PerfusionsCT

Perfusion CT, also known as CT perfusion imaging, is a dynamic imaging modality that assesses tissue perfusion by tracking intravenously injected iodinated contrast as it passes through the cerebral or other tissue vasculature. The technique uses rapid, repeated CT acquisitions after contrast injection to generate time-attenuation curves and parametric maps of perfusion.

In the brain, common parameters include cerebral blood flow (CBF), cerebral blood volume (CBV), mean transit time (MTT), and time to maximum enhancement (Tmax). These maps help distinguish irreversibly damaged tissue (ischemic core) from potentially salvageable tissue (penumbra).

Clinical use: In acute ischemic stroke, perfusion CT is used to extend the time window for reperfusion therapies and to select patients for thrombolysis and mechanical thrombectomy when noncontrast CT is non-diagnostic. It is also used in evaluating brain tumors for tumor grade assessment, treatment monitoring, and to characterize vascularity and breakdown of the blood-brain barrier.

Technical considerations: The protocol involves an IV contrast bolus and rapid CT scans over tens of seconds, followed by post-processing with deconvolution to derive CBF, CBV, MTT, and Tmax maps. Software algorithms and scanner characteristics influence values; thus interpretation should be in the context of clinical presentation and cross-validated thresholds. Considerations include radiation dose, contrast load, patient motion, and renal function.

Limitations include variations in thresholds for core vs penumbra, potential underestimation of CBF in flow-limited tissue, and susceptibility to hemodynamic delay. Safety concerns include contrast allergy risk and nephrotoxicity, especially in patients with preexisting renal impairment.

Research and guidelines: Perfusion CT findings are integrated into guideline recommendations for acute stroke management in many regions, alongside diffusion-weighted MRI and CT angiography.