RESUMEN
The effects of multiple photon scattering and the assumption of infinitesimal beam geometry on the results obtained with a clinical lung densitometer were investigated. In phantom materials, it was possible to account almost completely for the multiple scatter contribution by measurement of transmission for the 170Tm source. A theoretical analysis based on a simplified model showed that the influence of finite geometry was small. Measurements in six normal volunteers showed that lung density is a function of the fractional air content of the lung. To relate density to fractional water content of the lung, measurements must be made at a fixed lung volume. The height in the lung at which measurements are made appears to be unimportant. The results of these experiments enable predictions to be made concerning the clinical usefulness of lung density measurements.
Asunto(s)
Agua Corporal/análisis , Pulmón/análisis , Animales , Densitometría/instrumentación , Perros , Humanos , Modelos Estructurales , Edema Pulmonar/diagnóstico , Dispersión de RadiaciónRESUMEN
The applicability of 25 keV neutrons to the in vivo activation analysis of spinal calcium is examined both theoretically and experimentally. It is shown that the use of this energy results in an increase in sensitivity over higher energy neutrons so that patient dose may be significantly reduced.
Asunto(s)
Análisis por Activación , Calcio/análisis , Análisis de Activación de Neutrones , Columna Vertebral/análisis , Neutrones Rápidos , Humanos , Modelos Teóricos , Método de MontecarloRESUMEN
A system for the routine measurement of the density of the os calcis is described. Measurements are made of the number of photons scattered by the bone from a 153Sm photon beam. The first results from human subjects are presented.
Asunto(s)
Huesos/anatomía & histología , Densitometría , Dispersión de Radiación , Adulto , Enfermedades Óseas/diagnóstico , Partículas Elementales , Femenino , Humanos , Masculino , Persona de Mediana Edad , Radioisótopos , SamarioRESUMEN
The origins of inherent sources of error in results of measurements of bone density by a photon scattering technique are described and their effects are predicted theoretically. The predictions are confirmed experimentally. The prime source of error is multiple scattering. A procedure has been developed to correct the observed densities for effects of multiple scattering.
Asunto(s)
Huesos/anatomía & histología , Densitometría , Dispersión de Radiación , Enfermedades Óseas/diagnóstico , Partículas Elementales , Humanos , Radioisótopos , Samario , TulioRESUMEN
The deconvolution or unfolding of exponential response functions from experimental data has been examined through the use of a Bayesian based algorithm. The algorithm, which is founded upon the concepts of probability, ensures positivity of solution. This constraint leads to a significant reduction in the growth of statistical noise in deconvolved data when compared with the more common linear unfolding techniques. The algorithm is an iterative procedure which, in the absence of statistical noise, can ultimately result in complete signal recovery. When noise is present one must balance the degree with which the response function is removed against the growth in the noise and, at some point, terminate the iterative process. Criteria for determining the point at which this 'best estimate' is attained are examined and an operationally realisable test is given. Comparison of results is made with the inverse filter solution which, for an exponential response function, is shown to consist of the sum of the observed data and its first derivative.
Asunto(s)
Teoría de Sistemas , MatemáticaRESUMEN
The number of 103.2 keV (153Sm) gamma-rays scattered coherently and incoherently from the os calcis of three cadaver feet has been measured using a high purity Ge detector. The ratio of the intensities of coherent to incoherent scattered photons is dependent on elemental composition while the number scattered incoherently is dependent on density. The results indicate that techniques for the assessment of mineral status in the skeleton may be based on either of these measurements and each will exhibit a similar sensitivity to a given biological change. It is shown that a method based entirely on the detection of coherently scattered photons will be more sensitive to changes in mineral composition than either of the above. Such a system is proposed and optimised with respect to incident beam energy and scattering angle. For a dose of 4 mSV, coherent intensity measurements with a precision of 3% are anticipated.