Cerebral Perfusion Territories Research Articles

Effect of intracranial pressure on photoplethysmographic waveform in different cerebral perfusion territories: A computational study.

Background: Intracranial photoplethysmography (PPG) signals can be measured from extracranial sites using wearable sensors and may enable long-term non-invasive monitoring of intracranial pressure (ICP). However, it is still unknown if ICP changes can lead to waveform changes in intracranial PPG signals. Aim: To investigate the effect of ICP changes on the waveform of intracranial PPG signals of different cerebral perfusion territories. Methods: Based on lump-parameter Windkessel models, we developed a computational model consisting three interactive parts: cardiocerebral artery network, ICP model, and PPG model. We simulated ICP and PPG signals of three perfusion territories [anterior, middle, and posterior cerebral arteries (ACA, MCA, and PCA), all left side] in three ages (20, 40, and 60years) and four intracranial capacitance conditions (normal, 20% decrease, 50% decrease, and 75% decrease). We calculated following PPG waveform features: maximum, minimum, mean, amplitude, min-to-max time, pulsatility index (PI), resistive index (RI), and max-to-mean ratio (MMR). Results: The simulated mean ICPs in normal condition were in the normal range (8.87-11.35mmHg), with larger PPG fluctuations in older subject and ACA/PCA territories. When intracranial capacitance decreased, the mean ICP increased above normal threshold (>20mmHg), with significant decreases in maximum, minimum, and mean; a minor decrease in amplitude; and no consistent change in min-to-max time, PI, RI, or MMR (maximal relative difference less than 2%) for PPG signals of all perfusion territories. There were significant effects of age and territory on all waveform features except age on mean. Conclusion: ICP values could significantly change the value-relevant (maximum, minimum, and amplitude) waveform features of PPG signals measured from different cerebral perfusion territories, with negligible effect on shape-relevant features (min-to-max time, PI, RI, and MMR). Age and measurement site could also significantly influence intracranial PPG waveform.

Rapamycin Induces an eNOS (Endothelial Nitric Oxide Synthase) Dependent Increase in Brain Collateral Perfusion in Wistar and Spontaneously Hypertensive Rats.

Rapamycin is a clinically approved mammalian target of rapamycin inhibitor that has been shown to be neuroprotective in animal models of stroke. However, the mechanism of rapamycin-induced neuroprotection is still being explored. Our aims were to determine if rapamycin improved leptomeningeal collateral perfusion, to determine if this is through eNOS (endothelial nitric oxide synthase)-mediated vessel dilation and to determine if rapamycin increases immediate postreperfusion blood flow. Wistar and spontaneously hypertensive rats (≈14 weeks old, n=22 and n=15, respectively) were subjected to ischemia by middle cerebral artery occlusion (90 and 120 minutes, respectively) with or without treatment with rapamycin at 30-minute poststroke. Changes in middle cerebral artery and collateral perfusion territories were measured by dual-site laser Doppler. Reactivity to rapamycin was studied using isolated and pressurized leptomeningeal anastomoses. Brain injury was measured histologically or with triphenyltetrazolium chloride staining. In Wistar rats, rapamycin increased collateral perfusion (43±17%), increased reperfusion cerebral blood flow (16±8%) and significantly reduced infarct volume (35±6 versus 63±8 mm3, P<0.05). Rapamycin dilated leptomeningeal anastomoses by 80±9%, which was abolished by nitric oxide synthase inhibition. In spontaneously hypertensive rats, rapamycin increased collateral perfusion by 32±25%, reperfusion cerebral blood flow by 44±16%, without reducing acute infarct volume 2 hours postreperfusion. Reperfusion cerebral blood flow was a stronger predictor of brain damage than collateral perfusion in both Wistar and spontaneously hypertensive rats. Rapamycin increased collateral perfusion and reperfusion cerebral blood flow in both Wistar and comorbid spontaneously hypertensive rats that appeared to be mediated by enhancing eNOS activation. These findings suggest that rapamycin may be an effective acute therapy for increasing collateral flow and as an adjunct therapy to thrombolysis or thrombectomy to improve reperfusion blood flow.

Inhibition of PAI (Plasminogen Activator Inhibitor)-1 Improves Brain Collateral Perfusion and Injury After Acute Ischemic Stroke in Aged Hypertensive Rats.

Background and Purpose- Aging and hypertension, comorbidities prevalent in the stroke population, are associated with poor collateral status and worsened stroke outcome. However, underlying mechanisms by which these conditions affect stroke outcome are not clear. We studied the role of PAI (plasminogen activator inhibitor)-1 that is increased in aging and hypertension on brain and vascular expression of inflammatory factors and perfusion that may contribute to worse stroke outcomes. Methods- Aged (≈50 weeks) and young (≈18 weeks) spontaneously hypertensive rats (SHR) were subjected to ischemia by middle cerebral artery occlusion (2 hours) and reperfusion (2 hours) with or without treatment with the PAI-1 inhibitor TM5441. Changes in middle cerebral artery and collateral perfusion territories were measured by multisite laser Doppler. Reactivity to TM5441 was studied using isolated and pressurized leptomeningeal anastomotic arterioles. Brain injury was determined by 2,3,5-triphenyltetrazolium staining and quantitative immunohistochemistry of amyloid-β-42, PAI-1, and hemoglobin. Circulating inflammatory factors were measured by ELISA. Results- Changes in cerebral blood flow during middle cerebral artery occlusion were similar between groups, with both having poor collateral perfusion and incomplete reperfusion. However, aged SHR had greater brain injury versus young (41±2 versus 23±2%, P<0.05) as well as increased brain deposition of amyloid-β-42 and circulating oxLDL (oxidized low-density lipoprotein). Erythrocyte aggregation and hemorrhage within the injured brain was observed in 50% of aged but no young SHR, with increased circulating PAI-1 in this subgroup of aged SHR (16±3 versus 6±2 ng/mL, P<0.05). PAI-1 inhibition with TM5441 improved brain injury but did not affect hemorrhage. TM5441 increased collateral perfusion by 38±7% and dilated leptomeningeal anastomotic arterioles by 44±10%, which was abolished by nitric oxide synthase inhibition. Conclusions- Increased injury in aged SHR seemed to be related to poor collateral perfusion, hemorrhagic transformation, increased amyloid-β-42, and oxidative stress. PAI-1 inhibition reduced infarction in both groups of SHR that possibly due, in part, to increased collateral perfusion.

Perioperative Changes in Cerebral Perfusion Territories Assessed by Arterial Spin Labeling Magnetic Resonance Imaging Are Associated with Postoperative Increases in Cerebral Blood Flow in Patients with Carotid Stenosis.

The magnetic resonance imaging technique known as territorial arterial spin labeling (TASL) allows for noninvasive visualization of perfusion territories. The objective of this study was to use TASL to assess the relationship between perioperative changes in the perfusion territories of the internal carotid artery (ICA) and cerebral blood flow (CBF) after carotid revascularization. In 32 patients, ICA perfusion volume (PV) and CBF were measured before and after carotid endarterectomy/carotid artery stenting using TASL and single-photon emission computed tomography, respectively. ICA flow was measured during carotid endarterectomy before and after reconstruction, using an electromagnetic flowmeter. Eleven healthy volunteers, as the normal control group, underwent TASL evaluation. We classified patients into 2 groups: the normal PV group (ICA PV ≥ mean-2 standard deviation of healthy volunteers; n= 13) and the reduced PV group (ICA PV < mean-2 standard deviation; n= 19). The postoperative increase in the ICA PV and CBF were significantly greater in the reduced PV group than in the normal group (90.4% ± 131.8% vs. 10.5 ± 9.8%, P= 0.017, 32.0±25.7% vs. 10.5% ± 10.7%, P= 0.0032, respectively). ICA flow increased significantly after reconstruction in both the normal PV group (115.1 ± 48.1 mL/minute to 159.1± 53 mL/minute; P= 0.016) and reduced PV group (57.8 ± 38.3 mL/minute to 182.3 ± 52.6 mL/minute; P<0.0001). However, in some patients in the reduced PV group, the PV increased only slightly, whereas the ICA flow markedly increased, which resulted in a large CBF increase, such as hyperperfusion. The TASL study suggested that an imbalance between increases in the PV and ICA flow could play an important role in the pathophysiology underlying postoperative abnormal increases in CBF.

Brain oxygenation responses to an autonomic challenge: a quantitative fMRI investigation of the Valsalva manoeuvre.

In late age, the autonomic nervous system (ANS) has diminished ability to maintain physiological homeostasis in the brain in response to challenges such as to systemic blood pressure changes caused by standing. We devised an fMRI experiment aiming to map the cerebral effects of an ANS challenge (Valsalva manoeuvre (VM)). We used dual-echo fMRI to measure the effective transverse relaxation rate (R2*, which is inversely proportional to brain tissue oxygenation levels) in 45 elderly subjects (median age 80 years old, total range 75-89) during performance of the VM. In addition, we collected fluid-attenuated inversion recovery (FLAIR) data from which we quantified white matter hyperintensity (WMH) volumes. We conducted voxelwise analysis of the dynamic changes in R2* during the VM to determine the distribution of oxygenation changes due to the autonomic stressor. In white matter, we observed significant decreases in oxygenation levels. These effects were predominantly located in posterior white matter and to a lesser degree in the right anterior brain, both concentrated around the border zones (watersheds) between cerebral perfusion territories. These areas are known to be particularly vulnerable to hypoxia and are prone to formation of white matter hyperintensities. Although we observed overlap between localisation of WMH and triggered deoxygenation on the group level, we did not find significant association between these independent variables using subjectwise statistics. This could suggest other than recurrent transient hypoxia mechanisms causing/contributing to the formation of WMH.

The Significance of Cerebral Hemodynamics Imaging in Carotid Endarterectomy: A Brief Review

The indication of carotid endarterectomy (CEA) is principally determined by the presence or absence of symptoms and the degree of stenosis. However, the results of recent studies have implicated the usefulness of cerebral hemodynamics imaging for perioperative assessments. Many studies using single-photon emission computed tomography (SPECT) have demonstrated that cerebral hemodynamics imaging assessments are useful in the prediction and assessment of post-CEA hyperperfusion. In studies using transcranial Doppler ultrasonography, SPECT, or positron-emission tomography (PET), cerebral hemodynamic impairment is highly likely to increase the risk of cerebral infarction in patients with asymptomatic carotid artery stenosis. In other studies using the same modalities, cerebral hemodynamic impairment might be related to cognitive impairment in carotid artery stenosis, and this cognitive impairment might be improved with CEA. Nuclear medicine techniques involve the injection of radioactive tracers. Arterial spin labeling (ASL) is an emerging technique of perfusion magnetic resonance imaging (MRI) for the noninvasive measurement of cerebral perfusion. ASL could detect pathologic states such as hypoperfusion, impaired vasoreactivity, and postoperative hyperperfusion activities that are equivalent to SPECT. In addition, regional perfusion imaging visualizes cerebral perfusion territories by selective ASL. In conclusion, cerebral hemodynamic imaging would be useful for the perioperative assessment of CEA. However, there is a lack of sufficient scientific evidence to confirm the benefits, necessitating further study.

Abstract TP169: Perioperative Assessment of Cerebral Perfusion Territories using Arterial Spin Labeling Magnetic Resonance Imaging in Patients with Carotid stenosis

[Background] Territorial arterial spin labeling (TASL) MRI offers a unique opportunity to visualize non-invasively cerebral perfusion territory (PT) by selective labeling of the feeding arteries without contrast medium. The objective of this study was to evaluate the PT status in patients with carotid stenosis and effect of carotid endarterectomy (CEA) on PT. [Materials and Methods] This study included 22 patients with carotid stenosis (20 men and 2 women; mean age 73 years) treated by CEA. All of them underwent TASL preoperatively and on the day after surgery. Ipsilateral internal carotid artery (ICA) blood flow (ICF) was measured by electromagnetic flowmeter just before and after endarterectomy during the surgery. Perfused volume (PV) of each feeding artery was calculated from perfused area and thickness of slices. Cerebral blood flow (CBF) was calculated as ICF/PV. [Results] Before CEA, the PV of ipsilateral ICA were significantly smaller than those of contralateral ICA. After CEA, the ipsilateral PV significantly increased and the asymmetry of PV of ICA was corrected (Fig.1 &amp; 2). ICF also increased (82 to 178 ml/min). Accordingly, ipsilateral CBF defined by ICF/PV significantly increased (28 to 50 ml/100cm 3 /min). In a patient with postoperative hyperperfusion (HP), however, ICF remarkably increased from 10 to 200 ml/min while the PV increased only slightly (111 to 127 cm 3 , Fig.2). [Conclusion] TASL could evaluate the peri-operative change of cerebral PT non-invasively. CEA corrected the asymmetry of PT measured by TASL in patients with carotid stenosis. In a patient with HP after CEA, however, the increase of PT was small, which may suggest pathophysiological basis for HP.

Comparison of peri-procedural brain lesions by cerebral MRI after transcatheter aortic valve implantation and conventional aortic valve replacement

Aims: Prior studies have shown a high rate of cerebral embolic lesions after transcatheter aortic valve implantation (TAVI). We therefore compared the incidence of ischemic brain lesions and microbleedings with MRI in patients undergoing TAVI and conventional surgical aortic valve replacement. Methods: 25 consecutive patients (mean age 81 ± 5 years, mean log. EuroScore 32 ± 10%), who underwent TAVI and 25 patients who received surgical aortic valve replacement (AVR) (mean age 77 ± 5 years, mean log. EuroScore 12 ± 6%) were analyzed. Cerebral MRI studies were acquired one day before and within 6 days after the procedure. Standardized neurological assessment was performed preoperatively and every day postoperatively until discharge. Results: In 68% of the TAVI patients, new cerebral embolic lesions were detected by MRI. The maximum lesion size was 10 mm in 2 patients. Only one patient suffered from a permanent stroke. In the AVR group, 56% of the patients displayed new embolic lesions. In 4 patients, the maximum size of the lesion was 10 mm. No clinical neurological alterations were seen in this group. Differently from the TAVI group in the AVR group, lesions within the border zones of the cerebral arterial perfusion territories and cerebral microbleedings were more frequently seen. Conclusion: New embolic cerebral lesions could be detected by MRI in the majority of patients after TAVI as well as after AVR. Incidence was lower in the conventional surgical group but did not reach statistical significance. However after AVR increased microbleedings were seen.

Mapping of cerebral perfusion territories using territorial arterial spin labeling: techniques and clinical application

A knowledge of the exact cerebral perfusion territory which is supplied by any artery is of great importance in the understanding and diagnosis of cerebrovascular disease. The development and optimization of territorial arterial spin labeling (T-ASL) MRI techniques in the past two decades have made it possible to visualize and determine the cerebral perfusion territories in individual patients and, more importantly, to do so without contrast agents or otherwise invasive procedures. This review provides an overview of the development of ASL techniques that aim to visualize the general cerebral perfusion territories or the territory of a specific artery of interest. The first efforts of T-ASL with pulsed, continuous and pseudo-continuous techniques are summarized and subsequent clinical studies using T-ASL are highlighted. In the healthy population, the perfusion territories of the brain-feeding arteries are highly variable. This high variability requires special consideration in specific patient groups, such as patients with cerebrovascular disease, stroke, steno-occlusive disease of the large arteries and arteriovenous malformations. In the past, catheter angiography with selective contrast injection was the only available method to visualize the cerebral perfusion territories in vivo. Several T-ASL methods, sometimes referred to as regional perfusion imaging, are now available that can easily be combined with conventional brain MRI examinations to show the relationship between the cerebral perfusion territories, vascular anatomy and brain infarcts or other pathology. Increased availability of T-ASL techniques on clinical MRI scanners will allow radiologists and other clinicians to gain further knowledge of the relationship between vasculature and patient diagnosis and prognosis. Treatment decisions, such as surgical revascularization, may, in the near future, be guided by information provided by T-ASL MRI in close correlation with structural MRI and quantitative perfusion information.

Evaluation of the middle cerebral artery occlusion techniques in the rat by in-vitro 3-dimensional micro- and nano computed tomography

BackgroundAnimal models of focal cerebral ischemia are widely used in stroke research. The purpose of our study was to evaluate and compare the cerebral macro- and microvascular architecture of rats in two different models of permanent middle cerebral artery occlusion using an innovative quantitative micro- and nano-CT imaging technique.Methods4h of middle cerebral artery occlusion was performed in rats using the macrosphere method or the suture technique. After contrast perfusion, brains were isolated and scanned en-bloc using micro-CT (8 μm)3 or nano-CT at 500 nm3 voxel size to generate 3D images of the cerebral vasculature. The arterial vascular volume fraction and gray scale attenuation was determined and the significance of differences in measurements was tested with analysis of variance [ANOVA].ResultsMicro-CT provided quantitative information on vascular morphology. Micro- and nano-CT proved to visualize and differentiate vascular occlusion territories performed in both models of cerebral ischemia. The suture technique leads to a remarkable decrease in the intravascular volume fraction of the middle cerebral artery perfusion territory. Blocking the medial cerebral artery with macrospheres, the vascular volume fraction of the involved hemisphere decreased significantly (p < 0.001), independently of the number of macrospheres, and was comparable to the suture method. We established gray scale measurements by which focal cerebral ischemia could be radiographically categorized (p < 0.001). Nano-CT imaging demonstrates collateral perfusion related to different occluded vessel territories after macrosphere perfusion.ConclusionMicro- and Nano-CT imaging is feasible for analysis and differentiation of different models of focal cerebral ischemia in rats.

Relation Between Cerebral Perfusion Territories and Location of Cerebral Infarcts

The perfusion territories of the brain-feeding arteries are difficult to assess in vivo and therefore standard cerebral perfusion territory templates are often used to determine the relation between cerebral infarcts and the feeding vasculature. In the present study, we compared this infarct classification, using standard templates, with the individualized depiction of cerebral perfusion territories on MRI. The ethics committee of our institution approved the study protocol. A total of 159 patients (92 male, 67 female; mean age, 58.9 years) with first-time clinical symptoms of cerebral ischemia were included in the study. Diffusion-weighted imaging was used for depiction of the area of ischemia and the perfusion territories of the left internal carotid artery, right internal carotid artery, and vertebrobasilar arteries were visualized with territorial arterial spin labeling MRI. Infarct locations with respect to cerebral perfusion territories were evaluated with and without territorial arterial spin labeling MRI images. In 92% of the patients, the territorial arterial spin labeling images were of diagnostic quality. One hundred thirty-six patients showed areas of ischemia on diffusion-weighted images. The additional information from the territorial arterial spin labeling images changed the classification in 11% of the cortical or border zone infarcts (6 of 56), whereas no territorial changes were observed in lacunar, periventricular, cerebellar, and brainstem infarcts. The diagnostic information provided by perfusion territory imaging in patients with stroke is valuable for the classification of cortical and border zone infarcts, whereas no change of the textbook-based classification was observed for other infarct types.

Arterial spin labeling of cerebral perfusion territories using a separate labeling coil

To obtain cerebral perfusion territories of the left, the right, and the posterior circulation in humans with high signal-to-noise ratio (SNR) and robust delineation. Continuous arterial spin labeling (CASL) was implemented using a dedicated radio frequency (RF) coil, positioned over the neck, to label the major cerebral feeding arteries in humans. Selective labeling was achieved by flow-driven adiabatic fast passage and by tilting the longitudinal labeling gradient about the Y-axis by theta = +/- 60 degrees . Mean cerebral blood flow (CBF) values in gray matter (GM) and white matter (WM) were 74 +/- 13 mL . 100 g(-1) . minute(-1) and 14 +/- 13 mL . 100 g(-1) . minute(-1), respectively (N = 14). There were no signal differences between left and right hemispheres when theta = 0 degrees (P > 0.19), indicating efficient labeling of both hemispheres. When theta = +60 degrees , the signal in GM on the left hemisphere, 0.07 +/- 0.06%, was 92% lower than on the right hemisphere, 0.85 +/- 0.30% (P < 1 x 10(-9)), while for theta = -60 degrees , the signal in the right hemisphere, 0.16 +/- 0.13%, was 82% lower than on the contralateral side, 0.89 +/- 0.22% (P < 1 x 10(-10)). Similar attenuations were obtained in WM. Clear delineation of the left and right cerebral perfusion territories was obtained, allowing discrimination of the anterior and posterior circulation in each hemisphere.

Brain Perfusion Territory Imaging: Methods and Clinical Applications of Selective Arterial Spin-labeling MR Imaging

The ability to visualize perfusion territories in the brain is important for many clinical applications. The aim of this overview is to highlight the possibilities of selective arterial spin-labeling (ASL) magnetic resonance (MR) imaging techniques in the assessment of the perfusion territories of the cerebral arteries. In the past decade, the optimization of selective ASL MR techniques to image the cerebral perfusion territories has resulted in numerous labeling approaches and an increasing number of clinical applications. In this article, the methods and clinical applications of selective ASL MR imaging are described and the importance of perfusion territory information in studying cerebral hemodynamic changes in patients with cerebrovascular disease is shown. In specific patient groups with cerebrovascular disease, such as acute stroke, large artery steno-occlusive disease, and arteriovenous malformation, selective ASL MR imaging provides valuable hemodynamic information when added to current MR protocols. As a noninvasive tool for perfusion territory measurements, selective ASL may contribute to a better understanding of the relation between the vasculature, perfusion, and brain function.

Magnetic Resonance Imaging of Individual Cerebral Perfusion Territories Improves the Diagnosis of Embolic Stroke

This case study demonstrates the feasibility and diagnostic value of the oblique-plane arterial spin labeling method to visualize individual perfusion territories in a patient with embolic stroke. The perfusion territories obtained with this technique differed significantly from the standard anatomical situation. Imaging findings suggested that all acute embolic lesions in both hemispheres had arisen from one symptomatic internal carotid artery stenosis.

Measurement of cerebral perfusion territories using arterial spin labelling

The ability to assess the perfusion territories of major cerebral arteries can be a valuable asset to the diagnosis of a number of cerebrovascular diseases. Recently, several arterial spin labeling (ASL) techniques have been proposed for determining the cerebral perfusion territories of individual arteries by three different approaches: (1) using a dedicated labeling radio frequency (RF) coil; (2) applying selective inversion of spatially confined areas; (3) employing multidimensional RF pulses. Methods that use a separate labeling RF coil have high signal-to-noise ratio (SNR), low RF power deposition, and unrestricted three-dimensional coverage, but are mostly limited to separation of the left and right circulation, and do require extra hardware, which may limit their implementation in clinical systems. Alternatively, methods that utilize selective inversion have higher flexibility of implementation and higher arterial selectivity, but suffer from imaging artifacts resulting from interference between the labeling slab and the volume of interest. The goal of this review is to provide the reader with a critical survey of the different ASL approaches proposed to date for determining cerebral perfusion territories, by discussing the relative advantages and disadvantages of each technique, so as to serve as a guide for future refinement of this promising methodology.

Enhanced nitric oxide release during cortical spreading depression following infusion of glyceryl trinitrate in the anaesthetized cat.

Intravenous infusion of glyceryl trinitrate (GTN) into migraineurs induces an immediate headache followed by migraine. We studied the effect of GTN (0.25 microgram kg-1 min-1) on local cerebrovascular laser Doppler flux (rCBFLDF), artery diameter and NO concentration (selective NO microelectrode) in the pial middle cerebral artery perfusion territory of the anaesthetized cat, at rest and during cortical spreading depression (SD). GTN infusion induced a significant increase in pial artery diameter, rCBFLDF, and NO concentration. Following termination of infusion, NO concentrations remained significantly elevated above controls for 60 min, other parameters returned to baseline within 10 min (p < 0.05, ANOVA, post hoc Dunnett's multiple comparison procedure). Two hours after termination of infusion KCl-evoked SD was initiated. GTN-treated animals exhibited significantly (p < 0.05, Kruskal-Wallis) elevated SD-induced NO release compared to controls. All other parameters remained unaffected. Our results demonstrate that GTN induces a prolonged increase in local NO concentrations and enhances SD-induced NO release.

Cerebral vasoreactivity in unilateral carotid artery disease. A comparison of blood flow velocity and regional cerebral blood flow measurements.

Hemodynamic information obtained by assessing cerebral vasoreactivity is of clinical interest and may have prognostic significance in patients with occlusive carotid disease. The aim of this study was to compare the results of transcranial Doppler and regional cerebral blood flow studies when used to assess cerebral vasoreactivity. Blood flow velocities in both middle cerebral arteries and regional cerebral blood flow in their respective perfusion territories were compared in 52 patients with severe unilateral carotid stenosis or occlusion. The studies were first performed under basal conditions and repeated after the intravenous administration of 1 g acetazolamide. Asymmetry (normal compared with pathological side) in middle cerebral artery blood velocity increase was significantly greater than the asymmetry in cerebral blood flow increase in the perfusion territories of the arteries. A significant correlation (r = .63, P < .0001) was found between asymmetry in percent velocity increase and asymmetry in absolute cerebral blood flow increase. The two methods agreed in their assessment of either a normal or a reduced vasoreactivity in 38 subjects and disagreed in 14. In six of the latter patients, who had no evidence of cerebral infarction, the asymmetry in velocity increase was abnormal, whereas asymmetry in flow increase was assessed as normal. We found a good correlation between the asymmetry in regional cerebral blood flow increase in the middle cerebral artery perfusion territories and asymmetry in the velocity increase in the middle cerebral arteries after administration of acetazolamide. These results suggest that transcranial Doppler examination combined with the acetazolamide test may be used in clinical situations to assess cerebral vasoreactivity.

A comparison of transcranial Doppler and cerebral blood flow studies to assess cerebral vasoreactivity.

The aim of this study was to determine the ability of transcranial Doppler ultrasonography when used to assess cerebral vasoreactivity. The results of this method were compared with regional cerebral blood flow measurements. Forty-three patients with symptoms suggesting cerebrovascular disease took part. Transcranial Doppler findings in the middle cerebral arteries were compared with regional cerebral blood flow in the corresponding perfusion territories before and after acetazolamide administration. There was a significant positive correlation between the absolute increase in cerebral blood flow in milliliters per 100 g per minute and the percent increase in velocity (r = 0.63). The right-left, side-to-side difference of the acetazolamide response obtained by the two methods also showed a positive correlation (r = 0.80). Control limits obtained from healthy subjects were used for both the blood flow increase (absolute values and asymmetry in absolute values) and the velocity increase (percent increase and asymmetry in percent increase). The two methods then agreed in their evaluation of vasoreactivity in 74 (86%) of the 86 middle cerebral artery perfusion territories; 20 (23%) were assessed by both methods as having a reduced vasodilatory reserve. Eleven hemispheres with a slightly reduced regional cerebral blood flow response to acetazolamide were not detected by transcranial Doppler, whereas all territories with a marked reduction were identified by Doppler. Only one hemisphere with a normal cerebral blood flow increase after acetazolamide administration was assessed by Doppler as having reduced vasoreactivity. Transcranial Doppler and the acetazolamide test may be used in clinical situations to assess cerebral vasoreactivity.