Estimation of breast volume and its variation during the menstrual cycle using MRI and stereology

Unbiased estimates of breast volume may be obtained in vivo from systematic series of MR images acquired in accordance with the Cavalieri method of mo dern design-based stereology. The method does not require any assumptions t o be made regarding breast shape. If point counting techniques are used to obtain the required breast section areas estimates, 10-15 min analysis (i.e . counting about 250 points on 12 to 16 images) ensures that the contributi on of sectioning and paint counting to the coefficient of error (CE) on the volume estimate is less than 3%. The methods were applied to measure breas t volume in 15 healthy females aged between 22 and 44 years (mean 31.7 year s; SD 8.2 years). One subject was studied on every fourth day during two co nsecutive cycles. The other 14 subjects were studied on three occasions cor responding to menses, ovulation and pre-menses during a single menstrual cy cle. Repeat imaging after repositioning on three occasions within a period of 30 min and also at three different times of day for a single subject, bo th yielded a coefficient of variation (CV) of less than 3% in the estimatio n of breast volume. ANOVA indicates that there is no significant difference between the mean volume of the left and the right breast (p=0.294). The me an volume of the left breast is 561 ml (95% confidence interval (CI): 553 m l, 569 ml) and the mean volume of the right breast is 567 ml (95% CI: 559 m l, 576 ml). There are highly significant differences between the three name d stages of the menstrual cycle (p<0.0005), whereby the mean volume at ovul ation is 5.5% less than the mean volume at menses (95% CI: 3.0%, 7.9%) and the mean volume pre-menses is 8.1% greater than the mean volume at menses ( 95% CI: 5.3%, 10.9%). Overall, the volume of each breast varies by an avera ge of 76 ml (95% CI: 61 ml, 92 ml) during the menstrual cycle, which corres ponds to 13.6% of the volume at menses (95% CI: 13.3%, 13.8%). No significa nt interaction was found between the relative volumes of the left and right breast and the stage of the menstrual cycle (p=0.277), nor between subject s and stages of cycle (p=0.296). However, a significant interaction was obs erved between the volume of the left and right breasts in different subject s (p<0.005). The average difference in the volume of the left and right bre asts of all 15 subjects is 39.7 ml (95% CI: 21.3 ml, 58.1 ml), which is 7% of average breast volume and approximately 50% of the average variation in the volume of the breast during the menstrual cycle.