Interventional radiology

Assistant Editor-In-Chief: Anand Patel, MD [mailto:Anand.Patel@ucsf.edu]

Overview
Interventional radiology (abbreviated IR or sometimes VIR) is a subspecialty of radiology in which minimally invasive procedures are performed using image guidance. Some of these procedures are done for purely diagnostic purposes (e.g., angiogram), while others are done for treatment purposes (e.g., angioplasty). Pictures (images) are used to direct these procedures, which are usually done with needles or other tiny instruments like small tubes called catheters. The images provide road maps that allow the Interventional Radiologist to guide these instruments through the body to the areas of interest.

History
The advancements in the field of radiological imaging such as the Seldinger technique, together with innovations in instrumentation, led to a rapid development in interventional procedures in the 1970s. Cardiovascular procedures were found to be particularly well-suited for guided and minimally invasive operations, and catheterization remains as one of the main applications for interventional radiology.

See also: Interventional cardiology

Imaging methods
Common interventional imaging methods include X-ray fluoroscopy, computed tomography (CT), ultrasound (US), and magnetic resonance imaging (MRI). Fluoroscopy and computed tomography use ionizing radiation that may be potentially harmful to the patient and, in the case of fluoroscopy, the interventional radiologist. However, both methods have the advantages of being fast and geometrically accurate. Ultrasound suffers from image quality and tissue contrast problems, but is also fast and inexpensive. Magnetic resonance imaging provides superior tissue contrast, at the cost of being expensive and requiring specialized instruments that will not interact with the magnetic fields present in the imaging volume.

Procedures
Common IR procedures are:
 * Angiography: imaging the blood vessels to look for abnormalities with the use of various contrast media, including iodinated contrast, gadolinium based agents, and CO2 gas.


 * Balloon angioplasty/stent: opening of narrow or blocked blood vessels using a balloon; may include placement of metallic stents as well (both self-expanding and balloon expandable).
 * Chemoembolization: delivering cancer treatment directly to a tumour through its blood supply, then using clot-inducing substances to block the artery, ensuring that the delivered chemotherapy is not "washed out" by continued blood flow.


 * Drain insertions: placement of tubes into different parts of the body to drain fluids (e.g., abscess drains to remove pus, pleural drains)


 * Embolization: blocking abnormal blood (artery) vessels (e.g., for the purpose of stopping bleeding) or organs (to stop the extra function e.g. embolization of the spleen for hypersplenism) including uterine artery embolization for percutaneous treatment of uterine fibroids. Various embolic agents are used, including alcohol, glue, metallic coils, poly-viny alcohol particles, Embospheres, encapsulated chemo-microsphere, and gelfoam.


 * Thrombolysis: treatment aimed at dissolving blood clots (e.g., pulmonary emboli, leg vein thrombi, thrombosed hemodialysis accesses) with both pharmaceutical (TPA) and mechanical means


 * Biopsy: taking of a tissue sample from the area of interest for pathological examination from a percutaneous or transjugular approach


 * Radiofrequency ablation (RF/RFA): localized destruction of tissue (e.g., tumours) by heating


 * Cryoablation - localized destruction of tissue by freezing


 * Line insertion: Vascular access and management of specialized kinds of intravenous devices (IVs) (e.g. PICC lines, Hickman lines, subcutaneous ports including translumbar and transhepatic venous lines)


 * IVC filters: - metallic filters placed in the inferior vena cavae to prevent propagation of deep venous thrombus, both temporary and permanent.




 * Vertebroplasty: percutaneous injection of biocompatible bone cement inside fractured vertebrae


 * Nephrostomy placement: Placing a catheter directly into the kidney to drain urine in situations where normal flow of urine is obstructed. NUS catheters are nephroureteral stents which are placed through the ureter and into the bladder.


 * Radiologically Inserted Gastrostomy or RIG: Placement of a feeding tube percutaneously into the stomach and/or jejunum.


 * Dialysis access and related intervention: Placement of tunneled hemodialysis catheters, peritoneal dialysis catheters, and revision/thrombolysis of poorly functioning surgically placed AV fistulas and grafts.


 * TIPS : Placement of a Transjugular Intrahepatic Porto-systemic Shunt (TIPS) for management of select patients with critical end-stage liver disease and portal hypertension


 * Biliary intervention - Placement of catheters in the biliary system to bypass biliary obstructions and decompress the biliary system. Also placement of permanent indwelling biliary stents.


 * Endovenous laser ablation of varicose veins - Placement of thin laser fiber in varicose veins for non-surgical treatment of venous insufficiency