Direct measurement of mammographic x‐ray spectra using a CdZnTe detector

Abstract

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 Kalpha1, Kalpha2, Kbeta1, Kbeta2 radiations 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 lambda(h), dead layer of the CZT crystal and weight factor Wq) 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.

Simulation of the Mammography X-ray Spectrum

“…It should be noted that the CdZnTe detector was placed at a distance of 38 cm from the focal spot. Our measurement results by the CdTe detector agreed well with those simulated, which means that the spectral distortion of the CdTe detector was minor for the photon with energy ranged from 20 to 30 keV as found earlier by Matsumoto et al 7) for their CdZnTe detector. The 17.5 keV characteristic X-ray intensity of the present work for the tube voltage of 30 kV were higher than those of others as shown in Fig.…”

“…4,5) In the measurement of the mammography X-rays, the CdZnTe spectrometers have been introduced recently. [6][7][8] In any case, special devices are required to measure X-ray energy spectrum with reasonable accuracy.…”

Performance tests for mammographic film-screen combinations: use of absolute techniques

“…A 1 mm thick CdTe X-ray detector XR-100T (Amptek Inc., Bedford, Massachusetts, USA) with a 25 mm 2 active area was used to measure the screen quantum detection efficiencies (16). This detector was positioned 30 cm away from the focal spot and collimated with two tungsten collimators with 200 and 1000 μm diameters (Fig.…”

Energy Measurement of X-rays in Computed Tomography for Detecting Contrast Media

“…The obtained x-ray energy spectra suffered distortion caused by the escape of x-rays from the relatively small CZT crystal; the distortion was corrected via a stripping method. 2,14) By assigning the line that connected the x-ray tube and the CZT detector as x ¼ 0, the acrylic phantom was moved from x ¼ À20 mm (x-rays outside the acryl phantom) to x ¼ 0 mm (x-rays incident on the center of the acryl phantom) in steps of 0.5 mm. By using the axial symmetry of this phantom, the data from +0.5 to +20 mm were not measured but were constructed by reverse sorting of the order of the measured data set from x ¼ À20 to x ¼ À0:5 mm.…”