Needle phosphor based computed radiography(CR) systems promise improved image quality compared to powderphosphor based CR units for x-ray screening mammography. This paper compares the imaging performance of needle CR cassettes, powder based CR cassettes and a well established amorphous selenium (a-Se) based flat panel based mammography system, using consistent beam qualities.Methods:
Detector performance was assessed using modulation transfer function(MTF), normalized noise power spectrum (NNPS), and detective quantum efficiency (DQE). Mammography system performance was assessed against levels from the European Guidelines, including threshold gold thickness (c-d), relative signal difference to noise (SdNR) and mean glandular dose, for automatic exposure control settings suggested by the manufacturers. The needle based Agfa HM5.0 CRdetector was compared against the single sided readout Agfa MM3.0R and dual sided readout Fuji Profect CS powderCR plates using a 28 kV Mo/Rh spectrum, while a 28 kV W/Rh spectrum was used to compare the Agfa HM5.0 against the Siemens MAMMOMAT Inspirationa-Se based system.Results:
MTF at 5 mm−1 was 0.16 and 0.24 for the needle CRdetector in the fast and slow scan directions, respectively, indicating a slight improvement (∼20%) over the two powderCR systems but remained 50% lower than the result at 5 mm−1 for the a-Se detector (∼0.55). Structured screen noise was lower for the needle phosphor compared to the powder plates. CR system gain, estimated from the measured absorption fraction and NNPS results, was 6.3 for the (single sided) needle phosphor and 5.1 and 7.2 for the single sided and dual sided powderphosphor systems. Peak DQE at ∼100 μGy was 0.47 for the needle system compared to peak DQE figures of 0.33 and 0.46 for the single sided readout powder plates and dual sided readout plates. The high frequency DQE (at 5 mm−1) was 0.19 for the needle CR plates, a factor of approximately 3 greater than for the powderCR plates. At 28 kV W/Rh, 2 mm Al, peak DQE for the needle CR system was 0.45 against a value of 0.50 for the a-Se detector. The needle CRdetector reached the Acceptable limit for 0.1 mm details in the European Guidelines at a mean glandular dose (MGD) of approximately 1.31 mGy imaged at 28 kV Mo/Rh, compared to figures of 2.19 and 1.43 mGy for the single sided and dual sided readout powderCR systems. The a-Se detector could reach the limit at 0.65 mGy using a 28 kV W/Rh spectrum, while the needle CR system required 1.09 mGy for the same spectrum.Conclusions:
Imaging performance for the needle CRphosphor technology, characterized using MTF and DQE and threshold gold thickness demonstrated a clear improvement compared to both single and dual sided reading powderphosphor based CR systems.
II. MATERIALS AND METHODS
II.A. Digital mammography detectors studied
II.B. Detector response function
II.C. Detector uniformity error
II.D. Modulation transfer function(MTF)
II.E. Separation of noise sources using variance
II.F. Normalized noise power spectrum (NNPS)
II.G. System gain
II.H. Detective quantum efficiency (DQE)
II.I. Relative signal difference to noise ratio
II.J. Threshold gold thickness
III. RESULTS AND DISCUSSION
III.A. Detector response curve
III.B. Detector uniformity error
III.C. Presampling modulation transfer function
III.D. Separation of noise sources using variance
III.E. Normalized noise power spectrum
III.F. System gain
III.G. Detective quantum efficiency
III.H. Threshold gold thickness
III.I. Relative signal difference to noise ratio and mean glandular dose
- Image sensors
- Modulation transfer functions
- Computed radiography
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