Table 1.
Repeatability and range, averaging over diseased and non-diseased joints
| MR biomarker | Patients with two baseline scans | Treated patients at baseline | ||||
|---|---|---|---|---|---|---|
| N for repeatability | Repeatability (intra-subject CoV %) | Variability (inter-subject CoV %) | N for range | Geometric mean | Range | |
| K trans (min-1) | 14 | 30.0% | 59.3% | 45 | 0.069 | 0.025–0.273 |
| IRE (mM.s-1) | 14 | 29.5% | 51.3% | 45 | 0.003 | 0.001–0.013 |
| IAUC 60 (mM.s) | 14 | 31.4% | 58.3% | 45 | 7.69 | 1.92–28.17 |
| IAUC 120 (mM.s) | 14 | 29.3% | 55.7% | 45 | 18.23 | 5.58–70.27 |
| VEP (mL) | 15 | 22.0% | 41.3% | 45 | 1.06 | 0.20–2.48* |
| ME (mM) | 14 | 27.5% | 52.4% | 45 | 0.32 | 0.11–1.31 |
| v e (%) | 0 | n/a | n/a | 0 | n/a | n/a |
| v p (%) | 14 | 53.4% | 60.1% | 45 | 1.2 | 0.3–4.5 |
| RAMRIS synovitis score** | 13 | 1.30 (SD) | 6.20 (SD) | 31 | 6.95 (arithmetic mean) | 0.0–21.8 |
*VEP excludes non-enhancing pannus. The range for total (non-enhancing plus enhancing) pannus was 3.29-8.30 ml
** VEP and the DCE-MRI endpoints are log-normally distributed but RAMRIS synovitis score is not. Therefore geometric mean and intra-subject CoV were calculated for VEP and the DCE-MRI endpoints, while arithmetic mean and intra-subject SD were calculated for RAMRIS synovitis score. The intra-class correlation coefficients were respectively 0.958 for RAMRIS synovitis score and 0.777 for K trans. RAMRIS synovitis score is based on an ordinal scale (0–24) so there is a restriction on how many values the synovitis score can actually take, therefore increasing the chance of a repeatable result. Given this, a direct comparison in repeatability with K trans is difficult
CoV coefficient of variation, DCE-MRI dynamic contrast-enhanced MRI, IAUC 60 IAUC 120/mM.s initial area under the Gd-CA concentration curve over 60 s or 120 s post-arrival in tissue, IRE/ mM.s-1 initial rate (gradient) of enhancement following Gd-CA over 60 s post-arrival in tissue, K trans/min-1 volume transfer constant for Gd-CA between blood plasma and extravascular extracellular space, ME/mM maximum enhancement of Gd-CA concentration curve during DCE-MRI series, RAMRIS RA MRI score, SD standard deviation, T 1 /s longitudinal relaxation time, v e volume of extravascular extracellular space per unit volume tissue, v p volume of blood plasma volume per unit volume tissue, VEP/ml volume of enhancing pannus