Embolization coils, particles, plugs and liquid agents are materials used to reduce or stop blood flow through carefully selected vessels. Some are designed to remain permanently, while others create a temporary blockage or act on the vessel without leaving the same type of permanent implant.
The choice is not based on which material is newest or strongest. It depends on the size and type of vessel, how quickly blood is flowing, how precisely the vessel must be treated, whether the blockage should be temporary or permanent, and which tissues must be protected. Patients should ask which agent is planned for their procedure and why it suits that specific treatment.
What Is an Embolic Agent?
An embolic agent is a medical material delivered through a catheter to reduce or stop blood flow in a selected artery, vein or abnormal vascular channel.
During embolization, the doctor guides a catheter or smaller microcatheter towards the target vessel using live X-ray imaging. Once the position has been checked, the selected material is delivered in a controlled manner.
Depending on the clinical purpose, the agent may:
- Form a physical barrier inside a vessel
- Encourage clot formation around the material
- Travel into smaller branches and reduce blood flow
- Close an abnormal vein
- Seal a bleeding vessel
- Produce a temporary interruption of blood flow
- Create a more permanent vessel closure
Embolization is used for several different conditions. This is why one material cannot be used in the same way for every patient or every procedure. Coils, particles, plugs, foam and liquid agents have different properties and treatment roles.
Main Types of Embolization Materials
The main categories include:
- Coils
- Particles and microspheres
- Vascular plugs
- Temporary agents
- Liquid embolic agents
- Sclerosants and foam
Some procedures use one category. Others may use a combination.
What Are Embolization Coils?
Embolization coils are small metal devices placed inside a selected blood vessel.
Although they are called coils, their size and design vary. Some are pushed through the catheter, while others can be positioned more carefully and released only after the doctor is satisfied with their location.
Once placed, a coil creates a framework that slows blood flow and encourages clot formation around it. The vessel then becomes closed or substantially reduced in flow.
Coils are commonly used when the doctor wants to treat a defined vessel rather than distribute particles through many smaller branches.
They may be used for:
- Abnormal veins
- Selected bleeding vessels
- Aneurysms
- Abnormal artery-to-vein connections
- Vessel branches that need controlled closure
- Varicocele embolization
Varicocele embolization commonly uses coils, liquid material, sclerosant or a combination to close the abnormal testicular vein and redirect blood through healthier venous pathways.
Do Embolization Coils Stay in the Body?
Coils used for vascular embolization are generally intended to remain at the treatment site permanently.
They are not usually removed after the vessel has closed. Over time, clot and healing tissue form around the coil, helping maintain the intended vessel occlusion.
A permanent coil does not mean that the patient should continuously feel it. The coil is located inside a blood vessel and is usually not noticeable during normal daily activities.
Patients should nevertheless keep a record of:
- The procedure performed
- The date
- The hospital
- The treated vessel
- The type of implant, when available
- Any implant or device card provided
This information can be useful before future scans, operations or vascular procedures.
Can an Embolization Coil Move?
Coils are selected and positioned to remain within the intended vessel.
The doctor considers:
- Vessel diameter
- Blood-flow speed
- Coil size
- Coil shape
- Landing position
- Nearby branches
- Whether additional coils or another material are required
Coil migration is a recognised but uncommon complication. It means that a coil moves away from the intended treatment position. The clinical effect depends on where it moves and whether it affects another vessel.
Careful vessel measurement, controlled release and appropriate coil selection are used to reduce this risk. It should not be described as impossible, particularly because rare migration cases have been reported.
Patients should not assume that an occasional unfamiliar sensation after treatment means a coil has moved. New or persistent symptoms require clinical assessment rather than self-diagnosis.
Can Embolization Coils Be Removed?
Routine removal is not expected because embolization coils are designed to remain in place.
Retrieval may occasionally be considered when:
- A coil has not been released fully and can still be repositioned
- The device is recognised as being in an unintended location during the procedure
- Migration causes a clinically important problem
- Another unusual complication requires intervention
Removing a coil after tissue has healed around it can be technically difficult and may require another endovascular procedure or, rarely, surgery.
Patients should not plan embolization with the expectation that the material will be removed later. The intended permanence should be understood before consent.
What Are Embolization Particles?
Embolization particles are very small medical materials delivered through a catheter into selected arterial branches.
Unlike coils, which usually remain at a defined point in a vessel, particles can travel with blood flow into smaller downstream branches.
Particles may be:
- Irregular in shape
- More uniformly calibrated
- Available in different size ranges
- Designed for temporary or permanent vessel reduction
- Selected according to the tissue and treatment objective
Particle size matters because smaller particles may travel farther into the vascular network, while larger particles tend to stop in larger branches.
The doctor must match the material and size to the intended level of treatment. Using particles that travel too far could affect normal tissue. Using particles that stop too early may not achieve the intended treatment effect.
Do Embolization Particles Stay in the Body?
Many commonly used particles are intended to remain in the treated vessels.
They lodge within small arterial branches and contribute to a reduction in blood supply. The surrounding vessel then undergoes clotting and healing changes.
However, not every particle or embolic material is permanent. Some agents are designed to be absorbed or to create only a temporary blockage.
The answer therefore depends on:
- The exact product
- The material
- The procedure
- The intended duration of vessel closure
- The doctor’s treatment plan
Patients should ask for the name or type of material when they want a procedure-specific answer.
Where Are Particles Commonly Used?
Particle embolization may be used when treatment requires reduction of blood flow through multiple small arterial branches.
Examples include selected patients undergoing:
- Prostate artery embolization
- Uterine artery embolization
- Genicular artery embolization
- Thyroid artery embolization
- Transarterial microembolization
The exact material and particle size can differ between these procedures. A particle suitable for an enlarged prostate should not automatically be assumed to be the material used around a knee or thyroid.
Uterine fibroid embolization, for example, commonly uses small particles to reduce blood flow through uterine arterial branches supplying fibroids.
What Are Vascular Plugs?
A vascular plug is a mechanical device used to close a selected vessel.
It is delivered through a catheter in a compressed form and expands after placement. The plug slows or stops flow and supports clot formation within the target vessel.
Plugs may be considered when:
- A relatively defined vessel needs closure
- The vessel is larger than one typically treated with particles
- Controlled mechanical occlusion is preferred
- One device may provide an appropriate alternative to several coils
- Precise placement is possible
Like coils, vascular plugs are generally intended as permanent implants.
A plug is not the same as an angioplasty stent. A stent is usually used to support an open vessel. A vascular plug is used to help close a selected vessel.
What Are Temporary Embolization Agents?
Some situations require temporary rather than permanent interruption of blood flow.
Temporary agents may be used when the doctor expects the vessel to recanalise or wants the material to be absorbed over time.
One example is absorbable gelatin material, sometimes described as gelatin sponge or gelfoam. It can be cut or prepared into small pieces and delivered into a vessel.
Temporary embolization may be considered for selected bleeding situations or other clinical circumstances where permanent closure is not required.
“Temporary” does not mean that blood flow returns at an exact predictable time in every patient. The duration can vary according to:
- Material preparation
- Vessel size
- Blood flow
- Quantity used
- Patient clotting response
- The underlying condition
Temporary materials still require careful targeting and carry risks if they affect the wrong vessel.
What Are Liquid Embolic Agents?
Liquid embolic agents are materials delivered in a liquid state that solidify, polymerise or create vessel closure after injection.
They may reach vessel spaces that cannot be treated in the same way with a coil or plug.
Examples include medical adhesive agents and non-adhesive liquid embolic materials. These agents require careful technique because their movement depends on blood flow, catheter position, injection rate and the behaviour of the material.
Liquid agents may be used for selected:
- Abnormal vascular connections
- Vascular malformations
- Bleeding vessels
- Tumours
- Venous procedures
- Complex embolization targets
Many liquid embolic agents create permanent occlusion. They are not suitable for every vessel or procedure.
The treating doctor must understand how the agent behaves before and during delivery. Precise angiography and microcatheter positioning are particularly important.
What Are Sclerosants and Foam?
A sclerosant is a medicine that irritates the inner lining of a vein and causes it to close.
It may be delivered as a liquid or foam. The treatment effect comes from interaction with the vessel wall rather than from leaving a metal implant in the vein.
Sclerosants may be used alone or with coils in selected venous procedures, including some cases of varicocele embolization.
The choice between coils, sclerosant, plugs or a combined technique depends on:
- Venous anatomy
- Reflux pattern
- Side branches
- Previous surgery
- Flow
- Operator assessment
- Risk of material reaching unintended veins
A sclerosant should not be confused with arterial particles used for PAE, UAE or GAE.
Coils vs Particles: What Is the Practical Difference?
| Feature | Coils | Particles |
| Form | Small metal device | Tiny medical particles or microspheres |
| Placement | Usually positioned at a defined vessel segment | Travel into smaller downstream branches |
| Main action | Mechanical slowing and clot formation | Reduction of flow through multiple smaller branches |
| Typical target | A selected vessel or vein | A network of small arterial branches |
| Permanence | Usually permanent | Depends on the product, though many are permanent |
| Visibility during treatment | Usually clearly visible on X-ray | Delivery is monitored through contrast flow rather than seeing every individual particle |
| Common examples | Varicocele veins, selected bleeding vessels | PAE, UAE, GAE and other small-vessel arterial procedures |
| Can both be used together? | Yes, in selected procedures | Yes, when the treatment plan requires a combination |
This is a general comparison. The material is selected according to the vessel and treatment objective, not simply according to the name of the condition.
How Does the Doctor Choose an Embolic Agent?
The doctor considers several technical and clinical questions.
What size vessel is being treated?
A large, defined vessel may be suited to a plug or coils. A network of small branches may require particles.
Is the target an artery or vein?
Arterial and venous flow behave differently. A material used for a uterine artery is not automatically appropriate for a testicular vein.
Should the closure be temporary or permanent?
Some bleeding situations may require temporary flow interruption. Other treatments are intended to produce lasting closure.
How fast is blood flowing?
High-flow vessels may require a material that can be positioned securely. Flow also affects how far particles or liquid agents may travel.
How close are important normal branches?
The doctor must identify arteries or veins that supply healthy tissue. A more selective catheter position or different agent may be needed when important branches are nearby.
How far into the vessel should the treatment reach?
Some treatments aim for closure near the catheter position. Others require embolization of smaller downstream branches.
Does the patient have a clotting disorder?
Some mechanical agents partly depend on the patient’s clotting response. The wider medical situation may influence material choice.
Has the patient had previous treatment?
Surgery, prior embolization or altered anatomy may change which vessels remain open and which material is suitable.
Is One Embolization Material Better Than Another?
No embolic agent is universally better.
A material may be highly suitable for one vessel and inappropriate for another.
The quality of embolization depends on:
- Correct diagnosis
- Appropriate patient selection
- Detailed vessel mapping
- Selective catheter placement
- Choosing the correct agent
- Choosing the correct size
- Controlled delivery
- Protecting non-target vessels
- Confirming the final change in blood flow
Patients should be cautious about promotional claims suggesting that one coil, particle or glue technique is always safer, permanent or superior.
The correct question is:
Why is this material suitable for my vessel and my treatment goal?
Can Embolization Materials Affect MRI Scans?
The answer depends on the exact implant.
Many modern embolization coils and plugs are labelled MR Conditional. This means MRI may be performed only under the conditions stated for that particular device.
MR Conditional does not mean that every MRI scanner, field strength and scanning protocol is automatically acceptable.
Before an MRI:
- Tell the radiology team that you have undergone embolization
- Provide the procedure report when available
- Bring the implant card if one was supplied
- Mention the treated body area
- State when the procedure was performed
- Allow the MRI team to verify the device and its conditions
The FDA advises patients with implants to bring identifying device information so the MRI team can confirm whether the device is MR Safe, MR Conditional or unsuitable under the planned conditions.
Do not cancel a medically required MRI solely because a coil was placed. Do not proceed without informing the MRI team either.
Particles and liquid agents do not all carry the same MRI considerations as metallic implants, but the previous embolization should still be disclosed.
Will Coils Interfere With Future Scans or Procedures?
Coils can sometimes create a local imaging artefact, particularly near the treated area. This may affect how clearly nearby structures are seen on certain scans.
The importance depends on:
- Coil material
- Number of coils
- Coil location
- Imaging method
- Body area being examined
- Clinical question
Future doctors should also know about previous embolization before:
- Another vascular procedure
- Surgery near the treated vessel
- MRI
- CT angiography
- Catheter angiography
- Treatment requiring vascular access
Keeping the procedure report is more useful than trying to remember only that “a coil was placed.”
Are Embolization Materials Allergic?
The embolic material, contrast, medicines, dressings and anaesthetic agents are separate substances.
A previous reaction to contrast does not necessarily mean that a patient is allergic to a coil or particle. Similarly, a metal sensitivity from jewellery does not automatically predict a reaction to a vascular implant.
Tell the doctor about:
- Previous contrast reactions
- Known medicine allergies
- Previous implant reactions
- Latex allergy
- Dressing or adhesive reactions
- Any documented metal allergy
- The symptoms and severity of previous reactions
The team can then assess which part of the procedure may require modification.
What Are the Main Material-Related Risks?
Possible risks depend on the agent and treatment site.
They may include:
- Material reaching an unintended vessel
- Inadequate vessel closure
- Vessel reopening or development of collateral flow
- Coil migration
- Vessel injury
- Excessive reduction of blood supply
- Damage to non-target tissue
- Inflammation or pain
- Need for further embolization
- Difficulty with future imaging near a metallic implant
- Rare need for device retrieval or another procedure
The purpose of explaining these risks is not to suggest they are expected. It is to make clear why material selection and precise delivery matter.
What Is Non-Target Embolization?
Non-target embolization occurs when an embolic agent affects a vessel or tissue outside the intended treatment area.
This can happen if:
- The catheter is not sufficiently selective
- A small connecting branch is not recognised
- Blood-flow direction changes
- The selected particle size is unsuitable
- A liquid agent travels beyond the target
- A coil or other device changes position
Doctors reduce this risk through:
- Detailed angiography
- Selective microcatheter placement
- Careful study of nearby branches
- Controlled injection
- Appropriate material and size selection
- Repeated imaging during treatment
- Stopping delivery when flow changes
The risk cannot be reduced to zero. It must be discussed in relation to the specific procedure and organ being treated.
Questions to Ask Before Embolization
Patients may find it useful to ask:
- Which embolic agent are you planning to use?
- Why is this material appropriate for my condition?
- Is it temporary or permanent?
- Will anything remain in my body?
- Are coils, particles, a plug or a liquid agent planned?
- Could more than one agent be used?
- Will I receive an implant card?
- Can I undergo MRI afterward?
- What material-related complications should I know about?
- Could the vessel reopen or require another treatment?
- How will nearby normal vessels be protected?
The answers should be specific to the planned treatment.
Discussing Embolic Materials With Dr Sravan C.P.S
Dr Sravan C.P.S is a vascular and endovascular surgeon in Bangalore. His embolization-related practice includes evaluation for PAE, UAE, GAE, TAE, TAME and varicocele embolization where clinically appropriate.
When I discuss embolization with a patient, I do not describe the treatment only as “putting coils” or “injecting particles.” The material is one part of a larger decision.
The important questions are:
- What vessel is causing or contributing to the problem?
- How selectively can that vessel be reached?
- Does the flow need to be reduced temporarily or permanently?
- Which material provides the required control while protecting normal tissue?
A consultation should explain the planned agent, its intended permanence, alternatives and important risks before the procedure.
Conclusion
Embolization coils, particles, plugs and liquid agents all reduce blood flow, but they do so in different ways.
Coils and plugs are generally permanent mechanical implants placed within a defined vessel. Many particles are designed to remain within smaller arterial branches, while temporary agents may be absorbed over time. Liquid embolic agents and sclerosants have different behaviours and require procedure-specific selection.
The correct material depends on the target vessel, blood-flow pattern, treatment purpose, surrounding anatomy and intended duration of closure. Patients should know what is being used, whether it will remain in the body and what information should be retained for future scans or procedures.
Frequently Asked Questions
Do embolization coils stay in the body permanently?
Embolization coils are generally designed to remain permanently in the treated vessel. They are not routinely removed after the vessel has closed.
Do embolization particles dissolve?
Some particles are permanent, while certain temporary materials are gradually absorbed. The answer depends on the exact embolic agent used during the procedure.
Can embolization coils move after treatment?
Coils are sized and positioned to remain in the intended vessel. Migration is uncommon but recognised. New unexplained symptoms should be assessed rather than assumed to be caused by coil movement.
Can I have an MRI after embolization coils?
Many modern coils are MR Conditional, meaning MRI may be possible under specified conditions. Inform the MRI team and provide your implant card or procedure report so the exact device can be checked.
Are coils used in every embolization procedure?
No. Coils are useful for selected vessels, particularly when controlled mechanical closure is required. Other procedures may use particles, plugs, liquid agents, foam or a combination.
What is the difference between embolization coils and particles?
Coils are placed at a defined point within a vessel and promote mechanical closure. Particles travel into smaller downstream branches and reduce flow through a wider small-vessel network.
Can embolization materials be removed later?
They are not normally removed. Retrieval may be considered only in selected situations, such as an incorrectly positioned device or clinically important migration.
