[논문]단색에너지(keV)와 조영제 희석비율 변화에 따른 HU(Hounsfield Unit)값 분석: Spectral CT 이용

정희라; 강진우; 권오준; 김호진; 정다빈; 이재현; 허영철

doi:10.7742/jksr.2020.14.5.669

[국내논문] 단색에너지(keV)와 조영제 희석비율 변화에 따른 HU(Hounsfield Unit)값 분석: Spectral CT 이용
Spectral CT Analysis of Hounsfield Unit (HU) according to MonoE (keV) and Dilution Ratio of the Contrast Agent: Use of Spectral CT 원문보기

한국방사선학회 논문지 = Journal of the Korean Society of Radiology, v.14 no.5, 2020년, pp.669 - 676

정희라 (을지대학교 보건과학대학 방사선학과) , 강진우 (을지대학교 보건과학대학 방사선학과) , 권오준 (을지대학교 보건과학대학 방사선학과) , 김호진 (고려대학교안산병원 영상의학과) , 정다빈 (을지대학교 대학원 방사선학과) , 이재현 (분당서울대학교병원 영상의학과) , 허영철 (을지대학교 보건과학대학 방사선학과)

초록
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본 연구의 목적은 Spectral CT에서 단색에너지(keV)와 조영제 희석비율의 변화에 따른 HU 값의 변화를 분석하고자 하였다. 검사장비로는 Spectral CT를 사용하였고, 20 cc syringe의 팬텀을 이용하여 조영제의 희석비율을 8:2, 7:3, 6:4, 5:5, 4:6, 3:7 총 6단계로 설정하였다. 이때 조영제는 비이온성 요오드 조영제(350 mg/ml)를 이용하였다. 획득한 데이터를 IQon-Spectral CT V4.7.5 프로그램을 사용하여 Monoenergy(MonoE) 40 keV, 45 keV, 50 keV, 55 keV, 60 keV, 65 keV, 70 keV, 75 keV, 80 keV 총 9단계로 변화시켜 syringe axial 영상을 재구성하였다. 재구성한 syringe axial 단면 영상의 세 위치에서 HU 값을 측정하였으며, 총 1,620회 측정하였다. keV와 조영제 희석비율의 변화에 따른 HU 값을 분석한 결과, MonoE별 희석비율에 따른 HU 비교에서 모든 MonoE에서의 HU 값이 희석비율 8:2에서 가장 높았으며 3:7에서 가장 낮았다(p<0.05). 희석비율별 MonoE에 따른 HU 비교에서 모든 희석비율에서의 HU 값이 40 keV에서 가장 높았으며 80 keV에서 가장 낮았다(p<0.05). 인자별 상관성은 keV에 따른 HU 값은 -15.014 ± 0.298의 음의 상관성(R²=0.519)이 있었고 희석비율에 따른 HU값 은 -61.372 ± 3.608의 음의 상관성(R²=0.152)이 있었다(p<0.05). 결론적으로 keV 값과 조영제 희석비율이 증가할수록 HU 값은 감소하는 것을 확인하였으며 본 연구가 Spectral CT의 HU 값 관련 인자 연구에 있어 기초자료를 제공할 수 있을 것이라 사료된다.

Abstract ▼ AI-Helper

The purpose of this study was to analyze the changes in the values of Hounsfield Unit (HU) according to the changes in monoenergy (keV) and dilution ratio of the contrast agent, using the spectral CT. Spectral CT was used as the testing device, while 20 cc syringe phantom was used to set a total of six dilution ratios of the contrast agent: 8:2, 7:3, 6:4, 5:5, 4:6, and 3:7. Here, the non-ionic iodine solution (350 mg/ml) was used as a contrast agent. The syringe axial image was reconstructed by adjusting the obtained data on nine MonoE levels; 40 keV, 45 keV, 50 keV, 55 keV, 60 keV, 65 keV, 70 keV, 75 keV, and 80 keV. The HU values were measured at the three points of the reconstructed syringe axial image. The measurements were taken 1,620 times in total. In the analysis of the HU values according to the changes in keV and dilution ratio of the contrast agent, the highest and lowest HU values were obtained from dilution ratio 8:2 and dilution ratio 3:7, respectively, across every MonoE in the comparison of HU according to dilution ratio per MonoE (p<0.05), while the highest and lowest HU values were obtained from 40 keV and 80 keV, respectively, across all dilution ratios in the comparison of HU according to MonoE per dilution ratio (p<0.05). For the correlation per each parameter, a negative correlation of -15.014 ± 0.298 was found for HU per keV (R2=0.519) and a negative correlation of -61.372 ± 3.608 was found for HU per dilution ratio (R2=0.152) (p<0.05). To conclude, an increase in keV or dilution ratio of the contrast agent was shown to decrease the HU, and the findings in this study are anticipated to serve as the basic data in the research of HU-related parameters in Spectral CT.

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표/그림 (5)

그림 Fig. 1. IQon Spectral CT (A) and pillow to match the height of the abdominal aorta (B).
표 Table 1. Scan Parameter
그림 Fig. 2. Measurement Data at dilution ratio 8:2 and 40 keV, first slice (A) and 28th slice (B) and 56th slice (C). Arrow is the chosen axial slice image of syringe.
표 Table 2. The HU values according to keV and dilution rate changes
표 Table 3. Multiple linear regression analysis of HU values according to keV and dilution rate changes.

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제안 방법

5 horizontally. The CT imaging test was performed in the following conditions: tube voltage 120 kVp, tube current 105 mAs, slice thickness 2 mm, scan time 1.93 sec, FOV 50 mm, and length 57 mm, which were identical across all tests[Table 1]. For reliability, the tests were repeated ten times in the identical conditions for each dilution ratio.
^[19], in the MDCT test of the carotid artery, also reported no significant difference in the HU between the original solution of the contrast agent and the contrast agent of 9:1 and 8:2 dilution ratios. However, the two studies focused on the correlation between the HU and the contrast agent in MDCT, while there is still a general lack of studies analyzing the correlation between the HU and the contrast agent in spectral CT. It is thus anticipated that the analysis of the HU according to dilution ratio of the contrast agent per MonoE in spectral CT in this study would provide highly significant data.
The limitations in this study are that the phantom size could not be varied and that only 350 mg/ml iodine content in the contrast agent was used so that the analysis could not be performed according to the changes in iodine content. The unified testing condition of 120 kVp and 105 mAs was another limitation.
The unified testing condition of 120 kVp and 105 mAs was another limitation. Nevertheless, the significance of this study lies in the quantitative analysis of the correlation between the HU and keV and between the HU and dilution ratio of the contrast agent, through the use of spectral CT.
In the spectral CT analysis, the HU and keV showed a negative correlation, where an increase in keV led to a fall in the HU, while the HU and dilution ratio of the contrast agent also showed a negative correlation, where an increase in dilution ratio of the contrast agent led to a fall in the HU. To conclude, the findings in this study are anticipated to serve as the basic data in studies analyzing the HU using spectral CT, according to the changes in the phantom size, the changes in the content of the contrast agent, and the changes in the testing conditions.

대상 데이터

In this study, a CT device (IQon Spectral CT, Philips, Netherlands) was used for imaging analysis, while a 20 cc syringe was used as the phantom. Here, a nonionic iodine contrast agent (350 mg/mL) was used.
The data obtained from the scan were reconstructed for each dilution ratio at monoenergy (MonoE) 40 keV, 45 keV, 50 keV, 55 keV, 60 keV, 65 keV, 70 keV, 75 keV, and 80 keV, using the IQon-Spectral CT V4.7.5 program, while each reconstructed image was set to the ROI of 349.4 mm square (sq) to generate 56 axial sections from each image. The HU was measured at the following three points; the first slice (-103.
7 mm). From the measurement data, 10 times of scan data were obtained for each of the six different dilution ratios, and through the measurements at the three phantom points on the nine reconstructed MonoE images of each test, a total of 1,620 HU values were collected.
For the analysis, the images were reconstructed on nine levels of MonoE (40 - 80 keV), while the contrast agent was varied in dilution ratio on six levels from 8:2 to 3:7, and as a result, a total of 1,620 data were obtained. The results showed that the HU had a negative correlation of -15.

데이터처리

To analyze the mean values of the HU data per dilution ratio and per keV, the two way ANOVA test was performed using a statistical software (SPSS 18.0, IBM, USA). Dunnett test was used for the post-hoc analysis, and multiple regression analysis was performed to verify the correlations.
0, IBM, USA). Dunnett test was used for the post-hoc analysis, and multiple regression analysis was performed to verify the correlations. Here, statistical significance was set as p ≤ 0.

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