by Tyler McKay, University of Washington SOM 2016
So you’re interested in exploring the wonderful world of interventional radiology. Perhaps this is your first time hearing about the specialty and are interested to learn more. Maybe you are about to start an IR clerkship and want to brush up before you begin. Whatever sparked your interest in IR, the Medical Student Council is here to help. Half the battle with entering any new field is simply trying to understand what people are talking about. Some things may seem so basic that you are afraid to ask for a definition or explanation. In this article, I will provide a quick review of some of the basic words, phrases, and abbreviations that are used every day in IR to get you up to speed on the terminology, and give you an easy resource to refer to in times of need.
Catheter: a hollow tube that can go over wires to help guide and direct them into different blood vessels or body cavities (e.g., post-operative abscess). Catheters can be used to deliver contrast/fluids, collect blood samples, or drain pathologic body fluid collections (e.g., pus, bile, blood, etc.). Catheters come in a variety of shapes and various sizes. Size is classified using the French gauge system (1 French unit = 1/3 mm), which is a measure of outer circumference. You’ll hear them referred to by their specific names (SIM2, Cobra, etc).
Balloon catheter (or “balloon”): a special type of catheter that has an expandable and collapsible balloon along the tip of the catheter that can be inflated across a narrowing or stricture to increase the diameter of the narrowing. An insufflator device is used to expand and collapse the balloon. To expand the balloon, first push down the lever and then begin to turn it clockwise. To collapse, turn it counter-clockwise and when it reaches 0 pull the lever up. Always have the tip towards the ground. (image: genoss.com)
Wire (or Guidewire): Endovascular wires are used to guide catheters through blood vessels. Many times during a procedure catheters will need to be removed or exchanged, and the wire serves as a bookmark that allows the operator to return to where they were previously working. During a procedure, it is important to always have a firm grip on the wire, as dropping or inadvertently shifting it can lose the wire’s position. Also they are quite long so it is important to make sure the end does not fall off the table and become contaminated. Wires generally come in two diameters, 0.018in and 0.035in (“Oh one eight”, “oh three five”), and various lengths and stiffness. Some wires have a hydrophilic coating which makes them slippery and easier to maneuver (Glidewires). Glidewires need to be flushed before use. Wires are often referred to by their brand names (Amplatz, Rosen, Bentson, etc). (image: gadeliusmedical.com)
Sheath: a short, stiff hollow tube that traverses the skin and subcutaneous tissue and enters the endovascular space. The “hub” remains on the surface of the skin, and allows wires and catheters to easily enter the endovascular space. Unlike catheters, sheaths are measured in French by their inner diameter. Like catheters, they must be flushed with saline before use. (image: auntminnie.com)
Dilator: a type of sheath that has a tapered diameter along its length or tip for the purpose of dilating the tract around a wire to allow catheters and sheathes of larger sizes to be able to easily pass along the wire. (image: Bonsonscientific.com)
Stent: a device that is placed across a narrowing or blockage in a vessel or duct. In the vascular system, narrowed areas can be corrected by first dilating with a balloon, and then placing a stent to keep the vessel open. Stents come in a variety of shapes, lengths, diameters, and materials; some are self-expanding, others are balloon expandable. They can be “bare metal” stents, without any coating or can be coated with a polymer that is capable of holding eluting drugs. Stents can also be covered with a fabric-like material creating an impermeable conduit along its length (image: news.bostonscientific.com).
Coil: a coil is one available means of inhibiting blood flow through a vessel. It is a thin strip of metal that is introduced into a blood vessel via catheter and deployed. Coils are often made of high shape-memory alloys causing them to coil upon release and restrict blood flow. This may be done in trauma settings to prevent blood loss through a damaged vessel, or to strategically stop flow through vessel for other medical purposes such as limiting blood flow to tumors to induce ischemia. (image: medmovie.com)
Seldinger technique: the process by which a wire is introduced into a desired space (blood vessel, fluid collection, etc.). First, ultrasound is use to locate a vessel. After sterilization and anesthetization are achieved, a needle is advanced under ultrasound guidance into the desired vessel. A nick with a scalpel may be performed first to make insertion of sheaths and catheters less traumatic. A small wire is then inserted through the needle into the vessel. The needle is removed over the wire and replaced with a sheath. Access to the vessel is then available for wires and catheters through the sheath. (image: englishclass.jp) (Video 1, Video 2)
Angioplasty: The process of repairing a narrowed blood vessel. The narrowed segment is first identified by injecting contrast into the vessel under fluoroscopy (real-time x-ray imaging). A balloon catheter is inflated across the narrowing (called a stenosis) to dilate the stricture. A stent is often placed across the stenosis following the balloon to prevent restenosis. (Video)
TIPS: Transjugular intrahepatic portosystemic shunt. In cases of portal hypertension, portal pressure can be reduced by creating a new passage from the portal vein to the hepatic vein that bypasses the liver capillary bed. A catheter is advanced from the jugular vein down the IVC to the hepatic veins. Sometimes under intravenous ultrasound guidance, a shunt between the two vessels is created by passing a stiff probe through the liver parenchyma from hepatic vein to portal vein, dilating the tract with a balloon, and then placing a stent across the new opening. (image: depts.washington.edu) (Video)
Ablation: Radio frequency ablation. This procedure is an alternative to surgery in the treatment of small solitary tumors. Under CT guidance, a long needle called a probe is advanced through the skin into the site of the tumor, taking caution to avoid important structures like vessels, nerves, bowel, and non-target organs. Once in place, a radio frequency transducer is attached to the end of the probe outside of the patient’s body and radio waves heat up the other end of the probe inside the tumor. This process creates a spherical burn zone that kills the cancerous cells and spares all cells outside of the zone.
A similar procedure called cryoablation uses helium gas to cool the probe down to freezing temperatures, which also kills the tumor. (image: SIRweb.org) (Video)
Embolization: Embolization is the intentional occlusion of a vessel for a medical need. This can be done to restrict blood flow to tumors and inhibit growth such as uterine artery embolization for uterine fibroids. In the trauma setting a hemorrhaging vessel can be embolized to prevent ongoing blood loss. Non-target or collateral blood vessels can be embolized to achieve desired blood flow. A variety of materials exist to achieve embolization, including: metal coils, gelfoam, and acrylic “glue”.
Trans-arterial chemoembolization (TACE) is an alternative to surgery in the treatment of liver tumors. A catheter is inserted into the femoral artery and advanced into the hepatic artery via the aorta and celiac trunk. A contrast injection under fluoroscopy shows the presence of hypervascular tumors. The catheter is advanced into the arteries that directly supply the tumors, and chemotherapy drugs are injected with an embolic agent that limits blood flow to the tumor and bathes the tumor in the drug, while sparing normal healthy tissues. A variant of this method called DEB-TACE (drug-eluting bead) uses small-drug coated particles that lodge in the capillary bed and slowly transfer the drug into the tumor bed. (Video)
A similar procedure called radioembolization uses small particles coated with yttrium-90 (Y90) that emit beta radiation at the tumor bed to achieve similar tumoricidal effects.
If you’re interested in learning more about all that IR offers to patients, check out our YouTube channel for lectures, case studies, and more.