A comparison of Tc-99m HM-PAO and I-123 IMP cerebral SPECT images in Alzheimer's disease and multi-infarct dementia

Neuroimaging as a marker of the onset and progression of Alzheimer's disease

Several neuroimaging techniques are promising tools as early markers of brain pathology in Alzheimer's disease (AD). On structural MRI, atrophy of the entorhinal cortex is present already in mild cognitive impairment (MCI). In the autosomal dominant forms of AD, the rate of atrophy of medial temporal structures separates affected from control persons even 3 years before the clinical onset of cognitive impairment. The elevated annual rate of brain atrophy offers a surrogate tool for the evaluation of newer therapies using smaller samples, thereby saving time and resources. On functional MRI, activation paradigms activate a larger area of parieto-temporal association cortex in persons at higher risk for AD, whereas the entorhinal cortex activation is lesser in MCI. Similar findings have been detected with activation procedures and water (H(2)(15)O) PET. Regional metabolism in the entorhinal cortex, studied with FDG PET, seems to predict normal elderly who will deteriorate to MCI or AD. SPECT shows decreased regional perfusion in limbic areas, both in MCI and AD, but with a lower likelihood ratio than PET. Newer PET compounds allow for the determination in AD of microglial activation, regional deposition of amyloid and the evaluation of enzymatic activity in the brain of AD patients.

Brain SPECT with 123I-IMP for the early diagnosis of Creutzfeldt-Jakob disease

We performed brain CT and single-photon emission computed tomography (SPECT) using N-isopropyl-p-[123I] iodoamphetamine (123I-IMP) as a tracer in the early stage of seven patients with Creutzfeldt-Jakob disease (CJD). In four of the patients, we determined absolute values of regional cerebral blood flow (rCBF) in the frontal, temporal, parietal and occipital lobes, thalamus and cerebellum using an autoradiographic method with a single blood sample. Brain CT demonstrated no abnormal findings other than a mild age-related atrophy in all patients except for one patient with a low-density area in the left cerebellar hemisphere due to an old hemorrhage, whereas SPECT revealed a decreased uptake of the tracer in various parts of the cerebral cortex of all patients, sometimes in an asymmetrical pattern. Absolute values of rCBF showed a significant decrease in all examined regions of the patients as against healthy controls (P<0.0001). In three patients, SPECT demonstrated a decreased uptake throughout the cerebral cortex on visual inspection, whereas absolute values of rCBF revealed an obvious decrease of the uptake also in the thalamus and cerebellum. These results suggest that SPECT with quantification of rCBF using 123I-IMP might be a sensitive and useful technique not only for detecting a focal metabolic dysfunction but also for diagnosis in the early stage of CJD.

Positron emission tomography for diagnosis of Alzheimer's disease and vascular dementia

In mild or atypical cases of Alzheimer's disease (AD) the differential diagnosis to other dementing diseases, such as vascular dementia (VD), may pose a difficult problem. Beside computed tomography (CT) and magnetic resonance imaging (MRI), functional neuroimaging by positron emission tomography (PET) support the clinical diagnosis by visualizing cerebral function. PET of 18F-2-fluoro-2-deoxy-D-glucose (FDG) for measurement of regional cerebral glucose metabolism (rCMRGl) has shown a typical metabolic pattern in patients with probable AD: hypometabolism in temporoparietal and frontal association areas, but relative recessing of primary cortical areas, basal ganglia and cerebellum. In VD a different pattern is seen. It consists of scattered areas with reduction of rCMRGl typically extending over cortical and subcortical structures. Severity of dementia is correlated with rCMRGl reduction in the temporoparietal association cortex, irrespective of the cause of dementia. Also the total volume of hypometabolic regions is related to severity of dementia but did not differ between AD and VD, even in patients with small lacunar infarction. This indicates that the total volume of functional tissue loss is more important since it also includes the effects of incompletely infarcted tissue and morphologically intact but deafferented cortex. The characteristic metabolic pattern has a high diagnostic accuracy for the discrimination between probable AD, normals and VD, even in patients with mild cognitive impairment. Under clinical and therapeutic aspects the analysis of longitudinal changes of rCMRGl has shown that neuropsychological and metabolic changes are closely related in both, AD and VD.

Demonstration of decreased posterior cingulate perfusion in mild Alzheimer's disease by means of H215O positron emission tomography

Although decreased posterior cingulate metabolism in Alzheimer's disease (AD) has been previously reported, there have been no reports on posterior cingulate perfusion. In this study we evaluated posterior cingulate perfusion as a relative value using statistical parametric maps (SPMs) and as an absolute value using conventional region of interest (ROI) settings. Twenty-eight subjects, including 14 patients with mild AD (mean age: 66.4+/-12.1 years) and 14 normal controls (65.9+/-7.3 years) were studied. Regional cerebral blood flow (CBF) was measured with H215O and positron emission tomography (PET). In the SPM analysis, the left posterior cingulate and left parietotemporal CBFs were significantly decreased in the patients with mild AD (P<0.001). At a lower statistical threshold (P<0.05), the right posterior cingulate and right parietotemporal CBFs were also significantly decreased in the AD patients. In the ROI studies, the left parietal and posterior cingulate CBFs in the patients with mild AD were significantly lower than those of the normal controls by analysis of variance and post-hoc Scheffé's test (P<0.001). We conclude that posterior cingulate perfusion is decreased in mild AD, reflecting the pathological changes and metabolic reduction in the posterior cingulate gyrus that have previously been reported to occur in mild AD.

Sensitivity, specificity, and positive predictive value of technetium 99-HMPAO SPECT in discriminating Alzheimer's disease from other dementias

Investigators have reported high sensitivity and specificity values for single photon emission computerized tomography (SPECT) when distinguishing Alzheimer's disease (AD) patients from normal elderly controls or from selected patient groups. The role of SPECT in identifying AD among unselected patients with memory complaints requires investigation. We examined 139 consecutive patients with 99Tc-HMPAO SPECT. NINCDS-ADRDA diagnoses were determined blind to SPECT results, and scans were read and classified by visual inspection blind to clinical diagnoses. Bilateral temporoparietal hypoperfusion (TP) occurred in 75% of probable, 65% of possible, and 45% of unlikely AD patients, yielding a sensitivity of 75% and a specificity of 52% when comparing probable AD versus unlikely AD groups. A positive predictive value of 78% was obtained based on a 69% prevalence of AD in our total clinic population. Patients with false-positive results included a variety of dementing illnesses; all patients with bilateral hypoperfusion had dementia. A pattern of TP on SPECT scans is seen in most patients with AD, but could be found in other dementias as well and cannot be regarded as specific to AD. Reduced TP perfusion discriminated between demented and nondemented individuals. Further strategies for SPECT interpretation that improve diagnostic specificity should be sought.

The clinical utility of visual evaluation of scintigraphic perfusion patterns for Alzheimer's disease using I-123 IMP SPECT

The authors examined the role of SPECT perfusion pattern in the diagnosis of Alzheimer's disease (AD) using I-123 IMP. They studied 93 patients who had memory and cognitive disorders, including 42 patients with a diagnosis of probable AD, classifying SPECT images into determined perfusion patterns. The probability of AD was 54% with bilateral temporal and/or parietal defects, 69% with bilateral temporoparietal defects with additional defects, 17% with no defects, and 11% with frontal defects only. The sensitivity of bilateral temporoparietal perfusion defects for AD was 95.2%, whereas the specificity was 56.9%. In the absence of bilateral temporal and/or parietal defects on visual evaluation of SPECT, the diagnosis of AD was unlikely, although it is not pathognomonic for AD, because this sign would be seen in various neuropsychiatric diseases causing memory and cognitive impairments. Visual evaluation of SPECT is of value in the diagnosis of AD among patients with dementia.

Vascular dementia: perfusional and metabolic disturbances and effects of therapy

Positron emission tomography (PET) has elucidated basic pathophysiological mechanism that produce the cognitive decline in vascular dementia (VD). The typical pattern of glucose metabolism seen in VD with scattered areas of focal cortical and subcortical hypometabolism differs from that in AD with marked hypometabolism affecting the association areas. The total volume of metabolically inactive tissue is significantly related to severity of dementia. Rather than the quantity of tissue destruction, the critical effect may be the quantity of cortical hypometabolism caused by subcortically induced disconnection. Studies with HMPAO SPECT have shown focal deficits in VD and AD patients that are comparable to those seen with FDG PET. In mildly demented patients performance for the classification AD versus VD is much better by PET because it might be more sensitive for imaging small functional pathological changes. A longitudinal analysis of rCMRGl in VD showed that the progression of dementia can be delayed by the adenosine uptake blocker propentofylline and that neuropsychological and metabolic changes are closely related.

Neuropsychological tests and [99mTc]-HM PAO SPECT in the diagnosis of Alzheimer's dementia

Twenty-three patients with Alzheimer's dementia (AD) in relatively early stages and 40 patients with other cognitive disorders of vascular or degenerative aetiology underwent neuropsychological examination and [99mTc]-HM PAO single photon emission computed tomography (SPECT). In contrast to the commonly accepted notion of a posterior temporoparietal reduction of tracer uptake as the typical SPECT pattern of AD, the most consistent feature found in the SPECT images of our AD patients was a hippocampal uptake deficit, associated with a variable degree of temporal, parietal and frontal deficit (extending from the posterior to the anterior regions), according to the severity of the disease. These results support the theory of AD as a "hippocampal dementia", at least in the early stages. Neuropsychological tests were found to be somewhat more specific and more accurate than SPECT in distinguishing AD from non-AD cases.

Clinical brain radionuclide imaging studies

A recent survey of the knowledge and practice of both positron-emission tomography (PET) and single-photon emission computed tomography (SPECT) of the brain among referring physicians in Europe (neurologists and psychiatrists) showed a disquieting lack of knowledge of the potential of these methodologies in the investigation and management of patients of their own specialities. The need to bring the knowledge of the potential of these techniques to the practicing physicians is paramount. It is imperative that the methodologies and concepts that preside over the application of these techniques in neurology and psychiatry must become more uniform if an impact is to be felt at a clinical level. There is clear improvement in the instrumentation available with the new state-of-the-art tomographic devices and with the development of new technetium-based radiopharmaceuticals for the study of cerebral perfusion. The constant progress made with ligands that permit the study of neurotransmission, tumor metabolism, and turnover do expand our capability to improve the knowledge concerning neurophysiology, neuropathology, and neuropharmacology of a variety of disease states. PET and SPECT will be progressively included in protocols aimed at stratifying patients with dementia, monitoring therapeutic trials, and improving our ability to determine outcome. Clinical usefulness of PET and SPECT begin to emerge in cerebral vascular disease, in the identification of cerebral death, in epilepsy, in cerebral trauma, in the investigation of HIV-positive patients with cerebral involvement, and in the monitoring of tumor recurrence and postirradiation damage. This review article outlines a current perspective of SPECT and PET as practiced in Europe, its potential, and its limitations.

99mTc-HMPAO-SPECT in the diagnosis of senile dementia of Alzheimer's type--a study under clinical routine conditions

This study was designed to evaluate, whether investigations of cerebral blood flow can be a helpful diagnostic tool in the differential diagnosis between (senile) dementia of Alzheimer's type [(S)DAT] and geriatric depression with cognitive impairment. Under clinical routine conditions we performed Single Photon Emission Computed Tomography (SPECT) using 99mTc-Hexamethylpropyleneamine Oxime (HMPAO) in 23 patients with (S)DAT (14f, 9m; mean age 68.9 y), 17 patients with geriatric depression (9 f, 8 m; mean age 66.4 y) and 12 age-matched controls (9 f, 3 m; mean age 69.2 y). Semiquantitative analysis (corticocerebellar ratios) of eight different regions of interest (ROI) revealed a significantly (p < 0.05) reduced perfusion in the (S)DAT patients compared to the control group. The depression group exhibited perfusion values between the (S)DAT and control group. The difference between the depression and (S)DAT group was most prominent in the left parieto-occipital ROI (p = 0.008). We discuss the data with extensive regard to the literature and conclude that 99mTc-HMPAO SPECT is a valuable additional tool in the differential diagnosis of depression and dementia in the elderly.

Artificial neural networks that use single-photon emission tomography to identify patients with probable Alzheimer's disease

Single-photon emission tomographic (SPET) images using technetium-99m labelled hexamethyl-propylene amine oxime were obtained from 97 patients diagnosed as having Alzheimer's disease, as well as from a comparison group of 64 normal subjects. Multiple linear regression was used to predict subject type (Alzheimer's vs comparison) using scintillation counts from 14 different brain regions as predictors. These results were disappointing: the regression equation accounted for only 33.5% of the variance between subjects. However, the same data were also used to train parallel distributed processing (PDP) networks of different sizes to classify subjects. In general, the PDP networks accounted for substantially more (up to 95%) of the variance in the data, and in many instances were able to distinguish perfectly between the two subjects. These results suggest two conclusions. First, SPET images do provide sufficient information to distinguish patients with Alzheimer's disease from a normal comparison group. Second, to access this diagnostic information, it appears that one must take advantage of the ability of PDP networks to detect higher-order nonlinear relationships among the predictor variables.

The measurement of blood flow in humans using radioactive tracers

Since the first description of the movement of blood around the body by William Harvey, the accurate measurement of blood velocity has provided a major challenge for medical science. This review looks at the contribution made by techniques using radioactive tracers. Initially consideration is given to the fundamental problem of how to measure the amount of radiotracer in an organ with sufficient accuracy, using both single-photon and positron-emitting tracers. The various models used to link tracer behaviour with blood flow are then discussed and the article closes with a detailed review of the clinical applications of blood flow measurements.

Toward a definite diagnosis of Alzheimer's disease

There is a significant, and growing, number of patients who suffer from dementia of the Alzheimer's type (DAT). However, due to clinical variability and symptom overlap, and despite millions of dollars spent in diagnostic work-ups, the diagnosis of DAT remains one of exclusion or by neuropathologic study (usually postmortem). This report evaluates two promising methods, the newly refined clinical criteria sets (e.g., NINCDS-ADRDA) and single-photon emission computed tomography (SPECT), on their capacity for definite, accurate, and early diagnosis of DAT patients. We found that clinical diagnosis of DAT can achieve a weighted average for sensitivity of 72%, specificity of 86%, and diagnostic confidence of 72%; however, when NINCDS-ADRDA criteria are used, these results improve to 88%, 91%, and 92%, respectively. SPECT scans could differentiate DAT patients from normals with 86% sensitivity, 96% specificity, and 98% diagnostic confidence. Comparable figures for DAT versus multi-infarct dementia (MID) are 82%, 81%, and 86%, respectively. We conclude that, although a definite clinical diagnosis of DAT is still elusive and more research is needed, the use of either NINCDS-ADRDA criteria or SPECT scans may enhance diagnostic accuracy.

Cortical circumferential profile of SPECT cerebral perfusion in Alzheimer's disease

We developed a semiautomatic method termed "cortical circumferential profiling" for objective analysis of cerebral cortex function in emission tomographic neuroimaging studies. This method treats cortex as a continuous ring near the outer brain edge. A computer algorithm samples the cortex at 60 contiguous, equiangular locations, using 1-cm2 samples. These values are plotted as a function of cortical angle to produce the cortical circumferential profile. This method was used in a study of regional cerebral perfusion in 15 patients with Alzheimer's disease and 8 elderly control subjects using N-isopropyl[I-123]-iodoamphetamine. Cortical circumferential profiling decreases variability, examines the entire cortex within slices at preselected levels above the orbital-meatal line, and facilitates intrasubject and intersubject comparisons.

Diagnostic and pharmacological approaches in Alzheimer's disease

Alzheimer's disease is a chronic progressive disease affecting higher intellectual functioning. The clinical diagnosis is made when the onset of illness is insidious, the course slowly progressive and all the treatable causes of dementia have been ruled out. The use of more stringent criteria has improved clinical diagnosis, but at best only 80% of patients are accurately diagnosed. Ultimately the diagnosis depends upon pathological confirmation. The neuritic plaques and neurofibrillary tangles described by Alzheimer, although not pathognomonic for the disease, continue to be the basis for pathological diagnosis. The aetiology and pathophysiology of Alzheimer's disease are presently unknown. Epidemiological studies have suggested a genetic basis for the disorder, and many biochemical studies have linked it to degeneration of central cholinergic neurons, and possibly to abnormalities of other neurotransmitter systems. A marker which would permit accurate diagnosis early in the course of disease would be of major importance to researchers and clinicians alike. No marker has been found to date, although recent research results are promising. Various pharmacological strategies have been employed in the treatment of Alzheimer's disease. More recently attempts have focused on enhancing central cholinergic transmission. Despite the well-founded rationale for these studies, results have been modest.

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.

Comparison of I-123 IMP and Tc-99m HMPAO SPECT studies with PET in dementia

We compared I-123 IMP and 99m-Tc HMPAO SPECT studies with 0-15 H2O and F-18 FDG PET studies, and evaluated the clinical significance of SPECT studies in dementia. Seventeen patients including 9 patients with Alzheimer's disease, 3 patients with Pick's disease and 5 patients with multi-infarct dementia were studied. IMP and HMPAO SPECT studies could not detect mildly affected areas when compared with FDG PET. However, they revealed decreased perfusion in the bilateral parietal regions in Alzheimer's disease and in the bilateral frontal regions in Pick's disease, while MRI and/or CT showed mild to moderate cerebral atrophy. IMP and HMPAO SPECT studies can be easily performed in clinical practice, and these findings were useful in the differential diagnosis of dementia. Our preliminary results suggested that SPECT studies with I-123 IMP and Tc-99m HMPAO, despite their limitations, are useful in the differential diagnosis of dementia.

Hereditary cerebral hemorrhage with amyloidosis--Dutch type. Tc-99m HM-PAO single photon emission computed tomography

We performed single photon emission computed tomography (SPECT) and cerebral CT-scans in nine patients with hereditary cerebral amyloid angiopathy. CT-scans showed 23 focal hypodense lesions, 13 of which were visible on SPECT as a CBF-defect. One patient showed a CBF-defect on SPECT without CT-scan lesion and had a cerebral hemorrhage three months later in that particular region. In two additional patients, who were 50% at risk for this autosomal dominant disease, CBF-defects on SPECT, but no cortical lesions on CT-scan were found. CT-scans may be more sensitive than SPECT to detect chronic lesions caused by cerebral hemorrhages, but another possibility is that hemorrhages do not always lead to persistent CBF-defects. SPECT can show the effect of amyloid deposits on CBF before the angiopathy causes clinical symptoms.