| b | c | d | P-value | |
|---|---|---|---|---|
| UW - 1.5T | 131.8 (97.1, 172.9) | 258.7 (182.9, 297.2) | 255 (170.8, 333.7) | 0.005 |
| UW - 3T | 184.2 (155.4, 204.4) | 189 (160.4, 249.9) | 298.1 (287.5, 347.2) | 0.047 |
| ProHealth - 1.5T | 146.2 (111.5, 247.2) | 212.3 (148.6, 299.9) | 330.4 (208.6, 406.3) | <0.001 |
| All | 157 (112.1, 209.9) | 212 (163.8, 285.4) | 316.4 (208.6, 392.9) | <0.001 |
Proton Density Water Fraction as an MR-Based Measurement of Breast Fibroglandular Tissue Volume and Concentration
Statistical analysis
Water volume and and water fraction were summarized by median (inter-quartile range, IQR) for UW 1.5T, 3T, and ProHealth 1.5T, and tested across the three mammographic density categories (b, c, d) using a linear trend test. Receiver operating characteristic (ROC) analyses were performed to evaluate how water volume and fraction correlate with the density categories. P-values < 0.05 were considered statistically significant. All analyses were performed in R version 4.3.2 (R Foundation for Statistical Computing, Vienna, Austria).
Results
Water volume
The median (IQR) of water volume (cm\(^3\)) by mammographic density is tabulated in Table 1 for each field strength, site, and overall. P-values are based on a linear trend test. Boxplots are shown in Figure 1.
Water fraction
The median (IQR) of water fraction by mammographic density is tabulated in Table 2 for each field strength, site, and overall. P-values are based on a linear trend test. Boxplots are shown in Figure 2.
| b | c | d | P-value | |
|---|---|---|---|---|
| UW - 1.5T | 5.2% (4.3%, 8.7%) | 16.8% (12.9%, 26.8%) | 23.4% (21.1%, 53.7%) | <0.001 |
| UW - 3T | 6.1% (5.4%, 7.7%) | 15.4% (8%, 21.9%) | 39.4% (31.5%, 51%) | <0.001 |
| ProHealth - 1.5T | 6.6% (4.8%, 10.8%) | 13.6% (8%, 25%) | 30.6% (20.9%, 42.6%) | <0.001 |
| All | 6.1% (4.8%, 9.7%) | 14.7% (8.5%, 24.9%) | 30.6% (21.2%, 43.1%) | <0.001 |
ROC analyses
Receiver operating characteristic curves are plotted in Figure 3 to characterize the discriminating power of water volume or fraction for mammographic density (b vs (c+d); (b+c) vs d). The area under the curve (AUC) is rather robust to the cutoff, with water fraction > volume.
