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M A Flower

Publications and source records attributed to M A Flower.

At least 55 records · Page 3Linked to original sources
PubMed1989

The performance of a multiwire proportional chamber positron camera for clinical use.

The Rutherford Appleton Laboratory clinical positron camera consists of two opposed multiwire proportional chambers (MWPCS) mounted on a rotating gantry capable of performing routine nuclear medicine studies. The system has operated since the end of 1986 with complete reliability. It has a sensitivity of 37 kcps MBq-1 cm3 per axial cm for a 20 cm diameter uniformly filled cylinder of activity. The best spatial resolution obtainable is about 6 mm, although in practice images are smoothed in order to reduce statistical noise with a corresponding decrease in resolution. Cross-plane rays are utilised during image reconstruction and the resulting three-dimensional images exhibit the same spatial resolution in three orthogonal directions over a large cylindrical field of view 15 cm high by 30 cm in diameter. The maximum data-taking rate is limited to 1.5 to 2 kcps at present due to deadtime in the read-out system. The performance of the system is described with particular reference to the problems of imaging with the large fractions of random and scattered events which are a consequence of using large-area detectors. Images of phantoms and patients are presented and proposed modifications to the camera are described.

Algorithms↗
PubMed1988

Initial experience with Tc-99m-HM-PAO in the study of brain tumors.

A preliminary study of the distribution of the 99mTc complex of hexamethylpropylene amine oxime (HM-PAO) in 12 patients with brain neoplasms before, during, and after radiotherapy has been performed. Untreated brain tumors were found to exhibit a range of 99mTc-HM-PAO uptake, varying from areas of markedly increased isotope activity to photopenic areas, when compared to normal brain tissue. A ratio of 99mTc-HM-PAO tumor uptake to contralateral normal tissue uptake was calculated prior to and during radiotherapy. This ratio tended to return towards unity in lesions responding to therapy. A predictable alteration in whole brain 99mTc-HM-PAO uptake during radiotherapy was not demonstrated. Unlike the radiolabeled amines, 99mTc-HM-PAO localizes in primary tumors, probably indicating that its uptake mechanism is independent of non specific amine receptors. 99mTc-HM-PAO may be useful in the study of brain tumor physiology and response to therapy.

Adult↗
PubMed1988

A simple method of producing parenchymal renograms using parametric imaging.

Standard dynamic renography procedures are used to produce time-activity curves for defined regions of interest around the kidneys. Further analysis of the acquired data using Fitted Retention and Excretion Equations (FREE) to determine single kidney glomerular filtration rate (GFR) and kidney transit time is performed at the Royal Marsden Hospital, Sutton. The disadvantage of these methods is that the renal function is assessed for the whole kidney and not on a regional basis. The aim of this study was to use parametric imaging to extend the standard analysis so that the parenchyma could be identified and analysed separately from the collecting system. The parenchyma pixel time-activity curves have shorter time-to-peak (TTP) values than the collecting system. TTP parametric images were used to set limits on the TTP values and thus define the parenchyma pixels. The time-activity curves from the parenchyma were further analysed using FREE to produce parametric images of both GFR and effective blood volume. Finally, the original dynamic data were re-analysed so that time-activity and FREE curves were generated for the parenchyma alone. A study of 15 patients (30 kidneys) showed that the extended analysis indicated parenchymal isotope clearance. By comparing the time-activity and FREE curves of the whole kidney with those from the parenchyma alone, a more useful analysis of parenchymal function was obtained. This proved to be particularly useful for patients with pelvi-ureteric junction (PUJ) obstruction.

Humans↗
PubMed1988

Deconvolution of emission tomographic data: a clinical evaluation.

A method of improving the quality of images in single photon emission computed tomography (SPECT) is demonstrated using transaxial images of the liver and brain. Deconvolution of the nuclear medicine data by a point source response function (PSRF) acquired previously in a scattering medium attempts to compensate for scattered radiation within the patient. The average geometric response of the collimator of the gamma camera is also compensated for with this technique. Three patients with known metastatic lesions in the liver and three with primary lesions in the brain were imaged. Clinical assessment of reconstructed slices both before and after deconvolution demonstrates that compensating for the effects of scatter and of collimator blurring leads to enhanced detail of pathological lesions. In all cases, cold lesions seen prior to deconvolution were enhanced in detail and, in addition, new lesions were seen with this technique.

Adult↗
PubMed1987

Measurement of radiation dose to the thyroid using positron emission tomography.

Measurements of the functioning volume of thyroid tissue have been made in 22 patients undergoing radioiodine therapy for thyrotoxicosis, using a prototype multiwire proportional counter positron camera. Tomographic images were produced of the distribution of 124I in the thyroid. Functioning volumes were found to be in the range 21-79 cm3 with volume errors of the order of +/- 4% to +/- 14%. Radioiodine uptake varied from 28% to 98%. Using a value of 6 days for the effective half-life of radioiodine in hyperactive thyroids, radiation doses from a standard therapy administration of 75 MBq of 131I varied from 11 to 48 Gy (compared with a recommended 50-70 Gy). In five cases PET imaging showed a non-uniform distribution of radioiodine in thyroids thought to have uniform uptake from conventional pinhole scintigraphy.

Humans↗
PubMed1987

Three-dimensional display of data obtained by single photon emission computed tomography.

Three-dimensional display of radioactive distributions has been achieved using data generated by single photon emission computed tomography (SPECT). Computer techniques for constructing images are presented and the special problems associated with manipulating SPECT data are reviewed. The potential role of three-dimensional imaging in nuclear medicine is discussed and SPECT studies from several illustrative cases are presented.

Adult↗
PubMed1985

The measurement of radiation doses from P32 chromic phosphate therapy of the peritoneum using SPECT.

Single photon emission computed tomography (SPECT) has been shown to be of value in estimating the radiation dose to the peritoneum from 32P therapy. Simple dosimetry calculations, assuming uniform irradiation of tissue, indicate that radiation doses of approximately 40 Gy to the peritoneal surface are achieved. However, the images show that the radionuclide distribution is non-uniform, giving rise to radiation dose variations of at least a factor of 10.

Chromium↗
PubMed1985

High resolution SPECT using divergent geometry.

A special-purpose collimator with holes which converge in the plane of rotation has been used together with an IGE 400A gamma camera and STAR computer system in order to achieve high-resolution single-photon emission computed tomography (SPECT). The variation in width and shape of the reconstructed line-spread function with position in the field of view was quantified. A comparison with parallel-geometry SPECT showed an improved resolution and sensitivity.

Mathematics↗
PubMed1985

A preliminary investigation of dynamic transmission computed tomography for measurements of arterial flow and tumour perfusion.

An assessment of the meaning and accuracy of CT numbers in dynamic CT has been made using data obtained from both phantom and patient investigations. Following an injection of contrast material, a series of 5-s scans (at 125 kVp, 230 mAs) were taken of the same slice at a rate of 6 scans min-1 using a Siemens Somatom 2 scanner. In order to study rapid changes of CT number, each 5-s scan was split into three segmented and overlapping images of 3-s duration. The variation of the mean CT number within small regions of interest (ROIs) were displayed as density-time curves and the errors associated with the artery and tumour curves were studied. In order to investigate the errors in the arterial curve which are associated with the timing sequence, blood flow through a large vessel was simulated in an experimental model. The results show that the largest error is associated with the peak CT value but this error can be reduced by a factor of approximately 2 if the images are split. Dynamic CT has been carried out on six patients with retroperitoneal or pelvic lesions in a preliminary study to investigate its use as a tool for monitoring the effectiveness of therapy. The results demonstrate that this technique can provide useful information regarding tumour vascularity and perfusion. In the studies on patients, a large spread in the CT numbers within a ROI was found to be a useful indicator of an uneven iodine distribution. For example, in two tumours, necrotic centres which were not apparent on the pre-contrast scan were identified from the dynamic study.

Blood Flow Velocity↗
PubMed1984

A clinical evaluation of a prototype positron camera for longitudinal emission tomography.

A multiwire proportional-chamber positron camera, developed at the Rutherford Laboratory, has been evaluated at The Royal Marsden Hospital. The prototype camera consists of two opposing 30 X 30 cm2 chambers. Longitudinal tomograms of a positron-emitting radioactive distribution placed between the detectors are obtained via back-projection and 2D-deconvolution. Due to the limited stereoscopic angle achieved with stationary detectors, only five planes parallel to the detector faces are reconstructed. A selection of images is presented of phantoms using 68Ga and of patients using 18F, 18F fluorodeoxyglucose and Na124I, to illustrate the tomographic performance of the positron camera. A comparison between back-projected and deconvoluted images shows that the 2D-deconvolution process, which includes filtration of image noise, successfully removes the background due to scattered photons. The spatial resolution achieved depends on the half-height frequency cut-off used in the filtering process, and this parameter was chosen according to the count density in the back-projected images. A qualitative visual comparison was made between the positron images and equivalent single photon studies on the same patient. The results justify further development of this new detector, especially for use with generator-produced positron-emitting radionuclides. Three-dimensional deconvolution resulted in improved tomographic performance for phantom data, but was less successful for patient data. These problems associated with limited-angle tomography will be overcome by multi-view acquisition. This study has shown that a relatively low-cost positron imaging system can be used for routine organ imaging. Further developments in hardware and software should yield images which are superior to those from single-photon planar or tomographic studies.

Bone Marrow↗
PubMed1983

A comparison of attenuation correction methods for quantitative single photon emission computed tomography.

Transverse section tomograms of experimental phantoms and patients have been obtained using a GE 400T camera and a filtered back-projection reconstruction technique. These tomograms have been compared with the corresponding sections reconstructed from the same tomographic projection data, but using iterative algorithms with correction for photon attenuation. The comparison assesses the importance of including a correction for attenuation as well as demonstrating how closely a simple geometric attenuation correction, applied to the filtered back-projection reconstruction method, approximates to a more accurate correction incorporated in the computation of line integrals during iterative reconstruction. A comparison is also made between the behaviour of reconstruction algorithms with simulated projection data and real data in terms of convergence properties, and some shortcomings arising from simulation are noted.

Humans↗
PubMed1983

The limitations of the dual radionuclide subtraction technique for the external detection of tumours by radioiodine-labelled antibodies.

A dual radionuclide subtraction technique for external detection of tumours has been evaluated to determine the viability of the method for use with radioisotope labelled antibodies. A number of external scintigraphic investigations have been carried out with 131I-labelled antibodies to carcinoembryonic antigen (CEA). The investigations were performed on patients with metastatic disease known to produce CEA. The dual radionuclide subtraction technique was used to account for the blood and tissue background. The 131I-labelled antibodies were found to localise in the metastatic lesions, but the subtraction technique using 99Tcm-labelled HSA and pertechnetate gave ambiguous results, which included the production of artefacts. The ambiguities noted in the clinical results were substantiated by experimental data, which highlight the unreliability of this technique.

Antibodies, Neoplasm↗
PubMed1983

A comparison between 180 degrees and 360 degrees data reconstruction in single photon emission computed tomography of the liver and spleen.

Single photon emission computed tomography (SPECT) of the liver and spleen has been studied using a GE400T/STAR rotating gamma camera/computer system. We have compared section image contrast, in both phantom and patient studies, produced by 180 degrees and 360 degrees reconstructions of data from a full 360 degrees data acquisition. There is little difference in overall image quality between the two reconstruction modalities. Quantitatively, however, appropriate 180 degrees reconstructions significantly improve lesion contrast in both organs by as much as a factor of two. In all cases studied, the values of image contrast achieved when the 180 degrees arc of reconstruction was centred about the region of interest were higher than the values obtained from the 360 degrees reconstructions. These results are shown to be independent of the corrections made for photon attenuation. Clinically this technique may prove useful in clarifying the presence or absence of disease, particularly in equivocal cases where lesions have poor contrast or are small in size. An extended clinical trial of the technique is now in progress.

Adult↗