Direct Measurement of Mammographic X-Ray Spectra with a Digital CdTe Detection System

Abstract

In this work we present a detection system, based on a CdTe detector and an innovative digital pulse processing (DPP) system, for high-rate X-ray spectroscopy in mammography (1–30 keV). The DPP system performs a height and shape analysis of the detector pulses, sampled and digitized by a 14-bit, 100 MHz ADC. We show the results of the characterization of the detection system both at low and high photon counting rates by using monoenergetic X-ray sources and a nonclinical X-ray tube. The detection system exhibits excellent performance up to 830 kcps with an energy resolution of 4.5% FWHM at 22.1 keV. Direct measurements of clinical molybdenum X-ray spectra were carried out by using a pinhole collimator and a custom alignment device. A comparison with the attenuation curves and the half value layer values, obtained from the measured and simulated spectra, from an ionization chamber and from a solid state dosimeter, also shows the accuracy of the measurements. These results make the proposed detection system a very attractive tool for both laboratory research, calibration of dosimeters and advanced quality controls in mammography.

Silicon Photomultipliers for High-Performance Scintillation Crystal Readout Applications

“…At higher counting rates, the direct digitization of the preamplifier output pulses (DPP approach) is a very appealing solution, as reported in several works [7][8][9][10][11][12][13][14][15][16][17]. These systems showed good spectroscopic performance up to photoncounting rates of approximately 100 kcps, a limit due to the finite width of the shaped pulses and the difficulties on baseline restoration.…”

“…Some DPP systems are composed of a digitizer and a personal computer for data recording and analysis (offline analysis) [3][4][5][6]10,[12][13][14][15][16]. In a DPP system, the direct digitizing of the detector signals minimizes the drift and instability that are normally associated with analog pulse processing.…”

“…The DPP firmware is based on a revised version of a DPP method, developed by our group and successfully used for both offline [10,[12][13][14][15] and online analysis [17,18]. The pulse detection is performed by using a fast-shaping mode, whereas the PSHA starts with a slow-shaping mode.…”

“…As is well known [1,[12][13][14][15], the correlation between the height and the peaking time of the pulses can be generally used to minimize both incomplete charge collection ( Figure 6.8a) and peak pileup effects (Figure 6.8b). To compensate for incomplete charge collection, pulse shape discrimination (PSD) and pulse shape correction (PSC) techniques [14,17] were implemented.…”

Electrical characterization of CdTe pixel detectors with Al Schottky anode

“…To enhance the charge collection, CdTe detectors are typically developed with blocking contacts (i.e. working as diodes), with indium (In) as the anode electrode on a p-type CdTe and platinum (Pt) as the cathode [2,3,6]. Blocking contacts are characterized by lower leakage currents than an ohmic configuration (Pt/CdTe/Pt), allowing high bias voltage operation and accordingly better spectroscopic performance.…”