Mammography is the most widely accepted procedure for the early detection of breast cancer and Computed
Radiography (CR) is a cost-effective technology for digital mammography. We have demonstrated that CR
mammography image quality is viable for Digital Mammography. The image quality of mammograms acquired
using Computed Radiography technology was evaluated using the Modulation Transfer Function (MTF), Noise
Power Spectrum (NPS) and Detective Quantum Efficiency (DQE). The measurements were made using a 28 kVp
beam (RQA M-II) using 2 mm of Al as a filter and a target/filter combination of Mo/Mo. The acquired image
bit depth was 16 bits and the pixel pitch for scanning was 50 microns. A Step-Wedge phantom (to measure
the Contrast-to-noise ratio (CNR)) and the CDMAM 3.4 Contrast Detail phantom were also used to assess
the image quality. The CNR values were observed at varying thickness of PMMA. The CDMAM 3.4 phantom
results were plotted and compared to the EUREF acceptable and achievable values. The effect on image quality
was measured using the physics metrics. A lower DQE was observed even with a higher MTF. This could be
possibly due to a higher noise component present due to the way the scanner was configured. The CDMAM
phantom scores demonstrated a contrast-detail comparable to the EUREF values. A cost-effective CR machine
was optimized for high-resolution and high-contrast imaging.
Computed Radiography (CR) is a cost-effective technology for digital mammography. In order to optimize the quality of images obtained using CR Mammography, we characterized the effect on image quality of the electrooptical components of the CR imaging chain. The metrics used to assess the image quality included the Contrast
to Noise Ratio (CNR), Modulation Transfer Function (MTF), Noise Power Spectrum (NPS), Detective Quantum Efficiency (DQE) and Contrast Detail Response Phantom (CDMAM 3.4 Artinis Medical Systems). An 18×24 cm high-resolution granular phosphor imaging plate (AGFA MM3.0) was used to acquire the images. Contrast
detail was measured using a GUI developed for the CDMAM phantom that was scored by independent observers.
The range of theoretically acceptable values measured for the CR laser was (5-36) mW and voltage range for
PMT's was (4-8) V. The light detection amplifier was investigated, and the optimal Laser Power and PMT gain
used for scanning was measured. The tools that we used (CNR, MTF, NPS, DQE and Contrast-detail phantom)
provided an effective means of selecting optimal values for the electro-optical components of the system. The
procedure enabled us to obtain good quality CR mammograms that have less noise and improved contrast.
A number of complementary metrics are available to assess the performance of digital X-ray imaging systems.
However, the sensitivity of these metrics to changes in the electro-optical imaging chain is poorly understood.
Some of the commonly used metrics include Contrast to Noise ratio (CNR), limiting spatial resolution, Modulation
Transfer Function (MTF), Noise Power Spectrum (NPS) and the Detective Quantum Efficiency (DQE). We
evaluated the utility of these metrics in characterizing the imaging plate, imaging system optics and electronic
components of computed radiography (CR) systems. We developed practical and easy to use test objects (phantoms) and implemented software to aid in calculating each metric. The results of this research will facilitate the characterization of differences in CR systems using the appropriate metrics.
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