Biomedical subjects

T Radcliffe

Publications and source records attributed to T Radcliffe.

6 recordsLinked to original sources

PubMed1994

Optimization of metal/phosphor screens for on-line portal imaging.

Studies were conducted to determine the optimal metal/phosphor screen for on-line video verification of radiation treatment portals. Screens were evaluated for luminance and spatial resolution as a function of composition and thickness at 6- and 23-MV x-ray energies. A new video technique was used to determine modulation transfer functions. Gd2O2S was found to be the most efficient (brightest) phosphor for this application. Luminance was found to vary linearly with phosphor thickness up to a thickness of 500 mg/cm2. Metal plates made of iron, brass, copper, lead, and sintered tungsten of various thicknesses were also tested for luminance and resolution with Gd2O2S phosphor. Brightness peaked at about 2-mm thickness for most metals. Significant contributions to the brightness were found to come from x rays interacting with the phosphor itself.

Evaluation Studies as Topic↗

PubMed1994

Pseudocorrelation: a fast, robust, absolute, grey-level image alignment algorithm.

A new image alignment algorithm--pseudocorrelation--has been developed based on the application of Monte Carlo techniques to the calculation of a cross-correlation integral for grey-scale images. It has many advantages over cross-correlation: it is at least a factor of 10 faster than fast-Fourier-transform-based cross-correlation, and requires 8 times less memory. Its high speed allows for the search space of geometric transformations between images to include magnification and rotation as well as translations without the search time becoming too long. It allows noise to be taken into account, making calculation of a robust, absolute probability of good alignment possible. It is relatively insensitive to differences in quality between images. This article describes the pseudocorrelation algorithm in detail and presents the results of tests of the effects of contrast enhancement, resolution differences, and noise on the algorithm's performance. These tests show that the algorithm is well suited to the task of automated alignment of very low contrast images from video electronic portal imaging devices.

Algorithms↗

PubMed1989

Burnout among primary care physicians and mental health professionals in a managed health care setting.

This study assessed burnout within a large Health Maintenance Organization. Primary care physicians and one psychiatric clinic staff were studied. The Maslach Burnout Inventory was used to develop frequency data in the areas of emotional exhaustion, depersonalization, and personal achievement. Among the primary care physicians, moderate emotional exhaustion, and depersonalization were found. Personal achievement was high. Among the psychiatric staff, high emotional exhaustion and depersonalization were found. Again, personal achievement was high. The entire professional group, with the one exception, was significantly higher in emotional exhaustion, depersonalization, and personal achievement than Maslach's normative sample. Psychiatrists and social workers had significantly higher scores on depersonalization than the primary care physicians or psychologists. High burnout in a Health Maintenance Organization setting suggests that managed health care providers may be more prone to burnout than fee-for-service practitioners. Several suggestions were made for such organizations to help alleviate burnout in their staffs.

Adult↗

PubMedDate not supplied

Monte Carlo optimization of metal/phosphor screens at megavoltage energies.

The physics of imaging with metal/phosphor (Gd2O2S:Tb on brass) screens at megavoltage energies has been investigated using Monte Carlo simulation. It has been found that pair production is a significant contributor to energy deposition for Bremsstrahlung beams with energies greater than 6 MV. The effects of different thicknesses of phosphor and metal have been studied, and it is shown that the metal plays a significant role in establishing electronic equilibrium in the phosphor. The transport of optical photons through the phosphor has been modeled, and was found that only 10% to 20% of the light created in the phosphor escapes from the surface, with much of the loss being due to total internal reflection at the surface. Calculated results have been compared with experimental measurements of screen brightness for different phosphor and metal thicknesses. The SNR of a video electronic portal imaging device (VEPID) has been calculated as a function of x-ray and optical photon detection efficiency. The non-Poisson distribution of energy deposition in the phosphor is an important contributor to the SNR. The results of this paper should serve as a useful guide to the engineering design of future electronic portal imaging systems.

Biophysical Phenomena↗

PubMedDate not supplied

Grooved phosphor screens for on-line portal imaging.

Video-based systems for on-line portal imaging utilize a metal plate coated with Gd2O2S phosphor at a typical thickness of 500 mg/cm2. A new screen design is proposed wherein the conventional flat phosphor coating is replaced by a much thicker phosphor layer (1000-2000 mg/cm2) penetrated by either lineal grooves or pyramidal holes comparable to the system pixel size. By increasing the surface area of the phosphor, the grooves or holes allow light from deep layers of the phosphor to escape by a process of internal reflection. In addition, the escaping light is strongly forward peaked, improving optical coupling to the video camera. The processes by which grooved screens intensify light output have been modeled in a simple computer program that gives approximate agreement with experiment. Prototype screens have been constructed that provide several times the forward light output of flat screens, and that improve DQE(f) in light photon limited systems for spatial frequencies below 0.4 mm-1.

Computer Simulation↗

PubMedDate not supplied

Intraoesophageal rupture of a thoracic aortic aneurysm.

The intraoesophageal rupture of a large thoracic aortic aneurysm is reported in a 49 year old man. He had been hypertensive for some years while the aneurysm increased in size. Although a graft was successfully inserted to repair the leak, infection from the oesophagus with candida albicans, subsequently led to secondary haemorrhage and death 17 days later. A plea is made for the earlier referral of patients with aneurysm prior to rupture, as the operative mortality rises markedly after rupture has occurred and in this case the situation was virtually irreparable.

Angiography↗