Quantification Issues in Bolus-Tracking Perfusion MRI

Bolus-tracking perfusion MRI is based on the monitoring of the first passage of a bolus of contrast agent through the brain tissue and a brain-feeding artery. The contrast agent is injected rapidly in the antecubital vein in the patients arm by means of an MR-compatible power injector. This bolus of contrast agent is pushed in the direction of the heart by means of a saline flush. Continuous dynamic scanning with a typical temporal resolution of approximately 1-2 second is used to monitor the passage of the contrast agent through the brain tissue and a brain-feeding artery. The change in MR signal is hereafter converted into the concentration of contrast agent based on the physical properties of the contrast agent. The time evolution of the concentration of contrast agent in the brain-feeding artery is called the arterial input function. Deconvolving the passage through the brain tissue with the arterial input function, results in the tissue response function. Based on the theory of tracer kinetics, perfusion parameters are calculated from this tissue response function. To achieve quantitative measures of perfusion, all these different aspects should be considered.