Quantitative Spectroscopic Analysis of Ischemic Stroke

The ischaemic area (cerebral blood flow <30% of the normal value and Tmax >6 s) was automatically measured using F-STROKE perfusion software. As the obtained examination data were transferred to a dedicated workstation (spectral diagnostic suite [SPD]; Philips Healthcare), effective atomic number (Zeff) maps, iodine density maps, and iodine–no-water maps were obtained in real time in a post-processing workstation.
The Zeff characterizes the measured attenuation energy sensitivity of an unknown compound in terms of a resultant atomic number, which was estimated by the monochromatic attenuation ratio method since the monochromatic attenuation ratio is a monotonic as a function of effective atomic number (17 (link), 18 (link)).
First, the brain perfusion defect area was identified according to the color difference on the fusion map of the iodine density map and effective atomic number. Then, referring to the results of F-STROKE software, the largest layer of the abnormal perfusion area was selected, and the ROI of the perfusion defect area and contralateral mirror brain area was manually drawn. We selected the core infarct area as the ROI and measured it manually three times to get the average value (Figures 2–4). The selection of ROI should avoid blood vessels and calcification as much as possible and then switch to the effective atomic number map, iodine density map and anhydrous iodine map. We measured and recorded the values of the spectroscopic quantitative parameters (effective atomic number [Zeff value], iodine identity value, and iodine-no water value) in the ischaemic area and comparative normal area. All measurements were performed independently by 2 radiologists who had more than 6 years of experience in neural imaging diagnosis. They were blinded to the spectral data measurements on the corresponding values of the spectroscopic quantitative parameters.