Authors (including presenting author) :
Chiu WK(1), Yu PH (1), Chan WM (1), Yeung L (1)
Affiliation :
(1)X-Ray Department, Our Lady of Maryknoll Hospital
Introduction :
Pulmonary embolism (PE) is a life threatening condition requiring immediate emergency treatment. Signs and symptoms included chest pain, shortness of breath and weak pulse. Clinical test such as D-Dimer test can be performed to assess the possibility of PE. Computed Tomography Pulmonary Angiography (CTPA) is a non-invasive imaging modality providing fast diagnosis for PE. The demonstration of pulmonary arteries relies heavily on contrast bolus adequacy, which is affected by technical factors. High injection rate, high concentration of iodine in intravenous contrast and the correct timing for scan are crucial for enhancing bolus adequacy for CTPA. Iodinated contrast of 350 mg iodine/mL is routine injected at the rate of 3.5-4 ml/s for CTPA. The scan timing can be determined by two techniques: bolus tracking and timing bolus. Bolus tracking initiates the scan once the radio-density of the pulmonary trunk reaches 50 HU. Timing bolus used a test bolus to measure the time taken for maximum enhancement in the pulmonary trunk. The time taken measured is then used for time delay in CTPA.
Objectives :
Sufficient bolus adequacy can be defined in two means. Firstly, it was reported that radio-density of 210 HU is required in the vessel to identify thrombus from enhancing vessel. Secondly, pulmonary artery-to-aorta enhancement ratio> 1 can also be regarded as adequate pulmonary opacification. The objective of this study is to compare the performance of bolus tracking and timing bolus for providing sufficient bolus adequacy in pulmonary arteries.
Methodology :
Data was collected via PACS and RIS retrospectively. All CTPA cases performed by bolus tracking or timing bolus in Our Lady of Maryknoll Hospital and Kwong Wah Hospital from September to December in 2018 were included in this study. CTPA was scanned by GE Lightspeed VCT 64-slice CT scanner in caudal-cranial direction. Omnipaque 350 was injected at rate of 4ml/s. Circular ROIs occupying two-thirds of the vessels were drawn to measure the enhancement level at the (1) aorta, (2) pulmonary trunk, (3) left and (4) right pulmonary arteries, pulmonary braches at the level (5) just above the aortic arch (upper bracnhes), (6) pulmonary trunk (middle branches) and (7) left ventricle (lower branches). Patient demographic data such as age and gender and the volume of contrast injected were also recorded. The data was then analyzed by SPSS.
Result & Outcome :
79 CTPA was included in this study. 34 bolus tracking (43%) and 45 (57%) timing bolus cases were recorded. The mean enhancement in both groups in all pulmonary segments is all above 210 HU, indicating both protocols can provide sufficient enhancement for detection of PE. Generally, the enhancement level in bolus tracking group is higher than that of timing bolus group, except in lower pulmonary branches. The difference is significant at the pulmonary trunk, left and right pulmonary arteries and aorta (p<0.05), indicating better performance for opacifying those segements by bolus tracking. The Artery-to-aorta ratio in the group of timing bolus was significantly higher than that of the group of bolus tracking at upper pulmonary branch, lower pulmonary branch and the average enhancement in pulmonary branch (p<0.05), indicating better scan timing of timing bolus for opacifying those pulmonary segments Analysis also was performed to determine whether CTPA protocols can result in lumen enhancement above 210HU or artery-to-aorta ratio higher than 1. No significant results were demonstrated by Chi-square test.
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