Kypros Kouris

Cerebral blood flow abnormalities in adults with infantile autism.

Stuctural brain abnormalities have recently been discovered using magnetic resonance imaging in infantile autism, a neurodevelopmental disorder of unknown etiology. However, functional neuroimaging studies in autism using positron emission tomography have had conflicting results and have not explained how the known structural brain abnormalities in autism act in a functioning brain to produce autistic behavior. Using a new technology, highresolution brain single photon emission tomography, we studied and scanned four young adults with infantile autism and four age-matched controls using the labeled ligand 99mTc-D,Lhexamethyl- propylene amine oxime (99mTc-HMPAO). Total brain perfusion was significantly decreased in autism subjects (range, 58% to 72% of controls, p≤.02). In addition to the globally decreased perfusion, the autism group also had regionally decreased flow in the right lateral temporal and right, left, and midfrontal lobes compared with controls (p≤.02, Mann- Whitney t-test).

Collimator design for single photon emission tomography

We discuss recent trends in collimator design and technology, with emphasis on theoretical and practical issues of importance for single photon emission tomography (SPET). The well-known imaging performance parameters of parallel-hole collimators are compared with those of fan-beam collimators, which have enjoyed considerable success in recent years, particularly for brain SPET. We review a simplistic approach to the collimator optimization problem, as well as more sophisticated “task-dependent” treatments and important considerations for SPET collimator design. Practical guidance is offered for understanding trade-offs that must be considered for clinical imaging. Finally, selective comparisons among different SPET systems and collimators are presented for illustrative purposes.

Neuroactivation and neuroimaging with SPET

This book describes the application of single photon emission tomography (SPET) to neuroactivation imaging in particular and neuroimaging in general. Protocols for SPET, neuroactivation and neuroimaging are described in detail and results are given and discussed on the basis of clinical material and case histories. Normal functional anatomy is correlated with data from MRI. High resolution cerebral blood flow (CBF) imaging is described with the use of SPET technology. Split dose CBF imaging is also mentioned, for activation studies in a variety of normal and diseased states which include the dementias (AIDS, Alzheimers disease and multi-infarction dementia), cerebrovascular disease, depression, schizophrenia, obsessive compulsive disorders, movement disorders (Parkinsons disease, Gilles de la Tourette syndrome, Huntingdons chorea, Sydenhams chorea), epilepsy and tumours. Examples of motor, frontal and visual activation studies are also given.

Physical assessment of the GE/CGR Neurocam and comparison with a single rotating gamma-camera.

The GE/CGR Neurocam is a triple-headed single photon emission tomography (SPET) system dedicated to multi-slice brain tomography. We have assessed its physical performance in terms of sensitivity and resolution, and its clinical efficacy in comparison with a modern, single rotating gamma-camera (GE 400XCT). Using a water-filled cylinder containing technetium-99m, the tomographic volume sensitivity of the Neurocam was 30.0 and 50.7 kcps/MBq · ml · cm for the high-resolution (HR) and general-purpose (GP) collimators, respectively; the corresponding values for the single rotating camera were 7.6 and 12.8 kcps/(MBq/ml)/cm. Tomographic resolution was measured in air and in water. In air, the Neurocam resolution at the cente of the field-of-view (FOV) is 9.0 and 10.7 mm full width at half-maximum (FWHM) with the HR and GP collimators, respectively, and is isotropic in the three orthogonal planes; the resolution of the GE 400XCT with 13 cm radius of rotation is 10.3 and 11.7 mm, respectively. For the Neurocam with the HR collimator, the transaxial FWHM values in water were 9.7 mm at the centre and 9.5 mm radial (6.6 mm tangential) at 8 cm from the centre. The physical characteristics of the Neurocam enable the routine acquisition of brain perfusion data with technetium-99m hexamethyl-propylene amine oxime (99mTc-HMPAO) in about 14 min, yielding better image quality than with a single rotating camera in 40 min.

Alterations in regional cerebral blood flow, with increased temporal interhemispheric asymmetries, in the normal elderly: an HMPAO SPECT study

Single photon emission computed tomography (SPECT) with the tracer 99Tcm-hexamethylpropyleneamine oxime (HMPAO) provides images allowing semiquantitative estimation of regional cerebral blood flow (rCBF). Despite its widespread use there is little data on patterns of rCBF obtained using this tracer in normal elderly subjects, although other methods of measurement suggest a fall in cerebral blood flow with age. Furthermore, the detection of interhemispheric asymmetries on HMPAO SPECT is often used to identify areas of pathological abnormality yet there is little data on the prevalence of asymmetries in the normal elderly. An increased prevalence of asymmetries in the elderly may explain the difficulties recently reported in using functional imaging in the diagnosis of Alzheimers dementia. Patterns of HMPAO uptake were compared in 10 young (mean age 24.9 years; range 21-34 years) and 10 elderly (mean age 74.1 years; range 70-76 years) normal subjects. Percentage interhemispheric asymmetry ratios were calculated and found to be greater in the elderly, particularly for the temporal cortex (young 0.87%, elderly 3.73%, P < 0.001). The proportion of injected HMPAO taken up by the head was 29% higher in the younger age group. Analysis of regional uptake revealed that this trend towards reduced uptake in the elderly was a global phenomenon affecting all brain regions. The increased interhemispheric asymmetries seen in the elderly imply that a higher threshold for interpreting asymmetries as abnormal must be used in the elderly, particularly for the temporal cortex.

rCBF abnormalities detected, and sequentially followed, by SPECT in neuro-Behcet's syndrome with normal CT and MRI imaging

SummaryConventional imaging with computed tomography (CT) and magnetic resonance imaging (MRI) may show abnormalities in central nervous system Behcets syndrome but is normal in some cases. Recently in two cases positron emission tomography has shown abnormalities in blood flow and glucose metabolism far more extensive than the abnormalities seen on CT and MRI scans in the same patients. We report a patient with neuro-Behcets syndrome presenting with headache and personality change in whom CT and MRI brain imaging was normal, but regional cerebral blood flow imaging using single photon emission tomography with the tracer HMPAO showed extensive perfusion deficits which partially reversed after 3 months of prednisolone therapy. This technique may aid the diagnosis of cerebral involvement in Behcets syndrome, although the cause and incidence of the perfusion deficits need further evaluation.

Reproducibility and action levels for gamma camera uniformity.

Deciding on the action level for gamma camera non-uniformity is difficult because the reproducibilities of quality control measurements and service adjustments are usually unknown. This work evaluated the reproducibilities of integral uniformity (IU), differential uniformity (DU) and the corrected relative standard deviation (CRSD). The latter was calculated by removing from the relative standard deviation of the pixel counts the component due to statistical fluctuations. The reproducibility of each parameter was evaluated by analysing 10 intrinsic flood acquisitions with total counts of 2, 5, 10 and 30 million. All three parameters were less reproducible at the lower count densities, but as expected IU and DU also showed higher mean values. CRSD was consistent and highly reproducible, at all count densities. At 10 million counts CRSD had a coefficient of variation (COV) of 1.3% which was a five-fold improvement over the 6.6% and 6.1% found for IU and DU, respectively. The relative sensitivity of IU, DU and CRSD was compared in monthly measurements on 10 gamma cameras over one year. No significant difference in relative sensitivity was demonstrated: a change in camera performance produced about the same percentage change in each parameter. The precision with which service engineers adjust gamma cameras was also assessed by measuring the uniformity of 10 gamma cameras immediately after service adjustment at monthly intervals over one year. Finally, general action levels were defined for IU, DU and CRSD at 7%, 5% and 2.5% respectively.

Demonstration of human motor cortex activation using SPECT

Recent advances in single photon emission computed tomography (SPECT) have allowed improved image resolution with lower doses of labelled tracer. Capitalizing on these improvements, the authors have developed a new SPECT protocol for imaging neuronal activation. We outline this technique and describe how it can demonstrate increased human motor cortex activity in normal subjects performing a motor task. The ability to accurately demonstrate neuronal activation with SPECT using this method may have important scientific and clinical implications.

High-resolution renal SPECT in eight minutes using a multi-detector gamma camera

Planar renal scintigraphy with Tc-99m DMSA has become established as a standard diagnostic test to determine if a kidney has been scarred by infection. It has been suggested that high resolution SPECT may improve the sensitivity of detection of renal scars. To determine if it is possible to produce good quality renal SPECT with a short acquisition time, 10 adults were examined with a new multi-detector gamma camera using 8 minute, 16 minute, and 32 minute acquisitions. The number of defects seen (N = 16) with an 8 minute acquisition was not significantly different from the defects (N = 15) seen using a 16 minute and a 32 minute acquisition. In adults when Imaging with a multi-detector gamma camera there was no clinical advantage in using an acquisition of longer than 8 minutes.

Clinical experience with a multidetector SPET system (Toshiba GCA-9300A).

&NA; The clinical experience with the Toshiba GCA‐9300A single photon emission tomography (SPET) system is discussed along with typical acquisition protocols for various SPET studies. The system was used to perform SPET studies in normals and in a variety of brain and body disorders. Its three Anger‐type gamma cameras forming a triangular aperture offer a substantial increase in sensitivity compared to a single rotating gamma camera. This has allowed the routine use of lead fanbeam super high‐resolution collimators (SHR FB) for 99Tcm‐hexamethylpropyleneamine oxime (HMPAO) brain SPET studies and high‐resolution parallel‐hole collimators (HR PH) for cardiac and other body studies. The resulting improvement in spatial resolution coupled with the ease of patient positioning and the greater patient throughput compared to a conventional tomographic gamma camera, will enhance the role of brain and body SPET for both routine and research purposes.