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5 Liquid Embolic Agents 57
• Hold catheter hub in a vertical position and overfill and wash the luer hub with
DMSC to create a meniscus of DMSO.
• Attach Onyx syringe to microcatheter, meniscus to meniscus and then quickly
point the syringe vertically.
• Inject Onyx at a steady, slow rate of 0.16 ml/min (0.25 ml/90 sec). Do not exceed
0.3 ml/min. Once Onyx passes through the catheter hub, the syringe may be held
in a more comfortable position.
• Do not allow more than 1 cm of Onyx to reflux back over the catheter tip.
• Upon completion of injection, wait a few seconds, slightly aspirate syringe, and
gently pull the catheter to separate it from the Onyx cast.
• Do not interrupt Onyx injection for longer than 2 min prior to re-injection.
• Stop injection if increased resistance is observed.
When to Use
• FDA approved for presurgical embolization of cerebral arteriovenous
malformations.
• Visceral and cerebral arteries aneurysms.
When Not to Use It
• When optimal catheter placement is not possible.
• When vasospasm stops blood flow.
• History of reaction or hypersensitivity to DMSO.
• Premature infants (<1,500 g) or individuals with significant liver and kidney
function impairment.
Note
• DMSO has a characteristic aroma not unlike a patient with ketoacidosis. Warn
the patient that it is normal for them to smell of this until all DMSO has been
excreted from the body.
Lipiodol
• Brand name: Ethiodol (Savage Laboratories, Melville, NY, USA).
58 K. Kondo
Physical Description and Properties
• Sterile, injectable, low-viscosity radio-opaque diagnostic agent.
• Contains 37% iodine (475 mg/ml) organically combined with ethyl esters of the
fatty acids of poppy seed oil.
• Straw to amber colored oily fluid.
Fate of Injected Lipiodol
Lymphatic Injection
• Following intralymphatic administration, lipiodol enters the bloodstream and is
transported to the liver, lungs, spleen, and adipose tissue.
• In the lungs, the lipid droplets are dispersed in the pulmonary alveoli.
Disappearance of droplets in the lungs or other tissues occurs slowly.
• During metabolism, iodine is released, which is excreted through the urinary
system.
Hepatic Arterial Injection
• When injected into the hepatic artery, lipiodol is selectively retained by hepato-
cellular carcinoma (HCC) and other lipiodol-avid tumors.
• Selective uptake of lipiodol is thought to be due to a siphoning effect created by
the increased blood flow in a hypervascular tumor.
• The lipidol droplets divide into smaller globules as they travel in the blood vessels
and lodge in the liver parenchyma.
• Lipiodol is normally cleared through the hepatic lymphatics; Kupffer cells might
also contribute to the clearance of lipiodol from hepatic lobules. HCC does not
contain hepatic lymphatic tissue and thus is still stained with lipiodol even after
clearance from background liver tissue.
How to Prepare and Use It
• Can be injected as a single agent but often mixed (through two syringes with a
three-way stopcock) with other agents such as chemotherapy to form an emulsion
in ratios ranging from 1:1 to 1:4.
• Lipiodol can be prepared with I
radiotherapy.
131
a beta particle emitter and used to deliver
5 Liquid Embolic Agents 59
When to Use
• Chemoembolization.
• Diagnostic arteriogram for HCC.
• In combination with n-BCA to delay n-BCA polymerization.
• In combination with absolute alcohol to opacify alcohol delivery.
When Not to Use It
• History of reaction or hypersensitivity to iodine or lipiodol.
• Do not use for bronchography.
• Due to risk of lipiodol bypassing the liver via arteriovenous fistulae and lodging
in the pulmonary vasculature, lipiodol should be used with care in patients with
impaired lung function.
Keypoints
Liquid embolic agents are a valuable addition to the armamentarium of the
vascular radiologist.
They have widely differing modes of action.
They provide a different set of considerations and challenges from conven-
tional embolic agents.
Before using liquid agents, ensure that you have a thorough understanding
of the mechanism of action, use, and complications associated with the agent.
Suggested Reading
Weiss RA, Feied CF, Weiss MA. Sclerosing Solutions. In: Vein Diagnosis and Treatment: A
Comprehensive Approach. New York, NY: McGraw-Hill; 2001:119–130.
Society of Interventional Radiology (SIR) 33rd Annual Scientific Meeting Workshop book.
Chapters: Glue: Neuro and Beyond; Regional Cancer Therapy; Arterial Embolotherapy. 2008.
Pollak JS and White RI Jr. The Use of Cyanoacrylate Adhesives in Peripheral Embolization. J Vasc
Interv Radiol 2001; 12:907–13.
Ray CE Jr. and Bauer JR. Embolization Agents. In Mauro MA, Murphy KP, Thomson KR, et al.
(eds). Image-Guided Interventions. Vol. 1, Philadelphia, Saunders, Elsevier, 2008, 131–9.
Chapter 6
Miscellaneous Embolic Agents: Laser and Radiofrequency
David West
Embolization, the deliberate therapeutic occlusion of vessels, is normally undertaken using mechanical occlusion devices like coils, plugs, particles, or liquids such
as glues. An alternative approach is sclerosant therapy; this can be accomplished
using liquid agents such as alcohol or sodium tetradecyl sulphate or by temperature
change. Thermal ablation is most commonly used in the treatment of varicose veins
(see Chapter 45).
Sclerosis can be achieved by the following:
• Heating
◦ Laser
◦ Radiofrequency (RF)
• Cooling
◦ Cryotherapy
This chapter will consider laser and RF, as cryotherapy is not in common usage
for vascular occlusion.
The effects of heating tissues with laser or RF are dependent on the local
temperature achieved (Table 6.1).
Table 6.1 Effect of Heating Tissues to different Temperature
Temperature (◦C) Effect
45 Vasodilation
60 Denaturation of proteins
80 Contraction of collagen
100 Steam production, dehydration
>100 Carbonization
Remember the following when depositing heat energy:
• Tissue heating will depend on the rate of deposition of energy.
• Heating is effective over a limited radius. Thermal therapy is most effective and
controlled, if the target tissue is in direct apposition with the heating agent.
Transcatheter Embolization and Therapy,
Techniques in Interventional Radiology, DOI 10.1007/978-1-84800-897-7_6,
C
Springer-Verlag London Limited 2010
61
62 D. West
• Conduction of the local tissues (e.g., fast-flowing blood will act as a coolant).
• Surrounding tissues may be affected unless protected.
When using laser or RF, the principle is to introduce the probe or fiber to the
target site and then to pull back at a controlled rate while depositing energy in the
tissues. This rate will depend on the following:
• The desired energy deposition
• The power of the device
• The diameter of the target vessel
• Factors affecting local heat conduction
Laser
LASER is an acronym for Light Amplification by the Stimulated Emission of
Radiation. The absorption of laser light energy heats tissues, and different tissues
absorb different wavelengths of light. Blood absorbs best around 810–1064 nm, and
water in the cells of the vein wall absorbs best around 1320 nm. Most of the lasers
used for permanent occlusion of blood vessels are diode lasers operating at a wavelength between 810 and 980 nm. Nd/YAG lasers, operating at 1064 and 1320 nm,
can also be used. Diode lasers are very compact and relatively cheap and, being
solid state, robust.
About Lasers
Lasers produce light with certain characteristic properties.
• Monochromatic (i.e., one specific wavelength/color).
• Highly coherent (i.e., all the photons are moving in phase with one another).
• Highly directional (i.e., almost all photons are traveling in a parallel beam).
• They can be highly focused and all the energy within the light beam can be
targeted on a very small area of tissue, resulting in localized heating.
Laser light is delivered to the target via simple bare-tipped optical fibers.
The diameter of the fiber influences flexibility, durability, and energy deposition.
Normally these are 600 μm (0.6 m) diameter (which are quite robust), but 400 μm
and even 200 μm fibers are quite capable of delivering the necessary energy.
• The fibers are introduced through vascular sheaths or catheters of sufficient lumi-
nal diameter (usually 4–6Fr) (Fig. 6.1). The fiber has to protrude out of the end
of the catheter by a minimum of 2 cm to avoid burning the plastic sheath.
• Most manufacturers produce kits comprising the laser fiber, the introducer sheath,
needle, and guidewire. They tend to modify their lasers to prevent the use of other
manufacturer’s fibers. To reduce costs and limit supply problems, look for laser
6 Miscellaneous Embolic Agents: Laser and Radiofrequency 63
Fig. 6.1 Laser fiber in
position in calibrated sheath
manufacturers that allow use of generic fibers. Also check the numerical aperture
of the laser. The two common numerical apertures are 0.22 and 0.37 (NA). Either
works well but 0.37 NA lasers can only be used with 0.37 NA fibers, whereas
0.22 NA machines can use either 0.22 or 0.37 NA fibers.
Laser Power (Fig. 6.2)
• The power output required to induce vessel wall death and permanent occlusion
is 8–30 watts.
• The power and the length of time the power is applied for (determined by the pull
back rates) are adjusted to deliver a certain number of joules of energy deposition
per centimeter of vessel treated.
• The greatest shrinkage and fewest perforations occur using a power of 8–12 watts
and a slow pull-back rate.
Fig. 6.2 Typical diode laser
for EVLA with settings
indicating a power of 12.0
watts, 1.0 s pulse, and 1.0 s
pulse interval
64 D. West
Using Lasers
• When treating veins, the aim is to maximize damage to the vein wall while
minimizing thrombosis within the vessel lumen and damage to adjacent tissues.
• To achieve this, the vessel should be emptied and ideally compressed against the
laser fiber. This is easily achieved by injecting large quantities of saline into the
fascial envelope surrounding the vessel.
• Addition of adrenaline to this solution further helps contract the vessel, and
addition of anesthetic to the solution (“tumescent anaesthesia”) prevents pain.
• The vessel diameter influences the energy deposition required to occlude it, con-
tributes to the likelihood of collateral damage and vessel perforation. Typical
doses to cause permanent occlusion are shown below:
Vein diameter (mm) Pulsed Continuous
3 15J/cm15W 50J/cm
5 50 J/cm at 15 W 100 J/cm 150 J/cm
• Higher doses will damage the full thickness of a vessel wall (e.g., i n continuous
mode a 5 mm diameter vein needs minimum 100 J/cm to permanently damage
intima and 150 J/cm to permanently damage the media and adventitia).
• In practice, most operators tend to err on the side of effectiveness rather than
minimal energy deposition. Whether pulsed or continuous, a minimum energy
deposition of 80 J/cm is used.
• Perforations will occur in many patients leading to bruising, but other collateral
damage is very rare at these levels and permanent vessel occlusion is virtually
guaranteed.
Safety
The types of laser used for vessel occlusion are high-powered and potentially dangerous class 4 lasers. As such, any establishment using them must be registered.
In the UK, this registration is with the Healthcare Commission. Certain legal obligations are also in force. You must have a qualified laser protection advisor, an
in-house laser protection supervisor, designation of laser controlled areas, an operating manual specifying exactly how the laser will be used for different treatments,
a register of users, register of every time the laser is used, and any local rules and
regulations are followed. Regular risk assessments must be undertaken. Although
daunting to start with, these requirements are actually quite simple and cheap to
comply with and essential to avoid harm to staff or patients.
6 Miscellaneous Embolic Agents: Laser and Radiofrequency 65
The dangers specific to the use of lasers for vessel occlusion are as follows:
• Permanent eye damage. Safety spectacles are essential for anyone in the room.
These spectacles must protect against the specific wavelength of laser light being
used.
• Collateral damage to other tissues (e.g., adjacent nerves, skin). Restrict energy
delivered and apply copious tumescent anesthesia which acts as a heat sink and
minimizes this risk.
• Fire. It is possible to set combustible materials alight by a stray laser beam. Skin
cleaning solutions must be non-flammable.
Radiofrequency (Fig. 6.3)
Mode of action: this is akin to diathermy. Radiofrequency (RF) uses high-frequency
alternating electric current passed through an electrode inserted into the vessel and
positioned against the vessel wall. The electrical current passes through the vein
wall and back into a second electrode on the instrument. The current causes heating
of the tissue which has the same effect on the tissue as described under laser above.
Like laser, the probe is inserted through a vascular sheath and the vessel wall is
brought into contact with the probe by perivascular fluid injection.
The probe can be used like a guidewire and advanced directly to the target site.
If this fails, conventional catheter and wire techniques are used to place a sheath at
the target and the RF probe is inserted through this.
Fig. 6.3 Typical layout of ultrasound and RF generator. The RF generator settings indicate a
temperature of 86º C, impedance of 115 , and power of 1.3 watts
66 D. West
Monitoring Treatment
• As the tissue is heated, it dehydrates and the resistance to flow of electricity
(impedance) increases.
• Sensors in the probe can also measure temperature within the tissue.
• The treatment is controlled by measurement of either impedance, temperature or
a mixture of both.
Comparison of laser and radiofrequency for varicose veins
Laser Radiofrequency
Capital cost High Low
Consumables cost Low High
Regulations of use Tight None specific
Vessel occlusion effectiveness Almost 100% Almost 100%
Serious complications Very rare More common (e.g., burns, deep venous
Minor side effects (bruising,
discomfort)
Recanalization Very rare Very rare
Speed of procedure 10–30 min per leg 10–30 min per leg
Moderate Very mild
thrombosis, nerve injury)
Applications of Temperature-Induced Vessel Occlusion
By far and away the commonest application is in the treatment of varicose veins
(the technique is described in detail in Chapter 45). Due to its effectiveness, ease
of use, low cost, and permanence of heat-induced vessel occlusion, heat-induced
vessel occlusion is likely to have an increasing role in the following:
• Fallopian tube occlusion for female sterilization
• Permanent ureteric occlusion to seal fistulae
• Certain arterial situations
• Hemorrhoids
• Gastric varices
Keypoints
• Laser and RF ablation are relatively new techniques that are likely to have
an increasing role in endovascular therapy as well as tumor ablation.
6 Miscellaneous Embolic Agents: Laser and Radiofrequency 67
• These techniques will be useful in cases where permanent occlusion is
desirable; so like coils they should not be used when repeat vascular access
is likely to be necessary.
• The limitations of these techniques will be due to difficulty accessing some
of the target vessels with a sheath of sufficient size to allow the RF probe
or laser fiber to be positioned. At present these will typically be 4–6 F for
laser fibers, and 7F for RF probes.