Acetazolamide Test Research Articles

Does Intensive Management of Cerebral Hemodynamics and Atheromatous Aorta Reduce Stroke After Coronary Artery Surgery?

Atheromatous aorta and carotid artery disease are known predictors for stroke after coronary artery bypass grafting (CABG). The clinical significance of intracranial cerebral artery disease is not known. This study was designed to determine whether a therapeutic strategy based on perioperative detection of intracranial and extracranial occlusive cerebrovascular disease and atheromatous aorta could reduce perioperative stroke. We studied 485 patients who underwent isolated CABG. The control group was 247 patients who underwent standard-protocol CABG. The 238 subjects in the intervention group underwent preoperative magnetic resonance angiography of the head and neck and intraoperative epiaortic scanning. Cerebral hemodynamics were evaluated by single photon emission computed tomography and acetazolamide tests in patients with significant occlusive cerebrovascular disease. Surgical outcomes were compared. In the intervention group, magnetic resonance angiography detected significant intracranial or extracranial occlusive cerebrovascular disease, or both, in 40 patients. Prophylactic cerebrovascular interventions were performed in 7 patients who had disturbed cerebral hemodynamics. Aorta no-touch off-pump coronary artery bypass (OPCAB) was chosen intraoperatively in 37 patients with moderate to severe atheromatous aorta. The in-hospital stroke rate was 0.42% in the intervention group vs 2.8% in the control group (p = .068). A multivariate analysis revealed that the perioperative interventional protocol was the most powerful predictor of reduced risk of perioperative stroke (odds ratio, 0.023; 95% confidence interval, 0.001 to 0.469). Prophylactic cerebrovascular interventions and the selective use of aorta no-touch OPCAB can significantly reduce the incidence of perioperative stroke. Careful vascular evaluation before and during CABG can improve surgical outcomes.

Acceleration of cerebrovascular reactivity as a new supplemental TCD index in patients with severe carotid stenosis before and after carotid endarterectomy

Background and purpose: Cerebrovascular reactivity (CVR) examined by transcranial Doppler (TCD) is a useful tool for investigation of cerebrovascular reserve capacity of the normal and compromised brain. The aim of this study was to learn the acceleration of CVR as a possible additional index characterizing the process of cerebrovascular reserve recruitment and the application of this index in symptomatic and asymptomatic patients with severe unilateral carotid stenosis.Methods: Twenty-seven patients with severe unilateral internal carotid artery (ICA) stenosis were included in the study. TCD examination with acetazolamide test was used for the measurement of cerebrovascular reactivity before and after CEA. The acceleration (cm/s2) of CVR was calculated as ratio of ΔV before and after acetazolamide injection related to time of the velocity change.Results: The acceleration of CVR in patients with severe unilateral ICA stenosis before CEA was 0.03 ± 0.03 cm/s2 and after the operation was 0.07 ± 0.03 cm/s2 (p=0.001). CVR was 24.2 ± 20.4 and 42.9 ± 26% correspondently (p=0.01). The correlation index between CVR and acceleration was 0.86 and 0.5 before and after the surgery (p=0.009).Conclusions: The CVR acceleration may be used as a supplemental TCD index in evaluation of cerebrovascular reserve capacity.

Evaluation of Vasomotor Reactivity by Transcranial Doppler Sonography in Patients With Acute Stroke Who Have Symptomatic Intracranial and Extracranial Stenosis

In patients with large artery disease, determining the cerebral hemodynamic state and following its alterations may be a good marker for predicting long-term outcome. The aim of our study was to compare the changes in vasomotor reactivity (VMR) of patients with symptomatic intracranial and extracranial artery stenosis. We also examined whether VMR after stroke influences the long-term prognosis for these patients. Forty-one patients were included in the study. To determine the cerebral hemodynamic state, transcranial Doppler ultrasound examinations and acetazolamide tests were performed after acute stroke and repeated after 6 months. We compared the VMR on admission and at 6 months, together with changes in VMR, of the patients with symptomatic intracranial and extracranial artery stenosis. By calculating the Barthel index at 6 months, we examined whether VMR had an effect on an improvement in their quality of life. We observed a significantly higher initial VMR of the ipsilateral hemisphere in patients with intracranial stenosis (22.4 +/- 9.1 versus 13.4 +/- 12.8; P = .013). At 6 months, the VMR obtained from the ipsilateral hemisphere was better in patients with extracranial stenosis than in the patients with intracranial stenosis (P = .01). The ipsilateral VMR measured on admission showed a positive correlation with the Barthel index at 6 months (P = .007; r = 0.434). Our study showed that VMR in patients with acute stroke who have extracranial and intracranial artery stenosis measured by using a transcranial Doppler examination may have value in predicting long-term outcome.

ＰＥＴの可能性と限界―脳血管障害に対する血管拡張負荷試験の意義と新しい指標による脳循環評価の試み―

ＰＥＴの可能性と限界―脳血管障害に対する血管拡張負荷試験の意義と新しい指標による脳循環評価の試み―

Vasoreactivity in patients with periventricular white matter lucency.

Cerebral hypoperfusion has been evidenced in patients with periventricular white matter lucency (PWML), however, our knowledge is limited regarding vasoreactivity (VR) changes in these patients. Therefore, we compared the cerebral blood flow velocity (CBFV) responses during different vasoregulatory challenges in healthy volunteers, to those in patients with PWML. In 20 patients with PWML and in 20 healthy volunteers the VR of the middle cerebral artery (MCA) system was measured by analyzing the changes of CBFV during different stimulation paradigms (ventilation, tilting and acetazolamide tests). During transcranial Doppler (TCD) registration the systemic blood pressure, the expiratory partial CO(2) pressure (pCO(2)) and the electroencephalograph (EEG) were monitored. The relative velocity change was significantly smaller in the PWML group than in the normal control group during hypercapnia (16 +/- 12% vs 32 +/- 17%; P < 0.001) and this finding was confirmed by assessment of pCO(2)-corrected velocity change (4.7 +/- 3.7 cm/s/kPa vs 18.4 +/- 6.8 cm/s/KPa; P < 0.001). Although CBFV measurements during acetazolamide test tended to support these findings, the changes of other parameters measured did not reach the level of significance. One patient showed considerable orthostatic reaction (mean arterial blood pressure decrease by 70 mmHg) but it was not associated with significant changes in CBFV. Patients with PWML showed an impaired VR in the MCA flow territory supporting the concept of the microangiopathic origin of leukoaraiotic changes.

Acetazolamide as a vasodilatory stimulus in cerebrovascular diseases and in conditions affecting the cerebral vasculature.

Pathologic processes affecting the brain vessels may damage cerebral vasodilatory capacity. Early detection of cerebral dysfunction plays an important role in the prevention of cerebrovascular diseases. In recent decades acetazolamide (AZ) has frequently been used for this purpose. In the present work the mechanism of action and the previous studies are reviewed. The authors conclude that AZ tests are useful in cerebrovascular research. Further investigations are recommended to prove how impaired reserve capacity and reactivity influence the stroke risk in patients and whether these tests may indicate therapeutic interventions.

The cerebral hemodynamics of headache associated with sexual activity

Headache associated with sexual activity is an idiopathic headache disorder and regarded to be a vascular headache but no pathophysiological studies have been performed to date to elucidate the underlying mechanisms. We investigated 12 patients with the explosive type of sexual headache according to the criteria of the International Headache Society during a headache-free state by means of acetazolamide test and of stress Doppler sonography. Twelve age-matched migraine patients and 14 healthy subjects served as control groups. Changes of blood pressure, cerebral blood flow velocity (CBFV), and pulsatility index (PI) were evaluated. Patients with sexual headache showed a significantly higher increase of blood pressure during standardized physical exercise as compared to healthy subjects and migraine patients. Changes of CBFV by physical exercise were not different between the three examination groups. After 1 g acetazolamide, CBFV showed a significantly higher increase in patients with sexual headache (plus 66%±16%) than in healthy subjects (plus 46%±18%), and PI showed a significantly lower decrease as compared to healthy subjects and migraine patients. These data suggest that in patients with sexual headache the metabolic rather than the myogenic component of the cerebral vasoneuronal coupling is impaired.

Cerebral Haemodynamic Aspects of Severe Carotid Stenosis: Asymptomatic vs Symptomatic

Objectives: to compare cerebral haemodynamics in patients with asymptomatic and symptomatic severe (≥70%) internal carotid artery (ICA) stenosis.Methods: we assessed 195 consecutive patients, 116 with asymptomatic carotid stenosis (ACS) and 79 with symptomatic carotid stenosis (SCS). Using transcranial Doppler we assessed cerebral vasoreactivity (CVR) following acetazolamide test, the middle cerebral artery flow velocity ratio after/before carotid clamping (mv-MCA ratio), and the carotid back pressure (CBP) during crossclamping.Results: no significant differences between the two groups were demonstrated regarding CVR (47 vs 39%), mv-MCA ratio (50 vs 52%), or CBP (36 vs 44mmHg). However, in patients with contralateral ICA occlusion all three variables were significantly lower as compared to patients with patent contralateral ICA. Also patients who needed a shunt during surgery had significantly lower values of mv-MCA ratio and CBP. Patients who suffered peri-operative neurologic deficits (n=6; 3%) did not differ from patients who had an uneventful course.Conclusions: clinical state of ICA stenosis is independent of cerebral haemodynamics. Occluded contralateral ICA is more important for predicting cerebral ischaemia caused by carotid clamping. Finally, none of the haemodynamic parameters showed predictive value for peri-operative neurologic morbidity.

Use of technetium-99m hexamethylpropylene amine oxime SPET for the study of cerebral blood flow reactivity after acetazolamide infusion in patients with Behçet's disease.

The purpose of this study was to characterise the nature of the baseline perfusion defects found in patients with Behçet's disease using hexamethylpropylene amine oxime single-photon emission tomography in conjunction with acetazolamide test (Acz SPET). Eleven patients underwent both baseline and Acz SPET. Regions of interest (ROIs) were drawn on the areas with decreased perfusion (D-ROI) and, in the same section, on areas with normal perfusion (N-ROI). The ROIs were then repositioned on the corresponding section on Acz SPET. The mean ROI counts were then transformed into a perfusion index value (PIV) with reference to the global brain counts. In total we found 24 D-ROIs (17 in the cortical and 7 in subcortical grey matter). The influence of Acz infusion was selectively registered in the D-ROIs, where PIVs changed from 1.23+/-0.17 (baseline SPET) to 1.63+/-0.23 (Acz SPET) (P<0.001). No significant difference was seen in the N-ROIs (1.46+/-0.21 and 1.40+/-0.17, respectively, on baseline SPET and Acz SPET). Our results demonstrate that Acz infusion increases the regional cerebral blood flow within baseline grey matter perfusion defects. This finding suggests that baseline perfusion abnormalities could reflect a disconnection rather than local vasculitic involvement.

Is the acetazolamide test valid for quantitative assessment of maximal cerebral autoregulatory vasodilation? An experimental study.

The cerebral vasodilating effect of acetazolamide (ACZ) injection has been used as an index of the autoregulatory vasodilation (or cerebral perfusion reserve). The question of whether the ACZ test assesses the maximal autoregulatory vasodilating capacity is not definitely resolved. The effects of ACZ injection on this reserve at a dose producing maximal vasodilation have never been evaluated and may help to resolve this problem. The effect of ACZ injection on cerebral blood flow (CBF) autoregulation was tested in anesthetized rats. A pilot experiment evaluated the dose-effect relationship of injected ACZ, cumulative doses (n=4, group 1), and independent bolus doses (n=6, group 2). CBF was estimated by laser-Doppler flowmetry, and cerebrovascular resistance (CVR) was calculated from mean arterial blood pressure (MABP) and from CBF (expressed as a percentage of baseline CBF). A bolus of ACZ of 21 mg/kg produced the maximal cerebral vasodilation that could be obtained by ACZ administration. In the main experiment, MABP was lowered from 110 to 20 mm Hg by stepwise bleeding in 3 groups of 6 animals treated 10 minutes before bleeding by injection of saline (group 3), 7 mg/kg ACZ (group 4), or 21 mg/kg ACZ (group 5). The CVR-MABP relationship was linear in all groups, indicating that CBF autoregulation was still effective after ACZ administration. These results indicate that maximal ACZ-induced cerebral vasodilation is not quantitatively equivalent to maximal autoregulatory vasodilating capacity in anesthetized rats.

Influencia de la presión arterial en el estudio de la reactividad cerebrovascular en oclusiones carotídeas

Cerebrovascular reactivity (CVR) is the capacity of the cerebral microcirculation to increase cerebral blood flow on vasodilator stimulation. This is reduced in patients with carotid obstruction. The changes in arterial pressure produced whilst carrying out different tests for estimation of the CVR may affect its measurement by transcranial Doppler. To evaluate the concordance between the different methods for estimation of the CVR by transcranial Doppler in patients with carotid obstruction and to evaluate the importance of monitoring the arterial pressure during CVR tests. We evaluated 17 patients with internal carotid artery obstruction confirmed on arteriography. The CVR was determined by three different methods: apnea test. Breath-Holding Index (BHI) and intravenous acetazolamide test. During the tests of RCV the arterial pressure was monitored. We found that there was a reduction in the average basal rate of flow and of the pulsatile index on the obstructed side, with a statistically significant association in relation to the contralateral side (p < 0.001). There was good concordance between the different tests of CVR, with reduced CVR seen on the obstructed side as compared to the contralateral side (p < 0.001) for the different tests. However, this correlation was not seen in stenosis < 70%. During the apnea test changes in blood pressure occurred, with a tendency to increase in the systolic pressure. However, there were no significant changes in blood pressure during the acetazolamide test. There is good concordance in the CVR between the apnea, BHI and acetazolamide tests in carotid obstruction. Changes in arterial pressure occurred during the apnea and BHI tests. However, the acetazolamide test caused no change in arterial pressure.

Prematurity-associated nephrocalcinosis and kidney function in early childhood.

To assess the impact of prematurity-associated nephrocalcinosis on kidney function later in life, 20 premature children with neonatal nephrocalcinosis and 20 controls, matched for birth weight and postnatal age but without nephrocalcinosis, were examined (birth weight 905+/-209 vs. 957+/-226 g; study age 4.7+/-1.1 vs. 4.6+/-0.9 years). Distal tubular acidification capacity was measured with the oral acetazolamide test, in which the response was abnormal in 1 out of the 20 children with a history of nephrocalcinosis, but in none of the controls. Urinary calcium and beta(2)-microglobulin excretion were higher in the children with nephrocalcinosis, but no differences were found in fractional excretion of sodium and potassium or tubular reabsorption of phosphate. Estimated creatinine clearance was not different between the groups. Of the 6 children with nephrocalcinosis lasting beyond 2 years of age, 5 had had chronic lung disease neonatally and exhibited a tendency for compensated respiratory acidosis at the time of the examination. Neonatal nephrocalcinosis seems to lead to some signs of renal tubular dysfunction in early childhood of preterm infants. Glomerular function, however, appears not to be specifically disturbed by nephrocalcinosis.

Impaired Vasoreactivity of the Basilar Artery System in Patients with Brainstem Lacunar Infarcts

Background and Purpose: Diminished vasoreactivity (VR) has been evidenced in patients with hemispheric small vessel disease, however, there is no data regarding vertebrobasilar (VB) territory VR changes in patients with subcortical vascular encephalopathy located in the brainstem. Therefore, we compared the cerebral blood flow velocity (CBFV) responses of the VB system during different vasoregulatory challenges in healthy volunteers to those in patients with brainstem lacunar infarcts. Methods: In 20 patients with brainstem lacunar infarcts and in 10 healthy volunteers the VR of the VB system was measured by analyzing the CBFV changes during different stimulation paradigms (ventilation, tilting and acetazolamide tests). During transcranial Doppler registration the systemic blood pressure and the expiratory partial CO₂ pressure were monitored. Results: During hypercapnia the VR was significantly higher in the control group than in the patient group (10.1 ± 4.9 vs. 3.4 ± 5.0 cm/s/kPa, p = 0.0025). In a subgroup of patients with mean baseline CBFV <25 cm/s the VR was 1.5 ± 2.4 cm/ s/kPa, while patients with mean baseline CBFV >25 cm/s showed a significantly higher value (7.8 ± 6.9 cm/s/kPa). Furthermore, in patients with mean baseline CBFV <25 cm/s the pulsatility index was significantly higher than in patients with mean baseline CBFV >25 cm/s (1.11 ± 0.26 vs. 0.86 ± 0.19, p = 0.0325), reflecting significantly higher vascular resistance in the former group. Although CBFV measurements during tilting and acetazolamide tests tended to support these findings, they showed no significant differences between patients and controls. Conclusion: Patients with cerebral microangiopathy involving the brainstem showed impaired VR in the VB flow territory in association with baseline CBFV.

Regional cerebral blood flow single-photon emission tomography with 99mTc-HMPAO and the acetazolamide test in the evaluation of vascular and Alzheimer's dementia.

The diagnostic potential of technetium-99m hexamethylpropylene amine oxime (HMPAO) following systemic administration of the cerebral vasodilator acetazolamide (acetazolamide test) was evaluated by regional cerebral blood flow (rCBF) single-photon emission tomography (SPET) in patients with Alzheimer's disease (AD) or vascular dementia (VD). An initial, high-resolution SPET study was performed with 99mTc-HMPAO, and after 2 days the patients were re-evaluated with 99mTc-HMPAO following systemic administration of acetazolamide. Reconstructed SPET slices were evaluated visually and semiquantitatively by a semi-automatic rCBF map method. When 99mTc-HMPAO alone was used, bilateral hypoperfusion was found in the temporal and/or parietal regions in 33% (6/18) of the VD patients and in 70% (23/33) of the AD patients. The corresponding data obtained by quantitative evaluation were 41% (7/17) and 71% (15/21), respectively. The vascular reserve capacity, as determined with the acetazolamide test, was preserved visually in 22% (4/18) and quantitatively in 29% (5/17) of the VD patients, but in 73% (24/33) and 76% (16/21) of the AD patients. The differences in the perfusion patterns between the VD and AD patients were statistically significant (P<0.01, Fischer's exact test). Of the VD patients with hypoperfusion (bilateral temporal and/or parietal), 4/6 (67%, visual evaluation) and 4/7 (57%, quantitative evaluation) had a decreased vascular reserve capacity as determined with the acetazolamide test. In the AD group of patients the corresponding results were 3/23 (13%) and 4/15 (27%). It is concluded that the acetazolamide test is promising in rCBF SPET to differentiate VD from AD.

&lt;SUP&gt;133&lt;/SUP&gt;Xe SPECTによる定量的評価に基づいた慢性期内頸動脈系閉塞性病変に対するバイパス術の効果

To evaluate the efficacy of bypass surgery, we analyzed the clinical outcome and cerebral hemodynamics of patients treated with bypass surgery.Over a 3-year period, 21 patients were defined by clinical and laboratory criteria as suffering from hemodynamic cerebral ischemia. All patients had one or more episodes of focal cerebral ischemia due to unilateral internal carotid or middle cerebral artery occlusion. Computerized tomography scans either were normal or showed evidence of watershed infarction. The baseline cerebral blood flow (CBF) and cerebral vasodilatory capacity (CVC) were studied using 133Xe single-photon emission CT and acetazolamide test, and both were found to be significantly reduced in all patients. Based on these criteria, superficial temporal artery-middle cerebral artery anastomosis was performed. One patient suffered a postoperative stroke with complete recovery, resulting in a morbidity rate of 4.8%. Over a mean follow-up period of 20 months, no patient had another episode of cerebral ischemia. Follow-up studies of baseline CBF and CVC showed significant improvement of the latter while the former was essentially unchanged. In view of these findings, we conclude that bypass surgery constitutes appropriate therapy for patients with hemodynamic cerebral ischemia, defined using the strict selection criteria employed in this study.

Abstracts of Literature

Abstracts of Literature

Can cerebrovascular reactivity be assessed by dynamic susceptibility contrast-enhanced MRI?

The acetazolamide (ACZ) test is performed to evaluate the decrease in cerebral perfusion pressure (CPP) by investigation of vasomotor reactivity (VMR). Our aim was to study cerebral blood flow and blood volume changes induced by the ACZ test in healthy control subjects using dynamic susceptibility contrast-enhanced gradient-echo MRI (DSC-MRI). A FLASH sequence was used to produce susceptibility-weighted images during an intravenous injection of 0.1 mmol/kg gadopentetate dimeglumine (Gd-DTPA). After the first dynamic study, 1 g acetazolamide was given intravenously and 10 min later a second bolus of Gd-DTPA was injected. Using the indicator-dilution theory, relative cerebral blood volume and relative cerebral blood flow were estimated. In healthy subjects the ACZ test induced a significant increase in relative blood volume (from 80.5 +/- 10.7 to 113.4 +/- 11.9) and relative blood flow (from 5.73 +/- 0.96 to 7.5 +/- 0.97), symmetrically in the cerebral hemispheres. This approach might be promising in the understanding of cerebral haemodynamics in patients with vascular disorders.

Hand gripping and acetazolamide effect in normal persons and patients with carotid artery disease.

Transcranial Doppler measurement (TCD) of cerebrovascular reserve (CVR) is usually performed by the CO2 test, the acetazolamide test, or the breath-holding test. Since these tests are time-consuming and labor-intensive, alternative methods such as the hand-gripping test are of interest. Twenty-one normal persons and 25 patients with unilateral carotid artery disease were studied. Flow velocity changes in both middle cerebral arteries (MCAs) during bilateral hand gripping were measured by TCD and compared with acetazolamide test results. The increase in MCA mean flow velocity (FVmean) during hand gripping was 18.0 +/- 6.3% in normal persons; the increases in the post-stenotic MCA were 15.8 +/- 9.7% in all patients and 9.4 +/- 5.4% in patients with impaired CVR as determined by the acetazolamide test. Only in the group with impaired acetazolamide reactivity was the increase in the poststenotic MCA significantly lower compared to that in controls (p < 0.01) and to the contralateral, nonstenotic side (p < 0.01). Nevertheless the FVmean increases in both tests showed a weak, but significant correlation (r = 0.59, p < 0.01). All FVmean increases during hand gripping were significantly (p < 0.01) lower than those during the acetazolamide test. The test appears as a weaker stimulus for MCA blood flow velocity increase than the acetazolamide test. Thus, only a substantial reduction of acetazolamide reactivity leads to a reduced MCA FVmean increase using hand gripping. Although it is highly specific but less sensitive, hand gripping does not appear to be suitable as a screening measure of CVR, but might be useful in addition to standard tests.

Remote Effect of Brain Retraction on Regional Cerebral Blood Flow and Cerebrovascular Reserve on Single Photon Emission Computed Tomography

Background The purpose of this study is to evaluate the effect of brain retraction 1 year or more after intracranial aneurysm clipping, demonstrated by a regional cerebral blood flow (rCBF) imaging technique. Methods and Results rCBF and cerebrovascular reserve (CV) were evaluated in 40 patients 12–25 months after operation, using single photon emission computed tomography (SPECT) with Tc-99m-hexamethylpropylene amine oxime (HMPAO) combined with acetazolamide test. The images were analysed semiquantitatively, focusing on regions of interest (ROIs) chosen for places retracted during the operation. The regions of hypoperfusion in the retracted tissue were clearly visible in 26 cases. Assymmetry of measured activity, expressed in the Assymmetry Index, reached 12% (SEM ± 8). After injection of acetazolamide during hypercapnia, the assymmetry decreased. Conclusions The results confirm the negative role of brain retraction. However, these consequences seem to be diminished by good vasoreactivity.

Visualization of frontal postural hypoperfusion in patients with Takayasu arteritis wth upright 99Tcm-HMPAO brain SPET

Takayasu arteritis is a chronic inflammatory angiopathy involving the cerebral arteries. We performed upright and supine 99Tcm-HMPAO brain single photon emission tomography (SPET) to investigate the cerebral perfusion pattern in eight patients with Takayasu arteritis, and we compared the results with those acquired using 123I-IMP and acetazolamide in six patients. SPET images were evaluated visually and semi-quantitatively. Hypoperfusion was visually detected in all eight patients during the provocative upright test with 99Tcm-HMPAO, and in three of six tested using acetazolamide and 123I-IMP. Semiquantitative analysis revealed that the mean cortical-to-cerebellar ratio in the upright position was significantly changed compared to that in the supine position in the right frontal area (from 0.86 +/- 0.07 to 0.91 +/- 0.09; P < 0.05). Change was also seen in the left frontal area (from 0.85 +/- 0.08 to 0.91 +/- 0.08; P < 0.05). No significant change was seen in other cortical areas with the upright test or in any areas with the acetazolamide test. We postulate that reduced arterial compliance may cause frontal postural hypoperfusion in patients with Takayasu arteritis due to poor functioning of autoregulation and arterial stenosis or occlusion. We conclude that the provocative upright test with 99Tcm-HMPAO brain SPET can detect abnormal patterns of cerebral perfusion in patients with Takayasu arteritis that might be missed by brain SPET using 123I-IMP and acetazolamide.