Search PubMed⌕ Search

Biomedical subjects

S F Akber

Publications and source records attributed to S F Akber.

At least 19 recordsLinked to original sources
PubMed2000

Correlation of radiation tolerance dose of normal human organs with organ weight, blood, and water content.

The concerted effort to minimize the radiation exposure to normal human tissues while delivering a high radiation dose to the tumor often results in complications. This limits the efficacy of radiation treatment. Analysis of radiation tolerance dose with organ weight in 15 human organs yields a correlation coefficient of 0.62, whereas the correlation of radiation tolerance dose with blood and water content yields correlation coefficients of 0.82 and 0.60, respectively. Results indicate that as the organ weight and/or blood and water content increases, radiation tolerance dose decreases.

Blood↗
PubMed1998

Ion recombination and polarity effect of ionization chambers in kilovoltage x-ray exposure measurements.

Exposure measurements with ionization chambers are dependent on the correction factors related to the beam energy (ke), temperature and pressure (ktp), ionization recombination (Pion), and polarity (kpol) effects. In this work, six different chambers commonly used in diagnostic radiology were investigated for the Pion and kpol at various exposure rates by changing the tube voltage, beam current, exposure time, and distance. A special triaxial connector was used to connect chambers to an electrometer capable of measuring positive and negative polarity and 150 V and 300 V electrode potentials to measure the kpol and Pion, respectively. A mammography unit (24-35 kVp) and a diagnostic x-ray unit (60-125 kVp) were used. Results indicate that the magnitude of the Pion is linearly dependent on kVp for large volume (> 150 cm3) chambers and independent for small volume (< or = 150 cm3) chambers. In general, Pion is higher at higher exposures (increasing kVp, mAs, and decreasing distance); however, kpol is independent of exposure rate and kVp, but strongly depends on the sensitive volume of an ion chamber. Pion and kpol vary between 1-48% and 1-16%, respectively, among various chambers and exposure conditions. Chambers with larger volumes have higher values of Pion and kpol. The desired accuracy of +/- 5% in exposure measurements might not be feasible unless both the polarity and recombination effects are known and accounted accurately.

Biophysical Phenomena↗
PubMed1998

The efficacy of paramagnetic ions on spin lattice relaxation time in biological systems.

This paper summarizes the observations of different studies concerning the influence of paramagnetic ions on spin-lattice relaxation times. Neither the comparison between different organs, different animals nor the comparison between different tissues (normal and malignant) showed correlation of practical consequences between the paramagnetic ion concentrations in whole tissues and spin-lattice relaxation times.

Animals↗
PubMed1997

Organ weight: a new tissue parameter to assess water proton spin-lattice relaxation time.

Organ weight has not been considered as a parameter in tissue relaxometry to account for the dependency of spin-lattice relaxation time. Results presented here indicate that, as the organ weight increases, the spin-lattice relaxation time decreases. Furthermore, this relationship has an allometric function, an indication that the metabolic characteristic (oxygen consumption) of the organ is indeed dependent on organ weight and in turn influences spin-lattice relaxation time.

Aging↗
PubMed1997

An association between spin-lattice relaxation time and organ weight in humans.

It is observed that, in humans, the lighter the weight of the organ, the higher the spin-lattice relaxation time. Similarly, smaller animals tend to have a higher oxygen consumption rate per unit of body weight than larger animals. The allometric function relationship between oxygen consumption rate against body weight of different species is similar in shape to those of the spin-lattice relaxation times in 21 normal human organs against organ weight.

Animals↗
PubMed1996

Is spin lattice relaxation time independent of species?

It has been suggested that the spin lattice relaxation time is independent of species. It was further stated that, from a nuclear magnetic resonance standpoint, the human muscle is similar to rat muscle and to pig muscle, etc. However, it is observed that, in normal liver and kidney of human, rat, dog, rabbit and hamster, spin lattice relaxation time varies in different species as a function of percentage of body-weight of the organ. The result shows that spin lattice relaxation time is different in different species because of the organ weight which in turn dictates the metabolism in an individual species.

Animals↗
PubMed1996

NMR relaxation data of water proton in normal tissues.

The spin lattice relaxation time (T1) and spin spin relaxation time (T2) of water protons of normal human and animal tissues are archived to up-date those already published. The mechanisms for water proton relaxation times of tissues are reviewed with reference to water content, paramagnetic ion, protein dynamics content and organ weight.

Animals↗
PubMed1994

Dosimetric problems at low monitor unit settings for scanned and scattering foil electron beams.

Electron beam dosimetry at low monitor unit (MU) settings is important for dosimetric applications. Dose linearity, beam flatness, and beam energies were studied at low MU settings with various dose rates for different types of linear accelerators. It is observed that for the scattering foil units, the dose/MU is a smooth function of MU for all beam energies. Discrepancies in dose/MU are highest at the lowest MU. Significant variation (5%-245%) in dose linearity is observed among various linear accelerators at low MU settings. Dose rate has no effect on the dose linearity for all energies for the scattering foil units tested. On the contrary, for the scanned beam, there is no predictable pattern as dose/MU is random in nature and varies with time and beam energy. The maximum dosimetric error is observed for the highest energy beam where the beam width is most narrow. Using film, the beam uniformity was noticed to be very poor at low MU and high energy for scanned beams. The beam uniformity and dose linearity are random at low MU due to the random nature of the scan cycle. Under the adverse conditions, the deviation in dosimetric parameters was observed up to 200 MU.

Electrons↗
PubMed1993

Role of paramagnetic ions and water proton spin-lattice relaxation time in biological systems.

This paper summarizes the observations of different studies concerning the influence of paramagnetic ions on spin-lattice relaxation times in magnetic resonance imaging. Based on findings that manganese ion content in cancer tissues is decreased in comparison to normal tissues, the results of different papers analysing the influence of tissue manganese concentration on spin-lattice relaxation times are collected and compared. Neither the comparison between different organs, different animals nor the comparison between different tissues (normal and malignant) showed correlations of practical consequences between manganese concentrations and spin-lattice relaxation times. These results are consistent with those from studies with copper and iron ions in living systems.

Animals↗
PubMed1992

A new perspective to assess relaxation time of tumor.

The dissimilarities in spin-lattice relaxation time (T1) of water proton from one tumor to the other is due to the yield of hypoxic fraction in the tumor. The yield of higher relaxation time (T1) in the KHT tumor compared to the RIF-1 tumor as a function of growth is due to the hypoxic fraction of the tumor. The hypoxic fraction in the tumor is also responsible for the P-31 spectral parameter changes.

Animals↗