A single photon dynamic computer assisted tomograph (DCAT) for imaging brain function in multiple cross sections

Regional cerebral blood flow in affective disorder

The results of two-dimensional cerebral blood flow (CBF) studies in depression and the results of measurements of regional CBF (rCBF) using single photon emission computerized tomography (SPECT) are briefly reviewed. A technical outline of both types of method is described. The majority of SPECT studies point to a decreased CBF in untreated patients with a tendency towards normalization, but other studies suggest that, following treatment, there is an increase above normal either from a decreased or an abnormally high initial level. One study has pointed to unipolar patients having lower flow in the right temporal and parietal lobes relative to normals, whereas non-endogenous patients did not differ significantly from normal controls. Bipolar depressives have been found to have higher flow values than normals in the parietal and temporal lobes in the left hemispheres. This relevant aspect or a possible relationship between type of depression and hemispheric asymmetry needs further study for full classification. Thus, most investigations designed to determine which brain structures might be involved in regulating affect have not been very successful, which may be a consequence of the biological heterogeneity of these disorders or of the limited spatial resolution of the techniques used for investigation. Even if some of these technical difficulties can be overcome with measurements of receptor kinetics supplemented, other biological variables that have proved valuable in psychiatry (such as rapid eye movement latency and biogenic amines) should be studied to find more precise biological markers for depressive illness.

Evoked potentials and cerebral blood flow in solvent induced psycho-organic syndrome

Epidemiological studies have provided evidence that neuropsychiatric symptoms are induced by long term exposure to solvents; individual diagnosis with psychometric tests, however, is not always possible (for example, when the patient has linguistic difficulties). Therefore evoked potentials and cerebral blood flow were studied in 50 patients occupationally exposed to solvents who were referred to our department and for whom a solvent induced psycho-organic syndrome was suspected. Degree of exposure was evaluated by its duration (mean 13.9, range 1 to 37 years) and its intensity (from an interview). At the group level, P22 and N35 latencies and amplitude N20-P22 of somatosensory evoked potentials were higher in cases than in controls (p < 0.05), whereas there was no difference for brainstem and visual evoked potentials, nor for hemispheric cerebral blood flow (but a higher distribution in the left occipital region was seen in patients, p < 0.05). Some parameters were linked to degree of exposure (amplitude N20-P22 of somatosensory evoked potentials, interpeak latency I-V of brainstem evoked potentials, distribution of cerebral blood flow in the internal frontal left region). At the individual level, these examinations were not of diagnostic value because sensitivity was low.

Motor activation by single-photon emission computed tomography. A comparison of xenon-133 and technetium-99m HM-PAO "split-dose" methods

Single-photon emission computed tomography (SPECT) was used to investigate the feasibility of the technetium 99m-hexamethylpropyleneamineoxime ( 99mTc HM-PAO) split-dose method to evidence changes in regional cerebral blood flow during a motor activation task, in comparison with a quantitative method using the inhalatory xenon-133. Four subjects were studied twice with both methods, at rest and during finger opposition movements. On the activated cerebral hemisphere, a significant increase in regional cerebral blood flow was observed over the motor cortical areas. The average increases were +28.1 +/- 5.6% for the xenon-133 method and +12.3 +/- 5.2% for the 99mTc HM-PAO method. By using the linearization algorithm for the 99mTc HM-PAO method, a mean increase of +22.5 +/- 8.9% was calculated. This study demonstrated that the split-dose method allows the motor activation SPECT studies with 99mTc HM-PAO to be done in a single session.

Cerebral blood flow in patients with dementia of Alzheimer's type

In the normal brain as well as in Alzheimer's disease (AD), regional cerebral blood flow (CBF) is coupled to metabolic demand and, therefore, changes in CBF reflect variations in neuronal metabolism. The use of radionuclide techniques, such as positron emission tomography (PET) and single photon emission computed tomography (SPECT), provides an accurate assessment of regional functional activity, i.e., CBF and metabolism, and could be very helpful for the differential diagnosis of AD. This disease is characterized by a decrease in global CBF and metabolism. When found, a symmetric bi-parieto-temporal CBF reduction is highly diagnostic for AD, despite the fact that a similar CBF pattern could also be observed in other types of dementia. Many AD patients with parieto-temporal flow reduction also have a diffuse flow reduction in the frontal cortical areas, particularly in advanced stages of the disease. Lateral CBF asymmetry is also very frequent; speech disorders are highly characteristic of left-sided flow reduction, while visuospatial apraxia is dominating in the right-sided cases. In advanced and severe cases of AD, CBF and metabolism tend to be more uniformly reduced throughout the cortex, sparing only the primary visual and sensory-motor cortices. PET and SPECT measurement of brain perfusion and metabolism has added a new dimension to the knowledge of dementia disorders, with a better differential diagnosis between AD and other forms of dementia. The correlation with neuropsychological data has also given new insight into the disease.

Reduced regional cerebral blood flow in Huntington's disease studied by SPECT

Regional cerebral blood flow (rCBF) was studied in 18 patients with Huntington's disease (HD) and 19 age- and sex-matched controls with high resolution single photon emission computerised tomography (SPECT), using Tc-99m-HMPAO. Significant reductions in tracer uptake were found in the caudate and lentiform nuclei (20 and 8%) and in the cerebral cortex, especially in the frontal and parietal areas (11-13%). No significant reductions were found in the thalamus, mesial temporal cortex, and occipital cortex. Fourteen patients had neuropsychological testing. Relationship between rCBF and cognitive function was tested by regression analysis. A linear relationship was found between test scores of Wisconsin Card Sorting Test, Picture Arrangement Test and blood flow in the caudate nucleus. Other tests of cognitive function (Block Design Test, Face and Word Recognition Test, Street Fragmented Pictures Test, and Similarities Test) correlated better with flow in the cortical regions believed to be involved in solving those particular tests. These findings indicate, that blood flow is reduced in both cortical and subcortical structures in symptomatic HD, and that both reductions in cortical and subcortical blood flow may be related to cognitive function in HD.

A comparison of regional cerebral blood flow and middle cerebral artery blood flow velocities: simultaneous measurements in healthy subjects

Blood flow velocities were measured in both middle cerebral arteries (MCAs) of 36 healthy subjects using transcranial Doppler ultrasound. Measurements were first made using a hand-held probe. Velocities were then studied bilaterally with fixed probes under resting conditions and during simultaneous regional CBF (rCBF) measurements. A significant (p < 0.05) positive correlation was found between MCA flow velocities and rCBF in the estimated perfusion territory of this artery. The correlation coefficient was highest when the measurements were performed simultaneously (p < 0.001) or when velocities recorded with a hand-held probe were adjusted to take into account the significant velocity increase induced by the CBF study situation. The increased velocities during CBF measurements cannot be fully explained by the moderate but significant PCO2 increase. Other possible mechanisms are increased blood flow due to mental activation or MCA vasoconstriction secondary to stimulation of the sympathetic nervous system. The effect of mental activation and PCO2 differences should therefore be considered when comparing the results of repeated velocity and CBF measurements.

Cerebral vasodilation after the thermocoagulation of the trigeminal ganglion in humans

The resulting changes in the regional cerebral blood flow of 18 patients suffering from idiopathic trigeminal neuralgia and treated by selective thermocoagulation of the trigeminal ganglion were measured by xenon-133 emission tomography. One hour after thermal stimulation, there was an asymmetric increase (P < 0.05) in cerebral blood flow, with a 14.7% mean increase in the ipsilateral cerebral hemisphere (P < 0.001) and a 12.7% mean increase in the contralateral side (P < 0.01). The increase in regional cerebral blood flow was not uniform but was most marked in the ipsilateral middle cerebral artery territory (P < 0.001). There was a slight decrease in cerebellar blood flow, but the reduction in the ipsilateral cerebellar lobe was less than that in the contralateral lobe (P < 0.01). The topography of the most significant changes coincided with that of the innervation of the cerebral vessels by the trigeminal nerve. Several mechanisms are involved in the increase in regional cerebral blood flow, including overall nonspecific activation of the central nervous system and local mechanisms associated with the trigeminal-vascular system.

The capillary network: a link between IVIM and classical perfusion

MR measurements based on motion encoding gradients, such as intravoxel incoherent motion imaging, could provide, in principle, information on flowing blood volume and blood velocity. This note shows that, in addition, the knowledge of the capillary network organization may provide a link between these measurements and those obtained by conventional and MR perfusion techniques based on tracer uptake by tissues.

Increased cerebral blood flow in anemic patients on long-term hemodialytic treatment

CBF was measured in 15 patients on chronic hemodialytic treatment. CBF was measured with xenon-133 inhalation using single photon emission tomography. In addition, computerized tomography (CT) and a neurological examination were done prior to hemodialysis. Mean CBF was 66.2 +/- 17.3 (SD) ml 100 g-1 min-1, which was significantly higher (t-test, p less than 0.05) than for an age-matched control group (54.7 +/- 10.2 ml 100 g-1 min-1). However, the hematocrit for the patients was considerably lower, 0.30 +/- 0.07, as compared to 0.43 +/- 0.03 in the controls. A significant negative correlation was observed between CBF and the hematocrit (y = -1.79x + 120.7, r = -0.71, p less than 0.01). Calculating CBF from this equation in the dialyzed patients using a hematocrit of 0.43 yielded a mean CBF value of 43.7 ml 100 g-1 min-1, i.e., 20% below the expected. Two patients showed a focal CBF decrease. CT showed central or cortical atrophy in five patients, and two had small hypodense lesions. The neurological examination revealed slight to moderate dementia in seven cases. Although mean CBF was found to be increased by 21% as compared to the control group, an even higher CBF level would have been expected to outweigh the decreased oxygen carrying capacity of the blood. The findings suggest a lowered metabolic demand of the brain tissue, probably due to subtle brain damage.

The use of acetazolamide-enhanced regional cerebral blood flow measurement to predict risk to arteriovenous malformation patients

Regional hemodynamic disturbances may complicate the treatment of certain cerebral arteriovenous malformations (AVM) and occasionally produce life-threatening situations. Acetazolamide-enhanced quantitative regional cerebral blood flow studies were performed preoperatively in 35 patients to determine if patterns of vasoreactivity could be identified that might be markers for postoperative morbidity. Ipsilateral and contralateral regions of hypoperfusion were identified on resting studies, and a steal index was calculated by dividing the regional cerebral blood flow in the steal region by the flow in a normal cerebellar region. Flow in these regions of interest was again quantitated after the administration of acetazolamide, a known cerebral vasodilator. A delta value was calculated by subtracting the resting index values from the acetazolamide indices. Abnormally enhanced vasoreactivity (vasodilation) to acetazolamide stimulation was noted in these threatened territories in AVM that had perforating vessel feeding and angiographic steal phenomena, that developed hyperemic disturbances, and that resulted in poor outcomes. These findings call into question traditional theories of AVM-related hemodynamic decompensation and suggest unique smooth muscle derangements in cerebral vasculature in some AVM patients.

Regional cerebral blood flow in normal man during insulin-induced hypoglycemia and in the recovery period following glucose infusion

The effect of moderate hypoglycemia (p-glucose, 2.0 +/- 0.3 mmol/L; mean +/- SD) on regional cerebral blood flow (rCBF) was studied in a group of 10 healthy, right-handed men (aged 23 to 28 years) using an intravenous xenon 133 single photon emission computed tomography technique (SPECT). After 10 minutes of hypoglycemia, global CBF had increased to 46.3 +/- 9.6 mL/100 g/min compared with the initial normoglycemic flow of 38.6 +/- 6.8 mL/100 g/min (P less than .01). The relative distribution of the rCBF changed significantly (P less than .05, ANOVA) from before to during hypoglycemia. Of the 10 regions analyzed, the highest increments in rCBF during hypoglycemia were found in the frontal (21.5% +/- 15.2%) and parietal (20.6% +/- 14.2%) lobes, and the lowest (10.7% +/- 9.4%) were found in the pons/brainstem regions. The increase in rCBF persisted for 15 minutes after normalization of blood glucose. The persisting high flow after hypoglycemia affected all regions, but a further 10.1% +/- 7.2% increase was observed in the pons/brainstem area (P less than .05). The CBF was significantly higher in the right compared with the left hemisphere (2.8%, 1.2%, and 3.9%, respectively; P less than .05) in all measurements. A decrease in brain volume was found at the final examination, compared with the hypoglycemic state (2.6%; P less than .05). It is concluded that moderate hypoglycemia leads to a marked increase in CBF and in the relative distribution of rCBF, which persists in the immediate period after normalization of the blood glucose level.

Potential language and attentional networks revealed through factor analysis of rCBF data measured with SPECT

We used changes in regional cerebral blood flow (rCBF) to disclose regions involved in central auditory and language processing in the normal brain. rCBF was quantified with a fast-rotating, single-photon emission computerized tomograph (SPECT) and inhalation of 133Xe. rCBF data were obtained simultaneously from parallel, transverse slices of the brain. The lower slice was positioned to include both Broca's and Wernicke's areas. The upper slice included regions generally regarded by neurobehaviorists as less related to primary auditory or linguistic functions. We presented three types of auditory stimuli to ten healthy, young volunteers: (a) diotically presented Danish speech, (b) dichotic word stimulation, and (c) white noise. Wilcoxon's signed ranks sum test revealed increased rCBF in language-related areas of cortex, viz., Wernicke's area and its right-sided homologous area as well as in Broca's area (left hemisphere), when subjects listened to narrative speech, compared to white noise (baseline). No significant rCBF differences were detected with this test during dichotic stimulation vs. white noise. A more sophisticated statistical method (factor analysis) disclosed patterns of functionally intercorrelated regions. The factor analysis reduced the highly intercorrelated rCBF measures from 28 regions of interest to a set of three independent factors. These factors accounted for 77% of the total variation in rCBF values. These three factors appeared to represent statistical analogues of independent brain networks involved in (I) auditory/linguistic, (II) attentional, and (III) visual imaging activity.

Crossed hemispheric diaschisis in unilateral cerebellar lesions

BACKGROUND AND PURPOSE

We studied 12 patients with unilateral cerebellar hemorrhage to look at its effect on regional cerebral blood flow.

METHODS

We used single-photon emission computed tomography by continuous inhalation of xenon-133. The blood flow was quantified in the cerebellum and in nine areas of interest on the slice passing through the basal ganglia.

RESULTS

The comparison of the blood flow values of the patients and control subjects showed a significant reduction in the contralateral hemisphere of the patients, predominantly in the frontal region and in the lenticular nucleus of the contralateral hemisphere but also in the anterointernal frontal area of the ipsilateral hemisphere. The analysis of the asymmetry indexes revealed in the same way significant differences between patients and control subjects in the frontal cortex and in the lenticular nucleus.

CONCLUSIONS

These results provided concordant evidence suggesting a blood flow reduction in the contralateral hemisphere. This phenomenon of "crossed hemispheric diaschisis" is probably related to the interruption of cerebellocortical tracts.

Regional cerebral blood flow after long-term exposure to carbon disulfide

Sixteen former rayon viscose workers were investigated four years after the exposure to carbon disulfide was discontinued. Median age was 58 years (range 43-65 years), median exposure time was 17 years (range 10-35 years). Encephalopathy was diagnosed in altogether 14 workers. To further explore pathophysiological mechanisms, cerebrovascular investigations were employed. Doppler ultrasound examination of the precerebral vessels in 15 workers showed a slight stenosis of the left internal carotid artery in one. Regional cerebral blood flow investigation (rCBF) with single photon emission computerized tomography (SPECT) with Xenon-133 gas was performed in 14. There was no significant difference from a control group. Regional side-to-side asymmetries beyond reference limits were demonstrated in eight workers. The abnormalities were modest, but may indicate a tendency toward focal blood flow disturbances in workers with long-term exposure to carbon disulfide.

The effect of ketanserin on cerebral blood flow and cerebrovascular CO2 reactivity in healthy volunteers

The effect of the anti-hypertensive agent ketanserin on the cerebral blood flow (CBF) and the cerebrovascular CO2 reactivity was examined in 10 healthy volunteers. Ketanserin was administered as an intravenous bolus of 10 mg followed by an infusion of 6 mg/h. Before administration CBF was measured by single photon emission computerized tomography (SPECT) of inhaled 133Xenon. Then arterial CO2 tension was subsequently decreased by voluntary hyperventilation and increased by breathing an air/CO2 mixture. The relative changes in CBF induced by the changes in arterial CO2 tension were estimated by the cerebral arterio-venous oxygen content difference method. One hour following the start of ketanserin infusion the SPECT measurement and CO2 manipulations were repeated. The CO2 reactivity (expressed as the slope of the regression line of the linear relation between CBF and PaCO2), was unchanged, i.e. 3.2%/0.1 kPa before ketanserin and 4.1%/0.1 kPa during ketanserin, respectively. Using regression lines from a semi-logarithmic plot the CO2 reactivity was also unchanged 3.4%/0.1 kPa and 3.5%/0.1 kPa, respectively. Ketanserin did not change CBF. The cerebral oxygen metabolism (CMRO2) was decreased 19% one hour after the start of infusion of ketanserin. In conclusion administration of ketanserin in a clinically relevant dose to healthy volunteers does not change the regional CBF not the cerebrovascular CO2 reactivity, but a decrease in CMRO2 was observed. However further studies are needed to clarify whether ketanserin in fact has a depressing effect on CMRO2 or whether the different results are caused by methodological errors or stochastic variation.

Functional imaging of the brain using single photon emission computerized tomography (SPECT)

The use of tracers is an important technique available for studying cerebral function. Changes in 'signal' are large, but as a result of its photon limited nature, the measurement of this signal is limited: spatially, temporally and in terms of accuracy. The most commonly used single photon (SPECT) system (as apposed to positron) is that with a rotating gamma camera, although multi-headed devices and special purpose rings are now also commonly available. The problems of obtaining good functional information are however identical. Firstly the devices need to be optimised in terms of resolution and sensitivity. Secondly several sources of error, notably those associated with scatter, attenuation and limited spatial resolution, need to be corrected, with the aim of obtaining quantitative estimates of radioactivity concentration. Finally such quantitative estimates need to be converted into meaningful estimates of physiological variables by use of an appropriate model. The general aim of many SPECT measurements is to estimate blood flow for example using Tc-99m labelled HMPAO as a tracer. Good results have been obtained in many clinical conditions: stroke, dementia, tumour and epilepsy, for example. Many other tracers are also available, for example to measure density of receptor sites. The use of SPECT in conjunction with other techniques after image registration is suggested as being an essential tool in extracting maximal clinical information.

Focal reductions of cerebral blood flow in amyotrophic lateral sclerosis: a [99mTc]-d,l-HMPAO SPECT study

We investigated regional cerebral blood flow (rCBF) using the [99mTc]-d,l-HMPAO technique with brain dedicated high resolution single photon emission computer tomography (SPECT) in 14 consecutive patients with amyotrophic lateral sclerosis (ALS), median age 62 years (45-77). Global CBF, expressed in % relative to the cerebellum, was significantly lower (P less than 0.05) in the ALS group (80.5 +/- 6.7%) than in the control group of 14 age-matched healthy volunteers (87.0 +/- 7.5%). Eight patients (57%) had abnormal rCBF distribution maps with reduced flow, primarily in the frontal lobes. Three of the 8 patients with abnormal rCBF had mild to moderate dementia and another one had mild aphasia. None of the patients with normal rCBF distribution maps had dementia. In the group of ALS patients as a whole rCBF was significantly reduced in the frontal cortex, the hippocampus, and the central white matter. We conclude that reduced rCBF, primarily in the frontal lobes, is a frequent finding in patients with ALS. The decreased rCBF may be associated with cognitive deficits and is most likely caused by neuronal degeneration and reduced metabolic needs.

Perfusion mapping with Tc-HMPAO in cerebral haematomas

The cerebral distribution of HMPAO was mapped tomographically by SPECT in 20 patients with an intra cerebral haematoma. The images were assessed visually and by an analysis of an asymmetry index (AI) for various cerebral areas. Visual inspection identified the lesion in each of the 20 cases. Reduced tracer activity and abnormal AI were consistent findings. Remote effects (diaschisis) were also observed in the adjacent (19 cases) and frontal (14 cases) cortex, and in the controlateral cerebellum (16 cases). Sequential studies at 60, 150 and 300 minutes in 10 patients showed remarkably stable patterns. HMPAO maps were compared with cerebral blood flow (CBF) measured with 133 Xenon (133Xe) in eight cases. The two methods showed similar results in the region of a lesion, but remote effects were more obvious with the 133Xe in two patients.

Effect of ketanserin on cerebral blood flow autoregulation in healthy volunteers

The effect of a clinically relevant dose of ketanserin (10 mg as a bolus followed by an infusion of 6 mg/h) on cerebral blood flow (CBF) and CBF autoregulation was examined in 12 healthy volunteers. Changes in CBF were estimated by the cerebral arteriovenous-oxygen saturation difference method, while mean arterial blood pressure (MABP) was increased by norepinephrine and decreased by ganglionic blockade (trimethaphan camphosulphonate) combined with lower body negative pressure one hour after the infusion of ketanserin. During ketanserin infusion, MABP fell insignificantly by 2.5 mmHg (6 to -2), while CBF rose insignificantly by 5 ml/100 g/min. Autoregulation was preserved in all volunteers. CO2-correction factors from 0 to 4.6% CBF/0.1 kPa were used. The lower limit of CBF autoregulation was 82 mmHg (80-86) with an SE of 3 mmHg (1-5) similar to a previous control group of healthy volunteers. Aside from a major decrease in MABP in one subject, no adverse side effects were observed. The present study shows that CBF autoregulation is maintained during ketanserin infusion.

Glycerol injection into the trigeminal ganglion provokes a selective increase in human cerebral blood flow

Fourteen patients suffering from idiopathic trigeminal neuralgia (refractory to medication) were treated by injection of glycerol into the trigeminal ganglion. The changes in cerebral blood flow (CBF) after glycerol injection were quantified by intravenous 133Xe emission tomography. There was a significant 11% (P less than 0.01) increase in ipsilateral CBF and an 8% (P less than 0.05) increase in contralateral CBF 1 h after glycerol injection. The interhemispheric difference was significant (P less than 0.05). The increase was significantly greater in the ipsilateral internal carotid territory, in the anterior cerebral artery and middle cerebral artery territories (superficial (P less than 0.05), deep territories (P less than 0.001]. We suggest that these changes are due to the release of substance P and/or calcitonin gene-related peptide, from terminals of the trigeminal-vascular system during glycerol injection.

99mTc-d,l-HMPAO and SPECT of the brain in normal aging

Single photon emission computed tomography (SPECT) with 99mTc-d,l-hexamethylpropyleneamine oxime (99mTc-d,l-HMPAO) was used to determine global and regional CBF in 53 healthy subjects aged 21-83 years. For the whole group, global CBF normalized to the cerebellum was 86.4% +/- 8.4 (SD). The contribution of age, sex, and atrophy to variations in global CBF was studied using stepwise multiple regression analysis. There was a significant negative correlation of global CBF with subjective ratings of cortical atrophy, but not with ratings of ventricular size, Evans ratio, sex, or age. In a subgroup of 33 subjects, in whom volumetric measurements of atrophy were performed, cortical atrophy was the only significant determinant for global CBF, accounting for 27% of its variance. Mean global CBF as measured with the 133Xe inhalation technique and SPECT was 54 +/- 9 ml/100 g/min and did not correlate significantly with age. There was a preferential decline of CBF in the frontal cortex with advancing age. The side-to-side asymmetry of several regions of interest increased with age. A method was described for estimation of subcortical CBF, which decreased with advancing cortical atrophy. The relative area of the subcortical low-flow region increased with age. These results are useful in distinguishing the effects of age and simple atrophy from disease effects, when the 99mTc-d,l-HMPAO method is used.

The acute effect of nimodipine on cerebral blood flow, its CO2 reactivity, and cerebral oxygen metabolism in human volunteers

The present study was undertaken in 8 healthy volunteers to examine the effect of a clinically relevant dose of nimodipine (NIM) (15 and 30 microgram/kg/h) on CBF, its CO2 reactivity, and CMRO2. Mean arterial blood pressure (MABP) was measured intra-arterially. Regional CBF was measured by SPECT of inhaled Xenon-133. During the CO2 reactivity tests changes in CBF were estimated by the arterio-venous-oxygen-difference method. Median CBF was 52 ml/100 g/min (48-53) with a normal regional distribution, and median baseline MABP was 96 mmHg (92-99). MABP was slightly reduced, by 8 mmHg (7-9), and 9 mmHg (4-11) after infusion of NIM for 2 and 4 hours, respectively. CBF, however, remained constant, although correction for changes in PaCO2, revealed a slight increase after 4 hours (p = 0.08). CMRO2 was 3.5 ml/100g/min (3.2-3.5) and was not changed by the infusion of NIM. At arterial CO2 tensions ranging from 4.0 to 6.5 Kpa the CO2 reactivity was 3.0% CBF/0.1 kPa (2.6-3.7) and decreased significantly to 2.6% CBF/0.1 kPa (1.8-3.2) after the infusion of NIM for 3 hours (p = 0.02). The median slope of the LnCBFsat/PaCO2 relationship was 1.5 at baseline compared to 1.3 after NIM (p less than 0.01). No side effects were observed. The present study shows a decreased CO2 of the cerebral vessels and a maintained coupling of CBF and CMRO2 during the infusion of nimodipine.

Traumatic occlusion of the internal carotid artery in a healthy young male: effects on the regional cerebral blood flow

The effects of acute right internal carotid artery occlusion in a previously healthy young male, was studied over a period of 10 months, with angiography, TransCranial Doppler ultrasonography (TCD) and SPECT-rCBF. A clinically observed inability to meet increased metabolic demand in the right hemisphere was concommitant to a decreased Pulsatility Index (PI) in the right middle cerebral artery (MCA). Autoregulation studies showed almost dilatation of the resistance vessels in the right middle cerebral artery territory, at rest. A decreased blood flow velocity, in the right middle cerebral artery 7 months after the accident, suggesting a decreased rCBF, could not be confirmed by SPECT-rCBF studies. This finding strongly cautions against interpretation of chronical blood flow velocity changes in terms of changes in regional blood flow. The present study shows the benefits in the combined use of angiography, SPECT-rCBF, and TCD.

An MRI perfusion model incorporating nonequilibrium exchange between vascular and extravascular compartments

A model of MRI signal intensity which is a function of perfusion is developed based upon the assumption that biological tissue can be represented by a blood and tissue compartment. The longitudinal magnetization is derived from the Bloch equations which are modified to model the magnetization in both the blood and tissue as a function of the following physiological parameters: blood flow velocity; perfusion fraction, which in the model is parameterized in terms of the ratio of the cross-sectional areas of the tissue and blood compartments; diffusion; rate of exchange between the blood and extravascular tissue compartments. Simulations of slice profiles excited by a repetitive sequence of 90 degrees slice-selective pulses show that the signal intensity in the blood and tissue compartments are modulated by the physiological parameters. A key factor in the modulation of the MRI signal is a time-of-flight effect whereby unexcited spins perfuse the excited region and exchange with blood and tissue compartments, thus immediately increasing the slice signal intensity but also delaying the spin exits from the slice, thereby decreasing their contribution to slice signal intensity in future repetitive pulse measurements.

The cerebellum participates in mental activity: tomographic measurements of regional cerebral blood flow

Measurements in man of regional cerebral blood flow (rCBF) have demonstrated a number of cortical and subcortical events coupled to sensory stimulation or motor performance. It has also been shown that local activity changes take place in the cortex during 'pure' mental activity such as motor imagery (unaccompanied by sensory input or motor output). Thus, our group has previously shown that imagination of hand movements gives predominantly a frontal cortical rCBF activation while the corresponding hand movement activates the rolandic hand area mainly. In this paper we report tomographic rCBF measurements with a 133-Xenon SPECT technique during imagined tennis movements and silent counting. Both procedures gave rise to a significant cerebellar activation in addition to cortical rCBF changes. Apparently, the cerebellum may participate in pure mental activity. It possibly plays a role for the temporal organization of neuronal events related to cognition.

The effect of the benzodiazepine antagonist flumazenil on regional cerebral blood flow in human volunteers

The influence of the benzodiazepine antagonist flumazenil on regional cerebral blood flow (rCBF) was investigated in ten healthy, alert volunteers. The design was a randomized, placebo-controlled, double-blind, cross-over study. rCBF was measured by 133-Xe inhalation and single photon emission computerized tomography, SPECT, immediately before, and 5 and 35 min after intravenous injection of flumazenil 1.0 mg or placebo. In addition, mean arterial blood pressures or PaCO2, rCBF were analysed for changes in various regions of interest (RoI). No alterations were found either in the global CBF or in rCBF in RoI after flumazenil injection. The results showed that a clinically active dose of flumazenil did not directly affect the cerebral circulation in the normal brain and indicated absence of significant intrinsic activity of the drug.

Instrumentation and computers for brain single photon emission computed tomography

Cerebral single-photon emission computed tomography (SPECT) requires attention to the instrumentation because of the anatomical location of the head at one end of the body, with a generally narrower diameter than the rest of the body. For a number of years, there have been SPECT units designed especially for head work, as well as general-purpose units that have performed well in imaging the head. The current emphasis on cerebral perfusion, using either agents that wash in and out with blood flow or agents that reflect blood flow in their static distribution, has allowed a concentration on imaging hardware and computer hardware and software for this purpose.

Single photon tomography in Alzheimer's disease and the dementias

Measurements of brain blood flow has evolved over the past 50 years, and during the latter half of that time radionuclide techniques have been used to study this important function. Using Xenon 133 and scintillation multiprobe systems, several teams of investigators measured regional cerebral blood flow (rCBF), and noted that under many circumstances it could be equated with local brain physiological activity. The dementias were investigated using the scintillation multiprobe method, and posterior flow deficits were described in patients who were thought to have Alzheimer's disease. The multiprobe technique gave way first to planar, and then tomographic imaging, with initial favorable results achieved by positron emission tomography (PET). Soon investigators learned to measure rCBF with single-photon emission computed tomography (SPECT) using high-sensitivity systems and 133Xe as a tracer, or high-resolution systems with 123I-iodoamphetamine (IMP), and later, 99mTc-HMPAO. Three-dimensional tomographic imaging shows to advantage the flow patterns that characterize Alzheimer's disease, with rCBF reductions in temporal, parietal, and sometimes frontal areas, as opposed to randomly distributed deficits in multiinfarct dementia, reduced frontal flow in entities such as Pick's disease, and others. Herein we will review our own experience with high-sensitivity rCBF SPECT in 119 patients with dementia, and with high-resolution SPECT, using a new, three-camera scanner and 99mTc-HMPAO in an additional 39 patients. SPECT rCBF study of patients with dementia and Alzheimer's disease, will aid in separating patients with untreatable Alzheimer's from those patients who may have treatable causes of dementia, and will be useful in evaluating experimental drugs for the treatment of Alzheimer's disease.

Comparison of [99mTc]HMPAO SPECT with [18F]fluoromethane PET in cerebrovascular disease

Positron emission tomography (PET) of [18F]fluoromethane (FM) and single-photon emission tomography (SPECT) of [99mTc]hexamethylpropyleneamine oxime (HMPAO) were performed under identical conditions within 2 h in 22 patients suffering from cerebrovascular disease (8 ischemic infarction, 2 intracerebral hemorrhages, 7 transient ischemic attacks, and 5 multi-infarct syndrome). While gross pathological changes could be seen in the images of either procedure, focal abnormalities corresponding to transient ischemic deficits or to lesions in multi-infarct syndrome and areas of functional deactivation were sometimes missed on SPECT images. Overall, HMPAO SPECT images showed less contrast between high and low activity regions than the FM PET images, and differences between lesions and contralateral regions were less pronounced (6.4 vs 13.3% difference). Regional cerebral blood flow (rCBF) was calculated from FM PET studies in 14 large territorial regions and the pathological lesion, and the regional values relative to mean flow were compared to the relative HMPAO uptake in an identical set of regions defined on the SPECT images. Among individual patients, the Spearman rank-correlation coefficient between relative rCBF and HMPAO uptake varied between 0.48 and 0.89, with a mean of 0.70. While an underestimation of high flow with SPECT--which was demonstrated in a curvilinear relationship between all relative regional PET and SPECT values--could be corrected by linearization taking into account HMPAO efflux from the brain before metabolic trapping, correspondence of SPECT data with PET rCBF values was not improved since this procedure also increased the variance in high flow areas. In the cerebellum, however, a high HMPAO uptake in SPECT always overestimated CBF in relation to forebrain values; this finding might be due to high capillary density in the cerebellum. The differences observed between SPECT and PET data may be explained by technical and physical properties of the methods and by the incomplete first-pass extraction of HMPAO. Additionally, HMPAO or its metabolites may leak through a damaged blood-brain barrier (as observed in one infarct and in the surrounding of hemorrhages), impairing the contrast between lesion and normal tissue. The presented data indicate that the quantification of rCBF by HMPAO SPECT is limited.

Neuroimaging in child and adolescent psychiatry

Although less well studied in child and adolescent psychiatry than in adult psychiatry, brain imaging has significantly altered psychiatric research and practice. This review focuses on the modalities that are used to image the brain. These include structural imaging techniques of computer tomography (CT) and magnetic resonance imaging (MRI), as well as functional imaging techniques of computed electroencephalography (CEEG), positron emission tomography (PET), and single photon emission computed tomography (SPECT). The technologies are reviewed, strengths and weaknesses of modalities discussed, and research progress reported.

Hypofrontality and cognitive impairment in schizophrenia: dynamic single-photon tomography and neuropsychological assessment of schizophrenic brain function

Regional cerebral blood flow (rCBF) was assessed in 40 chronic male schizophrenic patients (20 medicated, 20 unmedicated) and 31 matched normal controls with Dynamic Single-photon Emission Computed Tomography (D-SPECT). Blind analyses of normalized color-coded tomograms revealed significant bifrontal and bitemporal rCBF deficits in the patient group. Frontal flow deficits were most prominent in paranoid patients (n = 21) and right temporal deficits were most prominent in nonparanoid patients (n = 19). These relative regional declines were observed within the context of significantly elevated hemispheric blood flow in schizophrenics compared with controls. Reduced left frontal rCBF was associated with neuropsychological impairment on the Wisconsin Card Sorting Test and Luria-Nebraska Battery. Increased hemispheric CBF was correlated with the presence of positive schizophrenic symptoms. Medication status was unrelated to rCBF. These findings demonstrate that hypofrontality has important implications for cognitive function in some schizophrenic individuals.

Acetazolamide effects on cerebral blood flow in acute reversible ischemia

Cerebral blood flow (CBF) was studied in 4 patients with acute reversible ischemia (RIND). To test the ischemic areas' vasoreactivity, CBF was measured by the Xenon-133 inhalation method, before and after acetazolamide injected intravenously. At the baseline CBF study, 3 patients presented hypoperfused areas while one patient had increased CBF over the affected hemisphere. The acetazolamide test, showed in this latter case a "steal phenomenon" while in the other 3 an increase of perfusion was evidenced, in areas of normal flow, as well as in areas with reduced flow. These results suggest that in the acute phase of patients with RIND, when brain regions of hypoperfusion and neurological signs are still present, the vasomotor response may be preserved.

The development of an epileptogenic focus. A case study with 99mTc-HMPAO SPECT

A patient is described who developed complex partial seizures with secondary generalization 3 years after a severe viral encephalitis with a CT and EEG identified lesion in the left insular cortex and its surrounding structures. When the seizures first occurred CT and MRI as well as repeated interictal conventional EEG recordings were entirely normal. Single photon emission computed tomography (SPECT), however, revealed an area of increased 99mTc-hexamethyl propyleneamine oxime (HMPAO) uptake in the left insular cortex. After anticonvulsive therapy the seizures and the SPECT findings disappeared. 99mTc-HMPAO SPECT is a highly sensitive method for the demonstration of functional alterations in brain tissue. It can improve diagnosis of epilepsy and may provide additional information to monitor anticonvulsive therapy.

Hemodilution increases cerebral blood flow in acute ischemic stroke

We measured cerebral blood flow in 10 consecutive, but selected, patients with acute ischemic stroke (less than 48 hours after onset) before and after hemodilution. Cerebral blood flow was measured by xenon-133 inhalation and emission tomography, and only patients with focal hypoperfusion in clinically relevant areas were included. Hemodilution was done according to the hematocrit level: for a hematocrit greater than or equal to 42%, 500 ml whole blood was drawn and replaced by the same volume of dextran 40; for a hematocrit between 37% and 42%, only 250 ml whole blood was drawn and replaced by 500 cc of dextran 40. Mean hematocrit was reduced by 16%, from 46 +/- 5% (SD) to 39 +/- 5% (SD) (p less than 0.001). Cerebral blood flow increased in both hemispheres by an average of 20.9% (p less than 0.001). Regional cerebral blood flow increased in the ischemic areas in all cases, on an average of 21.4 +/- 12.0% (SD) (p less than 0.001). In three patients, a significant redistribution of flow in favor of the hypoperfused areas was observed, and in six patients, the fractional cerebral blood flow increase in the hypoperfused areas was of the same magnitude as in the remainder of the brain. In the last patient, cerebral blood flow increased relatively less in the ischemic areas. Our findings show that cerebral blood flow increases in the ischemic areas after hemodilution therapy in stroke patients. The marked regional cerebral blood flow increase seen in some patients could imply an improved oxygen delivery to the ischemic tissue.

Influence of nimodipine on cerebral blood flow in human cerebral ischaemia

Cerebral blood flow (CBF) was measured by xenon-133 inhalation and single photon emission computerized tomography (SPECT) in 7 patients with acute cerebral ischaemia prior to and 30 min after intravenous infusion of nimodipine (1 mg). Neurological examination, CT and CBF study were performed no later than 6 h after the onset of symptoms. Regional perfusion abnormalities were seen in all patients when the CT scan was still normal. Follow-up CT revealed low-density areas roughly corresponding to the core of the perfusion defect. Nimodipine infusion significantly decreased the mean arterial blood pressure (P less than 0.01), while PaCO2 and clinical symptoms remained unchanged. A significant CBF improvement (P less than 0.05) after nimodipine was seen in the border zone of the ischaemic infarct but not in the core of the lesion or in the unaffected contralateral hemisphere.

Brain morphology and regional cerebral blood flow in anorexia nervosa

Cranial computed tomography (CT) was performed in 12 patients with anorexia nervosa, revealing that the majority of the patients displayed ventricular dilatation and/or sulcal widening. In addition, regional cerebral blood flow (rCBF) was measured at admission and once again after weight gain, using xenon-133 dynamic single-photon emission tomography (dSPECT). The mean flow rates assessed at the first examination did not significantly differ from those assessed at the second examination and from those of a control group. There was a significant inverse relationship between the size of the cerebrospinal fluid spaces and the cerebral blood flow in the anorectics; a decrease in ventricular size after weight gain was associated with an increase in cerebral blood flow in this area. This finding, however, has to be interpreted with caution, as partial volume effects render the flow rates ambiguous in brain areas, which, in addition to neuronal tissue, also include ventricular and sulcal structures.

SPECT study of cerebral blood flow reactivity after acetazolamide in patients with transient ischemic attacks

We investigated 15 patients with one or more transient ischemic attacks (TIAs) in the internal carotid artery territory within the month following the most recent TIA. Cerebral blood flow (CBF) was measured by single-photon emission computed tomography, using intravenous xenon-133 before and after injection of 1 g acetazolamide. Six patients had severe carotid stenosis or occlusion; the other nine patients had no significant carotid lesions. Twenty age-matched volunteers free of neurologic symptoms or history were used as controls. Mean CBF in the sylvian region was not significantly different between patients and controls. Seven patients exhibited a focal hypoperfusion at rest in the symptomatic hemisphere, and their hypoperfused areas were hyporeactive after administration of acetazolamide. Seven other patients exhibited hyporeactive areas after acetazolamide administration while their CBF tomograms at rest were normal. Thus, CBF abnormalities were detected in 14 of the 15 patients. Our findings suggest that CBF measured early after acetazolamide administration could be useful to confirm the clinical diagnosis of TIA. In the nine patients with no significant lesion of the internal carotid artery, the areas of hypoperfusion were small and were probably related to the focal ischemic event. In the six patients with severe lesions of the internal carotid artery, abnormalities were of variable size and intensity but were often large and pronounced. The discrepancy between these two subgroups of patients could be ascribed to the hemodynamic influence of the internal carotid artery lesions. Moreover, our findings may provide some insight into the pathophysiology of TIAs.

Regional cerebral function and blood flow: complementary single photon emission computed tomography of the brain using xenon-133 and [123I]iodoamphetamine

Regional cerebral function and blood flow can be imaged using isopropyl[123I]iodoamphetamine (IMP), or 133Xe (DSPECT), respectively. Both of these essentially non-invasive, quantitative, methods are suitable for many nuclear medicine laboratories. This study assessed the in vivo information about intracerebral disease provided by IMP and DSPECT techniques to determine the optimal diagnostic use of these modalities. Single photon emission computed tomograms of 53 subjects were acquired using similar displays for IMP and DSPECT data. Lobar tracer distributions were graded by three experienced observers and analyzed using a kappa statistic to eliminate chance agreements. Overall, both IMP and DSPECT had similar patterns. However, while similar, one or the other technique often displayed abnormalities not present on both. Although technical factors may account for some differences between the modalities, a case of arteriovenous malformation proves that discordant findings can result directly from tracer localization properties. Thus at least some discordances provide truly complementary diagnostic information lacking in either single study taken alone.

The retention of [99mTc]-d,l-HM-PAO in the human brain after intracarotid bolus injection: a kinetic analysis

[99mTc]-d,l-HM-PAO (HM-PAO) was injected rapidly into the internal carotid artery and its retention in the brain was recorded by external scintillation cameras in eight human subjects. A model is described based on three compartments: the lipophilic tracer in the blood pool of the brain, the lipophilic tracer inside the brain, and the hydrophilic form retained in the brain. The retention curve initially drops abruptly, corresponding to the nonextracted fraction of the injectate leaving the brain; it then falls exponentially towards the asymptotic level of the fractional steady-state retention R. Cerebral blood flow (F) was measured using the xenon-133 intracarotid injection method. The first-pass extraction E of HM-PAO was calculated from F using an empiric regression equation. The residue curves for the whole brain after intracarotid HM-PAO injection were analyzed to yield a retention fraction (R') and the brain clearance backflux constant of lipophilic HM-PAO (k). From the kinetic model and the measured values of R', k, and F, the following parameter values could be calculated: the average retained fraction of all tracer supplied to the brain, R = 0.38 +/- 0.05 (mean +/- SD), the conversion rate constant (lipophilic to hydrophilic tracer) in the brain k3 = 0.80 +/- 0.12 min-1, the efflux rate constant (brain to blood) k2 = 0.69 +/- 0.11 min-1, the conversion/clearance ratio alpha = k3/k2 = 1.18 +/- 0.25, the influx (blood clearance) constant K1 = 0.45 +/- 0.11 ml/g/min, and the brain/blood partition ratio lambda = K1/k2 = 0.67 +/- 0.23 ml/g. Using the kinetic model and assuming constancy of alpha, an algorithm was developed that corrects for the blood flow dependent backflux of HM-PAO and results in a more linear relation between regional cerebral blood flow (rCBF) and HM-PAO distribution.

Quantitative measurements of cerebral blood flow using SPECT and [99mTc]-d,l-HM-PAO compared to xenon-133

The uptake and retention in a 2 cm thick brain section was recorded serially by SPECT after i.v. injection of [99mTc]-d,l-HM-PAO (HM-PAO). In 16 patients, the fraction of the administered dose retained by the brain was 5.2 +/- 1%, showing a peak after 40-50s, then decreasing by 10% within the first 10 min and then by only 0.4% per hour. The image contrast was measured in each patient as the regional hemispheric asymmetry difference in percent of the highest value of the two regions. It decreased from 31% at 30-40 s to 25% at 10 min. At 24 h, a value of 19% was reached. Using the images obtained at 10 min after injection, a region to region comparison of the original and corrected HM-PAO images to the xenon-133 regional cerebral blood flow (rCBF) images was performed. Forty-four patients with stroke, epilepsy, dementia, basal ganglia disease, and tumors and control subjects were included in this comparison. The algorithm proposed by Lassen et al. was used to correct the original images for back diffusion of tracer (brain to blood); a good correlation very close to the line of identity between the corrected HM-PAO and xenon-133 data was obtained when using a conversion/clearance ratio of 1.5 and when the noninvolved hemisphere was used as a reference region (r = 0.86, p less than 0.0001). Serial arterial and cerebral venous blood sampling was performed over 10 min following i.v. injection of HM-PAO in six patients. An overall brain retention fraction of 0.37 +/- 0.03 (mean +/- SEM) was calculated from the data. An average CBF of 0.62 +/- 0.12 ml/g/min was determined on the basis of the Fick principle; this compared to a value of 0.59 +/- 0.09 ml/g/min (mean +/- SEM) measured by the xenon-133 inhalation method. The two sets of CBF values correlated linearly with a correlation coefficient of 0.97 (p less than 0.01). Inserting the average CBF value for the hemisphere as measured by the Fick principle into the algorithm described by Lassen et al. yields absolute rCBF values (ml/g/min) directly from the corrected HM-PAO images.(ABSTRACT TRUNCATED AT 400 WORDS)

Improvement of cerebral blood flow following stereotactic surgery in patients with putaminal haemorrhage

Changes in cerebral blood flow (CBF) after CT guided stereotactic aspiration of putaminal haematoma were investigated in 13 patients with Xe-133 inhalation and single photon emission computed tomography. The interval from onset to operation ranged from 13 to 82 days (mean 30 days). The mean estimated haematoma volume ranged from 20 to 50 ml (mean 31.9 ml). The percentage of haematoma aspirated ranged from 75 to 98% (mean 86.8%). Postoperative CBF in two thirds of the patients was improved even though all cases were operated on in the subacute stage. Both the mean hemispheric and regional CBF in the anterior territory of the middle cerebral artery and in the region of the thalamus and basal ganglia in the affected hemisphere were increased postoperatively. Also in the nonaffected hemisphere, regional CBF in the region of the thalamus and basal ganglia was improved.

Regional cerebral blood flow in normal pressure hydrocephalus

Regional cerebral blood flow (rcbf) was studied preoperatively and at 2 and 6 months postoperatively in 22 normal pressure hydrocephalus patients using xenon-133 inhalation and single photon emission computed tomography. Sixteen of the 22 patients improved (improved group) and six did not (unimproved group). The following comparisons were made: (1) preoperative rcbf in the improved group, to 14 normal elderly volunteers and to that in 59 SDAT (senile dementia of the Alzheimer type) patients; (2) preoperative rcbf in the improved and unimproved groups to determine if rcbf could predict surgical outcome; (3) pre- to postoperative rcbf in the improved group to see if increased cbf accounted for clinical improvement. The findings were: (1) preoperative rcbf in the improved group was lower than that in normal controls but was the same as that in SDAT; however, the ratios of rcbf values in anterior and posterior brain regions were significantly different between improved group and SDAT (p = 0.02); (2) an anterior/posterior ratio of 1.05 correctly classified surgical outcome in 19/22 patients; five of six in the unimproved group were above this cut off while 14/16 in the improved group were below; (3) in the improved group rcbf increased at 2 but not at 6 months after surgery without a corresponding reduction of clinical signs, supporting the notion that increase in cbf probably does not account for clinical improvement in normal pressure hydrocephalus.

SPECT instrumentation: performance, lesion detection, and recent innovations

The use of a gamma camera for single photon emission computed tomography (SPECT) imaging places greater demand on camera performance than does planar imaging, since camera specifications that are adequate for planar imaging may produce serious image artifacts in SPECT. Manufacturers have responded to the challenge with improvements in both hardware and software, but the user must pay careful attention to quality control procedures. Field nonuniformity is caused mainly by spatial distortion, which may vary during rotation; some cameras incorporate a means of automatically correcting for angular changes. The purpose of performing SPECT is to improve lesion detection, ie, to improve contrast, which is influenced by many factors. Attenuation corrections may be applied either before or after reconstruction. For Tc-99m an attenuation coefficient less than that for water, ie, either 0.11 or 0.12, would appear to give better results; the visual appearance is improved but the effect on contrast is minimal. Scattered photons are the major cause of loss of contrast in SPECT images. Recent developments in on-line energy corrections allow the use of narrower photopeak windows as well as asymmetric energy windows. Offpeak energy windows have demonstrated significant improvements in contrast; however, the increase in nonuniformity can cause artifacts which may limit their use. Simultaneous collection of separate images, one in the photopeak region and the other in the scatter region (92 to 125 keV) may enable a transaxial scatter image to be subtracted from the transaxial photopeak image. This may permit quantification of the true radioactivity distribution. New collimator designs introduced to improve SPECT resolution include cast collimators which can be made with more uniform hole construction than the lead-foil type; for brain imaging, long bore parallel hole and converging fan beam collimators as well as astigmatic collimators which converge in both planes with different lines of focus. Some of these improve both sensitivity and resolution compared to parallel hole collimators. Noncircular orbits have also been introduced in order to improve resolution, but their use presents many problems which require careful monitoring. Transaxial multicrystal systems have been developed over many years, but have not been widely used, primarily because of their inherent complexity, high costs, and limited applicability. Some of these drawbacks may be overcome by a new type of SPECT camera currently under development by several different groups.(ABSTRACT TRUNCATED AT 400 WORDS)

Cerebral blood flow in patients with normal-pressure hydrocephalus before and after shunting

Cerebral blood flow (CBF) was measured by xenon-133 inhalation and single photon emission tomography in 17 demented patients with normal-pressure hydrocephalus before and after shunt treatment. All patients had a decreased conductance to outflow (C out) of cerebrospinal fluid as measured by lumboventricular perfusion (C out less than 0.12 ml X mm Hg-1 X min-1). Computerized tomography (CT) scanning, clinical assessment, and neuropsychological grading were performed pre- and postoperatively. The preoperative CBF studies revealed abnormal flow patterns in all patients. Fourteen patients showed moderate-sized, large, or very large central low-flow areas, and four patients had reduced flow bilaterally in the occipital and contiguous temporoparietal regions. After shunting, six patients had a significant reduction in the size of the central low-flow area on the CBF map, agreeing well with the changes of ventricular size on the CT scan. All six patients showed an improvement in either clinical or neuropsychological grading. In 10 of the remaining 11 patients flow patterns were essentially unchanged; one patient deteriorated further. Four of these 11 patients improved on postoperative clinical or neuropsychological testing. Thus, a positive correlation was found between the changes in CBF and the reduction of the ventricular size on the CT scan, but changes in CBF as measured by the present technique did not accompany improvement in the functional state in all patients.

Positron emission tomography: standardisation of labelling procedures

As positron emission tomography is becoming a very important tool to obtain metabolic images, we thought it useful to give recent EEC workshop reports on this subject greater circulation.