Non-contrast MRI of synovitis in the knee using quantitative DESS

Abstract

Objectives: To determine whether synovitis graded by radiologists using hybrid quantitative double-echo in steady-state (qDESS) images can be utilized as a non-contrast approach to assess synovitis in the knee, compared against the reference standard of contrast-enhanced MRI (CE-MRI).

Methods: Twenty-two knees (11 subjects) with moderate to severe osteoarthritis (OA) were scanned using CE-MRI, qDESS with a high diffusion weighting (qDESS_High), and qDESS with a low diffusion weighting (qDESS_Low). Four radiologists graded the overall impression of synovitis, their diagnostic confidence, and regional grading of synovitis severity at four sites (suprapatellar pouch, intercondylar notch, and medial and lateral peripatellar recesses) in the knee using a 4-point scale. Agreement between CE-MRI and qDESS, inter-rater agreement, and intra-rater agreement were assessed using a linearly weighted Gwet's AC2.

Results: Good agreement was seen between CE-MRI and both qDESS_Low (AC2 = 0.74) and qDESS_High (AC2 = 0.66) for the overall impression of synovitis, but both qDESS sequences tended to underestimate the severity of synovitis compared to CE-MRI. Good inter-rater agreement was seen for both qDESS sequences (AC2 = 0.74 for qDESS_Low, AC2 = 0.64 for qDESS_High), and good intra-rater agreement was seen for both sequences as well (qDESS_Low AC2 = 0.78, qDESS_High AC2 = 0.80). Diagnostic confidence was moderate to high for qDESS_Low (mean = 2.36) and slightly less than moderate for qDESS_High (mean = 1.86), compared to mostly high confidence for CE-MRI (mean = 2.73).

Conclusions: qDESS shows potential as an alternative MRI technique for assessing the severity of synovitis without the use of a gadolinium-based contrast agent.

Key points: The use of the quantitative double-echo in steady-state (qDESS) sequence for synovitis assessment does not require the use of a gadolinium-based contrast agent. Preliminary results found that low diffusion-weighted qDESS (qDESS_Low) shows good agreement to contrast-enhanced MRI for characterization of the severity of synovitis, with a relative bias towards underestimation of severity. Preliminary results also found that qDESS_Low shows good inter- and intra-rater agreement for the depiction of synovitis, particularly for readers experienced with the sequence.

Keywords: Gadolinium; Knee joint; Magnetic resonance imaging; Osteoarthritis; Synovitis.

Figure 1:

Equation used to create qDESS hybrid images. The white arrow indicates the fluid region overlaid by the synovium. The second qDESS echo was multiplied by the weighting factor β and then subtracted from the first qDESS echo, suppressing fluid.

Figure 2:

Regions used for grading of synovitis. [a] Sagittal view of the knee from a CE-MRI image. The white arrowhead indicates the suprapatellar pouch while the void arrowhead indicates the intercondylar notch region (sometimes referred to as Hoffa’s or infrapatellar fat pad, however we have used intercondylar notch to maintain consistency with reference 30). [b] Axial multiplanar reformat of the knee from a CE-MRI image. The white arrowhead indicates the lateral peripatellar recess, while the void arrowhead indicates the medial peripatellar recess.

Figure 3:

Example case for each region where radiologists tended to agree on severity of synovitis on CE-MRI, qDESS_Low, and qDESS_High images. In the suprapatellar images, mild uniform synovial thickening is demonstrated in the suprapatellar pouch without obvious nodularity (grade 1, white arrowhead). In the medial and lateral recess images, synovial thickening is more conspicuous with the suggestion of nodularity in the lateral recess images (grade 2, green and blue arrowheads respectively). In the intercondylar notch images, there is nodular synovial enhancement anterior to the anterior horn of the lateral meniscus visible on all sequences (grade 2, red arrowhead). Note qDESS_Low and CE-MRI demonstrate better spatial resolution than qDESSHigh on the axial reformats used to grade the medial and lateral recesses due to reduced slice thickness.

Figure 4:

Example case for each region where radiologists tended to grade severity of synovitis higher on CE-MRI compared to qDESS_Low and qDESS_High. In the suprapatellar region, diffuse smooth synovial enhancement is definitely present on CE-MRI images (grade 1, white arrowhead) but no discernable synovial thickening is apparent on the qDESS images (grade 0, white arrowhead). In the lateral recess, nodularity is evident posteriorly on the CE-MRI images (grade 2, blue arrowhead) but not on the qDESS images (grade 1, blue arrowhead). Similarly, in the medial recess, an area of possible nodularity is visible medially on the CE-MRI images (grade 2, green arrowhead) but not as conspicuous on the qDESS images (grade 1, green arrowhead). In the intercondylar notch region, the posterior surface of Hoffa’s fat pad has a nodular appearance (grade 2, red arrowhead) but appears as uniform linear enhancement on the qDESS images (grade 1, red arrowhead). Note that in all illustrative cases synovitis has been graded as present on both CE-MRI and qDESS, but with a lower qDESS grade.

Figure 5:

Tables of agreement between qDESS_Low and CE-MRI and qDESS_High and CE-MRI for the overall impression of synovitis and regional grading.

Figure 6:

Radiologist diagnostic confidence in CE-MRI, qDESS_Low, and qDESS_High gradings. A rating of 3 represented high confidence, 2 represented moderate confidence, 1 represented low confidence, and 0 represented no confidence.