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KMID : 1131320150170020115
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Journal of Korean Society of Computed Tomographic Technology
2015 Volume.17 No. 2 p.115 ~ p.121
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A study on the correlation between Heart Rate in Coronary Artery and Monitoring Delay Time using Dual Source CT
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Chang Jae-In
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Abstract
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Purpose : High contrast is required for Coronary Artery CT. For this reason, it is important to determine the monitoring delay time after injection of contrast agents. Bolus tracking is used because appropriate monitoring delay time varies from individual to individual. Purpose of this study was to find out it monitoring delay time is affected by heart rate and accurate delay time contributes to dose reduction.
Materials and Methods: From July to September 2014, 100 patients (67 men, 33 women), ranging in age from 29 to 85 years (mean, 55.5 years), underwent coronary artery CT using a dual source CT machine (Somatom Definition Flash, Siemens Health care, Germany). We set a region of interest (ROI) on ascending aorta using bolus tracking and started a CT scan when the value of ROI was over 100 HU. Heart rate and monitoring delay time were measured and comparatively analyzed.
Results : Mean heart rates dropped by 5.6 in inspiration states. Mean heart rate was 69.2 (101~44) and 63.3 (105~44) before CT exams and during Ca scoring, respectively. After injecting contrast agents, mean heart rate 61.1 (97~36) dropped by 2.5 compared with that of Ca scoring. Starting scan time was 17.15 seconds on average (11.1~24.2 seconds).
Average scan delay time according to the heart rate was as follows: 18. 7 (15.2~21.1) seconds for eight patients with heart rate 36-49, 17.9 (12.2~24.1) seconds for 43 patients with heart rate 50~59, 16.7(11.1~23.1) seconds for 33 patients with heart rate 60~69, 14.7 (13.1~17.3) seconds for 10 patients with heart rate 70~79, and 13.7 (12.2~16) seconds for five patients with heart rate 80~89.
Conclusions : Monitoring delay time after contrast agents was longer in patients with lower heart rate. Value of CTDIvol increased by 1.71 mGy as 1 second of delay time increased. We can reduce radiation dose on patients by adjusting delay time according to their heart rate.
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KEYWORD
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coronary artery, monitoring delay time, bolus tracking
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