Low contrast dose in CCTA

Key images

Findings

Chest discomfort. CT was performed to assess the presence of coronary stenosis.

CT attenuation of the cardiac chambers and coronary arteries was enhanced at lower energy levels using spectral virtual monoenergetic images, which was useful for quantitative analysis of the coronary tree with dedicated software.

Axial images, curved planar reformations (CPR), multiplanar reformations (MPR) and volume rendering (VR)

The CCTA injection protocol consisted of injection of 18 mL of iodinated contrast media (concentration 400 mgI/mL) at a flow rate of 2 mL/s. The poor coronary enhancement at conventional CT made small coronary artery branches invisible. Spectral low keV virtual monoenergetic imaging was used to increase attenuation of iodine-containing coronary arteries, which was conclusive to observe small coronary branches and detect a latent lesion in the right atrium. The iodine density of the lesion in the right atrium was about 0.3 mg/mL, which was indicative of low enhancement.

Discussion

Conventional CCTA demands a relatively large amount of contrast agent to achieve satisfactory contrast enhancement of the coronary lumen, while spectral low keV virtual monoenergetic imaging will achieve equivalent or better enhancement with a reduced dose of contrast agent. In addition, Spectral CT improves the detection of latent lesions, which is complementary to qualitative diagnosis.

Conventional Image

Conventional image: Coronary artery lumen appears smaller in conventional CT images compared to spectral low keV virtual monoenergetic image. Note invisibility of small branches.

Monoenergetic 40 keV Image

Conventional Image Monoenergetic 40 keV Image

Spectral virtual monoenergetic 40 keV image: Shows better depiction of both the main coronary arteries (white arrow) as well as small coronary artery branches (yellow arrows).

Conventional image CPR: Shows poor enhancement of the coronary artery lumen. The plaque border in proximal LAD is not clear and image noise is high.

Spectral virtual monoenergetic 40 keV image CPR: Shows excellent coronary enhancement despite low contrast dose. The plaque border in the proximal LAD is clear, and there is less image noise compared to the conventional image.

Iodine density

Conventional image: The left ventricle exhibits good enhancement but opacification of the right half of the heart is poor, limiting differentiation of the myocardium from the blood pool.

Spectral virtual monoenergetic 40 keV image: Shows clear enhancement of both the left and right cardiac chambers, despite the low concentration of contrast agent in the right half of the heart. The improved contrast unveils a lowdensity filling defect in right atrium and the boundary of lesion is clear.

Spectral iodine density map: Shows iodine concentration in different cardiac structures. The lesion in right atrium has no iodine uptake, and the boundary of lesion is clear.

The iodine density of the lesion in right atrium was about 0.3 mg/mL, which demonstrated that iodine uptake was low, indicating low blood supply of the lesion.

Postoperative pathology: The volume of tumor is about 2 x 1 x 1cm, the basal area of tumor is about 1.5 x 0.7cm. Pathological diagnosis: Right atrial myxoma.

History