Trading off Iodine and Radiation Dose in Coronary Computed Tomography

Abstract

Coronary CT angiography (CCTA) has seen steady progress since its inception, becoming a key player in the non-invasive assessment of coronary artery disease (CAD). Advancements in CT technology, including iterative and deep-learning-based reconstruction, wide-area detectors, and dual-source systems, have helped mitigate early limitations, such as high radiation doses, motion artifacts, high iodine load, and non-diagnostic image quality. However, the adjustments between ionizing radiation and iodinated contrast material (CM) volumes remain a critical concern, especially due to the increasing use of CCTA in various indications. This review explores the balance between radiation and CM volumes, emphasizing patient-specific protocol optimization to improve diagnostic accuracy while minimizing risks. Radiation dose reduction strategies, such as low tube voltage protocols, prospective ECG-gating, and modern reconstruction algorithms, have significantly decreased radiation exposure, with some studies achieving sub-millisievert doses. Similarly, CM volume optimization, including adjustments in strategies for calculating CM volume, iodine concentration, and flow protocols, plays a role in managing risks such as contrast-associated acute kidney injury, particularly in patients with renal impairment. Emerging technologies, such as photon-counting CT and deep-learning reconstruction, promise further improvements in dose efficiency and image quality. This review summarizes current evidence, highlights the benefits and limitations of dose control approaches, and provides practical recommendations for practitioners. By tailoring protocols to patient characteristics, such as age, renal function, and body habitus, clinicians can achieve an optimal trade-off between diagnostic accuracy and patient safety, ensuring optimal operation of CT systems in clinical practice.

Keywords: contrast-induced acute kidney injury; coronary CT angiography; coronary artery disease; iodinated contrast media; patient-specific protocols; radiation dosage.

Figure 1

A simulation of the effect of lumen attenuation differences in a 54-year-old patient (A1–C1) with corresponding schematic representations (A2–C2). The image shows a single small, calcified plaque in the circumflex artery (arrow), using different display windows, simulating hyperattenuated (A1,A2), optimal (B1,B2), and hypoattenuated (C1,C2) lumen. A hyperattenuated lumen impairs calcification detection, while a hypoattenuated lumen affects visual lumen analysis.

Figure 2

Factors influencing vascular attenuation, separated into contrast-related factors and patient-related factors. CM: contrast media, HU: Hounsfield unit.

Figure 3

An example of a thoracic CTA in a 23-year-old woman with suspected Ehlers–Danlos syndrome, presenting with exercise-related chest pain. The scan was performed with a low-dose protocol (80 kV, 460 mA, and 0.23 s rotation), resulting in an effective dose of 1.13 mSv. The aorta and coronary arteries are visualized in a 3D volume-rendered reconstruction (A), with a full curved MPR at 90° rotation (B), and a zoomed-in curved MPR at 0° rotation (C), focusing on the left anterior descending artery (LAD). The image quality was optimal, allowing us to rule out both coronary and aortic disease.

Figure 4

An example of the effect of suboptimal iodine delivery in a 63-year-old patient with endocarditis and severe aortic stenosis, undergoing coronary CT angiography (CCTA) to rule out coronary stenosis. The initial scan, performed at 87 bpm via an 18 G peripherally inserted central catheter (PICC), resulted in a limited maximum flow rate (50 mL, approximately 3 mL/s). Due to insufficient lumen attenuation and limited diagnostic accuracy (A1,A2), this scan did not allow for ruling out a stenosis of 50% or more, with a plaque of undetermined diameter stenosis (white arrow with a question mark). While the PICC model was designed to handle up to 5 mL/s flow, several factors can influence whether this flow is achievable, including the catheter length, contrast medium (CM) viscosity, and injection pressure. A repeat CCTA, following proper venous access (18 G IV catheter in the antecubital fossa) and beta-blocker preparation (72 bpm), achieved optimal image quality using 50 mL of CM at 5 mL/s with motion correction (B1,B2) and showed a <50% stenosis (white arrow). The images are displayed in a curved MPR view at 0° and 90° rotation, respectively. The CT protocol was exactly the same for both acquisitions: tube voltage, 100 kVp; tube current, 900 mA; and gantry revolution time, 0.23 s. The difference in noise between (A1,A2) and (B1,B2) is due to the lower heart rate in the repeat scan. At a lower heart rate, more projections (or data samples) contribute to the reconstruction of a single slice, resulting in lower noise despite identical acquisition parameters.

Figure 5

Suggestions for practitioners regarding radiation dose and iodine dose optimization based on patient characteristics, as well as general optimization parameters. Note that although obese patients are not specifically mentioned in this algorithm, they require both higher X-ray and contrast medium doses. Reducing either dose can compromise the clinical usefulness of CCTA in this patient group.