British Journal of Radiology (2004) 77, 395-404
© 2004 British Institute of Radiology
doi: 10.1259/bjr/32514512
Comprehensive analysis of the spectrometric determination of voltage applied to X-ray tubes in the radiography and mammography energy ranges using a silicon PIN photodiode
R A Terini, PhD
1,2
M A G Pereira, BSc
1
R Künzel, MSc
1,3
P R Costa, PhD
1 and
S B Herdade, PhD
1
1 Serviço Técnico de Aplicações Médico-Hospitalares, Instituto de Eletrotécnica e Energia, Universidade de São Paulo, Av. Prof. Luciano Gualberto, 1289, Cidade Universitária, CEP. 05508-010, São Paulo, SP, 2 Departamento de Física, Pontifícia Universidade Católica de São Paulo, R. Marquês de Paranaguá, 111, Consolação, CEP. 01303-050, São Paulo, SP and 3 Instituto de Física, Universidade de São Paulo, R. do Matão, Travessa R, 187, Cidade Universitária, CEP. 05508-900, São Paulo, SP, Brazil
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Figure 1. Three 241Am X-ray and gamma-ray spectra obtained with the detector configurations used in this work (Hamamatsu S3071 photodiode + Ortec 142 IH pre-amplifier, Hamamatsu S3071 photodiode + eV 550 pre-amplifier and Amptek XR 100CR), after corrections for the variations of detector full energy absorption efficiency with photon energy [13]. All spectra were normalized to the 59.54 keV peak maximum.
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Figure 2. Schematic cross-sectional view of Amptek detector housing. A: aluminium box; C: tungsten collimators spaced by a lead/copper cylinder; D: Si PIN detector; P: lead and copper sheets; W: detector beryllium window. Full box dimensions are 92 mm x 140 mm.
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Figure 3. Theoretical spectra N(E) generated using the model of Tucker et al [17], taking into account the characteristics of the Philips X-ray tube, for 28 kV and some values of added aluminium filtration, without molybdenum.
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Figure 4. Ratio between squared counts at the end and at the maximum of the Bremsstrahlung spectrum (Nend)2/Nmax, for several aluminium filtration thicknesses x (mmAl), with 28 kV tube potential. In this case, the maximum corresponds to 0.6 mm Al additional filtration.
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Figure 5. (a) Raw spectra at 90 kVp, with single-phase and constant potential generators, measured with the Amptek PIN photodiode system, with two different amplifier gains. (b) Details of the high energy region of the same raw spectra showing the straight lines that best fit the experimental data in the linear regression process, according to the method described in the text.
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Figure 6. (a) Raw and corrected spectra obtained with a cooled PIN photodiode in an Amptek XR100 CR system for a nominal applied voltage of 35 kV and additional filtration 0.04 mm Mo, to simulate a mammographic beam. The 22 keV peak of the measured spectrum corresponds to fluorescence X-rays from the photodiode Ag back contact; this peak was suppressed in the spectrum stripping process. (b) Details of the end region of the measured spectrum with the straight lines corresponding to the linear regression and to the background. The value adopted, in this case, as the spectrum end point was 417.76 (equivalent to 35.012 keV) for determination of the kVp value.
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Copyright © 2004 by the British Institute of Radiology.
) as a function of the number of energy lines utilized for spectrometer calibration, for the same set of measurements with 50 kV nominal three-phase potential applied to the tube. In the same graph, the percentage total kVp error for each number of lines used is shown (
). This is affected only by the change of calibration conditions.