| UW (N = 53) | UTSW (N = 42) | JHU (N = 29) | Stanford (N = 37) | Overall (N = 161) | |
|---|---|---|---|---|---|
| Age | 50 (23, 59) | 46 (36, 56.8) | 47 (20, 59) | 17 (13, 22) | 41 (19, 56) |
| Sex - m | 34 (64.2%) | 25 (59.5%) | 15 (51.7%) | 20 (54.1%) | 94 (58.4%) |
| Sex - f | 19 (35.8%) | 17 (40.5%) | 14 (48.3%) | 17 (45.9%) | 67 (41.6%) |
| Weight | 75.3 (65.4, 97.1) | 83.6 (61.5, 105.7) | 66.2 (59, 79.4) | 52.5 (35.2, 67.2) | 69 (58.8, 90.1) |
| Height | 172.7 (162.6, 178) | 172.7 (162.5, 182.9) | 167.6 (160, 174) | 155 (139.3, 165.1) | 168 (158, 177.9) |
| Ferriscan | 3.4 (1.9, 6.5) | 1.4 (0.7, 2.5) | 3.2 (1.2, 7) | 3 (1.4, 7.7) | 2.6 (1.2, 6.5) |
Multi-Center Multi-Vendor Validation of Liver QSM in Patients with Iron Overload
Subject characteristics
Descriptive statistics for subject-level variables are tabulated below by site and overall. Quantitative variables are summarized by median (inter-quartile range; IQR) and categorical variables by N (%).
Linear regressions of QSM vs R2* and QSM vs LIC
Numbers of observations per site, field strength (FS), and test/retest are tabulated below.
| Site | FS | Retest | n |
|---|---|---|---|
| UW | 1.5 | test | 47 |
| UW | 1.5 | retest | 10 |
| UW | 3.0 | test | 50 |
| UW | 3.0 | retest | 7 |
| UTSW | 1.5 | test | 42 |
| UTSW | 1.5 | retest | 33 |
| UTSW | 3.0 | test | 42 |
| UTSW | 3.0 | retest | 20 |
| JHU | 1.5 | test | 18 |
| JHU | 1.5 | retest | 6 |
| JHU | 3.0 | test | 24 |
| JHU | 3.0 | retest | 4 |
| Stanford | 1.5 | test | 32 |
| Stanford | 3.0 | test | 25 |
QSM vs R2*
Site-specific regression lines of QSM vs R2* for each FS and test/retest scenario are plotted below.
We perform F-tests (with 2 degrees of freedom for intercept and slope) to compare the regression lines between pairs of sites. The p-values are summarized in Table 3a.
| UW vs UTSW | UW vs JHU | UW vs Stanford | UTSW vs JHU | UTSW vs Stanford | JHU vs Stanford | |
|---|---|---|---|---|---|---|
| 1.5T | 0.324 | 0.16 | 0.054 | 0.556 | 0.003 | 0.067 |
| 3.0T | 0.385 | <0.001 | <0.001 | <0.001 | 0.205 | <0.001 |
QSM vs LIC
Site-specific regression lines of QSM vs liver iron concentration (LIC) for each FS and test/retest scenario are plotted below. Test data also show stronger associations than retest data do.
Similarly, we perform F-tests to compare the regression lines between pairs of sites. The p-values are summarized in Table 3b.
| UW vs UTSW | UW vs JHU | UW vs Stanford | UTSW vs JHU | UTSW vs Stanford | JHU vs Stanford | |
|---|---|---|---|---|---|---|
| 1.5T | 0.298 | 0.069 | 0.052 | 0.469 | 0.002 | 0.023 |
| 3.0T | 0.066 | <0.001 | <0.001 | 0.195 | 0.16 | 0.003 |
Repeatability & reproducibility of QSM
Test-retest repeatability
Bland-Altman plots (difference vs mean) for test-retest QSM are plotted by FS and overall below. Data points are color-coded by site.
The bias (mean test-retest difference), repeatability coefficient (RC; range covering 95% test-retest differences), intraclass correlation coefficient (ICC) with 95% confidence interval (CI) and p-value (for testing ICC = 0) are presented in Table 4 below.
| FS | Bias | RC | ICC | P |
|---|---|---|---|---|
| 1.5T | -0.005 | 0.228 | 0.96 (0.93, 0.977) | <0.001 |
| 3T | 0.005 | 0.166 | 0.984 (0.968, 0.992) | <0.001 |
| Overall | -0.001 | 0.205 | 0.971 (0.955, 0.981) | <0.001 |
Field strength reproducibility
The Bland-Altman plot for reproducibility between 1.5T and 3T is shown below, with bias, ICC (95% CI), and p-value indicated on the figure.
Sex differences in LIC
LIC values are compared between females and males by site and overall in Table 5 below. The p-values are based on the Wilcoxon rank sum test.
| Site | Female | Male | P |
|---|---|---|---|
| UW | 3.8 (2.3, 6.1) | 3.3 (1.7, 7.3) | 0.926 |
| UTSW | 2.4 (1.4, 5.8) | 0.9 (0.7, 1.6) | 0.021 |
| JHU | 5.4 (2, 7.3) | 2.4 (1, 5.2) | 0.149 |
| Stanford | 6.2 (2.3, 9.4) | 2.5 (1.2, 3.9) | 0.037 |
| Overall | 3.9 (1.9, 6.9) | 2 (1, 4.1) | 0.003 |
The following boxplot visualizes the comparisons.
Sex differences in QSM vs (R2*, LIC)
Sex-specific regression lines of QSM vs R2* for each FS and test/retest scenario are plotted below, with F-test p-values comparing the two lines indicated on the plots.
Similarly, sex-specific regression lines of QSM vs LIC for each FS and test/retest scenario are plotted below, with F-test p-values comparing the two lines indicated on the plots.
