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D L Hastings

Publications and source records attributed to D L Hastings.

8 recordsLinked to original sources
PubMed1998

Feasibility of imaging photodynamic injury to tumours by high-resolution positron emission tomography.

One early effect of the treatment of tumours by the new modality photodynamic therapy (PDT) is a reduction in tumour glucose levels. We have employed the widely used positron-emitting glucose analogue flurorine-18 fluoro-2-deoxy-D-glucose ([18F]-FDG), to determine whether, in principle, PDT-induced injury might be delineated non-invasively and quantitatively by positron emission tomography (PET). The scanner was of the high-density avalanche-chamber (HIDAC) type with a resolution of 2.6 mm. Subcutaneous T50/80 mouse mammary tumours, sensitised by haematoporphyrin ester, were illuminated by graded doses of interstitial 630 nm light. Thirty hours later, any remaining viable tumour was detected (a) by region-of-interest analysis of the PET images and (b) by gamma counting the excised tumour. PET measurements of % uptake of [18F]-FDG into tumour correlated closely with ex vivo gamma counting (slope=0.976, r2=0. 995), validating the in situ method. Uptake into untreated, control tumours was 3.8%+/-1.1% of the injected activity. Uptake of [18F]-FDG into treated tumours decreased by 0.7% for every 100 mm3 reduction in remaining viable histological volume. Outcome was further compared with that measured by (a) T2-weighted proton imaging on a 4.7-T magnetic resonance imaging (MRI) system and (b) histological analysis of subsequently sectioned tumours. PET using [18F]-FDG described the absolute volume of surviving tumour histological mass to the same degree as high-resolution MRI. The conclusion of these initial studies is that PET with [18F]-FDG, although non-specific, quantitatively described at early times the extent of tumour destruction by PDT.

Animals↗
PubMed1997

An assessment of finger doses received by staff while preparing and injecting radiopharmaceuticals.

Good working practice and legal obligation impose a duty on nuclear medicine departments to check syringe activities before administration to a patient. If syringe guards are used to reduce staff exposure while drawing up injections, the guard has to be removed to measure the activity in a conventional reentrant ionization chamber type calibrator. Alternatively, the activity may be checked in a purpose-built syringe calibrator which allows the assay of the activity in the syringe without the need to remove the syringe guard. Finger doses received during the dose preparation and injection are a cause for concern. This study investigated the finger and whole-body doses received when using each of these calibrators, and compared the results with those obtained by an operator who did not measure the dose at all. The results demonstrated that although the finger doses are small, measurement of the syringe activities in a conventional ionization chamber increases the dose by a factor of 2 above that which would occur if no activity measurements were made, whereas the use of the specialized syringe calibrator gave finger doses only marginally above those obtained with no activity measurement.

Fingers↗
PubMed1995

The effect on diagnostic quality of using dual isotope imaging for 81Krm ventilation and 99Tcm-MAA perfusion lung scanning.

It is the practice in some centres to use dual isotope imaging to reduce imaging times in lung ventilation and perfusion studies with 81Krm gas and 99Tcm-macroaggregated albumin (99Tcm-MAA) by simultaneous acquisition of the two images. The resulting loss of image caused by cross-talk between the two energy windows was investigated using two phantoms, one with cold 99Tcm lesions of varying size and contrast, and the other a uniform field of 81Krm. It was found that, under scatter conditions typical of a patient study, the use of dual isotope acquisition and a krypton generator of 470 MBq or greater resulted in a perceptible loss of image quality with lesions up to 4 cm in diameter being missed. On an older camera system, without modern energy and linearity correction facilities, a lower generator activity of only 120 MBq was sufficient to cause image degradation even under very low scatter conditions. Seventy-five patient studies were performed using both single and dual isotope imaging with generator activities ranging from 80 to 282 MBq. At these low generator activities, the studies did not demonstrate any differences between the images that would result in a different diagnosis. We conclude that the use of dual isotope V/Q scanning reduces the diagnostic value of the perfusion image if the activity of the 81Krm generator is too high, although at generator activities of 300 MBq or less no loss of image quality will occur on modern camera systems.

Humans↗
PubMed1995

The effect of phantom wall thickness on volume determination in SPET.

Assessment, using phantoms, of a a three-dimensional, second-derivative, surface-detection algorithm for accurately determining the volumes of structures in single photon emission tomography (SPET) has shown the performance of the algorithm to be highly dependent on phantom wall thickness. With a 30% background activity level, the volume of a 600-cm3 cylinder with wall thickness approximately 0.4 mm was measured to an accuracy of approximately 1%, whereas for an almost identical cylinder with a wall thickness of approximately 3 mm the measured volume was underestimated by about 14%. To further investigate this 'wall-thickness' effect, theoretically generated SPET data have been produced, simulating a set of low-contrast cylindrical phantoms with identical internal dimensions and wall thicknesses ranging from 0 to 6 mm. These image data have demonstrated a 10% reduction in the calculated volume for wall thicknesses as thin as 1 mm. A less acute dependence is also demonstrated for a threshold-based quantitation algorithm, where a wall thickness of 4-5 mm is required to produce an effect of similar magnitude. The underlying cause behind this 'wall-thickness' effect is undoubtedly the perturbation in the count profile across the surface boundary, which results form the cold region of the phantom wall. Thus, phantom wall thickness will have an effect on the performance of most automated quantitation techniques, both two- and three-dimensional, since the majority must incorporate some form of analysis on this count profile.

Algorithms↗
PubMed1993

A three-dimensional second-derivative surface-detection algorithm for volume determination on SPECT images.

Most existing techniques for determining volumes on single-photon-emission computed tomography (SPECT) data employ thresholding, two-dimensional edge detection, or manual delineation of edges. These methods, however, are limited in both accuracy and applicability. In seeking to overcome these limitations, a truly three-dimensional (3D) second-derivative-based algorithm which can be implemented with relative ease has been developed. The method incorporates 3D matrix operators; these are convoluted with the SPECT count data in order to produce a 3D voxel map whose data elements correspond to the second derivative of counts in the image. This map is then searched, a suitable derivative-based edge-defining criterion being applied to each voxel position, in order to locate the derivative surface boundary which defines the volume. Validation is obtained using phantom data from 99Tcm-filled bottles of volumes 200, 580 and 2500 cm3 placed within a body-sized tank containing background activities set to give a range of contrasts between 1.00 and 0.75 (i.e. background 0% to 25%). The performance of the algorithm is encouraging: the volumes of the two larger bottles are determined to within a 3% accuracy without the need for any prior calibration, and the results obtained over all bottle sizes are found to be contrast independent to within approximately 4%.

Algorithms↗
PubMed1989

Evaluation of myocardial thallium tomography in patients with chest pain.

Thirty-seven patients with chest pain have been studied by exercise thallium tomography and coronary arteriography to assess the accuracy of thallium tomography in the identification of patients with coronary artery disease and to evaluate whether knowledge of clinical data improves this accuracy. Thallium tomography was also used to identify which coronary arteries were stenosed. Thallium tomography when compared with coronary arteriography has a sensitivity of 97%, a specificity of 75%, and an overall accuracy of 92% for the detection of coronary artery disease. When clinical information was made available, these results improved to a sensitivity of 100%, a specificity of 75%, and an overall accuracy of 95%. In the identification of which coronary arteries were stenosed, thallium tomography had a sensitivity of 85%, a specificity of 89%, and an overall accuracy of 86%. These results show that exercise thallium tomography can be an accurate non-invasive screening test in patients with chest pain thought to be angina.

Angina Pectoris↗
PubMed1980

HIDA scanning in gall-bladder disease.

HIDA labelled with 99Tcm is a new hepatobiliary imaging radiopharmaceutical which is selectively taken up by the liver and excreted into the biliary tree; it has been shown to demonstrate the gall bladder in normal subjects. Using a gamma-camera computer system, dynamic liver scans were performed during the first hour on 97 patients who, on the basis of standard investigations and on the findings at surgery, were divided into six groups as follows. 1. Normal. 2. Hepatocellular disease. 3. Biliary obstruction. 4. Chronic gall-bladder disease. 5. Acute gall-bladder disease. 6. Acute abdomen (not due to gall-bladder disease). Pictures were taken and activity-time curves of "regions of interest" were generated from the computer data. From these the presence or absence of a gall-bladder image was easily determined. The gall bladder was visualized in all normals but in none of the patients with acute gall-bladder disease. In the group with an acute abdomen suggestive of acute gall-bladder disease, but subsequently shown to be otherwise, the gall bladder was visualized in all cases. The gall bladder was not visualized in 42% of hepatocellular disease patients, nor in any of those with biliary obstruction, due to poor uptake or poor secretion of the HIDA. In cases of chronic gall-bladder disease, visualization of the gall bladder corresponded with gall-bladder opacification on the oral cholecystogram; in these cases the HIDA scan offers no advantage over the oral cholecystogram. These results suggest that in cases of "acute abdomen" an absent gall bladder image with a normal hepatogram will strongly support the diagnosis of acute gall-bladder disease, and that visualization of the gall bladder excludes such a diagnosis, making the HIDA scan a useful first-line investigation in these patients.

Abdomen, Acute↗