Britijh zyxwvutsrqpo .lournal of Obstetrics arid Gynaecologv zyxwvu July 1990, Vol 97, zyxwvutsr pp 595-602 Cyclic changes in composition and volume of the breast during the menstrual cycle, measured by magnetic resonance imaging P. A. FOWLER, C. E. CASEY, G. G. CAMERON, M. A. FOSTER, C. H. KNIGHT Summary. The volumes and spin-lattice (T,) relaxation timer of breast tissues and parenchymal water content were measured non-inva\ively by magnetic resonance imaging (MRI) in eight healthy women during four to eight consecutive menstrual cycles. Total breast volume, and parenchymal volume, TI relaxation time and water content were lowest between days 6 and 15. Between days 16 and 28, parenchymal volume, T, relaxation time and water content rose sharply by 38.9”/:,, 15.1 zyx % and 24.5%. respectively, and peaked after day 2.5. Within 5 days of the oncet of menses, parenchymal volume fell sharply by 3@3?0, while watcr con- tent declined by 17.5%. Rising parenchymal volume in the second half of the menstrual cycle is not solely due to increased tissue water content and provides in vivo evidence for both growth and increaqed tissue fluid at this time. Changes in qize, histology and activity of thc breast during the menstrual cycle in adult women have dttracted considerable clinical attention (McCance et al. 1937; Ferguson & Anderbon 1981a, h; Vogel et zyxwvut a1 1981; Anderson ef al 1982: Going at ul 1988). ‘I’echniques for volume estimation, including water displace- ment (Hytten 1951; Milligan zyxwvu rf ul. 1975) md University of Aberdeen. Foresterhill, Aherdeen AH9 2ZD Department of Obstetrics and Gynaecolog? P A I-OWLEK Research Fellow Department ot Medicine and rhWdpCutiCS C b CASEY Lectriier Department of Bio-Medical Phy\ics G G CAMERON Rewurch Assistant M A FOSTER Senior Lecturer Hannah Research Institute, Ayr KA6 SHL C H KNlCiHT Senior Sczerifrfic Offrcer Conespondence P A Fowler plaster casting (Ingleby 1949), provide no infor- mation about changes within the hreast, while techniques such as mammography and ultra- sound do not readily provide volumetric data. Detailed studies of conlposition or activity require invasive techniques such as the excision of healthy tissue during surgery (Potten et nl. 1988). Magnetic resonance imaging (MRI) has been used to characterize breast tissues, includ- ing studies of spin-lattice (TI) relaxation during the menstrual cycle (Nelsonetul. 1985; Marlin & Yousef 1986). The T, relaxation time is a measure of the rate of energy loss from tissues following NMR excitation. This cnergy loss is dependent upon the biophysical environmcnt of the excited protons. A short T,, therehe. indi- cates the presence of lipids and/or organic struc- tures which can bind cellular water tightly. A longer TI is expected from tissues of greater hydration and with the greatest amount of ccl- lular water. Volumetric studies of the breast have been made using MRI (Foster & Knight 1983), and the technique can also be employed 595