Segment-wise analysis

Comparison of scores between active vs inactive segments for each modality

From the figures above, the scores are in general significantly different between active and inactive (\(p\)-values based on the Wilcoxon-rank-sum test). However, MRI appears to be less discriminating than PET and PET/MR.

Comparison of diagnostic strength between modalities

We plot the receiver operating characteristic (ROC) curves for each modality below, along with the area under the curve (AUC) and 95% confidence limits (CL). Table 1 shows the \(p\)-values comparing the modality-specific AUCs by the DeLong et al. (1988) test.

Table 1. Modality-specific AUC (95% CL) and p-values comparing the modalities.
MR AUC PET AUC PET/MR AUC MR v PET MR v PET/MR PET v PET/MR
Overall 0.803 (0.699, 0.907) 0.876 (0.79, 0.963) 0.892 (0.813, 0.971) 0.152 0.020 0.562
A colon/TI/cecum 0.902 (0.783, 1) 0.907 (0.795, 1) 0.956 (0.877, 1) 0.948 0.307 0.220
Colon T 0.708 (0.404, 1) 0.917 (0.794, 1) 0.931 (0.82, 1) 0.051 0.051 0.386
Rectum/sigmoid/descending 0.679 (0.433, 0.925) 0.792 (0.563, 1) 0.775 (0.554, 0.996) 0.343 0.294 0.774

Overall, it appears that PET/MR > PET > MRI in terms of diagnostic performance.

SUVmax and change score from MRI to PET/MRI

The distributions of change score (\(-1, 0, 1, 2, 3\)) for active and inactive cases are plotted below (\(p\)-values based on the Wilcoxon-rank-sum test). The scores for inactive cases mostly stay put (i.e., change score 0), and those for active cases are mostly increased (i.e., change score 1–3). This explains the improvement of diagnostic performance by PET/MR as compared to MRI.

Boxplots of SUVmax in active and inactive cases are shown below (\(p\)-values based on the Wilcoxon-rank-sum test). The values are increased in active cases to varying degrees by segment.

Patient-level analysis

Boxplots and ROC curves for patient-level status are plotted below by modality. it appears that PET/MR > MRI > PET in terms of diagnostic performance.

Table 2. Modality-specific AUC (95% CL) and p-values comparing the modalities for patient-level status.
MR AUC PET AUC PET/MR AUC MR v PET MR v PET/MR PET v PET/MR
Patient-level 0.873 (0.737, 1) 0.828 (0.664, 0.993) 0.931 (0.839, 1) 0.667 0.349 0.07

References