Magnetic resonance imaging of the knee: does foot restraint improve the examination?

Involuntary movement by the patient can cause severe artefacts in magnetic resonance imaging of the knee. We have designed and constructed a device that immobilizes the foot, and thereby the knee. In this way the knee still remains accessible for the application of a variety of surface coils. A retrospective subjective analysis was performed of the magnetic resonance images from a control group of 23 patients who were examined without the restraint device and a study group of 26 patients in whom the device was used. The differences in the central tendency of subjective scores between the control and study groups were not significant for either motion artefact or anatomical conspicuity. However, in terms of dispersion the observed reduction in the study group was significant for anatomical conspicuity (p < 0.05) and almost significant for motion artefact (p < 0.10). These findings suggest that the restraint device may improve image quality by eliminating some of the worst motion artefacts. The device also significantly improves positioning of the knee in relation to the magnet isocentre (p < 0.01).