Keywords:
Case-control study, Retrospective, Image verification, Contrast agent-intravenous, CT-Angiography, CT, Vascular, Contrast agents, Arteries / Aorta, Performed at one institution
Authors:
Y. Ohka1, K. Takegami1, S. Kudomi1, T. uehara1, S. Tokurei2, M. Okada 1, T. Nomura1, K. miyoshi1; 1Yamaguchi/JP, 2Fukuoka/JP
DOI:
10.26044/ecr2020/C-08958
Methods and materials
This retrospective study was approved by our institutional review board. We selected 150 patients who underwent aortic CTA using a dual-source scanner (SOMATOM Force, Siemens Healthineers) between 19th July and 31st October 2018. Body weight, volume CT dose index (CTDIvol) values indicated in the dose report of the CT system, and injection conditions were reviewed for all patients. During the period, 100 patients underwent standard-voltage CTA with standard iodine dose as the reference protocol (protocol 1), and the remaining 50 patients underwent 70-kV aortic CTA with the low-concentration CM of 140 mg/mL (protocol 2) as shown in Fig. 2.
Scan and Contrast Medium Injection Protocols (Fig. 2)
In protocol 1 group for the standard aortic CTA, the iodine dose of 320 mg per kilogram body weight using the CMs of 300, 350 or 370 mg/mL was delivered over 16 seconds; thus, the injection flow rate was set as 20 mg I/sec per kilogram. Using a dual-syringe injector (Dual shot GX7, Nemoto-Kyorindo), we used a biphasic injection protocol with a 16 second CM followed by 40 mL saline chaser. The tube voltages were selected from 100-, 110-, or 120-kV with use of automated kilovoltage selection technology (CARE kV, Siemens Healthineers).
In protocol 2 group, the low-concentration CM of 140 mg/mL iohexol (Omnipaque 140, 220-mL vial, Daiichi Sankyo) was applied to 70-kV aortic CTA with half the iodine dose of protocol 1. The resulting iodine dose of 160 mg per kilogram body weight was delivered at 10 mg I/sec per kilogram using a triple-chamber mechanical power injector (CT motion, Ulrich medical), with which two bottles for contrast injection could be seamlessly switched and delivered, followed by 40 mL saline chaser.
In both protocols, scanning for CTA ranging from the upper level of the clavicle to the lesser trochanter was started 6 seconds after the attenuation of the descending aorta increased 150 HU using a bolus-tracking method.
Image Analysis (Fig. 3)
For evaluating the contrast enhancement, we measured the mean CT attenuation values, standard deviation (SD) and the signal to noise ratio (SNR) within the regions of interest (ROIs) at top of aortic arch and descending aorta at the celiac axis level. Additionally, the residual CM was evaluated based on the maximum CT value within the ROI drawn at the right subclavian vein.