Physical characterization of a high-resolution CCD detector for mammography

Abstract

The physical characteristics of charge-coupled device (CCD) mammography detector with 16-bit dynamic range and 27 microm detector element size were investigated. The detector, with an active area of 1 cm x 20 cm is suitable for slot-scanning systems. We evaluated the detector resolution by measuring the modulation transfer function (MTF) using a tilted edge. We also measured the noise power spectra (NPS) and detective quantum efficiency (DQE) using tungsten spectra filtered with 3 mm Al. We carried out measurements in two modes of operation: the frame mode where the detector is stationary and the scan mode where the detector operates in a slot-scanning configuration. The specific beam qualities and exposure ranges employed were 30 kVp, HVL 1.4 mm Al, 1.24 microC kg(-1) to 12.44 microC kg(-1), and 40 kVp, HVL 2.1 mm Al and 3.26 microC kg(-1) to 16.64 microC kg(-1). The product of the normalized noise power spectrum and exposure was also computed to evaluate the quantum limited characteristic of the detector. The detector MTF was 12% at 15 lp mm(-1). The product of the noise power spectra and exposure was independent of exposure level, indicating a quantum limited detector. The DQE in the scan and frame modes near zero frequency was 40% and 60%, respectively. Our results show that the slot-scanning configuration was less efficient than the performance capabilities of the detector. This detector is comparable to other digital mammography sensors evaluated in the literature.

Physical characterization and performance comparison of active- and passive-pixel CMOS detectors for mammography

“…Generally, the DQE falls within the range of results reported in the literature for other CMOS and digital mammography detectors. Keeping the differences in measurement setups and conditions in mind, one can tentatively state that the DQE values of the APS and PPS considered in this study are higher than those reported for amorphous silicon flat panels (Vedantham et al 2000), comparable to CCD and CMOS detectors with similar del sizes (Suryanarayanan et al 2005, Tesic et al 1999, Elbakri et al 2007 and lower than that of amorphous selenium flat panels (Saunders et al 2005). A similar statement can be made about the detectors resolution performance.…”

“…Edge images were dark and gain corrected according to equation (1), and then processed using a MATLAB program developed in house and described elsewhere (Elbakri et al 2007).…”

Technical Note: Modification of the standard gain correction algorithm to compensate for the number of used reference flat frames in detector performance studies

“…7,[13][14][15] or to max Flat raw ðx; yÞ À Darkðx; yÞ À Á . 16,17 Usually, the scaling factor K is equal to the average over all pixels of the offset-corrected average (over n f frames) reference flat image (i.e., to the first of the three cases in the above list).…”

Evaluation of digital X-ray detectors for medical imaging applications

“…raw Flat x y Dark x y − (Elbakri et al, 2007 andElbakri et al, 2009). Usually, the scaling factor K equals to the average value of the offset corrected average reference flat image (first case).…”

“…There are several commercial and scientific software packages available to calculate the MTF, NPS and DQE of digital x-ray detectors. A commercial available software package is JDQE (Elbakri, 2010) which is an ImageJ (Rasband, 1997(Rasband, -2011 plugin based on Elbakri's work on x-ray characterization of digital detectors (Elbakri et al, 2006, Elbakri et al, 2007and Elbakri et al, 2009. Two available software packages distributed to researchers and members of the scientific community are MIQuaELa (Ayala et al, 2009) which is a MATLAB-based GUI and OBJ_JQ_reduced (Marshall, 2009c) which is an IDL-based GUI based on Marshall's work (Marshall, 2006a, Marshall, 2006b, Marshall, 2007, Marshall, 2009aand Marshall, 2009b.…”