[2] With the ability to ascertain data on the blood flow to vital organs such as the heart and the brain, doctors are able to make quicker and more accurate choices on treatment for patients.
[4] The method by which perfusion to an organ measured by CT is still a relatively new concept, although the first dynamic imaging studies of cerebral perfusion were reported on in 1979 by E. Ralph Heinz et al. from the Duke University Medical Center, Durham, North Carolina,[5] itself citing a reference on a presentation on "Dynamic Computed Tomography" at the XI.
[6] The original framework and principles for CT perfusion analysis were concretely laid out in 1980 by Leon Axel at University of California San Francisco.
[7] It is most commonly carried out for neuroimaging using dynamic sequential scanning of a pre-selected region of the brain during the injection of a bolus of iodinated contrast material as it travels through the vasculature.
Various mathematical models can then be used to process the raw temporal data to ascertain quantitative information such as rate of cerebral blood flow (CBF) following an ischemic stroke or aneurysmal subarachnoid hemorrhage.
Practical CT perfusion as performed on modern CT scanners was first described by Ken Miles, Mike Hayball and Adrian Dixon from Cambridge UK [8] and subsequently developed by many individuals including Matthias Koenig and Ernst Klotz in Germany,[9] and later by Max Wintermark in Switzerland and Ting-Yim Lee in Ontario, Canada.
As Gadolinium passes through the tissues, it induces a reduction of T2* in the nearby water protons; the corresponding decrease in signal intensity observed depends on the local Gd concentration, which may be considered a proxy for perfusion.
Modelling of DCE-MRI yields parameters related to vascular permeability and extravasation transfer rate (see main article on perfusion MRI).
A number of ASL schemes are possible, the simplest being flow alternating inversion recovery (FAIR) which requires two acquisitions of identical parameters with the exception of the out-of-slice saturation; the difference in the two images is theoretically only from inflowing spins, and may be considered a 'perfusion map'.
SPECT imaging performed after stress reveals the distribution of the radiopharmaceutical, and therefore the relative blood flow to the different regions of the myocardium.
MPI has been demonstrated to have an overall accuracy of about 83% (sensitivity: 85%; specificity: 72%),[13] and is comparable (or better) than other non-invasive tests for ischemic heart disease, including stress echocardiography.
The reason for this is that 99mTc is extracted from relatively simple technetium-99m generators which are delivered to hospitals and scanning centers weekly, to supply fresh radioisotope, whereas FDG PET relies on FDG which must be made in an expensive medical cyclotron and "hot-lab" (automated chemistry lab for radiopharmaceutical manufacture), then must be delivered directly to scanning sites, with delivery-fraction for each trip limited by its natural short 110 minute half-life.