Single photon emission tomography with 123I-isopropylamphetamine in Alzheimer's disease and multi-infarct dementia

Hybrid Imaging of Vascular Cognitive Impairment

Cerebrovascular disease is a significant cause of cognitive impairment leading to a reduction or loss of functioning, including social and occupational. The connection cause-effect between cerebrovascular disease and cerebral infarction was originally theorized by the studies from Newcastle-Upon-Tyne, England, in the 1960s, where vascular dementia (VaD) was defined as a disease originated from several infarctions that overcome a determined threshold. It differs from Alzheimer's disease (AD), although there are various overlaps in risk factors, symptomatology, the similarity of vascular lesions, and treatment benefits. Nevertheless, AD is one-half of all cases of dementia. Cognitive impairment and dementia (VCID) has recently been proposed to include different entities such as VaD, Vascular cognitive impairment, subcortical (ischemic) VaD, and vascular cognitive disorders. VaD is the most common cause of dementia after AD. Neuroimaging is an essential part of the workup of patients with cognitive decline and in those with suspected VCID it should be used to assess the extent, location, and type of vascular lesions. Computed tomography (CT) or structural magnetic resonance imaging (MRI) are usually used for the diagnosis of vascular diseases of the brain. However, images obtained from new hybrid devices could help the neurologist in the differential diagnosis between various neuropathological entities related to VCID. Single-photon emission computed tomography (SPECT) combined with CT or MRI and positron emission tomography (PET) combined with CT or MRI represent the future of neuroimaging tools as morphological and functional data can be provided simultaneously. New prospects have been developed such as hybrid PET/SPECT/CT, a high-performance prototype able to produce high-quality images but for now suitable only for small animals. Nowadays, PET/CT and PET/MRI are good performance and high-quality instruments, even if the magnetic field of MRI represents a limitation that affects the PET electronics and positron detection ability. SPECT/MRI delineates as a potential and tempting device. It could give us both functional and anatomical details, with the advantage of lack of extra ionizing radiation and high soft-tissue contrast, important features, and considerable auxiliary for differential diagnosis in the variegate word of vascular cognitive impairment. The aim of this review is to summarize the newest viewpoints in hybrid imaging in the diagnosis of VaD and to highlight pros and cons of each methodic.

Clinical applications of neuroimaging in patients with Alzheimer's disease: a review from the Fourth Canadian Consensus Conference on the Diagnosis and Treatment of Dementia 2012

In May 2012, the Fourth Canadian Consensus Conference on the Diagnosis and Treatment of Dementia brought together in Montreal experts from around Canada to update Canadian recommendations for the diagnosis and management of patients with neurodegenerative conditions associated with deterioration of cognition. Multiple topics were discussed. The present paper is a highly condensed version of those recommendations that were produced to support discussions in the field of neuroimaging for clinical diagnosis of those conditions.

Relationship between cognitive function and regional cerebral blood flow in different types of dementia

PURPOSE

We assessed relationships between cognitive impairment and regional cerebral blood flow (rCBF) in the different types of dementia.

SUBJECTS AND METHODS

Subjects, who included 27 with Alzheimer's disease (AD), seven with frontotemporal dementia (FTD), six with vascular dementia (VaD), and 12 normal controls, were evaluated using the Mini-mental State (MMS), Kana-hiroi Test, an auditory verbal learning test (AVLT), a word fluency test (WFT) and Raven's Coloured Progressive Matrices (RCPM). The rCBF was measured using a three-dimensional stereotaxic ROI template method (3DSRT).

RESULTS

In all dementia types, left superior frontal hypoperfusion was demonstrated. In AD and VaD significant CBF reduction also was seen in both angular, temporal, occipital, and precentral, both hippocampi, thalami, and pericallosal regions, and the left lenticular nucleus. MMS, Kana-hiroi Test, and AVLT scores correlated with CBF in all regions. WFT scores were correlated highly with CBF in the left side in frontal, temporal, and angular regions and right and left lenticular nuclei, thalami, and pericallosal regions. RCPM scores correlated with CBF in posterior regions.

CONCLUSION

Close coupling was evident between reduced rCBF and cognitive dysfunction in patients with dementia. Use of neuropsychologic tests and rCBF determinations in combination should enhance diagnostic accuracy.

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.

Iodine-123 labelled radiopharmaceuticals and single-photon emission tomography: a natural liaison

Most nuclear medicine departments possess one or more imaging apparatuses for single-photon emission tomography (SPET). Molecules of biological interest to assess metabolism and receptor function are often labelled with 123I, which allows proper SPET imaging. The various methods for radiolabelling are reviewed. As the biological integrity of these agents has been demonstrated for numerous radiopharmaceuticals, the purpose of this review is to summarize the efficacy in various fields of medicine, including the imaging of tumours, infection, myocardium and cerebrum.

Brain SPECT of Creutzfeldt-Jakob disease

SPECT imaging with I-123 IMP or Tc-99m HMPAO was performed in two patients with Creutzfeldt-Jakob disease to evaluate abnormalities in brain perfusion. In the first patient, there was decreased perfusion of the left frontal, parietal, and temporal lobes. CT and MRI were negative. In the second patient, there was patchy perfusion and slightly decreased perfusion of the right hemisphere. MRI revealed slight brain atrophy and bilateral high intensity areas in the basal ganglia on T2 weighted images. Subsequent SPECT imaging revealed severely decreased perfusion of the entire brain. Subsequent MRI demonstrated severe brain atrophy.

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.

First-pass extraction fraction of iodine-123 labeled perfusion tracers in living primate brain

The cerebral extraction and retention of three radioiodinatéd SPECT perfusion tracers were measured using residue detection in a baboon. A permeability-surface area product PS' with special relevance to SPECT was calculated from the retention of tracer in the brain after 10 min. PS' differs from the traditional PS value, which is calculated from the tracer clearance curve at 2 min. The PS' values ranged from 50 to 95 mL/min/100 g, decreased in the order [123I]IMP > [123I]iodoperidol approximately [123I]HIPDM, and did not differ for specific activities of 10 MBq/mmol to 74 TBq/mmol. These radioiodinated compounds exhibited extraction characteristics superior to those of [99mTc]HMPAO but underestimated cerebral blood flow when flows were above 20-30 mL/min/100 g, underscoring the need for development of a more ideal SPECT perfusion tracer.

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.

Metabolism in vitro of radioiodinated N-isopropyl-p-iodoamphetamine by isolated hepatocytes

An in vitro technique for the determination of radiopharmaceutical metabolism has been developed using isolated hepatocytes. Radioiodinated N-isopropyl-p-iodoamphetamine (IMP; iofetamine, USP) was employed a model tracer in these studies because its labeled metabolites are well-characterized. Hepatocytes isolated from the rat and human produced labeled metabolites in vitro for up to 4 h in a manner similar to that reported for humans in vivo. Identical metabolites were generated by all cell types investigated, but the rate of metabolism differed (rat >> human; female > male; fresh > frozen). The utility of this methodology for the preclinical evaluation of potential radiopharmaceuticals is described.

Association of atrophy of the medial temporal lobe with reduced blood flow in the posterior parietotemporal cortex in patients with a clinical and pathological diagnosis of Alzheimer's disease

A combination of medial temporal lobe atrophy, shown by computed tomography, and reduced blood flow in the parietotemporal cortex, shown by single photon emission tomography, was found in 86% (44/51) of patients with a clinical diagnosis of senile dementia of the Alzheimer type (SDAT). The same combination of changes was found in four out of 10 patients with other clinical types of dementia and in two out of 18 with no evidence of cognitive deficit. Of the 12 patients who died, 10 fulfilled histopathological criteria for Alzheimer's disease, nine of them having a clinical diagnosis of SDAT, and one a clinical diagnosis of multi-infarct dementia. All 10 patients with histopathologically diagnosed Alzheimer's disease had shown a combination of hippocampal atrophy and reduced parietotemporal blood flow in life. In 10 patients (nine with SDAT) out of 12 in whom the hippocampal atrophy was more noticeable on one side of the brain than on the other the parietotemporal perfusion deficit was also asymmetrical, being greater on the side showing more hippocampal atrophy. These results suggest that the combination of atrophy of the hippocampal formation and reduced blood flow in the parietotemporal region is a feature of dementia of the Alzheimer type and that the functional change in the parietotemporal region might be related to the loss of the projection neurons in the parahippocampal gyrus that innervate this region of the neocortex.

[Comparison of SPECT and quantified EEG features in Alzheimer's type dementia]

Forty-one patients with probable dementia of the Alzheimer type (DAT) have been studied by computerized EEg (C-EEG) and single photon emission tomography (SPECT) using 123-IMP. Four groups have been distinguished according to SPECT hypoperfusion topography: frontal, temporo-parietal, fronto-parietal and fronto-temporo-parietal. C-EEG parameters were much more disturbed in the 2 latter than in the 2 former groups. Thus a normal C-EEG could indicate a dominant frontal or temporo-parietal form of DAT. Therefore some bias due to duration or rate of disease progression cannot be excluded. So far the important finding is that EEG changes are diffuse and do not reflect the topography of SPECT hypoperfusion questioning the value of EEG topographical analysis in DTA.

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.

SPECT in the diagnosis of Alzheimer's disease and multi-infarct-dementia

SPECT with Tc-99m HM-PAO as a radiopharmaceutical was performed in 17 patients meeting research criteria for Alzheimer's disease (AD), in 10 patients with a clinical diagnosis of multi-infarct-dementia (MID) and in 12 healthy volunteers. Regional tracer uptake was measured in frontal, parietal, and temporoparietal regions. A statistically significant decrease of tracer uptake in the temporoparietal region was found in AD-patients compared with controls. AD-patients showed less activity in this region than MID-patients, but this difference did not reach statistical significance. In both AD- and MID-patients decrease of tracer uptake was not correlated with dementia severity. We conclude that SPECT brain imaging is not yet ready for routine use in the distinction between AD and MID.

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.

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.

Multimodal imaging in Alzheimer's disease. The relationship between MRI, SPECT, cognitive and pathological changes

Patients with a clinical diagnosis of Alzheimer's disease were studied using MRI, SPECT, and psychometric tests. Significant correlations between focal perfusion deficits and focal cognitive deficits were found. Significant correlations between regional relaxation time of white matter and psychometric tests of diffuse and focal categories were also found. Pathological examination confirmed Alzheimer's disease as the only diagnosis.

Differentiation of bronchogenic carcinoma from secondary changes, obstructive pneumonitis and/or collapse by I-123 IMP lung imaging

Serial lung images with N-isopropyl-p-[I-123]-iodoamphetamine (I-123 IMP) were obtained to assess the imaging findings and to clarify the lesion to uptake relationships in 74 lesions in 73 patients with various histological types of bronchogenic carcinoma. A decreased uptake area was observed in all 74 lesions in the initial one or two-min I-123 IMP image. The initial image was analogous to a Tc-99m MAA lung perfusion image in 70 patients in whom both lung imaging procedures were performed. The imaging findings changed following this initial phase. At 4 hr, the lesion was depicted as either areas of decreased uptake or increased uptake or a combination of the two. Comparison between the lesion findings in the 4-hr I-123 IMP images, radiograms and removed specimens revealed that areas of decreased uptake corresponded to the cancerous portions of the lung mass or pleural effusion and areas of increased uptake corresponded to inflammatory portions including obstructive pneumonitis and/or collapse. Thus, the 4-hr I-123 IMP lung images can be used to discriminate the cancerous portion from associated secondary changes, obstructive pneumonitis and/or collapse.

Iofetamine hydrochloride I 123: a new radiopharmaceutical for cerebral perfusion imaging

Iofetamine hydrochloride I 123 permits cerebral blood perfusion imaging with single photon emission computed tomography (SPECT). SPECT is more widely available than positron emission tomography, and complements anatomic visualization with X-ray computed tomography (CT) or magnetic resonance imaging. Iofetamine is an amphetamine analog that is rapidly taken up by the lungs, then redistributed principally to the liver and brain. The precise mechanism of localization has not been determined, but is believed to result from nonspecific receptor binding. Brain uptake peaks at 30 minutes postinjection and remains relatively constant through 60 minutes. The drug is metabolized and excreted in the urine, with negligible activity remaining at 48 hours. When compared with CT in stroke patients, visualization may be performed sooner after symptom onset and a larger zone of involvement may be evident with iofetamine. Localization of seizure foci and diagnosis of Alzheimer's disease may also be possible. As CT has revolutionized noninvasive imaging of brain anatomy, SPECT with iofetamine permits routine cerebral blood flow imaging.

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

SPECT images of the brain can be obtained using either 123I labelled amines or 99mTc-hexamethylpropyleneamineoxime (HM-PAO). Both materials produce images which are blood flow dominated and so appear similar in normal subjects, although the respective mechanisms of uptake are not yet finally established. It seems likely, however, that the different mechanisms of uptake are responsible for recent reports of some differences seen in images obtained with the two types of agent in patients with cerebral pathology, mainly cerebrovascular disease. In this study, 12 demented patients, 6 with dementia of the Alzheimer type (DAT) and 6 with multi infarct dementia (MID), were imaged with 123I-isopropylamphetamine (IMP) and 99mTc-HM-PAO and the images compared. Significantly more lesions were seen with IMP than HM-PAO (P less than 0.02); out of a possible 120 sites, 41 lesions were seen with IMP compared to 28 with HM-PAO, 23 being seen with both agents. However, it is concluded that either agent can be used for the differential diagnosis of dementia, a task for which the new cerebral blood flow agents seem well suited.

Increased accumulation of iodine-123-IMP in the pulmonary inflammatory lesion surrounding a lung cancer

In a patient with primary lung cancer, increased accumulation of I-123-IMP was observed in a pulmonary inflammatory lesion surrounding a lung cancer which was delineated as a photon deficient area. Ga-67-citrate uptake was observed in both the inflammatory and cancerous areas. These findings suggest that I-123-IMP may have the potential to accumulate differently in a variety of pathological conditions of the lung and thus may be a clinically useful lung imaging agent.

Focal cerebral hypoperfusion and selective cognitive deficit in dementia of the Alzheimer type

Regional cerebral blood flow was investigated using single photon emission computed tomography and xenon-133 intravenous injection in six patients with dementia of the Alzheimer type (DAT) with atypical focal clinical presentation, and in 20 age-matched healthy volunteers. The patients had a progressive and preponderant cognitive deficit and a focal hypoperfusion that correlated with the neuropsychological findings, whereas the average flow did not significantly differ from that of controls. The assessment of concordant haemodynamic and neuropsychological focal abnormalities could be useful in the diagnosis of atypical cases of DAT.

Single photon emission tomography using 99mTc-HM-PAO in the investigation of dementia

Single photon emission tomographic imaging of the brain using 99mTc HM-PAO was carried out in patients with a clinical diagnosis of Alzheimer's disease, non-Alzheimer frontal-lobe dementia, and progressive supranuclear palsy. Independent assessment of reductions in uptake revealed posterior hemisphere abnormalities in the majority of the Alzheimer group, and selective anterior hemisphere abnormalities in both other groups. The findings were consistent with observed patterns of mental impairment. The imaging technique has potential value in the differential diagnosis of primary cerebral atrophy.

Functional imaging of the brain

The radionuclide tracer method is unique amongst all other imaging methodologies in its ability to trace organ or tissue function and metabolism. It derives this advantage from the nature of the signal used for image generation, and its single interaction with the organ or system under examination. Physical processes such as electron or proton density assessment or resonance, edge identification, electrical or ultrasonic impedence, do not pertain to the image generation process in nuclear medicine, and if so, only in a rather secondary manner. The nuclear medicine imaging study is primarily a study of the chemical nature, distribution and interaction of the tracer/radiopharmaceutical utilised with the cellular system which requires investigation: the thyroid cells with sodium iodide, the recticular endothelial cells with colloidal particles, the adrenal medulla cells with metaiodobenzylguanidine, and so on. In the two most recent areas of nuclear medicine expansion, oncology (with labelled monoclonal antibodies) and neurology and psychiatry (with a whole new series of lipid soluble radiopharmaceuticals), specific cell systems can also be targeted and hence imaged and investigated. The study of structure as masterly performed by Virchow and all his successors over more than a century, is now definitely the prerogative of such imaging systems which excel with spatial and contrast resolution (x-ray computed transmission tomography, nuclear magnetic resonance imaging, diagnostic ultrasound). However the investigation of function and metabolism (as performed by Claude Bernard, Georg von Hevesy, and so many others), has clearly passed from the laboratory animal protocol and experiment to the direct investigation in man, this being the achievement of the radionuclide tracer methodology. In this article, we review present interest and developments in that part of nuclear medicine activity which is aimed at the study of the neurological or psychiatric patient.

Antemortem markers of Alzheimer's disease

This review examines various approaches to the development of antemortem markers of Alzheimer's disease. Among the procedures discussed are: neurochemical and histopathologic studies of the cholinergic system, concentrating on CSF and blood plasma; genetic studies; imaging and electrophysiological studies; and neuroendocrine studies.

[123I]iodoamphetamine SPECT imaging

SPECT imaging of [123I]IMP is reviewed. Methods for radiopharmaceutical production are discussed with an emphasis on labeling small quantities of IMP. Limited angle tomography and full angle SPECT with standard cameras and special imaging systems are reviewed. Selection of collimator and methods of reconstruction are discussed. Clinical studies are described with emphasis on stroke, epilepsy and dementia. The efforts to perform quantitative imaging of rCBF with [123I]IMP are reviewed.