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Biomedical subjects

W C Barker

Publications and source records attributed to W C Barker.

At least 37 records · Page 2Linked to original sources
PubMed1996

Left ventricular ejection fraction: comparison of results from planar and SPECT gated blood-pool studies.

UNLABELLED: Global ejection fraction (EF) from planar gated blood-pool (GBP) imaging is a widely accepted measure of cardiac function. It has been suggested that planar GBP could be replaced by SPECT. In this article, we compare counts-based global EF measured from SPECT and planar images and investigate reasons for discrepancies between the two. METHODS: Twenty-three subjects were imaged with both planar and SPECT GBP. SPECT short-axis slices were projected to create reprojected images. Reprojected SPECT (rSPECT) images were created in both the true long-axis view and also in a view typical of planar studies (found to be 60 degrees from the true long-axis). Thus, angle of view effects on global EF could be investigated. In addition, we studied the effects of background and attenuation. RESULTS: Long-axis rSPECT EF correlated well with planar EF (r = 0.89) but EF values were significantly higher for rSPECT than for planar (slope = 1.4, intercept = -8 EF units; p < 0.001). We found that background correction may not be necessary with rSPECT, but neither background nor attenuation explained the observed discrepancy between rSPECT and planar EFs. This discrepancy was found to be caused by atrial overlap in the planar image and disappeared when the SPECT slices were reprojected at the same angle of view as the planar images. CONCLUSION: Global EF can be easily measured from rSPECT GBP images. Long-axis rSPECT EFs are, however, greater than planar EFs by a factor of 1.4 because atrial overlap causes a significant drop in planar EF in planar images. These results suggest that (long-axis) rSPECT EFs may be more accurate than planar EFs.

Adult↗
PubMed1995

Continuous intraoperative external monitoring of perfusate leak using iodine-131 human serum albumin during isolated perfusion of the liver and limbs.

Regional isolated perfusion using tumor necrosis factor (TNF) shows significant promise for treatment of cancer which is limited to limbs or organs. The high toxicity of TNF requires very sensitive real time monitoring of leakage in order to avoid serious patient complications. Human serum albumin labeled with iodine-131 is used with an externally mounted and collimated NaI(Tl) detector to track the leakage of blood from the isolated perfusion blood circuit into the general systemic vascular space. Blood activity levels measured using the monitor demonstrated a very good correlation with blood serum samples taken concurrently with external monitoring. External monitoring can reduce the risks of perfusion leakage intraoperatively with the precision necessary to safely perform isolated perfusion using TNF.

Chemotherapy, Cancer, Regional Perfusion↗
PubMed1995

Cytokine levels and systemic toxicity in patients undergoing isolated limb perfusion with high-dose tumor necrosis factor, interferon gamma, and melphalan.

PURPOSE: Isolated limb perfusion (ILP) with tumor necrosis factor (TNF), interferon gamma, and melphalan (M) has been reported to result in high response rates for extremity melanoma and sarcoma. We have evaluated the relationship of systemic TNF exposure to induction of several secondary mediators and incidence of systemic toxicity. PATIENTS AND METHODS: Nineteen patients with extremity melanoma (n = 16) or sarcoma (n = 3), underwent 90-minute ILP with TNF-alpha, interferon gamma (0.2 mg), and M (10 to 13 mg/L of limb volume) (TNF/IFN/M) (n = 12), or M alone (n = 7). Continuous intraoperative monitoring (CIM) for systemic leak from the perfusion circuit was performed using radioactive iodine-131 albumin. Cytokine levels in the perfusate and systemic circulation during and after ILP were measured by enzyme-linked immunosorbent assay. RESULTS: Systemic leaks > or = 1% from the perfusion circuit occurred in six patients who received TNF/IFN/M and in four who received M alone. Hypotension that required vasopressor support occurred in six of six patients with evidence of a leak (> or = 1%) and zero of six patients without a leak (< 1%). These six patients had significantly higher peak systemic TNF levels during and after perfusion than patients without a leak (2.8 and 8.2 ng/mL v 0.7 and 2.0 ng/mL, respectively; P < .05). All patients who received TNF/IFN/M had significantly greater increases in systemic interleukin-6 (IL-6) levels than in patients with M alone (12,395 +/- 10,374 pg/mL v 79.4 +/- 7.2 pg/mL, respectively; P < .001). Intracellular adhesion molecule (ICAM), IL-8, and TNF-R levels were also increased after ILP with TNF/IFN/M. CONCLUSION: ILP with TNF/IFN/M can be safely performed, as I131 albumin provides a sensitive measure of systemic leakage from the perfusion circuit. Patients with a measured leak of > or = 1% develop mild and transient postoperative hypotension with significantly higher systemic TNF levels and lower perfusate TNF levels than in patients without leaks.

Adult↗
PubMed1994

The PIR-International Protein Sequence Database.

PIR-International is an association of macromolecular sequence data collection centers dedicated to fostering international cooperation as an essential element in the development of scientific databases. A major objective of PIR-International is to continue the development of the Protein Sequence Database as an essential public resource for protein sequence information. This paper briefly describes the architecture of the Protein Sequence Database and how it and associated data sets are distributed and can be accessed electronically.

Amino Acid Sequence↗
PubMed1993

The PIR-International databases.

PIR-International is an association of macromolecular sequence data collection centers dedicated to fostering international cooperation as an essential element in the development of scientific databases. PIR-International is most noted for the Protein Sequence Database. This database originated in the early 1960's with the pioneering work of the late Margaret Dayhoff as a research tool for the study of protein evolution and intersequence relationships; it is maintained as a scientific resource, organized by biological concepts, using sequence homology as a guiding principle. PIR-International also maintains a number of other genomic, protein sequence, and sequence-related databases. The databases of PIR-International are made widely available. This paper briefly describes the architecture of the Protein Sequence Database, a number of other PIR-International databases, and mechanisms for providing access to and for distribution of these databases.

Amino Acid Sequence↗
PubMed1991

The precision of positron emission tomography: theory and measurement.

The limits of quantitation with positron emission tomography (PET) are examined with respect to the noise propagation resulting from radioactive decay and other sources of random error. Theoretical methods for evaluating the statistical error have been devised but seldom applied to experimental data obtained on human subjects. This paper extends the analysis in several ways: (1) A Monte Carlo method is described for tracking the propagation of statistical error through the analysis of in vivo measurements; (2) Experimental data, obtained in phantoms, validating the Monte Carlo method and other methods are presented; (3) A difference in activation paradigm, performed on regional CBF (rCBF) data from five human subjects, was analyzed on 1.6-cm diameter regions of interest to determine the mean fractional statistical error in PET tissue concentration and in rCBF before and after stereotactic transformation; and (4) A linear statistical model and calculations of the various statistical errors were used to estimate the magnitude of the subject-specific fluctuations under various conditions. In this specific example, the root mean squared (RMS) noise in flow measurements was about three times higher than the RMS noise in the concentration measurements. In addition, the total random error was almost equally partitioned between statistical error and random fluctuations due to all other sources.

Brain↗
PubMed1990

Escherichia coli K12 genomic database.

We have compiled the genomic nucleic acid sequence data of Escherichia coli K12 available from the existing major data collections and from the literature. The collected data are structured as a database for easy access and analysis. The sequence segments in the database are ordered by genetic map position. Sequence redundancy has been completely removed by combining overlapping sequences; therefore, our sequence data are amenable to statistical analysis. We have specified with a plus or minus (+ or -) on which of the two DNA strands the segment exists. The database currently contains a total of 954,392 bp, which corresponds to about 20% of the entire genome size. The sequence data are available on request.

Base Sequence↗