Intracranial Arterial Flow Research Articles

Neuroimaging assessment of pediatric cerebral changes associated with SARS-CoV-2 infection during pregnancy.

SARS-CoV-2 infection and perinatal neurologic outcomes are still not fully understood. However, there is recent evidence of white matter disease and impaired neurodevelopment in newborns following maternal SARS-CoV-2 infection. These appear to occur as a consequence of both direct viral effects and a systemic inflammatory response, with glial cell/myelin involvement and regional hypoxia/microvascular dysfunction. We sought to characterize the consequences of maternal and fetal inflammatory states in the central nervous system of newborns following maternal SARS-CoV-2 infection. We conducted a longitudinal prospective cohort study from June 2020 to December 2021, with follow-up of newborns born to mothers exposed or not exposed to SARS-CoV-2 infection during pregnancy. Brain analysis included data from cranial ultrasound scans (CUS) with grayscale, Doppler studies (color and spectral), and ultrasound-based brain elastography (shear-wave mode) in specific regions of interest (ROIs): deep white matter, superficial white matter, corpus callosum, basal ganglia, and cortical gray matter. Brain elastography was used to estimate brain parenchymal stiffness, which is an indirect quantifier of cerebral myelin tissue content. A total of 219 single-pregnancy children were enrolled, including 201 born to mothers exposed to SARS-CoV-2 infection and 18 from unexposed controls. A neuroimaging evaluation was performed at 6 months of adjusted chronological age and revealed 18 grayscale and 21 Doppler abnormalities. Predominant findings were hyperechogenicity of deep brain white matter and basal ganglia (caudate nuclei/thalamus) and a reduction in the resistance and pulsatility indices of intracranial arterial flow. The anterior brain circulation (middle cerebral and pericallosal arteries) displayed a wider range of flow variation than the posterior circulation (basilar artery). Shear-wave US elastography analysis showed a reduction in stiffness values in the SARS-CoV-2 exposed group in all analyzed regions of interest, especially in the deep white matter elasticity coefficients (3.98 ± 0.62) compared to the control group (7.76 ± 0.77); p-value < 0.001. This study further characterizes pediatric structural encephalic changes associated with SARS-CoV-2 infection during pregnancy. The maternal infection has been shown to be related to cerebral deep white matter predominant involvement, with regional hyperechogenicity and reduction of elasticity coefficients, suggesting zonal impairment of myelin content. Morphologic findings may be subtle, and functional studies such as Doppler and elastography may be valuable tools to more accurately identify infants at risk of neurologic damage.

Abstract Number ‐ 70: Combined Trans‐arterial Flow Diversion and Trans‐venous Embolization Management of High‐Flow Traumatic Cavernous‐Carotid Fistula (CCF)

Introduction Carotid‐Cavernous fistulas (CCF) are abnormal vascular shunts between the internal carotid artery (ICA) and the cavernous sinus. Most commonly due to trauma (75%), CCF occurs in 4%(1) of skull‐base fracture patients. Visual impairment, diplopia, and headache are typical presenting symptoms (88%). Proptosis, chemosis, ophthalmoparesis, and orbital bruits are notable exam findings. Cerebral angiography is the gold standard for diagnosis, showing cavernous sinus enlargement and ophthalmic vein or leptomeningeal vessel dilatation. CCF is typically treated endovascularly andballoon embolization has achieved cure rates of 88–99%(2). Successful obliteration using stents, however, has been reported(3, 4). While both trans‐arterial and the trans‐venous approach embolization are feasible depending on local vascular anatomy and accessibility of fistula points, the combination of trans‐arterial and trans‐venous approach is rarely employed.We present a case of traumatic, high‐flow CCF treated with combined trans‐arterial and trans‐venous coiling embolization and telescoped flow‐diverting stents. Methods A case report of successful treatment of traumatic high‐flow CCF with a combined trans‐arterial and trans‐venous coiling embolization with telescoped flow‐diverting stents. Results A 26‐year‐old woman presented with right eye proptosis, periorbital ecchymosis, and chemosistwo weeks after severe closed head injury treated with decompressive hemicraniectomy and subdural hematoma evacuation. Examination was notable for right eye blindness without light perception and right‐sided third, fourth, and sixth cranial nerve palsies and elevated intraocular pressure. CT head showed a skull base fracture involving the right carotid canal and angiography of ICA confirmed a high‐flow multi‐channel right CCF with diminished intracranial arterial flow and engorged bilateral ophthalmic veins. After unsuccessful attempts to catheterize the fistula via arterial approach, superior‐segment coil embolization was performed using an inferior petrosal venous approach; but further embolization of the cavernous sinus was unsuccessful. Using the cavernous‐petrous segment of the right ICA, a flow‐diversion stent was placed that significantly decreased cross‐fistula blood flow, improved intracranial arterial flow, and reduced bilateral ophthalmic vein congestion. After two months, intraocular pressure normalized and right eye vision returned, though moderate exophthalmos persisted. Angiography showed decreased but persistent residual CCF flow. Another flow‐diversion stent was successfully placed via trans‐arterial approach, covering the previous pipeline stent through petrous‐to‐ophthalmic right ICA. Three‐month follow‐up angiogram showed closure of the CCF with complete restoration of right eye vision. She ultimately underwent right cranioplasty and was able to return to work. Conclusions A combined trans‐venous coiling embolization and trans‐arterial flow‐diversion stenting may be effectively employed in the treatment of CCF with reversal of clinical symptoms and restoration of visual loss. Larger studies are needed to explore the role of this combined approach in the management of CCF.

Intracranial arterial flow velocity mapping in quantitative time-of-flight MR angiography using deep machine learning

PurposeTo evaluate the application of deep machine learning (DML) to 3D quantitative time-of-flight (qTOF) magnetic resonance angiography (MRA) to measure blood flow velocity within the intracranial arteries. Materials and methodsIntracranial qTOF MRA was acquired in 15 subjects at 3 T. Blood flow velocity quantitation with qTOF MRA was done using a non-DML computer-vision procedure, and using convolutional DML neural networks. 3D phase contrast (PC) MRA was used as the comparator. Using PC velocity measures as the output target and qTOF two-echo source image data as inputs, DML neural networks were trained to predict component blood flow velocities. Total velocities and peak intracranial arterial blood flow velocities were computed from component velocities. ResultsCompared to non-DML image analysis, DML-based analysis of qTOF MRA image data improved agreement with PC for mean component velocity (intraclass correlation coefficient (ICC) = 0.966 versus 0.939), mean total velocity (ICC = 0.835 versus 0.723), and peak velocity (ICC = 0.816 versus 0.597), as well as narrowed the 95% Bland-Altman limits of agreement for mean component velocity ([−5.16, +4.31]cm/s versus [−6.86, +6.53]cm/s), mean total velocity ([−6.78,+3.59]cm/s versus [−9.39, +7.09]cm/s) and peak velocity ([−13.5,+10.2]cm/s versus [−21.3, +10.2]cm/s). Compared to non-DML analysis, DML image analysis reduced the root-mean-square deviation from PC velocity measures by 28%–36%, and shortened calculation times by 35-fold. ConclusionThe application of DML image analysis to intracranial qTOF MRA for velocity quantitation markedly shortened calculation times, substantially improved the agreement of component, total, and peak arterial blood flow velocities, and provided excellent agreement of hemodynamic measures with respect to 3D PC.

Intracranial Flow Velocity Quantification Using Non-Contrast Four-Dimensional Flow MRI: A Prospective Comparative Study with Transcranial Doppler Ultrasound.

Four-dimensional (4D) flow magnetic resonance imaging (MRI) allows three-dimensional velocity encoding to measure blood flow in a single scan, regardless of the intracranial artery direction. We compared blood flow velocity quantification by non-contrast 4D flow MRI and by transcranial Doppler ultrasound (TCD), the most widely used modality for measuring velocity. Twenty-two patients underwent both TCD and non-contrast 4D flow MRI. The mean time interval between TCD and non-contrast 4D flow MRI was 0.7 days. Subsegmental velocities were measured bilaterally in the middle cerebral and basilar arteries using TCD and non-contrast 4D flow MRI. Intracranial velocity measurements using TCD and non-contrast 4D flow MRI demonstrated a strong correlation in the bilateral M1, especially at the proximal segment (right r = 0.74, left r = 0.78; all p < 0.001). Mean velocities acquired with 4D flow MRI were approximately 8 to 10% lower than those acquired with TCD according to the location of M1. Intracranial arterial flow measurements estimated using non-contrast 4D flow MRI and TCD showed strong correlation. 4D flow MRI enables simultaneous assessment of vascular morphology and quantitative hemodynamic measurement, providing three-dimensional blood flow visualization. 4D flow MRI is a clinically useful sequence with a promising role in cerebrovascular disease.

Identification of intra-individual variation in intracranial arterial flow by MRI and the effect on computed hemodynamic descriptors.

To determine the intra-individual flow variation in serially acquired studies, and the influence of this variation on subsequent hemodynamic simulations using the inlet flow as a boundary condition. Author: Kindly check and confirm whether the corresponding authors are correctly identified.Confirmed. This prospective study included 51 patients (37 females and 14 males) with unruptured intracranial aneurysms who have received more than three times follow-up of 2D phase-contrast MR. The flow and velocity parameters were extracted to calculate the reproducibility and variation. Patient-specific computational fluid dynamics simulations were performed using the measured flows. Intraclass correlation coefficients for mean and maximum velocity and flow parameters ranged from 0.77 to 0.90. A 10% CV of mean flow was identified. Variations of 10% in inlet flow resulted in hemodynamic changes including 41.41% of peak systolic wall shear stress; 39.13% of end-diastolic wall shear stress; 2.79% of low shear area at peak systole; 2.12% of low shear area at end diastole: 47.57% of time-averaged wall shear stress; and 0.17% of oscillatory shear index. This study identified 10% of intra-individual mean flow variation on phase-contrast MR. Intra-individual flow variation resulted in a non-negligible variation in wall shear stress, but relatively small variation in low shear area in hemodynamic calculations.

Abstract P344: Validation of Computational Fluid Dynamics Against PC-MRI Measurements of Blood Flow in Healthy Intracranial Arteries: On the Threshold to Clinical Utility for Stroke Prediction

Aim: Computational Fluid Dynamics (CFD) modeling of blood flow is a promising technique to obtain hemodynamic biomarkers and predict recurrent strokes. Few studies, however, have validated CFD against other methods for measuring hemodynamics, e.g. phase contrast MRI (PC-MRI). To resolve the uncertainties about the accuracy of CFD, this study validates the results of an automated software that combines deep learning and CFD for simulating blood flow given an MR angiogram against PC-MRI. Methods: Intracranial arteries in 10 healthy volunteers (60% male, mean age 38 ± 16 years) were automatically segmented from TOF MRA obtained at 3T using deep learning. Subject-specific CFD modelling was undertaken. PC-MRI flow rate for each subject was used at the inlet boundary condition, but not at the outlets. Outlet boundary condition was set to lumped parameter Windkessel model, with the resistance programmatically determined using allometric scaling laws based on the dimension and branching of vasculature. For comparison, two commonly used outlet conditions (exponent 2 &amp; 3 in Murray’s Law) were also considered. CFD results for flow rate and wall shear stress were compared against PC-MRI using Pearson’s correlation coefficient. Results: The flow rate across major intracranial arteries from CFD was in excellent agreement with the PC-MRI (MCA: r = 0.83, ACA: r = 0.81 &amp; PCA: r = 0.82). In addition, there was good correlation for both wall shear stress (WSS) and WSS Ratio (WSSR, i.e. the ratio of WSS between a branch and its parent vessel) (MCA (WSS/WSSR): r = 0.6/0.77, ACA (WSS/WSSR): r = 0.86/0.93 &amp; PCA (WSS/WSSR): r = 0.72/0.85). The inter-subject variability of the flow rate (i.e. standard deviation) obtained from CFD matched closely the variation range observed from PC-MRI and the literature. The two alternative outlet models behaved similarly but suffered from vessel truncation and high errors in some cases. Conclusion: CFD modelling of blood flow in intracranial arteries from static images has good agreement with PC-MRI measurements when allometric scaling laws are applied for setting Windkessel outflow conditions. This lays the foundation for using CFD to predict recurrent strokes as the technique uses standard MRA images already commonly acquired for stroke evaluation.

Characteristics of cerebral hemodynamics in patients with chronic brain ischemia

Background. Literature sources report conflicting results regarding the severity of clinical symptoms of hydrocephalus (HC) and their association with cerebral arterial blood flow (CABF); most studies do not show a direct relationship, while some suggest a link between clinical severity and progressive decrease in CABF. The study of hemodynamic changes in the brain of patients with chronic brain ischemia (CBI), elucidation of their relationship with cognitive impairments helps to improve diagnostic approaches and optimize the prognosis of the disease. The purpose of this study is to investigate the state of cerebral hemodynamics and to establish its relationship with changes in cognitive functions in patients with CBI and HC. Materials and Methods. A comprehensive examination of 110 patients with CBI and HC was performed. The localization of the HC and results of Montreal Cognitive Test (MoCA scale) were taken into account. Computed tomography of the brain was performed with subsequent determination of morphometric parameters and indices. The state of cerebral blood flow and structural changes of blood vessels were studied using transcranial color-coded duplex ultrasonography (TCCS) of intracranial vessels and extracranial divisions. Microsoft Excel 2011 and Statistica were used for statistical processing of the results. Results. It was found that there was a significantly larger diameter of both common carotid arteries (CCA), thickness of complex intima\media (CIM), maximum systolic velocity (Vs), velocity at the end of the diastolic cycle (Vd), as well as peripheral resistance (IR) in left CCA (p &lt;0,05) in patients with CBI and HC compared with patients with CBI without HC. Significantly larger diameter of left internal carotid artery (ICA), Vs, Vd and IR was revealed; Vs and Vd in the right ICA; Vd in the extracranial devision of vertebral artery (VA) in patients with HC. A significant relationship was found between the following blood flow parameters and the values of the MoCA scale: Vs MCA/MoCA (r = 0,45, p &lt;0,05), Vs ACA/MoCA (r = 0,38, p &lt;0.05), ICA diameter/MoCA (r = -0,51, p &lt;0,05). It was found that the diameter of CCA and the thickness of CIM were significantly larger in patients with CBI with internal HC in comparison with patients with CBI with external HC (p &lt;0,01). Vs and Vd in patients with internal hydrocephalus were significantly lower, and IR was significantly higher compared with patients with external hydrocephalus (p &lt;0,01). The diameter of ICA and IR in patients with CBI with internal HC was significantly higher, and Vs was significantly lower compared with patients with CBI and external HC (p &lt;0,01). Significantly different values were found in Vs and IR meanings in middle cerebral artery (MCA) and Vs in anterior cerebral artery (ACA) in patients with CBI with internal HC compared with patients with CBI with external HC.Conclusions. Functional parameters of blood flow and structural changes of cerebral arteries in patients with CBI with concomitant hydrocephalus differed significantly from those in patients without hydrocephalus and depended on the type and severity of hydrocephalus. ICA occlusion, ICA stenosis &gt;50%, and intracranial venous stasis were significantly more common in patients with severe and moderate HC compared with those with mild HC. A weak relationship was found between the structure of carotid arteries and blood flow in intracranial arteries in patients with CBI and HC. There was a significant relationship between blood flow indices and the values of the MoCA scale, which indicated the effect of changes in the vessels of the anterior circular basin on the cognitive functions and the lack of such connection with blood flow indices in vertebrobasilar basin.

A novel sequence for simultaneous measurement of whole-brain static and dynamic MRA, intracranial vessel wall image, and T1 -weighted structural brain MRI.

To propose a highly time-efficient imaging technique named improved simultaneous noncontrast angiography and intraplaque hemorrhage (iSNAP) for simultaneous assessment of lumen, vessel wall, and blood flow in intracranial arteries. iSNAP consists of pulsed arterial spin labeling preparations and 3D golden angle radial acquisition. Images were reconstructed by k-space weighted image contrast (KWIC) method with optimized data-sharing strategies. Dynamic MRA for blood flow assessment was obtained from iSNAP by reconstruction at multiple inversion times and image subtraction, static MRA by both image subtraction approach and phase-sensitive inversion recovery technique, and vessel wall images by both reconstruction at zero-crossing time-point of blood and phase-sensitive inversion recovery. A T1 -weighted brain MRI was also reconstructed from iSNAP. Preliminary comparison of iSNAP against the dedicated dynamic MRA sequence 4D-TRANCE, MRA/vessel wall imaging sequence SNAP, and vessel wall imaging sequence T1 -weighted VISTA was performed in healthy volunteers and patients. iSNAP has whole-brain coverage and takes ~6.5 min. The dedicated reconstruction strategies are feasible for each iSNAP image contrast and beneficial for image SNR. iSNAP-dynamic MRA yields similar dynamic flow information as 4D-TRANCE and allows more flexible temporal resolution. The 2 types of iSNAP static MRA images complement each other in characterizing both proximal large arteries and distal small arteries. Depiction of vessel wall lesions in iSNAP vessel wall images is better than SNAP and may be similar to T1 -weighted VISTA, although the images are slightly blurred. iSNAP provides a time-efficient evaluation of intracranial arteries and may have great potential for comprehensive assessment of intracranial vascular conditions using a single sequence.

Association of Cardiovascular and Alzheimer's Disease Risk Factors with Intracranial Arterial Blood Flow in Whites and African Americans.

Alzheimer's disease (AD) has a higher prevalence among African Americans. Targeting cardiovascular and metabolic risk factors may be potential mechanisms to modify AD risk and address racial/ethnic disparities in AD dementia. This study investigated relationships among cardiovascular and metabolic risk factors, APOE genotype, AD biomarkers, and intracranial arterial blood flow in Whites and African Americans enriched for AD risk. 399 cognitively unimpaired adults from the Wisconsin Alzheimer's Disease Research Center completed physical and neuroimaging examinations. A 4D Flow MRI sequence (phase-contrast vastly under sampled isotropic projection imaging) measured intracranial arterial flow in the Circle of Willis. Linear mixed-effects regression models estimated relationships between risk factors and intracranial arterial flow and tested interactions with racial group, APOE genotype, and AD biomarkers, with separate models per risk factor. Higher fasting glucose was associated with lower intracranial arterial flow; no additional relationships between flow and risk factors were observed. Main effects of racial group were observed, without an interaction, indicating lower flow in African Americans compared to Whites. In race-stratified analyses, higher glucose and triglycerides were associated with lower flow for African Americans, but not for Whites. No main effects or interactions among risk factors, APOE, or AD biomarkers, and flow were observed. Elevated fasting glucose and triglycerides were associated with lower intracranial arterial flow; these relationships were more prominent in African Americans. Targeting metabolic risk factors may impact intracranial arterial health. Additional research is needed to determine if this will impact disparities in dementia prevalence.

Vascular responses to abrupt blood flow change after bypass surgery for complex intracranial aneurysms.

Bypass surgery for complex intracranial aneurysms (IAs) results in drastic blood flow changes in intracranial arteries. The aim of the study was to elucidate how vessels adapt to blood flow changes after bypass surgery with phase-contrast magnetic resonance imaging (PC-MRI). This is a prospective observational study to assess changes of the blood flow in intracranial arteries after bypass surgery for IAs. Flow rates and vessel diameters were measured with PC-MRI in 52 intracranial arteries of 7 healthy volunteers and 31 arteries of 8 IA patients who underwent bypass surgery. Wall shear stress (WSS) was calculated with the Hagen-Poiseuille formula. In 18 arteries of 5 patients, the same measurement was performed 1, 3, and 12months after surgery. PC-MRI showed a strong positive correlation between the flow rate and the third power of vessel diameter in both healthy volunteers (r = 0.82, P < 0.0001) and IA patients (r = 0.90, P < 0.0001), indicating the constant WSS. Of the 18 arteries in 5 patients, WSS increased in 7 arteries and decreased in 11 arteries immediately after surgery. In the WSS-increased group, WSS returned to the preoperative value in the third postoperative month. In the WSS-decreased group, WSS increased in the 12th month, but did not return to the preoperative level. In a physiological state, WSS was constant in intracranial arteries. Changed WSS after bypass surgery tended to return to the preoperative value, suggesting that vessel diameter and flow rate might be controlled so that WSS remains constant.

Macrovascular and microvascular cerebral blood flow in adults at risk for Alzheimer's disease

IntroductionCapillary hypoperfusion is reported in asymptomatic adults at-risk for Alzheimer's disease (AD), but the extent that can be explained by reduced flow in intracranial arteries is unknown. MethodsOne hundred fifty-five asymptomatic adults enriched for AD risk (mean age 61 years) completed arterial spin labeling (pcASL) and 4D-flow MRI sequences. Voxel-wise regression models investigated the relationship between mean flow in bilateral cerebral arteries and capillary perfusion, and tested potential moderators of this relationship. ResultsMean arterial blood flow through middle cerebral arteries (MCAs) and internal carotid arteries was positively associated with perfusion in large cortical clusters (P < .05, false discovery rate corrected). Trends were observed for the interactions MCA flow × age and MCA flow × cardiovascular risk on cerebral perfusion (P < .001, uncorrected). DiscussionThese findings provide evidence that capillary perfusion measured via pseudocontinuous arterial spin labeling is strongly dependent on inflow from larger cerebral arteries. Further studies are warranted to investigate possible alterations between macrovascular and microvascular flow in advanced age and elevated cardiovascular risk in asymptomatic adults at risk for AD.

Intracranial Blood Flow Velocity in Patients withβ-Thalassemia Intermedia Using Transcranial Doppler Sonography: A Case-Control Study

Introduction. Patients with β-thalassemia intermedia have a higher incidence of thromboembolic events compared to the general population. Previous studies have shown that patients with sickle cell disease, who are also prone to ischemic events, have higher intracranial arterial blood flow velocities measured by transcranial Doppler sonography (TCD). The aim of this study is to evaluate intracranial arterial flow velocities in patients with β-thalassemia intermedia and compare the results with those found in healthy subjects. Methods. Sixty-four patients with β-thalassemia intermedia and 30 healthy subjects underwent transcranial Doppler sonography. Results. Significantly higher flow velocities were found in intracranial arteries of patients compared to controls (P = 0.001). Previously splenectomized patients with thrombocytosis showed higher flow velocities than nonsplenectomized patients without thrombosis. Conclusion. The increased flow velocities in patients with β-thalassemia intermedia may point to a higher risk of ischemic events. Preventive measures such as blood transfusion or antiplatelet treatment may be beneficial in these patients.

Intracranial Hemodynamics Is Altered by Carotid Artery Disease and After Endarterectomy

Carotid endarterectomy (CEA) has become a routine procedure to treat symptomatic carotid artery disease and reduce the risk of recurrent cerebral ischemic events. The purpose of this study was to use an arterial spin labeling dynamic magnetic resonance angiography technique to characterize intracranial hemodynamics before and after CEA. Thirty-seven carotid artery disease patients participated in this study, of whom 24 underwent magnetic resonance imaging before and after CEA. Seventeen control subjects spanning 5 decades underwent magnetic resonance imaging to assess age-related changes. Hemodynamic metrics (that is, relative time to peak and amplitude) were calculated with a γ-variate model. Linear regression was used to relate carotid artery disease burden to downstream hemodynamics in the circle of Willis. Relative time to peak increased with age in controls (P<0.020). For patients, relative time to peak was positively correlated with percent stenosis (P<0.050), independent of age. At 1 day after CEA, the middle cerebral artery ipsilateral to the CEA showed significant dynamic magnetic resonance angiography changes: relative time to peak decreased (P<0.017) and the flow amplitude increased (P<0.009). No pre- versus post-CEA changes were significant in the contralateral middle cerebral artery or posterior segments. This noninvasive, arterial spin labeling-based method produced time-resolved images that were used to characterize intracranial arterial flow associated with aging, extracranial carotid artery disease, and CEA. Results demonstrate that the technique has the sensitivity to detect hemodynamic changes after CEA.

Should ancillary brain blood flow analyses play a larger role in the neurological determination of death?

We present two patients who regained spontaneous respiration following clinical neurological determination of death (NDD) while ancillary radiological imaging demonstrated brain blood flow. A 26-yr-old male with chronic otitis media presented with a Glasgow Coma Scale (GCS) score of 3 and fixed 7-mm pupils. Computed tomography demonstrated right-sided mastoiditis and a temporal lobe abscess associated with uncal herniation. The patient was diagnosed brain dead seven-hr later when motor responses and brainstem reflexes were absent and his apnea test was positive. Approximately 28-hr after NDD, during post-declaration organ resuscitation, the patient regained spontaneous respiration and magnetic resonance imaging revealed brain blood flow. Spontaneous respirations persisted for five-days before cardiovascular collapse occurred. In the second case, a 50-yr-old female presented with a GCS score of 3 and fixed 6-mm pupils following a traumatic brain injury and a five-minute cardiac arrest. The patient was deemed clinically brain dead six-hr later when physical examination revealed absent motor responses and brainstem reflexes and her apnea test was positive. As confirmation of brain death, a cerebral radionuclide angiogram was performed, which surprisingly revealed intracranial arterial flow. During organ resuscitation, 11-hr after NDD, the patient regained spontaneous respiration. She expired hours after family decision to withdraw treatment. For both patients, several unrecognized confounding factors for NDD were present. These cases illustrate the difficulties encountered by experienced clinicians in determining brain death using clinical criteria alone, and they suggest that more routine use of ancillary brain blood flow analyses should be recommended.

Complete Intracranial Arterial and Venous Blood Flow Evaluation with 4D Flow MR Imaging

Time-resolved, 3D velocity-encoded MR imaging (4D Flow) allows for the acquisition of dynamic, multidirectional data on blood flow and has recently been used for the evaluation of intracranial arterial flow. Using a 3T system with optimization of both temporal resolution and k-space subsampling with a combination of parallel imaging and cut-corner acquisition, we present the clinical assessment of a patient with an arteriovenous malformation by providing complete intracranial arterial and venous coverage in a reasonable scan time.

Visualization of hemodynamics in intracranial arteries using time‐resolved three‐dimensional phase‐contrast MRI

To visualize the hemodynamics of the intracranial arteries using time-resolved three-dimensional phase-contrast (PC)-MRI (4D-Flow). MR examinations were performed with a 1.5T MR unit on six healthy volunteers (22-50 years old, average = 30 years). 4D-Flow was based on a radiofrequency (RF)-spoiled gradient-echo sequence, and velocity encoding (VENC) was performed along all three spatial directions. Measurements were retrospectively gated to the electrocardiogram (ECG), and cine series of three-dimensional (3D) data sets were generated. The voxel size was 1 x 1 x 1 mm, and acquisition time was 30-40 minutes. 4D data sets were calculated into time-resolved images of 3D streamlines, 3D particle traces, and 2D velocity vector fields by means of flow visualization software. We were able to see the 3D streamlines from the circle of Willis to the bilateral M2 segment of the middle cerebral arteries (MCAs). Time-resolved images of 3D particle traces also clearly demonstrated intracranial arterial flow dynamics. 2D velocity vector fields on the planes traversing the carotid siphon or the basilar tip were clearly visualized. These results were obtained in all six volunteers. 4D-Flow helped to elucidate the in vivo 3D hemodynamics of human intracranial arteries. This method may be a useful noninvasive means of analyzing the hemodynamics of intracranial arteries in vivo.

Carotid Artery Stenosis

Seemant Chaturvedi, Peter M. Rothwell, eds 359 pages. Boca Raton, Fla: Taylor and Francis; 2005. $199.95. ISBN 0-8247-5417-4 Carotid Artery Stenosis is a complete review of atherothrombotic disease at the bifurcation of the common carotid artery, its history, pathology, epidemiology, diagnosis, and management. The book naturally divides itself into 5 general areas that are not acknowledged by headings. The first area (chapters 1 through 3) deals with the history, epidemiology, and pathophysiology of atherothrombotic carotid disease. The second area (chapters 4 and 5) deals with the evaluation of atherothrombotic disease at the bifurcation of the common carotid artery. It includes computed tomographic angiography (CTA) and carotid duplex Doppler imaging with flow analysis. Magnetic resonance angiography (MRA) and conventional cerebral angiography are dealt with only in passing. There is no chapter dedicated to transcranial Doppler (TCD) assessment of the effects of pathology in the carotid artery on intracranial arterial flow. The third area (chapters 6 through 11) covers the various medical therapeutic options for preventing progression of atherothrombotic disease. The fourth area (chapters 12 through 16) discusses the rationale for the various surgical therapeutic options, including a welcomed chapter on extracranial and intracranial bypass grafting. The fifth area (chapters 17 through 20) covers the endovascular considerations for management of atherothrombotic carotid disease. An editor’s summary chapter at the end of the book would have been helpful in binding all of the chapters together to provide a practical guide for the practicing physician at the bedside. My reaction to these general areas and some individual chapters follows. The first group of chapters deals with the introduction, epidemiology, pathology, and pathophysiology of carotid disease. The introductory chapter …

Construction of 3-D arterial volume meshes from magnetic resonance angiography

Finite element methods are well-suited for solving problems in arterial fluid dynamics, primarily due to their ability to handle flows in complex geometries. However, in order to use these computational methods to develop realistic models of pulsatile flow in intracranial arteries and associated aneurysms, it is necessary to construct a 3-D mesh, or grid, that accurately duplicates the arterial geometry of interest. In this paper, we present an efficient method to accurately develop realistic 3-D computational meshes of human intracranial arteries and aneurysms from serial magnetic resonance angiography images. However, these techniques may be applied to any other form of imaging data including computed tomographic angiography. First, raw grayscale images are segmented, converted to their binary form and arterial contours are extracted at each image slice. Next, the arterial contours are stacked and cubic splines are computed along the axial direction. This creates an affect similar to smooth integration in the axial direction and provides a set of points that define the 3-D arterial surface geometry. Then, surface patches are constructed and merged. A surface mesh is then computed with the ability to locally vary the mesh density as desired. Finally, nodal points on the surface mesh are used to compute the finite element volume mesh. The 3-D volume mesh accurately describes the arterial geometry and is used to develop patient-specific computational fluid dynamic models of flow phenomena in intracranial arteries and aneurysms. These flow models are then suitable for investigating the hemodynamics of intracranial aneurysm formation and test the end-effects of various medical and surgical treatments.

Transcranial Doppler ultrasound for the assessment of intracranial arterial flow velocity—Part 2. Evaluation of intracranial arterial disease

Transcranial (TC) pulsed Doppler ultrasound was used to evaluate flow velocity within the intracranial basal cerebral arteries in 71 patients with cerebrovascular disease as revealed by arteriography. Abnormalities of the fast-Fourier transformed (FFT) Doppler spectra were used to detect and classify obstructive lesions as well as dilative arteriopathy of the carotid siphon, the middle, anterior, and posterior cerebral arteries, and the basilar artery. Functional stenosis due to large shunting volumes in patients with arteriovenous malformations and in the presence of significant collateralization of extracranial obstructive lesions were similarly diagnosed.

Transcranial doppler ultrasound for the assessment of intracranial arterial flow velocity—Part 1. Examination technique and normal values

We present the examination technique and normal values of flow velocity from intracranial basal cerebral arteries for a recently developed pulsed Doppler system operating at 2 MHz emitting frequency. Peak systolic, peak diastolic, and mean flow velocity values are analyzed from fast-Fourier transformed (FFT) Doppler spectra at selected depths for 50 presumed normal subjects ranging in age from 22 to 79 years. Interindividual variation is high for peak flow but moderate for mean flow velocity values, which hence are more likely to discriminate normal from abnormal. Flow velocity values within the posterior cerebral artery (PCA) and the basilar artery (BA) are significantly lower than in the anterior cerebral artery (ACA) and the middle cerebral artery (MCA), which is also unique in showing significantly decreasing values with increasing age: calculated mean flow velocities are 47.3 ± 13.6 and 45.3 ± 13.5 cm/sec in the ACA, and 58.4 ± 8.4 and 44.7 ± 11.1 cm/sec in the MCA in patients <40 years and >60 years, respectively, but 34.2 ± 7.8 and 29.9 ± 9.3 (PCA) (patients <40 years and patients >60 years), and 34.9 ± 7.8 and 30.5 ± 12.4 (BA) (patients <40 years and patients >60 years). A new scanning system is introduced, which we suggest will reduce interindividual variations and improve the accurate separation of nearby vessels, which are major causes for the comparatively large standard deviations at present.