**Core Concept**
Penile angiography is a diagnostic imaging technique used to visualize the blood vessels of the penis, particularly in cases of erectile dysfunction (ED). The procedure involves injecting a contrast agent into the penile arteries, which are then visualized using X-ray imaging. The reliability of penile angiography depends on the presence of adequate blood flow to the penis, which is ensured by the intracavernosal injection of vasoactive substances.

**Why the Correct Answer is Right**
The intracavernosal injection of vasoactive substances, such as papaverine or alprostadil, is necessary to induce an erection and ensure that the penile arteries are visualized accurately. This is because the penile arteries are not always patent, and the injection of vasoactive substances helps to overcome any vascular resistance and promote blood flow to the penis. Without this injection, the penile angiography may not be reliable, as the arteries may not be adequately visualized.

**Why Each Wrong Option is Incorrect**
**Option A:** Peyronie's disease is a condition characterized by the development of fibrous scar tissue in the penis, leading to curvature and pain. Penile angiography may be used to evaluate the vascular component of Peyronie's disease, making it a valid indication for the procedure.
**Option B:** Priapism is a condition characterized by a prolonged and painful erection, which can be caused by various factors, including vascular disorders. Penile angiography may be used to diagnose and treat priapism, making it a valid indication for the procedure.
**Option C:** Erectile dysfunction (ED) is a common condition characterized by the inability to achieve or maintain an erection. Penile angiography is a valid diagnostic tool for ED, as it can help identify any underlying vascular or anatomical abnormalities.

**Clinical Pearl / High-Yield Fact**
When performing penile angiography, it is essential to ensure that the patient is properly informed and consented for the procedure, as it involves the injection of a contrast agent and the use of X-ray imaging.

**Correct Answer: D.**