In a dual contrast spin echo sequence, what characteristic does the second echo image have compared to the first echo image?

In a dual contrast spin echo sequence, the second echo image typically demonstrates more T2 contrast compared to the first echo image. This occurs due to the inherent differences in T1 and T2 relaxation times of tissues.

The first echo image is often captured shortly after the initial 90-degree RF pulse and reflects a combination of both T1 and T2 effects. As time progresses to the second echo, T2 weighting becomes more significant since T2 decay occurs faster than T1 recovery. Tissues with longer T2 times will retain more signal, allowing for differentiation based on T2 characteristics. Thus, the second echo is more sensitive to the differences in T2 decay rates among various tissues, enhancing the visibility of structures such as edema or fluid collections.

This increased T2 contrast can be advantageous in identifying pathologies where T2 effects are pronounced, making this technique valuable in clinical MRI applications.