X-ray Performance Evaluation of the Dexela CMOS APS X-ray Detector Using Monochromatic Synchrotron Radiation in the Mammographic Energy Range

Abstract

Digital detectors based on complementary metaloxide-semiconductors (CMOS) active pixel sensor (APS) technology have been introduced recently in many scientific applications. This work is focused on the X-ray performance evaluation of a novel CMOS APS detector in low energy medical imaging applications using monochromatic synchrotron radiation (i.e. 17-35 keV), which also allows studying how the performance varies with energy. The CMOS sensor was coupled to a Thallium-activated structured cesium iodide (CsI:Tl) scintillator and the detector's X-ray performance evaluation was carried out in terms of sensitivity, presampling modulation transfer function (pMTF), normalized noise power spectrum (NNPS) and the resulting detective quantum efficiency (DQE). A Monte Carlo simulation was used to validate the experimentally measured low frequency DQE. Finally, the effect of iodine's secondary generated K-fluorescence X-rays on pMTF and DQE results was evaluated. Good agreement (within 5%) was observed between the Monte Carlo and experimentally measured low frequency DQE results. A CMOS APS detector was characterized for the first time over a wide range of low energies covering the mammographic spectra. The detector's performance is limited mainly by the detectability of the scintillator. Finally, we show that the current data could be used to calculate the detector's pMTF, NNPS and DQE for any mammographic spectral shape within the investigated energies.

Three-dimensional cascaded system analysis of a 50µm pixel pitch wafer-scale CMOS active pixel sensor x-ray detector for digital breast tomosynthesis

“…A polished W edge plate was attached to the detector surface at a small tilted angle (1.5 -3°) with respect to the detector rows or columns (Konstantinidis et al 2013, Zhao et al 2015b. At oblique projection angles, partial transmission of x-ray photons through the edge may affect the MTF.…”

“…Then the averaged ESF was differentiated to obtain the line spread function (LSF). The 1D presampling MTF in either x (horizontal MTF(u)) or y direction (vertical MTF(v)) was calculated from the fast Fourier transform (FFT) of the oversampled LSF (Fujita et al 1992, Konstantinidis et al 2013, Zhao et al 2015b. The horizontal presampling MTF at θ i is given by…”

“…where I(x j , y j , θ i ) is the corrected flat-field image at θ i within a 256 × 256 region of interest (ROI), S(x j , y j , θ i ) is a 2D second order polynomial fit for I(x j , y j , θ i ) to remove the low frequency trends, ∆x and ∆y are the pixel pitches in x and y directions (∆x = ∆y = 50 μm), M is the number of ROIs (M = 243 to reach at least three million independent pixels (IEC 62220-1-2: 2007)), N x and N y are the number of columns and rows in each ROI (N x = N y = 256) (IEC 62220-1-2: 2007, Konstantinidis et al 2013, Zhao et al 2015b. The 1D horizontal (NPS(u)) and vertical NPS (NPS(v)) were extracted and averaged from seven lines on either side of zero spatial frequency.…”

Evolution of spatial resolution in breast CT at UC Davis

“…The dexel pitch at native binning mode is 75×75 µm with a typical fill factor of 84%. 15 The x-ray source, specifically designed for breast scanning purposes, is a water-cooled, rotating anode x-ray tube with a nominal focal spot size of 0.3 mm coupled with a 14 kW rad/pulse-rad x-ray generator (CMP200SE, CPI, Ontario, Canada). The x-ray focal spot distribution was measured with a 0.030 mm pinhole camera made from a 90:10 goldplatinum alloy (07-613, Nuclear Associates, Carle Place, NY).…”

Synchrotron based planar imaging and digital tomosynthesis of breast and biopsy phantoms using a CMOS active pixel sensor

“…The X-ray performance evaluation of the detector has been tested with monochromatic synchrotron radiation in the mammographic energy range and reported in Ref. [11]. The authors measured the detective quantum efficiency (DQE), which ranges from 0.79 to 0.85 at a frequency of 0.5 lp/mm and at 17 keV and 0.75 to 0.79 at 20 keV.…”