Positron emission tomography imaging of regional cerebral glucose metabolism

Monitoring arterio-venous differences of glucose and lactate in the anesthetized rat with or without brain damage with ultrafiltration and biosensor technology

Continuous monitoring of arterio-venous glucose and lactate differences may serve as a diagnostic tool to assess normal brain function and brain pathology. We describe a method and some results obtained with arterio-venous measurements of glucose and lactate in the blood of the halothane-anesthetized rat and after brain injury. The method is based on low flow rate ultrafiltration for continuous collection of blood filtrate combined with flow injection analysis and biosensors for the detection of glucose and lactate. We measured the glucose and lactate concentration every minute in the jugular vein and the aorta at control conditions and during and after inflation of an embolectomy-balloon for 2 min. Net cerebral lactate efflux and glucose uptake was seen under control conditions and at low blood lactate levels. During brain injury both lactate release and glucose uptake were reduced and there was a net lactate influx at high arterial lactate levels. These results indicate that the flux of lactate in and out of the brain is not only dependent on the lactate concentration in the brain, but on blood levels as well, possibly because of bi-directional flux through the monocarboxylate transporter type 1.

Regional cerebral glucose metabolism in healthy volunteers determined by fluordeoxyglucose positron emission tomography: appearance and variance in the transaxial, coronal, and sagittal planes

PURPOSE

In this study, the contribution of the transaxial, coronal, and sagittal planes in evaluations of regional cerebral glucose metabolism was investigated in healthy volunteers as determined by fluorine-18-labeled 2-deoxy-2-fluoro-D-glucose (FDG) and high-resolution positron emission tomography (PET).

METHODS

One hundred twenty-seven healthy right-handed volunteers were injected with 4.2 MBq/kg (0.11 mCi) body weight FDG and imaged in a PENN PET H 240 scanner. Images were corrected for scatter and random coincidences and reconstructed in all three planes into 6- to 8-mm-thick slices. The reconstructed images were corrected for attenuation using the Chang algorithm. The transverse, coronal, and sagittal images were read independently of each other using a qualitative scale in which 1 = equal to, 2 = mildly, 3 = moderately, and 4 = markedly less than the area with the highest glucose metabolism in the respective plane.

RESULTS

The areas with the highest glucose metabolisms were the posterior cingulate gyri with mean scores of 1.1 to 1.2, thalami (1.2 to 1.3), basal ganglia (1.5 to 1.9), and visual cortex (1.6). The lowest values were found in the occipital cortex (2.7 to 2.8) and the cerebellum (2.3 to 2.4). Whereas reliable analysis of the mesial temporal aspects was not feasible in the sagittal plane, the anterior poles of the temporal and frontal lobes could not be evaluated in the coronal or the inferior temporal areas in the transaxial slices. In all three planes, regional glucose metabolism was less in the lateral temporal areas on the left than on the right (P < 0.001). The consistency of readings as measured in terms of coefficients of variation was greatest in the coronal plane for the caudates and posterior cingulate gyri, in the transaxial plane for the lateral temporal regions, and in the sagittal plane for the visual cortex. Age-dependent decreases in regional glucose metabolism in the inferior and lateral frontal regions and the parietal lobes were found in all three planes.

CONCLUSIONS

All three projection planes must be used for a comprehensive qualitative evaluation of the regional glucose metabolism of the brain.

Bioenergetics in Huntington's disease

Huntington's disease (HD) is an autosomal dominant inherited neurodegenerative disorder with relentless course and prototypical clinical symptoms. In 1993 HD was associated with an expanded CAG triplet repeat stretch on chromosome 4 in the coding region of its target protein, huntington. The length of the resulting polyglutamine++ extensions correlates with lower age of onset and a higher density of ubiquitin-positive neuronal intranuclear inclusions. Recently it has been proposed that mutant huntington induces progressive neuronal cell death by an apoptotic mechanism. There is strong evidence that disturbances in cellular energy homeostasis and oxidative damage contribute to neurodegeneration. This review will summarize and discuss the current concepts that point towards an involvement of free radical-induced oxidative stress, glutamate excitotoxicity and mitochondrial respiratory chain defects in pathogenesis of HD.

The relationship between fMRI activation and cerebral atrophy: comparison of normal aging and alzheimer disease

Functional MRI has recently been used to examine activation associated with aging and dementia, yet little is known regarding the effect of cerebral atrophy on fMRI signal. The purpose of this study was to examine the relationship between measures of global and regionally specific atrophy and fMRI activation in normal aging and in Alzheimer disease (AD). Two groups of subjects were studied with echoplanar imaging and quantitative structural volumetry: healthy controls spanning a broad age and atrophy range (n = 16) and patients with mild AD (n = 8). Results from a semantic task previously found to activate left inferior frontal (LIFG) and left superior temporal (LSTG) gyri were analyzed. The correlations between clusters of activation in the LIFG and LSTG and measures of local atrophy in the LIFG and LSTG regions were evaluated. For control subjects, there was no significant correlation between activation and regional or total brain atrophy (for LIFG r = -0.03, NS; for LSTG r = 0.20, NS). In contrast, for AD patients, there was a significant positive correlation between atrophy and activation in LIFG (r = 0.70, P = 0.05) but not LSTG (r = 0.00, NS). These results suggest that activation of language regions and atrophy within those regions may be independent among healthy adults spanning a broad age and atrophy range. However, in AD, a relationship exists in the LIFG that may reflect compensatory recruitment of cortical units or disease-specific changes in the hemodynamic response.

Evaluation of extra- and intracellular apparent diffusion in normal and globally ischemic rat brain via 19F NMR

The biophysical mechanism(s) underlying diffusion-weighted MRI contrast following brain injury remains to be elucidated. Although it is generally accepted that water apparent diffusion coefficient (ADC) decreases after brain injury, it is unknown whether this is associated with a decrease in intracellular or extracellular water displacement, or both. To address this question, 2-[19F]luoro-2-deoxyglucose-6-phosphate (2FDG-6P) was employed as a compartment-specific marker in normal and globally ischemic rat brain. Through judicious choice of routes of administration, 2FDG-6P was confined to the intra- or extracellular space. There was no statistical difference between intra- and extracellular 2FDG-6P ADCs in normal or in globally ischemic brain (P > 0.16), suggesting that water ADCs in both compartments are similar. However, ischemia did result in a 40% ADC decrease in both compartments (P < 0.001). Assuming that 2FDG-6P reflects water motion, this study shows that water ADC decreases in both spaces after ischemia, with the reduction of intracellular water motion being the primary source of diffusion-weighted contrast.

Positron emission tomography in asymptomatic gene carriers of Machado-Joseph disease

OBJECTIVES

The metabolic changes in the brain of symptomatic subjects affected with Machado-Joseph disease have been previously documented using PET with fluorine-18-fluorodeoxyglucose (FDG). The aim of this study was to evaluate these changes in asymptomatic Machado-Joseph disease gene carriers.

METHODS

Seven asymptomatic Machado-Joseph disease gene carriers, identified using a molecular test, and 10 normal control subjects were recruited for PET studies using FDG. Regional uptake ratios of FDG were calculated from the radioactivity of the cerebellar hemispheres, brainstem, and the temporal, parietal and occipital cortices, divided by the activity in the thalamus.

RESULTS

In comparison with data obtained from normal control subjects, there was significantly decreased FDG utilisation in the cerebellar hemispheres, brainstem, and occipital cortex, and increased FDG metabolism in the parietal and temporal cortices of asymptomatic Machado-Joseph disease gene carriers, suggesting preclinical disease activity. Discriminant analysis of regional FDG uptake correctly classified genetic status (Machado-Joseph disease mutation carriers v mutation negative subjects) in 25 of 25 subjects (100% sensitivity and 100% specificity), and clinical status (asymptomatic mutation carriers v symptomatic patients) in 14 of 15 subjects (100% sensitivity and 85.7% specificity).

CONCLUSION

Subclinical changes of FDG consumption, as measured by noninvasive PET, can act as an objective marker of preclinical disease activity in Machado-Joseph disease.

PET and the investigation of dementia in the parkinsonian patient

Parkinsonism and dementia are present in a number of neurodegenerative conditions. They may be a manifestation of isolated brain stem (Parkinson's disease) or diffuse Lewy body disease (DLBD), or be secondary to combined Lewy body and Alzheimer's disease (AD) pathologies. Positron emission tomography (PET) studies show a resting pattern of fronto-temporo-parietal hypometabolism in both, AD and in parkinsonism-dementia (PD-dementia) patients, even when only isolated brain stem Lewy body disease is found at pathology. We have studied three patients fulfilling clinical criteria for diagnosis of DLBD. Their 18F-fluorodeoxyglucose (FDG) PET results showed an AD pattern of fronto-temporo-parietal hypometabolism, though these patients had only mild cognitive dysfunction. Parkinsonism associated with apraxia is observed in corticobasal degeneration (CBD) while impairment of frontal functions, such as planning and sorting, is seen in patients with progressive supranuclear palsy (PSP). PET studies in CBD patients have shown an asymmetric hypometabolism of cortex and thalamus contralateral to the affected limbs, while in PSP patients there is a global metabolic reduction most pronounced in frontal areas and the basal ganglia. These results suggest that metabolic PET studies can help to distinguish PD-dementia, PSP and CBD, but are unable to distinguish PD-dementia from AD. Further studies with post-mortem confirmation are required to establish if DLBD is associated with a distinctive pattern of resting hypometabolism.

Reduced steady-state levels of mitochondrial RNA and increased mitochondrial DNA amount in human brain with aging

The contribution of the mitochondrial genetic system in the degenerative processes of senescence remains unclear. This study deals with age-related changes in brain mtDNA expression in humans. Brain tissue from the frontal lobe cortex was obtained from autopsy of 13 humans aged between 21 and 84 years. No structural changes were detected in mtDNA, increased mtDNA content and reduced steady-state level of mitochondrial transcripts and transcription ratio (mtRNA/mtDNA) were associated with aging. These findings suggest that the increase of the mtDNA levels could be considered as an inefficient compensatory mechanism to maintain the normal levels of mtRNA transcripts. This unbalanced mitochondrial condition could play a role in the process of senescence in human brain.

Single photon emission computed tomography (SPECT) measures of brain function in schizophrenia

This study explores SPECT measured in schizophrenic patients at rest. Left temporal lobe activity was found to be decreased with increasing positive symptoms' scores scores. Medicated patients showed a reversal of this pattern underlying this positive symptom effect. Patients with a recent history of auditory hallucinations showed an atypical right temporal lobe dominance, which occurred independently of medication status. These preliminary data are suggestive of the potential utility of SPECT to elucidate symptom/medication/brain activity interrelationships in schizophrenia.

SPECT for differential diagnosis of dementia and correlation of rCBF with cognitive impairment

99mTc-HM-PAO single photon emission computed tomography (SPECT) was used to image 30 patients referred for the assessment of dementia. SPECT images revealed various patterns of regional cerebral perfusion (rCBF) in the subgroups of patients with the clinical diagnoses of Alzheimer's disease (AD, n = 14), Pick's disease (n = 1), and multi-infarct dementia (n = 7). In three patients, SPECT clarified the clinical differential diagnostic possibilities. Using a relative rCBF quantification technique, the relationship between specific cognitive impairments and rCBF in the AD patients was determined. There was a significant correlation between language impairment and left hemisphere hypoperfusion, whereas, apraxia correlated with hypoperfusion in the left parietal region. Thus, HM-PAO SPECT is useful as an aid in the differential diagnosis of dementia and the technique of relative rCBF quantification with SPECT may contribute to the understanding of the clinico-anatomical relations of cognitive deficits in dementia.

Quantitative EEG analysis in early onset Alzheimer's disease: correlations with severity, clinical characteristics, visual EEG and CCT

We report EEG findings in 15 presenile Alzheimer patients (probable Alzheimer's disease according to NINCDS-ADRDA criteria) in relation to clinical characteristics. The quantitative EEG was analysed in terms of absolute band power while accounting for EOG and EMG artifacts, respectively. The degree of dementia is strongly reflected by an increase of power in the delta frequency band, accentuated on the left hemisphere, as well as decrease of alpha activity. Longer duration of disease is associated with a decrease of power in the alpha frequency band, earlier age at onset with an additional increase of power in the theta frequency band. Visual EEG evaluation correlates highly with the degree of dementia, in contrast to visually assessed CCT.

Alterations of cerebral metabolism in probable Alzheimer's disease: a preliminary study

Previous in vitro and in vivo 31P MRS studies of Alzheimer's disease patients have revealed alterations in membrane phospholipid metabolism and PET studies have shown alterations in glucose and oxidative metabolism. This study of probable Alzheimer's disease patients demonstrates severity dependent alterations in measures of both high-energy phosphate and membrane phospholipid metabolism. Mildly demented Alzheimer's patients compared to the controls, have increases in the levels of phosphomonoesters, decreases in the levels of phosphocreatine and probably adenosine diphosphate, and an increased oxidative metabolic rate. As the dementia worsens, the levels of phosphocreatine and adenosine diphosphate increase, the levels of phosphomonoesters decrease, and the oxidative metabolic rate decreases. The phosphomonoester findings replicate previous findings and provide a new dimension to the molecular pathology of Alzheimer's disease, implicating basic defects in membrane metabolism. The changes in oxidative metabolic rate suggest the AD brain is under energetic stress. The changes in energy metabolites with increasing dementia could be a consequence of nerve terminal degeneration and are consistent with previous PET findings. 31P MRS provides new diagnostic and metabolic insights into this disease and would be a noninvasive method to follow the progression of the disease and the metabolic response to therapeutic interventions.

Algebraic reconstruction techniques can be made computationally efficient [positron emission tomography application]

Algebraic reconstruction techniques (ART) are iterative procedures for recovering objects from their projections. It is claimed that by a careful adjustment of the order in which the collected data are accessed during the reconstruction procedure and of the so-called relaxation parameters that are to be chosen in an algebraic reconstruction technique, ART can produce high-quality reconstructions with excellent computational efficiency. This is demonstrated by an example based on a particular (but realistic) medical imaging task, showing that ART can match the performance of the standard expectation-maximization approach for maximizing likelihood (from the point of view of that particular medical task), but at an order of magnitude less computational cost.

Do brief bursts of spike and wave activity cause a cerebral hyper- or hypoperfusion in man?

The correlation between brain activity and cerebral blood flow velocities during brief bursts of generalized spike and wave activity was analysed by simultaneous registration of the EEG and the intracranial flow patterns. The flow patterns of the middle cerebral artery were continuously recorded by means of transcranial Doppler ultrasonography using a specially developed monitoring system. A total of 25 bursts was investigated in 3 patients with spontaneous occurrence of generalized 3 Hz spike and wave activity and normal background EEG. Characteristic changes of the flow patterns were found in all cases: 3.41 +/- 0.98 s (n = 25) after the beginning of generalized spike and wave patterns, the flow velocity decreased by 25.84 +/- 10.45% (n = 25) below the 'preictal' flow velocity level. The period of flow velocity changes lasted several times longer than the phase of spike and wave activity.

Neuro-imaging and positron emission tomography of congenital homonymous hemianopsia

Congenital homonymous hemianopsia is an uncommon asymptomatic visual field defect discovered typically in young adult life that is caused by a diverse group of insults to the retrochiasmal afferent visual system occurring prenatally, at birth, or during early childhood. We treated eight patients with congenital homonymous hemianopsia; seven with damage involving the optic radiations and one with an abnormality of the optic tract. We performed positron emission tomography using 18F-fluoro-2-deoxyglucose on two patients with dense homonymous hemianopsias, lesions of the contralateral optic radiations, and largely intact occipital cortex. These studies showed minimal abnormalities in resting visual cortex glucose metabolism of the affected visual cortex.

Brain imaging in dementia of the Alzheimer type

Neuroimaging modalities have increased understanding of brain abnormalities in dementia of the Alzheimer type (DAT), and is important in assessment of dementia syndromes by revealing focal disorders, demonstrating potentially treatable conditions, and by documenting progression of disease severity. Computed tomography (CT) and magnetic resonance imaging (MRI) have delineated structural changes in DAT, including cerebral atrophy associated with cortical sulci widening and ventricular enlargement, and deep white-matter lesions with periventricular distributions. Positron emission tomography (PET) has demonstrated diminished regional glucose metabolism at parietal and temporal lobes in DAT, while frontal hypometabolism tends to occur in more severe cases. Metabolic dysfunction assessed by PET appears to be the first indication of a degenerative cortical process in DAT, while anatomic changes on CT or MRI may become evident later in the disease process. This selective overview provides an analysis of the current status and future prospects of brain imaging in DAT.

Performance evaluation of an iterative image reconstruction algorithm for positron emission tomography

An image reconstruction method motivated by positron emission tomography (PET) is discussed. The measurements tend to be noisy and so the reconstruction method should incorporate the statistical nature of the noise. The authors set up a discrete model to represent the physical situation and arrive at a nonlinear maximum a posteriori probability (MAP) formulation of the problem. An iterative approach which requires the solution of simple quadratic equations is proposed. The authors also present a methodology which allows them to experimentally optimize an image reconstruction method for a specific medical task and to evaluate the relative efficacy of two reconstruction methods for a particular task in a manner which meets the high standards set by the methodology of statistical hypothesis testing. The new MAP algorithm is compared to a method which maximizes likelihood and with two variants of the filtered backprojection method.

Studies of central nervous system disorders with single photon emission computed tomography and positron emission tomography: evolution over the past 2 decades

Single photon emission computed tomography (SPECT) was introduced in the 1960s to detect breakdowns in the blood-brain barrier and was replaced by x-ray computed tomography in the mid-1970s. The development of the deoxyglucose (DG) technique to measure regional cerebral glucose metabolism by employing either autoradiography, using 14CDG, or positron emission tomography (PET), using 18FDG, added a major dimension to the investigation of brain function. In the late 1970s and early 1980s, the FDG-PET technique was widely used to examine a variety of neuropsychiatric disorders. It soon became apparent that functional imaging was more sensitive than anatomic imaging in detecting abnormalities of the brain related to aging, dementia, tumors, seizures, cerebral vascular accidents, and psychiatric problems. Because of its complexity and the cost involved, PET was used in a limited number of centers in the United States. However, the success of PET resulted in the resurgence of interest in SPECT as an alternative technology after almost a decade. This became possible because of the synthesis of iodine 123- and technetium 99m-labeled radiopharmaceuticals to determine regional cerebral blood flow. Since blood flow and metabolism are coupled in most pathological states, patterns of abnormality noted on SPECT were similar to those seen on PET in many disorders. Since the introduction of high resolution SPECT imaging instruments, the role of SPECT has been further enhanced. The successful synthesis of both positron and single emitting radioligands to image dopamine and other receptors has started a new era in neurosciences and will have a far-reaching impact on the day-to-day practice of neuropsychiatry.

The scintigraphic evaluation of Huntington's disease and other movement disorders using single photon emission computed tomography perfusion brain scans

The increasing availability of single-photon emission computed tomography (SPECT) perfusion brain scans has led to the investigation of a variety of neuropsychiatric conditions including the movement disorders such as Huntington's and Parkinson's disease. In general, observers have noted that Huntington patients have bilaterally decreased uptake of technetium 99m HM-PAO and iodine 123 IMP in the basal ganglia regions involving the heads of the caudate nucleic and adjacent structure, which reflects decreased neuronal function. These functional changes precede the morphological changes due to caudate nucleus atrophy that are observed on computed tomography and magnetic resonance imaging. Cortical changes occur in severely diseased Huntington's patients but are more nonspecific. Prediction of individuals at risk for Huntington's disease using SPECT scans should be done with caution and in association with other clinical data. In contrast, in Parkinson's disease mild diffusely decreased perfusion is commonly noted throughout the cerebral structures, except for the cerebellum. In Parkinson's disease, there is less agreement among observers as to whether the basal ganglia are abnormal. Some observers report that there are no specific basal ganglia perfusion defects in excess of those changes seen elsewhere in the brain. Others report diminished basal ganglia uptake associated with L-dopa therapy in some Parkinson's patients, and in patients with hemi-parkinsonism there have been perfusion deficits reported in the contralateral basal ganglia. In some Parkinson patients, bilateral Alzheimer's-like posterior temporoparietal cortical perfusion defects have been observed in association with progressive dementia. Basal ganglia and cortical perfusion changes also have been reported in a few patients with a variety of other less common movement disorders.

Positron emission tomography to study the effect of eye closure and optic nerve damage on human cerebral glucose metabolism

We used 18F-2-fluoro-2-deoxyglucose and positron emission tomography to evaluate the effect of visual deprivation on brain glucose metabolism. In experiment 1, we compared local cerebral metabolic rates for glucose in seven normal volunteers studied with eyes closed to 11 age- and sex-matched normal volunteers studied with eyes open. Whole brain metabolism was similar in the two groups, and region/whole brain analysis of metabolic data showed that metabolism in the calcarine posterior cortex was decreased by 14% (P less than .05) with eye closure. Glucose metabolism in other regions was not different between the two groups. In experiment 2, we compared glucose metabolism in six patients with severe bilateral optic neuropathies to 12 age- and sex-matched normal controls. Whole brain glucose metabolism was unchanged in the optic neuropathy group compared to controls. However, statistically significant reductions in glucose metabolism in the optic neuropathy group were found in anterior calcarine cortex (17%), posterior calcarine cortex (27%), peristriate cortex (27%), and lateral occipital cortex (15%). The metabolic effects of damage to the pregeniculate visual system went well beyond those of simple eye closure.

Alzheimer's disease with prominent visual symptoms. Clinical and metabolic evaluation

The authors examined eight patients with dementia of the Alzheimer's type (DAT), five with prominent visual symptoms early in the illness (VS) and three with no visual symptoms (NVS). Results of neuro-ophthalmologic examinations on VS patients showed relatively consistent abnormalities in figure copying, color vision tested by isochromatic plates, and stereopsis. Cerebral glucose metabolism determined by 18F-fluoro-2-deoxyglucose positron emission tomography (PET) was unchanged in primary visual cortex of VS and NVS patients compared with 12 normal volunteers of similar age and sex. Glucose metabolism in VS patients was decreased by 45 and 34% in left and right visual association cortex (P less than 0.01 and P less than 0.05, respectively) and 34 and 37% in left and right inferior parietal cortex (P less than 0.05) compared with controls; NVS patients had no significant metabolic alteration in these areas. Symptoms, physical examination, and metabolic imaging imply that these patients are a heterogenous but distinct clinical subgroup of DAT often with mild dementia who have visual symptoms due primarily to visual agnosia.

Positron emission tomography in patients with glioma. A predictor of prognosis

Positron emission tomography (PET) studies have been performed using 18-F-fluorodeoxyglucose in 29 adult subjects with primary brain tumors. Seventy-two percent of the patients were treated previously. The glucose metabolic state in the lesions was increased in 16 patients, and was normal or decreased in 13 patients. The hypermetabolic tumors tended to behave in a more malignant fashion. Patients with hypermetabolic tumors had a median survival of 7 months after PET scan, compared to 33 months for those with hypometabolic lesions. Among the high-grade glioma patients, the PET results separated them into a good prognosis group (hypometabolic, with 78% 1-year survival) and a poor prognosis group (hypermetabolic, with a 29% 1-year survival after PET). These results suggest that glucose metabolic studies may provide an independent measure of the aggressiveness of a brain tumor, and may supplement pathologic grading.

Thick brain slices model the ischemic penumbra

Hypothalamic brain slices, varying in thickness from 400 mu to 1,000 mu, were assessed by studying 2-deoxyglucose (2DG) metabolism, lactate accumulation, inulin spaces, and morphology at the light and ultrastructural levels. Evidence of increased glycolytic flux due to anaerobic metabolism is found at thickness greater than 600 mu in association with a progressive increase in the inulin-exclusion space. The metabolic profiles, as a function of depth into the slices, reveal that 700-mu slices function in a manner similar to 540-mu slices at the surfaces, but with a core of increased 2DG phosphorylation at the slice center. In contrast, the 1,000-mu slices show significant reduction of 2DG and increases in 2DG6P relative to the 540-mu slices at the slice surface as well as in the slice interior, suggesting impaired transport of 2DG into cells and spread of ischemic injury from the slice interior to the slice surface. Despite these metabolic changes, only minor morphologic changes of ischemic injury were found at the center of thicker slices, and in vitro glucose utilization of 1000-mu slices remained constant for up to 15 h. These three slice thicknesses should provide a useful model for studying the neurochemistry and neuropharmacology of the ischemic penumbra.