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To evaluate whether arterial phase CT using the downslope injection method improves the detection of liver metastases from colorectal cancer (LMCC) compared with portal venous phase (PVP) imaging alone.

This retrospective study included 57 patients with 180 confirmed LMCC lesions who underwent CT using the downslope injection method. Early arterial phase (EAP, 25 s) and late arterial phase (LAP, 40 s) images were evaluated by three radiologists for lesion detection and enhancement patterns. Detection rates were compared using generalized estimating equations with PVP as reference.

Among 180 LMCC, 42 (23%) were hyperenhancing, 78 (43%) ring-enhancing, 50 (28%) hypoenhancing, and 10 (6%) not detectable on arterial phases. Small lesions (≤ 10 mm) showed the highest proportion of arterial hyperenhancement (42%). LAP images (162/180, 90%) significantly outperformed PVP alone (143/180, 79%; odds ratio 2.29; 95% confidence interval [CI] 1.05-4.98; p = 0.037). For hyperenhancing lesions, EAP (86%; p = 0.011) and LAP (81%; p = 0.024) demonstrated significantly higher sensitivity than PVP (52%). Interobserver agreement was moderate to good for detectability (κ = 0.64-0.77) and almost perfect for enhancement pattern classification (Cohen's κ = 0.87-0.95).

Adding arterial phase CT using the downslope injection method to PVP significantly improves the detection of LMCC, particularly small hyperenhancing lesions.

Question Can arterial phase CT with optimized contrast injection improve the detection of small colorectal liver metastases frequently missed on portal venous phase imaging? Findings Late arterial phase CT detected 90% of colorectal liver metastases and significantly outperformed portal venous phase alone (79%) using the downslope injection method. Clinical relevance Arterial phase CT improves the detection of small colorectal liver metastases, enabling more accurate preoperative staging. The downslope injection method optimizes arterial phase enhancement without increasing contrast dose.