Biomedical subjects

S H Cohn

Publications and source records attributed to S H Cohn.

151 records · Page 9Linked to original sources

PubMedDate not supplied

In vivo neutron activation analysis: state of the art and future prospects.

From the inauspicious beginning arising in the aftermath of a reactor accident in 1957, in vivo analysis of body elements by neutron activation has become an important tool in medical research. In particular, it provides a much needed means to make quantitative assessments of body composition of human beings in vivo. The data are useful both for basic physiological understanding and for diagnosis and management of a variety of diseases and disorders. The paper traces the development of the in vivo neutron activation technique in the past quarter of a century from basic systems to the present state of the art facilities, and discusses the advantages and disadvantages of the various systems. A scan of some of the numerous clinical applications that have been made of this technique reveals the broad potentialities of in vivo neutron activation. The paper also considers alternative routes of future development and raises some of the questions now faced in making the techniques more widely available to both medical practitioners and medical investigators.

Activation Analysis↗

PubMedDate not supplied

Silicon measurement in a lung phantom by neutron inelastic scattering.

A study was made to assess the feasibility of determining the silicon level in human lungs in vivo by measuring the gamma rays arising from the neutron inelastic scattering reaction 28Si(n, n' gamma)28Si. Neutron energies in the range 5--8 MeV represent the best compromise between the conflicting requirements of high energy for good detection statistics and low energy to minimize the dose to the subject. The sensitivity of measurement was enhanced by pulsing the neutron beam and counting only during the period of bombardment. This effectively reduced the background counts emanating from thermal neutron reactions in the phantom and from the fast neutron reaction 31P(n, alpha)28 A1. In measurements with an anthropomorphic phantom, no interference peaks from other prompt inelastic scattering reactions were observed. With one Ge(Li) detector of 19% relative efficiency, a detection limit of 0.6 g of silicon per 10 mSv was obtained. On this basis, it is estimated that six Ge(Li) detector of 25% efficiency each would be capable of measuring 0.15 g of silicon in the lungs, the average level found in nonoccupationally exposed adults.U

Humans↗

PubMedDate not supplied

Feasibility of noninvasive analysis of lead in the human tibia by soft x-ray fluorescence.

A postmortem study was conducted to assess the feasibility of measuring bone lead concentrations noninvasively in vivo. Characteristic L x rays were induced with an external source of 125I in the superficial tibial cortex of the intact legs of six adults who had no history of occupational exposure to lead. Tibial lead concentrations in the same bones subsequently determined by flameless atomic absorption spectroscopy varied from 15 to 35 micrograms Pb/g wet weight. The upper limit for the modern normal range of lead in the bone is about 25 mg Pb/g wet tissue. The linear correlation coefficient (r) between the measurements made with x-ray fluorescence and lead concentration by absorption spectroscopy was 0.90. Radiation doses of 10 mGy (1 rad) to 1 cm2 of skin, with associated doses to the marrow of adjacent bone of about 0.6 mGy (60 mrad), yielded net lead fluorescence signals ranging from one to seven times the standard deviation of background.

Humans↗

PubMedDate not supplied

Application of the library least-squares analysis to whole-body counter spectra derived from an array of detectors.

The library least-squares method was applied to the analysis of gamma-ray spectra obtained from an array of 54 NaI(T1) detectors in a whole-body counter. The analysis of spectra which were obtained over a period of 8 yr demonstrates the applicability of the method despite inherent variations encountered in large counting systems. The elements of interest analyzed were total-body K, Ca, Na, Cl, and P. Least-squares fits obtained with library standards derived from distributed sources were better than those obtained from library standards derived from localized sources.

Activation Analysis↗

PubMedDate not supplied

Polyacrylamide-based phantoms as tissue substitute in experimental radiation physics.

Polyacrylamide-based tissue-equivalent phantoms simulating cortical bone and muscle are described. The equivalency is based upon similar elemental composition and density, and partial similarity in the morphology of bone. Satisfactory results were obtained when the phantoms were tested at low (20 keV) and high (15 MeV) gamma radiation. Applicability of this phantom material to neutron transport is discussed. The material can be molded and shaped and its composition is easily modified by altering the proportions of the constituents. Trace elements or radionuclides are easily added. Details of the physical and radiation characteristics of the formulated systems are given together with the manufacturing procedures.

Acrylic Resins↗

PubMedDate not supplied

Nuclear resonance scattering measurement of human iron stores.

Hepatic iron stores were measured noninvasively in 31 patients (thalassemia, hemodialysis, hemosiderosis, refractory anemia) with suspected iron overload, employing a nuclear resonance scattering (NRS) technique. The thalassemia patients were undergoing desferrioxamine chelation therapy during the NRS measurements. The hemodialysis patients were measured before chelation therapy. Iron levels measured by NRS were in general agreement with those determined in liver biopsies by atomic absorption spectroscopy. In addition, NRS measurements from the thorax of some of these patients suggest that this method may also prove useful for clinical assessment of cardiac iron.

Adolescent↗

PubMedDate not supplied

In vivo measurement of lithium in the body by a neutron activation analysis technique.

A technique has been developed for in vivo determination of lithium content in the head (and potentially in the whole body and in selected organs) of patients undergoing lithium therapy. It is based on the measurement of tritium induced by the 6Li(n,alpha)T nuclear reaction after neutron irradiation of the body. The fraction of tritium exhaled in the expired air in the form of HT is collected, separated from the other gases, and counted in a high-sensitivity beta counter. The feasibility of the technique was demonstrated by measurements of lithium in the head of a sheep and in the whole body of rats, following the administration of 6LiCl (enriched 6Li isotope, 95.46% abundancy). The precision of the technique is acceptable for clinical applications based on a maximum propagated error of 8.4%. The sensitivity is 1 count/d (from T activity) per 10 mSv (total dose) and 1 microgram of 6Li. This indicates that studies on patients under 6Li treatment can be performed successfully with a radiation dose to the head of 1-2 mSv.

Animals↗