Optimization of Radiation Dose and Image Quality using ADMIRE Algorithm and Quantitative Evaluation

Abstract

목적: 최신 반복적 재구성법인 ADMIRE 알고리즘을 물질의 종류, 검사 조건, 적용 단계에 관하여 정량적으로 평가하고 이를 활용하여 환자 피폭선량과 영상의 질을 최적화 하고자 한다. 대상 및 방법: 증류수와 조영제의 혼합용액으로 밀도가 다른 네 종류의 물질 A(30~40 HU), B(60~70 HU), C(100~110 HU), D(200~210 HU)를 제작하여 AAPM phantom의 저 대조도 측정 부위에 주입하였다. 100, 120 kVp 두 종류의 관전압과 250~ 50 mAs 관전류로 선량을 50 mAs 단위로 감소시켜 영상을 획득하고 FBP와 1~5단계의 ADMIRE를 적용하여 CT number, SNR, CNR을 정량적으로 평가하였다. 결과: CT number(HU)값은 FBP와 ADMIRE의 적용 단계에 따라서는 차이가 없었고(P>0.05), 120 kVp와 비교하여 100 kVp를 사용하였을 경우 23±2%(P<0.05) 증가하였다. SNR은 ADMIRE를 1~5단계까지 순차적으로 적용하였을 경우 각각 10%, 23%, 38%, 60%, 98% 증가하였고, CNR은 10%, 22%, 36%, 58%, 97% 증가하였다. 120 kVp, 200 mAs, FBP영상을 기준으로 선량이 150 mAs(75%), 100 mAs(50%), 50 mAs(25%)로 감소하였을 때, 영상의 질을 유지하기 위해서는 1, 3, 5단계 이상의 ADMIRE 적용을 필요로 하였다. 결론: ADMIRE를 적용할 경우 영상의 질 저하 없이 최대 75%의 선량감소 효과를 기대할 수 있으며, 50%이상의 선량을 감소시켰을 경우에는 3단계 이상의 ADMIRE적용을 필요로 한다.Purpose: The ADMIRE algorithm which is the latest iterative reconstruction (IR) was quantitatively evaluated depending on the type of substances, scan parameter, and the stages of application to optimize patient exposure dose and image quality. Material and method: The four different types of substances; A(30~40 HU), B(60~70 HU), C(100~110 HU), and D(200~210 HU), were manufactured by using mixture of water and contrast medium and injected into the hole of the low contrast measuring part of AAPM phantom. The signal to noise ratio (SNR) and contrast to noise ratio (CNR) were quantitatively evaluated with CT numbers depending on the two types of tube voltage(100, 120 kVp), the five types of tube current by reducing the dose to 50 mAs(250, 200, 150, 100, 50 mAs), and the five types of algorithms (FBP, 1 to 5 steps in ADMIRE). Result: There were no significant differences of CT number (HU) among images depending on the application phase of FBP and ADMIRE algorithms(p>0.05); however, HUs with 100 kVp were increased up to 23±2% compared to 120 kVp(p<0.05). SNR was increased by 10%, 23%, 38%, 60%, and 98% when ADMIRE algorithms were applied sequentially to steps 1 to 5. Also, CNR was increased by 10%, 22%, 36%, 58%, and 97% in the same ADMIRE algorithm condition. Equal quality of filtered back projection (FBP) image taken with 120 kVp and 200 mAs, was maintained by applying more than 1, 3, and 5 strengths of ADMIRE in case of 150 mAs(75%), 100 mAs(50%), and 50 mAs(25%) patient dose reduction. Conclusion: ADMIRE can reduce patient dose up to 75% without degradation of image quality. In addition, the application of ADMIRE more than 3 strengths are required if the patient dose reduced by more than 50%.