A number of authors have calculated x-ray energies for mammography using, as a criterion, the maximum signal-to-noise ratio (SNR) obtainable per unit dose to the breast or conversely the minimum exposure for constant SNR. The predicted optimum energy increases with increasing breast thickness. Tungsten anode x-ray spectra have been measured with and without various added filter materials to determine how close the resultant spectra can be brought to the predicted optimum energies without reducing the x-ray output to unacceptable levels. The proportion of the total number of x-rays in a measured spectrum lying within a narrow energy band centred on the predicted optimum has been used as an optimum energy index. The effect of various filter materials on the measured x-ray spectra has been investigated both experimentally and theoretically. The resulting spectra have been compared with molybdenum anode, molybdenum filtered x-ray spectra normally used for mammography. It is shown that filters with K-absorption edges close to the predicted optimum energies are the most effective at producing the desired spectral shape. The choices of filter thickness and Vp are also explored in relationship to their effect on the resultant x-ray spectral shape and intensity.

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A number of authors have calculated the optimum X-ray energies for mammography using, as a criterion, the maximum signal to noise ratio (SNR) per unit dose to the breast, or conversely the minimum exposure for constant SNR. Filters having absorption edges at appropriate energy positions have been used to modify the shape of tungsten anode spectra to bring them close to the calculated optimum. The suitability of such spectra for practical use has been assessed by comparing both the film image quality and the incident breast dose obtained using a K-edge filtered tungsten anode tube with that obtained using a molybdenum anode tube. Image quality has been assessed both by using a "random" phantom and by comparing mammograms of women attending a screening clinic where one breast was radiographed using a filtered tungsten anode tube and the other using a standard molybdenum anode unit. Relative breast doses were estimated from both ionisation chamber measurements with a phantom and thermoluminescent dosimetry measurements on the breast. The film image quality assessment indicated that the filtered tungsten anode tube gave results which were not significantly different from those obtained with a molybdenum anode tube for a tissue thickness of about 4 cm and which were better for larger breast thicknesses. The dose could be reduced to between one-half and one-third with the filtered tungsten anode tube.

Study objective-The aim ofthe study was to determine whether thermography could be used to identify women with breast cancer or women at risk of developing the disease within five years.Design-Women were screened for breast cancer and a documentary follow up was conducted five years later through general practitioner records.Setting MethodsWomen were recruited to the project by two methods:(1) We identified 8235 women aged 40 to 65 through the age/sex registers of six general practices in the Bath area, who were then sent personal letters from their own doctors inviting them to take part. Of these, 4284 (52% ) accepted.(2) There were also 5954 women in the same age group who volunteered to take part after reading about the project on posters in general practitioners' waiting rooms throughout the Bath Health District, or hearing about it from friends and work mates. Within this group there were 229 symptomatic women. As pain was such a common complaint, for the purpose of this study symptoms were confined to skin tethering, a discrete lump, or nipple abnormality.After receiving an explanation of the aims ofthe project and the methods employed, each woman gave a history while cooling for her thermogram. Two thermographic systems were used: a scanner developed by AWRE, Aldermaston, in conjunction with Barr and Stroud, and a system made by Rank Precision Industries. The women cooled for 10 min at an ambient temperature of

The potential of thermography as a screening technique for the early detection of breast cancer was assessed by using difference of Gaussian filtering to isolate and quantify the vascular contents of breast thermograms. Forty-five patients found to have breast cancer and 49 patients who developed breast cancer within 5 years of being screened were paired with normal variants and the thermograms of each group were assessed. No statistically significant separation was resolved between either of the two paired groups implying that the vascular content of isolated thermograms is unable to provide meaningful indications of breast cancer. The processing algorithm, although developed initially for thermograms, is equally valid for other diagnostic imaging techniques and could be of use where it is required to isolate vascularity or other fine detail from larger body structures.