Application Of Perfusion Computed Tomography In Cerebral Vasospasm After Aneurysmal Subarachnoid Hemorrhage

Cerebral vasospasm(CVS) is a common complication in the early clinical course after subarachnoid hemorrhage(SAH). As one of the devastating neurological disorders, the overall outcome in patients with aneurysmal (SAH) is still poor. CVS can be divided into early and late onset according to its occurrence time. The former is more common in SAH after 0.5h-3d, often mitigate in 4h, which is also called acute cerebral vasospasm. The latter was also known as delayed cerebral vasospasm (DCV), 4-15d after hemorrhage, peak at 7～10d, relieve at 2～4 weeks, some part can develop into cerebral infarction. At present, there is no clinical approach to judge and evaluate the delayed cerebral infarction risk. The golden standard of anatomic demonstration of aneurysm and cerebral vasospasm is digital subtraction angiography (DSA), which provides an accurate depiction of the intracranial vessels. However, it is an invasive procedure with complication, major in the intervention. Multisection CT angiography (MSCTA) has recently emerged as a reliable and accurate method for the rapid diagnosis and monitoring of cerebral vasospasm. But both DSA and MSCTA are difficult to access the cerebral ischemia secondary to cerebral vasospasm accurately and objectively.Perfusion is the process that the oxygen and nutrients are carried through the capillary network to the tissue cells, reflect hemodynamic status and functions of the organs and tissues. CT perfusion imaging refers to dynamic or continuous scanning the selected level after the intravenous bolus injection of contrast medium, to obtain the time-density curve (TDC) of each pixel within the slice, then evaluate the perfusion status of tissues and organs according to the hemodynamic parameters calculated using different mathematical models of the curve. Perfusion imaging can reflect the blood perfusion volume changes of organs and tissues, which has became a hot and widely used method to study the kinetics of tissues and organs. Therefore, CT perfusion imaging is expected to reflect a series of secondary pathology, physiological changes caused by the cerebral vasospasm after SAH.The first DSCT came into use at November,2005. It not only optimized the conventional perfusion, but also put forward a new model of global cerebral perfusion, accompany with two parameters PBV and PWM, expected to reflect cerebral ischemia secondary to SAH. There is not relevant report at home and abroad currently, therefore, further exploration is needed. In the subject, we intended to evaluate the importance of vasospasm after SAH and the secondary cerebral ischemic changes through dual-source CT whole-brain and routine perfusion.Materials and Methods1. PatientsDuring the period from June 2008 to October 2009,58 consecutive patients (23 men and 35 women) aged 37-75 years (median age 53.2 years) were recruited in First hospital of China Medical University, diagnosed with aneurysmal subarachnoid hemorrhage. All together,13 patients underwent routine CT perfusion,16 underwent whole-brain CT perfusion and 29 underwent both. There were 23 patients with dizziness in control group, aged 22-56 years (median age 43.9 years), underwent CT angiography, routine or whole-brain CT perfusion.5 underwent both routine and whole-brain CT perfusion. And all the imaging results were normal.2. Imaging Protocols(1) Routine CT perfusion was performed using DSCT (SOMATOM Definition, Siemens Medical Solutions, Germany). The scanning protocol was Specials/Neuro PCT. The target perfusion slice was performed after the whole-brain plain CT scan.30 ml of contrast agent was injected by intravenously ulnar vein at a flow rate of 4 ml/s followed by 30 ml of saline flush. The scan plane was performed at the level of basal ganglia and the above with 8s delayed, range 28.8mm for 40s.(2) Whole-brain CT perfusion was performed using 64-row DSCT (SOMATOM Definition, Siemens Medical Solutions, Germany). The scanning protocol was Specials/Neuro PBV. After the whole-brain plain CT scan according to section thickness,1.0mm and reconstruction interval,0.7mm,50 ml of nonionic contrast agent was injected by ulnar vein at a flow rate of 4 ml/s followed by 50 ml of saline flush. The whole perfusion was triggered by contrast agent tracer technique. The other parameters were the same as the routine.3. Imaging Process and Analysis(1) Routine CT perfusion:The data was analyzed using Siemens post-processing workstation for rebuild normal perfusion images,6-8 regions of interest (ROI) were set for calculatoion. All the regions of interest measured on the mean perfusion parameters of all the ROIs was considered as brain perfusion value of the case, comparing the perfusion difference among the delayed infarction group, no delayed infarction group and the control group, the reference criterion of cerebral ischemia was regarded as the perfusion parameters for significant differences, in accordance with the normal distribution through the 95% confidence in each group. And then two radiologists diagnosis the 42 cases of patients with SAH through CT perfusion parameter maps and CT plain images. The detection rate of cerebral ischemia of CT perfusion imaging and plain scan was compared, the the perfusion values were compared between low perfusion area and the contralateral corresponding parts.(2) Whole-brain CT perfusion:The data was analyzed using Syngo MMWP post-processing workstation for rebuild whole-brain PBV, PWM and CTA images, to calculate all the ROI s and mean perfusion value on the PBV and PWM images. The perfusion differences of brain lobe was compared between the SAH group and the control group, the dead and survival cases, for the correlation between predominant hemorrhage and low perfusion area. The PBV, PWM differences were compared among the control group, no delayed infarction group and the delayed infarction group. The reference criterion was regarded as the perfusion parameters for significant differences, in accordance with the normal distribution through the 95% confidence in each group.4. Statistical AnalysisThe statistic software SPSS 13.0 (SPSS, Chicago, IL, USA) was used. A result was considered significant if the P value was less than 0.05.Results1. The limited ischemic lesions secondary to aneurysmal SAH on routine CT perfusion imaging are detected with a higher rate than that on CT plain scan. There is significant difference, P<0.05.2. For CBF, significant difference was accepted among the delayed infarction group, no delayed infarction group and the control group. For PEP, there was significant difference between the control group and the delayed infarction group, no delayed infarction group, meanwhile, no significant difference between the delayed infarction group and no delayed infarction group. For MIP and AP, there were significant difference between the delayed infarction group and the control group. For TTS and TPP, there were significant difference between the delayed infarction group and the control group, no delayed infarction group, not significant between the latter two groups.3. For PBV, there was a significant difference among the delayed infarction group, no delayed infarction group and the control group, P<0.05(F=103.665). For PWM, there was a significant difference between no delayed infarction group and the control group, no significance between the other groups.4. There was significant difference on the detection of local ischemia among PBV, PWM and CT plain scan, PBV>PWM>CT plain scan.5. PBV of patient lobes is lower than that in control group, with a significant difference, P<0.05.6. PBV in dead cases is lower than that in survival cases, but there is significant difference only in the parietal lobe, P<0.05(t=2.474).7. There may be association between predominant side of subarachnoid hemorrhage and low perfusion area, P<0.05.Conclusion1. Routine CT perfusion imaging can reflect the cerebral hemodynamic changes after subarachnoid hemorrhage, and sensitive to the detection of ischemic lesions secondary to SAH. It also can evaluate whether there is cerebral perfusion reduction, the possibility of delayed cerebral infarction or not. CBF<25ml/min/100ml can be regarded as evaluation criteria of low cerebral perfusion. MIP>47HU or AP>34HU can be used as the evaluation criteria of impossible delayed cerebral infarction.2. Whole-brain perfusion CT can reflect the cerebral hemodynamic changes after SAH, cerebral perfusion reduced after SAH. PBV is not only sensitive in the detection of ischemic lesions secondary to SAH, but also possiblely assess the delay cerebral infarction and low perfusion. PBV< 10ml/1 can be used as delayed cerebral infarction criteria in high-risk, PBV< 14 ml/1 can be used as a standard reduction of low cerebral perfusion, has important clinical value.