sensitivity with HAP images by comparing with standard injection method of CM (SIM). MATERIALS AND METHODS: This retrospective study included 25 patients with 39 HHL (20 metastases, 11 HCC (hepatocellular carcinoma), 3 intrahepatic cholangiocarcinoma) who underwent two different HAP examinations consisting of both early (1st) and late arterial-phase (2nd)) or 2nd alone with the two comparative injection methods within 1.5 months between November 2022 and May 2023. An injection rate of CM was constant with the SIM, while was linearly decelerated based on 0.3 of slope index (SI
end injection rate/initial injection rate) with the DIM during 30 s of the injection duration of CM. Lesion-to-liver contrast (LLC) and contrast-to-noise ratio (CNR) were calculated based on the CT-number measurement of each organ. The lesion conspicuity and the sensitivity were also analyzed using the results of interpretation by three radiologists. RESULT: The quantitative mean LLC and CNR, the qualitative mean lesion conspicuity and the sensitivity with the DIM were significantly higher on the 1st, the 2nd, and the combination of the 1st and the 2nd than those with the SIM. CONCLUSION: The DIM was useful to significantly improve the image contrast and the lesion sensitivity on HAP images for detecting HHL.