Patient organ radiation doses during treatment for aneurysmal subarachnoid hemorrhage.

PURPOSE: The aim of this retrospective study was to estimate risk organ doses and to estimate radiation risks during the imaging work-up and treatment for aneurysmal subarachnoid hemorrhage (SAH). METHODS: The imaging procedures comprised computed tomography and digital subtraction angiography studies for diagnosis or endovascular interventional procedures in 50 consecutive patients. Equivalent organ doses (H(T)) to skin, brain, eye lens, salivary glands, thyroid and oral mucosa were measured using thermoluminescence dosimeters in an anthropomorphic head phantom. Picture archiving and communication system (PACS) and radiological information system (RIS) records were analyzed and the frequency of each imaging procedure was recorded as well as the registered individual kerma-length product (P(KL)) and the kerma-area product (P(KA)). The doses were computed by multiplying the recorded P(KL) and P(KA) values by the conversion coefficients H(T)/P(KL) and H(T)/P(KA) from the head phantom. RESULTS: The mean fluoroscopy time, P(KL) and P(KA) were 38 min, 7269 mGy cm and 286 Gy cm(2), respectively. The estimated mean equivalent doses were as follows: skin 2.51 Sv, brain 0.92 Sv, eye lens 0.43 Sv and salivary glands 0.23 Sv. Maximum organ doses were 2.3-3.5 times higher than the mean. Interventional procedures contributed 66 % to skin dose, 55 % to brain dose and 25 % to eye lens dose. Of the patients with an estimated skin dose exceeding 6 Sv, only 1 developed temporary epilation. CONCLUSION: The risk for radiation-induced cancer for SAH patients is low (2-3 cases per 1,000 patients, of which 90 % are expected to be benign types) compared with the risk of tissue reactions on the head such as skin erythema and epilation (1 temporary epilation per 50 patients).

3D Road-Mapping in the Endovascular Treatment of Cerebral Aneurysms and Arteriovenous Malformations.

SUMMARY: 3D road-mapping with syngo iPilot was used as an additional tool for assessing cerebral aneurysms and arteriovenous malformations (AVMs) for endovascular therapy. This method provides accurate superimposition of a live fluoroscopic image (native or vascular road-map) and its matching 2D projection of the 3D data set, delivering more anatomic information on one additional display. In the endovascular management of cases with complex anatomy, 3D road-mapping provides excellent image quality at the intervention site. This method can potentially reduce intervention time, the number of DSA runs, fluoroscopy time and the amount of contrast media used in a procedure, with reservation for these factors being mainly operator-dependent. 3D road-mapping probably does not provide any advantage in the treatment of cerebral aneurysms or AVMs with very simple configuration, and it should not be used when acquisition of an optimum 3D data set is not feasible.

Endovascular coiling of intracranial aneurysms using bioactive coils: a single-center study.

BACKGROUND: Some degree of recanalization is reported in up to one-third of intracranial aneurysms treated with endovascular coiling. A technical development potentially effective in avoiding recanalization is the Matrix Detachable Coil (MDC), which is covered with a biodegradable polymeric material that enhances intra-aneurysmal clot organization and fibrosis. PURPOSE: To report the initial clinical experience of MDC for endovascular aneurysm coiling in a single-center, single-operator, and well-defined population setting. MATERIAL AND METHODS: 118 aneurysms in 104 patients (73 with subarachnoid hemorrhage, SAH) were embolized with MDC alone (n = 52) or combined with bare platinum coils (n = 66). RESULTS: Initial aneurysm obliteration was class 1 (complete obliteration) in 45 aneurysms (38.1%), class 2 (residual neck) in 44 (37.3%), and class 3 (residual aneurysm) in 29 (24.6%). Procedure-related morbidity was 4.8%, and mortality 0.96%. Clinical follow-up of 61 patients with SAH (mean 5.9 months, range 1-17 months) showed good outcome (Glasgow Outcome Scale, GOS 4-5) in 39 (63.9%), and poor outcome or death (GOS 1-3) in 22 (36.1%). Imaging follow-up of 73 aneurysms (average 6.5 months, range 1-17 months) showed class 1 in 47 (64.4%), class 2 in 18 (24.7%), and class 3 in eight (10.9%). Recanalization occurred in 11 aneurysms (15%), of which four (5.5%) required re-treatment. CONCLUSION: This study confirms that aneurysm coiling with MDC is feasible, effective, and safe.

Preoperative embolization of lower-falx meningiomas with ethylene vinyl alcohol copolymer: technical and anatomical aspects.

PURPOSE: To report the feasibility of using ethylene vinyl alcohol copolymer (EVAC) for embolization of lower-falx meningiomas. MATERIAL AND METHODS: Three patients were treated. The procedures were done under general anesthesia. A terminal branch of the middle cerebral artery in the proximity of the tumor was catheterized as near as possible or into the pre-falcine arterial anastomotic network around the superior sagittal sinus, and embolization with EVAC was performed with a standard injection technique. RESULTS: This technique resulted in filling of the tumor-supplying dural arteries including all collaterals from both sides, filling of the dural territory of the tumor circulation, and some obliteration of the tumor's pial supply. On later operation, the tumors could be removed from the inside out with minimal brain retraction. CONCLUSION: Effective preoperative embolization of lower-falx meningiomas using EVAC is feasible. This technique has a sound anatomical basis, and it can be used with benefit even in falx meningiomas with predominantly pial vascular supply.

High-resolution carotid artery MRA. Comparison with fast dynamic acquistion and duplex ultrasound scanning.

PURPOSE: To determine whether the diagnostic accuracy of contrast-enhanced MR angiography (CE-MRA) of the carotid arteries is improved by using a slow-injection, high-resolution technique. MATERIAL AND METHODS: In 22 patients suspected to have internal carotid artery (ICA) stenosis at duplex ultrasound scanning (DUS), CE-MRA was performed both with a fast, dynamic (8 s/phase) and with a slower, high-resolution technique (scan time 2:20 min). RESULTS: There was conformity between the CE-MRA techniques regarding the degree of stenosis in 34/40 extracranial ICAs. In 3/6 discrepant cases, short occlusions were seen with the fast dynamic technique, whereas both the high-resolution CE-MRA technique and DUS showed patent vessels. There was an overall tendency toward higher stenosis grading with the dynamic technique. Overlying veins could be removed on a workstation in all high-resolution examinations. CONCLUSION: The high-resolution carotid CE-MRA technique proposed herein seems to improve the diagnostic accuracy, at least for differentiation between high-grade stenoses and occlusions.

Absence of the common carotid artery in a patient with a persistent trigeminal artery variant.

We found the present case when retrospectively reviewing the files of patients with intracranial aneurysm in our institution. It concerns the coexistence of a rare developmental anomaly of the aortic arch vessels and a persistent carotid-vertebrobasilar communication variant. Since no common embryologic basis is known, this association was probably fortuitous. Each of these particular anomalies can pose unique diagnostic and therapeutic difficulties. Rossitti, S. and Raininko, R. (2001). Clinical Radiology56, 79-81.

MR imaging of experimentally induced intracranial hemorrhage in rabbits during the first 6 hours.

PURPOSE: To evaluate the MR appearance of intracranial, especially intraparenchymal, hemorrhage during the first 6 hours after bleeding with various pulse sequences in an animal model. MATERIAL AND METHODS: Intracerebral hematomas and subarachnoid hemorrhage were created by injecting autologous blood in 9 rabbits. MR studies were performed using a 1.5 T scanner with pixel size and slice thickness comparable to those used in clinical practice before blood injection, immediately after injection, and at regular intervals during 6 hours. The images were compared with the hematoma sizes on formalin-fixed brain slices. RESULTS: In every animal, susceptibility-weighted gradient-echo (GRE) pulse sequences depicted the intraparenchymal hematomas and blood escape in the ventricles or subarachnoid space best as areas of sharply defined, strong hypointensity. The findings remained essentially unchanged during follow-up. The sizes corresponded well to the post-mortem findings. Gradient- and spin-echo (GRASE) imaging revealed some hypointensities, but these were smaller and less well defined. Spin-echo (SE) sequences (proton density-, T1- and T2-weighted) as well as a fluid-attenuated inversion recovery turbo spin-echo sequence (fast FLAIR) depicted the hemorrhage sites as mostly isointense to brain. CONCLUSION: Susceptibility-weighted GRE imaging at 1.5 T is highly sensitive to both hyperacute hemorrhage in the brain parenchyma and to subarachnoid and intraventricular hemorrhage.

Shear stress in cerebral arteries carrying saccular aneurysms. A preliminary study.

PURPOSE: To investigate whether the branching geometry determines an underlying increase of shear stress (SS) on the vessel wall in cerebral arteries of patients with aneurysms located distally to the circle of Willis. Increased SS is regarded as a major factor in the etiology of intracranial saccular aneurysm. Aneurysms occur commonly in the Willisian arteries, where the role of hemodynamic forces are evident, but they occur also in more peripheral arteries. MATERIAL AND METHODS: The ratio between SS in the branches and SS in the parent vessel at bifurcations was estimated using exponential relations of vessel caliber. The absolute difference of SS branch ratios in every bifurcation represents the SS gradient at the apex. Cerebral angiograms of 10 patients with aneurysm of the distal anterior cerebral artery were analyzed and compared with normal values from an earlier study. RESULTS: The branching geometry determines a relatively small but significant increase of SS in branches and of SS gradients at bifurcation apices in cerebral arteries of patients with aneurysm. CONCLUSION: The results may reflect increased cerebral vessel tone after subarachnoidal hemorrhage, or alternatively an underlying derangement of the regulation of cerebral arterial caliber and SS in these patients.

Relative dispersion analysis enhances perimetric sensitivity.

Objective identification of minor visual field defects is problematic. A possible solution is to examine spatial correlations by means of relative dispersion analysis, a tool of fractal analysis. We studied patients with glaucoma, previous optic neuritis, chiasmal compression and lesions of the brain hemispheres, using high-pass resolution perimetry. One-hundred visual field records were drawn consecutively for each category and ranked according to severity of defects. Records with scores ranking below the 35th percentile, i.e. those with the smallest field defects, were analysed. Relative dispersion analysis recognized 1.3-2.4 times more abnormal subjects than did pattern standard deviation. A previously described form index was intermediate in sensitivity. Specificity was 96%. Relative dispersion analysis appears to capture a novel aspect of visual field abnormality, with good sensitivity and specificity. The analysis is easily performed.

[Changes in pulsatility of the middle cerebral artery during the hyperemic phase after carotid compression. Studies with simultaneous bilateral transcranial Doppler]. / Pulsatilitätsänderungen der Arteria cerebri media während der hyperämischen Phase nach Karotiskompression. Untersuchungen mittels simultaner bilateraler TCD.

AIM: The aim of the present study was to investigate the hypothesis that the transient hyperaemic response (THR), i.e. the TCD measured increase in MCA blood flow velocity, indicate an intact cerebral autoregulation. METHOD: THR tests were performed repeatedly in 6 healthy volunteers during simultaneous bilateral TCD recording of the MCA Doppler spectrum. The changes in the pulsatility index (PI) and the pulsatility transmission index (PTI) during the THR were compared with their baseline values. RESULTS: THR was observed in all subjects on each side. PTI of the MCA decreased during the THR. PI did not change on the side of carotid compression, but increased in the contralateral MCA. CONCLUSION: The results suggest that the cerebrovascular resistance is decreased during the THR and that the THR indicates a functioning cerebral autoregulation. While PI is strongly influenced by upstream haemodynamic forces, PTI seems to be an indicator of cerebrovascular resistance downstream to the sample volume.

Energetic and spatial constraints of arterial networks.

The principle of minimum work (PMW) is a parametric optimization model for the growth and adaptation of arterial trees. A balance between energy dissipation due to frictional resistance of laminar flow (shear stress) and the minimum volume of the blood and vessel wall tissue is achieved when the vessel radii are adjusted to the cube root of the volumetric flow. The PMW is known to apply over several magnitudes of vessel calibers, and in many different organs, including the brain, in humans and in animals. Animal studies suggest that blood flow in arteries is approximately proportional to the cube of the vessel radius, and that arteries alter their caliber in response to sustained changes of blood flow according to PMW. Remodelling of the retinal arteriolar network to long-term changes in blood flow was observed in humans. Remodelling of whole arterial networks occurs in the form of increase or diminishing of vessel calibers. Shear stress induced endothelial mediation seems to be the regulating mechanism for the maintenance of this optimum blood flow/vessel diameter relation. Arterial trees are also expected to be nearly space filing. The vascular system is constructed in such a way that, while blood vessels occupy only a small percentage of the body volume leaving the bulk to tissue, they also crisscross organs so tightly that every point in the tissue lies on the boundary between an artery and a vein. This review describes how the energetic optimum principle for least energy cost for blood flow is also compatible with the spatial constraints of arterial networks according to concepts derived from fractal geometry.

Regulation of vascular tone.

The intimal surface of the blood vessel in vivo is subject to shear stress resulting from blood flow, which in most of the circulation, at least at rest, is laminar. Turbulence can occur at bifurcations, especially those of the large arteries, and where vessels curve significantly. Shear stress is a frictional tangential force exerted at the fluid-intimal interface in the long axis of the vessel. It is now known that hemodynamic shear stress can influence a large variety of biological processes in endothelial cells, which vary from those with a short response time, just a few milliseconds, such as the opening of ion channels, to those that change over a period of minutes to several hours, for example, endocytosis and cytoskeleton rearrangement, and those features that alter much more slowly, such as cell shape and stiffness. In addition to these types of changes, there are suggestions that flow acting through shear stress may be responsible for several basic attributes of the vasculature, including the relative size and diameter of the components of a branching vascular system. In this symposium on the flow regulation of the blood vessel, the first presentation dealt with optimality principles that appear to govern the dimensions of the vasculature, in particular the geometry of the arterial branching and the role of shear stress. An optimally designed system is one that requires the least metabolic work to perform its function.(ABSTRACT TRUNCATED AT 250 WORDS)

Shear stress in cerebral arteries supplying arteriovenous malformations.

Arteries supplying cerebral arteriovenous malformations (AVMs) are known to dilate with time. These changes are reversible, and the feeders have been shown to slowly decrease in calibre after removal of the AMV. There is evidence that arteries alter their internal diameters in response to sustained changes of blood flow so that shear stress is kept constant. This implies that blood flow-induced shear stress might be the driving force for remodelling of the cerebral vascular network in the presence of an AVM, and for reversion of these changes after radical operation. The objective of this study is to examine the hypothesis that the shear stress in cerebral arteries supplying AMVs is of the same magnitude as in arteries supplying normal brain tissue in spite of larger blood flow rate. Fifteen patients with supratentorial cerebral AVMs admitted for endovascular treatment were examined with transcranial Doppler ultrasound in the distal Willisian vessels. Vessel calibres were measured in angiograms with magnification correction. Shear stress was estimated assuming a constant value for blood viscosity. Corresponding arteries in the cerebral hemisphere with AVM and in the contralateral one were compared in pairs. Thirty-four pairs of homonymous arteries were studied. The arteries on the AVM side presented larger calibres, higher axial blood flow velocities, lower pulsatility index and larger blood flow rates than the contralateral side. There was a clear positive correlation between blood flow velocities and vessel calibres. The estimates of shear stress did not differ significantly in corresponding arteries of both hemispheres (p = 0.18). The results indicate a precise adjustment of cerebral arterial calibre and blood flow-induced shear stress that presumably induces the progressive dilation of AVM feeders, and the slow regression of the vessel calibres to average dimensions after removal of the lesion. Each vessel seems to remodel itself in response to long-term changes in blood flow rate so that the vessel calibre is reshaped to maintain a constant level of wall shear stress.