Advances in cardiac CT contrast injection and acquisition protocols

Abstract

Cardiac computed tomography (CT) imaging has become an important part of modern cardiovascular care. Coronary CT angiography (CTA) is the first choice imaging modality for non-invasive visualization of coronary artery stenosis. In addition, cardiac CT does not only provide anatomical evaluation, but also functional and valvular assessment, and myocardial perfusion evaluation. In this article we outline the factors which influence contrast enhancement, give an overview of current contrast injection and acquisition protocols, with focus on current emerging topics such as pre-transcatheter aortic valve replacement (TAVR) planning, cardiac CT for congenital heart disease (CHD) patients, and myocardial CT perfusion (CTP). Further, we point out areas where we see potential for future improvements in cardiac CT imaging based on a closer interaction between CT scanner settings and contrast injection protocols to tailor injections to patient- and exam-specific factors.

Keywords: Contrast injection protocol; cardiac computed tomography (CT); coronary CT angiography (CTA); iodine contrast agent.

Figure 1

Contrast-enhancement-related factors.

Figure 2

Triphasic injection protocol for coronary CT angiography providing high attenuation in the left cardiac chambers, right coronary artery (arrow), and aorta with only slight increased attenuation in the right cardiac chambers allowing additional evaluation of the right heart structures and septum.

Figure 3

Coronary CT angiography injection protocol of a dual-head power injector (A, iodine contrast medium; B, saline). The protocol displays injection rate, volume (upper part), and flow rate over time (lower rate). Protocol started with a saline bolus to test venous access [1]. Second was an undiluted CM test bolus [3] followed by saline flush [4]. Finally, triphasic injection protocol contained undiluted CM bolus [6], followed by 21% diluted CM bolus [7] and saline chaser [8].

Figure 4

Test-bolus to determine correct timing of contrast enhancement (left) and region of interest placement in the ascending aorta (right).

Figure 5

Increased lumen attenuation in 70- and 80-kVp coronary CTA curved multiplanar reconstruction of the LAD compared to standard 120-kVp. Lower tube voltage resulted in higher noise (80-kVp). The additional use of iterative reconstruction resulted in reduced noise in the 70-kVp image.

Figure 6

Spectral computed tomography angiography based on dual-source image acquisition at 80- and 150-kVp. Linear-blended 0.6 image series has similar image characteristics as 120-kVp acquisition. Improved attenuation of iodine CM in virtually reconstructed 60-keV monoenergetic image.

Figure 7

Spectral computed tomography angiography of the aorta (left) with virtually reconstructed unenhanced image (right) at the same height visualizing an aortic valve replacement.

Figure 8

Pre-TAVR thoraco-abdominal-pelvis CTA of the heart and CTA using 60 mL CM with excellent opacification of all target vessels.

Figure 9

Visualization of pulmonary veins and left atrium in a patient with atrial fibrillation before ablation. LA, left atrial; PV, pulmonary vein.

Figure 10

Hypoplastic left heart syndrome after final stage 2 (Fontan) procedure. Contrast injection only via the upper extremity through SVC. IVC contained unenhanced blood with mixture of unenhanced and enhanced blood within the lateral tunnel Fontan conduit (stent). Visualization of patent atrial septal defect (ASD).