Biomedical subjects

K S Shah

Publications and source records attributed to K S Shah.

7 recordsLinked to original sources

PubMed2004

Performance measurements of a depth-encoding PET detector module based on position-sensitive avalanche photodiode read-out.

We are developing a high-resolution, high-efficiency positron emission tomography (PET) detector module with depth of interaction (DOI) capability based on a lutetium oxyorthosilicate (LSO) scintillator array coupled at both ends to position-sensitive avalanche photodiodes (PSAPDs). In this paper we present the DOI resolution, energy resolution and timing resolution results for complete detector modules. The detector module consists of a 7 x 7 matrix of LSO scintillator crystals (1 x 1 x 20 mm3 in dimension) coupled to 8 x 8 mm2 PSAPDs at both ends. Flood histograms were acquired and used to generate crystal look-up tables. The DOI resolution was measured for individual crystals within the array by using the ratio of the signal amplitudes from the two PSAPDs on an event-by-event basis. A measure of the total scintillation light produced was obtained by summing the signal amplitudes from the two PSAPDs. This summed signal was used to measure the energy resolution. The DOI resolution was measured to be 3-4 mm FWHM irrespective of the position of the crystal within the array, or the interaction location along the length of the crystal. The total light signal and energy resolution was almost independent of the depth of interaction. The measured energy resolution averaged 14% FWHM. The coincidence timing resolution measured using a pair of identical detector modules was 4.5 ns FWHM. These results are consistent with the design goals and the performance required of a compact, high-resolution and high-efficiency PET detector module for small animal and breast imaging applications.

Equipment Design↗

PubMed2000

Strategies to improve the signal and noise performance of active matrix, flat-panel imagers for diagnostic x-ray applications.

A theoretical investigation of factors limiting the detective quantum efficiency (DQE) of active matrix flat-panel imagers (AMFPIs), and of methods to overcome these limitations, is reported. At the higher exposure levels associated with radiography, the present generation of AMFPIs is capable of exhibiting DQE performance equivalent, or superior, to that of existing film-screen and computed radiography systems. However, at exposure levels commonly encountered in fluoroscopy, AMFPIs exhibit significantly reduced DQE and this problem is accentuated at higher spatial frequencies. The problem applies both to AMFPIs that rely on indirect detection as well as direct detection of the incident radiation. This reduced performance derives from the relatively large magnitude of the square of the total additive noise compared to the system gain for existing AMFPIs. In order to circumvent these restrictions, a variety of strategies to decrease additive noise and enhance system gain are proposed. Additive noise could be reduced through improved preamplifier, pixel and array design, including the incorporation of compensation lines to sample external line noise. System gain could be enhanced through the use of continuous photodiodes, pixel amplifiers, or higher gain x-ray converters such as lead iodide. The feasibility of these and other strategies is discussed and potential improvements to DQE performance are quantified through a theoretical investigation of a variety of hypothetical 200 microm pitch designs. At low exposures, such improvements could greatly increase the magnitude of the low spatial frequency component of the DQE, rendering it practically independent of exposure while simultaneously reducing the falloff in DQE at higher spatial frequencies. Furthermore, such noise reduction and gain enhancement could lead to the development of AMFPIs with high DQE performance which are capable of providing both high resolution radiographic images, at approximately 100 microm pixel resolution, as well as variable resolution fluoroscopic images at 30 fps.

Feasibility Studies↗

PubMed1993

The age at marriage of female and family welfare.

"One of the critical factors affecting population growth is age at marriage, more specifically the female age of marriage.... The efforts made by Good Parents Groups (USA) in this direction to solve this problem are discussed in this paper." The geographical focus is on India.

Asia↗

PubMed1991

Factors influencing sema-natal mortality.

"In this paper an attempt has been made to examine the crude impact of the factors: birth weight, maternal age, gravida and sex on sema-natal mortality [defined by the author as mortality occurring within the first seven days of life], on the one hand, and the relative effect of each of these factors individually, in the absence of the influence of other factors, on the other hand. For this study, data are collected from the case card records of mothers registered for delivery, during the period 1978-80 in Anand Municipal Hospital, Anand (India).... Out of [3,050] live births, 99 are found to have ended in deaths within seven days of their birth."

Age Factors↗

PubMed1990

The distribution of number of births.

"In this note a probability model for the number of births during a given marital duration of a woman is derived assuming the risk of conception to follow a gamma distribution." The model is applied to recent data for India.

Asia↗

PubMed1988

Induction of Symbiotically Defective Auxotrophic Mutants of Rhizobium fredii HH303 by Transposon Mutagenesis.

Symbiotically defective auxotrophic mutants were isolated by transposon Tn5 mutagenesis of Rhizobium fredii HH303, a fast-growing microsymbiont of North American commercial soybean cultivars such as Glycine max cv. Williams. Three different Tn5-carrying suicide vectors, pBLK1-2, pSUP1011, and pGS9, were used for mutagenesis with transposition frequencies of 4 x 10, 3 x 10, and 1 x 10, respectively, while the frequency of background mutation resistant to 500 mug of kanamycin per ml was 1 x 10. From 2,600 Tn5-induced mutants, 14 auxotrophic mutants were isolated and classified in seven groups including adenosine (four), aspartate (two), cysteine or methionine (two), isoleucine and valine (two), nicotinic acid (one), pantothenic acid (one), and uracil (two). All the auxotrophs induced nodulation on soybean, but the symbiotic effectiveness of each mutant was different. Three auxotrophs (two cysteine or methionine and one pantothenic acid) formed effective nodules similar to those of the wild type. Three auxotrophs (one nicotinic acid and two aspartate) produced mature nodules like those of the wild type, but the nodules lacked the characteristic pink color inside and were unable to fix nitrogen. Four auxotrophs (two adenosine and two uracil) induced pseudonodules unable to fix nitrogen. The other four auxotrophs repeatedly induced both effective and ineffective nodules, but bacteroids isolated from the effective nodules were prototrophic revertants. The symbiotic phenotype and the degree of effectiveness of the auxotrophic mutants varied with the type of mutation.

Journal Article↗

PubMed1986

Urinary excretion of benzidine in relation to the acetylator status of occupationally exposed subjects.

Twenty-four male workers engaged in the manufacture of benzidine dihydrochloride for 1-4 years were included in this study. Urinary levels of free benzidine were estimated by high-pressure liquid chromatography in all the workers. Acetylator status of the workers was determined with sulphamethazine. There was substantial absorption of benzidine over an 8-h work shift. A significant correlation was observed between the rate of sulphamethazine acetylation and urinary excretion of free benzidine.

Acetylation↗