B J Thomas

The use of body hydrogen as an internal standard in the measurement of nitrogen in vivo by prompt neutron capture gamma-ray analysis

The previously established technique of analysis of neutron capture γ-rays for the determination of nitrogen in-vivo has been modified to make estimates of absolute quantities of nitrogen mass. Hydrogen is used as an internal standard and the nitrogen mass is determined from the observed ratio of nitrogen to hydrogen counts, together with the hydrogen mass, estimated from body parameters. Phantom and cadaver studies indicate that nitrogen mass can be estimated to ±4% or better by this means.

MEASUREMENT OF WHOLE-BODY NITROGEN BY NEUTRON-ACTIVATION ANALYSIS

Abstract Whole-body nitrogen was measured in man using a new technique of neutron-activation analysis. Patients were irradiated with a small dose of fast neutrons and the capture γ rays arising from neutron interactions with nitrogen nuclei were recorded. Sixty-five patients with various diseases have been studied on 190 occasions. The technique has proved to be highly reproducible and offers a new experimental approach to the study of metabolic disorders in clinical medicine.

A transportable system for the measurement of liver cadmium in vivo

A system is described for liver cadmium measurement. The neutron source is a 10 Ci238Pu/Be source which is double-encapsulated in a stainless steel cylinder. The neutron output is collimated by placing it in a specially designed box. LiF-doped resin effectively limits the beam spot to a diameter of 10 cm. The detector used is a coaxial lithium-drifted germanium semiconductor.

Cadmium-Its in vivo detection in man

Neutron capture gamma-ray analysis has been applied to the in vivo detection of Cd in man. The technique was designed for the screening of industrial workers at risk. The limit of sensitivity in a liver-sized phantom is 0-5 ppm for a dose of 0-4 rad. Reproducibility and the effects of positional uncertainties have been investigated. A number of cadavers were studied to establish normal limits prior to commencement of a programme of clinical investigation. A patient with known Cd poisoning was estimated to contain 65-110 ppm of Cd in his liver. A liver dose of 0-05 rad was required.

Spinal calcium: its in vivo measurement in man.

Abstract A new facility for in vivo measurement of the calcium content of a section of lumbar spine by neutron activation analysis is described. The irradiation conditions and detection of induced radioactivity are discussed. Special consideration is given to the control and monitoring of positional changes. The results of phantom studies of reproducibility and sensitivity are presented. These established that the long term reproducibility of the system was ±2% (1 S.D.). Some preliminary measurements involving patients and volunteers are also presented.

MEASUREMENT OF LIVER-CADMIUM CONCENTRATIONS IN PATIENTS AND INDUSTRIAL WORKERS BY NEUTRON-ACTIVATION ANALYSIS

A new, rapid, non-invasive technique for measuring tissue-cadmium concentrations in patients and industrial workers has been designed and developed with a view to studying the cadmium content of the liver. The method utilises the principle of neutron-activation analysis whereby the specific changes produced by the inter action of nuclei and neutrons are analysed. Liver-cadmium content has been studied in cadavers and in four men with known of suspected cadmium poisoning. The patients all showed very high liver-cadmium levels of between 35 and 200 p.p.m. compared with under 1.0 p.p.m. in non-exposed subjects. The dose of radiation used in clinical studies was 0.4-1.0 rem and the detection limit of cadmium was 1.0 p.p.m.

Prompt gamma neutron activation analysis to measure whole body nitrogen absolutely: Its application to studies of in-vivo changes in body composition in health and disease

Whole body nitrogen has been measured absolutely in male volunteers and patients by in-vivo neutron activation analysis using whole body hydrogen as an internal standard. The 10.8 MeV and 2.2 MeV prompt gamma rays from nitrogen and hydrogen respectively give a result reproducible to 4% for a dose of 100 mRem. Whole body potassium measured by whole body counting natural40K and whole body nitrogen have been correlated in normal adult males and patients. In the normals the correlation coefficient was 0.96 with coefficient of variation 4%. In the patients these parameters were 0.92 and 8% in 140 measurements. The ratio of N/K increased significantly as the degree of clinical wasting progressed.

Fractional charge collection technique for pile-up reduction - counting low intensity radiation in presence of intense gamma-ray and neutron background

Abstract Properties of a fractional charge collection technique for pile-up reduction in large volume NaI(Tl) crystals have been investigated for the particular use of measurement of whole body nitrogen by in vivo neutron activation analysis. The resolution of the system and the photomultiplier anode pulse length has been measured as a function of pulse clipping times. A comparison between conventional voltage mode and the fractional charge collection mode has been made from the point of view of pile-up effect. The performance of the system has been tested in our application to a total count rate of 2×10 5 pulses/s.

Total body nitrogen measured by the 14N(n, 2n)13N method: a study of the interfering reactions and the variation of spatial sensitivity with depth.

Abstract A study has been made of the interferences present to the measurement of whole body nitrogen by the 14N(n, 2n)13N method of in vivo neutron activation analysis. The interferences were found to amount to 29% of the counts from nitrogen alone after a 6 min cooling period; the major contribution arising from the reaction 16O(p, α)13N. The spatial insensitivity with depth of the method, for a 25 cm thick phantom, was assessed as being ±81% of the mean value. It was concluded that this insensitivity, together with the level of interference present, indicates that considerable care must be exercised in the interpretation of any measurement made by this method.

In vivo neutron activation analysis measurements of calcium using the 40Ca(n, α)37Ar reaction

Abstract An in vivo neutron activation analysis (IVNAA) technique is used to measure calcium. When the subject is irradiated with fast neutrons one of the reactions induced is 40 Ca( n , α ) 37 Ar. The argon produced is eventually collected as part of the mixture of exhaled gases, which is processed to remove the unwanted O 2 , N 2 , CO 2 and H 2 O. The activity of the 37 Ar is monitored in a gas proportional counter. The system has a reproducibility of about 2% when applied to animal studies.