EFFECT OF KNEE POSITIONING DURING MRI SCAN ON SEGMENTED CARTILAGE VOLUME

INTRODUCTION

Non-invasive monitoring of VC using segmentation of MRI images has become vital part of clinical trials and longitudinal OA studies. Many parts of protocol such as MR sequence parameters, MR hardware or time between follow-ups are fixed to ensure that the observed change in VC caused by degenerative/regenerative processes and not by other confounders. Consistent patient positioning during follow-up visits improves the overall precision, however due to various reasons, such as pain, same positioning might not be possible.

OBJECTIVE

Objective of this study was to assess an effect of the patient positioning on the femoral VC.

METHODS

The left knees of eight healthy volunteers (4 male, 4 female, mean age: 35.5 ± 10.2 years) were scanned on 3T Siemens PrismaFit (Siemens Healthineers AG, Forchheim, Germany). The 3D DESS (TE=5ms, TR=14.1ms, 160 slices, 0.6x0.6x0.6mm3, flip angle=25°, acquisition=5:58min) was used. Each volunteer's patella center was marked with a black line, and two additional lines spaced 1cm apart were drawn on each side. A dedicated 15-channel knee coil was positioned to align these lines with the scanner laser, resulting in five different knee positions: neutral, two medial rotations, and two lateral rotations. Knee rotation angles were measured using RadiAnt DICOM Viewer (Medixant, Poznań, Poland) (Fig. 1). Images were segmented automatically using MR ChondralHealth version 3.1 research application software (Siemens Healthineers AG, Forchheim, Germany), then manually edited if needed. Voxel volume times number of voxels yielded the VC for nine femoral cartilage regions: medial anterior (MaF)/central (McF)/posterior (MpF); trochlear lateral (TL)/central (TC)/medial (TM) and lateral anterior (LaF)/central (LcF)/posterior (LpF). The correlation between knee rotation angle and VC was assessed using Spearman's correlation coefficient.

RESULTS

Observed correlations were as follows: MaF = -0.06, McF = -0.18, MpF = -0.3, TL = 0.07, TC = 0.05, TM = 0.01, LaF = 0.15, LcF = -0.12, LpF = -0.2.

CONCLUSION

While there are observable correlations between knee rotation angle and femoral VC in healthy individuals, these correlations are generally weak and vary across different cartilage regions. Volume of trochlear cartilage is essentially unaffected by knee positioning, while the posterior condyle region exhibit weak negative correlation, implying the false VC decrease. Further quantification of the effect using linear mixed effects models is planned in the future. While the impact of positioning on VC is negligible, if the anticipated change in VC is expected to be small in longitudinal studies, it's crucial to validate the intended segmentation method in comparable situations.