Quantitative assessment of regional cerebral blood flows by perfusion CT studies at low injection rates: a critical review of the underlying theoretical models

Viability of the cerebral parenchyma is dependent on cerebral blood flow (C BF), which is usually kept in a very narrow range due to efficient autoregu lation processes and can be altered in a variety of pathological conditions . An accurate method allowing for a quantitative assessment of regional cer ebral blood flows (rCBF) and available for the routine clinical practice wo uld, for sure, greatly contribute to improving the management of patients w ith cerebrovascular diseases. Different imaging techniques are now availabl e to evaluate rCBF: positron emission tomography; single photon emission CT ; stable-xenon CT; perfusion CT: and perfusion MRI. Each of these imaging t echniques uses an indicator, with specific biological properties, and is su pported by a model, which consists of a few simplifying assumptions, necess ary to state and solve the equations giving access to rCBF The obtained res ults are more or less reliable, depending on whether modeling hypotheses ar e fulfilled by the used indicator. The purpose of this article is to review the various supporting models in the assessment of rCBF with special empha sis on perfusion CT studies at low injection rates and on iodinated contras t material used as an indicator.