Regional cerebral blood flow in patients with transient ischemic attacks studied by Xenon-133 inhalation and emission tomography

Total cerebral blood flow and total brain perfusion in the general population: the Rotterdam Scan Study

Reduced cerebral perfusion may contribute to the development of cerebrovascular and neurodegenerative diseases. Little is known on cerebral perfusion in the general population, as most measurement techniques are too invasive for application in large groups of healthy individuals. Total cerebral blood flow (tCBF) can be noninvasively measured by magnetic resonance imaging (MRI) but is highly correlated with brain volume. We calculated total brain perfusion by dividing tCBF by brain volume, and we investigated determinants of total brain perfusion in comparison with tCBF. Secondly, we studied whether persons with a low tCBF or low total brain perfusion have a larger volume of white matter lesions (WML). This study is based on 892 persons aged 60 to 91 years from the Rotterdam Study, a population-based cohort study. We performed two-dimensional (2D) phase-contrast MRI for tCBF measurement. Brain volume and WML volume were quantitatively assessed. Cardiovascular determinants were assessed by interview and physical examination. We assessed associations between cardiovascular determinants and flow measures with linear regression models, adjusted for age and sex. Associations between tCBF or total brain perfusion and WML volume were assessed using general linear models. We found that determinants of tCBF and total brain perfusion differed largely due to the large influence of brain volume on tCBF values. Persons with low total brain perfusion had a significantly larger WML volume compared with those with high total brain perfusion. Prospective studies are required to unravel whether hypoperfusion contributes to WML formation or that tissue damage, manifested by WML, leads to brain hypoperfusion.

Long-term changes of functional MRI-based brain function, behavioral status, and histopathology after transient focal cerebral ischemia in rats

BACKGROUND AND PURPOSE

The relation between recovery of brain function and neurological status after clinical and experimental cerebral ischemia is incompletely characterized. We assessed the evolution of ischemic injury, behavioral status, and brain activity at acute to chronic periods after transient middle cerebral artery occlusion (tMCAO) in rats.

METHODS

Male Sprague-Dawley rats were subjected to 20-minute tMCAO (n=10) or sham operation (n=10). Sensorimotor behavioral testing and multimodal (diffusion, perfusion, T2, and functional) MRI, as well as postmortem hematoxylin-eosin staining, were performed before and up to 21 days after tMCAO. MRI and histological parameters were evaluated in 5 regions of interest within the sensorimotor network. Diffusion, perfusion, and T2 lesion volumes were calculated according to previously established viability thresholds.

RESULTS

Diffusion and perfusion lesions were present during occlusion but disappeared completely and permanently within 30 minutes after reperfusion, with no T2 lesions seen. Functional MRI and behavioral deficits did not normalize until 1 and 21 days after tMCAO, respectively. Histology demonstrated selective neuronal cell death at 7 and 21 days after reperfusion.

CONCLUSIONS

Twenty-minute tMCAO produced distinct changes on multimodal MRI, histology, and behavioral parameters acutely and chronically. Normal findings on MRI after transient ischemia may not indicate normal tissue status, as behavioral and histological anomalies remain. Behavioral dysfunction persisting long after the recovery of MRI parameters may relate to the subtle neuronal damage seen on histology. Together, these results may help explain unremitting neurological deficits in stroke or transient ischemic attack patients with normal MRI findings.

Factors causing prolonged hypoperfusion after transient ischemic attack

Even during the symptom-free stages, patients with a TIA often experience cerebral blood flow disturbances. In order to evaluate the factors which cause this abnormality, we studied the cerebral blood flow disturbance, anatomy and clinical status in 21 patients after TIAs. The results of 99mTc-hexamethyl-propylene-amine oxime SPECT were compared with CT, cerebral angiogram, cerebrovascular risk factors and clinical findings to determine which factor is most responsible for the hypoperfusion of brain after TIA. The overall sensitivity rates in detecting a lesion were 67% in SPECT and 19% in CT. The hypoperfused area tended to be large in patients who had intracranial, severe stenotic, multiple, or hemodynamically significant arterial lesions on the ipsilateral side. No such relationships were found between other examinations. We conclude that hypoperfusion after TIA essentially reflects a continuous cerebral blood flow disturbance that can be attributed to atherosclerosis of the cerebral arteries, with subsequent embolic and/or hemodynamic cerebral ischemia, although there may be a variety of processes.

Blood flow asymmetry in carotid occlusive disease

Patterns of anterior border zone (ABZ) and middle cerebral artery (MCA) cerebral blood flow (CBF) asymmetry were readily seen during both normocapnic room air (RA) and induced hypercapnic (CO2) inhalation using fluoro-methane and a multislice, high-resolution positron scanner. Wilcoxon two-sample rank testing showed symptomatic-over-nonsymptomatic CBF ratios for unilateral greater than 75% carotid stenosis patients (n = 8) to be 1.05 +/- 0.07 (p less than 0.008 as compared with control of 0.97 +/- 0.02) ABZ RA, 0.98 +/- 0.11 ABZ Co2, 0.98 +/- 0.04 MCA RA, and 0.98 +/- 0.06 MCA CO2. Unilateral carotid occlusion patients (n = 8) had ratios of 0.90 +/- 0.16 ABZ RA, 0.81 +/- 0.19 (p less than 0.002) ABZ CO2, 0.90 +/- 0.12 and 0.89 +/- 0.13 for MCA RA and CO2, respectively (both p less than 0.008 as compared with control 0.99). These preliminary results suggest an upgrade of autoregulation (ie, very high ratio) in the ABZ of high-grade stenosis patients during normocapnia. CBF was preferentially higher on the symptomatic side and then either did not increase or paradoxically fell in response to hypercapnia. In comparison, carotid occlusion patients had low ABZ and MCA ratios during normocapnia, also unable to increase with hypercapnia. The fall in ratios from normocapnia to hypercapnia indicates that these areas, already subject to maximal vasodilation, fail to increase CBF or actually become hypoperfused following induced hypercapnia. These results aid in understanding the concept of "hemodynamic significance."

Transient ischemic attacks: an update

This is a review of extant concepts of transient ischemic attacks (TIAs), their definitions, prognostic significance, pathogenesis, physiology, and management. The natural history of TIAs depends upon the risk factors of the population group studied, so that therapeutic trials should be controlled and randomized and not dependent upon published natural history data. A strong association between TIAs and coronary artery disease has now been established. It may be difficult to establish the cause or pathogenesis of TIAs in any given patient in view of the relatively poor correlation between the patient's symptoms and location of arterial plaques. Recent studies have suggested mechanisms aside from impaired perfusion or embolization from carotid plaques or vertebral basilar disease. There are no proven indications for carotid endarterectomy, a procedure which has been excessively used in the United States, but presently ongoing prospective, randomized, controlled multi-center studies will likely resolve this important issue. Neither is there scientific validation for the use of long-term anticoagulants, but data support the efficacy of ASA in reducing the incidence of stroke and myocardial infarction in patients with TIAs.

Reduced regional cerebral blood flow in aged noninsulin-dependent diabetic patients with no history of cerebrovascular disease: evaluation by N-isopropyl-123I-p-iodoamphetamine with single-photon emission computed tomography

Regional cerebral blood flow was measured using N-isopropyl-123I-iodoamphetamine with single-photon emission computed tomography (CT) in 16 aged patients with noninsulin-dependent diabetes mellitus (NIDDM, average age 72.8 years, average fasting plasma glucose 7.7 mmol/L), and 12 nondiabetic subjects (71.6 years, 5.3 mmol/L). None had any history of a cerebrovascular accident. Systolic blood pressure (SBP), total cholesterol, and triglyceride levels did not differ between groups. Areas of hypoperfusion were observed in 14 diabetic patients (12 patients had multiple lesions) and in 6 nondiabetic subjects (3 had multiple lesions). Areas where radioactivity was greater than or equal to 65% of the maximum count of the slice was defined as a region with normal cerebral blood flow (region of interest A, ROI-A), and areas where the count was greater than or equal to 45% were defined as brain tissue regions other than ventricles (ROI-B). The average ROI-A/B ratio of 16 slices was used as a semiquantitative indicator of normal cerebral blood flow throughout the entire brain. Mean ROI-A/B ratio was 49.6 +/- 1.7% in the diabetic group, significantly lower than the 57.9 +/- 1.6% at the nondiabetic group (p less than 0.005). The ratio was inversely correlated with SBP (r = -0.61, p less than 0.05), total cholesterol (r = -0.51, p less than 0.05), and atherogenic index (r = -0.64, p less than 0.01), and was positively correlated with high-density lipoprotein (HDL) cholesterol (r = 0.51, p less than 0.05) in the diabetic, but not the nondiabetic group. These observations suggest that the age-related reduction in cerebral blood flow may be accelerated by a combination of hyperglycemia plus other risk factors for atherosclerosis.

An overview of the contribution of regional cerebral blood flow studies in cerebrovascular disease: is there a role for single photon emission computed tomography?

Regional cerebral blood flow (rCBF) findings and their application to cerebrovascular disease are reviewed. Although the coupling of cerebral blood flow and metabolism are best studied with positron emission tomography, single-photon emission computed tomography measurements of rCBF can contribute to patient management. Potential indications for the use of rCBF functional brain imaging include differential diagnosis, early prediction of late recovery in the late subacute and chronic phases of stroke (3 months or more postonset), and evaluation of vasospasm following subarachnoid hemorrhage.

Regional cerebral blood flow in chronic alcoholics measured by single photon emission computerized tomography

Regional cerebral blood flow (CBF) was measured by single photon emission computerized tomography of inhaled 133-Xe in 20 chronic alcoholic men. Mean CBF was 51 ml/(100 g x min) compared with 53 ml/(100 g x min) in 20 normals. Reduced cerebellar blood flow correlated both to structural abnormalities seen on CT scan and to cognitive dysfunction. Slight abnormalities of the regional CBF was observed in the alcoholics. They had a higher incidence of regional low flow areas than a control group. Low flow areas were found in frontal and posterior parts of the brain not only in patients with atrophia, but also in patients without CT abnormalities, suggesting neuronal dysfunction. The occurrence of regional low flow areas was associated with the severity of alcoholism, cerebral atrophy and intellectual impairment.

Computed tomography in patients with transient ischaemic attacks: when is a transient ischaemic attack not a transient ischaemic attack but a stroke?

In a prospective community-based study, 184 patients with transient ischaemic attacks (TIAs) were identified from a study population of about 105,000 between 1981 and 1986. Computed tomography (CT) was attempted in all those with cerebral ischaemic attacks (n = 152, 83%); patients with amaurosis fugax only (n = 32, 27%) were not scanned routinely. Scans were obtained in 120 (79%) of those with cerebral attacks and 12 (38%) of those with amaurosis fugax. The scans were reported by a neuroradiologist who was blinded to the patients' clinical features. Of 120 (27%:95% confidence interval 19-35) scans in patients with cerebral attacks, 32 showed a focal area of hypodensity or cortical loss, but in only 14 (12%:95% confidence interval 6-18) was this in an area of the brain appropriate to the patients' symptoms. There were no significant differences in the clinical features, the duration of attacks or the prognosis (i.e., risk of death, stroke or myocardial infarction) of patients with and without ischaemic lesions on CT. It is concluded that patients with clinically definite TIAs who have a presumed ischaemic and appropriately sited lesion on CT should not be re-classified as having had a stroke.

Cerebral blood flow mapping using stable xenon-enhanced CT in sickle cell cerebrovascular disease

The cerebral blood flow (CBF) of 25 patients with sickle cell cerebrovascular disease (SCCVD) was examined using a Xenon-CT flow mapping method. Brain CT and MR findings were correlated with those of the Xenon-CT flow studies. CBF defects on Xenon-CT correlated reasonably well with the areas of cortical infarctions on the MR images, but in 27% of the cases, flow defects were slightly larger than the areas of infarctions on the MR images. In deep watershed or basal ganglia infarctions, abnormal CBF was noted about the cerebral cortex near infarctions in 72% of the patients, regardless of infarction sizes on the MR images. However, decreased CBF was recognized in 4 of the 9 children whose MR images were virtually normal. Thus, the extent of flow depletion cannot be predicted accurately by MR imaging alone. Xenon-CT flow mapping proved a safe and reliable procedure for evaluation of the CBF of patients with SCCVD. Although this study is preliminary, it may have a potential in selecting patients for hypertransfusion therapy, as a noninvasive test and for following children with SCCVD during their therapy. Careful correlation of results of CBF with those of MR imaging or of CT is important for objective interpretations of flow mapping images.

Regional cerebral blood flow (rCBF) and cerebral vasoreactivity in patients with retinal ischaemic symptoms

Regional cerebral blood flow (rCBF) and cerebral vasoreactivity were assessed in 28 consecutive patients who presented with retinal ischaemic symptoms, without clinical or cerebral CT evidence of cerebral ischaemia. rCBF was measured using xenon-133 inhalation and single photon emission computed tomography before and 20 minutes after the intravenous administration of 1 g acetazolamide. The findings suggest that patients with retinal ischaemic symptoms alone due to carotid atherosclerosis often have a carotid lesion which is of haemodynamic significance with regard to cerebral perfusion and vasoreactivity. Furthermore, localized areas with reduced cerebral perfusion may also be present in some patients, without evidence of precerebral carotid occlusive disease.

Chronic cerebrovascular insufficiency on the xenon CT scan

Several investigators have described CT-negative low flow areas in TIA and stroke patients in the chronic phase. The emission tomographic SPECT image they employed has, in contrast to the xenon CT method, no direct relation to the x-ray transmission CT scan. The aim of our study was to study the phenomenon of CT-negative low flow areas using the xenon CT method, a method especially well suited for such cases. 57 xenon CT examinations were performed in 40 TIA patients. Flow data from brain tissue which appeared to be anatomically intact in a slice 5 cm above the canthomeatal plane were analyzed. In the TIA group, the flow in the gray matter was found to be significantly lower on the clinically affected side: symptomatic side, 61.8 +/- 14.7 ml/100 g/min; asymptomatic side, 66.4 +/- 15.8 ml/100 g/min (p less than 0.001). In the stroke group, the flow in the white matter was also affected; symptomatic side, 31.2 +/- 9.8 ml/100, g/min; asymptomatic side, 35.3 +/- 11.1 ml/100 g/min (p less than 0.01). Gray matter: symptomatic side, 56.1 +/- 11.4 ml/100 g/min; asymptomatic side, 66.0 +/- 11.0 ml/100 g/min (p less than 0.001). The findings indicate that the appearance of CT-negative low flow areas in TIA and stroke patients during the chronic phase is the rule rather than the exception. Flow adaptation to anatomic changes not discernible by CT can be differentiated from clinically relevant flow impairment only by testing the cerebrovascular reserve.

Long-term prognosis and quality of life after reversible cerebral ischemic attacks

The long-term prognosis and quality of life of 201 patients admitted to hospital with reversible ischemic attacks (RIA) were estimated in a prospective study. The median follow-up time was 58 months. Further RIAs were reported by 91 patients (45%) and 48 (24%) suffered a stroke. The risk of stroke was markedly higher in the first 6 months after RIA, after which the annual stroke rate was rather constant with an average of 4.8%, about 8 times higher than expected. The average annual mortality rate for the RIA patients was 5.9%, which is significantly higher than expected. Cardiovascular deaths accounted for more than half of all deaths, stroke for one fourth. Life-table analysis of subgroups disclosed a much more favorable prognosis for women under 60 years. High systolic blood pressure, diabetes, and previous myocardial infarction were identified as risk factors. The occurrence of RIA had significantly influenced the quality of life and occupational status for the majority of the patients, even for those who did not suffer a subsequent stroke. Decreased working capacity, general asthenia and fatigue and impaired memory were the most common complaints. We conclude that RIA may be a more serious vascular event than generally believed. Apart from carrying a substantial risk of stroke and death, even a single RIA can cause permanent psychological dysfunction influencing the quality of life.

Hemodynamic significance of internal carotid artery disease

Neurologic symptoms in the region of an internal carotid artery stenosis are considered to be embolic in most instances. Only in a subgroup has carotid occlusive disease with impairment of the collateral supply, caused a state of hemodynamic failure with marked reduction of perfusion pressure. Though unproven, it is reasonable to assume that without surgical intervention, the risk is higher than average for patients with hemodynamic failure. Equally, should there be any postoperative improvement of cerebral blood flow or neurologic deficits, it should be looked for in this group. Thus, it is necessary to distinguish those with low perfusion pressure from the population of patients with carotid artery disease. Preoperative clinical evaluation and direct visualization of the carotid bifurcation should be supplemented by indirect physiological tests which allow assessment of collateral perfusion. Examination of periorbital flow direction or oculoplethysmography could be used as a screening procedure. Negative tests most certainly rule out any severe pressure gradient across the stenosis, irrespective of the luminal reduction. A positive result, on the other hand, should be further quantified since most indirect tests become positive at relatively small pressure gradients. Studies of cerebral blood flow at rest and during cerebral vasodilation makes it possible to identify patients with severe reduction of cerebral perfusion pressure. Such hemodynamic failure of one hemisphere may be identified in most cases by a conventional non-invasive xenon-133 technique and stationary detectors. Smaller focal regions of hypoperfusion may be identified by computer emission tomography, either by the detection of single-photon emission or by paired detection of annihilation photons. Endarterectomy does improve cerebral hemodynamics in terms of increased flow through the reconstructed vessel and elimination of pressure gradients. The cerebral blood flow, though remains unchanged in the majority of patients, at least when measured at baseline. Only in those patients with a reduction in perfusion pressure can a significant improvement in baseline flow occur. Flow reserve determined by cerebral vasodilation, however, will improve in most patients with hemodynamic failure. In addition, some patients in the low-pressure group develop marked, but temporary, hyperperfusion after reconstruction of very high grade carotid stenosis. This is considered a result of chronic low perfusion pressure with subsequent loss of autoregulation, and autoregulatory control is first regained after some days.(ABSTRACT TRUNCATED AT 400 WORDS)

Computed tomography in reversible ischaemic attacks: clinical and prognostic correlations in a prospective study

Two hundred and nineteen patients admitted with reversible atherothrombotic ischaemic attacks were prospectively evaluated by computed tomography. Of these patients, 122 were diagnosed as suffering from transient ischaemic attacks, 58 from reversible ischaemic neurological deficits and 39 from reversible ischaemic neurological deficits with incomplete resolution. In 133 cases the ischaemic event affected the carotid system, in 63 the vertebrobasilar system and in 23 cases the system could not be determined. Brain infarctions were observed in 64 patients (29.2%), cerebral atrophy in 96 (44.4%) and dilatation of a ventricle in 17 (7.8%). The frequency of brain infarction was related to the duration of the neurological deficit, being 20.5% in those with transient ischaemic attacks, 37.9% in those with reversible ischaemic neurological deficits and 43.6% in patients with reversible ischaemic neurological deficits with incomplete resolution (P = 0.005). Ischaemic lesions were closely correlated with abnormalities on supra-aortic trunk angiography or Doppler ultrasonography. During an average follow-up period of 21 months, a higher percentage of recurrence was found in those patients with CT infarctions, but the difference was not significant.

Cerebral hemispheric and contralateral cerebellar hypoperfusion during a transient ischemic attack

We studied a 79-year-old woman within 3 h of the onset of a motor aphasia and a right hemiparesis. Single photon emission computed tomography (SPECT) showed a 24% decrease in the perfusion of the left middle cerebral artery territory and a 16% reduction in the perfusion of the right cerebellum. A mild naming difficulty was the neurological deficit at the end of the SPECT examination, and complete recovery was achieved within 24 h. Repeated SPECT study 10 days later was normal. This is the first report of focal hemispheric and contralateral cerebellar hypoperfusion in transient cerebral ischemia.

Cerebral hyperperfusion following carotid endarterectomy

Serial measurements of cerebral blood flow (CBF) were performed in 56 patients before and one to four times after uncomplicated carotid endarterectomy. The findings were related to the ratio between internal carotid artery (ICA) and common carotid artery (CCA) mean pressures. Within the 1st postoperative day CBF increased by a median of 37% in the ipsilateral and 33% in the contralateral hemisphere. Later recordings showed a gradual return of CBF toward the preoperative level. Sixteen patients with an ICA/CCA pressure ratio below 0.7 showed a significantly more pronounced and longer-lasting flow increase than did 40 patients with a ratio above this level. On Day 1, the median CBF increase in the ipsilateral hemisphere was 61% and 24% in the two groups, respectively (p less than 0.01). A significant improvement in side-to-side asymmetry, resulting from a higher gain in the ipsilateral hemisphere, occurred in the low pressure ratio group, while the hemispheric asymmetry on average was unchanged in the high pressure ratio group. This relative hyperemia was most pronounced 2 to 4 days following reconstruction. The marked hyperemia, absolute as well as relative, in patients with a low ICA/CCA pressure ratio suggests a temporary impairment of autoregulation. Special care should be taken to avoid postoperative hypertension in such patients, who typically have preoperative hypoperfusion, to avoid the occurrence of cerebral edema or hemorrhage.

Cerebral and cerebellar uptake of 99mTc-(d,1)-hexamethyl-propyleneamine oxime (HM-PAO) in patients with brain tumor studied by single photon emission computerized tomography

The cerebral and cerebellar distribution of 99mTc-(d,1)-hexamethylpropyleneamine oxime (HM-PAO) was investigated by means of a rotating gamma camera in 12 patients with cerebral glioma. Using the corresponding contralateral region as control, reduced uptake of HM-PAO in the tumor region was demonstrated in 10 of the 12 patients. Reduced blood flow in a brain area remote from a circumscribed lesion reflects reduced activation following the interruption of afferent nervous pathways. Reduced HM-PAO uptake indicative of such diaschisis was demonstrated in the visual cortex contralateral to homonymous hemianopia in the two patients with this deficit. In the three patients with the most marked hemiparesis, the cerebellar hemisphere contralateral to the tumor showed significantly reduced HM-PAO uptake indicative of crossed cerebellar diaschisis. SPECT using commonly available gamma cameras and 99mTc-HM-PAO seems capable of depicting reduced flow in functionally inactivated brain areas, and may be clinically interesting as an alternative to more specialized techniques for the investigation of local cerebral blood flow.

The effect of reconstructive vascular surgery on clinical status, quantitative EEG and cerebral blood flow in patients with cerebral ischaemia. A three month follow-up study in operated and unoperated stroke patients

Follow-up studies over a period of 3 months were carried out on 100 patients with a unilateral ischaemia in the territory of the middle cerebral artery. Twenty-six patients underwent an STA-MCA bypass operation and 23 patients, a carotid endarterectomy. Fifty-one unoperated patients served as a reference group. A clinical examination, quantitative electroencephalogram (qEEG) and cerebral blood flow study (CBF) were performed before, 2 weeks after and 3 months after surgery. In the unoperated patients these examinations were carried out shortly after admission, 3 weeks later and 3 months thereafter. In the unoperated group, a highly significant improvement of clinical score and qEEG was found, but there were no changes in CBF values. The bypass patients showed a transient deterioration of clinical score and qEEG after surgery. Further, over the 3 month post-operative period, the bypass patients and the endarterectomy patients showed no improvement in CBF and qEEG. Thus, a beneficial effect of reconstructive surgery over the period studied could not be demonstrated.

Carotid surgery, cognitive function, and cerebral blood flow in patients with transient ischemic attacks

Psychological testing, cerebral blood flow (CBF) measurement, and computed tomographic scan were performed before and 3 months after operation in 31 patients subjected to endarterectomy of the internal carotid artery (ICA) because of transient ischemic attacks and in 11 control patients operated on for atherosclerosis of the lower extremities. In preoperative psychological testing both carotid surgery patients and controls performed somewhat below the normal level for their age group. Postoperatively, cognitive functions improved in the carotid surgery group but not in the control group. The improvement was related to the laterality of the operation, being more marked in verbal tests in patients with left ICA operation and in visuospatial tests in patients with right ICA operation. Postoperatively regional CBF improved in 2 patients only. Hence the intellectual improvement could not be related to changes in CBF. Intellectual deterioration in patients with internal carotid atherosclerosis may be delayed or terminated by surgical abolition of the source of multiple cerebral embolizations.

Cerebral blood flow tomography with xenon-133

Cerebral blood flow (CBF) can be measured tomographically by inhalation of Xenon-133. The calculation is based on taking a sequence of tomograms during the wash-in and wash-out phase of the tracer. Due to the dynamic nature of the process, a highly sensitive and fast moving single photon emission computed tomograph (SPECT) is required. Two brain-dedicated SPECT systems designed for this purpose are mentioned, and the method is described with special reference to the limitations inherent in the soft energy of the 133Xe primary photons. CBF tomography can be used for a multitude of clinical and investigative purposes. This article discusses in particular its use for the selection of patients with carotid occlusion for extracranial/intracranial bypass surgery, for detection of severe arterial spasm after aneurysm bleeding, and for detection of low flow areas during severe migraine attacks. The use of other tracers for CBF tomography using SPECT is summarized with emphasis on the 99mTc chelates that freely pass the intact blood-brain barrier. The highly sensitive brain-dedicated SPECT systems described are a prerequisite for achieving high resolution tomograms with such tracers.

rCBF after TIA and during migraine attacks

TIA is usually caused by embolism from a carotid stenosis. The stenosis has no hemodynamic significance, but recent studies of regional cerebral blood flow have indicated that this occurs in a few cases. Traditionally, TIA are not considered to cause cerebral damage, but CT-studies have revealed a number of silent infarcts and rCBF measurements have shown even more persistent abnormalities of blood flow. In classic migraine, alterations of rCBF are completely different, indicating a mechanism progressing in the cerebral cortex, probably the spreading depression of Leao. Similar blood flow changes are not seen in common migraine, where tomographic rCBF determinations have been normal.

Regional cerebral blood flow in hemiparkinsonian patients. Emission computerized tomography of inhaled 133Xenon before and after levodopa

Regional and mean cerebral blood flow (rCBF, CBF) were measured by tomography of inhaled 133Xe in 18 hemiparkinsonian patients before and after levodopa (L-dopa). Baseline mean CBF was 55 ml/ (100 g X min) after an L-dopa-free interval of at least 10 h (range 10-13) and remained unchanged at 56.1 ml/ (100 g X min) after optimal clinical improvement was achieved by L-dopa. However, L-dopa reduced rCBF significantly (P less than 0.05) in the striatum contralateral to the symptomatic limbs. In patients with adverse reactions such as hyperkinesias and on/off symptoms, flow tended to increase bilaterally in striatum and often markedly in midline structures anatomically related to globus pallidus and thalamus. Compared with a normal population, the subcortical rCBF distribution was asymmetrical with a reduced flow (-18%) in the striatum contralateral to the symptomatic limbs and in midline structures anatomically related to globus pallidus and thalamus (-12%). Cortical CBF was inverse related to the duration of Parkinson's disease (P less than 0.05), probably reflecting an increasing mental deterioration with time.

Stable xenon CT blood flow mapping for evaluation of patients with extracranial-intracranial bypass surgery

Xenon computerized tomography (Xe CT) blood flow studies were conducted in 25 patients referred for a possible extracranial-intracranial bypass procedure for occlusive vascular disease in one or more extra- or intracranial vessels. These studies were helpful in selecting eight candidates for surgery. The Xe CT studies were performed at one or two brain levels using a prototype Xe CT system for measurement of cerebral blood flow which was designed in collaboration with the General Electric Co., and adapted for the GE 9800 scanner. In those patients selected to undergo operation, Xe CT demonstrated compromise of flow reserve regionally, globally, and/or in the watershed area. All eight patients who underwent the procedure showed a favorable clinical response postoperatively, and seven had a dramatic increase in flow. The 17 patients whose baseline CT studies showed no reduction of flow with the Xe CT method were not selected for surgery. All 25 patients have remained neurologically stable to date. Case studies of three of the eight patients undergoing bypass surgery are presented. This limited but consistent experience suggests that Xe CT blood flow mapping makes possible the recognition of brain regions in which flow reserves are compromised. This is due to the relatively high degree of spatial resolution that this technique provides and to the fact that mapping can be correlated directly with the anatomy. Used in combination with a careful clinical examination and an accurate medical history, this study method appears to be a useful guide in the selection of patients who are most at risk from hemodynamic instability and those who are most likely to benefit from flow-augmentation surgery.

Ophthalmopneumoplethysmography (OPG-Gee) without and with bypass-compression for quantification of hemodynamic significance of superficial temporal artery-middle cerebral artery (STA-MCA) anastomosis

The Extracranial-Intracranial (EC/IC) Bypass Procedure is a new method in order to try to increase the Intracranial Perfusion Pressure (ICPP). Postoperative patency of the bypass can be shown by means of Seldinger angiography. By this method no information however is obtained on the hemodynamic function of the bypass. OPG-Gee measures the Ophthalmic Artery Pressure (OAP) which is related to the ICPP. In this study OPG-Gee is performed without and subsequently with compression of the bypass. Quantification of the hemodynamic significance of the bypass is obtained by measuring the pressure decay in the ophthalmic arteries during this procedure. The Rest Pressure Difference (RPD), i.e. the pressure difference between the two ophthalmic arteries without bypass compression is measured. By subtracting the RPD from the BCD the remaining pressure is called the Net Bypass Pressure (NBP), i.e. the pressure difference, which the EC/IC bypass contributes to the ICPP. If, however, at constant systemic arterial blood pressure (SABP) the OAP drops during bypass compression on both sides, we hypothesize that the NBP is the sum of both drops, because, as a result of the interhemispheric steal mechanism, the less perfused hemisphere steals from the better perfused hemisphere. In a group of 40 patients OPG-Gee without and subsequently with bypass compression was applied. Twenty two of 40 OPG-Gee's showed NBP's of 4 mm of mercury or more (55%). In the group of 29 patients with unilateral internal carotid artery occlusion in 21 patients (72%) an NBP of 4 mm of mercury or more was found (mean of 13 mm of mercury).(ABSTRACT TRUNCATED AT 250 WORDS)

Serial measurement of regional cerebral blood flow in patients with SAH using 133Xe inhalation and emission computerized tomography

A noninvasive three-dimensional method for measuring cerebral blood flow (CBF), xenon-133 inhalation and emission computerized tomography, was used to investigate the CBF changes accompanying delayed neurological deterioration following subarachnoid hemorrhage (SAH). A total of 67 measurements were performed on 20 patients in Hunt and Hess' clinical Grades I to III in the first 21 days post SAH. Five patients with normal CBF tomograms on admission developed delayed neurological deficits in the 2nd week after hemorrhage, at which time repeat CBF tomograms in four patients revealed large areas of well defined regional flow decrease in the vascular territories of the anterior or middle cerebral arteries. Severe vasospasm was noted in three of these patients in whom arteriography was performed in the 2nd week post SAH. Diffuse bihemispheric CBF decreases were noted later in the course of delayed neurological deficits; however, measurements obtained soon after the onset of focal symptoms suggest that the only CBF decreases directly produced by vasospasm in Grade III patients are regional changes.

Hemodynamically significant stenosis of the internal carotid artery treated with endarterectomy. Case report

Repeated cerebral blood flow (CBF) measurements with xenon-133 inhalation and single photon emission tomography were performed in a patient suffering a minor stroke with subsequent orthostatic-provoked transient ischemic attacks (TIA's). Angiography revealed a thread-like internal carotid artery and an occluded external carotid artery on the side of the ischemic neurological symptoms. Computerized tomography and technetium-99m-pertechnetate brain scintigraphy 2 weeks after stroke were both normal. Before reconstructive vascular surgery, resting CBF showed a hypoperfused area corresponding to the clinical symptoms. Diamox (acetazolamide, 1 gm) increased CBF by 24% in the unaffected hemisphere, whereas even a slight decrease in flow ("steal") was seen in the maximally affected region. In contrast, theophylline (220 mg) reduced CBF in the unaffected hemisphere and caused a slight increase in the previously maximally hypoperfused area ("inverse steal"). After surgery, the flow pattern practically normalized and the TIA's disappeared. The CBF measurements before surgery and also after the injection of the vasoactive drugs indicated that focal hemodynamic insufficiency elicited the TIA's, and pointed at a low mean arterial blood pressure of about 35 mm Hg in the affected hemisphere. The perioperative finding of a mean blood pressure in the internal carotid artery of 31 mm Hg on the symptomatic side confirmed that the brain tissue had a severely reduced perfusion pressure. On clamping the artery, a stump pressure of 22 mm Hg and electroencephalogram flattening was noted, so a temporary internal shunt was inserted. The findings demonstrate that preoperative CBF measurements, including studies of the regional vasoreactivity, may identify patients with hemodynamic TIA's. These patients are at particular risk of developing cerebral ischemia during carotid endarterectomy, as any further compromise of the inflow may precipitate frank ischemia.

Evidence suggestive of diffuse brain damage following cardiac operations

In 37 patients regional cerebral blood flow (rCBF) was measured by single photon emission computerised tomography (SPECT) after inhalation of xenon-133 before and within the first 10 days after open heart surgery for acquired or congenital heart disease. None of the patients had motor deficits postoperatively and no focal abnormalities were disclosed by the rCBF tomograms. However, rCBF was generally reduced and mean CBF fell from a normal value of 53.5 to 44.7 ml/100 g X min (p less than 0.001). Changes in rCBF occurred uniformly throughout the brain. The reduction in CBF correlated positively with increasing years (p less than 0.05), duration of extracorporeal circulation (p less than 0.05), and low mean arterial blood pressure during the bypass (p less than 0.02). It was generally more pronounced after valve replacement than after coronary bypass (p less than 0.16). In 11 patients investigated 1 year after surgery CBF remained slightly reduced, 50.5 ml/100 g X min (p less than 0.05). No CBF reduction occurred in a control group of 15 patients who underwent carotid endarterectomy or extracranial-intracranial shunt operations. The findings are consistent with the suggestion that the extracorporeal circulation causes early postoperative central nervous system dysfunction.