Biomedical subjects

A Skretting

Publications and source records attributed to A Skretting.

9 recordsLinked to original sources

PubMed1992

Evaluation of labelled monoclonal antibodies by simultaneous estimation of the association constant, the immunoreactive fraction, and the number of effective binding sites on the specific target.

The reaction between a labelled monoclonal antibody (MoAb) and its specific target is characterised by three parameters: the association constant (Ka) of the labelled MoAb, the number (N) of effective binding sites on the specific target, and the immunoreactive fraction (F) of the labelled MoAb preparation. Immunological binding parameters are usually estimated graphically, by fitting the experimental data to linear equations derived from the first order law of mass action (FLMA) at equilibrium. However, only two parameters can be estimated simultaneously in a two-dimensional plot. Consequently, graphical estimation of Ka, F and N must be performed stepwise, using at least two different plots. The three parameters are interdependent, and therefore a stepwise estimation procedure might give suboptimal results. In order to investigate whether this is a problem of practical significance in the evaluation of labelled MoAbs, a computerised iterative nonlinear least squares (INLSQ) method was applied to estimate the three parameters simultaneously. The binding parameters in reactions between different 125I-labelled MoAbs and different types of targets were significantly changed when a graphical procedure was replaced by the computerised INLSQ method, and the goodness of fit to FLMA was improved. Hence, the nonlinear least squares method is the preferred procedure. Values were affected when only a subset of the data was included in the estimation procedure, indicating some heterogeneity even in these presumably homogeneous MoAb reactions. The radiolabelling procedure was presumed to be the main reason for this heterogeneity.

Alkaline Phosphatase↗

PubMed1992

[Intravenous drug users and the HIV epidemic].

Data are taken from a study of 1,765 arrested intravenous drug users at the Oslo Central Police Station. Intravenous drug users in Oslo seem to get themselves tested for HIV regularly. In 1990-91 the average number of HIV-tests was 5.3, and the time since last test was, an average, between eight and nine months. Most intravenous drug users do not share needles and syringes. The most important source of needles and syringes in Oslo is an ambulant bus which can be found in city centre at night. HIV-seropositive drug users seem to have more regular contact with treatment programmes than those who are HIV-seronegative. Most of the HIV-seropositive drug users who are under treatment are to be found in a few institutions.

Acquired Immunodeficiency Syndrome↗

PubMed1992

Blood flow in six human melanoma xenograft lines with different growth characteristics.

Blood flow in six human melanoma xenograft lines grown s.c. in BALB/c-nu/nu mice was studied and analyzed in relation to tumor growth characteristics. Two different methods were used to measure blood flow, i.e., uptake of 86Rb and clearance of 133Xe. The percentage of the injected 86Rb taken up per g of tumor tissue and the 133Xe clearance rate were used as parameters for blood flow. The results achieved with these two methods were consistent. Blood flow differed significantly among individual tumors of the same line, even for tumors of similar size. All lines showed a decrease in blood flow with increasing tumor volume. This was due to an increase in necrotic fraction as well as a decrease in blood supply per viable tumor cell. Blood flow also differed significantly among the xenograft lines. All lines showed a lower blood flow than the kidney, spleen, liver, and foot. The blood flow was generally lower in the xenograft lines than in the EMT6 and Lewis lung murine tumor lines. There was no correlation between tumor blood flow and volumetric growth rate. The xenograft lines could be divided into two distinct groups of three lines each with respect to blood supply per viable tumor cell. The three lines showing a high blood supply also showed a high fraction of cells in S phase (23-31%), whereas the three lines showing a low blood supply had a low fraction of S-phase cells (11-13%). Thus, blood supply per viable tumor cell was probably decisive for the cell proliferation activity in the tumors. Moreover, necrotic fraction increased with increasing tumor volume, and the magnitude of this increase was largest for the three lines showing the lowest blood supply per viable tumor cell. These observations were possibly consequences of basic differences in vascular architecture between the two groups of xenograft lines.

Animals↗

PubMed1990

Migration of 99mTc-labelled syngeneic lymphocytes in the rat. Biological and theoretical models predict radiation damage and poor scintigraphic detectability.

The possibility of obtaining useful scintigrams of secondary lymphoid organs after infusion of syngeneic lymphocytes labelled with technetium-99m (99mTc) was explored in a rat model. Thoracic duct lymphocyte (TDL) accumulation in various organs was measured with both 99mTc and 51Cr labelled cells, the latter processed with a method that has been shown not to damage lymphocytes. 99mTc labelled TDL did not localize properly in the lymph nodes and spleen. We could not visualize lymph nodes in scintigrams, neither could we demonstrate any difference between normal and hyperplastic spleens. Our conclusion is that radiation from the 99mTc label readily influences lymphocyte migration so that useful scintigraphy in rats and other small experimental animals becomes impossible. This was supported by results from culture experiments with 99mTc labelled, radiosensitive mouse haemopoietic progenitor cells. Theoretical considerations, including the calculations of lymphocyte self-irradiation and signal/noise ratios during scintigraphy of rat tissues, supported our conclusion that scintigraphy in small animals, to disclose the physiological migration of lymphocytes, may be impossible with the present sensitivity of gamma cameras.

Animals↗

PubMed1990

[Intravenous drug users and contact with the health care system].

Intravenous drug users in the Oslo area seem to have rather limited contact with treatment programmes (outpatient or inpatient). The data are taken from a survey of intravenous drug use among arrestees at Oslo Central Police Station. 1,394 intravenous drug users were examined. Less than one third reported having had any contact with a treatment programme during the last six months, and less than 50% reported such contact during the last two years. More than 50% said that they had never been admitted to an inpatient treatment institution.

Adult↗

PubMed1990

A Norwegian nationwide quality assurance project in nuclear medicine: total performance in bone scintigraphy measured with a new transmission phantom.

A prototype version of a recently developed transmission phantom for simulation of radionuclide bone studies was used in a Norwegian nationwide quality assurance project. The design of the phantom made it possible to perform a receiver operation characteristic (ROC) examination with respect to the detection of radionuclide accumulation in the ribs. The participants were also asked to report accumulation in the spinal column. Images obtained by means of a uniform source and a four-quadrant bar pattern were used to judge resolution and homogeneity with the collimator used in the bone studies. The overall performance of the laboratories was satisfactory, but considerable variations were found. There was a marked correlation between the physician's performance and the resolution and homogeneity of the camera. Reports from stationary imaging were generally better than those that were based on whole-body scans.

Bone and Bones↗

PubMed1978

Clinical results with 131I-toluidine blue and triple radionuclide subtraction for preoperative localization of enlarged parathyroid glands.

Clinical results from the application of a triple radionuclide subtraction study for preoperative localization of enlarged parathyroid glands are presented in this paper. A scintillation camera image was recorded after i.v. injection of 131I-toluidine blue. The contributions to this image from activity in the thyroid gland and in blood were determined after recording of additional images (obtained after injection of 99mTcO4- and 113mIn, respectively) using an iterative computer algorithm that also provides an estimate for a uniform background. Subtraction of these contributions gives an image that may be interpreted as an image of the selective accumulation of 131I-toluidine blue in the parathyroids. One or more enlarged glands were correctly localized in 17 of 21 cases, but in four cases there were only false positives. In ten cases the correctly localized glands weighed 900 mg or less.

Adult↗

PubMed1977

A computer algorithm for triple radionuclide subtraction studies applied for preoperative localization of enlarged parathyroid glands.

This paper presents a computer algorithm for triple radionuclide subtraction studies and its application to preoperative localization of enlarged parathyroid glands. In the clinical examination procedure, 131I-toluidine blue was used as the principal radionuclide, 99mTcO4 and 113mIn were used to obtain additional images of the thyroid and the blood distribution respectively. A scintillation camera with a pinhole collimator and connected to a digital data aquisition system was used to record the images. Subtraction of uniform background, thyroid and blood contributions to the principal image is done automatically in the computer program. The results from a clinical study is used to illustrate the method.

Computers↗

PubMed1975

An iterative computer algorithm for optimization of radionuclide subtraction studies.

A new algorithm for off-line computer optimization of radionuclide subtraction studies is presented. Within the digitized image, any region of interest may be chosen for study. No prior knowledge is required concerning the position and extent of the principal and interfering objects, nor concerning their image intensities. Tests show that even when statistical fluctuations are relatively large, the intensity quotient calculated by this algorithm may be used to estimate a uniform background and correct for its contribution. The effect of smoothing the images prior to the use of the algorithm has been investigated. The method has also been used for pancreas imaging and one example of this application is presented.

Computers↗