Generation of realistic HMPAO SPECT images using a subresolution sandwich phantom.

UNLABELLED: 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.

Impact of 123I-FP-CIT (DaTSCAN) SPECT on the diagnosis and management of patients with dementia with Lewy bodies: a retrospective study.

OBJECTIVE: To assess the impact of imaging the presynaptic dopaminergic terminal using DaTSCAN single-photon emission computed tomography (SPECT) on the clinical diagnosis and subsequent management of patients with possible dementia with Lewy bodies (DLB), who were referred for imaging. METHODS: A retrospective case note study was undertaken, involving a series of consecutive patients who had undergone DaTSCAN SPECT 12-24 months earlier. RESULTS: Case notes of 80 patients were reviewed. DaTSCAN imaging results were abnormal (indicating DLB) in 20 (25%) and normal (suggesting an alternative diagnosis or absence of disease) in 60 (75%) patients. Of the 20 patients with an abnormal scan, 18 had a postscan working clinical diagnosis of DLB (90%), one had diagnosis of vascular dementia (5%) and another had no recorded outcome (5%). Fifty-eight out of the 60 patients with a normal DaTSCAN image result had an alternative clinical diagnosis of DLB (95%). Consequently, DaTSCAN findings were concordant with the outcome clinical diagnosis in 76 out of the 80 (95%) cases. Subsequent to DaTSCAN SPECT, scan findings and diagnoses were discussed with patients and/or their carers in 94% of cases and subsequent treatment options discussed in 93% of cases. CONCLUSION: It would seem that DaTSCAN imaging has a marked influence on the working clinical diagnosis and subsequent management of patients with suspected DLB.

Imaging in dementia with Lewy bodies: a review.

This review discusses the role of functional and structural imaging in patients with suspected dementia with Lewy bodies, with particular emphasis on SPECT and PET dopaminergic and cerebral perfusion/metabolic techniques. It is envisaged that this information may be useful to nuclear medicine physicians, radiologists, psychiatrists, neurologists, geriatricians and physicians.

Limitations of the HMPAO SPECT appearances of occipital lobe perfusion in the differential diagnosis of dementia with Lewy bodies.

OBJECTIVE: To assess the utility of the appearances of occipital lobe perfusion on HMPAO SPECT in the diagnosis of dementia with Lewy bodies (DLB) using the 123I-FP-CIT findings as the diagnostic 'gold standard'. METHODS: Eighty-four consecutive patients underwent both HMPAO SPECT and 123I-FP-CIT as part of their routine investigations for suspected DLB. RESULTS: Thirty-nine of the 84 FP-CIT scans were abnormal indicating a prevalence of 44% of patients with DLB in this series. In those patients classified as DLB, 28% of HMPAO SPECT scans demonstrated occipital hypoperfusion. In those patients with a dementia other than DLB 31% of patients demonstrated occipital hypoperfusion (P=0.8). CONCLUSION: Occipital lobe hypoperfusion as demonstrated by HMPAO SPECT in patients with suspected Lewy body dementia does not appear to be able to either rule in, or rule out, the diagnosis of DLB.

Quantification of [123I]FP-CIT SPECT brain images: an accurate technique for measurement of the specific binding ratio.

PURPOSE: A technique is described for accurate quantification of the specific binding ratio (SBR) in [(123)I]FP-CIT SPECT brain images. METHODS: Using a region of interest (ROI) approach, the SBR is derived from a measure of total striatal counts that takes into account the partial volume effect. Operator intervention is limited to the placement of the striatal ROIs, a task facilitated by the use of geometrical template regions. The definition of the image for the analysis is automated and includes transaxial slices within a "slab" approximately 44 mm thick centred on the highest striatal signal. The reference region is automatically defined from the non-specific uptake in the whole brain enclosed in the slab, with exclusion of the striatal region. A retrospective study consisting of 25 normal and 30 abnormal scans-classified by the clinical diagnosis reached with the scan support-was carried out to assess intra- and inter-operator variability of the technique and its clinical usefulness. Three operators repeated the quantification twice and the variability was measured by the coefficient of variation (COV). RESULTS: The COVs for intra- and inter-operator variability were 3% and 4% respectively. A cutoff approximately 4.5 was identified that separated normal and abnormal groups with a sensitivity, specificity and diagnostic concordance of 97%, 92% and 95% respectively. CONCLUSION: The proposed technique provides a reproducible and sensitive index. It is hoped that its independence from the partial volume effect will improve consistency in quantitative measurements between centres with different imaging devices and analysis software.

The contribution of statistical parametric mapping in the assessment of precuneal and medial temporal lobe perfusion by 99mTc-HMPAO SPECT in mild Alzheimer's and Lewy body dementia.

AIM: To assess the role of 99mTc-hexamethylpropyleneamine oxime single-photon emission computed tomography (99mTc-HMPAO SPECT) imaging of the precuneus and medial temporal lobe in the individual patient with mild Alzheimer's disease and dementia with Lewy bodies (DLB) using statistical parametric mapping and visual image interpretation. METHODS: Thirty-four patients with mild late-onset Alzheimer's disease, 20 patients with early-onset Alzheimer's disease, 15 patients with DLB and 31 healthy controls were studied. All patients fulfilled appropriate clinical criteria; the DLB patients also had evidence of dopaminergic presynaptic terminal loss on 123I-N-omega-fluoropropyl-2beta-carbomethoxy-3beta-(4-iodophenyl)-tropane imaging. 99mTc-HMPAO SPECT brain scans were acquired on a multidetector gamma camera and images were assessed separately by visual interpretation and with SPM99. RESULTS: Statistical parametric maps were significantly more accurate than visual image interpretation in all disease categories. In patients with mild late-onset Alzheimer's disease, statistical parametric mapping demonstrated significant hypoperfusion to the precuneus in 59% and to the medial temporal lobe in 53%. Seventy-six per cent of these patients had a defect in either location. No controls had precuneal or medial temporal lobe hypoperfusion (specificity, 100%). Statistical parametric mapping also demonstrated 73% of patients with DLB to have precuneal abnormalities, but only 6% had medial temporal lobe involvement. CONCLUSION: These findings illustrate the capability of statistical parametric mapping to demonstrate reliable abnormalities in the majority, but not all, patients with either mild Alzheimer's disease or DLB. Precuneal hypoperfusion is not specific to Alzheimer's disease and is equally likely to be found in DLB. In this study, medial temporal hypoperfusion was significantly more common in Alzheimer's disease than in DLB. Statistical parametric maps appear to be considerably more reliable than simple visual interpretation of 99mTc-HMPAO images for these regions.

Imaging the dopaminergic system in suspected parkinsonism, drug induced movement disorders, and Lewy body dementia.

This review discusses the role of pre- and post-synaptic dopaminergic imaging in suspected Parkinson's disease, vascular parkinsonism, the parkinsonian syndromes, drug induced movement disorder, and Lewy body dementia. It is envisaged that this information may be useful to neurologists, psychiatrists, physicians/geriatricians, radiologists and nuclear medicine physicians.

The specific uptake size index for quantifying radiopharmaceutical uptake.

Quantitative indices of radionuclide uptake in an object of interest provide a useful adjunct to qualitative interpretation in the diagnostic application of radionuclide imaging. This note describes a new measure of total uptake of an organ, the specific uptake size index (SUSI). It can either be related in absolute terms to the total activity injected or to the specific activity in a reference region. As it depends on the total activity in the object, the value obtained will not depend on the resolution of the imaging process, as is the case with some other similar quantitative indices. This has been demonstrated in an experiment using simulated images. The application of the index to quantification of dopamine receptor SPECT imaging and parathyroid-thyroid subtraction planar scintigraphy is described. The index is considered to be of potential value in reducing variation in quantitative assessment of uptake in objects with applications in all areas of radionuclide imaging.