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KMID : 1149020170190020083
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Journal of Korean Society of Computed Tomographic Technology
2017 Volume.19 No. 2 p.83 ~ p.96
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Research on dose reduction and image quality by changing tracker spot in lower extremity CT angiography
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Jeon Chan-Il
Park Jun-Cheol
Lee Seong-Hyeon
Park Kye-Yeon
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Abstract
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Purpose : Examine results such as tibial artery and dorsalis pedis & plantar artery were not caught in contrast enhancement when testing lower extremity CTA ; because the old patients had arteriosclerosis, DM, claudication, medial calcification, which are diversity of blood circulation. Patients' exposure is to be decreased after re-examination and the quality of reconstruction image of 2D and 3D is to be improved by changing the method that tested bolus tracker site on abdominal aorta, and placed then on the knee joint level to examine contrast enhancement manually. This study aims to acquire adequate contrast enhancement and dose reduction by changing the tracker’s spot into popliteal artery level.
Materials and Methods : The resources were collected from January in 2016 to February in 2017, with 120 CTA patients of male and female. Brilliance 64's conditions is 120 kVp, 250 mAs, and pitch 0.681. Aquilion one is 120 kVp, sure exp3D and pitch 0.861. Somatom is CARE kV, CARE mA and pitch 1.2. Also the injection flow rate is 5.0 ml/s and total volume is 140 ml with 30 ml normal saline. First, we divided 4 groups for comparison and analysis : Group A was an independent group before changing the protocol, and Group B, C, and D were dependent groups. Group A was tested with threshold limit of HU 200 using Brilliance 64 with ROI on abdominal artery. The other three groups were tested with threshold limit of HU 250 using Aquilion one and Definition AS with ROI on popliteal artery. Especially, group D was leveled at HU 300 to compare with the group B, and it was intended for analyzing the image quality with the variation of HU value. After injecting contrast, we assessed the average of 5 ROI that is, abdominal aorta, both politeal artery, both dorsalis pedis & plantar artery, to examine the differences of threshold limit time among patients. Then, the value of DLP and the portion of re-examination between group A and group B and D. We use Voxar 3D Enterprise program for 3D re-construction and SPSS version 18 for analysis.
Results : First, we compared threshold limit time among group A, B, and C. It took 13s (min.), 20s (max.), and 15.5s (average) in group A. It took 20s (min.), 71s (max.), and 33s (average) in group B. In group C, it took 19s (min.), 45s (max.), and 27.5s (average). The average HU of abdoman aorta, politeal artery, dorsalis pedis & plantar artery in four groups are as follows: Starting from upper blood vessel, group A had 442.5, 372.5, and 151.1 HU. Group B had 417.2, 511.2, and 189.2 HU. Group C had 598.5, 550.2, and 329.3 HU. Finally, group D had 481.8, 465.5, and 240.7 HU. In case of Aquilion one, we consulted radiologist to evaluate the re-examined images of group D for comparison with group B and C. The results are follows : Group A scored 3 out of 5. Group B got 3 points except one case in 3D re-construction. Among the equipments, Somatom showed best score. The average DLP of equipments was 1562.9 mSv cm for Brilliance 64, 895.6 mGy cm for Somatom, and 752.4 mGy cm for Aquilion one. In the case of exposure, Brilliance 64(Philips) rated highest in 1 phase test. After changing tracker, the re-examination portion of Aquilion one and Somatom decreased to 0%. The reexamination portion and extra section exposure was 9.5% and 48 %, respectively, in 40 cases before changing the protocol. Due to the protocol changes, patient dose reduced up to 37% by reducing unnecessary testing and retesting.
Conclusion : This study expects that dose reduction and appropriate contrast enhancement images will be acquired without unnecessary retesting, once the tracker is on popliteal artery as lower extremity CT angiography is examined. Also it suggests that we have better quality in 3D.
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KEYWORD
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Lower extremity CTA, Popliteal artery, ROI, Dosalis pedis & plantar artery, HU
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