Parameterized algorithms for quantitative differentials in spectrally equivalent medical diagnostic x-ray beams

Qualitative and quantitative equivalence of spectra transmitted by two different elemental filters require a good match in terms of shape and size over the entire energy range of 0-150 keV used in medical diagnostic radiology. However, the photoelectric absorptions and Compton scattering involved in the interaction of x rays with matter at these relatively low photon energies differ in a nonuniform manner with energy and atomic number. By careful choice of thicknesses for filter materials with an atomic number between 12 and 39, when compared with aluminum, it is possible to obtain transmitted beams of the same shape (quality) but not of the same size (quantity). In this paper, calculations have been carried out for the matching of the shapes and sizes of beams transmitted through specified thicknesses of aluminium filter and spectrally equivalent thicknesses of other filter materials (different from aluminium) using FORTRAN source codes traceable to the American Association of Physics in Medicine (AAPM), College Park, MD, USA. Parametrized algorithms for the evaluation of quantitative differentials (deficit or surplus) in radiation output (namely, photon fluence, exposure, kerma, energy imparted, absorbed dose, and effective dose) from these transmitted spectrally equivalent beams were developed. These differentials range between 1%, and 4% at 1 mm Al filtration and between 8%, and 25% for filtration of 6 mm Al for different filter materials in comparison with aluminum. Also developed were models for factors for converting measures of photon fluence, exposure-area product, (EAP), and kerma-area product (KAP) to risk related quantities such as energy imparted, absorbed dose, and effective dose from the spectrally equivalent beams. The thicknesses of other filter materials that are spectrally equivalent to given thicknesses of aluminum filter were characterized using polynomial functions. The fact that the use of equivalent spectra in radiological practice can provide means of ranking the differentials in radiographic image quality and stochastic risk is discussed.     

Portable x-ray diagnostic equipment

Scientific-Industrial Association “Spektr”, Moscow. Translated from Meditsinskaya Tekhnika, No. 4, pp. 22–28, July–August, 1992.     

Ionometric x-ray diagnostic devices

Scientific-Research Institute for Introscopy, Moscow. Moscow Scientific-Research Institute for Diagnostics and Surgery. Translated from Meditsinskaya Tekhnika, No. 3, pp. 29–31, May–June, 1995.     

CdZnTe detector in diagnostic x-ray spectroscopy

A method to utilize CdZnTe (CZT) detectors in diagnostic x-ray spectroscopy is described in this article. Spectral distortion due to transmission of primary x rays, the escape of cadmium- and tellurium-K fluorescent x rays, and tailing was severe in measured x-ray spectra. Therefore, correction for the distortion was performed with the stripping method using response functions. The response functions were calculated with the Monte Carlo method. The Hecht equation was employed to approximate the effects of carrier trapping in the calculations. The parameters in the Hecht equation, the mean-free path (lambda) of electrons and holes, were determined such that the tailing in calculated response functions fit that in measured gamma-ray spectra. Corrected x-ray spectra agreed well with the reference spectra measured with an HPGe detector. The results indicate that CZT detectors are suitable for diagnostic x-ray spectroscopy with appropriate corrections.     

Update on domestic x-ray diagnostic equipment

All-Russian Scientific-Research and Testing Institute for Medical Engineering, Moscow. Translated from Meditsinskaya Tekhnika, No. 2, pp. 37–39, March–April, 1995.     

Temperature dependence of x-ray induced luminescence from medical x-ray screens

Texts in diagnostic radiography give rules for adjustment of exposure parameters to compensate for the effect of temperature on the efficiency of film-screen combinations. These rules are appropriate for traditional phosphors, such as calcium tungstate (CaWO4) and lead barium sulfate (BaSO4:Pb) but may not be applicable to newer screens in current use such as those of the rare-earth type. The effect of temperature on x-ray induced luminescence from modern and traditional screens has been compared over a temperature range of approximately-130 to approximately 60 degrees C and has been found to differ markedly. Typically, the luminescent emission from rare-earth phosphors varies by less than 10% over this temperature range compared to the 60% change in efficiency for conventional screens over the same temperature range. One type of modern screen, however, shows a continuous decrease in luminescent efficiency as the temperature is lowered. Qualitative physical explanations for these effects are presented.     

Progress in dental x-ray diagnostic equipment

Moscow Scientific-Research Institute for Diagnostics and Surgery. Translated from Meditsinskaya Tekhnika, No. 2, pp. 35–37, March–April, 1995.     

Monte Carlo simulation of diagnostic x-ray scatter

A Monte Carlo method was developed and implemented to simulate x-ray photon transport. Simulations consisted of a pencil beam of monoenergetic photons with energies from 50 to 110 keV incident on water and aluminum slabs. The dependence of scatter fraction and multiple scattering on x-ray energy, scatterer thickness, and material is reported in both number and energy fluence. The average energy of scattered photons reaching the detector plane is also reported. Comparisons are made to previous x-ray scatter computations.     

Laplace reconstruction of experimental diagnostic x-ray spectra

This paper displays the results of a blind study used to determine the capability of a Laplace transform pair model to accurately reconstruct diagnostic x-ray spectra from experimental attenuation data. Spectra reconstructed from attenuation measurements are compared to experimental spectra obtained on the same unit using an intrinsic germanium spectrometer system. The results show that when pure attenuation materials are used, good agreement is obtained between the experimental and computed spectra. If an alloy attenuator like 1100 aluminum is used, the proportion of contaminants must be included in the Laplace formulation for accurate reconstruction.     

Apparatuses for medical x-ray electrography

Institute for Electrography and Oncological Center, Vilnius. Translated from Meditsinskaya Tekhnika, No. 6, pp. 27–30, November–December, 1995.     

Thin CdTe detector in diagnostic x-ray spectroscopy

A CdTe Schottky diode detector of 1 mm thickness was employed in diagnostic x-ray spectroscopy. The detector response to monoenergetic photons was investigated with gamma rays from the calibration sources (241Am and 133Ba). As spectral distortion due to carrier trapping, known as tailing, was small in gamma-ray spectra, the effects of carrier trapping were not taken into account in the calculation of response functions. The distortion due to the transmission of primary x rays and the escape of secondary x rays (K-fluorescent x rays and Compton-scattered x rays) from the crystal was included in the calculated response functions. X-ray spectra corrected using the response functions were in good agreement with the reference spectra obtained with a high-purity germanium detector. The results indicated that correction for the distortion due to carrier trapping is not necessary when using a thin CdTe detector in diagnostic x-ray spectroscopy.