Establishing the Cut-Off Values for a Quality Assurance Test Using an Ultrasound Phantom for Screening Ultrasound Examinations for Hepatocellular Carcinoma: an Initial Report of a Nationwide Survey in Korea

To evaluate the results of the testing of ultrasound devices using an US phantom and to determine the cut-off values of the phantom test for the quality assurance in US examinations of the liver in Korea. US phantom images were acquired from the general Hospitals in Korea that participated in the National Cancer Screening Program for hepatocellular carcinoma. Images were acquired using a 3.0 – 5.0 MHz convex transducer and evaluated in terms of the dead zone, vertical and horizontal measurement, axial & lateral resolution, sensitivity and gray scale/dynamic range. The appropriate cut-off values were determined to guarantee minimal qualification of the performance. 357US scanners were tested in this study using the following cut-off values: less than 2 mm for dead zone, 5% discrepancy for vertical measurement, 7.5% discrepancy for horizontal measurement, all 11 identifiable line targets for axial & lateral resolution, more than 14 cm for sensitivity, and more than 4 cylindrical structures for gray scale/dynamic range. With these criteria, 283 US scanners (79.3%) passed the test. The most common cause of disqualification was the dynamic range/gray scale. No statistical difference was observed in the disqualification rate between three groups based on different years of manufacture. We have defined the cut-off values for phantom images acquired using US scanners, where these will be used in performing screening US examinations for hepatocellular carcinoma in Korea.