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Bone mineral densitometry with x‐ray and radionuclide sources: A theoretical comparison
Author(s) -
Chakraborty Dev P.,
Barnes G. T.
Publication year - 1991
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.596613
Subject(s) - attenuation , radionuclide , materials science , photon , enhanced data rates for gsm evolution , effective atomic number , filtration (mathematics) , optics , nuclear medicine , physics , computational physics , computer science , mathematics , nuclear physics , statistics , medicine , telecommunications
Two methods of dual‐photon absorptiometry (DPA) utilizing an x‐ray tube instead of a radionuclide source have recently been introduced. In one method kVp switching is employed and two transmitted intensities at each pixel are determined. In the other method, K ‐edge filtration combined with a single kVp spectrum is used, but photons in two energy windows are counted. We present a theoretical analysis of the two methods, focusing on a figure of merit which is essentially the exposure efficiency (the precision for a given entrance exposure) and tube loading. We also compare their exposure efficiencies to theoretical limits that no DPA system can exceed. Our study indicates that the K ‐edge‐filtered method is more exposure efficient by about a factor of 2. The switched‐kVp method requires less heat units per scan by about a factor of 3. A hybrid K ‐edge switched‐kVp method is suggested which achieves the same exposure efficiency as the K ‐edge‐filtered method at lesser tube loading. Our theoretical model is based on published x‐ray spectra and attenuation coefficients and is in good agreement with other simulation work. It is of interest that a point source of Gd‐153 would be even more exposure efficient, achieving about 90% of the theoretical limit. However, in practice, the Gd source is of finite size and limited strength, and consequently the radionuclide method cannot achieve as good a precision as either x‐ray method in similar scan times.