FATTY AND FIBROGLANDULAR-TISSUE VOLUMES IN THE BREASTS OF WOMEN 20-83YEARS OLD - COMPARISON OF X-RAY MAMMOGRAPHY AND COMPUTER-ASSISTED MR-IMAGING

OBJECTIVE. A method for segmenting MR images of the breast was applied to determine fatty and fibroglandular tissue volumes in breasts of wo men in different age groups. The results were compared with subjective assessments of breast density from X-ray mammograms in the same patie nts. MATERIALS AND METHODS. Two experienced mammographers assessed the percentage of fat in the breasts of 40 women who were 20-83 years old . MR images were obtained on a 1.0-T scanner equipped with a bilateral receive-only breast coil. Images were acquired using a three-dimensio nal T1-weighted, gradient-echo sequence with a 1.25 x 1.4 x 2.5 mm res olution. On average, breast parenchyma appeared in 30 images in each b reast. Image segmentation was based on a semiautomated, two-compartmen tal (fatty and fibroglandular tissue) model that accounts for partial volume effects. To validate the accuracy of the MR imaging segmentatio n technique, we performed a phantom study using an identical imaging s equence. RESULTS. The accuracy of the MR imaging segmentation of the p hantom was of the order of 2%. In our subjects, fat content was 42.5% +/- 30.3% (mean +/- SD) on mammography versus 66.5% +/- 18% on MR imag es. Although we found a significant correlation (r = .63) between the two techniques, mammography poorly differentiated breasts containing l ess than 45% fat. When our analysis included only dense breasts (i.e., those containing less than 75% fat on MR images), the correlation coe fficient decreased to .34. The largest discrepancies between mammograp hy and MR imaging occurred in breasts that had 60-80% fat as measured on MR imaging. CONCLUSION. Fatty and fibroglandular tissue can be diff erentiated on MR images of the breast with high precision and accuracy , therefore allowing assessment of breast density. The conclusions of researchers who used mammographic density patterns should be reassesse d.