Neurovascular Imaging Of Stroke

BackgroundIntracranial aneurysms are common lesions with a reported prevalence of 1%-5% in the adult population. Rupture of an intracranial aneurysm represents the most common etiology of nontraumatic subarachnoid hemorrhage (SAH). Digital subtraction angiography (DSA) is the current method of choice for the detection and characterization of intracranial aneurysms. However, it is an invasive technique that was associated a significant 0.5% risk of permanent neurological complications. Computed tomographic angiography (CTA) is a noninvasive imaging modality that has increasingly been used for evaluation of suspected intracranial aneurysms. In previous reports, the diagnostic performance of multidetector CTA for the detection of intracranial aneurysms has been compared favorably with that of DSA. Recently, the introduction of 64-section spiral CT scanners has greatly advanced the role of CTA in the neurovascular imaging. 64-section spiral CT offers rapid acquisition of isotropic data sets which allows image reconstruction in arbitrarily chosen planes without loss of spatial resolution. In addition to the increased spatial resolution, various postprocessing techniques may also help improve the diagnostic accuracy of 64-section CTA in detection of intracranial aneurysms.ObjectivesThe purpose of our study was to investigate the diagnostic performance of 64-section CT angiography in detection and characterization of intracranial aneurysms and to assess whether 64-section CTA would triage patients between surgical clipping and endovascular coiling.Materials and MethodsPatientsPatients who underwent 64-section CTA for suspected intracranial aneurysms at our institution were included into our study. All patients were scheduled to have CTA and DSA examination on the basis of clinical findings, including signs and symptoms suggestive of aneurysm, presentation of SAH confirmed by nonenhanced CT scan or xanthochromia at lumbar puncture. Patients were considered eligible if they had undergone both CTA and DSA examinations for nontraumatic SAH. Patients with history of prior clipping or endovascular coiling of aneurysms were excluded from our study. In our present study, 108 patients (62 men and 46 women; average age, 49 years; age range 19-72 years) were enrolled into our study.Imaging protocolAll CTA studies were performed using a 64-section multidetector CT scanner (Lightspeed VCT; GE Medical Systems, Milwaukee, WI). All patients'heads were fixed during the CT scan to prevent motion artifacts. Test bolus injection was employed to assess the individual circulation time and individualize the timing of contrast material injection. To determine the scan delay, a test bolus of 20 mL Iopromide was given at a rate of 4ml/s. Parameters for the CTA acquisition included a pitch of 0.531, section thickness of 0.5mm with 0.5mm increment, 0.6-mm section collimation, 0.625-mm reconstruction interval, a matrix of 512×512, a 180-240mm field of view, 120 kV, and 300mA. The scanning coverage extended from the bottom of the anterior arch of the first cervical vertebra to the cranial vault. After a starting point was set, 80mL contrast material was intravenously injected through a 18- or 22-gauge needle via antecubital vein by using a power injector at a rate of 4ml/s. All acquired CTA data were transferred to a workstationfor postprocessing. DSA was performed transfemorally by using a a biplane DSA unit. DSA was performed with bilateral selective internal carotid artery injections and either unilateral or bilateral vertebral artery injections, as necessary. Anteroposterior, lateral and oblique projections were routinely obtained to clarify aneurysm anatomy. Additional angiographic views were acquired at the discretion of the neuroradiologists who performed the DSA procedure. Image InterpretationDSA images were evaluated by the interventional neuroradiologist who performed the examination. The CT angiograms were reviewed retrospectively by two reviewers in a blinded manner. The readers had to evaluate the size, shape, location of an aneurysm as well as its relationship with the parent artery and adjacent structures. The image quality of CTA was rated as excellent, good, moderate and poor for visualization of intracranial aneurysms.ResultsThere were no complications or technical failures during CTA and DSA examinations. The image quality of CT angiograms was rated excellent in 107(99.1%) of 108 patients. One CT angiogram was rated moderate by both readers due to the artifacts produced by severe head motion during the scanning process. However, the artifact did not interfere with interpretation of the causative aneurysm.In our study, the combination of DSA and surgical findings were used as the reference standard to determine the accuracy of CTA for detection of aneurysms. According to the reference standard, 107 aneurysms were present in 96 patients. No aneurysm was identified in 12 patients. Of the 96 patients, 10 had multiple aneurysms. Nine patients had 2 aneurysms each and one patient had 3 aneurysms. The aneurysms were located at the anterior communicating artery (n= 34), the posterior communicating artery (n=38), the middle cerebral artery (n=14), the internal carotid artery (n=15), the anterior cerebral artery (n=5) and the vertebrobasilar artery (n=2). Of the 107 aneurysms in our study, CTA prospectively detected 106 aneurysms in 96 patients. In interpretation of CTA images, reader 1 correctly identified 105 aneurysms, and reader 2 correctly identified 106 aneurysms.Sensitivity, specificity, positive and negative predictive values were calculated according to the size of the aneurysm. For aneurysms < 3mm, sensitivity was 93.7% for reader 1 and 96.8% for reader 2. However, the sensitivity and specificity were both 100% for aneurysms > 3mm. The diagnostic performance of 64-section CTA was also calculated on a per-aneurysm and per-patient basis for both readers. On a per-aneurysm basis, the sensitivity and specificity of CTA were 98% and 100% for reader 1, 99% and 100% for reader 2. However, the overall sensitivity and specificity were 100% on a per-patient basis.Conclusion64-section multidetector CT facilitates the coupling of image acquisition with peak vascular enhancement, which may provide isotropic data with spatial resolution comparable to those of DSA.The diagnostic performance of 64-section multidetector CTA was equal to DSA in detection and surgical planning of suspected intracranial aneurysms.In most cases, 64-section multidetector CTA could supplement DSA as the primary method of choice in the diagnostic workup of patients with subarachnoid hemorrhage. BackgroundRupture of a cerebral aneurysm is the most common cause of subarachnoid hemorrhage. Patients with ruptured cerebral aneurysm should be evaluated and treated on an emergency basis to prevent subsequent medical and neurological complications. Digital subtraction angiography (DSA) has long been considered the gold standard in detection of intracranial aneurysms. However, DSA false-negative aneurysms have been reported in the literature. CT angiography (CTA) is a fast, noninvasive imaging method that has been widely used in the diagnostic work-up of patients with subarachnoid hemorrhage. In previous studies, it is reported that the diagnostic performance of CTA is approaching that of DSA for detection and treatment planning of aneurysms. It is well established that 3D rotational angiography may depict more aneurysm than DSA. Now 3D rotational angiography has been accepted as the new gold standard imaging method for detection of intracranial aneurysms. In previous studies, most authors used DSA as the gold standard against which the diagnostic accuracy of CTA was compared. Therefore, the diagnostic performance of 64-section CTA may be overestimated in previous reports. ObjectivesTo assess the diagnostic performance of 64-section CT angiography (CTA) for detection of cerebral aneurysms by comparison with the new gold standard 3D rotational angiography.Materials and MethodsA total of thirty-six patients who underwent both 64-section CT angiography and 3D rotational angiography for suspected intracranial aneurysms were retrospectively analyzed. The CTA images were reformatted as 3D volume rendered and maximun intensity projection angiograms for further review. The location, size and shape of the aneurysm were assessed and compared with 3D rotational angiography results. The sensitivity, specificity, positive and negative predictive values of 64-section CTA were calculated by using 3D rotational angiography as reference standard.ResultsAll patients have successfully completed both CTA and 3D DSA examinations. There were no technical failures or procedure related neurological complications. All the angiograms were diagnostic. In 28 of 36 patients, a total of 43 aneurysms were detected on 3D rotational angiography. No aneurysm was detected in 8 patients. Of these 43 aneurysms, 64-section CTA detected 41 aneurysms in 28 patients. On a per-patient basis, the sensitivity, specificity, positive and negative predictive values were 100%. On a per-aneurysm basis, the sensitivity, specificity, positive and negative predictive values were 95%, 100%, 100% and 80%, respectively. For aneurysms >3mm, the sensitivity, specificity, positive and negative predictive values were 100%. For aneurysms <3mm, the sensitivity, specificity, positive and negative predictive values were 84.6%,100 %,100 % and 80%, respectively.ConclusionCompared with the new gold standard 3D rotational angiography, 64-section CTA offers high sensitivity and specificity for detection of intracranial aneurysms. It could be readily used as an screening imaging method for detection of intracranial aneurysms. ObjectivesThe circle of Willis is a major collateral circulation that plays an important role in various ischemic events. The purpose of our study was to investigate the collateral circulation in a Chinese population with 64-section multidetector CT angiography (CTA).Materials and MethodsA total of 170 subjects (86 men, 84 women, mean age, 46 years) who underwent 64-section CT angiography at our institution were included in our study. All the angiograms were retrospectively reviewed for evaluation of the circle of Willis configurations. Subjects were included into our study if they had successfully completed the 64-section CT angiography examination and the angiograms were diagnostic for delineation of Circle of Willis. Subjects were excluded from our study if they had disabling neurological signs or detected brain abnormalities detected at unenhanced CT scan or CT angiograms. All subjects underwent 3D cranial CTA with a 64-section multidetector CT scanner (Lightspeed VCT; GE Medical Systems, Milwaukee, WI). Before CTA examination, patients'heads were comfortably fixed by a head holder to prevent motion artifacts. Image postprocessing was performed at a workstation (Advantage for Windows, GE Medical Systems). After successful acquisition of CTA datasets, the source images were reformatted as 3D volume rendering (VR) and maximum intensity projection (MIP) angiograms. The circle of Willis configuration was assessed based on source images as well as 3D VR and MIP angiograms. Two observers, who were blinded to each other's assessments, independently reviewed the CT angiograms at the circle of Willis.All component vessels at the circle of Willis were assessed in each individual. In interpretation of the CT angiograms, the observers had to assess the presence or absence of each arterial segment in the circle of Willis. Arterial segments that were larger than 1mm were considered to be normal. Arterial segments that were less than 1mm were judged to be hypoplastic. In evaluation of the posterior part of the circle of Willis, the P1 segment was assessed in relation to the ipsilateral posterior communicating artery. The posterior collaterals were classified as one of three variants: an adult configuration, a transitional configuration and a fetal configuration. Vessels arising from the internal carotid artery that had diameters larger than P1 and continued as posterior cerebral arteries were regarded as fetal type posterior cerebral artery. The transitional configuration was defined as a variant in which the diameters of posterior communicating artery and the P1 segment were the same. In the adult configuration, the posterior communicating artery was smaller than the ipsilateral P1.ResultsAll subjects have undergone 64-row CTA examination in our institution. There were no technical failures or complications. Of the 170 subjects who underwent CTA examination, 7 were excluded. Another 3 subjects were excluded from the final analysis because assessment of some arterial segments at the circle of Willis was obscured by motion artifacts. Consequently, 160 subjects (82 men, 78 women, mean age, 46 years) were included in the final analysis.Anterior circle of Willis was complete in 126 (79%) of 160 subjects. Of the 126 subjects with complete anterior collaterals, normal configuration was seen in 122 subjects. In 4 subjects, two anterior communicating arteries were observed. Of these 34 subjects, anterior communicating artery was invisible in 15 subjects. The remaining 19 subjects had A1 hypoplasia or aplasia. There were no statistically significant sex-related differences in the anterior part of the circle.The most common type of posterior variations was types E, in which bilateral posterior communicating arteries were absent. Of the 50 subjects with complete posterior circles, an adult configuration was observed in 28 subjects, a very rare transitional variant was observed in 7 cases, a fetal type posterior circle of Willis (FTP) was seen in 15 subjects. In the combined analysis, entirely complete circle of Willis was seen in 43(27%) of 160 subjects. Incomplete anterior and posterior circle of Willis was found in 28 (17%) of 160 subjects. The remaining 89 (56%) subjects had partially complete circle of Willis configuration.ConclusionIn summary, this is the first study to investigate cerebral collateral circulation in a Chinese population with multidetector CTA. A significantly higher prevalence of compromised posterior collaterals (31%) was observed in a general Chinese population. The anatomical variations of cerebral collaterals reported here may contribute to our understanding of collaterals as well as various underlying mechanisms of cerebrovascular diseases.