Overview Penile Duplex Doppler Ultrasound is the way to look inside the penis and to understand what is going on. The Doctors will interpret this important test in a way that will help you finally know whether it is in your head or in your penis. 80% of the time it is a blood flow problem and it isn't a psychological issue. This information is often invaluable in helping couples to understand the cause of ED and in accepting that it is indeed a physical problem. The acceptance often begins an important aspect of the healing process allowing the couple to work past psychological second-guessing.