Validation of statistical parametric mapping (SPM) in assessing cerebral lesions: A simulation study

A Comprehensive Survey on the Detection, Classification, and Challenges of Neurological Disorders

Simple Summary

This study represents a resourceful review article that can deliver resources on neurological diseases and their implemented classification algorithms to reveal the future direction of researchers. Researchers interested in studying neurological diseases and previously implemented techniques in this field can follow this article. Various challenges occur in detecting different stages of the disorders. A limited amount of labeled and unlabeled datasets and other limitations is represented in this article to assist them in finding out the directions. The authors’ purpose for composing this article is to make a straightforward and concrete path for researchers to quickly find the way and the scope in this field for implementing future research on neurological disease detection.

Abstract

Neurological disorders (NDs) are becoming more common, posing a concern to pregnant women, parents, healthy infants, and children. Neurological disorders arise in a wide variety of forms, each with its own set of origins, complications, and results. In recent years, the intricacy of brain functionalities has received a better understanding due to neuroimaging modalities, such as magnetic resonance imaging (MRI), magnetoencephalography (MEG), and positron emission tomography (PET), etc. With high-performance computational tools and various machine learning (ML) and deep learning (DL) methods, these modalities have discovered exciting possibilities for identifying and diagnosing neurological disorders. This study follows a computer-aided diagnosis methodology, leading to an overview of pre-processing and feature extraction techniques. The performance of existing ML and DL approaches for detecting NDs is critically reviewed and compared in this article. A comprehensive portion of this study also shows various modalities and disease-specified datasets that detect and records images, signals, and speeches, etc. Limited related works are also summarized on NDs, as this domain has significantly fewer works focused on disease and detection criteria. Some of the standard evaluation metrics are also presented in this study for better result analysis and comparison. This research has also been outlined in a consistent workflow. At the conclusion, a mandatory discussion section has been included to elaborate on open research challenges and directions for future work in this emerging field.

Evaluating the efficacy of hearing aids for tinnitus therapy - A Positron emission tomography study

Brain imaging studies have revealed neural changes in chronic tinnitus patients that are not restricted to auditory brain areas; rather, the engagement of limbic system structures, attention and memory networks are has been noted. Hearing aids (HA) provide compensation for comorbid hearing loss and may decrease tinnitus-related perception and annoyance. Using resting state positron emission tomography our goal was to analyze metabolic and functional brain changes after six months of effective HA use by patients with chronic tinnitus and associated sensorineural hearing loss. 33 age and hearing loss matched participants with mild/moderate hearing loss were enrolled in this study: 19 with tinnitus, and 14 without tinnitus. Participants with tinnitus of more than 6 months with moderate/severe Tinnitus Handicap Inventory (THI) and Visual Analogue Scale (VAS) scores composed the tinnitus group. A full factorial 2X2 ANOVA was conducted for imaging analysis, with group (tinnitus and controls) and time point (pre-intervention and post-intervention) as factors. Six months after HA fitting, tinnitus scores reduced statistically and clinically. Analysis revealed increased glycolytic metabolism in the left orbitofrontal cortex, right temporal lobe and right hippocampus, and reduced glycolytic metabolism in the left cerebellum and inferior parietal lobe within the tinnitus group. The hearing loss control group showed no significant metabolic changes in the analysis. Parsing out the contribution of tinnitus independent of hearing loss, allowed us to identify areas implicated in declines in tinnitus handicap as a result of the intervention. Brain regions implicated in the present study may be part of chronic tinnitus-specific network.

Striatal Dopaminergic Depletion Pattern Reflects Pathological Brain Perfusion Changes in Lewy Body Diseases

PURPOSE

In Lewy body diseases (LBD), various symptoms occur depending on the distribution of Lewy body in the brain, and the findings of brain perfusion and dopamine transporter single-photon emission computed tomography (DAT-SPECT) also change accordingly. We aimed to evaluate the correlation between brain perfusion SPECT and quantitative indices calculated from DAT-SPECT in patients with LBD.

PROCEDURES

We retrospectively enrolled 35 patients with LBD who underwent brain perfusion SPECT with N-isopropyl-p-[¹²³I] iodoamphetamine and DAT-SPECT with ¹²³I-ioflupane. Mini-mental state examination (MMSE) data were also collected from 19 patients. Quantitative indices (specific binding ratio [SBR], putamen-to-caudate ratio [PCR], and caudate-to-putamen ratio [CPR]) were calculated using DAT-SPECT. These data were analysed by the statistical parametric mapping procedure.

RESULTS

In patients with LBD, decreased PCR index correlated with hypoperfusion in the brainstem (medulla oblongata and midbrain) (uncorrected p < 0.001, k > 100), while decreased CPR index correlated with hypoperfusion in the right temporoparietal cortex (family-wise error corrected p < 0.05), right precuneus (uncorrected p < 0.001, k > 100), and bilateral temporal cortex (uncorrected p < 0.001, k > 100). However, there was no significant correlation between decreased SBR index and brain perfusion. Additionally, the MMSE score was correlated with hypoperfusion in the left temporoparietal cortex (uncorrected p < 0.001).

CONCLUSIONS

This study suggests that regional changes in striatal ¹²³I-ioflupane accumulation on DAT-SPECT are related to brain perfusion changes in patients with LBD.

Parietal Involvement in the Semantic Variant of Primary Progressive Aphasia with Alzheimer's Disease Cerebrospinal Fluid Profile

Semantic variant of primary progressive aphasia (svPPA) is typically associated with non-Alzheimer's disease (AD) pathology. However, some anatomopathological studies have found AD lesions in those patients. We compared brain perfusion SPECT of 18 svPPA patients with cerebrospinal fluid (CSF) biomarkers indicative of non-AD pathology (svPPA-nonAD) and three svPPA patients with CSF biomarkers indicative of underlying AD (svPPA-AD). All svPPA patients had severe left temporopolar hypoperfusion. SvPPA-nonAD had additional anterior cingulate and mediofrontal hypoperfusion, whereas svPPA-AD had greater left parietal and posterior cingulate involvement. Parietal damage in svPPA constitutes a biomarker for underlying Alzheimer pathology thus refining the classification of this PPA variant.

Optimization of Statistical Single Subject Analysis of Brain FDG PET for the Prognosis of Mild Cognitive Impairment-to-Alzheimer's Disease Conversion

BACKGROUND

Positron emission tomography (PET) with the glucose analog F-18-fluorodeoxyglucose (FDG) is widely used in the diagnosis of neurodegenerative diseases. Guidelines recommend voxel-based statistical testing to support visual evaluation of the PET images. However, the performance of voxel-based testing strongly depends on each single preprocessing step involved.

OBJECTIVE

To optimize the processing pipeline of voxel-based testing for the prognosis of dementia in subjects with amnestic mild cognitive impairment (MCI).

METHODS

The study included 108 ADNI MCI subjects grouped as 'stable MCI' (n = 77) or 'MCI-to-AD converter' according to their diagnostic trajectory over 3 years. Thirty-two ADNI normals served as controls. Voxel-based testing was performed with the statistical parametric mapping software (SPM8) starting with default settings. The following modifications were added step-by-step: (i) motion correction, (ii) custom-made FDG template, (iii) different reference regions for intensity scaling, and (iv) smoothing was varied between 8 and 18 mm. The t-sum score for hypometabolism within a predefined AD mask was compared between the different settings using receiver operating characteristic (ROC) analysis with respect to differentiation between 'stable MCI' and 'MCI-to-AD converter'. The area (AUC) under the ROC curve was used as performance measure.

RESULTS

The default setting provided an AUC of 0.728. The modifications of the processing pipeline improved the AUC up to 0.832 (p = 0.046). Improvement of the AUC was confirmed in an independent validation sample of 241 ADNI MCI subjects (p = 0.048).

CONCLUSION

The prognostic value of voxel-based single subject analysis of brain FDG PET in MCI subjects can be improved considerably by optimizing the processing pipeline.

Generation of realistic HMPAO SPECT images using a subresolution sandwich phantom

Traditional interpretation of rCBF SPECT data is of a qualitative nature and is dependent on the observer's understanding of the normal distribution of the tracer. The use of a normal database in quantitative regional analysis facilitates the detection of functional abnormality in individual and group studies by accounting for inter-subject variability. The ability to simulate realistic images would allow various important areas related to the use of normal databases to be studied. These include the optimisation of the detection of abnormal blood flow and the portability of normal databases between gamma camera systems. To investigate this further we have constructed a hardware phantom and scanned various configurations of radioactive brain patterns and simulated skull configurations.

METHODS

A subresolution sandwich phantom was constructed with a simulated skull which was assembled using a high-resolution segmented MR scan printed with a (99m)TcO₄ - mixture and scanned using a double-headed gamma camera with parallel-hole collimators. Various different grey-to-white matter (GM:WM) ratios and aluminium simulated skull configurations were used. A single difference measure between the phantom data and a control database mean image was used for optimisation. The realism of phantom data was assessed using statistical parametric mapping (SPM) and ROI analysis.

RESULTS

Optimisation was achieved with a range of WM:GM ratios from 1.9 to 2.4:1 with various simulated skull configurations.

CONCLUSION

The ability to simulate realistic HMPAO SPECT scans has been demonstrated using a subresolution sandwich phantom. Further work, involving scanning the optimised phantom on different gamma camera systems and comparison with camera-specific normal databases should further refine the phantom configuration.

IgA NMDA receptor antibodies are markers of synaptic immunity in slow cognitive impairment

OBJECTIVE

To report that antibodies to synaptic proteins may occur in association with slow, progressive cognitive decline.

METHODS

A total of 24 patients with progressive cognitive dysfunction of unclear etiology were examined for onconeuronal and synaptic receptor antibodies. The effect of serum was examined in cultures of dissociated mouse hippocampal neurons.

RESULTS

Seven patients had immunoglobulin A (IgA), but no immunoglobulin G (IgG), antibodies against NMDA receptor (NMDAR). Anti-NMDAR IgA positive patients' serum, but not serum from control individuals, caused dramatic decrease of the levels of NMDAR and other synaptic proteins in neurons, along with prominent changes in NMDAR-mediated currents. These effects correlated with the titer of IgA NMDAR antibodies and were reversed after removing patients' serum from the culture media. When available, comprehensive clinical assessment and brain metabolic imaging showed neurologic improvement after immunotherapy.

CONCLUSIONS

A subset of patients with slowly progressive cognitive impairment has an underlying synaptic autoimmunity that decreases the density of NMDAR and other synaptic proteins, and alters synaptic currents. This autoimmunity can be demonstrated examining patients' serum and CSF for NMDAR IgA antibodies, identifying possible candidates for immunotherapy.

Optimization of the parameters of a method for computer-aided detection of perfusion deficiencies in brain images

OBJECTIVE

Simulated data from the recent Institute of Physics and Engineering in Medicine audit of quantitative cerebral perfusion were used to optimize the parameters of eigenimage analysis, a method for computer-aided detection.

METHODS

Twenty normal images provided by the audit were registered to the International Consortium for Brain Mapping 452 template using HERMES multimodality software and normalized to total counts. Six normal atlases were formed using the mean image and from zero to five eigenimages. Eight patient images, with computer-simulated lesions at known positions, were similarly registered and normalized. For each atlas, z-score images were formed for each patient. Thresholds of z0 = 2-5 in intervals of 0.5 were applied to the z-score images to form binary images of normal and abnormal voxels. A lesion was defined as a connected group of abnormal voxels with a minimum size of 1 ml. Lesions were assigned to one of 12 regions defined by the template. For eight patients, this gave 96 regions, 19 of which were known to contain an abnormality. Receiver-operating characteristic analysis was performed for the regions using z0 as a variable threshold.

RESULTS

For the receiver-operating characteristic analysis, an optimal area under the curve of approximately 0.90 was found using either one or three eigenimages, whereas good results (sensitivity = 0.75%; specificity = 90%) were obtained for a threshold of z0 approximately equal to 3. When the number of images in the normal dataset was considered, a meta-analysis showed consistency with other studies.

CONCLUSION

Eigenimage analysis was shown to give good diagnostic accuracy for cerebral perfusion images based on objective evaluation using simulated images.

Converging evidence for abnormalities of the prefrontal cortex and evaluation of midsagittal structures in pediatric posttraumatic stress disorder: an MRI study

Volumetric imaging research has shown abnormal brain morphology in posttraumatic stress disorder (PTSD) when compared with control subjects. We present results on a study of brain morphology in the prefrontal cortex (PFC) and midline structures, via indices of gray matter volume and density, in pediatric PTSD. We hypothesized that both methods would demonstrate aberrant morphology in the PFC. Further, we hypothesized aberrant brainstem anatomy and reduced corpus callosum volume in children with PTSD. Twenty-four children (aged 7-14) with history of interpersonal trauma and 24 age- and gender-matched controls underwent structural magnetic resonance imaging (sMRI). Images of the PFC and midline brain structures were first analyzed using volumetric image analysis. The PFC data were then compared with whole brain voxel-based techniques using statistical parametric mapping (SPM). The PTSD group showed significantly increased gray matter volume in the right and left inferior and superior quadrants of the PFC and smaller gray matter volume in the pons and posterior vermis areas by volumetric image analysis. The voxel-by-voxel group comparisons demonstrated increased gray matter density mostly localized to ventral PFC as compared with the control group. Abnormal frontal lobe morphology, as revealed by separate-complementary image analysis methods, and reduced pons and posterior vermis areas are associated with pediatric PTSD. Voxel-based morphometry may help to corroborate and further localize data obtained by volume of interest methods in PTSD.

Choice of reference area in studies of Alzheimer's disease using positron emission tomography with fluorodeoxyglucose-F18

At present, there is still no consensus on the choice of the reference area in positron emission tomography (PET) studies of Alzheimer's disease (AD). In this study, PET scans with fluorodeoxyglucose-F18 were carried out in the following groups of subjects: 47 patients with probable AD, 8 patients with mild cognitive impairment, and 15 age-similar healthy subjects. Scans normalized to the cerebral global mean (CGM), cerebellum (CBL), and the primary sensorimotor cortex (SMC). We evaluated the effect of the different count normalization procedures on the accuracy of (18)F-FDG PET to detect AD-specific metabolic abnormalities (voxel-based group comparison) and to differentiate between patients and healthy subjects (ROI-based discriminant analysis) with regard to the degree of clinical deterioration. Metabolic reductions in groups of very mildly, mildly and moderate-to-severely affected patients appeared, respectively, 2.2, 2.6, and 2.7 times greater in spatial extent when tracer uptake was normalized to SMC rather than to CGM. The overall accuracy of discrimination was 94%, 91%, and 80% after normalization to SMC, CBL, and CGM, respectively. In general, normalization to SMC was somewhat superior to cerebellar normalization, allowing the detection of more pronounced metabolic deficits and the more accurate discrimination of patients from non-patients. Normalization to CGM should be used with great caution not only in advanced stages of dementia, but also in very mild AD cases.

Reduced thalamic 18F-flurodeoxyglucose retention in adults with neurofibromatosis type 1

OBJECTIVE

Neurofibromatosis type1 (NF1) is associated with cognitive and motor deficits whose pathogenesis is not well understood. 18F-Flurodeoxyglucose positron emission tomography (FDG PET) might be used to investigate putative functional correlates in the brain.

METHODS

Whole-body FDG PET including the brain had been performed in 29 NF1 patients suspected for malignant peripheral nerve sheath tumours (20 females, nine males, age 31.2+/-11.8 years). Twenty-nine age-matched and sex-matched subjects without evidence of neurological/psychiatric disease in whom FDG PET had been performed for NF1-unrelated oncological indication served as controls. Individual brain FDG retention images were stereotactically normalized and scaled to a common median retention value within the brain. Scaled FDG retention was compared between the NF1 group and the control group on a voxel-by-voxel base using ANCOVA in SPM2 with the FDG uptake period as covariate. The corrected significance level alpha=0.05 was used. Voxel-based analysis was complemented by volume of interest (VOI)-based analysis using predefined standard VOIs.

RESULTS

The voxel-based group comparison revealed a significant reduction of scaled FDG retention in the thalamus of the NF1 subjects within a cluster of 11.6 ml. There were no further significant effects, neither hypo-retention nor hyper-retention. Reduction of relative FDG retention in the thalamus in the NF1 subjects was confirmed by VOI analysis. The magnitude of the reduction was about 8%.

CONCLUSIONS

The thalamus appears to be affected in adults with NF1. The observed magnitude of the reduction of scaled thalamic FDG retention in adults is smaller than previously reported in children. This may be consistent with a stabilization of the disease process with age.

Effect of anatomical variability, reconstruction algorithms and scattered photons on the SPM output of brain PET studies

Statistical parametric mapping (SPM) has become the standard technique to statistically evaluate differences between functional images. The aim of this paper was to assess the effect of anatomical variability of skull, the reconstruction algorithm and the scattering of photons in the brain on the output of an SPM analysis of brain PET studies. To this end, Monte Carlo simulation was used to generate suitable PET sinograms and bootstrap techniques were employed to increase the reliability of the conclusions. Activity distribution maps were obtained by segmenting thirty nine T1-weighted magnetic resonance images. Foci were placed on the posterior cingulate cortex (PCC) and the superior temporal cortex (STC) and activation factors ranging between -25% and +25% were simulated. Preprocessing of the reconstructed images and statistical analysis were performed using SPM2. Our findings show that intersubject anatomical differences can cause the minimum sample size to increase between 10 and 42% for posterior cingulate Cortex and between 40 and 80% for superior temporal cortex. Ideal scatter correction (ISC) allowed us to diminish the sample size up to 18% and fully 3D reconstruction reduced the minimum sample size between 8 and 33%. Detection sensitivity was higher for hypo-activation than for hyper-activation situations and higher for superior temporal cortex than for posterior cingulate cortex.

Ecstasy-induced reduction of the availability of the brain serotonin transporter as revealed by [11C](+)McN5652-PET and the multi-linear reference tissue model: loss of transporters or artifact of tracer kinetic modelling?

In a previous positron emission tomography (PET) study with the serotonin transporter (SERT) ligand [(11)C](+)McN5652, we found protracted reduction of the availability of the brain SERT in users of the drug ecstasy. However, the multi-linear reference tissue method for the quantification of SERT availability used in this study is prone to effects of altered levels of statistical noise that could simulate reduction of SERT. The aim of the present study was to take into account this confound by re-evaluation of the data now using a modelling approach that is rather insensitive to alterations in the level of statistical noise. A total of 116 subjects (30 current, 29 former ecstasy users, 29 drug-naive, 28 polydrug controls) in whom [(11)C](+)McN5652-PET had been performed previously were re-evaluated. The equilibrium specific-to-non-specific partition coefficient V"( 3) was obtained voxel-wise by application of the simplified reference tissue method (SRTM), which provides quite unbiased results up to rather large noise levels. Voxel-based comparisons between the groups were performed using statistical parametric mapping. V"(3) was reduced in the striatum and in the thalamus in current ecstasy users. This was confirmed by volume-of-interest-based analysis. This result suggests that the ecstasy-induced reduction of SERT availability in SERT-rich brain regions reported previously indicates reduced SERT binding potential rather than being an artifact of tracer kinetic modelling. SRTM analysis did not confirm previous findings in neocortical brain areas.

Statistical parametric mapping and statistical probabilistic anatomical mapping analyses of basal/acetazolamide Tc-99m ECD brain SPECT for efficacy assessment of endovascular stent placement for middle cerebral artery stenosis

INTRODUCTION

Statistical parametric mapping (SPM) and statistical probabilistic anatomical mapping (SPAM) were applied to basal/acetazolamide Tc-99m ECD brain perfusion SPECT images in patients with middle cerebral artery (MCA) stenosis to assess the efficacy of endovascular stenting of the MCA.

METHODS

Enrolled in the study were 11 patients (8 men and 3 women, mean age 54.2 +/- 6.2 years) who had undergone endovascular stent placement for MCA stenosis. Using SPM and SPAM analyses, we compared the number of significant voxels and cerebral counts in basal and acetazolamide SPECT images before and after stenting, and assessed the perfusion changes and cerebral vascular reserve index (CVRI).

RESULTS

The numbers of hypoperfusion voxels in SPECT images were decreased from 10,083 +/- 8,326 to 4,531 +/- 5,091 in basal images (P = 0.0317) and from 13,398 +/- 14,222 to 7,699 +/- 10,199 in acetazolamide images (P = 0.0142) after MCA stenting. On SPAM analysis, the increases in cerebral counts were significant in acetazolamide images (90.9 +/- 2.2 to 93.5 +/- 2.3, P = 0.0098) but not in basal images (91 +/- 2.7 to 92 +/- 2.6, P = 0.1602). The CVRI also showed a statistically significant increase from before stenting (median 0.32; 95% CI -2.19-2.37) to after stenting (median 1.59; 95% CI -0.85-4.16; P = 0.0068).

CONCLUSION

This study revealed the usefulness of voxel-based analysis of basal/acetazolamide brain perfusion SPECT after MCA stent placement. This study showed that SPM and SPAM analyses of basal/acetazolamide Tc-99m brain SPECT could be used to evaluate the short-term hemodynamic efficacy of successful MCA stent placement.

Correlation between changes in regional cerebral blood flow and pain relief in complex regional pain syndrome type 1

OBJECTIVE

Analyzing changes in regional cerebral blood flow (rCBF) with SPECT in complex regional pain syndrome type 1 (CRPS 1), formerly known as reflex sympathetic dystrophy, is an optimal method for evaluating effective pain relief. We attempted to investigate the correlation of changes in rCBF with pain relief during treatments of sympathetic blockade and multimodal epidural pain control.

CASE REPORT

We describe a patient with severe CRPS 1 in whom conventional treatment failed to relieve the pain. Combined repeated lumbar sympathetic blocks and long-term epidural morphine, bupivacaine, and ketamine administration provided satisfactory pain relief and functional activity recovery. Six normal control subjects having one Tc-99m HMPAO scan each and the patient with CRPS having 3 Tc-99m HMPAO scans (once before treatment and twice at 4 months and 6 months after treatment, respectively). The patient with CRPS showed lower rCBF than normal controls in the left thalamus and higher rCBF than normal controls in the right parietal lobe and left frontal lobe. After subsequent treatment, the subtraction images showed increased rCBF in the left thalamus and decreased rCBF in the right parietal and left frontal lobes.

CONCLUSIONS

Tc-99m HMPAO SPECT showed a relationship of rCBF in the thalamus, parietal lobe, and frontal lobe with pain relief. rCBF alterations may provide an indicator for the quality of pain management for neuropathic pains. Subtraction analysis between pre- and posttreatment, by using statistical parametric mapping (version 2), can be used as an objective indicator for the effectiveness of therapy.

Imaging the neurobiological substrate of atypical depression by SPECT

PURPOSE

Neurobiological abnormalities underlying atypical depression have previously been suggested. The purpose of this study was to explore differences at functional brain imaging between depressed patients with and without atypical features and healthy controls.

METHODS

Twenty-three out-patients with chronic depressive disorder recruited from a service for patients with audiological symptoms were investigated. Eleven fulfilled the DSM-IV criteria for atypical depression (mood reactivity and at least two of the following: weight gain, hypersomnia, leaden paralysis and interpersonal rejection sensitivity). Twenty-three healthy subjects served as controls. Voxel-based analysis was applied to explore differences in (99m)Tc-HMPAO uptake between groups.

RESULTS

Patients in the atypical group had a higher prevalence of bilateral hearing impairment and higher depression and somatic distress ratings at the time of SPECT. Significantly higher tracer uptake was found bilaterally in the atypical group as compared with the non-atypicals in the sensorimotor (Brodmann areas, BA1-3) and premotor cortex in the superior frontal gyri (BA6), in the middle frontal cortex (BA8), in the parietal associative cortex (BA5, BA7) and in the inferior parietal lobule (BA40). Significantly lower tracer distribution was found in the right hemisphere in the non-atypicals compared with the controls in BA6, BA8, BA44, BA45 and BA46 in the frontal cortex, in the orbito-frontal cortex (BA11, BA47), in the postcentral parietal cortex (BA2) and in the multimodal association parietal cortex (BA40).

CONCLUSION

The differences found between atypical and non-atypical depressed patients suggest different neurobiological substrates in these patient groups. The putative links with the clinical features of atypical depression are discussed. These findings encourage the use of functional neuroimaging in psychiatric disorders.

IBZM tool: a fully automated expert system for the evaluation of IBZM SPECT studies

PURPOSE

Visual reading of [(123)I]IBZM SPECT scans depends on the experience of the interpreter. Therefore, semi-quantification of striatal IBZM uptake is commonly considered mandatory. However, semi-quantification is time consuming and prone to error, particularly if the volumes of interest (VOIs) are positioned manually. Therefore, the present paper proposes a new software tool ("IBZM tool") for fully automated and standardised processing, evaluation and documentation of [(123)I]IBZM SPECT scans.

METHODS

The IBZM tool is an easy-to-use SPM toolbox. It includes automated procedures for realignment and summation of multiple frames (motion correction), stereotactic normalisation, scaling, VOI analysis of striatum-to-reference ratio R, classification of R and standardised display. In order to evaluate the tool, which was developed at the University of Hamburg, the tool was transferred to the University of Hannover. There it was applied to 27 well-documented subjects: eight patients with multi-system atrophy (MSA), 12 patients with Parkinson's disease (PD) and seven controls. The IBZM tool was compared with manual VOI analysis.

RESULTS

The sensitivity and specificity of the IBZM tool for the differentiation of the MSA subjects from the controls were 100% and 86%, respectively. The IBZM tool provided improved statistical power compared with manual VOI analysis.

CONCLUSION

The IBZM tool is an expert system for the detection of reduced striatal D(2) availability on [(123)I]IBZM SPECT scans. The standardised documentation supports visual and semi-quantitative evaluation, and it is useful for presenting the findings to the referring physician. The IBZM tool has the potential for widespread use, since it appears to be fairly independent of the performance characteristics of the particular SPECT system used. The tool is available free of charge.

Simulation of realistic abnormal SPECT brain perfusion images: application in semi-quantitative analysis

Simulation is useful in the validation of functional image analysis methods, particularly when considering the number of analysis techniques currently available lacking thorough validation. Problems exist with current simulation methods due to long run times or unrealistic results making it problematic to generate complete datasets. A method is presented for simulating known abnormalities within normal brain SPECT images using a measured point spread function (PSF), and incorporating a stereotactic atlas of the brain for anatomical positioning. This allows for the simulation of realistic images through the use of prior information regarding disease progression. SPECT images of cerebral perfusion have been generated consisting of a control database and a group of simulated abnormal subjects that are to be used in a UK audit of analysis methods. The abnormality is defined in the stereotactic space, then transformed to the individual subject space, convolved with a measured PSF and removed from the normal subject image. The dataset was analysed using SPM99 (Wellcome Department of Imaging Neuroscience, University College, London) and the MarsBaR volume of interest (VOI) analysis toolbox. The results were evaluated by comparison with the known ground truth. The analysis showed improvement when using a smoothing kernel equal to system resolution over the slightly larger kernel used routinely. Significant correlation was found between effective volume of a simulated abnormality and the detected size using SPM99. Improvements in VOI analysis sensitivity were found when using the region median over the region mean. The method and dataset provide an efficient methodology for use in the comparison and cross validation of semi-quantitative analysis methods in brain SPECT, and allow the optimization of analysis parameters.

A Monte Carlo analysis technique applied to cerebral perfusion SPECT scans

OBJECTIVE

Voxel-based techniques are used to provide objective analyses of SPECT scans. The aim of this study was to develop a voxel-based analysis technique that uses a Monte Carlo method of statistical inference and assess this analysis technique for application to cerebral perfusion SPECT scans.

METHODS

Assessment of the validity of this non-parametric, Monte Carlo method of statistical inference has been performed for a range of study designs, image characteristics and analysis parameters using phantom SPECT and Gaussian images. The Monte Carlo method of statistical inference and the voxel-based analysis technique were clinically evaluated for the analysis of individual cerebral perfusion SPECT scans using control subject data. In addition, a comparison has been performed with an existing analysis package that uses a theoretical parametric method of statistical inference (statistical parametric mapping).

RESULTS

The Monte Carlo method was found to provide accurate statistical inference for phantom SPECT and Gaussian images independent of degrees of freedom, acquired counts, image smoothness and voxel significance level threshold. The clinical evaluation of the analysis of individual cerebral perfusion SPECT scans demonstrated satisfactory statistical inference and characterization of perfusion deficits.

CONCLUSION

An analysis method incorporating a Monte Carlo method of statistical inference has been successfully applied for the analysis of cerebral perfusion SPECT scans.

Voxel-based assessment of spinal tap test-induced regional cerebral blood flow changes in normal pressure hydrocephalus

OBJECTIVE

Normal pressure hydrocephalus (NPH) is a cause of dementia that may be amended by medical intervention. Its diagnosis is therefore of major importance and the establishment of response criteria to cerebrospinal fluid (CSF) shunting is essential. One of these criteria is the clinical response to spinal tap. The accuracy of the spinal tap test could potentially be improved by adding neuroimaging of regional cerebral blood flow (rCBF) changes to the response criteria. Statistical parametric mapping (SPM) is a voxel-based method of image analysis that may be used to statistically assess the significance of rCBF changes. The objective of this study was to evaluate, by SPM, spinal tap test-induced rCBF changes in patients with NPH syndrome.

METHODS

Forty patients with NPH syndrome underwent hexamethylpropylene amine oxime (HMPAO) brain single photon emission computed tomography (SPECT) before and after a spinal tap test (1-day split-dose protocol). The differences in rCBF between these pairs of scans were analysed by SPM in the whole group and between subgroups divided according to gait improvement at the spinal tap test.

RESULTS

In the whole group of patients, there was no statistical difference between pre- and post-spinal tap SPECT images. SPM analysis of patients grouped as a function of their clinical response to the spinal tap test revealed a significant post-spinal tap rCBF increase in the bilateral dorsolateral frontal and left mesiotemporal cortex in clinically responding compared with non-responding patients.

CONCLUSION

According to SPM analysis, gait improvement at the spinal tap test in patients with NPH syndrome is associated with an rCBF increase localized in the bilateral dorsolateral frontal and left mesiotemporal cortex.

Global cognitive impairment should be taken into account in SPECT-neuropsychology correlations: the example of verbal memory in very mild Alzheimer's disease

PURPOSE

To examine the impact of severity of global cognitive impairment on SPECT-neuropsychology correlations, we correlated a verbal memory test with brain perfusion in patients with very mild Alzheimer's disease (AD), taking into account the Mini-Mental State Examination (MMSE) score as an index of global cognitive impairment.

METHODS

Twenty-nine outpatients (mean age 78.2+/-5.5 years) affected by very mild, probable AD underwent brain SPECT with 99mTc-ethylcysteinate dimer and a word list learning test. SPM99 was used for voxel-based correlation analysis after normalisation to mean cerebellar counts (height threshold: p<0.01). In a first analysis, only age and years of education were inserted as nuisance covariates, while in a second analysis the MMSE score was inserted as well.

RESULTS

In the first analysis, two clusters of significant correlation were found in both hemispheres, mainly including regions of the right hemisphere, such as the inferior parietal lobule, the middle temporal gyrus and the posterior cingulate. Significant correlation in the left hemisphere was observed in the lingual lobule, the parietal precuneus and the posterior cingulate. After taking into consideration the MMSE, the largest cluster of correlation was found in the left hemisphere, including the parietal gyrus angularis, the posterior cingulate and the middle temporal gyrus.

CONCLUSION

The wide differences observed between the correlations achieved with and without taking into account the MMSE score indicate that severity of global cognitive impairment should be considered when searching for brain perfusion-neuropsychology correlations. In the present case, this strategy resulted in correlations that more closely matched neuropsychological models of verbal memory deficit.

On the modeling, construction, and evaluation of a probabilistic atlas of brain perfusion

To detect subtle, abnormal perfusion patterns in brain single photon emission computer tomography (SPECT) images, it is necessary to develop quantitative methods in which computer-aided statistical analysis takes advantage of information present in databases of normal subjects. The purpose of this study was to evaluate and examine aspects of the creation and the modeling power of three statistical models for representing brain perfusion as observed in ECD-SPECT. The first model is a local model of voxel-by-voxel mean and variance. The second model is a PCA-based global model that accounts for covariance patterns in the images. The third model is an original model that is a non-linear extension to the second model. This model is based on robust statistics for modeling abnormalities. To evaluate the models, a leave-one-out procedure combined with simulations of abnormal perfusion patterns was adopted. Abnormal perfusion patterns were simulated at different locations in the brain, with different intensities and different sizes. The procedure yields receiver operator characteristics (ROC) that present a combined measure of model-fit and model-sensitivity at detecting abnormalities. The scheme can further be used to compare models as well as the influence of different preprocessing steps. In particular, the influence of different registration approaches is studied and analyzed. The results show that the original non-linear model always performed better than the other models. Finally, location-dependent detection performance was found. Most notably, a higher variation of perfusion was observed in the right frontal cortex than in the other locations studied.

Cognitive Neuroactivation Using SPECT and the Stroop Colored Word Test in Patients with Diffuse Brain Injury

Psychomotor slowing in patients with diffuse brain injury frequently underlies impaired cognitive performance on neuropsychological tests, for example, the Stroop Colored Word test. The aim of the present study was to determine the neural basis associated with performance on the Stroop interference subtask in patients with diffuse brain injury. We hypothesized that patients would be slower than healthy controls, and that this would be associated with brain activations other than those seen in healthy subjects. Brain perfusion, using a split-dose activation paradigm with single photon emission tomography (SPECT) and the Stroop test, was assessed in 9 patients with diffuse brain injury. The Stroop interference score was calculated as a behavioral parameter, and functional imaging data were analyzed with statistical parametrical mapping (SPM99) to determine significant voxel-wise differences of activation between the control and the activation condition. Patients were impaired on the interference subtask of the Stroop test. Comparison of the SPECT data obtained during the activation condition with those obtained during the control condition by means of SPM showed significant activations in the left inferior parietal lobe, the right anterior cingulate extending into the right middle frontal gyrus and the right caudate, and the left posterior cingulate cortex. Patients with diffuse brain injury were slower than healthy controls on the interference subtask of the Stroop test, suggesting difficulty with resistance to distractions. This finding was associated with activation effects in posterior (mainly parietal) brain areas in addition with activation of previously observed anterior (mainly anterior cingulate) brain regions.

Single photon emission computed tomography and statistical parametric mapping analysis in cirrhotic patients with and without minimal hepatic encephalopathy

OBJECTIVE

The early diagnosis and treatment of cognitive impairment in cirrhotic patients is needed to improve the patients' daily living. In this study, alterations of regional cerebral blood flow (rCBF) were evaluated in cirrhotic patients using statistical parametric mapping (SPM). The relationships between rCBF and neuropsychological test, severity of disease and biochemical data were also assessed.

METHODS

99mTc-ethyl cysteinate dimer single photon emission computed tomography was performed in 20 patients with non-alcoholic liver cirrhosis without overt hepatic encephalopathy (HE) and in 20 age-matched healthy subjects. Neuropsychological tests were performed in 16 patients; of these 7 had minimal HE. Regional CBF images were also analyzed in these groups using SPM.

RESULTS

On SPM analysis, cirrhotic patients showed regions of significant hypoperfusion in the superior and middle frontal gyri, and inferior parietal lobules compared with the control group. These areas included parts of the premotor and parietal associated areas of the cortex. Among the cirrhotic patients, those with minimal HE had regions of significant hypoperfusion in the cingulate gyri bilaterally as compared with those without minimal HE.

CONCLUSIONS

Abnormal function in the above regions may account for the relatively selective neuropsychological deficits in the cognitive status of patients with cirrhosis. These findings may be important in the identification and management of cirrhotic patients with minimal HE.

Platelet abnormalities associated with cerebral perfusion defects in cocaine dependence

BACKGROUND

This study assessed whether reduced regional cerebral blood flow (rCBF; hypoperfusion) in cocaine-dependent (CD) patients is associated with platelet abnormalities and whether these platelet abnormalities predict improvement in hypoperfusion after 1 month of abstinence.

METHODS

We correlated platelet number and aggregation with rCBF hypoperfusion in 54 CD patients at baseline and after a month of abstinence while taking either 325 mg aspirin or placebo. We measured rCBF by (SPECT) with (Tc-HMPAO). Platelet aggregation to adenosine diphosphate was compared at baseline and after treatment.

RESULTS

At baseline the number of hypoperfused voxels positively correlated with higher platelet aggregation, and five brain regions (bilateral frontal, right insula, right cingulate, left temporal lobes) showed significantly more hypoperfusion in the high than low platelet aggregation group. After abstinence, hypoperfusion significantly improved regardless of treatment assignment, and greater platelet aggregation at baseline predicted greater improvement in hypoperfusion. After abstinence, only the cingulate continued to show more hypoperfusion in the high- than low-aggregation group.

CONCLUSIONS

Because platelet function was related to hypoperfusion primarily in the distribution of the middle cerebral artery, where CD patients most commonly have strokes, more potent antiplatelet agents than aspirin might be effective.

Executive dysfunction and avoidant personality trait in myotonic dystrophy type 1 (DM-1) and in proximal myotonic myopathy (PROMM/DM-2)

A previous study in proximal myotonic myopathy (PROMM/DM-2) and myotonic dystrophy type 1 (DM-1) using brain positron emission tomography demonstrated a reduced cerebral blood flow in the frontal and temporal regions associated with cognitive impairment. The objective was to investigate further cognitive and behavioural aspects in a new series of patients with DM-1 and PROMM/DM-2. Nineteen patients with genetically determined PROMM/DM-2 and 21 patients with moderately severe DM-1 underwent neuropsychological testing and neuropsychiatric interviews. DM-1 and PROMM/DM-2 patients had significantly lower scores on tests of frontal lobe function compared to controls. Neuropsychiatric interviews demonstrated an avoidant trait personality disorder in both patient groups. Brain single photon emission computed tomography showed frontal and parieto-occipital hypoperfusion. The results suggest that there is a specific cognitive and behavioural profile in PROMM/DM-2 and in DM-1, and that this profile is associated with hypoperfusion in frontal and parieto-occipital regions of the brain.

Aspirin or amiloride for cerebral perfusion defects in cocaine dependence

Cocaine dependent (CD) patients have regional cerebral blood flow (rCBF) deficits that may be related to occlusion of blood vessels by vasoconstriction and abnormal platelet aggregation. This study determined whether aspirin, which reverses platelet aggregation, or amiloride, a vasodilator, significantly reversed this rCBF hypoperfusion. This 1-month randomized trial compared clusters of voxels with significant hypoperfusion in recently abstinent CD patients after aspirin (325 mg daily), amiloride (10 mg daily) or placebo treatment. Forty-nine primary CD patients and 18 non-drug abusing controls were compared using single photon emission computed tomography (SPECT) neuroimaging with 99mTc-hexamethyl-propyleneamine-oxime and statistical parametric mapping (SPM). Platelet aggregation to adenosine diphosphate (ADP) was examined after treatment to determine whether rCBF improvement was related to decreased platelet aggregation. Following treatment, areas of hypoperfusion were improved with amiloride, unchanged with aspirin, and worsened with placebo in comparison to baseline levels. Platelet aggregation after ADP showed no significant change during the month, but reduced rCBF significantly improved after 1-month treatment with amiloride compared with placebo and cocaine abstinence alone.

[Statistical parametric mapping (SPM) in nuclear medicine]

In the scope of medical research, functional neuroimaging analysis permits the study of pathological or cognitive cerebral processes by using statistical quantification techniques. A tool of increasing use is the SPM (Statistical Parametric Mapping) software due to its wide availability and the variety of statistical studies that can be made. Nevertheless, being unaware of the theoretical background on which it is based may easily lead to inaccurate results and even to the reaching of erroneous conclusions. The present article summarizes these theoretical principles and discusses the main key points of the method without requiring advanced mathematical knowledge.

Cerebral perfusion defects in combined cocaine and alcohol dependence

BACKGROUND

Cocaine abuse has been associated with widely distributed areas of significant cerebral blood flow (CBF) reductions or hypo-perfusion as well as CBF hyper-perfusion, but these perfusion abnormalities have not been examined using newer technologies such as statistical parametric mapping (SPM). These areas of abnormal CBF may be more likely among those who abuse cocaine and alcohol together.

METHODS

Using SPECT with HMPAO for CBF we compared proportional scaling (PS) to histogram normalization (HEQ) in SPM among 20 controls and 32 recently abstinent cocaine abusers. We then separated the cocaine abusers into two groups (12 cocaine plus alcohol abusers and 20 cocaine alone abusers) and compared both groups to the 20 controls for brain areas of hypo- and hyper-perfusion.

RESULTS

Sensitivity to hypo-perfusion was greater with HEQ than PS. Hypo-perfused areas were more likely in the 12 alcohol plus cocaine abusers than in the 20 cocaine alone abusers or 20 controls, and hyper-perfused areas were significantly more likely among the cocaine abusers than controls. The type of CBF abnormality varied by brain location with hypo-perfusion significantly more likely in occipital and temporal cortex or cerebellum and hyper-perfusion more likely in frontal and parietal cortex.

CONCLUSIONS

These abnormalities in brain perfusion are consistent with previous non-SPM approaches that showed more hypo-perfusion in cocaine abusers than controls and appear to reflect vasospasm and potential compensations in cerebral blood flow.

Experimental performance assessment of SPM for SPECT neuroactivation studies using a subresolution sandwich phantom design

The validity domain of voxel-based statistical analysis of SPECT neuroactivation studies with statistical parametric mapping (SPM) has been investigated by a limited number of theoretical and simulation studies. In this work, an experimental setup is described with an assessment of its activation detection performance together with the influence of acquisition and processing parameters. A subresolution sandwich phantom was constructed using a printed high-resolution digital Hoffman phantom with a (99m)TcO(4)-ink mixture. Activations of 8, 16, and 24 mm diameter, with an intensity ranging from 5 to 60%, were constructed in the right frontal cortex, anterior and posterior cingulate, and left striatum. Triple-headed SPECT acquisitions were carried out using both fan-beam and parallel beam geometry. The impact of activation characteristics (size, intensity and location), study size, physical degradation factors, and reconstruction technique were studied using SPM99 in a group comparison design with correction for multiple comparisons. For a 15 x 15 design, all 24-mm activations of 5% intensity were detected for the fan-beam data. Decreased focus or study size, lower SPECT resolution, absence of scatter, and attenuation correction resulted in an increase in minimally detectable activation. For a single study referred to 15 control studies, only 24-mm activation foci with a minimal intensity of 10% were detected in the optimal configuration. This approach allows experimental parameter optimization of SPM-based group or single-subject SPECT activation studies compared to normal data, as used in clinical applications. In principle, these findings can be extended to SPECT receptor studies or PET data.

Characterization of BOLD-fMRI signal during a verbal fluency paradigm in patients with intracerebral tumors affecting the frontal lobe

Previous studies have indicated that the BOLD-fMRI signal can be modified by tumor processes in close vicinity to functional brain areas. This effect has been investigated primarily for the perirolandic area but there is only a limited number of studies concerning frontal cortical regions. Therefore, the aim of the current study was to characterize BOLD-fMRI signal and activation patterns in patients with frontal brain tumors while performing a verbal fluency task. Six patients (ages 31-56 years) suffering from frontal (5 left sided and 1 right sided) intracerebral tumors were examined with fMRI while performing a verbal fluency task in a blocked paradigm design. Eight healthy volunteers served as the control group. The patients (5 right and 1 left handed) demonstrated left frontal activation which could be clearly located outside the tumor area and adjacent edema with varying degrees of additional right frontal activation. In the predominant left frontal activation cluster, the mean voxel based z-score and cluster size were not statistically different between patients and controls. The present fMRI study is indicating that language related BOLD signal changes in the frontal cortex of patients with tumors close to functional areas were comparable to the signal in normal controls. Additionally, the temporal hemodynamic response characteristic was comparable in both groups. This is an important finding consistent with PET results and corroborates the feasibility of functional mapping approaches in patients with tumors affecting the frontal lobe. Additional studies investigating alterations of the hemodynamic response depending on tumor location and histology are required in order to further elucidate the association between pathophysiology and BOLD fMRI signal.

Comparison of statistical parametric mapping and SPECT difference imaging in patients with temporal lobe epilepsy

PURPOSE

Statistical parametric mapping (SPM) is an image-analysis tool that assesses the statistical significance of cerebral blood flow (CBF) changes on a voxel-by-voxel basis, thereby removing the subjectivity inherent in conventional region-of-interest (ROI) analysis. Our platform of single-photon emission computed tomography (SPECT) ictal-interictal difference imaging in clinical epilepsy has been validated for localizing seizure onset. We extend the tools of SPM by further applying statistical measures for the significance of perfusion changes in individual patients to localize epileptogenic foci in patients with defined temporal lobe epilepsy by using paired scans in this preliminary study.

METHODS

Twelve patients with pairs of periictal and interictal SPECT scans were analyzed in this comparison study between SPECT difference imaging and SPM difference analysis by using a reference database of paired normal healthy images. These 12 patients possessed seizure foci localized to the mesial temporal lobe as confirmed by surgical outcome and by hippocampal sclerosis on pathology. SPM was used to identify clusters of increased or decreased CBF in each patient in contrast to our control group.

RESULTS

The regions having the most significant increased or decreased CBF by SPM analysis were in agreement with regions identified by conventional difference imaging and visual analysis by viewers blinded to the results of the SPM analysis. Differentiated further by time of radiopharmaceutical injection, six of seven patients injected within 100 s of seizure onset displayed hyperperfusion changes localized to the corresponding epileptogenic temporal lobe by both techniques. Among patients receiving injections after 100 s, both techniques showed primarily regions of hypoperfusion, which again were similar between these two methods.

CONCLUSIONS

The results provide strong evidence supporting SPM difference analysis in assessing regions of significant CBF change from baseline in concordance with our current clinically used technique of SPECT ictal--interictal difference imaging in epilepsy patients. Difference analysis using SPM could serve as a useful diagnostic tool in the evaluation of seizure focus in temporal lobe epilepsy.

Spatial normalization of lesioned HMPAO-SPECT images

We investigated the effect of nonlinear alignment on SPECT images with lesions. Linear alignment produces reliable results but the introduction of nonlinear methods can improve matching by accounting for global brain shape. We examined the hypothesis that nonlinear alignment can introduce unwanted image distortions when lesions are present. We set out to quantify possible distortions by constructing artificial lesions in order to obtain images with controllable characteristics. We examined the use of basis functions (in SPM96 and SPM99) and other nonlinear models (in AIR3.08) designed to achieve optimum alignment between image and template. We found that the use of models with high degrees of nonlinearity will result in unwanted deformations and that the safest way to align images with lesions is to use 12-point linear affine transformations. Masking was examined as a remedy to distortions caused by nonlinear methodologies and produced significantly improved results.

Padrões de ativação cerebral em idosos sadios durante tarefa de memória verbal de reconhecimento: a single-photon emission computerized tomography study

INTRODUÇÃO: Estudos que utilizam as técnicas de PET, SPECT e ressonância magnética funcional têm permitido o mapeamento dos circuitos cerebrais ativados durante diversas tarefas cognitivas. O campo da memória declarativa tem sido um dos mais intensamente estudados. No presente estudo, usa-se a técnica de mapeamento do fluxo sangüíneo cerebral regional (FSCr) por SPECT para investigar mudanças na atividade cerebral durante uma tarefa de memória episódica, em voluntários idosos sadios (n=15). MÉTODOS: Duas avaliações de SPECT foram realizadas na mesma sessão, usando a técnica de dose dividida do traçador 99 m-Tc-HMPAO. Medidas de FSCr foram registradas durante uma tarefa de reconhecimento de material verbal previamente aprendido e durante uma tarefa-controle mais simples. Comparações de FSCr foram realizadas automaticamente, utilizando o programa Statistical Parametric Mapping (SPM). RESULTADOS: Observou-se aumento de FSCr durante a tarefa de memória em várias regiões cerebrais, incluindo: córtex pré-frontal lateral bilateralmente (mais acentuadamente à esquerda); porções posteriores e mediais de córtex parieto-occipital à esquerda; hemisférios cerebelares bilateralmente; e córtex temporal lateral bilateralmente (p<0,001, não corrigido para comparações múltiplas). Foram observados também focos inesperados de diminuição de FSCr em cíngulo posterior direito, córtex orbitofrontal esquerdo, córtex temporal inferior direito e vérmis cerebelar esquerdo (p<0,05, corrigido para comparações múltiplas). CONCLUSÃO: Esses resultados sugerem que circuitos neuronais multifocais são engajados durante memória de reconhecimento e replicam localizações cerebrais descritas anteriormente na literatura. O uso desse protocolo em pacientes com transtornos neuropsiquiátricos poderá permitir a investigação de anormalidades cerebrais subjacentes aos déficits de memória presentes nesses transtornos.

Assessing the performance of SPM analyses of spect neuroactivation studies. Statistical Parametric Mapping

Several simulations of SPECT neuroactivation studies have been performed in order to determine the influence of both study size and activation focus characteristics on the detection of brain activation foci following a pixel-based statistical analysis. This was achieved by developing a methodology based on the Hoffman software brain phantom, SPECT acquisition simulation software, standard reconstruction software, and the Statistical Parametric Mapping (SPM96) package. We present results on the minimal activation levels required for focus detection. Furthermore, the improved sensitivity of the analysis resulting from the use of an iterative reconstruction technique (OSEM) with regard to the classical filtered backprojection (FBP) is assessed quantitatively, and the various physical, processing, and physiological parameters that potentially influence the detection of foci are discussed. Finally, the influence is investigated of the height threshold as implemented in SPM96 upon the size of the detected foci. Practical guidelines are proposed with regard to the number of subjects per group for SPECT activation studies following the split-dose design.