Estimating liver perfusion parameters from triphasic CT

Here, we show how to estimate the hepatic artery and portal vein blood supply to each portion of the liver, using standard triphasic CT. These perfusion parameters provide an estimate of the fraction of each pixel that is occupied by microscopic branches of the hepatic artery and portal vein. Using this method, we were able to quantitate the increase in hepatic artery perfusion in hepatocellular carcinoma (see figure), and the decrease in portal perfusion with cirrhosis.

Hepatic artery supply
Portal vein supply

In the color image, the color indicates the phase of enhancement (arterial is red, portal venous is blue, and delayed is green). The saturation indicates the degree of enhancement (gray is non-enhancing, and color is enhancing). The brightness indicates the Hounsfield units.

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Boas FE, Kamaya A, Do B, Desser TS, Beaulieu CF, Vasanawala SS, Hwang GL, Sze DY. (2015) "Classification of hypervascular liver lesions based on hepatic artery and portal vein blood supply coefficients calculated from triphasic CT scans." Journal of Digital Imaging. 28: 213-23.

Boas F, Kamaya A, Do B, Beaulieu C, Desser T, Vasanawala S, Hwang G, Sze D. (2013) "Hepatic artery and portal vein blood volumes in hypervascular liver lesions: Estimation from triphasic CT scans." Presented at ARRS, Washington, DC, 2013-04-15.

Perfusion CT of the liver typically involves scanning the liver at least 20 times, resulting in a large radiation dose. We developed and validated a simplified model of tumor blood supply that can be applied to standard triphasic scans, and evaluated whether this can be used to distinguish benign and malignant liver lesions. Triphasic CTs of 46 malignant and 32 benign liver lesions were analyzed. For each phase, regions of interest were drawn in the arterially enhancing portion of each lesion, as well as the background liver, aorta, and portal vein. Hepatic artery and portal vein blood supply coefficients for each lesion were then calculated by expressing the enhancement curve of the lesion as a linear combination of the enhancement curves of the aorta and portal vein. Hepatocellular carcinoma (HCC) and hypervascular metastases on average both had increased hepatic artery coefficients compared to the background liver. Compared to HCC, benign lesions on average had either a greater hepatic artery coefficient (hemangioma), or greater portal vein coefficient (focal nodular hyperplasia, or transient hepatic attenuation difference). Hypervascularity with washout is a key diagnostic criterion for HCC, but it had a sensitivity of 72% and specificity of 81% for diagnosing malignancy in our diverse set of liver lesions. The sensitivity for malignancy was increased to 89% by including enhancing lesions that were hypodense on all phases. The specificity for malignancy was increased to 97% (p=0.039) by also examining hepatic artery and portal vein blood supply coefficients, while maintaining a sensitivity of 76%.

Keywords: triphasic CT; enhancement; washout; hepatocellular carcinoma; liver lesions; computer-aided diagnosis

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