Strategy of application of dual energy computed tomography to identify of uric acid stones and dose reduction

• Main Authors: Yi-Ru Chang, 張宜儒
• Other Authors: Tou-Rong Chen
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/25167842340893742006

碩士 === 中山醫學大學 === 生物醫學科學學系碩士班 === 103 === Purpose The purpose of this study is using dual-energy computed tomography (DECT) to evaluate different analysis methods of identification for uric acid stones. By adjustment of the reference tube current time product (Ref. mAs), the effective dose reduction of patient and the identified accuracy of methods were assessed. Material & Method A total of 132 urinary stones were collected in the study. Stones are placed in the CTDI acrylic phantoms with 16 and 32 cm diameter and in the 25 and 38 cm elliptic-like polyethylene phantoms to simulate stones in the human body. Phantoms were scanned by Siemens dual-source dual-energy, 100 / Sn 140 kVp, and the images reconstructed automatically by the program, a built-in analysis software in CT workstation, that can distinguish uric acid stone by a color-coded method. In addition, the images were reconstructed by the filtered back projection method. ROIs of two energy images for 100 and Sn140 kVp were manual selected directly on CT monitor of workspace and their corresponding CT numbers were recorded. The CT number ratio (DR ratio) and quadrant methods were used to identify uric acid stones from the images produced by three to four reference dose levels. The monoenergetic images also reconstructed to assess stones. The analysis items include accuracy, sensitivity and specificity. Result The CT numbers of uric acid stones are similar compared to other kinds of stones in two tube voltages. The DE ratio is less than 1.13 and it agrees with other studies. Using the Ref. mAs of 53/41 mAs(100 / Sn 140 kVp) to scan and the kidney stone program to reconstruct the image and the accuracy is 98%. The quadrant method that are the CT no. less than 648 HU for Sn 140 kVp and 737 HU for 100 kVp, with the scan of the Ref. mAs setting at 27/21 mAs still had 90% accuracy. In monoenergetic images, the range of 60 to 80 keV is optimized to distinguish the uric acid stones and non-uric acid stones. In the monoenergetic method, the slope of uric acid stone was in the range of -3.3 ~ -7.2 HU / keV. The accuracy was more than 92%, sensitivity was 100%, and the specificity was more than 92% of identification of uric acid stones. By analysis of ROC curve and AUC can be found there are undifferentiated by using lower scanning dose parameters setting to identify uric acid or non- uric acid when the threshold set at 700 ~ 800 HU value . Conclusion Using the analysis by the Siemens DECT kidney stone program, the accuracy of uric acid stone is 98% and is better than that identified by personal judgment. Stone size and its thickness could affect the CT number of voxel. The quadrant method, setting the center at (648, 737) and using the third quadrant to identify uric acid stones, can reduce the effective dose and maintain a considerable accuracy. The range of 60 to 80 keV of monoenergetic images presented the best accuracy of uric acid stones by analyzing the slope. Uric acid and non-uric acid stones have the largest difference at 50 keV images. The monoenergetic method may be an innovative method that is worthy to study and develop application software by manufacturers. By the strategy of reducing scan length and Ref. mAs, the effective dose can be decreased to the dose level of KUB or IVP examination.