**Core Concept**
Therapeutic embolization is a minimally invasive procedure used to block blood flow to a specific area of the body, typically to treat bleeding, tumors, or other vascular malformations. Various materials are used for embolization, each with its own properties and applications.

**Why the Correct Answer is Right**
The correct answer is a material not typically used for therapeutic embolization. Commonly used embolic agents include:
* **Gel foam**: a porous, non-absorbable material that promotes clotting and is often used for temporary embolization.
* **Microcoils**: small, spring-like coils made of metal that are deployed to block blood flow.
* **PVA particles**: polyvinyl alcohol particles that are biocompatible and promote thrombosis.
* **Onyx**: a liquid embolic agent that polymerizes and blocks blood flow.

**Why Each Wrong Option is Incorrect**
**Option A:** Not a commonly used embolic agent, but might be confused with other materials like gel foam.
**Option B:** Not typically used for therapeutic embolization, but might be used in other medical procedures.
**Option C:** This option is not a commonly used embolic agent, and might be confused with other materials like microcoils.

**Clinical Pearl / High-Yield Fact**
When choosing an embolic agent, consider the desired duration of embolization, the size and location of the target vessel, and the potential for complications.

**Correct Answer:** D.