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Biomedical subjects

S Webb

Publications and source records attributed to S Webb.

At least 253 records · Page 14Linked to original sources
PubMed1989

Vitamin A and bone formation. Different responses to retinol and retinoic acid of chick bone cells in organ culture.

The response of bone cells in organ culture to retinol and retinoic acid was studied. Both stimulated incorporation of [3H]thymidine into DNA by 16-day embryonic chick calvaria, but the time-course of the responses differed; the peak responses to retinol and retinoic acid occurred at about 18 h and 48 h, respectively. Although retinol inhibited chick bone collagen synthesis retinoic acid had no effect, but it did stimulate non-collagenous protein synthesis, whereas the effect on the latter of retinol was, if anything, inhibitory. When present with retinol, retinoic acid was able to attenuate the inhibitory effect of the former on chick bone collagen synthesis, but preincubation with retinoic acid had no such effect. In neonatal murine calvarial cultures, retinoic acid inhibited collagen synthesis selectively in the same manner as did retinol. The ability of chick osteoblasts to respond differently to retinol and retinoic acid suggests that both forms of the vitamin may have a role in bone formation and that their intracellular models of action may differ although the attenuation response indicates there may be some interaction between the two.

Animals↗
PubMed1989

Image quantification with a large area multiwire proportional chamber positron camera (MUP-PET).

A large area multi wire proportional chamber positron camera system is under evaluation for clinical Nuclear Medicine investigation using isotopes both from the house generators (68Ga) and from remote cyclotrons (18F, 124I, 64Cu and 81Rb). Images are reconstructed using a fully three dimensional (3D) algorithm and exhibit equal resolution in all three orthogonal directions. The axial field of view of 15 cm is large enough to allow coverage of the whole brain. This paper discusses the performance of the MUP-PET system with particular emphasis on quantification and the development of an attenuation correction scheme for a large area detector system. The distribution of scattered and accidental events is investigated and observed to contribute a fairly uniform background to the image. Dead time correction factors are calculated from an analytical expression obtained by considering the various sources of dead time present in the system. Following correction for attenuation, accidentals, scattered events and dead time, reconstructed phantom images show a strong linear correlation (r = 0.998) between count density and regional isotope concentration. The extension of the methods to clinical studies is discussed.

Image Processing, Computer-Assisted↗
PubMed1989

Optimisation of conformal radiotherapy dose distributions by simulated annealing.

A method of computing the beam profiles for multi-element multiple-beam radiotherapy treatment is presented. This is applicable to the treatment planning of conformal radiotherapy using an isocentric rotation technique. The method begins with the treatment dose prescription and calculates the beam profiles rather than the reverse 'conventional' planning technique. The method is the iterative optimisation method of simulated annealing. It is shown using published 'difficult' clinical treatment planning problems that the high-dose region can be very precisely tailored to the tumour volume even when this has a re-entrant (concave) periphery. Simultaneously the dose can be constrained in other sensitive regions. The mathematics of the method is explained together with this implementation. The analogy of this optimisation with certain reconstruction problems in medical imaging is drawn and by way of experiment dose distributions are presented in image form and beam profiles as sinograms.

Computer Simulation↗
PubMed1989

SPECT reconstruction by simulated annealing.

The technique of simulated annealing has been introduced for reconstruction in single photon emission computed tomography (SPECT) of data from rotating gamma camera systems. This is a much used technique in fields other than medical imaging but has only been used for one previous medical imaging application by Barrett et al (1983). It is shown that for noiseless data, the method can give perfect quantitative results, even when photon attenuation is included in the problem. This is true whatever the object distribution. With noisy data, mean level quantitation is still achievable although image mottle is worse. This paper describes simulated annealing in the language of SPECT, paying particular attention to the computational tricks which are central to a practicable implementation. The results of many computer simulations are presented to show the potential power of the method. A short comparison with other reconstruction techniques is made.

Brain Neoplasms↗
PubMed1989

The performance of a multiwire proportional chamber positron camera for clinical use.

The Rutherford Appleton Laboratory clinical positron camera consists of two opposed multiwire proportional chambers (MWPCS) mounted on a rotating gantry capable of performing routine nuclear medicine studies. The system has operated since the end of 1986 with complete reliability. It has a sensitivity of 37 kcps MBq-1 cm3 per axial cm for a 20 cm diameter uniformly filled cylinder of activity. The best spatial resolution obtainable is about 6 mm, although in practice images are smoothed in order to reduce statistical noise with a corresponding decrease in resolution. Cross-plane rays are utilised during image reconstruction and the resulting three-dimensional images exhibit the same spatial resolution in three orthogonal directions over a large cylindrical field of view 15 cm high by 30 cm in diameter. The maximum data-taking rate is limited to 1.5 to 2 kcps at present due to deadtime in the read-out system. The performance of the system is described with particular reference to the problems of imaging with the large fractions of random and scattered events which are a consequence of using large-area detectors. Images of phantoms and patients are presented and proposed modifications to the camera are described.

Algorithms↗
PubMed1988

Legibility of health warnings on billboards that advertise cigarettes.

At present only subjective criteria exist to determine the legibility of health warnings on billboards that display advertisements for cigarettes. We constructed a set of objective standards and used them to assess the legibility of warnings on a sample of 37 billboards in Perth, Western Australia. The three features that were analysed were the apparent size of the letters, the colour contrast between the letters and their background, and the obliqueness of the message. We also compared the size and legibility of the health warning with that of the brand name. Health warnings were not legible to passing motorists in 51% of cases and not legible to motorists who were stopped at nearby intersections in 74% of cases, whereas almost all the brand names could be read easily. These results indicate that the present system of voluntary regulation of advertisements for cigarettes has failed to ensure that health warnings on billboards are legible. For health warnings on advertisements to have any useful effect it is essential that they are legible. The only way to ensure legibility is to adopt objective requirements for it.

Advertising↗
PubMed1988

Stimulatory effect of prolactin on the mitotic activity of the adrenal cortex in snell mice with hereditary dwarfism.

Effects of thyrotropin (TSH), growth hormone (GH), prolactin (Prl), and ACTH on the proliferation of adrenocortical cells in male Snell dwarf mice and in phenotypically normal male mice from the same strain were examined by means of the colchicine metaphase-arrest technique. After 6 days of treatment, ACTH increased significantly the mean mitotic activity rate (MMAR) of adrenocortical cells in both the normal (nondwarf) and dwarf mice as compared to the corresponding control groups receiving physiologic saline. None of the remaining examined pituitary hormones did exert a mitogenic action on the adrenal cortex of normal mice. It was, however, recorded the significant elevation of the MMAR of the adrenocortical cells in Prl-treated Snell dwarf mice, while TSH and GH did not stimulate mitogenesis. The acquired data corroborates a well-known proliferogenic effect of ACTH on the adrenal cortex in vivo. The increase of the MMAR of the adrenal cortex of Snell dwarfs following Prl-treatment is in agreement with earlier reports.

Adrenal Cortex↗
PubMed1988

Brain blotting: a method to detect multiple DNA copies in specific brain regions.

We developed a method to detect multiple DNA copies (both cellular and viral) in specific brain regions by blotting thick frozen sections onto nylon membranes. This was achieved by "printing" the frozen sections on standard blotting paper immediately after cryotome sectioning and performing blotting according to the standard Southern technique. A "replica" of the blotted section was obtained by keeping on the glass slide the next frozen section cut, which was then stained for conventional histopathological analysis and the cell nuclei counted to give an estimate of the total amount of DNA present in each section. The blotted membranes were then denatured and hybridized with a nick-translated Alu probe either at 42 degrees C with 50% formamide or at 68 degrees C without formamide. Brain sections from mice infected with Herpes simplex virus 1 (HSV1), blotted and hybridized with a nick-translated HSV1 probe, clearly showed the focal nature of the Herpes simplex infection, which was also demonstrated immunohistologically using a virus specific antiserum. This method of DNA detection, conveniently modified, might also be used to detect nuclear and cytoplasmic RNAs in specific coronal sections of whole brain before localization at high power by standard in situ techniques.

Animals↗
PubMed1988

Deconvolution of emission tomographic data: a clinical evaluation.

A method of improving the quality of images in single photon emission computed tomography (SPECT) is demonstrated using transaxial images of the liver and brain. Deconvolution of the nuclear medicine data by a point source response function (PSRF) acquired previously in a scattering medium attempts to compensate for scattered radiation within the patient. The average geometric response of the collimator of the gamma camera is also compensated for with this technique. Three patients with known metastatic lesions in the liver and three with primary lesions in the brain were imaged. Clinical assessment of reconstructed slices both before and after deconvolution demonstrates that compensating for the effects of scatter and of collimator blurring leads to enhanced detail of pathological lesions. In all cases, cold lesions seen prior to deconvolution were enhanced in detail and, in addition, new lesions were seen with this technique.

Adult↗
PubMed1988

Comparison of the effects of nebulized terbutaline with intravenous enprofylline in patients with acute asthma.

We compared the bronchodilating effects of intravenously administered enprofylline (2 mg/kg) with nebulized terbutaline (10 mg) in patients presenting to hospital with acute asthma in a multicenter double-blind parallel study. One hundred twenty three patients were randomized into the study, and 69 of these fulfilled the inclusion criteria and a retrospective time to study entry criterion; 34 received enprofylline and 35 received terbutaline. There was no significant difference in maximum increase in forced expired volume in 1 second (FEV1) between the enprofylline group (0.24 +/- 0.33 L) and the terbutaline group (0.25 +/- 0.28 L) (p greater than 0.05), nor for the increase in FEV1 over the 1-hour study period. Tremor was reported more in the group receiving terbutaline, and nausea was reported more in the group receiving enprofylline. Two patients experienced hypotension and one patient had a vasovagal episode with enprofylline treatment. Both agents acted as bronchodilators with similar efficacy in patients with acute asthma in this study.

Acute Disease↗
PubMed1988

Fetal alcohol syndrome: report of case.

A report of a patient with fetal alcohol syndrome has been presented with a review of the syndrome and the literature. Although the patient was treated in the operating room, many patients with less severe medical involvement or less extensive dental needs can be treated as outpatients. Each case must be considered individually with the prime concern being the patient's safety. Such patients may have numerous emotional or physical problems that the dentist must recognize. These patients are at high risk for several types of heart defects, many of which will require consultation for bacterial endocarditis precautions. The major and minor anomalies associated with fetal alcohol syndrome have been outlined.

Child↗
PubMed1987

Downregulation of T cell responses by antibodies to the T cell receptor.

We have derived a T cell clone that recognizes and responds to three different types of antigen: self + X (fowl gamma globulin + H-2d), allo-H-2p,b, and minor lymphocyte-stimulating (Mlsa,d) determinants. Anti-TcR mAb and their F(ab')2 and Fab fragments were tested for their capacity to block the response of this clone. When responses were assayed on day 4 or later, addition of KJ16 or F23.1 mAb caused a marked inhibition of the response to each of the three antigens recognized by the clone. Responses measured at earlier time points however were unaffected or enhanced. This finding suggested that the inhibitory effects of anti-TcR mAb that followed the phase of enhancement might have reflected downregulation of the cells rather than simple blockade of TcR. In support of this possibility it was found that addition of anti-TcR mAb caused marked inhibition of the response of the clone to IL-2, i.e., a response that is not known to involve the TcR.

Animals↗
PubMed1987

Isotope computed tomography using cone-beam geometry: a comparison of two reconstruction algorithms.

A CT scanner has been constructed specifically to determine the three-dimensional distribution of bone mineral in the medullary cavities of the radius, ulna and femur. A source of x-rays (153Gd) and a multiwire proportional counter (MWPC) are mounted at opposite ends of a diameter of an annular mounting. The limb is placed on the axis of rotation of the annulus and a series of two-dimensional transmission projections are obtained at equal angular spacings over 360 degrees. The distribution of bone mineral is reconstructed from the projections either by the method of maximum entropy (ME) or by convolution and back projection (CBP). These two methods have been evaluated by reconstructing a single slice of a phantom, representing the forearm, from projections simulated by computer. With a clinically acceptable exposure time, the mean medullary densities of the ulna and radius were determined with systematic errors of less than 3.5% (ME) and 11% (CBP), although for the latter method of reconstruction the systematic error was reduced to less than 2% by increasing the number of views. The mean medullary densities of the ulna and radius were determined with precisions better than 2.5% (ME) and 3.5% (CBP).

Algorithms↗
PubMed1987

Clinical dosimetry for radiotherapy to the breast based on imaging with the prototype Royal Marsden Hospital CT simulator.

The result of conservative management of breast cancer is strongly dependent on the homogeneity of the dose delivered a schedule of post-surgical radiotherapy. In addition to improvements in local control, late normal-tissue effects should be minimised by achieving a good dose homogeneity. The Royal Marsden Hospital prototype CT simulator has been used to image patients in the treatment position. With the CT data incorporated into the planning process a quantitative measure of the dose homogeneity was made. There are strong indications that unless tissue compensators are used and/or conformation therapy is performed, the dose inhomogeneity in a widely used treatment geometry is too large to be clinically acceptable.

Breast Neoplasms↗