Low radiation dose imaging of myocardial perfusion and coronary angiography with a hybrid PET/CT scanner

Abstract

Objectives: To test the image quality and feasibility of a sequential low radiation dose protocol for hybrid cardiac PET/CT angiography (CTA).

Background: Multidetector computed tomography (MDCT) is a non-invasive method for coronary angiography. The negative predictive value of MDCT is high but perfusion imaging has a role in detecting functional significance of coronary lesions. This has encouraged combining these techniques. However, radiation dose is of concern. We report our first experiences with a low dose sequential CTA mode applicable to hybrid imaging.

Methods: In the first phase, 10 consecutive cardiac MDCT angiographies were performed with spiral acquisition and compared in terms of image quality and dose with the following 10 patients performed with a new sequential mode. In the second phase, feasibility and radiation dose of a combined (15)O-water rest-stress PET perfusion/sequential CTA protocol were assessed in another group of 61 consecutive patients.

Results: Mean effective radiation dose was 60% lower in the sequential group than in the spiral group (19.3 versus 7.6 mSv, P<0.001). In the second phase, the new sequential hybrid protocol proved possible in 87% of the patients given the preconditions determined by the manufacturer. Mean effective dose of the CT acquisition was 7.6 mSv and total dose from the PET/CTA hybrid study 9.5 mSv.

Conclusion: Low dose PET/CT allows cardiac hybrid studies with <10 mSv. The protocol can be applied to almost nine out of 10 patients with CT image quality comparable to spiral acquisition.

Figure 1

Principle of prospectively triggered step-and-shoot cardiac CT. Top: Heart rate trend graph; Bottom: Patient ECG during step-and-shoot CT angiography acquisition. White segments denote the time periods with X-ray tube on. White vertical line: 75% of the R-R-Interval. Vertical lines with diamonds: ECG triggering points.

Figure 2

Combined cardiac CT angiography and PET perfusion protocol.

Figure 3

Example of sequential CT angiography with normal result. Radiation dose was 5.5 mSv.

Figure 4

Example of hybrid PET perfusion and CT angiography. a: CT angiography (spiral mode) shows multi-vessel disease with occluded left anterior descending artery (LAD) and poorly visualized mid right coronary artery (RCA). Moderate disease in left circumflex artery LCX. b: Hybrid display during adenosine stress demonstrates severe perfusion reduction in LAD associated region (anterior view) while perfusion was best preserved in LCX related region (posterior view). Perfusion was colour scaled so that red colour denotes 3.5 ml/min/g. Resting perfusion was normal (not shown). Total radiation dose of the hybrid study was 22.3 mSv.

Figure 5

Example of hybrid PET perfusion and CT angiography. a: CT angiography (step-and-shoot mode) shows multi-vessel disease with massive coronary calcifications and severe stenoses in all major coronary arteries. b: Hybrid display during adenosine stress demonstrates quite preserved perfusion in anterolateral wall but moderate reduction in septal wall (anterior view). In RCA related region the perfusion was the most severely reduced (posterior view) indicating culprit stenosis in this vessel. Perfusion was colour scaled so that red colour denotes to 3.5 ml/min/g. Resting perfusion was normal (not shown). Total radiation dose of the hybrid study w as 11.3 mSv.