Dual-energy CT, Perfusion CT, Diffusion Weighted Imaging References

The primary goals in acute stroke imaging are to identify distinguish intracranial hemorrhage (ICH) from infarction and to select patients most likely to benefit from thrombolytic therapy. Currently, the gold standard for identification of ICH is non-contrast CT; however, its predictive power for subsequent tissue infarction is limited. Because the administration of thrombolytic agents can lead to hemorrhagic complications and possibly death, it is of utmost importance to find the biomarkers, or combination of biomarkers, that can optimally distinguish cerebral parenchyma that has already become infarcted (infarct core) and cerebral parenchyma likely to undergo infarction (penumbra). Computed tomography (CT) and magnetic resonance (MR)-based imaging methods have become crucial in providing such biomarkers to distinguish infarct core from penumbral tissue. The current gold standard for the identification of the infarct core in acute stroke imaging is diffusion-weighted imaging (DWI). While DWI can be a powerful diagnostic tool, its use in the acute stroke setting has been hindered by limited availability and technical and safety concerns. Perfusion CT is the most practical choice for acute stroke imaging because of its wide availability and rapid scanning capability. While perfusion CT offers strong diagnostic value, there is still debate with regard to its ability to identify the infarct core, in part due to systematic differences in acquisition techniques and postprocessing algorithms between CT manufacturers. Background on dual-energy CT: Since the invention of CT in the 1970’s, the use of CT measurements at multiple energies has been proposed to better differentiate materials in the body. This concept is based on the observation that when x-ray photons of the diagnostic energy range interact with materials of the body, two main interactions can occur: (1) photoelectric absorption and (2) Compton scattering. Because two main interactions can occur, one CT measurement is insufficient to distinguish the photoelectric signature of a tissue from the Compton signature of the same tissue, just as two equations are needed to solve for two unknown variables. Therefore, dual-energy CT has the ability to better differentiate materials in the body, such as calcium versus iodine, or contrast enhancement versus inherent underlying tissue properties.