The sagittal proton density images (Fig. 8.2) are critical for evaluation for the menisci, cruciate ligaments, and articular cartilage. With the timing parameters shown, joint fluid has high signal intensity, providing high contrast against the articular cartilage. These images are prescribed from the coronal T1-weighted images and cover from just medial to the medial collateral ligament to just lateral to the lateral collateral ligament. Evaluation of the menisci in this plane requires the use of short echo trains and reduced inter-echo spacing to avoid blurring of meniscal tears due to T2 relaxation and low SNR in the peripheral portions of k-space. With the reduced echo spacing available on the Signa LX platform, an echo train length of 6 allows adequate visualization of meniscal tears while optimizing scan efficiency. The use of the 512 matrix should not increase the scan time if the bandwidth is set correctly.

Figure 8.2 (click on image to see enlarged view) Sagittal PD-weighted image showing a joint effusion (arrow).