EFFECT OF AUTOMATIC KV SELECTION ON DOSE AND CONTRAST FOR A MAMMOGRAPHIC X-RAY SYSTEM

The effect of automatic tube potential (kV) selection on breast dose a nd contrast has been assessed using a Philips MammoDiagnost 3000 mammo graphy X-ray set. The performance of the X-ray set using automatic kV selection has been compared with that found using a fixed kV of 28. Th e AUTOKV mode selected 25 kV for breasts with thickness up to about 50 mm, which increased the contrast by 5-10%, and increased the mean gla ndular dose (MGD) per Rim by, on average, 30-40%. For large breasts wi th a compressed thickness of 70 mm and above, kVs up to 30 were select ed so that the average MGD per him was reduced by 19% from 3.62 to 2.9 4 mGy, with an estimated loss in contrast of about 4-8%. For all breas ts the mean MGD per film was 1.85+/-0.05 mGy where AUTOKV was used, an d 1.74+/-0.08 mGy per film when 28 kV was used. The overall image qual ity of the mammograms was found to be higher when AUTOKV was used. Ove rall, the AUTOKV facility on this X-ray set generally worked well and resulted in slightly higher contrast and slightly better image quality at the price of a small increase in the average dose for this patient group when compared with the usual UK procedure of using a fixed 28 k V.