Comparison of breast density measured on MR images acquired using fat-suppressed versus nonfat-suppressed sequences

Abstract

Purpose: To investigate the difference of MR percent breast density measured from fat-suppressed versus nonfat-suppressed imaging sequences.

Methods: Breast magnetic resonance imaging (MRI) with and without fat suppression was acquired from 38 subjects. Breasts were divided into subgroups of different morphological patterns ("central" and "intermingled" types). Breast volume, fibroglandular tissue volume, and percent density were measured. The results were compared using nonparametric statistical tests and regarded as significant at p < 0.05.

Results: Breast volume, fibroglandular volume, and percent density between fat-suppressed and nonfat-suppressed sequences were highly correlated. Breast volumes measured on these two sequences were almost identical. Fibroglandular tissue volume and percent density, however, had small (<5%) yet significant differences between the two sequences-they were both higher on the fat-suppressed sequence. Intraobserver variability was within 4% for both sequences and different morphological types. The fibroglandular tissue volume measured on downsampled images showed a small (<5%) yet significant difference.

Conclusions: The measurement of breast density made on MRI acquired using fat-suppressed and nonfat-suppressed T1W images was about 5% difference, only slightly higher than the intraobserver variability of 3%-4%. When the density data from multiple centers were to be combined, evaluating the degree of difference is needed to take this difference into account.

Figure 1

Anatomical landmark on axial, precontrast fat-suppressed and nonfat-suppressed images. The fat-suppressed imaging sequence was a 3D gradient echo with SPAIR fat-suppression, with TR = 6.20 ms, TE = 1.26 ms, flip angle = 12°, matrix size = 480 × 480, FOV = 31–38 cm, slice thickness = 1 mm, and 160 axial slices. The nonfat-suppressed sequence was a 2D turbo spin-echo with TR = 800 ms, TE = 8.6 ms, flip angle = 90°, matrix size = 480 × 480, FOV = 31–38 cm, slice thickness = 2 mm, and 84 axial slices. The spatial location 5 mm posterior to the dorsal margin of the sternum, indicated by the arrow, is used as the point through which a horizontal line is drawn (a). The nonbreast tissue is excluded (b), resulting in defined breast tissue (c). The contrast between breast tissue and the pectoral muscle on both fat-suppressed and nonfat-suppressed images is very clear, showing reverse signal intensities, which allows a successful segmentation to remove the pectoral muscle on both sets of images.

Figure 2

An example of density segmentation on a “Central” type breast of a 39-year-old patient, showing confined fibroglandular tissue surrounded by fatty tissue. The contrast between fibroglandular tissue and fatty tissue is strong on both sets of images. On nonfat-suppressed images, the fibroglandular tissue is dark; on fat-suppressed images, the fibroglandular tissue is bright and nearly mirrored and reversed. Some subtle differences exist on the segmented fibroglandular tissues, but the quality is acceptable on both sets of images without obvious errors. Compared with the original image, the downsampled image is blurred, yet the contrast remains very strong for segmentation. The measurement results are listed in Table TABLE II..

Figure 3

An example of density segmentation on an “Intermingled” type breast of a 31-year-old patient, showing mixed fibroglandular tissue and fatty tissue. The segmented fibroglandular tissue region is slightly larger on fat-suppressed images. Nevertheless, the quality is acceptable on both sets of images without obvious errors. Compared with the original image, the downsampled image is blurred, yet the contrast remains very strong for segmentation, and the segmentation results are similar. The measurement results are listed in Table TABLE II..

Figure 4

Spearman’s Rho between measurements from fat-suppressed and nonfat-suppressed images for (a) breast volume, (b) fibroglandular tissue volume, and (c) percent density. The parameters measured from the fat-suppressed sequence are on the y-axis; from the nonfat-suppressed sequence are on the x-axis. They are highly correlated with p < 0.001. The best-fit line passing through the origin is plotted on the figure, with a slope of 1.0019 for breast volume, 1.0276 for fibroglandular tissue volume, and 1.0247 for percent density. The dotted black line indicates the unity line representing 1:1 correlation. The least squares regression line lies close to the unity line.