Proton density weighted spin-echo images

Proton density (PD) weighted images are related to the number of nuclei in the area being imaged (number of hydrogen protons), as opposed to the magnetic characteristics of the hydrogen nuclei. They are produced from the first echo. Proton density weighted images result when the contribution of both T1 and T2 contrast is minimized.  They have a long TR (2000+ms) to minimize T1 differences because all tissues exhibit full longitudinal relaxation before the next 90 degrees RF pulse. They have a short TE (TE1, 20ms) to minimize T2 differences. High proton density tissues appear bright.