Multiplanar gradient recalled images of the knee: comparison of different flip angles and echo times

To determine the most appropriate combination of echo time (TE) and flip angle in gradient echo images of the knee, the authors used different TEs (10, 20 and 30 msec) and flip angles (10, 30, 50, 70, 90, 120 and 150 degrees) to perform a systematic study of MRI on 10 volunteer knees. Contrast-to-noise ratios of cartilage-fat, fluid-cartilage, fluid-fat and fluid-ligament were calculated and compared. Images with a 30-degree flip angle combined with 20 msec of TE were found to have the best contrast-to-noise ratios in both objective data analysis and subjective observation. Hyaline cartilage of the knee was hyperintense and was well delineated on this pulse sequence, appearing distinct in contrast to the intra-articular fluid. It is concluded that this T2-weighted gradient echo pulse sequence is an alternative to conventional spin echo T2-weighted imaging of the knee.