Publication: Modified contrast volume and saline chaser to reduce artifacts in computed tomography pulmonary angiography (CTPA)
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Date
2022
Authors
Pin, Chia Fui
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Abstract
Background: Computer tomography pulmonary angiography (CTPA) is the gold standard imaging for the diagnosis of pulmonary embolism (PE). Therefore, the quality of the images plays a big role in the diagnosis and patient’s management later. The image quality is mainly assessed by the pulmonary artery enhancement in the Hounsfield Unit (H.U.) and the impact of the streak artifacts from the high concentration of contrast in the adjacent vessels. In Hospital Universiti Sains Malaysia (HUSM), the major problem that we faced was poor enhancement of the pulmonary artery as most of the contrast remained in the subclavian vein, brachiocephalic vein, and superior vena cava (SVC). Many factors contributed to these problems, which were divided into 2 categories: scanning protocol and patient-related factors. The patient-related factor is a component that is difficult and almost impossible to adjust. Thus, the purpose of the study is to modify the CT protocol to improve the image quality and correlate with the body mass index (BMI) factor. Methods: A prospective study was conducted in HUSM, Kota Bharu, Kelantan, Malaysia on patients who were suspected to have PE and underwent CTPA using Toshiba Aquilion PRIME computer tomography (CT) scanner. All the patients who underwent CTPA from 1st June 2020 to 14th February 2021 used a standard protocol (contrast volume 40 ml and saline flush 60 ml). While those who underwent CTPA from 15th February 2021 to 31st October 2021, used a modified protocol (contrast volume 30ml and saline flush 70ml). It is a non-randomized, convenient sampling based on inclusion and exclusion criteria. All the scans were performed using the bolus tracking technique. Both protocols were compared for pulmonary trunk enhancement and degree of artifacts from the SVC and subclavian vein. The pulmonary trunk enhancement was also correlated with patient’s BMI. Results: A total of 254 patients with suspected PE underwent CTPA. Based on the inclusion and exclusion criteria, 199 patients were enrolled. Of these, 83 patients underwent CTPA with standard protocol and 116 patients underwent modified protocol. The age range of the subjects for standard protocol was 13 to 86 (mean age 50.5) years old, and the modified protocol was 13 to 95 (mean age 52.7) years old. The mean BMI for standard protocol was 26.0 (range 14.3 to 43.0) and for modified protocol was 24.8 (15.6 to 43.8). The mean H.U. of pulmonary trunk showed significant difference between the two protocols, which was higher in the modified protocol [Mean difference (95% CI) = -41.97 (-80.60, -3.34), p = 0.033]. However, the difference in mean H.U. of pulmonary trunk between the protocols showed no significant difference after adjusted to BMI and HR as covariates. Majority of subjects had artifact grade 3 for SVC (75.4%) and subclavian vein (62.8%). The modified protocol had a lower proportion of grade 3 artifacts for both SVC and subclavian vein (p<0.001). BMI and H.U. of pulmonary trunk revealed a significant correlation, overall (r=-0.4) and by each type of protocol (standard protocol r=- 0.3, modified protocol r=-0.4). Conclusion: The modified protocol showed better contrast enhancement in pulmonary trunk and lower artifacts than the standard protocol in this study. BMI was a cofounding factor and showed significant correlation with pulmonary trunk enhancement
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Keywords
CT Scan , Computer tomography pulmonary angiography