PubMed Health⌕ Search

Biomedical subjects

D P Boyd

Publications and source records attributed to D P Boyd.

17 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↗
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↗
PubMed1977

Bronchobiliary and bronchopleural fistulas.

In the course of treating approximately 2,000 patients with postoperative stricture of the bile duct, 16 bronchopleural and bronchobiliary fistulas were encountered. Three patients have been seen in the past year. This has prompted a review of our experience since it was previously recorded in 1955. Fistulous complications of obstructive biliary tract disease take three forms: (1) massive fulminating biliary empyema; (2) acute necrotizing bile bronchiolitis and pneumonia when pleural symphysis exists; and (3) a more indolent, chronic, recurring form of bronchobiliary communication. We have learned that transdiaphragmatic perforation occurs at a certain characteristic location in the diaphragm. An understanding of the pathological anatomy and pathogenesis has provided a specific and sequential mode of surgical treatment. When this has been adhered to strictly, cure has resulted.

Adult↗
PubMed1977

Initial performance of the Stanford Medical pion generator.

A novel, cylindrical geometry, superconducting pion channel has been constructed at Stanford. It can simultaneously deliver up to 60 radially converging pion beams of the same mean momentum but with individually variable momentum spread (0.0-4.3%). Virtually no tuning of the pion beam is required Preliminary tests have demonstrated many of the performance characteristics which facilitate the treatment of selected human tumors.

Cold Temperature↗
PubMed1976

Infected aortic grafts and aortic fistulas.

Infection in prosthetic grafts of the aorta and in the groin present different problems. Retroperitoneal sepsis must be treated by total removal of the graft. This is probably equally true for acutely infected grafts seen in enteric fistula. The surgical technique described can be performed in one stage. The principles of treatment for groin infections are the same as for infections associated with prosthetic grafts. The hazard is more to limb than to life, since the infection tends to point outward in the groin and thus be confined. The technique for dealing with groin infections, as presented, is straightforward.

Aged↗
PubMedDate not supplied

A prototype high-purity germanium detector system with fast photon-counting circuitry for medical imaging.

A data-acquisition system designed for x-ray medical imaging utilizes a segmented high-purity germanium (HPGe) detector array with 2-mm wide and 6-mm thick elements. The detectors are contained within a liquid-nitrogen cryostat designed to minimize heat losses. The 50-ns pulse-shaping time of the preamplifier electronics is selected as the shortest time constant compatible with the 50-ns charge collection time of the detector. This provides the detection system with the fastest count-rate capabilities and immunity from microphonics, with moderate energy resolution performance. A theoretical analysis of the preamplifier electronics shows that its noise performance is limited primarily by its input capacitance, and is independent of detector leakage current up to approximately 100 nA. The system experimentally demonstrates count rates exceeding 1 million counts per second per element with an energy resolution of 7 keV for the 60-keV gamma ray photon from 241Am. The results demonstrate the performance of a data acquisition system utilizing HPGe detector systems which would be suitable for dual-energy imaging as well as systems offering simultaneous x-ray transmission and radionuclide emission imaging.

Americium↗
PubMedDate not supplied

Attenuation changes of the normal and ischemic canine kidney. Dynamic CT scanning after intravenous contrast medium bolus.

The potential of CT scanning to explore total and regional renal blood flow was evaluated in a dog model with unilateral renal artery stenosis (n = 7, reduction of renal blood flow: 32-75% of base line flow). Attenuation versus time curves were generated for the renal cortex and medulla, as well as for the aorta and renal vein. A fast CT scanner was used which allowed for up to 24 scans/minute at the same level (slice thickness: 10 mm). A total of 10 ml contrast medium was injected into a peripheral vein for each scan series taken. During baseline conditions, the curve of the renal cortex and medulla demonstrated 2 peaks. The first peak was mainly related to early vascular enhancement, whereas the second peak corresponded mainly to the appearance of contrast medium in the distal convolutes and collecting ducts. Ischemia of the kidney resulted in a reduction of the first peak and a flattening of the leading edge slope. Transport of contrast medium through the extravascular compartments of the kidney was delayed during ischemia. Relative renal blood flow was obtained from the CT data by dividing peak enhancement by rise-time as assessed from the cortical curve. All measurements were related to baseline flow and validated by flow measurements using radioactive labeled microspheres (n = 5). Correlation was found to be r = 0.97.

Animals↗