Contrast-enhanced pseudo-CT of finger joints: Improved diagnostic confidence for detection of inflammatory erosions

Purpose: To evaluate the interest of additional pseudo-CT images to standard clinical contrast-enhanced MR images (CE-MRI) in the detection of inflammatory erosions and to differentiate them from intraosseous ganglia at the finger joints.

Method: 47 prospectively included patients with suspected or diagnosed rheumatoid arthritis received a CE-MRI of the fingers. Additionally, pseudo-CT images were derived from non-contrast MRI (pCT) and from contrast-enhanced MRI data (CE-pCT) using a high-resolution gradient-echo 3D fast low-angle shot sequence (FLASH), respectively. CE-MRI, pCT, and CE-pCT images were evaluated for erosions and intraosseous ganglia at the metacarpophalangeal and proximal interphalangeal joints by two musculoskeletal radiologists. Findings were defined on CE-MRI by an experienced independent 3rd reader which served as reference standard. Diagnostic confidence (1 = worst, 4 = best) was rated for 3 different image sets (1 = CE-MRI, 2 = CE-MRI + pCT, 3 = CE-MRI + CE-pCT) and compared.

Results: Reference standard revealed 44 erosions and 37 intraosseous ganglia on CE-MRI. Diagnostic confidence for CE-MRI was moderate for erosions (both readers) and intraosseous ganglia (reader 2). For the combination of CE-MRI and pCT, high confidence levels were observed for erosions for both readers (median 3 (Q1-Q3: 2.5-3) and 3 (3-3); p<.001 and p<.001) and for intraosseous ganglia for reader 2 (3 (3-3); p<.001). CE-MRI combined with CE-pCT showed very high confidence levels for both readers for erosions (4 (3-4) and 4 (4-4); p<.001 and p<.001) and for intraosseous ganglia (4 (4-4) and 4 (4-4); p<.001 and p<.001).

Conclusions: Pseudo-CT combined with CE-MRI increases the confidence in detection of inflammatory erosions at the finger joints, with CE-pCT being superior to pCT.