Does the Pixel Size of a Full-Field Digital Mammography Detector Matter for Early Detection of Breast Cancer?

This Agfa white paper examines to what extent the pixel size of full-field digital mammography (FFDM) detectors affects diagnostic image quality and the detection of microcalcifications. To do so, it compares the technical image quality characteristics of several commercial FFDM, retrofit and CR systems with pixel sizes of 50 to 100 µm.

Highlights

• In the 50 to 100 µm range, pixel size alone has no systematic effect on the detectability of small objects.
• Under quantum-noise-limited conditions, SNR is proportional to pixel size; a 76 µm detector may need about 24% more dose than a 100 µm detector to reach the same SNR.
• Pixel size limits the minimum size of detectable detail, but it does not determine the overall resolution of the system.
• DQE is a more comprehensive measure of image quality, covering detector sensitivity, MTF and noise.
• In the CDMAM phantom test, pixel size in the 50 to 100 µm range had no effect on detail contrast visibility.
• MUSICA image processing with the patented Fractional Multiscale Processing (FMP) technology improves diagnostic quality independently of pixel size.

Systems compared

System	Pixel size (µm)	Pixel matrix	Technology
Agfa DR 24M (on Siemens Nova analog modality)	76	3072 x 3840	CsI / a-Si TFT
Agfa DX-M HM5.0 (on Siemens Nova analog modality)	50	4708 x 5844	CR Needle IP
Fuji Amulet	50	3540 x 4740	a-Se / optical switch
GE Essential	100	2394 x 3062	CsI / a-Si TFT
Hologic Selenia	70	2560 x 3328	a-Se / TFT
Siemens Inspiration	85	2658 x 3318	a-Se / TFT

CDMAM test results

System	kV	A/F	Air Kerma (µGy)	Log(T) 0.1 mm disc	Log(T) 0.25 mm disc
Agfa DR 24M	30	Mo/Rh	80	0.00	-0.63
Agfa DX-M HM 5.0	29	Mo/Rh	104	0.013	-0.52
Fuji Amulet	29	Mo/Rh	88	0.03	-0.55
GE Essential	29	Rh/Rh	83	0.06	-0.59
Hologic Selenia	29	W/Rh	100	0.08	-0.62
Siemens Inspiration	28	W/Rh	98	0.08	-0.57

A lower value indicates better detectability of low-contrast details.

Paper summary

Early detection of breast cancer often relies on identifying microcalcifications and their geometry, which is why system resolution is considered very important in mammography. FFDM detectors come in different designs: CR with storage phosphor plates, indirect flat panels based on a CsI scintillator, and direct flat panels based on a-Se. CR systems and retrofit panels make it possible to keep using existing mammography modalities.

According to the MTF data, the achievable resolution at high contrast depends mainly on the detector technology: a-Se detectors have the highest MTF at 4 lp/mm, and CR with needle-based plates is nearly on par with CsI detectors. However, the actual visual resolution depends on the ability to display small details with sufficient contrast above the noise.

In addition to the detector, image processing, optimization of the X-ray spectrum through AEC calibration, and the way the user operates the system, including positioning, correct compression, recommended exposure conditions, acceptance tests and regular quality control, play a decisive role in final diagnostic quality.