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Direct measurement of mammographic x‐ray spectra using a CdZnTe detector
Author(s) -
Matsumoto Masao,
Yamamoto Akihide,
Honda Ikuko,
Taniguchi Akira,
Kanamori Hitoshi
Publication year - 2000
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 - 10.1118/1.599015
Subject(s) - spectral line , detector , physics , compton scattering , monte carlo method , photon , optics , semiconductor detector , scattering , attenuation , atomic physics , statistics , mathematics , astronomy
Our purpose is to directly measure mammographic x‐ray spectra with collimators and a low‐efficiency CdZnTe detector developed recently and to find out the best fit response function of CdZnTe detector to correct the measured spectra. Photon spectra (target Mo or Rh) produced by a mammographic x‐ray unit at 25–32 kV and 240 mAs (=3 times of 80 mAs) and transmitted through 0.03 mm Mo or 0.025 mm Rh filter and object (0.1 mm Al to 0.8 mm Al phantoms) have been analyzed. Since detected spectra were distorted by the response of CdZnTe detector and did not present the true photon spectra, the correction was applied by the stripping procedure. The response function of detector used in this procedure has been determined by the evaluation of interactions ( K ‐escape, coherent scattering, and Compton scattering processes) and incomplete charge collection calculated using the Monte Carlo method. We have used K α 1,K α 2,K β 1,K β 2radiations of Cd, Zn, and Te, respectively and have used the weight function for the incomplete charge collection and have considered Compton scattering. The Monte Carlo simulations were continued by changing the important factors (mean path length of hole λ h , dead layer of the CZT crystal and weight factor W q ) of incomplete charge collection until the best fit response function was found out. Corrected photon spectra were compared with the mammographic x‐ray spectral data of Bureau of Radiological Health (BRH) measured using a Ge detector. Attenuation curves of aluminum for 25–32 kV were calculated from the corrected photon spectra and compared with the attenuation curves measured using an ionization chamber. These results obtained using the CdZnTe detector agreed with the mammographic x‐ray spectral data of BRH and attenuation curves obtained by the ionization chamber.