A computer-aided temporal and dynamic subtraction technique of the liver for detection of small hepatocellular carcinomas on abdominal CT images

Abstract

22It is often difficult for radiologists to identify small hepatocellular carcinoma (HCC) due to 23 insufficient contrast enhancement. Therefore, we have developed a new computer-aided 24 temporal and dynamic subtraction technique to enhance small HCC, after automatically 25 selecting images set at the same anatomical position from the present (non-enhanced and 26 arterial-phase CT images) and previous images. The present study was performed with CT 27 images from fourteen subjects. First, we used template-matching based on similarities in liver 28 2 shape between the present (non-enhanced and arterial-phase CT images) and previous 1 arterial-phase CT images at the same position. Temporal subtraction images were then obtained 2 by subtraction of the previous image from the present image taken at the same position of the 3 liver, and dynamic subtraction images were also obtained by subtraction of non-enhanced CT 4 images from arterial-phase CT images taken at the same position of the liver. Twenty-one of 22 5 nodules (95.5%) with contrast enhancement were visualised in temporal and dynamic 6 subtraction images. Increases of 150% and 140% in nodule-to-liver contrast were observed on 7 dynamic and temporal subtraction images compared with present arterial-phase CT images, 8respectively. These subtraction images may be useful as reference images in detection of small 9 moderately differentiated HCC. 10 11

Effectiveness of temporal and dynamic subtraction images of the liver for detection of small HCC on abdominal CT images: comparison of 3D nonlinear image-warping and 3D global-matching techniques

“…Cases with suspected A-P shunt that increases in size over time have an increased likelihood of moderately differentiated HCC, and temporal subtraction images show ring enhancement in such cases [8].…”

“…It is especially difficult for radiologists to distinguish true HCC from a small nodular A-P shunt in patients with hepatic cirrhosis. To assist radiologists in follow-up examination, we have developed a computer-aided detection (CAD) system for detecting increases in the size of nodular early enhancement and new enhancement on temporal and dynamic subtraction with a 3D global-matching technique plus a 2D nonlinear image-warping technique (previous technique) [8,9].…”

Improvement of temporal and dynamic subtraction images on abdominal CT using 3D global image matching and nonlinear image warping techniques

“…All 37 nodules on the dynamic and temporal subtraction images obtained using the standard and new techniques were assessed by three experienced radiologists after consultation regarding the known position of HCC demonstrated on the previous arterial-phase CT images, current non-enhanced and arterial-phase CT images, CTHA and CTAP, etc. This visual assessment was performed using a three-point score only on axial slices demonstrating the nodule (Okumura et al 2006): grade 3 (good), the whole nodule was visualized; grade 2 (fair), the nodule was partially visualized; and grade 1 (poor), the nodule was not visualized.…”

“…We measured CT nodule in the nodule region in the same manner as described for the measurement of CT number in the liver region. We measured the standard deviation (SD air ) of the background to estimate image noise (Okumura et al 2006). Respective data for CNR of both subtraction images using the standard and new techniques with good rating scores were analyzed using the two-tailed paired t-test, and P 0.05 was considered statistically significant.…”

“…In a recent study of 430 patients by the transplantation correlation, the prospective and retrospective sensitivities of triphasic helical CT for detecting HCC were 59% and 68%, respectively (Peterson et al 2000). To assist radiologists in such a comparative observation, we developed a temporal and dynamic subtraction based on the 2D global image matching technique (Okumura et al 2006).…”