Characterization of on-site digital mammography systems: Direct versus indirect conversion detectors

Abstract

We investigated the performances of two digital mammography systems. The systems use a cesium-iodide (CsI) scintillator and an amorphous selenium (a-Se) photoconductor for X-ray detection and are installed in the same hospital. As physical metrics, we measured the modulationtransfer function (MTF), the noise-power spectrum (NPS), and the detective quantum efficiency (DQE). In addition, we analyzed the contrast-detail performances of the two systems by using a commercial contrast-detail phantom. The CsI-based indirect conversion detector provided better MTF and DQE performances than the a-Se-based direct conversion detector whereas the former provided a poorer NPS performance than the latter. These results are explained by the fact that the CsI-based detector used an MTF restoration preprocessing algorithm. The a-Se-based detector showed better contrast-detail performance than the CsI-based detector. We believe that the highfrequency noise characteristic of a detector is more responsible for the visibility of small details than its spatial-resolution performance.

Planar cone-beam computed tomography with a flat-panel detector

“…Their corresponding LSFs are also shown in figure 2. While the CBCT-LSF showed a typical Gaussian shape, the pCT-LSF showed the broad undershoot relative to baseline occurring on both sides that was a characteristic of a processed impulse response [16]. Therefore, the pCT-LSF reflected the edge enhancement associated with the filter function used for reconstruction [17].…”

Impacts of photon counting CT to maximum intensity projection (MIP) images of cerebral CT angiography: theoretical and experimental studies

“…Among the major contributors to the poor performance of CTA in imaging small vessels is the physical performance of the MDCT detector. Conventional MDCT scanners Impacts of photon counting CT to maximum intensity projection (MIP) images of cerebral CT angiography: theoretical and experimental studies use scintillator-based energy-integrating detectors (EIDs) that have excellent zero-frequency detective quantum efficiency (DQE) but poor high frequency DQE performance due to the isotropic spatial spreading of secondary quanta (light photons) (Youn et al 2015). To reduce spatial resolution loss and inter-pixel crosstalk, septa are usually placed in between detector pixels, which inevitably reduces the percent active area of the detector or the so-called geometric efficiency (Miess and Stefan 2011).…”

Theoretical investigation of partially pixelated scintillators for high-resolution imaging with less aliasing

“…Non-negligible T(u) beyond the Nyquist frequency, as shown in figure 6, can cause an aliasing problem in images obtained using the pixelated scintillator detectors. As well known from directconversion detectors [19,26], noise aliasing increases the NPS at high frequencies, and which may impair the detectability of fine details [36][37][38]. From figure 7, the partially pixelated design may reduce the magnitude of noise aliasing compared to the completely pixelated design.…”