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Biomedical subjects

W Chang

Publications and source records attributed to W Chang.

At least 145 records · Page 8Linked to original sources
PubMed1984

Assessment of methods for cytomegalovirus antibody testing of blood donations.

As part of a programme to establish a panel of individuals with high titres of anticytomegalovirus (CMV) IgG for the production of CMV Ig, the CMV serostatus of 139 normal blood donors was determined by indirect haemagglutination assay, enzyme immunoassay, and complement fixation. The indirect haemagglutination assay was the most accurate and convenient method for the detection of CMV antibody negative donations. Plasma for production of hyperimmune CMV IgG could best be selected by an IgG-specific enzyme immunoassay procedure.

Antibodies↗
PubMed1984

The sources of overestimation in the quantification by SPECT of uptakes in a myocardial phantom: concise communication.

A single photon emission computerized tomographic (SPECT) system's overestimation of the tracer concentration in a myocardial perfusion defect was examined by physical phantom studies. An empirical attenuation correction was used to isolate the problem of overestimation from imperfect attenuation correction. The overestimation of defect concentration in our SPECT system was found to come from three sources: software error, finite spatial resolution of the system, and scattered photons generated inside the phantom. The findings confirmed the current belief that the two major problems remaining in quantification with the SPECT technique are attenuation correction and scatter correction.

Heart↗
PubMed1983

The occurrence of carcinoma of the rectum following ileoproctostomy for familial polyposis.

Ileoproctostomy was performed in 32 patients (13 Female and 19 male), with polyposis coli ranging in age from 10 to 54 years. Seven patients (22%) developed cancer of the retained rectum with a median follow-up of 14 years. Two (20%) of ten patients, followed for 10 to 15 years, and three (50%) of six patients, followed for 15 to 20 years, developed rectal cancer. Rectal cancer developed in two of 14 patients who had their ileoproctostomy at 14 cm and in five of 18 patients who had their ileoproctostomy at a higher level, with a median followup of 7 and 11 years, respectively. Rectal cancer developed in two of 15 teenage patients undergoing ileoproctostomy and in nine of 17 patients aged 20 to 54 years. The present average ages of the two groups were 25 and 41 years, and the average age at which rectal cancer appeared was 40 years. Three of the patients who developed rectal cancer had numerous polypectomies over the years, and there was a tendency to develop tubulovillous and villous adenomas with a variable degree of atypia leading to carcinoma. One patient also showed a return to high levels of coprostanol and secondary fecal bile acids. Proctocolectomy, if acceptable, may be the treatment of choice; ileoproctostomy may mean that the patient eventually will undergo a proctectomy. The ileoanal endorectal pull-through procedure has a great deal to offer to these patients, and further study is necessary to evaluate this procedure.

Adolescent↗
PubMed1982

Synthesis and comparison of some cardiovascular properties of the stereoisomers of labetalol.

A useful method for the separation of labetalol into its two racemic diastereomers, as well as a stereoselective synthesis of its four stereoisomers, is described. The absolute stereochemistry of each isomer was determined by analysis of the DC spectra and confirmed by X-ray analysis. The alpha- and beta 1-adrenergic blocking properties, as well as the relative antihypertensive activities, have been measured in rats. The R,R isomer, 2a (SCH 19927), possesses virtually all of the beta 1-blocking activity elicited by labetalol and displays little alpha-blocking activity. In contrast, the S,R isomer, 3a, has most of the alpha-blocking activity. Of the four isomers, only 2a has antihypertensive potency comparable to that of labetalol. These findings, coupled with published data showing that labetalol possesses beta-adrenergic mediated peripheral vasodilating activity deriving essentially from its R,R isomer, lead to the following conclusion: The antihypertensive activity of labetalol can be ascribed to at least three identified complementary mechanisms, beta-adrenergic blockade, beta-adrenergic mediated vasodilatation, and alpha-adrenergic blockade, whereas the antihypertensive activity of 2a derives from the first two mechanisms only.

Adrenergic alpha-Antagonists↗
PubMed1982

A new collimator for cardiac tomography: the quadrant slant-hole collimator.

A quadrant slant-hole (QSH) collimator was constructed for myocardial perfusion tomography on a 15-inch large-field gamma camera. This system optimizes the crystal area for multiple-view photon detection while at the same time offering excellent tomographic performance. In addition to the advantages associated with parallel slant-hole collimation, this system's four orthogonal views provide a solution to the problem of patient positioning, namely, proper alignment of the long axis of the left ventricle to the camera. Rapid data acquisition, together with fast reconstruction, make the QSH system a practical approach to tomographic imaging of the myocardium.

Heart↗
PubMed1980

Methods for detection of left ventricular edges.

The ability to accurately and reproducibly measure left ventricular performance offers significant clinical advantages in patient management. Specifically, data on wall motion of the left ventricle, the characteristics and shape of the left ventricular volume curve, and measurement of ejection fraction are the general parameters of interest evaluated. These parameters may be measured with either first-pass studies or gated equilibrium blood pool images. Either method is relatively simple, economical, and presents little risk to the patient. Over the last several years both methods have undergone considerable study, and relatively standardized techniques for the two methods exist at present. Both techniques require moderate to extensive data processing. In general, a region of interest (ROI) must be defined before further quantitative analysis is possible. There are at present multiple approaches to the establishment of an ROI for the left ventricle. The major differences between these approaches is in the algorithms used to generate the boundary of the ROI or "the edge". In order for the computer to recognize the edge of the left ventricle, objective and reproducible edge-detection processes are needed. It is the purpose of this paper to review computerized edge-detection algorithms as they apply particularly to the noisy and blurry images obtained in nuclear medicine studies.

Heart Ventricles↗
PubMed1980

The effect of radiopharmaceutical incubation time on bone scan quality.

Clinical variability in the quality of bone scans led to an evaluation of the effect of incubation time on the bone scanning agent as it affects the background quality of the scan. Results of the study suggest that an incubation time of 30 minutes produces optimal bone to soft-tissue ratios with 99mtechnetium methylene diphosphonate.

Adult↗
PubMed1980

Seven-pinhole multigated tomography and its application to blood-pool imaging: technical parameters.

The application of seven-pinhole tomography has been predominantly to thallium-201 myocardial imaging. In view of the stationary nature of the collimator, with all views accumulating simultaneously, seven-pinhole tomography can be adapted to dynamic cardiac imaging, namely, multigated blood-pool imaging. Existing reconstruction software was modified to process the gated blood-pool data. The performance parameters of the seven-pinhole system were investigated at Tc-99m energy. This work provides an additional understanding of the seven-pinhole system as well as its potential application to abnormalities of ventricular wall motion or the quantitation of other cardiac parameters from reconstructed data.

Coronary Disease↗
PubMed1979

Optimization of the gray scale for photoscanners: concise communication.

A gray scale providing easy visual interpretation of black-and-white photoscan transparencies was determined empirically from psychophysical studies conducted on 50 observers. This optimum gray scale provides equal visualization for equal countrate changes over the entire film range.

Densitometry↗