The objective imaging characteristics of three systems that use charge coupled devices (CCD) for small-field digital mammography (SFDM) have been compared in terms of spatial resolution and signal to noise ratio. The results indicate that although they are designed for nominally the same tasks of stereotactic localization and spot imaging these detectors have significantly differing physical imaging properties. Imaging system design parameters such as the phosphor screen type and thickness, screen configuration and method of optically coupling the phosphor to the CCD have significant effects on the imaging performance of the detectors.

The need for rigorous image quality assurance in mammography is well documented (Pritchard Report, 1989). However, there is still debate over the suitability of those image quality test objects commercially available. We have been able to compare three contemporary test objects with the “Barts” test object which has been in use since 1980 and has been used as a standard by many workers (Kirkpatrick & Law, 1987). The four mammographic test objects have been compared using six mammographic film-screen combinations. The following test objects were used. The “Barts” mammographic image quality test object (White & Tucker, 1980). This object contains several series of opacities designed to mimic mammographic diagnostic features, some being fat equivalent, some water equivalent, some skin equivalent and some equivalent to calcifications, which are immersed in an epoxyresin scattering medium. The object is designed to assess contrast and resolution combined in various ways. The Dupont mammographic image quality test object (Ackermann, personal communication, 1988). This simulates microcalcifications, fibrous structures and small spherical objects. It also allows an assessment of minimal detail contrast, line resolution in two dimensions and point resolution. A selection of organic materials is included to simulate benign and malignant tumours, lymph nodes and tissues characteristic of a dense breast. It is designed to be used with a stack of attenuator plates to provide the appropriate absorption, scatter and geometrical unsharpness in test exposures.

The use of K-edge filters and fast speed dental (non-screen) film have been separately shown to reduce the radiation dose imparted during dental radiography. The effect of these on image quality has been unclear. This study objectively examines the effect on image quality of eight film/filter systems: E- and D-speed film and four filter systems (the existing aluminium filter used alone or with erbium, niobium or yttrium). The components of the image quality parameters assessed were contrast, resolution, the minimum perceptible contrast (noise) and the square wave response function. No clinically significant difference in image quality was observed. This was confirmed by subjective assessment of images of an anatomical phantom. It is concluded that the use of faster speed film in addition to K-edge beam filtration has no major effect on the clinical image.

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