MOTION ARTIFACT AS A PITFALL IN DIAGNOSIS OF MENISCAL TEAR ON GRADIENT REORIENTED MRI OF THE KNEE

Objective: Reorientation of the phase and frequency encoding gradients is frequently performed for knee MRI to improve visualization of the cruciate ligaments. This technique allows pulsation artifacts arising from the popliteal vessels to be redirected away from the intercondyla r notch. The objective of this study was to evaluate the potential for this method to result in false-positive depictions of meniscal tears based on subtle patient motion. Materials and Methods: Magnetic resona nce imaging of the knee was performed in five patients using gradient reorientation. Repeat examinations were then performed following delib erate instruction to the patients regarding the importance of refraini ng from moving the extremity. Results: The MRI performed with gradient reorientation demonstrated apparent meniscal tears using standard cri teria. However, the repeat examinations following deliberate patient i nstructions to refrain from moving demonstrated the affected menisci t o be normal in all patients. Conclusion: Knee motion during image acqu isition may result in ghosting artifacts of relatively high signal int ensity structures such as marrow within the femoral condyles and hyali ne cartilage along the articular surfaces. These artifacts may travers e the menisci on gradient-reoriented images and result in confusion wi th meniscal tear. Whereas gradient reorientation is a valuable tool fo r improving depiction of the cruciate ligaments, one must be aware of the potential for this technique to result in simulation of meniscal t ears.