Direct analysis of molybdenum target generated x-ray spectra with a portable device.

In routine applications, information about the photon flux of x-ray tubes is obtained from exposure measurements and cataloged spectra. This approach relies mainly on the assumption that the real spectrum is correctly approximated by the cataloged one, once the main characteristics of the tube such as voltage, target material, anode angle, and filters are taken account of. In practice, all this information is not always available. Moreover, x-ray tubes with the same characteristics may have different spectra. We describe an apparatus that should be useful for quality control in hospitals and for characterizing new radiographic systems. The apparatus analyzes the spectrum generated by an x-ray mammographic unit. It is based on a commercial CZT produced by AMPTEK Inc. and a set of tungsten collimator disks. The electronics of the CZT are modified so as to obtain a faster response. The signal is digitized using an analog to digital converter with a sampling frequency of up to 20 MHz. The whole signal produced by the x-ray tube is acquired and analyzed off-line in order to accurately recognize pile-up events and reconstruct the emitted spectrum. The energy resolution has been determined using a calibrated x-ray source. Spectra were validated by comparison of the HVL measured using an ionization chamber.

[1]  S. Evans.  Catalogue of Diagnostic X-Ray Spectra and Other Data , 1998 .

[2]  J. Boone,et al.  An accurate method for computer-generating tungsten anode x-ray spectra from 30 to 140 kV. , 1997, Medical physics.

[3]  R Birch,et al.  Computation of bremsstrahlung X-ray spectra and comparison with spectra measured with a Ge(Li) detector. , 1979, Physics in medicine and biology.

[4]  G T Barnes,et al.  Molybdenum target x-ray spectra: a semiempirical model. , 1991, Medical physics.

[5]  K Aoki,et al.  Measurement of diagnostic x-ray spectra using a silicon photodiode. , 1989, Medical physics.

[6]  G. Barnes,et al.  Semiempirical model for generating tungsten target x-ray spectra. , 1991, Medical physics.

[7]  P. Kristiansson,et al.  Pile-up and defective pulse rejection by pulse shape discrimination in surface barrier detectors , 1994 .

[8]  W D McDavid,et al.  Modification and benchmarking of MCNP for low-energy tungsten spectra. , 2000, Medical physics.

[9]  M J Yaffe,et al.  X-ray characterization of breast phantom materials. , 1998, Physics in medicine and biology.

[10]  Satoshi Miyajima,et al.  CdZnTe detector in diagnostic x-ray spectroscopy. , 2002, Medical physics.

[11]  E. Wilkinson,et al.  A comparison of mammography spectral measurements with spectra produced using several different mathematical models. , 2001, Physics in medicine and biology.

[12]  G Panayiotakis,et al.  A Monte Carlo simulation model of mammographic imaging with x-ray sources of finite dimensions. , 2002, Physics in medicine and biology.

[13]  H Kanamori,et al.  Direct measurement of mammographic x-ray spectra using a CdZnTe detector. , 2000, Medical physics.

[14]  D. Marquardt.  An Algorithm for Least-Squares Estimation of Nonlinear Parameters , 1963 .

[15]  T R Fewell,et al.  Photon energy distribution of some typical diagnostic x-ray beams. , 1977, Medical physics.

[16]  B. Archer,et al.  On the measurement of half-value layer in film-screen mammography. , 1990, Medical physics.

[17]  Satoshi Miyajima,et al.  Thin CdTe detector in diagnostic x-ray spectroscopy. , 2003, Medical physics.

[18]  CdZnTe detector in mammographic x-ray spectroscopy. , 2002, Physics in medicine and biology.