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Biomedical subjects

M A Chaudhri

Publications and source records attributed to M A Chaudhri.

At least 19 recordsLinked to original sources
PubMed1997

Charged photoparticle production in tissue during radiotherapy.

Photon-induced proton and alpha particle production in tissue is estimated for the photon energy range from 3 to 28 MeV, using the authors' previously established methods. It is shown that charged particle emission exceeds neutron emission for energies greater than 11 MeV by a factor that reaches a maximum of 7.0 at 17 MeV. Due to uncertainties in the source data this maximum value should be regarded as indicative only. Above 17 MeV the neutron yield rises sharply and the ratio of charged particle emission to neutron emission declines to values of 3.0 and 1.7 at 20 and 28 MeV, respectively.

Alpha Particles↗
PubMed1991

Production of neutrons from water, polyethylene, tissue equivalent material and CR-39 irradiated with 2.5-30 MeV photons.

Photoneutron yields from water, polyethylene, tissue substitute and CR-39 have been calculated for the photon energy range of 2 to 30 MeV, using a previously established method and photoneutron production data on hydrogen, carbon, nitrogen and oxygen. The rarer isotopes of the constituent elements of these compounds, namely 2H, 13C, 15N, 17O and 18O, have been taken into account and neutrons are shown to be produced for photon energies above 2.2 MeV, the (gamma, n) threshold for 2H. The data are useful for estimating neutron production in materials located in the vicinity of a megavoltage radiotherapy beam. Substances such as those considered here are often used as filtration, phantom or scattering material and as components of neutron dosimetry detectors. Photoneutrons produced in such materials may need to be taken into consideration when carrying out neutron dosimetry in the presence of photons in this energy range, especially when the neutron flux is several orders of magnitude less than that of the photons.

Models, Structural↗
PubMed1991

Effect of different pump mechanisms on transfusion of blood.

Sometimes infusion pumps are used to deliver whole blood to patients. However, in doing so there is a potential for damage to red cells from mechanical stresses in the pump, resulting in haemolysis. In order to investigate the degree of haemolysis caused by different pumps and therefore their suitability for whole blood infusion, we compared the performances of commonly used volumetric pumps (AVI 400; IVAC 560; IVAC 631 and IMED 927) with different pumping mechanisms. Our results show that the maximum haemolysis (3.9 mg/100g) was caused by the IVAC 560 and the least (1.08 mg/100g) by the AVI 400.

Blood Transfusion↗
PubMed1988

Photoneutron production in tissue during high energy bremsstrahlung radiotherapy.

The total yield of photoneutrons from soft-tissue-equivalent material irradiated with bremsstrahlung of end-point energy from 6 to 28 MeV has been measured using the 35 MeV University of Melbourne Betatron and a 4 pi Halpern-type neutron detector. The results are compared with calculations based on the cross sections for neutron production of the constituent elements of tissue (H, C, N and O). It is shown that the less common isotopes of the constituent elements (2H, 13C, 15N, 17O, 18O) must be included to obtain agreement with the measured yields. The dose imparted to tissue by the photoneutrons is calculated for the energy range from 6 to 30 MeV and is compared with other available estimates. Further, the dose equivalent due to all photonuclear reactions in tissue is estimated for energies of 24 and 30 MeV.

Models, Structural↗
PubMed1982

Energy spectra of secondary neutrons produced by high-energy bremsstrahlung in carbon, nitrogen, oxygen and tissue.

The energy spectra of secondary neutrons produced when bremsstrahlung of end-point energy in the range 10-30 MeV is incident on oxygen, carbon and nitrogen have been calculated. Photonuclear reactions of the type (gamma, n) and (gamma, pn)( have been included. The respective contributions of various nuclear reactions have been adjusted using the published values of experimentally determined cross-sections, or branching-ratios, where these are available. Where no such information exists in the literature, the values have been empirically estimated. Agreements has been obtained between the calculated photoneutron spectra from C, N and O at various energies and the available experimentally-measured spectra. The photoneutron spectra from C, N and O have been combined in the right proportion (C5H40O18N) to compute the spectra of secondary neutrons from tissue irradiated with bremsstrahlung of end-point energy from 10-30 MeV. Mean neutron energies and kerma factors for these spectra have been calculated.

Carbon↗
PubMed1975

The potential and applications of cyclotrons in biomedical fields.

Applications of cyclotrons in biomedical fields like radioisotope production; activation and reaction analysis with charged particles and neutrons both in-vitro and in vivo types; production of fast neutron beams for therapy, etc. are described. Production yields of various isotopes in use through different nuclear reactions have been compared with the yields calculated using experimentally measured or empirically constructed excitation functions. Detection sensitivities of various elements in tissue through activation induced by protons, deuterons and alphas of different energies are presented. Fast neutron beams produced from Be, D2, D2O and 7Li targets with different sized and priced cyclotrons are critically compared. It is suggested that a Li-7, deuteron or even a heavy water target would produce a more penetrant neutron beam with relatively smaller cyclotrons than the commonly used Be target.

Fast Neutrons↗
PubMedDate not supplied

Nuclear analytical methods for trace element studies in calcified tissues.

Various nuclear analytical methods have been developed and applied to determine the elemental composition of calcified tissues (teeth and bones). Fluorine was determined by prompt gamma activation analysis through the 19F(p, alpha gamma) 16O reaction. Carbon was measured by activation analysis with He-3 ions, and the technique of Proton-Induced X-ray Emission (PIXE) was applied to simultaneously determine Ca, P, and trace elements in well-documented teeth. Dental hard tissues: enamel, dentine, cementum, and their junctions, as well as different parts of the same tissue, were examined separately. Furthermore, using a Proton Microprobe, we measured the surface distribution of F and other elements on and around carious lesions on the enamel. The depth profiles of F, and other elements, were also measured right up to the amelodentin junction.

Activation Analysis↗
PubMedDate not supplied

Carbon determination in human teeth by activation with He-3 ions.

A nuclear analytical method, involving activation with 3He ions, was developed to determine carbon content in human teeth with well-documented histories. The tooth samples were irradiated with 2.7-MeV3He particles at 50 nA intensity, and the activity of 14O induced through the reaction 12C(3He, n)14O, determined by counting the 2.31-MeV gammas. Different dental hard tissues were studied separately. A solid piece of silver steel, the carbon content of which was accurately determined by chemical means, was used as the standard. The carbon content in different teeth varied from 4-7%. The overall experimental accuracy was better than 4.5%.

Activation Analysis↗