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Biomedical subjects

R P Parker

Publications and source records attributed to R P Parker.

At least 19 recordsLinked to original sources
PubMed1986

Tissue analysis by dual-energy computed tomography.

A straightforward method of tissue analysis from dual-energy computed tomography (CT) is presented which does not rely on previous inaccurate or incorrect formulations of the X-ray attenuation coefficient. The attenuation coefficients of tissue and bone were represented by a mixture of two reference materials. For convenience, water and calcium chloride were chosen. After careful calibration of the CT scanner, a dual-energy CT scan yields the water and calcium chloride in units of kg/kg multiplied by the specific gravity of the tissue. For an error of +/- 2 HU on dual-energy scans at 140 kVp and 87 kVp on an EMI CT5005 general-purpose scanner, the error on the calcium chloride coefficients is +/- 0.004 kg/kg. Fat concentrations greater than 25% by weight may be detected when the coefficients are averaged over at least 200 pixels. Bone mineral content could be measured with a precision of 0.01 (in units of kg/kg multiplied by specific gravity) for averaging regions of 24 pixels. Iodine concentrations in tissue can be deduced if water and iodine are chosen as the reference materials. Clinical examples are presented to illustrate the technique for scans of both the head and the abdomen.

Abdominal Neoplasms↗
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

The respective roles of the simulator and computed tomography in radiotherapy planning: a review.

The advent of computed tomography (CT) scanners and the development of a CT facility on treatment simulators has provided an array of expensive equipment for use in radiotherapy treatment planning. The object of this paper is to review the requirements necessary for accurate radiotherapy planning and to present guidelines regarding the system which appears best suited to plan individual tumour sites, based on our experience of CT scanning and related techniques over the past 6 years.

Brain Neoplasms↗
PubMed1983

The use of CT in radiotherapy treatment planning.

A prospective study is reported comparing conventional localisation with computed tomography (CT) localisation of tumours for radiotherapy treatment planning. One hundred and five out of 320 (33%) patients had an alteration in treatment plan and details are given according to the tumour site. CT planning enables more accurate localisation of both tumour and normal organs in addition to providing an accurate body contour and inhomogeneity corrections. Implications for integration of CT into radiotherapy planning practice are discussed and the impact of CT on treatment policy evaluated.

Abdominal Neoplasms↗
PubMed1981

The implementation of a generalised Batho inhomogeneity correction for radiotherapy planning with direct use of CT numbers.

A method for performing inhomogeneity corrections using a generalised Batho equation is described. The corrections are performed using the quantitative anatomical data produced by a CT scanner. The generalised Batho equation has been implemented on an EMIPLAN 7000 interactive treatment planning system. Details are given of the acquisition of the required data from the CT scan and from the existing stored beam data of the therapy machines.

Computers↗
PubMed1980

Quantitative imaging using the Cleon emission tomography system: recent developments.

A revised method of correcting for attenuation has been investigated through experiments using discrete sources within a radioactive background. The effects of changing the source size, the source position relative to the central axis, and the ratio of the concentrations in the source and background have been studied. A comparison of the results obtained using old and new attenuation corrections show marked improvement. The measurement of radioactive concentration on the central axis had a typical systematic error of -14%, compared to -60% previously, but is generally dependent on source size, source position, and source and background concentrations. An allowance can be made for this error using experimental data.

Brain↗
PubMed1979

The direct use of CT numbers in radiotherapy dosage calculations for inhomogeneous media.

Techniques by which the quantitative anatomical data inherent in a CT scan can be directly used in treatment planning are described. The correction algorithms used in the RAD-8 system, based on an effective path length, have been extended to a pixel-by-pixel approach. By calibrating the X-ray transmission CT scanner in terms of electron densities (electron cm-3) inhomogeneity corrections may be made automatically.

Humans↗
PubMed1979

Computed tomography applied to radiotherapy treatment planning: techniques and results.

In order to assess the role of computed tomography (CT) in radiotherapy treatment planning, tumors were localized by conventional techniques and with CT using an EMI CT5005 scanner. CT scans were obtained under conditions simulating radiotherapy. A comparison between the two localizations was made, and detailed results are given. Forty-seven of 123 patients had their treatment plan altered, implying that, provided information is obtained and used correctly, CT can play a significant role in radiotherapy treatment planning.

Abdominal Neoplasms↗
PubMed1979

Feasibility of absolute activity measurements using the Cleon emission tomography system.

Large volume and small discrete sources of Tc-99m were used to study the spatial resolution, sensitivity, linearity and reproducibility of the radionuclide brain images. The spatial resolution is constant both within and perpendicular to the section. For uniform distributions of activity the response is uniform over the field of view, and the mean pixel count rate is a linear function of the radioactive concentration and is independent of the diameter of the source. However, for discrete sources, the sensitivity was found to vary with the position of the source, and the potential of the system for quantitative assessment of the uptake of radioactivity in organs and tumors was limited initially. Later studies, with modified software, show that this undesirable effect has been reduced.

Brain↗
PubMed1976

Radiation doses to staff in a department of nuclear medicine.

A survey of data concerning radiation protection of staff working in the Nuclear Medicine Department and associated sections of the Physics Department at the Royal Marsden Hospital (Surrey Branch) is given for the period 1972 to 1975 inclusive. Results of routine film monitoring and whole-body counting are presented. Additional film monitors were used to check working areas, finger doses and any discrepancies between doses to the upper and lower trunk of personnel. In general, exposure to staff in the Nuclear Medicine Department is below 220 mrad per person per year, and below 1,000 mrad per person per year in the Radioisotope Dispensary. The dose received by radiographers is primarily due to spending time close to patients. Since about 5,000 intravenous injections of radionuclides are given each year in our department, the resulting finger doses to the staff involved may give rise to concern unless the task is shared.

Body Burden↗
PubMed1975

Digital reconstruction of point sources imaged by a zone plate camera.

Zone plate cameras are used for high sensitivity imaging of X- and gamma-ray sources. The image thus obtained requires decoding and numerical techniques are devised for this purpose. The response function and the signal-to-noise ratio for a single point source have been evaluated for zone plates with varying numbers of zones. Autocorrelation is the best of the methods examined, and the results are in good aggreement with those obtained using Monte Carlo techniques. The autocorrelation method can give a gain of 50% in signal-to-noise for a single point source over the maximum obtainable with optical decoding. Criteria for the choice of number of zones are discussed.

Computers↗
PubMed1975

Digital processing of images from a zone plate camera.

A method for the digital decoding of data obtained with a gamma camera fitted with a zone plate aperture is described. Taking a line source as the object, computer simulations have been used to examine the effects of noise, solid angle variations, shape of detector and detector resolution and methods of dealing with these effects are considered. Using an Anger gamma camera and a zone plate aperture both a line source and a thyroid phantom containing 99Tcm have been well reconstructed. The behaviour of the system with regard to resolution, signal-to-noise ratio and tomographic capability is discussed.

Computers↗