The stress myocardial computed tomography perfusion (CTP) imaging is a CT-based exam that combines the information provided by anatomy and perfusion. CT assessment of myocardial perfusion is based on the distribution of iodinated contrast material during its first pass through the myocardium. Because the contrast material's distribution is determined by the arterial blood supply, myocardial perfusion defects can be identified as hypo-attenuating areas containing reduced amounts of contrast material.
Myocardial CTP protocol is composed of:
- a stress phase acquisition, performed under pharmacological administration of stress agents, such as adenosine, to induce a vasodilatation;
- a rest phase acquisition, similar to a nuclear myocardial perfusion imaging (MPI) exam;
- a third delayed-phase acquisition, optional, that can be performed in cases where late contrast enhancement evaluation for myocardial scar is desired.
Heart rhythm and symptoms are monitored throughout the entire exam. The acquisitions are evaluated for myocardial perfusion information but also coronary anatomy as well, generally using the rest acquisition.
Patient preparation. In addition to the standard setup of a coronary CTA, myocardial CTP protocol requires a few additional components:
- additional intravenous catheter if adenosine/dipyridamole infusion is being used;
- a 12-lead electrocardiogram (ECG) machine
- a blood pressure monitor.
Image acquisition. In the study, the rest coronary CTA performed with a Revolution CT scanner (GE Healthcare, Milwaukee, Wisconsin) according to the recommendations of the Society of Cardiovascular Computed Tomography (SCCT). For the stress phase, at the end of the third minute of the adenosine infusion, a single data sample during first-pass enhancement of coronary CTA was acquired with the same protocol used for rest coronary CTA.
Image interpretation. All coronary artery imaging datasets were combined with stress CTP according to the following interpretation:
- nonobstructive CAD with negative matched CTP was considered negative;
- obstructive CAD with negative stress CTP was considered negative;
- obstructive CAD with positive matched stress CTP was deemed positive.
A perfusion defect under pharmacological stress that reverses at rest is, by definition, stress-induced ischemia. A fixed (irreversible defect) is characteristic of myocardial infarction. Note that myocardial infarction also exhibits late contrast enhancement in a fashion similar to late gadolinium enhancement in cardiac magnetic resonance.