MR imaging of healthy knees in varying degrees of flexion using a stretchable coil array provides comparable image quality compared to a standard knee coil array

• A stretchable 8-channel knee coil array for MR-imaging of the knee was built.
• The stretchable 8-channel knee coil was compared to a standard 8-channel knee coil.
• The stretchable coil provides equal SNR and visibility of anatomical structures.
• The stretchable coil keeps its SNR and image quality even if the knee is flexed.
• This will allow for MR-imaging of the knee under more physiological conditions.

ObjectiveStretchable coils allow knee imaging at varying degrees of flexion. Purpose was to compare a new-developed stretchable 8-channel to a standard 8-channel knee coil array by means of quantitative and qualitative image analysis.Material and methodsIRB approved prospective study. Knee MR imaging in 10 healthy volunteers was performed at 3T using a standard 8-channel and a new-developed stretchable 8-channel coil array at 0°, 45°, and 60° of flexion and at 0° (standard coil). Image parameters were identical. Signal-to-noise ratio (SNR) was determined by combining the images with separately acquired noise data on a pixel-by-pixel basis using MATLAB routines (Natick, MA, USA). Images were qualitatively analysed by two independent radiologists who graded the visibility of several anatomic structures from 1 = not visible to 5 = excellent. ANOVA, Wilcoxon and kappa statistics were used.ResultsMean SNR ± standarddeviation of bone was 54.7 ± 10.4 and of muscle 28.0 ±  4.4 using the stretchable coil array and 54.6 ± 8.2 and 33.4 ± 4.5, respectively, using the standard knee coil array. No statistically significant SNR differences were found between both arrays (bone, p = 0.960; muscle, p = 0.132). SNR was not degraded at higher degrees of flexion. The qualitative image analysis did not reveal statistically significant differences between the stretchable and standard coil array with regard to the visibility of anatomic structures (p = 0.026–1.000). Overall kappa was 0.714.ConclusionStretchable 8-channel coil arrays provide similar SNR and visibility of anatomic structures compared to standard 8-channel knee coil arrays. MR imaging with high SNR will now be possible in flexed knees.