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D P Boyd

Publications and source records attributed to D P Boyd.

At least 19 recordsLinked to original sources
PubMed1987

Assessing the type A behaviour pattern with the Jenkins Activity Survey.

Controversy has arisen over the usefulness and reliability of the Jenkins Activity Survey (JAS) as a measure of Type A behaviour. Ray & Bozek (1980), Jenkins & Zyzanski (1982) and Ray (1984) have exchanged contrasting views. Our data show low internal consistency scores for the four components of the JAS: i.e. the Type A scale itself and factors speed and impatience (S), job involvement (J), and hard-driving competitiveness (H); and a low test-retest reliability result for the Type A scale. Further, the weighted scoring scheme of the JAS is questioned. Recommendations are made to eliminate the weighted scoring scheme, delete factors S, J, and H, and revise specific items in the JAS.

Female↗
PubMed1986

Spatial resolution analysis of computed tomographic images.

Methods are presented for the quantification of spatial resolution in x-ray computed tomographic (CT) images. Model-dependent methods are derived and compared with model independent methods for computation of the Modulation Transfer Function (MTF). These techniques are applied to phantom images of point, line, edge, and ring discontinuities. The model-dependent methods utilize multiparameter fits of a two-dimensional model function to the image data. Model predictions are compared with results obtained in a model-independent way by numerical transformation of the data. Results of resolution measurements of an Imatron C-100 CT scanner at UCSF and a second experimental scanner at the UCSF Physics Research Laboratory are presented.

Humans↗
PubMed1985

In vivo assessment of left ventricular wall and chamber dynamics during transient myocardial ischemia using cine computed tomography.

Using a new computed tomographic (CT) scanner design that uses a rapidly moving focused electron beam, 50-ms CT scans were obtained at 2 axial levels simultaneously through the hearts of 6 dogs in order to analyze left ventricular (LV) wall thickness and cross-sectional chamber area after acute occlusion of the left anterior descending coronary artery (LAD). Ten or fifteen 50-ms CT scans (rate of 17 scans/s through the middle of the left ventricle were performed in 1 second (cine acquisition) during intravenous administration of contrast medium at rest, 60 seconds after acute occlusion of the LAD, and 60 seconds after release of the occlusion. The percent extent of systolic wall thickening of the potentially ischemic anterior segment was 37 +/- 15% (+/- standard deviation) in the control state and -5 +/- 6.5% during LAD occlusion (p less than 0.01). There was no significant difference in the percent change in LV luminal area from end-diastole to end-systole between the control state (50 +/- 19%) compared with LAD occlusion (47 +/- 21%). There were no significant differences in the extent of systolic wall thickening or LV luminal area between the control state and 60 seconds after release of occlusion. The alterations in regional myocardial function during acute ischemia are characterized by wall thinning during systole in the jeopardized segment and no significant change in global LV function. These features can be assessed by cine computed tomography during a solitary heart cycle.

Animals↗
PubMed1985

Computed tomography of the heart: evaluation of anatomy and function.

Diseases of the heart and blood vessels represent one of the most challenging problems for advanced diagnostic imaging systems. Computed tomographic scanning is potentially an ideal cardiac imaging modality since it is a cross-sectional imaging method with very high resolution. Currently available computed tomographic scanners have exposure speeds of 1 to 5 seconds, which are inadequate for the majority of cardiovascular imaging applications. Nevertheless, a variety of limited computed tomographic scanning techniques have been successfully performed in selected patient subgroups. These methods require the administration of contrast medium injected or infused into a peripheral vein, combined with either dynamic computed tomographic scanning or some form of electrocardiographic gated computed tomography. The newer conventional computed tomographic scanners can display anatomic structures in the heart and great vessels with considerable fidelity and provide not only cross-sectional displays but also, by means of computer manipulation, any selected reconstructed images in oblique, coronal or sagittal projections. Feasibility studies indicate improved accuracy of computed tomographic measurements of cardiac chamber volumes. Physiologic measurements include estimation of shunt flows and cardiac output and analysis of myocardial wall thickening. The full potential of computed tomography should be reached once fast, multiple slice, computed tomographic scanners using scanning electron beam techniques become available. The prototype CVCT (cine computed tomographic C-100 scanner) designed at the University of California, San Francisco, is now undergoing evaluation. This instrument images up to eight contiguous slices at the rate of 16 to 24 images/s. The computed tomographic scanner specifically designed for cardiac imaging should extend the utility of computed tomography in the evaluation of cardiac diseases and the study of cardiovascular physiology.

Heart↗
PubMed1984

Cardiac imaging with a high-speed Cine-CT Scanner: preliminary results.

CT scans were obtained with a Cine-CT Scanner that uses a rapidly moving focused electron beam. The 50-msec CT scans were obtained at two transverse levels simultaneously through the hearts of a series of four normal dogs and six patients, four with coronary artery disease and two with hypertrophic cardiomyopathy. Two scanning mode options were chosen. Myocardial wall thickening and motion were studied by obtaining ten 50-msec CT exposures during one heart-beat within less than one second (cine-CT mode). Regional myocardial blood flow was assessed by obtaining approximately 20 scans at the same level of the left ventricle; each 50-msec exposure was gated to the same phase of 20 sequential heartbeats after intravenous administration of contrast medium (dynamic mode). These initial studies show the feasibility of defining regional and global myocardial contraction using the cine-CT mode, and the considerable potential for measuring regional myocardial perfusion using the flow (dynamic) mode.

Animals↗
PubMed1983

CT scanning of the heart.

It is generally agreed that all present diagnostic cardiac methods including echocardiography, nuclear medicine, and coronary arteriography have significant limitations. Nuclear cardiology provides excellent diagnostic sensitivity using small amounts of radioactive tracers, but it currently lacks the spatial fidelity needed to differentiate many anatomic structures in the heart. CT complements the capabilities of these alternative imaging modalities. Computed tomography offers accurate reconstruction of the whole myocardium with far greater spatial and density resolution in three dimensions. CT may eventually find its most important and clinically useful application in the diagnosis and management of heart disease.

Animals↗
PubMed1980

The desirable properties of computed tomography scanners.

The purchase of a CT scanner is a costly venture. Given the number of companies in the field and the tremendous financial involved, certain guidelines must be considered: (a) reputation and longevity of the firm; (b) merits of the machine; and (c) possibility of updating technologically. The authors discuss the most desirable properties of the scanners and list advanced features which manufacturers should be able to supply in the near future.

Tomography, X-Ray Computed↗
PubMed1980

Development of a computed tomographic scanner for radiation therapy treatment planning.

The authors describe a low-cost CT scanner integrated with a radiotherapy simulator and designed for treatment planning. The standard rotational gantry and x-ray tube of the simulator are used with a multiwire xenon lonization chamber and simple current-proportional readout system to measure patient attenuation, avoiding problems associated with diagnostic CT scanners in treatment planning. Although design constraints limit performance, software compensation techniques have reduced artifacts and given satisfactory images.

Evaluation Studies as Topic↗
PubMed1979

Coronal and sagittal reconstructions using a 4.8 second CT body scanner: developments and applications.

A computer program was developed which enables CT scans obtained on the General Electric body scanner to be reconstructed in coronal and sagittal planes. The program may be installed in minutes and requires no additional hardware. Multiplanar reconstructions can be produced within a few minutes, using the data available from a standard series of scans. No overlapping slices or other special techniques are needed. Large areas (e.g., the entire chest or abdomen) can be reconstructed and each plane of interest separately displayed. Resolution can approximate that available in transverse scans, and the patient receives no additional radiation exposure. Multiplanar reconstruction has proven very useful in a variety of clinical situations.

Female↗
PubMed1978

Computed tomography in detecting calvarial metastases: a comparison with skull radiography and radionuclide scanning.

A clinical study comparing the relative sensitivities of computed tomography, skull radiography, and radionuclide scanning in the detection of skull metastases indicated that CT was the least sensitive of these three modalities. CT could however detect a majority of lesions if scans were viewed at appropriate window settings. Phantom studies showed that the limitations of CT can be related to limited spatial resolution, the density of the lesions, partial volume averaging, and plane of section.

Humans↗
PubMed1978

Computed tomographic scanning in children: comparison of radiation dose and resolving power of commercial CT scanners.

Surface and internal radiation doses for abdominal computed tomography (CT) of children were determined using child-sized phantoms and seven models of CT body scanners. Resolving power of each scanner was determined simultaneously with the radiation dose determination. The average surface skin dose for a complete CT body examination ranged from 0.39 to 5.60 rad, varying with patient size and model of CT scanner employed. A high contrast (12%) resolving power phantom of water-filled holes in acrylic showed a range of 1.75--2.25 mm.

Child↗