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Biomedical subjects

P H Murphy

Publications and source records attributed to P H Murphy.

At least 19 recordsLinked to original sources
PubMed1992

Stability of fixation in healthy subjects during automated perimetry.

The stability of fixation of 12 healthy young subjects was assessed with a high-resolution eye tracker during automated perimetry. All the subjects exhibited eye movements and fixation shifts during the examination. The average shift in eye position between successive 1-minute intervals ranged from 0.41 degrees to 2.11 degrees, and the average standard deviation of eye position around the average of each interval ranged from 0.56 degrees to 2.55 degrees. In nine of the subjects the eye remained within 3 degrees of centre for 96% or more of the stimuli. The remaining three subjects experienced difficulty maintaining central fixation: the eye was more than 3 degrees away from centre for 28% or more of the stimuli. In the latter subjects the ability to repeatedly stimulate the intended retinal test locations was substantially reduced. The authors discuss the effects of unstable fixation on short-term fluctuation and on fixation loss.

Adult↗
PubMed1991

Monocular blurring. A complication of YAG laser iridotomy.

Laser iridotomy is the procedure of choice for primary angle-closure glaucoma. The authors report a new visual disturbance after neodymium (Nd): YAG laser iridotomy. Thirteen patients presented with monocular blurring or a bluish or colored line after the laser procedure. Each eye had a patent iridotomy partially exposed by the upper lid. When the iridotomy was fully covered or fully exposed, symptoms disappeared. Symptoms also were relieved with tinted lenses. The authors suggest close preoperative examination with careful placement of the laser iridotomy entirely under the upper lid to prevent this potential visual disturbance.

Adult↗
PubMed1991

Inaccuracies in quantitative radionuclide renal imaging due to patient position or diverging collimation.

Radionuclide renal studies with quantitative measurements in patients confined to intensive care units usually require the use of a 10-inch field-of-view mobile gamma camera and a diverging collimator to image both kidneys simultaneously. The patient must frequently be in the lateral decubitus position so imaging can be performed in the posterior projection. Due to spatial distortion caused by the diverging collimator, variations in detector angulation and kidney depth produce different detection efficiencies for each kidney. Counts in regions of interest over the kidneys were compared as a function of detector angulation and patient position (prone and lateral decubitus). Substantial variations were observed comparing the diverging collimator data to 15-inch field-of view parallel hole acquisitions. Significant variation can also be obtained with parallel hole collimators when the patient's position is changed.

Gamma Cameras↗
PubMed1991

Acceptable risk as a basis for regulation.

In recent years, guidelines for radiation protection have increasingly been based on estimates of the risks associated with radiation exposures and judgments regarding acceptable levels of risk. This leads to a more objective basis for regulations if the risk estimates are accurate. However, as enthusiasm for this approach expands, the large uncertainties in the risk estimates are often overlooked, and unreasonable, restrictive applications are possible. Several recent examples of radiation protection guidelines illustrate the risk-based emphasis underlying today's radiation safety philosophy.

Adult↗
PubMed1990

Nuclear magnetic resonance velocity spectra of steady flow.

Nuclear magnetic resonance (NMR) velocity spectra are a compact way to represent the flow information in a velocity-resolved image set. Fully developed steady flow in long tubes gives NMR velocity spectra with average velocities which correlate well with the values derived from the flow rate. The ratio of average velocity to peak velocity correlates well with the Reynolds number. Tubes with compressed cross sections have velocity spectra similar to those of circular tubes. Tubes with irregular walls have velocity spectra in the entrance region that are markedly different from those from smooth-walled tubes.

Arteriosclerosis↗
PubMed1989

Characterization of fluid flow using low-spatial-resolution velocity spectra from NMR images.

Flow velocity distributions or spectra may be obtained by NMR imaging using an anisotropic three-dimensional Fourier transform pulse sequence in which the low-resolution direction encodes perpendicular velocity. Velocity spectra from regions of interest covering the entire lumens of pipes in a flow phantom containing straight sections, a jet, and a constriction suggest that velocity spectra provide useful information even when the vessels are not spatially well-resolved. The flow in the phantom was characterized and limited measurements were made.

Blood Flow Velocity↗
PubMed1988

MR imaging of susceptibility-induced magnetic field inhomogeneities.

A 90 degrees-tau 1-90 degrees-tau 2-image acquisition pulse sequence allows spatial mapping of resonant frequency. This sort of sequence has previously been used for magnet shimming, and its use in chemical-shift imaging has been proposed. The authors used this sequence in magnetic resonance imaging of a phantom to demonstrate the magnetic field gradients arising from susceptibility differences within the phantom and allow those gradients to be measured. Gradients may arise near interfaces between substances that cannot support the same magnetic flux density. The pulse sequence was found to work well in lower-field-strength instruments.

Brain↗
PubMed1987

Acceptance testing and quality control of gamma cameras, including SPECT.

The measurement of several performance parameters of a scintillation camera at the time of installation and thereafter at regular intervals is necessary to ensure that the camera is operating within specifications and to detect changes over time that can initiate a request for service. There are varied opinions on what constitutes a satisfactory acceptance test and quality control program. Few individuals would disagree that either an acceptance test or routine quality control measurements are necessary, yet agreement on the contents and frequencies of these tests is lacking. This paper discusses the performance parameters of scintillation cameras that are usually measured for planar imaging and also for SPECT with rotating cameras.

Quality Control↗
PubMed1986

Guidelines for radiation protection.

Guidelines for radiation protection originate from numerous federal, state, and local agencies. Webster defines a guideline as a line by which one is guided, especially as an outline (as by a government) of policy or conduct. Guidelines in radiation protection can be either mandatory or advisory. Regulations by federal, state, and local governments for the use of radioactive materials define operating practices. Adherence to these regulations is required by law and there are penalties for noncompliance. Regulations generally constitute the minimum requirements for good practice and are usually supplemented by less formal recommendations from regulatory agencies and advisory groups. The regulatory guides published by the Nuclear Regulatory Commission (NRC) and by radiation control groups of agreement states are intended to assist the user of radioactive material in maintaining compliance with regulations. These guides recommend good practice but are not mandatory in that the user can propose alternatives to the regulatory agencies to meet the regulations. Many groups serve in an advisory capacity in formulating reports and recommendations for the safe use of radioactive material. The most prominent and influential among these are the National Council in Radiation Protection and Measurements (NCRP) and the International Commission on Radiological Protection (ICRP). Often the recommendations of these advisory groups evolve into either regulatory guidelines or regulations for the use of radioactive materials. At the present time, the backbone of the Nuclear Regulatory Commission's regulations relating to the medical use of radionuclides, "Standards for Protection Against Radiation" (10CFR20) and "Human Use of Byproduct Material (10CFR35), are undergoing extensive review with major revisions anticipated within the very near future. These proposed changes could have a significant impact on the practice of nuclear medicine. The changes will have some influence on radiation safety practice as it relates to the radiation worker, the patient, and the environment.

Air Pollutants, Radioactive↗
PubMed1985

Phase alterations of spin echoes by motion along magnetic field gradients.

Using a Taylor series expansion of the phase shift of a moving isochromatic spin group in the presence of a magnetic field gradient, the refocusing effects of the Carr-Purcell-Meiboom-Gill pulse sequence on stationary nuclei and those with constant, rectilinear velocity are readily demonstrated. Continuing the analysis to higher orders of motion reveals that nuclei with a constant, rectilinear acceleration have a phase shift at the spin echoes which increases linearly with echo number. Constant, rectilinear jerk (the time rate of change of acceleration) leads to an increase in phase shift from echo to echo which is quadratic in nature with an overlying reduction of the odd-numbered echoes by a constant amount. Motion parameters may be measured by parameter identification techniques. These principles may be applied to phase-sensitive NMR imaging.

Magnetic Resonance Spectroscopy↗
PubMed1985

Integration of database capabilities into a patient reporting system.

A database design is described which automatically archives computer-generated patient imaging and radioassay reports. Selected phrases are condensed so that data storage will be efficient without sacrificing a prose style of report. An indexed file structure has been used to facilitate rapid record retrieval even when several hundred thousand records are stored. Personnel time is considerably reduced for recalling patient records, preparing periodic summaries of studies completed, and performing administrative functions such as billing and keeping track of checked out images. Complex queries, such as "list all the patients between the ages of 50 and 60 on digitalis referred for a stress cardiac study, with left ventricular ejection fraction less than 40% and apical dyskinesis," become feasible. A system for data backup is described to protect against catastrophic data loss.

Computers↗
PubMed1979

Radionuclide computed tomography of the body using routine radiopharmaceuticals. I. System characterization.

A whole-body computed tomography system for single-photon emitters was evaluated from the standpoint of spatial resolution, sensitivity, and thresholds for count densities with reference to standard doses of currently used radiopharmaceuticals in patients. In air and tissue equivalents, spatial resolution was relatively constant throughout the field of view and attentuation correction algorithms returned uniformity of response to within 10%. In a phantom of the human abdomen 1.5-cm spherical "cold" lesions and 1-cm "hot" lesions could be resolved. Aspects of the partial-volume effect were observed and investigated. To detect 1.5 cm-cold lesions in an abdominal phantom, five million events were required.

Computers↗
PubMed1979

Radionuclide computed tomography of the body using routine radiopharmaceuticals. II. Clinical applications.

A whole-body computed tomography system for single-photon emitters was used to investigate the clinical utility of this imaging modality. We have explored its application in brain, lung, liver, kidney, cardiac, bone, and gallium imaging in over 200 patients. Brain images demonstrated better lesion contrast than that in standard scintiphotos. Images of the lung and liver showed radionuclide distribution that was not readily apparent in standard scintiphotos. Moderate or strongly positive pyrophosphate myocardial images demonstrate the potential for infarct quantitation. ECG-gated cardiac blood-pool images in cross section, displayed in cine formate, permit evaluation of segmental motion of the free and septal walls of both ventricles. These results suggest significant clinical potential for this imaging modality using standard radiopharmaceuticals, but some increase in system sensitivity will likely be necessary to realize the full benefit of the technique.

Abdomen↗
PubMed1978

Cassette videotape recording of computer images.

Direct videotape recording of images from computer display terminals is often not possible because of the nonstandard outputs of these systems. A video-sync mixer is described that permits black-and-white recording on standard 3/4-in. videotape cassettes.

Data Display↗