Single photon tomography in Alzheimer's disease and the dementias

Positron Emission Tomography-Based Assessment of Cognitive Impairment and Dementias, Critical Role of Fluorodeoxyglucose in such Settings

Positron emission tomography (PET) has been a key component in the diagnostic armamentarium for assessing neurodegenerative diseases such as Alzheimer or Parkinson disease. PET imaging has been useful for diagnosing these disorders, identifying their pathophysiology, and following their treatment. Further, PET imaging has been extensively used for both clinical and research purposes, particularly for helping with potential therapeutic approaches for managing neurodegenerative diseases. This article will review the current literature regarding PET imaging in patients with neurodegenerative disorders. This includes an evaluation of the most commonly used tracer fluorodeoxyglucose that measures cerebral glucose metabolism, tracers that assess neurotransmitter systems, and tracers designed to reveal disease-specific pathophysiological processes. With the continuing development of an expanding variety of radiopharmaceuticals, PET imaging will likely play a prominent role in future research and clinical applications for neurodegenerative diseases.

Combining SPECT and Quantitative EEG Analysis for the Automated Differential Diagnosis of Disorders with Amnestic Symptoms

Single photon emission computed tomography (SPECT) and Electroencephalography (EEG) have become established tools in routine diagnostics of dementia. We aimed to increase the diagnostic power by combining quantitative markers from SPECT and EEG for differential diagnosis of disorders with amnestic symptoms. We hypothesize that the combination of SPECT with measures of interaction (connectivity) in the EEG yields higher diagnostic accuracy than the single modalities. We examined 39 patients with Alzheimer's dementia (AD), 69 patients with depressive cognitive impairment (DCI), 71 patients with amnestic mild cognitive impairment (aMCI), and 41 patients with amnestic subjective cognitive complaints (aSCC). We calculated 14 measures of interaction from a standard clinical EEG-recording and derived graph-theoretic network measures. From regional brain perfusion measured by 99mTc-hexamethyl-propylene-aminoxime (HMPAO)-SPECT in 46 regions, we calculated relative cerebral perfusion in these patients. Patient groups were classified pairwise with a linear support vector machine. Classification was conducted separately for each biomarker, and then again for each EEG- biomarker combined with SPECT. Combination of SPECT with EEG-biomarkers outperformed single use of SPECT or EEG when classifying aSCC vs. AD (90%), aMCI vs. AD (70%), and AD vs. DCI (100%), while a selection of EEG measures performed best when classifying aSCC vs. aMCI (82%) and aMCI vs. DCI (90%). Only the contrast between aSCC and DCI did not result in above-chance classification accuracy (60%). In general, accuracies were higher when measures of interaction (i.e., connectivity measures) were applied directly than when graph-theoretical measures were derived. We suggest that quantitative analysis of EEG and machine-learning techniques can support differentiating AD, aMCI, aSCC, and DCC, especially when being combined with imaging methods such as SPECT. Quantitative analysis of EEG connectivity could become an integral part for early differential diagnosis of cognitive impairment.

Meditation and neurodegenerative diseases

Neurodegenerative diseases pose a significant problem for the healthcare system, doctors, and patients. With an aging population, more and more individuals are developing neurodegenerative diseases and there are few treatment options at the present time. Meditation techniques present an interesting potential adjuvant treatment for patients with neurodegenerative diseases and have the advantage of being inexpensive, and easy to teach and perform. There is increasing research evidence to support the application of meditation techniques to help improve cognition and memory in patients with neurodegenerative diseases. This review discusses the current data on meditation, memory, and attention, and the potential applications of meditation techniques in patients with neurodegenerative diseases.

Initial clinical comparison of 18F-florbetapir and 18F-FDG PET in patients with Alzheimer disease and controls

The purpose of this study was to determine how clinical interpretations of the (18)F-amyloid tracer florbetapir compares diagnostically with (18)F-FDG PET when evaluating patients with Alzheimer disease (AD) and controls.

METHODS

Nineteen patients with a clinical diagnosis of AD and 21 elderly controls were evaluated with both (18)F-florbetapir and (18)F-FDG PET scans. Scans were interpreted together by 2 expert readers masked to any case information and were assessed for tracer binding patterns consistent with AD. The criteria for interpreting the (18)F-florbetapir scan as positive for AD was the presence of binding in the cortical regions relative to the cerebellum. (18)F-FDG PET scans were interpreted as positive if they displayed the classic pattern of hypometabolism in the temporoparietal regions. Scans were interpreted as either positive or negative for AD. In addition, a relative scoring system was used to assess the degree of either hypometabolism or amyloid binding in specified regions. The metabolism and amyloid binding scores for each region were compared across subjects. An overall ratio was calculated on the basis of values in regions expected to be affected by AD and those not expected to be affected. The metabolic ratio and amyloid ratio were then correlated with the mini-mental status examination (MMSE) score.

RESULTS

The sensitivity and specificity, compared with the clinical diagnosis of AD or controls, for the (18)F-florbetapir scans were 95% and 95%, respectively, and for the (18)F-FDG scans 89% and 86%, respectively. When a comparison with MMSE scores was made, (18)F-FDG significantly correlated with MMSE when both controls and AD patients were included (r = 0.79, P < 0.0001) and in AD patients alone (r = 0.70, P = 0.001). The (18)F-florbetapir scores significantly correlated with MMSE scores only when both controls and AD patients were included (r = 0.62, P < 0.001) but not in the AD group alone (r = 0.12, P = 0.66).

CONCLUSION

Overall, both scans performed well in detecting AD in patients with known clinical AD. Both scans correlated well with cognitive status as determined by MMSE when the entire cohort of controls and AD patients was evaluated. However, only the (18)F-FDG scans correlated with cognitive status when AD patients were evaluated separately.

The role of PET imaging in the management of patients with central nervous system disorders

PET will continue to play a critical role in both clinical and research applications with regard to CNS disorders. PET is useful in the initial diagnosis of patients presenting with CNS symptoms and can help clinicians determine the best course of therapy. PET studies can also be useful for studying the response to therapy. From the research perspective, the various neurotransmitter and other molecular tracers currently available or in development will provide substantial information about pathophysiologic process in the brain. As such applications become more widely tested, their introduction into the clinical arena will further advance the use of PET imaging in the evaluation and management of CNS disorders.

Sleep and quantitative EEG in neurodegenerative disorders

This paper reviews current knowledge on sleep problems, sleep architecture changes and quantitative EEG alteration brought on by various neurodegenerative diseases, such as Alzheimer's disease (AD), progressive supranuclear palsy (PSP), REM sleep behavior disorder (RBD), Parkinson's disease (PD), dementia with Lewy bodies (DLB), multiple system atrophy MSA, Huntington's disease and Creutzfeldt-Jakob disease, in comparison to normal aging. The study of sleep variables and that of the spectral composition of the EEG can provide valuable information for understanding the pathophysiology and for assisting the diagnosis of neurodegenerative diseases.

Determination of regional cerebral function with FDG-PET imaging in neuropsychiatric disorders

Functional brain imaging using 18F fluorodeoxyglucose (FDG) and positron emission tomography (PET) has greatly enhanced our understanding of brain function both in normal conditions as well as in a wide variety of neuropsychiatric disorders. We review the uses of FDG PET in the diagnosis, management, and follow-up of patients with neuropsychiatric disorders. This article will also explore what FDG-PET imaging has revealed in these neuropsychiatric disorders and how these findings relate to both research and clinical applications.

SPECT monitoring of improved cerebral blood flow during long-term treatment of elderly patients with nootropic drugs

PURPOSE

In normal aging persons, oxygen and glucose consumption progressively decreases with reduced cerebral blood flow (CBF), which could be responsible for age-related changes in cognitive functions. A data processing model with the use of Tc-99m SPECT of the human brain has been developed and found to be sensitive for monitoring the effects of drugs that increase CBF. In this study, the effect of two vasodilator drugs (the combination of pentifylline and nicotinic acid versus piracetam) was compared with the effect of placebo on CBF.

MATERIALS AND METHODS

Thirty elderly volunteers had three different procedures using the Peelproc method to spatially standardize and compare CBF patterns by SPECT before and after drug intervention. The 30 patients were divided into five groups of six persons each who were randomly assigned in a 1:1 ratio to the treatment sequences consisting of three phases: the combination of pentifylline and nicotinic acid (C), piracetam (N), and placebo (P), or C-N-P; P-N-C; P-C-N; N-C-P; C-P-N; or N-P-C. Phases 1 to 3 each consisted of a baseline recording of parameters (day 0), treatment for 60 days (days 1 to 60), and recording of parameters after treatment (day 61).

RESULTS

In elderly human volunteers (ages, 52 to 70 years), after 2 months of oral treatment with a combination of pentifylline and nicotinic acid (800 mg pentifylline, 200 mg nicotinic acid daily), SPECT results for the Peel-proc program indicated a statistically significant improvement in CBF of the total brain, with a more pronounced improvement in the cerebellum and frontal regions, where a definite shift from abnormal to normal blood flow was detected. Spontaneous communication from most of the volunteers suggested that they experienced an improvement in memory and general well-being from the combination treatment. After 2 months of oral treatment with piracetam (2.4 g daily) in elderly human volunteers, SPECT results indicated a regional improvement in CBF, particularly in the cerebellum. However, no beneficial effects with this drug were spontaneously reported.

CONCLUSION

The in vivo method to quantitatively monitor the progress of long-term drug therapy on CBF described here could be useful to assess and even direct changes in therapy.

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.

Brain SPECT in dementia. A clinical-scintigraphic correlation

The aim of this study was to compare the accuracy of computed tomography (CT) and single photon emission computerized tomography (SPECT) in the diagnosis of dementia. Fifty-two patients with clinical diagnosis of dementia and 11 controls were studied. The scans were interpreted by one experienced neuroradiologist and one nuclear radiologist, both blinded to the clinical data. In the diagnosis of dementia, CT and SPECT showed equal sensitivity (82.7%) and statistically similar specificity (63.8 and 81.8%, respectively). The specificity of SPECT in diagnosing Alzheimer's disease (100%) was statistically superior to CT (69%). However, both methods showed similar sensitivity in detecting Alzheimer's disease. In conclusion, SPECT and CT showed similar accuracy in the diagnosis of dementia. The quite high specificity of SPECT in Alzheimer's disease may be useful for confirming that diagnosis, particularly for patients with presenile onset of the disease.

Response to tacrine in patients with dementia of the Alzheimer's type: cerebral perfusion change is related to change in mental status

We evaluated change in cerebral hypoperfusion by single photon emission computed tomography (SPECT) in 12 patients with a clinical diagnosis of dementia Alzheimer's type (DAT) before and after treatment with Tacrine. Based on clinical evaluation of the SPECT scans before and after treatment, two groups of patients were identified. One (N = 5) experienced a relative decrease in cerebral perfusion and a decrease in mini-mental status examination (MMSE) scores across the treatment interval and was labeled "non-responders". A second group consisting of 7 patients was judged as showing an increase in cerebral perfusion at follow-up compared to baseline and an increase in MMSE scores. These were termed "responders". The group difference in MMSE score change was significant (Fisher's exact test: p < 0.008). Sensitivity (0.85) and specificity (1.0) and Receiver Operating Characteristic values (discriminability or d' = 3.12 and bias or beta = 4.6) indicated that direction of change in cerebral perfusion was a reasonable indicator of direction of change in MMSE scores. These results suggest that SPECT determined changes in cerebral perfusion may be useful in identification of DAT patients who are more likely to respond to centrally active agents such as tacrine.

SPECT functional brain imaging. Technical considerations

The technical aspects of functional brain single-photon emission computed tomography (SPECT) imaging, referring primarily to the most common SPECT brain function measure--regional cerebral blood flow--are reviewed. SPECT images of regional cerebral blood flow are influenced by a number of factors unrelated to pathology, including tomographic quality, radiopharmaceuticals, environmental conditions at the time of radiotracer administration, characteristics of the subject (e.g., age, sex), image presentation, and image processing techniques. Modern SPECT scans yield excellent image quality, and instrumentation continues to improve. The armamentarium of regional cerebral blood flow and receptor radiopharmaceuticals is rapidly expanding. Standards regarding the environment for patient imaging and image presentation are emerging. However, there is still much to learn about the circumstances for performances and evaluation of SPECT functional brain imaging. Challenge tests, primarily established in cerebrovascular disease (i.e., the acetazolamide test), offer great promise in defining the extent and nature of disease, as well as predicting therapeutic responses. Clearly, SPECT brain imaging is a powerful clinical and research tool. However, SPECT will only achieve its full potential in the management of patients with cerebral pathology through close cooperation among members of the nuclear medicine, neurology, psychiatry, neurosurgery, and internal medicine specialties.

Neurophysiology and SPECT cerebral blood flow patterns in dementia

A series of elderly patients with dementia of Alzheimer type (AD), multi-infarct dementia (MID) and functional (non-organic) psychiatric illness (major depressive disorder) were selected by DSM III-R criteria and had the following investigations: a battery of cognitive tests, EEG with power and coherence spectral analyses of T4-T6, T3-T5, P4-O2, P3-O1 channels, visual evoked potential (flash and pattern reversal) and P300 recordings as well as single photon emission tomography (SPECT) using 99mTc HMPAO. Three subsets of patients were chosen on clinical and SPECT criteria. These were as follows: patients with a clinical diagnosis of AD and a SPECT rCBF pattern showing bilateral temporo-parietal perfusion deficits (AD type), patients with a clinical diagnosis of MID and a SPECT rCBF pattern showing single focal perfusion deficits or multiple areas of low perfusion in the cerebral cortex suggestive of ischaemic change (MID type SPECT picture) and functionally ill patients with normal rCBF (controls). The AD type group differed from the MID rCBF group in having significantly less alpha and more delta 2 (2- < 4 Hz) power. The latter had significantly lower alpha power than the controls. The 2 dementia groups with abnormal rCBF patterns did not differ in terms of coherence spectra or P300 latencies, but both had lower within and between hemisphere alpha coherence values and longer P300 latencies than the "controls" with normal rCBF. There were no group differences in the flash VEP P2-pattern reversal P100 latency difference values.

General paresis: neuropsychological and SPECT study of five cases

Although much less common than before the advent of the antibiotics, cognitive impairment due to general paresis can still be found in clinical practice. Five patients with general paresis underwent longitudinal neuropsychological assessment; on the occasion of the final evaluation, Single Photon Emission Tomography (SPECT) was also performed in four cases. The most frequent cognitive deficit at admission was long term spatial memory impairment, which was present in four patients. Only the two patients who received the highest dosage of intravenous penicillin therapy showed significant improvement at neuropsychological tests after treatment. SPECT findings included areas of cortical hypoperfusion and/or perfusion asymmetry in three out of four patients.

Regional spectral analysis of the REM sleep EEG in mild to moderate Alzheimer's disease

Regional spectral analyses of the EEG during wakefulness and REM sleep was performed in eight patients with mild to moderate Alzheimer's disease and compared to that of healthy age-matched controls. Alzheimer patients presented some EEG slowing in frontal, parieto-occipital and temporal regions in the waking state. However, this EEG slowing was much better revealed in REM sleep, whether expressed by the ratio of slow to fast frequencies or by changes in each of the frequency bands. Moreover, regional differences in EEG slowing, relatively nonexistent in the awake EEG, were a prominent feature of the REM sleep EEG. Importance of cholinergic basal forebrain in the desynchronization of the REM sleep EEG might explain these results because this structure is affected in early Alzheimer's disease.

SPECT imaging in psychiatry. A review

In the last two decades, brain imaging has become an integral part of clinical and research psychiatry. Single photon computed emission tomography (SPECT) is rapidly gaining acceptance as one of the major imaging techniques available, along with computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography (PET). Each of these techniques has its assets and drawbacks. This review concerns SPECT, a highly prevalent imaging technique whose potential value in brain imaging has not been appreciated until recently. Its purpose is to expose practicing clinicians and research psychiatrists alike to the attributes of this instrument, which is available in most nuclear medicine departments today. An effort is made to provide a comprehensive account of this technique, including a brief summary of the basic principles, the various methods of its application, and recent findings in most psychiatric disorders. Analogies to its "aristocratic cousin," PET, are presented to emphasize similarities and differences. Finally, directions for future development and implementation of SPECT are suggested.

Spectral analysis of the rapid eye movement sleep electroencephalogram in right and left temporal regions: a biological marker of Alzheimer's disease

Spectral analysis of electroencephalograms (EEGs) for both wakefulness and rapid eye movement (REM) sleep was performed over the temporal regions in 8 patients with mild to moderate Alzheimer's disease and in 8 age-matched control subjects. EEG slowing in Alzheimer patients was found to be much more prominent during REM sleep than during wakefulness. In addition, asymmetry on the awake EEG of Alzheimer patients was found to be even more prominent than on the REM sleep EEG. When EEG values of the most impaired hemisphere during REM sleep were examined, no overlap was found between the two groups either for the ratio of slow to fast frequencies or for percent power of each of the frequency bands. This was not the case for the awake EEG. These results suggest that diagnostically meaningful cutoff values for discriminating patients with mild to moderate Alzheimer's disease from age-matched control subjects can be derived from the REM sleep EEG of the temporal lobe.

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.

Diagnosing dementia. Current clinical concepts

Increasing numbers of Americans who live to advanced age are at risk for dementia. Despite an array of sophisticated assessment measures, a specific diagnostic test is lacking for dementia and it has been found to be both under- and overdiagnosed. Misdiagnosis is of concern because treatable conditions that mimic dementia may go untreated, and families of those who lack correct diagnosis are unable to properly plan for subsequent care needs. Well-informed nurses can serve important roles by sharing accurate information within the community, supporting and educating families during the diagnostic process, and referring families to appropriate resources.

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.