AJR: Arterial enhancement fraction may best perfusion CT for liver studies

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The arterial enhancement fraction (AEF) calculated from simulated multi-phasic liver CT images correlates strongly with the hepatic perfusion index (HPI) obtained at cine mode perfusion CT, according to a study in the January issue of the American Journal of Roentgenology.

Kyung Won Kim, MD, from the department of radiology and the Institute of Radiation Medicine at the Seoul National University College of Medicine in Seoul, South Korea, and colleagues performed a cine mode perfusion CT after VX2 tumor implantation in the livers of 10 rabbits.

They obtained HPI and its color map with a computer application. With raw data from cine mode perfusion CT, images were extracted in the unenhanced, arterial, and portal venous phases to simulate multiphasic liver CT. On the basis of simulated multiphasic CT images, the researchers obtained AEF color maps with prototype software. HPI and AEF were compared for the same regions of interest in the liver parenchyma, whole liver tumor and viable tumor portion.

In the liver parenchyma, the mean HPI was 23.3 percent and the AEF 24.4 percent; in whole liver tumor, 73.4 percent and 78.4 percent; and in the viable tumor portion, 78 percent and 78.3 percent. However, the differences were not statistically significant.

The authors wrote that the “measurement agreement between the two parameters was moderate, but there was a strong positive correlation between AEF and HPI.” Also, functional maps of HPI and AEF correlated with the histologic findings.

Won Kim and colleagues noted that the “greatest advantage” of using AEF rather than HPI to assess liver vascularity is its “practicality,” adding that perfusion CT of the liver has been of limited use in clinical practice for several reasons—the most important of which is the greater radiation exposure at perfusion CT. “However, when low tube current or low tube voltage is used to reduce radiation dose, image quality is compromised,” they wrote.

The researchers concluded that quantitative color mapping of the AEF of the liver with routine multiphasic liver CT has none of the “disadvantages” of perfusion CT, as it requires no additional contrast injection or scanning and covers the entire liver with high-spatial resolution. The procedure can be incorporated into routine liver CT exams with an additional postprocessing time of less than two minutes, the authors noted.

“We, therefore, believe that the AEF of a tumor is a practical, helpful parameter that provides useful information and good anatomic detail regarding the arterioportal perfusion balance of the entire liver and liver tumors,” Won Kim and colleagues concluded.