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Biomedical subjects

B K McCandless

Publications and source records attributed to B K McCandless.

12 recordsLinked to original sources
PubMed1996

Development of cross-platform computer-based tutorials.

The development, distribution, and support of computer-based instruction in radiology is complicated by the fact that many radiology departments use computers with different operating systems: Macintosh and Windows. A program for developing cross-platform on-line documentation was adapted to develop a graphical hypertext tutorial that would run identically on both types of computers. A tutorial for interpreting ventilation-perfusion scans was created that would run on the Windows platform. The graphics were converted to Macintosh format, and the identical source information was recompiled to run on the Macintosh platform. It was found that the tutorial, with its hypertext, full-color graphics, graphical links, searching, user annotation, and bookmarks, could be displayed and operated identically between platforms. Cross-platform tutorials must be developed on a Windows-based computer but require only one source file for both Windows-based and Macintosh computers. These tutorials can be distributed free of charge, and minimal training is required for those who already know how to use Windows on-line help.

Computer-Assisted Instruction↗
PubMed1995

Preventing patient motion during tomographic myocardial perfusion imaging.

UNLABELLED: We evaluated whether use of a device that positions and supports the upper extremities and back during tomographic myocardial perfusion imaging reduces the incidence and severity of patient motion and patient motion artifact. METHODS: We enrolled 190 patients referred for stress/redistribution myocardial perfusion imaging. All patients were imaged once with the patient support device (PSD) and once without it. Patients were randomly assigned to use the PSD either during poststress or redistribution imaging. The presence and severity of patient motion was determined by visual inspection and quantitative motion detection. The presence of reconstruction artifact due to motion was detected visually and confirmed by motion correction. RESULTS: Use of the PSD reduced the incidence of motion from 38% +/- 3.7% to 26% +/- 3.3% (p < 0.05) and reduced the amount of motion by 5.3 +/- 2.2 mm (p < 0.05). Patients who did move, moved less when using the PSD by both visual (p < 0.02) and quantitative criteria (p < 0.05). Use of the PSD reduced the incidence of reconstruction artifacts to one third of control (p < 0.05). CONCLUSION: The use of this positioning and support device during tomographic myocardial perfusion imaging reduces the incidence and severity of patient motion and motion artifact.

Artifacts↗
PubMed1994

Mediation of lung neutrophil uptake after endotoxin by CD18-integrin-dependent and -independent mechanisms.

We studied polymorphonuclear neutrophil (PMN) uptake in lungs of endotoxemic rabbits using 111In-labeled PMN and isotope imaging by gamma scintigraphy. Rabbits were challenged intravenously with 100 micrograms Escherichia coli endotoxin either 4 or 24 h before an intravenous injection of 111In-labeled PMN, which was obtained from donor rabbits. The contribution of CD18 glycoprotein (beta 2-integrin) on PMN was examined using an anti-CD18 monoclonal antibody (MAb) IB4 infused 20 min before 111In-labeled PMN injection. In control rabbits, 111In-labeled PMN uptake in lungs was maximal within 5 min [36 +/- 2% increase above baseline (+/- SE)] and then fell exponentially with a disappearance half-time (t1/2) of 10 +/- 2 min. In rabbits challenged with endotoxin for either 4 or 24 h, maximum 111In-labeled PMN lung uptake and t1/2 values increased to 52 +/- 3 and 56 +/- 3% and to 26 +/- 2 and 31 +/- 6 min, respectively. Pretreatment with MAb IB4 (0.5 mg/kg iv) did not alter the PMN uptake response and t1/2 values in the 4-h endotoxin-challenged rabbits (i.e., maximum uptake of 52 +/- 3% above baseline and t1/2 of 26 +/- 2 min), whereas MAb IB4 prevented the increases in lung PMN uptake and t1/2 in 24-h endotoxin-challenged rabbits (maximum PMN uptake of 26 +/- 5% and t1/2 of 7 +/- 3 min; P < 0.001). In contrast, the control MAb OKM-1 did not prevent lung PMN uptake and the disappearance of PMN from lungs at either times.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Tomographic imaging of the distal extremities using cone-beam collimation.

UNLABELLED: We evaluated the feasibility of cone-beam tomography (SPECT with a converging collimator) for detecting bone pathology of the distal extremities. METHODS: We examined 11 patients: seven with hand or wrist pain, three with ankle pain and one with tibial pain. Cone-beam tomography was performed using a high-resolution converging collimator with a 45-cm focal length. Tomograms were then compared to high-resolution planar images. RESULTS: Cone-beam tomography was successfully performed in all patients and tomograms were reconstructed in time for inclusion in the clinical report. In five patients, cone-beam tomography identified abnormalities that were equivocal or poorly defined on planar images. All other cone-beam studies provided the same information as the planar images. CONCLUSIONS: Tomographic imaging of the distal extremities can be successfully performed by using cone-beam tomography which has been found to be feasible and potentially useful in the clinical setting.

Adult↗
PubMed1993

Detection of patient motion during tomographic myocardial perfusion imaging.

We compared the effectiveness of four methods for detecting patient motion during tomographic myocardial perfusion imaging: visual inspection of a cine of the raw data, cross-correlation, diverging squares and a new method called two-dimensional fit. The methods were evaluated for their ability to detect the presence of motion, localize the camera angle at which motion occurred and measure the distance of motion. Patient motion was simulated by shifting motion-free images and then masking their periphery so that the field of view did not move on the image matrix. None of the methods detected 3.25 mm of motion with clinically useful accuracies. Visual inspection, cross-correlation and two-dimensional fit most accurately detected axial patient motion (p < 0.05), whereas cross-correlation most accurately detected lateral motion (p < 0.05). For axial motion, cross-correlation and two-dimensional fit most accurately localized the camera angle at which patient motion occurred (p < 0.05). For lateral motion, cross-correlation most accurately localized patient motion (p < 0.05). Two-dimensional fit measured the distance of axial patient motion to +/- 1.1 mm and measured the distance of lateral motion to +/- 8.7 mm. All other methods frequently overestimated or underestimated the distance of motion by > 13 mm. We conclude that cross-correlation adequately screens tomographic myocardial perfusion studies for both axial and lateral patient motion, although visual inspection is adequate for detection of axial motion. Cross-correlation best localizes the camera angle at which the motion occurred. Two-dimensional fit is the only method studied that accurately measures the distance of motion.

Coronary Disease↗
PubMed1992

Effect of patient motion on tomographic myocardial perfusion imaging.

We evaluated the effect of patient motion on inducing false-positive tomographic 201Tl myocardial perfusion studies. The effects of the angle of camera rotation at which movement occurs, the direction of movement and the distance of movement were studied. Movement was stimulated by shifting the raw data from normal motion-free 201Tl tomographic myocardial perfusion studies. The visual detectability of motion artifact was evaluated with receiver-operating characteristic curve analysis. The clinical importance of patient movement was determined by measuring the incidence of quantitative bull's-eye abnormalities induced by motion. Visual artifacts were more detectable and quantitative abnormalities more frequent as the distance of movement increased. Artifacts from 3.25 mm of movement were not visually detectable. Artifacts from 6.5 mm of movement were visually detectable, but were infrequently clinically important. Movement of 13 mm or greater frequently caused quantitative abnormalities. Quantitative abnormalities from axial movement were more frequent than artifacts from lateral movement. Quantitative abnormalities were more frequent when the movement occurred at the beginning or end. We conclude that when patients move during 201Tl tomographic myocardial perfusion imaging, the incidence and character of false-positive results depend on the angle of camera rotation at which the movement occurs, the direction of the movement and distance of the movement.

Artifacts↗
PubMed1992

Diagnosis of sternal wound infection by technetium-99m-leukocyte imaging.

An imaging study is needed that can detect sternal wound infections and distinguish between superficial and deep sternal wound infection when a clinical diagnosis is uncertain and a decision regarding surgical intervention must be made. We retrospectively reviewed the 99mTc-leukocyte scans of 29 patients referred to rule out sternal wound infection. The presence or absence of deep or superficial sternal wound infection was determined by microbiology and long-term follow-up. Images obtained 4 and 20 hr after injection were reviewed by two nuclear physicians who were blinded to the clinical history. Findings were categorized as normal or abnormal. Abnormal images were further defined as having intense uptake at 4 and 20 hr, increasing uptake between 4 and 20 hr, or other patterns such as focal cold regions, irregular uptake at 4 and 20 hr or increasing uptake between 4 and 20 hr were 100% sensitive and 89% specific for the detection of deep sternal wound infection. The images were also useful for determining the extent of infection. Superficial sternal wound infection could not be reliably detected. The results indicate that 99mTc-leukocyte imaging is useful for the diagnosis of deep sternal wound infection.

Adult↗
PubMed1991

Effect of albumin on hydraulic conductivity of pulmonary artery endothelial monolayers.

We tested the hypothesis that albumin reduces the vascular wall hydraulic conductivity by an interaction with the endothelium. The system consisted of luminal and abluminal chambers separated by a microporous filter onto which was grown a confluent monolayer of ovine pulmonary artery endothelial cells. The abluminal chamber filtrate was collected for timed periods during increases in transendothelial pressures of 5, 10, 15, and 20 cmH2O. The transendothelial water flux was linearly related to the hydrostatic pressure. Hydraulic conductivity (Lp) was determined from the slope of this relationship per unit surface area. In the absence of albumin, Lp of the endothelium and the filter was 14.8 +/- 3.8 x 10(-5) cm.s-1.cmH2O-1. The addition of either 2.5 or 5.0 mg/ml ovine serum albumin to the medium reduced Lp values similarly to 2.0 +/- 0.3 x 10(-5) and 2.5 +/- 1.1 x 10(-5) cm.s-1.cmH2O-1, respectively. Removal of albumin from the media reversed the effect of albumin on Lp. The filter Lp value of 3.2 +/- 0.3 x 10(-3) cm.s-1.cmH2O-1 was unaffected by albumin. Endothelial Lp value did not decrease with 5.0 mg/ml of 70-kDa neutral dextran. Albumin decreased Lp in the presence of epsilon-amino-caproic acid to the same extent as albumin alone, suggesting that the positively charged lysine sites on albumin did not mediate the effect. The results indicate that albumin decreases Lp due to an interaction between albumin and the endothelial cell.

Animals↗
PubMed1990

Leukotriene B4 increases pulmonary transvascular filtration by a neutrophil-independent mechanism.

We examined the role of circulating granulocytes in the pulmonary microvascular response to leukotriene B4 (LTB4) by prior depletion of circulating granulocytes using hydroxyurea. LTB4 (2 micrograms/kg injection followed by infusion of 2 micrograms/kg over 15 min) produced transient increases in pulmonary arterial pressure and pulmonary vascular resistance, indicating that neutrophils were not required for the pulmonary hemodynamic effects of LTB4. Infusion of LTB4 in granulocyte-depleted sheep also resulted in transient increases in pulmonary lymph flow (QL) with no significant change in the lymph-to-plasma protein concentration ratio (L/P), findings similar to those in control animals. In vitro studies indicated that LTB4 (10(-7) or 10(-9) M) produced a transient adherence of neutrophils to cultured pulmonary artery endothelial monolayers. Maximal responses occurred at 10 min after the addition of LTB4 to the endothelial cell-neutrophil coculture system, and the adherence decreased to base line within 60 min. LTB4 infusion in sheep also produced a transient uptake of autologous 111In-oxine-labeled neutrophils. The results indicate that LTB4-mediated increase in pulmonary transvascular protein clearance (QL x L/P) is independent of circulating granulocytes.

Animals↗
PubMed1990

Pulmonary edema induced by phagocytosing neutrophils. Protective effect of monoclonal antibody against phagocyte CD18 integrin.

We studied the changes in pulmonary hemodynamics and lung wet weight induced with opsonized zymosan (OZ) in isolated guinea pig lungs perfused with Ringer-albumin solution containing neutrophils (PMNs). Addition of OZ to the PMN-perfused lungs caused pulmonary vasoconstriction and weight gain; neither OZ nor PMNs added individually to the perfusate altered pulmonary vasomotor tone or wet weight. The steady gain in lung weight by 1,588 +/- 464 mg over the 45-minute study period was associated with pulmonary capillary hypertension and an increase in the capillary filtration coefficient, indicative of increased lung vascular permeability. These responses may not be due to generation of oxygen radicals, because the alterations in pulmonary hemodynamics and lung weight were not reduced by addition of superoxide dismutase, catalase, or superoxide dismutase plus catalase. We examined the basis of the PMN-mediated effects by layering PMNs on bovine pulmonary artery endothelial monolayers. Challenge with OZ resulted in increased endothelial permeability to 125I-albumin. The monoclonal antibody IB4 (directed against CD18, the common beta-subunit of structurally related adhesion receptors on phagocytes, LFA-1, Mac-1, and P150,95) prevented the OZ-mediated increase in PMN adherence to endothelial cells and the increase in endothelial permeability to 125I-albumin. IB4 also inhibited the lung weight gain mediated by the OZ-stimulated PMNs in intact lungs. The protective effect of IB4 could be ascribed neither to inhibition of uptake of OZ by PMNs nor to inhibition of release of oxygen radicals, myeloperoxidase, and elastase.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Determinants of platelet kinetics: effects of pulmonary microembolism.

We examined the mechanisms of platelet uptake in the lungs after alpha-thrombin-induced pulmonary microembolism. Platelets labeled with 111In-oxine were reinfused into chronically prepared sheep. Pulmonary microembolism resulted in an increase in lung platelet radioactivity (95.5 +/- 15.3%; n = 4), which was followed by an exponential washout (half-life = 115 +/- 4 min). Platelet uptake in the lungs was more sustained after prior fibrinolytic inhibition with tranexamic acid (half-life = 178 +/- 11 min), although the initial increase was similar (90.7 +/- 9.6%; n = 7). Prior depletion of fibrinogen with ancrod (Arvin), blunted the initial increase in lung platelet uptake after alpha-thrombin challenge (31.7 +/- 11.3%, n = 5), indicating that the effect of thrombin was markedly dependent on fibrinogen. We examined the role of circulating granulocytes, since platelets may bind to subendothelial matrix exposed after granulocyte-mediated lung vascular injury. Maximal pulmonary platelet uptake after thrombin in granulocytopenic sheep was not different from control (71.7 +/- 14.4%; n = 4). The results indicate that pulmonary microembolism results in lung platelet sequestration. Platelet uptake is not dependent on granulocyte-mediated vascular injury but requires fibrin deposition and is sustained if fibrinolysis is inhibited.

Animals↗