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K Kouris

Publications and source records attributed to K Kouris.

At least 19 recordsLinked to original sources
PubMed1995

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.

Adolescent↗
PubMed1994

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

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.

Bone and Bones↗
PubMed1993

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 Alzheimer's 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.

Adult↗
PubMed1993

Clinical high resolution skeletal single photon emission tomography using a triple-headed gamma camera.

Planar skeletal scintigraphy has become established as a standard diagnostic test performed within the nuclear medicine department. Since the 1970s good quality images have been produced using an Anger gamma camera and 99Tcm-labelled diphosphonates. Single photon emission tomography (SPET) has improved the sensitivity of detection and the ability to localize bony pathology, particularly benign bone disease in the spine. Recently multi-detector gamma cameras dedicated to SPET have become available. One such system, the Toshiba GCA-9300A, has been used to perform routine clinical skeletal SPET in 81 patients. Good quality images have been obtained using an 8 min acquisition in the axial skeleton and a 16 min acquisition protocol in the peripheral skeleton. Multiple sites can be tomographed in the same patient during the same examination using two or more 8 min acquisitions. Such a multi-detector gamma camera offers advantages over the standard single-headed rotating camera for skeletal SPET in terms of both imaging time and image quality. A cost analysis was performed which demonstrated that the additional cost of purchasing such a multidector gamma camera was less than 30.00 pounds per SPET study.

Bone Neoplasms↗
PubMed1993

Physical performance evaluation of the Toshiba GCA-9300A triple-headed system.

The physical performance of the Toshiba GCA-9300A triple-headed SPECT system has been assessed. Using a water-filled cylinder containing 99mTc, the tomographic volume sensitivity was 33.8 and 34.8 kcps/(MBq/ml)/cm for the high-resolution, parallel-hole (HR-PH) collimator and the super high-resolution, lead fanbeam (SHR-FB) collimator, respectively, excluding the rotation time(s) during scanning when data are not acquired. The tomographic spatial resolution at the center, in air, with 132 mm radius of rotation was 10.2 and 7.8 mm FWHM with the HR-PH and SHR-FB collimators, respectively; in water it was 11.0 and 7.8 mm. Reconstructed relative activity concentrations were accurate for both collimator sets if attenuation correction was used. With the SHR-FB collimators, the average peak-to-valley ratio of five-line sources in water improved significantly when an asymmetric energy window was used. Using the three-dimensional Hoffman brain phantom which simulates a 4:1 grey matter-to-white matter ratio and the usual choice of acquisition and processing parameters for brain studies, the reconstructed grey matter-to-white matter ratio was only about 1.7 for total counts typically acquired in a 99mTc-HMPAO study (4.0 M counts) and only 2.3 for 40 M counts. There was a qualitative improvement with an asymmetric energy window.

Brain↗
PubMed1992

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.

Brain↗
PubMed1992

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.

Equipment Design↗
PubMed1992

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

Conventional imaging with computed tomography (CT) and magnetic resonance imaging (MRI) may show abnormalities in central nervous system Behcet's 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-Behcet's 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 Behcet's syndrome, although the cause and incidence of the perfusion deficits need further evaluation.

Behcet Syndrome↗
PubMed1992

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.

Adult↗
PubMed1992

Cerebral blood flow abnormalities in adults with infantile autism.

Structural 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, high-resolution 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,L-hexamethyl-propylene amine oxime (99mTc-HMPAO). Total brain perfusion was significantly decreased in autism subjects (range, 58% to 72% of controls, p less than or equal to .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 less than or equal to .02, Mann-Whitney t-test).

Adult↗
PubMed1992

Left ventricular ejection fraction and volumes calculated from dual gated SPECT myocardial imaging with 99Tcm-MIBI.

Dual gated (DG) cardiac single photon emission computed tomographic (SPECT) studies at end-diastole (ED) and end-systole (ES) were acquired in 27 ischaemic heart disease (IHD) patients after intravenous injection of 555-740 MBq 99Tcm-MIBI. Acquisition parameters were: 180 degrees from LPO to RAO, 32 projections, 64 x 64 matrix, 75 cardiac beats per projection, 80 ms at ED and 80 ms at ES for each cardiac cycle. A computer program was developed to calculate the ED and ES left ventricular (LV) volumes and LV ejection fraction (EF). The computational approach is interactive, semi-automatic and iterative with built-in visual quality control. Short axis slices are used with corresponding ED and ES slices processed as pairs from apex to base. Left ventricular cavity pixels are identified and summed on a slice-by-slice basis. Myocardial pixels are similarly identified. The computed LVEF and ED and ES volumes have been correlated with those from contrast ventriculography (CV). The mean calculated EF for 27 patients was 53.6 +/- 10.7% from DG SPECT versus 55.3 +/- 12.1% from CV (NS). The EF linear correlation coefficient was r = 0.97.

Gated Blood-Pool Imaging↗
PubMed1991

Evaluation of red blood cell and plasma flow and volume by the use of a dynamic and dual static acquisition radionuclide technique in arterial flaps in sheep.

The aim of this study was to investigate whether in the distal, poorly perfused part of a flap the pressure gradient remains sufficient to allow flow of plasma and red blood cells (RBCs) within the first hour after flap elevation. For this purpose 99Tcm-labelled RBCs and 111In-chloride-labelled plasma proteins in an arterial skin flap that extended beyond the boundaries of its vascular territory in sheep has been used. Flow information was derived for both plasma and RBCs from dynamic acquisitions, while volume information was derived from dual energy static acquisition at equilibrium (steady-state). Results indicate that the mean flow and the mean volume of plasma are equal through the entire length of the flap. Although the flow is minimal, there is no stasis of plasma in the poorly perfused part of the flap. By comparing the mean flow of RBCs to their mean volume, no difference is seen in the well-perfused proximal two-thirds of the flap. In the distal, poorly perfused part, flow decreases while the volume increases. The increased volume of RBCs at minimal flow indicate pooling of RBCs in this region already in the first hour after flap elevation.

Animals↗
PubMed1991

Effect of Ridogrel, a thromboxane receptor blocker and synthesis inhibitor on plasma and red blood cell flow in an arterial skin flap in sheep.

This study evaluates the effect of the new combined thromboxane synthesis inhibitor and receptor blocker, ridogrel, on the circulation of arterial skin flaps in sheep. Sixteen flaps, 8 controls and 8 treated with 5 mg/kg ridogrel, were investigated using 111Indium chloride labelled plasma and 99mTc labelled red blood cells (RBCs). Dynamic imaging was performed after a bolus injection using a GE 400 AT gamma camera. For each flap quantitative analysis of plasma and RBC flow was based on time activity curves obtained from 12 regions of interest. Analysis of flow data was made immediately after flap elevation and three hours later. Both plasma and RBC flows declined after 3 hours. Treatment with ridogrel significantly prevented deterioration of perfusion by increasing plasma and RBC flow mostly in the distal, ischaemic regions of the flap where stasis was evident in the control flaps.

Animals↗
PubMed1990

Increased skin flap viability after treatment with forskolin or with ridogrel, a thromboxane synthesis inhibitor and receptor blocker.

Two ventral skin flaps were raised in each of 60 rats and viability was assessed 48 h after operation. Twenty animals served as controls and immediately preoperatively 20 received an intraperitoneal injection of either 5 mg/kg body weight ridogrel, a combined thromboxane synthesis inhibitor and receptor blocker, or 4 mg/kg forskolin, a cAMP stimulator. The mean total and surviving flap areas measured 14.3 +/- 1.4 and 10.1 +/- 3.2 cm2 respectively for the control group. In the treated groups it was 16.4 +/- 1.3 cm2 and 15.6 +/- 2.6 cm2 for ridogrel and 17.8 +/- 1.1 cm2 and 15.8 +/- 4.3 cm2 for forskolin respectively. The differences between the areas of each treated group and the control group were statistically significant (p less than 0.0001). It can be concluded that both ridogrel and forskolin afford protection against skin necrosis probably because of improved conditions in the microcirculation due to reduced platelet aggregation in the vasculature of the distal part of the flap.

Animals↗
PubMed1990

Experimental complete ureteric occlusion in sheep: radionuclide renography and histopathologic findings.

Complete ureteric occlusion produces various pathophysiological changes that can be monitored externally by technetium 99m diethylenetriamine penta-acetic acid (99mTc-DTPA) diuretic renography (RDR). Being a dynamic imaging study, it reflects the function of the kidneys and the urodynamics of the urinary tract. The aim of this study was to correlate the changes in parameters of RDR with the histological changes before and after the release of complete ureteric occlusion. In 9 sheep, RDR studies were performed serially after various periods of complete ureteric occlusion (up to 7 weeks) and after release of the occlusion (up to 5 weeks). The histological changes were correlated with changes in RDR. The progressive decrease in renal flow seen on renal images and flow time-activity curves (TACs) was explained by the development of endarteritis and thrombosis of small renal arteries. The progressive decrease in the renal uptake as indicated by the percentage renal uptake and the extraction slope of TAC is related to the progressive damage to the renal parenchyma, initially affecting the collecting ducts and tubules, with increasing interstitial fibrosis in the later stages. Obstruction for 3 weeks or less was associated with moderate damage to the parenchyma from which recovery was possible. Obstruction for 7 weeks was associated with marked damage without chance of recovery. The RDR is a non-invasive technique that can be used to monitor kidney damage after various periods of complete ureteric occlusion and to predict the outcome of surgery before the release of occlusion.

Animals↗
PubMed1990

Evaluation of the microcirculation in a sheep island pedicle flap with laser Doppler flowmeter and 99m-Tc-labelled red blood cells.

The aim of the study was experimentally to evaluate the capability and reliability of laser Doppler flowmetry (LDF) in conditions of circulatory deficiency, by correlating it to flow-related parameters measured by a radionuclide-imaging technique and using 99m-Tc red blood cells (RBCs). For this purpose, a pedicle island flap in the sheep was used, with well-perfused proximal parts and with evident stasis in the distal third of the flap. No correlation was found between results obtained with the two techniques. In regions with evident stasis, falsely high LDF readings were recorded. This may be due to a back-and-forth motion of the RBCs under the probe, rather than to true flow. It was concluded that, while LDF seems reliable in detecting complete arterial occlusion, it is unreliable in predicting either complete venous occlusion or partial obstruction of the flow to and from the flap. Clinical use for this purpose cannot be recommended.

Animals↗
PubMed1990

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.

Gamma Cameras↗