A study of acetazolamide-induced changes in cerebral blood flow using 99mTc HMPAO SPECT in patients with cerebrovascular disease

Perfusion computed tomography evaluation of cerebral hemodynamic impairment in patients with unilateral chronic steno-occlusive disease: a comparison with the acetazolamide challenge 99mTc-hexamethylpropyleneamine oxime single-photon emission computed tomography

PURPOSE

The purpose of this study was to determine which pefusion computed tomography (PCT) parameter is the most valid predictor of cerebral vascular reserve (CVR) as determined by Tc-hexamethylpropyleneamine oxime single-photon emission computed tomography (SPECT).

METHODS

Single-photon emission computed tomography with acetazolamide challenge and PCT were used in 23 patients with unilateral steno-occlusive vascular disease. After coregistration of the PCT and SPECT images, we assessed the relationship between the PCT parameters and SPECT findings and the predictive values of the PCT parameters for decreased CVR.

RESULTS

All PCT parameters of cerebral blood flow, cerebral blood volume, and mean transit time (MTT) were significantly correlated with SPECT regional cerebral blood flow ratios (P < 0.01). The MTT values more strongly correlated with acetazolamide effect than with cerebral blood volume or cerebral blood flow (P < 0.001). The MTT difference (values in the pathological hemisphere minus the values in the contralateral hemisphere) was a threshold of 1.5 seconds, with a sensitivity of 88% and a specificity of 70% for predicting decreased CVR.

CONCLUSION

Mean transit time is the most predictive parameter for assessing decreased CVR in patients with unilateral steno-occlusive vascular disease.

Low cerebrovascular reserve capacity in long-term follow-up after subarachnoid hemorrhage

BACKGROUND

Intradural arteries formerly in vasospasm after subarachnoid hemorrhage (SAH) show structural changes that result in arterial wall thickening and luminal narrowing. To evaluate if these changes lead to maldistribution of cerebral perfusion and reduced cerebrovascular reserve capacity (CVRC) in surviving patients, a long-term follow-up study of 18 adult patients after SAH was performed.

METHODS

Eighteen patients were selected for the study, all had shown vasospasm after an early operation on a ruptured aneurysm, were in good neurological condition (GOS [Glasgow Outcome Score] 4 or 5 ), and had no residual infarcts. A technetium-99m-hexamethyl-propylenamine oxime (HMPAO) single-photon emission computed tomography was performed 15 to 73 months after SAH. To study CVRC, a second investigation after application of acetazolamide was performed 1 week later.

RESULTS

Single-photon emission computed tomography showed areas of focally reduced HMPAO uptake predominantly in the hemisphere ipsilateral to the vessels more affected by posthemorrhagic vasospasm. The thalamus and the basal ganglia, the frontal lobe, and the temporal lobe were the regions most frequently showing reduced uptake. The individual change of HMPAO uptake after acetazolamide application ranged from -7% to 44% (mean, 17% +/- 15%).

CONCLUSIONS

These results show a remarkable reduction of CVRC compared with findings in healthy individuals. Based on these new findings, further investigations focusing on CVRC in routine SAH follow-up are worth being considered.

Assessment of borderzone ischemia with a combined MR imaging-MR angiography-MR spectroscopy protocol

We attempted to assess whether magnetic resonance imaging (MRI)-MR angiography (MRA)-MR spectroscopy (MRS) measurements can be used in the differentiation of patients in whom severe carotid lesions result in chronically hypoperfused regions and in whom the collateral capacity is sufficient to maintain a normal cerebral blood flow. Sixty-six patients with severe stenosis of the internal carotid artery (ICA) and 19 control subjects underwent MRI, 1H MRS, and MRA. Anaerobic metabolic changes in the middle cerebral artery (MCA) territory were studied by assessing N-acetyl-L-aspartate (NAA)/choline and lactate/ NAA ratios. Quantitative flow was measured in the ICA, in the basilar artery, and in the MCA. Thirty-four patients had borderzone infarcts, 16 patients had territory infarcts, and 16 patients had no infarcts on MRI. Patients with border-zone infarcts had significantly reduced flow in the ICA (P < 0.001) and in the MCA (P < 0.05) and decreased NAA/ choline ratios (P < 0.001) in non-infarcted regions compared with control subjects (P < 0.001) but also compared with patients with territory infarcts (P < 0.05) and patients without infarcts (P < 0.05). Flow measurements in the ICA and MCA and metabolic measurements in the MCA territory can be applied to select patients in whom cerebral perfusion pressure is insufficient to maintain normal cellular integrity.

Flow-related anaerobic metabolic changes in patients with severe stenosis of the internal carotid artery

BACKGROUND AND PURPOSE

We sought to investigate whether the combination of blood flow measurements in the major cerebral arteries and measurements of cerebral metabolism can provide new insight into the hemodynamic effect of carotid lesions in patients with severe stenosis (> 70% reduction in diameter) of the internal carotid artery (ICA).

METHODS

Fifty-six patients with unilateral severe stenosis of the ICA and 14 control subjects underwent MR imaging, 1H MR spectroscopy, and MR angiography. Anaerobic metabolic changes were studied by assessing N-acetyl aspartate/choline and lactate/N-acetyl aspartate ratios in the symptomatic and asymptomatic hemispheres. Quantitative flow was measured in the common carotid arteries (CCAs), the ICAs, the basilar artery, and the middle cerebral arteries (MCAs).

RESULTS

Blood flow was significantly decreased in the CCA, ICA, and MCA on the ipsilateral side compared with the contralateral side. Flow in the basilar artery was increased, whereas flow in the contralateral MCA was decreased compared with control subjects. We found a significant correlation between anaerobic metabolic changes and the reduction in blood flow in the CCA, ICA, and MCA on the ipsilateral side.

CONCLUSIONS

This study shows that cerebral metabolism is less impaired in patients with relatively high flow in the major cerebral arteries on the ipsilateral side than in patients with relatively low flow on that side. The combination of MR spectroscopy and MR angiography can be of additional value in the understanding of cerebral hemodynamics and metabolism in patients with vascular disorders.

Is image subtraction necessary in the clinical interpretation of single-day split-dose stress cerebral perfusion single-photon emission tomography using technetium-99m compounds?

The aim of this study was to validate a simplified semiquantitative method of evaluating a single-day stress cerebral perfusion test to obtain cerebrovascular reserve capacity (CVRC) for routine clinical uses. A split-dose protocol was tested in 36 pairs of technetium-99m hexamethylpropylene amino oxime baseline (low dose) and acetazolamide (high dose) stress brain single-photon emission tomographic (SPET) studies from 16 patients with cerebrovascular disease. The images were displayed on a semiquantitative color scale with (corrected) and without (uncorrected) image subtraction, dose adjustment, and decay correction. The representative CVRC was determined by placing 3x3 pixel regions of interest on midthalamic and midcerebellar slices. The corrected and uncorrected relative changes in CVRC were correlated using linear regression. The relative changes of corrected (x) and uncorrected (y) CVRC by quantitative analysis were highly correlated in a linear fashion (y=0.67x+0.002, r=0.998, P<0.0005). As predicted by theory, the slope was related to the ratio of split dose and independent of ROI sampling. Single-day split-dose stress brain SPET can be accurately performed without image subtraction and complicated dose adjustment or decay correction for clinical studies.