Background and Purpose-Besides the delineation of hypoperfused brain tissue, the characterization of ischemia with respect to severity is of major clinical relevance, because the degree of hypoperfusion is the most critical factor in determining whether an ischemic lesion becomes an infarct or represents viable brain tissue. CT perfusion imaging yields a set of perfusion related parameters which might be useful to describe the hemodynamic status of the ischemic brain. Our objective was to determine whether measurements of the relative cerebral blood flow (rCBF), relative cerebral blood volume (rCBV), and relative time to peak (rTP) can be used to differentiate areas undergoing infarction from reversible ischemic tissue. Methods-In 34 patients with acute hemispheric ischemic stroke Ͻ6 hours after onset, perfusion CT was used to calculate rCBF, rCBV, and rTP values from areas of ischemic cortical and subcortical gray matter. Results were obtained separately from areas of infarction and noninfarction, according to the findings on follow-up imaging studies. The efficiency of each parameter to predict tissue outcome was tested. Results-There was a significant difference between infarct and peri-infarct tissue for both rCBF and rCBV but not for rTP.Threshold values of 0.48 and 0.60 for rCBF and rCBV, respectively, were found to discriminate best between areas of infarction and noninfarction, with the efficiency of the rCBV being slightly superior to that of rCBF. The prediction of tissue outcome could not be increased by using a combination of various perfusion parameters. Conclusions-The assessment of cerebral ischemia by means of perfusion parameters derived from perfusion CT provides valuable information to predict tissue outcome. Quantitative analyses of the severity of ischemic lesions should be implemented into the diagnostic management of stroke patients.
Purpose Recent developments in medical technology have broadened the spectrum of X-ray procedures and changed exposure practice in X-ray facilities. For this reason, diagnostic reference levels (DRLs) for diagnostic and interventional X-ray procedures were updated in 2016 and 2018, respectively. It is the aim of this paper to present the procedure for the update of the DRLs and to give advice on their practical application.
Materials and Methods For the determination of DRLs, data from different independent sources that collect dose-relevant data from different facilities in Germany were considered. Seven different weight intervals were specified for classifying pediatric X-ray procedures. For each X-ray procedure considered, the 25th, 50th, and 75th percentile of the respective national distribution of the dose-relevant parameters were determined. Additionally, effective doses that correspond to the DRLs were estimated.
Results In procedures with already existing DRLs before 2016, the values were lowered by circa 20 % on average. Numerous DRLs were established for the first time (9 for interventional procedures, 10 for CT examinations).
Conclusion For dose optimizations even below the new national DRLs, the BfS recommends establishing local reference levels, using dose management software (particularly in CT and interventional radiology), adapting dose-relevant parameters of X-ray protocols to the individual patient size, and establishing internal radiation protection teams responsible for optimizing X-ray procedures in clinical practice. When applying good medical practice and using modern equipment, the median dose values of the nationwide dose distributions can not only be easily achieved but can even be undercut.
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