Ans is 'b' i.e. USG The presentation of a lactating female with painful palpable breast lump is highly suggestive of breast abscess. Ultrasound would be the most useful investigation to diagnose the condition and in delineating the required extent of the drainage procedure. Mammography would be non specific for breast abscess and would not differentiate it from a carcinoma or other breast masses. Moreever, generally mammography is not helpful in young women (< 35 years). This is because of dense breast. In young women, ultrasound is more useful than mammography.