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Characterization of tissue via coherent‐to‐Compton scattering ratio: Sensitivity considerations
Author(s) -
Karellas Andrew,
Leichter Isaac,
Craven J. D.,
Greenfield M. A.
Publication year - 1983
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 - 10.1118/1.595330
Subject(s) - collimated light , photon , optics , compton scattering , scattering , physics , incoherent scatter , coherent backscattering , sensitivity (control systems) , effective atomic number , semiconductor detector , atomic number , detector , computational physics , atomic physics , laser , electronic engineering , engineering
It is known that the ratio ( R ) of the detected coherent and Compton scattered photons from bone can be used in order to determine its mineral density. This technique utilizes the dependence of the coherent scattering on the effective atomic number ( Z ̄) of the scattering medium. It is generally accepted that a small scatter angle is preferred in order to ensure adequate counting statistics by favoring the detection of more coherent photons. Moreover, it has been assumed that a change in the scatter angle does not affect the sensitivity of the measurement. Our theoretical calculations for 60‐keV photons and for the range of Z ̄ that corresponds to trabecular bone, indicate that increasing the scatter angle results in a stronger power dependence of the measured ratio on Z ̄. This implies that by increasing the scatter angle, smaller changes in the mineral density can be detected, thus improving the sensitivity of the measurement. This effect was investigated experimentally by using a collimated beam of 59.54‐keV photons from Am‐241 (44.4 GBq) and a collimated intrinsic germanium detector. Solutions of K 2 HPO 4 with different concentrations were used in order to simulate trabecular bone. The scatter spectra were recorded for all solutions at six scatter angles between 37° and 98° and the value of R was computed for each spectrum. The sensitivity of the measurement, evaluated from these experiments increased, with the increase of the scatter angle.