Spektral CT med redusert dose jodkontrastmiddel i utredning av hjerte- og karsykdom

Abstract

Background: Spectral CT enables significant reduction of iodine contrast medium (ICM) due to the increased attenuation of iodine, especially with virtual monoenergetic images (VMI) at low energy levels. Cardiovascular diseases remain a leading cause of mortality, making CT angiography (CTA) a crucial diagnostic tool in this field. Objective: The main goal of this project was to explore the potential for reducing ICM in CTA using dual-energy techniques and to identify the contrast administration strategies that yield the best results. Method: Article I: Patients referred to lower limb CTA were recruited for this randomized controlled trial. The experimental group underwent dualenergy CT with half the standard dose of ICM, while the control group received conventional CT with standard dose. Two VMI series were reconstructed at 40 and 50 keV in the experimental group. The main endpoint was vascular attenuation, with secondary endpoints including image noise, contrast-to-noise ratio (CNR), signal-to-noise ratio (SNR) and subjective examination quality (SEQ). Article II: An artificial coronary artery with 100% and 50% CM doses was placed in a thoracic phantom with varying heart rates and patient sizes. The phantom was scanned using a clinical coronary CTA protocol at 120 and 140 kVp. Virtual monoenergetic images of VMI were reconstructed from 40 to 70 keV. The reference was a 100% dose of ICM at 60 keV, and non-overlapping 95% confidence intervals for CNR indicated significant differences from the reference. Article III: Patients referred for CT pulmonary angiography were prospectively randomized into a control group or one of two experimental groups. The control group received CM diluted 1:1 with saline. Experimental Group B received low-flow CM, and Group C received a low-concentration CM. VMI at 40 and 55 keV were reconstructed, measuring vascular attenuation, noise, SNR, and SEQ at three anatomical levels. Results: Article I: A total of 103 and 108 patients were analyzed in the experimental and control groups, respectively. Vascular attenuation was higher at experimental 40 keV than control (p < 0.0001) but lower at 50 keV (p = 0.022). Noise was higher at 40 keV (p = 0.00022) but lower at 50 keV (p = 0.0033). CNR and SNR were higher than control at experimental 40 keV (both p < 0.0001) and 50 keV (p = 0.0058 and p = 0.0023, respectively). SEQ was better in both VMI in the experimental group than in the control (both p < 0.0001). Article II: Higher CM doses, reduced keV, lower heart rates, higher tube voltages, and smaller patient sizes tended to show higher CNR. No significant differences in contrast-to-noise ratio were found between experimental scans with 50% CM dose at 40 keV and the reference Article III: A total of 328 patients were randomized. Analysis included 112 in the control group and 115 and 101 in experimental Groups B and C, respectively. No differences were observed in vascular attenuation in the pulmonary trunk between groups: A vs. B (p = 0.96), B vs. C (p = 0.14), and A vs. C (p = 0.18). Group C showed higher vascular attenuation across all anatomical levels, with no differences in SEQ. Conclusion: Using dual-energy techniques makes it possible to reduce the ICM dose by 50% in CTA due to the increased attenuation of iodine, especially with VMI at low energy levels. Although noise is lower at higher energy levels, increased attenuation at low energy levels is more critical for CNR. All ICM administration strategies can be clinically applied, but low iodine concentration may yield better results when assessing the entire vascular tree. This highlights the importance of personalized and efficient ICM use and the adoption of new technology.