Intraoperative evaluation of aneurysmal architecture: comparative study with transluminal images of 3D MR and CT angiograms

BACKGROUND AND PURPOSE: When exposure and visual access in aneurysmal microsurgery are limited, exact intraoperative information must be obtained regarding the whole shape of the aneurysm, property of the aneurysmal wall, vessels hidden behind the aneurysmal sac, and surrounding bony structures of the skull base. We developed a transluminal imaging technique that uses 3D MR and CT angiograms and applied it for intraoperative transparent evaluation of the angioarchitecture of cerebral aneurysms. METHODS: Transluminal images were reconstructed from a perspective volume-rendering algorithm by selecting information on the luminal margin from the whole volume data sets of MR and CT angiograms. The images show the vessel and aneurysmal walls as a series of rings and provide direct visualization of the underlying objects through the spaces between the rings. By connecting a graphic workstation to the operative microscope, data were reconstructed intraoperatively and adjusted to coincide with the operative views by manipulating the projection and visual angle. The aneurysmal angioarchitecture could then be evaluated transparently on the reconstructed transluminal images through the operative approach. RESULTS: Transluminal images provided direct transparent visualization of the aneurysmal architecture, including orifices at the neck, dome, and bleb and the parent arteries though the vessel and aneurysmal walls. The angioarchitecture of the neck complex was evaluated intraoperatively with transluminal 3D MR and CT angiograms through the operative approach before actual aneurysmal neck clipping. CONCLUSIONS: Intraoperative exact evaluation of aneurysmal angioarchitecture with transluminal images would be a feasible and useful adjunct for aneurysmal microsurgery. Merging of data across modalities including 3D MR and CT angiography may improve preoperative or intraoperative evaluation of the angioarchitecture of cerebral aneurysms.     

Transluminal color-coded three-dimensional magnetic resonance angiography for visualization of signal Intensity distribution pattern within an unruptured cerebral aneurysm: preliminarily assessment with anterior communicating artery aneurysms

The natural history of unruptured cerebral aneurysm is not known; also unknown is the potential growth and rupture in any individual aneurysm. The authors have developed transluminal color-coded three-dimensional magnetic resonance angiography (MRA) obtained by a time-of-flight sequence to investigate the interaction between the intra-aneurysmal signal intensity distribution patterns and configuration of unruptured cerebral aneurysms. Transluminal color-coded images were reconstructed from volume data of source magnetic resonance angiography by using a parallel volume-rendering algorithm with transluminal imaging technique. By selecting a numerical threshold range from a signal intensity opacity chart of the three-dimensional volume-rendering dataset several areas of signal intensity were depicted, assigned different colors, and visualized transparently through the walls of parent arteries and an aneurysm. Patterns of signal intensity distribution were analyzed with three operated cases of an unruptured anterior communicating artery aneurysm and compared with the actual configurations observed at microneurosurgery. A little difference in marginal features of an aneurysm was observed; however, transluminal color-coded images visualized the complex signal intensity distribution within an aneurysm in conjunction with aneurysmal geometry. Transluminal color-coded three-dimensional magnetic resonance angiography can thus provide numerical analysis of the interaction between spatial signal intensity distribution patterns and aneurysmal configurations and may offer an alternative and practical method to investigate the patient-specific natural history of individual unruptured cerebral aneurysms.     

Transluminal imaging of three-dimensional CT and MR angiograms for transluminal observation of angioarchitecture of cerebral aneurysms

To investigate the angioarchitecture of cerebral aneurysms, we studied various opacity curves to select specific volume data of CT and MR angiograms from the opacity charts of CT density or MR signal intensity distribution. We developed the method of transluminal imaging of CT and MR angiograms; the vessels and aneurysms were depicted transluminally through spaces between the rings of the vessel walls. Two cases of unruptured cerebral aneurysms were studied by transluminal imaging of three-dimensional CT and MR angiograms. The technical aspects of transluminal imaging and characteristics of volume data, obtained by CT and MR angiograms, were discussed.     

Visualization of aneurysmal contours and perianeurysmal environment with conventional and transparent 3D MR cisternography

We have developed conventional and transparent 3D MR cisternography to investigate the spatial relationship between the contours of aneurysmal complex and the perianeurysmal structures including the cranial nerves, dural fold, cranial base bone, and brain parenchyma. Volume data obtained by a T2-weighted 3D fast spin-echo sequence were reconstructed by using a perspective volume-rendering algorithm with a transluminal imaging technique. 3D MR cisternograms provide useful anatomic information in the therapeutic and follow-up management of unruptured cerebral aneurysms.     

Intraaneurysmal flow: evaluation with Doppler guidewires.

Flow dynamics in cerebral aneurysms were studied with the use of Doppler guidewires in two patients. In both cases it was possible to reach the aneurysmal sac and to assess intraaneurysmal flow. Torquability and flexibility of the new Doppler guidewires permitted continuous assessment of flow velocity and flow pattern at the dome as well as in the neck area. Flow velocities were higher at the neck than within the aneurysmal sac (88 cm/s > 28 cm/s). Because of the limited area of interrogation (sample volume, 5 mm) it was not possible to investigate the complete intraaneurysmal space.     

Time-of-flight MR angiography targeted to coiled intracranial aneurysms is more sensitive to residual flow than is digital subtraction angiography

BACKGROUND AND PURPOSE: For intracranial aneurysms treated with Guglielmi detachable coils, long-term follow-up is mandatory because coil compaction may occur and aneurysms may recur. The purpose of this study was to establish a noninvasive technique to visualize residual flow in coiled aneurysms. METHODS: We designed a 3D time-of-flight (3D-TOF) MR angiography (MRA) technique targeted to depict coiled aneurysms that employed a very short TE (1.54-1.60 ms) and a high spatial resolution (0.3 x 0.3 x 0.3 mm3 with zero-filling) to diminish spin dephasing. To diminish spin saturation, image volume was carefully positioned so that the neck of the targeted aneurysm was within 2 cm of the inflow portion along the stream of blood. Fifty-one MRA images of 39 coiled aneurysms in 39 patients were compared with digital subtraction angiography (DSA) images. DSA and MRA findings were interpolated retrospectively for parent and branch arteries' patency, as well as residual flow in aneurysms. In the latest 11 MR studies, a dark-blood 3D turbo spin-echo sequence was added to MRA to negate the effect high-signal-intensity thrombus. RESULTS: MRA visualized all parent and branch arteries with DSA confirmation. MRA visualized residual flow more frequently (38 studies) than did DSA (25 studies). Residual flow space visualized with MRA was always similar to or larger than that with DSA. The dark-blood sequence completely suppressed intraluminal high signal intensity on MRA images and confirmed that the high signal intensity was not due to thrombus. CONCLUSION: TOF MRA targeted to depict coiled intracranial aneurysms is noninvasive and superior to DSA in visualization of residual flow and, hence, useful for follow-up of coiled aneurysms.     

Contrast-enhanced three-dimensional MR angiography with an elliptical centric view for the evaluation of intracranial aneurysms

The purpose of this study was to assess the feasibility of high spatial resolution, selective arterial phase, 3D contrast-enhanced (CE) MR angiography with first pass bolus, software-trigger, elliptical centric view ordering in the detection of intracranial aneurysms. Our study included nine consecutive patients with ten intracranial aneurysms. 3D TOF MR angiography and 3D CE MR angiography were carried out with a 1.5-T MR scanner. 3D CE MR angiography was performed with an automated bolus detection algorithm and elliptical centric view order using ultrafast SPGR with a spatial resolution of 0.63×0.83×0.5 mm and imaging time of 55 s. Observers detected seven of ten aneurysms on 3D TOF MR angiograms and nine of ten aneurysms on 3D CE MR angiograms. 3D CE MR angiography clearly revealed an IC-PC aneurysm with a relatively smaller neck, a broad-based small aneurysm originating from tortuous and dilated MCA bifurcation, and a residual aneurysm and parent vessels adjacent to metallic aneurysmal clips, which had relatively low signal intensities on 3D TOF MR angiograms. 3D CE MR angiography was found to be a good and promising technique for detecting intracranial aneurysms with small necks and slow flow, vasculature with aneurysmal clips and tortuous vasculature with disturbed flow.     

Identification of the Inflow Zone of Unruptured Cerebral Aneurysms: Comparison of 4D Flow MRI and 3D TOF MRA Data

BACKGROUND AND PURPOSE:The hemodynamics of the inflow zone of cerebral aneurysms may be a key factor in coil compaction and recanalization after endovascular coil embolization. We performed 4D flow MR imaging in conjunction with 3D TOF MRA and compared their ability to identify the inflow zone of unruptured cerebral aneurysms.MATERIALS AND METHODS:This series comprised 50 unruptured saccular cerebral aneurysms in 44 patients. Transluminal color-coded 3D MRA images were created by selecting the signal-intensity ranges on 3D TOF MRA images that corresponded with both the luminal margin and the putative inflow.RESULTS:4D flow MR imaging demonstrated the inflow zone and yielded inflow velocity profiles for all 50 aneurysms. In 18 of 24 lateral-projection aneurysms (75%), the inflow zone was located distally on the aneurysmal neck. The maximum inflow velocity ranged from 285 to 922 mm/s. On 4D flow MR imaging and transluminal color-coded 3D MRA studies, the inflow zone of 32 aneurysms (64%) was at a similar location. In 91% of aneurysms whose neck section plane angle was <30° with respect to the imaging section direction on 3D TOF MRA, depiction of the inflow zone was similar on transluminal color-coded 3D MRA and 4D flow MR images.CONCLUSIONS:4D flow MR imaging can demonstrate the inflow zone and provide inflow velocity profiles. In aneurysms whose angle of the neck-section plane is obtuse vis-a-vis the imaging section on 3D TOF MRA scans, transluminal color-coded 3D MRA may depict the inflow zone reliably.

Although endovascular coil embolization has become a major tactic to address cerebral aneurysms, recanalization or recurrence, which may result in rebleeding, are important problems. Recanalization was reported in 6.1%–39.8% of patients who had undergone endovascular treatment,^1–6 and a meta-analysis found that 20.8% of treated aneurysms recurred.³ The rate of rerupture after endovascular treatment for ruptured aneurysms has ranged from 0.11% to 5.3%,^1,4,6 and the rupture rate in the first year after coil embolization was reported as 2.5%⁷ and 2.2%.⁸ Because hemodynamics acting on the aneurysmal inflow zone may play a key role in the development of coil compaction or recanalization after endovascular coil embolization, the aneurysmal inflow zone must be packed densely to preserve the durability of aneurysm obliteration and to prevent rerupture.^9–15The inflow through the aneurysmal neck into the dome can be seen on 3D TOF MRA images.^13,16,17 Satoh et al,^16,17 who used conventional 3D TOF MRA techniques to select threshold ranges based on the signal intensity of the volume-rendering data, determined the spatial signal-intensity distribution in aneurysms. They developed transluminal color-coded 3D MRA (TC 3D MRA) to improve visualization of the aneurysmal inflow. More recently, 4D flow MR imaging based on time-resolved 3D cine phase-contrast MR imaging techniques was used to evaluate the hemodynamics of cerebral aneurysms.^18–27 However, 4D flow MR imaging requires additional time for data acquisition, and TC 3D MRA may be a convenient alternative to 4D flow MR imaging for identifying the aneurysmal inflow zone.Here, we compared the ability of 4D flow MR imaging and TC 3D MRA to identify the inflow zone of cerebral aneurysms.     

Inflow hemodynamics evaluated by using four-dimensional flow magnetic resonance imaging and the size ratio of unruptured cerebral aneurysms

Purpose

Prediction of the rupture risk is critical for the identification of unruptured cerebral aneurysms (UCAs) eligible for invasive treatments. The size ratio (SR) is a strong morphological predictor for rupture. We investigated the relationship between the inflow hemodynamics evaluated on four-dimensional (4D) flow magnetic resonance (MR) imaging and the SR to identify specific characteristics related to UCA rupture.

Methods

We evaluated the inflow jet patterns and inflow hemodynamic parameters of 70 UCAs on 4D flow MR imaging and compared them among 23 aneurysms with an SR ≧2.1 and 47 aneurysms with an SR ≦2.0. Based on the shape of inflow streamline bundles with a velocity ≧75% of the maximum flow velocity in the parent artery, the inflow jet patterns were classified as concentrated (C), diffuse (D), neck-limited (N), and unvisualized (U).

Results

The incidence of patterns C and N was significantly higher in aneurysms with an SR ≧2.1. The rate of pattern U was significantly higher in aneurysms with an SR ≦2.0. The maximum inflow rate and the inflow rate ratio were significantly higher in aneurysms with an SR ≧2.1.

Conclusions

The SR affected the inflow jet pattern, the maximum inflow rate, and the inflow rate ratio of UCAs. In conjunction with the SR, inflow hemodynamic analysis using 4D flow MR imaging may contribute to the risk stratification for aneurysmal rupture.

     

In vivo visualization and analysis of 3-D hemodynamics in cerebral aneurysms with flow-sensitized 4-D MR imaging at 3 T

INTRODUCTION: Blood-flow patterns and wall shear stress (WSS) are considered to play a major role in the development and rupture of cerebral aneurysms. These hemodynamic aspects have been extensively studied in vitro using geometric realistic aneurysm models. The purpose of this study was to evaluate the feasibility of in vivo flow-sensitized 4-D MR imaging for analysis of intraaneurysmal hemodynamics. METHODS: Five cerebral aneurysms were examined using ECG-gated, flow-sensitized 4-D MR imaging at 3 T in three patients. Postprocessing included quantification of flow velocities, visualization of time-resolved 2-D vector graphs and 3-D particle traces, vortical flow analysis, and estimation of WSS. Flow patterns were analyzed in relation to aneurysm geometry and aspect ratio. RESULTS: Magnitude, spatial and temporal evolution of vortical flow differed markedly among the aneurysms. Particularly unstable vortical flow was demonstrated in a wide-necked parophthalmic ICA aneurysm (high aspect ratio). Relatively stable vortical flow was observed in aneurysms with a lower aspect ratio. Except for a wide-necked cavernous ICA aneurysm (low aspect ratio), WSS was reduced in all aneurysms and showed a high spatial variation. CONCLUSION: In vivo flow-sensitized 4-D MR imaging can be applied to analyze complex patterns of intraaneurysmal flow. Flow patterns, distribution of flow velocities, and WSS seem to be determined by the vascular geometry of the aneurysm. Temporal and spatial averaging effects are drawbacks of the MR-based analysis of flow patterns as well as the estimation of WSS, particularly in small aneurysms. Further studies are needed to establish a direct link between definitive flow patterns and different aneurysm geometries.     

Characterization of cerebral aneurysms for assessing risk of rupture by using patient-specific computational hemodynamics models

BACKGROUND AND PURPOSE: Hemodynamic factors are thought to play an important role in the initiation, growth, and rupture of cerebral aneurysms. This report describes a pilot clinical study of the association between intra-aneurysmal hemodynamic characteristics from computational fluid dynamic models and the rupture of cerebral aneurysms. METHODS: A total of 62 patient-specific models of cerebral aneurysms were constructed from 3D angiography images. Computational fluid dynamics simulations were performed under pulsatile flow conditions measured on a normal subject. The aneurysms were classified into different categories, depending on the complexity and stability of the flow pattern, the location and size of the flow impingement region, and the size of the inflow jet. The 62 models consisted of 25 ruptured and 34 unruptured aneurysms and 3 cases with unknown histories of hemorrhage. The hemodynamic features were analyzed for associations with history of rupture. RESULTS: A large variety of flow patterns was observed: 72% of ruptured aneurysms had complex or unstable flow patterns, 80% had small impingement regions, and 76% had small jet sizes. By contrast, unruptured aneurysms accounted for 73%, 82%, and 75% of aneurysms with simple stable flow patterns, large impingement regions, and large jet sizes, respectively. Aneurysms with small impingement sizes were 6.3 times more likely to have experienced rupture than those with large impingement sizes (P = .01). CONCLUSIONS: Image-based patient-specific numeric models can be constructed in an efficient manner that allows clinical studies of intra-aneurysmal hemodynamics. A simple flow characterization system was proposed, and interesting trends in the association between hemodynamic features and aneurysmal rupture were found. Simple stable patterns, large impingement regions, and jet sizes were more commonly seen with unruptured aneurysms. By contrast, ruptured aneurysms were more likely to have disturbed flow patterns, small impingement regions, and narrow jets.     

Inflow Jet Patterns of Unruptured Cerebral Aneurysms Based on the Flow Velocity in the Parent Artery: Evaluation Using 4D Flow MRI

BACKGROUND AND PURPOSE:Inflow jet characteristics may be related to aneurysmal bleb formation and rupture. We investigated the visualization threshold on the basis of the flow velocity in the parent artery to classify the inflow jet patterns observed on 4D flow MR imaging.MATERIALS AND METHODS:Fifty-seven unruptured aneurysms (24 bifurcation and 33 sidewall aneurysms) were subjected to 4D flow MR imaging to visualize inflow streamline bundles whose velocity exceeded visualization thresholds corresponding to 60%, 75%, and 90% of the maximum flow velocity in the parent artery. The shape of the streamline bundle was determined visually, and the inflow jet patterns were classified as concentrated, diffuse, neck-limited, and unvisualized.RESULTS:At the 75% threshold, bifurcation aneurysms exhibited a concentrated inflow jet pattern at the highest rate. At this threshold, the inflow jets were concentrated in 13 aneurysms (group C, 22.8%), diffuse in 18 (group D, 31.6%), neck-limited in 11 (group N, 19.3%), and unvisualized in 15 (group U, 26.3%). In 16 (28.1%) of the 57 aneurysms, the inflow jet pattern was different at various thresholds. Most inflow parameters, including the maximum inflow velocity and rate, the inflow velocity ratio, and the inflow rate ratio, were significantly higher in groups C and D than in groups N and U.CONCLUSIONS:The inflow jet pattern may depend on the threshold applied to visualize the inflow streamlines on 4D flow MR imaging. For the classification of the inflow jet patterns on 4D flow MR imaging, the 75% threshold may be optimal among the 3 thresholds corresponding to 60%, 75%, and 90% of the maximum flow velocity in the parent artery.

The inflow jets of cerebral aneurysms have been characterized as flow structures composed of strongly directed inflow with higher speeds than in other parts of the aneurysm.^1,2 Computational fluid dynamics analyses by using human cerebral aneurysm models suggested that inflow jets may be related to bleb formation and aneurysmal rupture.^3–5 Cebral et al³ reported that most blebs formed at sites where the inflow jet impacted the aneurysmal wall, and they qualitatively classified the inflow jets of ruptured and unruptured cerebral aneurysms into concentrated and diffuse inflow jets.^3–5 They found that most ruptured aneurysms featured concentrated inflow jets, while diffuse inflow jets tended to be seen in unruptured aneurysms.^4,5 This finding suggests that bleb formation and aneurysm rupture may be attributable to a degenerative change in the aneurysm wall exposed to the increased hemodynamic stress exerted by the inflow jet. Therefore, the assessment of inflow jet patterns and quantitative estimation of the inflow hemodynamics may contribute to a more precise prediction of the risk for bleb formation and aneurysm rupture.Computational fluid dynamics analysis uses human aneurysm models based on a number of assumptions and approximations regarding blood properties, vessel wall compliance, and flow conditions.^3–8 For the quantitative evaluation of the hemodynamics in real human cerebral aneurysms, 4D flow MR imaging, which is based on time-resolved 3D cine phase-contrast MR imaging techniques, has been used.^9–20 In this study, we investigated the visualization threshold on the basis of the flow velocity in the parent artery to classify the inflow jet patterns of unruptured cerebral aneurysms on 4D flow MR imaging. We applied different thresholds to visualize the inflow streamlines, evaluated the inflow jet patterns, and examined the relationship between the inflow jet pattern and the inflow hemodynamics.     

Blood flow imaging through detection of temporal variations in magnetization.

Two hypotheses were tested: (a) that view-to-view variations in bulk phase and modulus of magnetization in vascular volume elements can indicate the presence of disordered blood flow, and (b) that a substantial loss of signal intensity on magnetic resonance (MR) angiograms of poststenotic regions is due to view-to-view changes in magnetization. To test these hypotheses, a technique was developed in which view-to-view variations in transverse magnetization were used to create angiographic projection images, which showed only disordered flow (disordered flow maps) in vitro and in vivo. In phantom studies, this technique recovered signal intensity downstream from stenoses. A combination of disordered flow maps with morphologic images improved visualization of stenotic regions and provided information on characteristics of local flow. These results show that view-to-view variations in transverse magnetization occur in regions of disordered flow and are an important cause of loss of signal intensity. This technique can provide information about dynamic blood flow and improve depiction of anatomic structures on MR angiograms.     

Influence of perianeurysmal environment on the deformation and bleb formation of the unruptured cerebral aneurysm: assessment with fusion imaging of 3D MR cisternography and 3D MR angiography

BACKGROUND AND PURPOSE: Surface irregularity and bleb formation are anatomical factors that are associated with aneurysm rupture. The perianeurysmal environment has been proposed as one factor that may influence aneurysm morphology. We have developed a fusion imaging technique of 3D MR cisternography and angiography that allows clear visualization of an aneurysm and its environment. This technique may prove useful in further understanding of the natural history of intracranial aneurysms. METHODS: Fusion images of 3D MR cisternography and angiography were reconstructed by a perspective volume-rendering algorithm from the volume datasets of MR cisternography, obtained by a T2-weighted 3D fast spin-echo sequence, and coordinated MR angiography, by a 3D time-of-flight sequence. On the fusion images, the anatomic relationship of an aneurysm to the perianeurysmal structures was assessed, and the influence of perianeurysmal environment on the deformation and bleb formation of the aneurysm was investigated. RESULTS: Marked and minor deformation and bleb formation of the aneurysmal dome were found at the areas confronted or adjacent to a certain contact with perianeurysmal structures, including cranial nerves, brain parenchyma, cranial base bones, petroclinoidal dural folds, and dura mater. CONCLUSION: Fusion images of 3D MR cisternography and angiography can depict the contact of an aneurysm with its perianeurysmal environment; this may provide an additional parameter in consideration for the natural history of cerebral aneurysms.     

Comparison of 3D TOF-MRA and 3D CE-MRA at 3 T for imaging of intracranial aneurysms

Purpose

To compare 3 T elliptical-centric CE MRA with 3 T TOF MRA for the detection and characterization of unruptured intracranial aneurysms (UIAs), by using digital subtracted angiography (DSA) as reference.

Materials and methods

Twenty-nine patients (12 male, 17 female; mean age: 62 years) with 41 aneurysms (34 saccular, 7 fusiform; mean diameter: 8.85 mm [range 2.0–26.4 mm]) were evaluated with MRA at 3 T each underwent 3D TOF-MRA examination without contrast and then a 3D contrast-enhanced (CE-MRA) examination with 0.1 mmol/kg bodyweight gadobenate dimeglumine and k-space elliptic mapping (Contrast ENhanced Timing Robust Angiography [CENTRA]). Both TOF and CE-MRA images were used to evaluate morphologic features that impact the risk of rupture and the selection of a treatment. Almost half (20/41) of UIAs were located in the internal carotid artery, 7 in the anterior communicating artery, 9 in the middle cerebral artery and 4 in the vertebro-basilar arterial system.All patients also underwent DSA before or after the MR examination.

Results

The CE-MRA results were in all cases consistent with the DSA dataset. No differences were noted between 3D TOF-MRA and CE-MRA concerning the detection and location of the 41 aneurysms or visualization of the parental artery. Differences were apparent concerning the visualization of morphologic features, especially for large aneurysms (>13 mm). An irregular sac shape was demonstrated for 21 aneurysms on CE-MRA but only 13/21 aneurysms on 3D TOF-MRA. Likewise, CE-MRA permitted visualization of an aneurismal neck and calculation of the sac/neck ratio for all 34 aneurysms with a neck demonstrated at DSA. Conversely, a neck was visible for only 24/34 aneurysms at 3D TOF-MRA. 3D CE-MRA detected 15 aneurysms with branches originating from the sac and/or neck, whereas branches were recognized in only 12/15 aneurysms at 3D TOF-MRA.

Conclusion

For evaluation of intracranial aneurysms at 3 T, 3D CE-MRA is superior to 3D TOF-MRA for assessment of sac shape, detection of aneurysmal neck, and visualization of branches originating from the sac or neck itself, if the size of the aneurysm is greater than 13 mm. 3 T 3D CE-MRA is as accurate and effective as DSA for the evaluation of UIAs.     

Evaluation of cerebral aneurysms with high-resolution MR angiography using a section-interpolation technique: correlation with digital subtraction angiography

BACKGROUND AND PURPOSE: The objective was to evaluate the results of high-resolution, fast-speed, section-interpolation MR angiography and digital subtraction angiography (DSA), thereby examining the potential use of a primary noninvasive screening test for intracranial aneurysms. METHODS: The images were obtained in 39 cerebral aneurysmal lesions from 30 patients with a time-of-flight MR angiographic technique using a 1.5-T superconducting MR system. The total image volume was divided into four slabs, with 48 partitions each. To save time, only 24 phase-encoded steps were measured and interpolated to 48. The parameters used included 30/6.4 (TR/TE), a flip angle of 25 degrees , a 160x512 matrix, a field of view of 150x200, 7 minutes 42 seconds of scan time, an effective thickness of 0.7 mm, and an entire thickness of 102.2 mm. Maximum intensity projection was used for the image analysis, and a multiplanar reconstruction technique was used for patients with intracranial aneurysms. RESULTS: Among 39 intracranial aneurysmal lesions in 30 patients, 21 were ruptured and 18 were unruptured. Twelve lesions were less than 2 mm in size, 12 were 3 to 5 mm, 12 were 6 to 9 mm, and three were larger than 10 mm. At initial examinations, 38 of 39 aneurysmal lesions were detected by both MR angiography and DSA, with 97% sensitivity. In confirming aneurysms in neck and parent vessels, multiplanar reconstruction was successful in detecting all 39 aneurysms, whereas MR angiography was successful in detecting 27 (69%) and DSA was successful in detecting 32 (82%) of the lesions. CONCLUSION: High-resolution MR angiography with a section-interpolation technique showed equal results to those of DSA for the detection of intracranial aneurysms and may be used as a primary noninvasive screening test. In the evaluation of aneurysms in neck and parent vessels, the concurrent use of MR angiography and multiplanar reconstruction was far superior to the use of either MR angiography or DSA alone.     

Comparison of 2D and 3D digital subtraction angiography in evaluation of intracranial aneurysms

BACKGROUND AND PURPOSE: Although digital subtraction angiography (DSA) is considered the criterion standard for depiction of intracranial aneurysms, it is often difficult to determine the relationship of overlapping vessels to aneurysms when using 2D DSA. We compared 2D and 3D DSA in evaluation of intracranial aneurysms. METHODS: Thirty-six consecutive patients with cerebral aneurysms underwent 2D and 3D DSA. After standard 2D DSA, rotational DSA was performed. Maximum intensity projection (MIP) and shaded surface display (SSD) images were created from the rotational DSA data sets. All images were assessed randomly for overall image quality, presence of aneurysm, presence of aneurysmal lobulation, visualization of aneurysmal neck, and relationship to adjacent vessels. Data analysis was conducted for 40 aneurysms treated by clip placement. RESULTS: One aneurysm that was not detected at 2D DSA was classified as uncertain on the basis of rotational DSA. All aneurysms were classified as probably or definitively present on the basis of MIP and SSD findings. Overall image quality of rotational DSA, MIP, and SSD was statistically inferior to that of the standard 2D DSA for visualization of distal arteries. However, MIP and SSD images were significantly superior to those of standard 2D DSA for all other evaluations. For detection of lobulation, SSD images were significantly superior to other images, and for visualization of aneurysmal neck and relationship to neighboring arteries, SSD images were significantly superior to those of rotational DSA. For evaluation of the relationship to neighboring arteries, MIP images were significantly superior to those of rotational DSA. CONCLUSION: Three-dimensional DSA, especially SSD, provided more detailed information for evaluating cerebral aneurysms than did standard 2D and rotational DSA.     

Ex vivo study of the physical effect of coils on pressure and flow dynamics in experimental aneurysms

BACKGROUND AND PURPOSE: Recent experimental studies and a few case reports reveal that coiling may not lead to permanent occlusion of aneurysms by an organized thrombus. Therefore, biologic long-term prognosis seems to be doubtful, and the physical effect of coils may be important. The purpose of this study was to investigate the physical effect of coils on pressure and flow dynamics in aneurysms. METHODS: Bifurcation aneurysms were created in eight rabbits, explanted after 3 weeks, and tested in a model with pulsatile perfusion with 0.9% saline and heparinized blood. Before and after densely packing with coils, systemic and intraaneurysmal pressure, aneurysmal pulsation, and impact measurements were recorded. RESULTS: The peak and shape of the pressure waves in the aneurysm and in the delivery system were not significantly different before and after coiling. Under physiological intraaneurysmal pressure (while being perfused with saline), significant reduction (P = .022) of aneurysmal wall pulsation after coil embolization was noted. Overall, the aneurysmal impact on surrounding structures was statistically unchanged after coiling. However, in a few cases, after coil embolization, the observed increase of impact was more than doubled compared with the original values before coiling. CONCLUSION: Coils do not physically affect intraaneurysmal pressure. After coiling, there is no significant reduction of flow rates through the aneurysm and no reduction of aneurysmal impact, but aneurysmal wall pulsation may be decreased.     

MR angiography with three-dimensional time-of-flight and targeted maximum-intensity-projection reconstructions in the follow-up of intracranial aneurysms embolized with Guglielmi detachable coils.

BACKGROUND AND PURPOSE: Intra-arterial contrast angiographies are generally used to confirm treatment results of endovascular neurointerventions such as aneurysm obliteration. We compared MR angiography with digital subtraction angiography (DSA) as a follow-up technique for the detection of aneurysmal remnant cavities and arterial patency in patients treated for intracranial aneurysms with Guglielmi detachable coils (GDCs). METHODS: In 20 consecutive patients, follow-up MR angiography and routine intra-arterial cerebral angiography were performed on the same day 1 to 7 months (mean, 4.5 months) after embolization with GDCs. MR angiographic data were postprocessed for subvolume maximum intensity projections centered on the region of the treated aneurysm. Hard copies of both imaging studies were interpreted independently in a blinded fashion to record and compare remnant cavities, location of residual flow, and adjacent arterial narrowing, using DSA as the standard of reference. The interpreters also established an occlusion grade for the treated aneurysms as evidenced on DSA images and evaluated MR angiograms for artifactual effects. RESULTS: Overall sensitivity and positive predictive value of MR angiography in revealing aneurysmal remnant cavities were both 90%. Specificity in ruling out a remnant cavity with MR angiography was 91%. One remnant cavity was missed by MR angiography, and in five patients, false adjacent arterial encroachments were reported. CONCLUSION: MR angiography may be useful in the long-term follow-up of successfully treated small and medium-sized aneurysms after concurrent primary verification of their occlusion with DSA.     

MR evaluation of large intracranial aneurysms using cine low flip angle gradient-refocused imaging

MR imaging has proved to be useful in evaluating large intracranial aneurysms. The parent artery and patent lumen can be identified as flow voids and differentiated from thrombus. However, in the presence of slow flow, even-echo rephasing, and motion artifact, increased intraluminal signal may be present, which may be difficult to distinguish from thrombus. Aneurysms are also dynamic lesions and exert pulsatile mass effect on adjacent structures. Further definition of vascular anatomy and physiology may aid in therapeutic planning and assessment. Cine MR is a new technique using a movie loop of sequential GRASS (gradient-recalled acquisition in the steady state) images obtained during various points in the cardiac cycle. The combination of GRASS images and cardiac gating thus allows cinegraphic display of vascular structures. A comparison of this method with routine T1- and T2-weighted MR imaging and angiography was made in a group of 13 patients with intracranial aneurysms greater than 1.5 cm in diameter. Eight of these patients underwent transvascular detachable balloon occlusion. With cine MR, flowing blood has high intensity due to flow-related enhancement. Turbulent and high-velocity flow can be recognized on the basis of signal loss, which occurs during systole. Thrombus demonstrated variable signal intensity, which remained unchanged during the cardiac cycle. Compared with routine MR sequences, there was less image degradation from phase-encoding artifacts and improved visualization of the neck of the aneurysm. Pulsatile mass effect was uniquely assessed. After transvascular embolization, cine MR demonstrated improved conspicuity of acute thrombus and higher contrast between flowing blood and the occlusion balloon when compared with routine MR. Confirmation of flow within the parent vessel, residual aneurysm lumen, and distal arterial branches is possible. If the parent vessel was occluded, cine MR yielded greater information than angiography. Cine MR provides additional anatomic and physiologic data in the evaluation and assessment of therapy of intracranial aneurysms. Information can be obtained that is not available with either routine MR or angiography. The inherent limitations of this new technique include partial-volume artifacts, less than optimal flow-related enhancement or spatial resolution, and poor data acquisition due to cardiac arrhythmias.