Interventional Radiology (IR) is a medical specialty which provides minimally invasive image-guided diagnosis and treatment of disease. Although the range of procedures performed by interventional radiologists is broad, the unifying concept behind these procedures is the application of image guidance and minimally invasive techniques in order to minimize risk to the patient.

Training for interventional radiology occurs in the residency portion of medical education, and has gone through developments.

In 2000, the Society of Interventional Radiology (SIR) created a program named "Clinical Pathway in IR", which modified the "Holman Pathway" that was already accepted by the American Board of Radiology to including training in IR; this was accepted by ABR but was not widely adopted. In 2005 SIR proposed and ABR accepted another pathway called "DIRECT (Diagnostic and Interventional Radiology Enhanced Clinical Training) Pathway" to help trainees coming from other specialities learn IR; this too was not widely adopted. In 2006 SIR proposed a pathway resulting in certification in IR as a speciality; this was eventually accepted by the ABR in 2007 and was presented to the American Board of Medical Specialities (ABMS) in 2009, which rejected it because it did not include enough diagnostic radiology (DR) training. The proposal was reworked, at the same time that overall DR training was being revamped, and a new proposal that would lead to a dual DR/IR specialization was presented to the ABMS and was accepted in 2012 and eventually was implemented in 2014.^[1][2][3] By 2016 the field had determined that the old IR fellowships would be terminated by 2020.^[3]

A handful of programs have offered interventional radiology fellowships that focus on training in the treatment of children.^[4]

In Europe the field followed its own pathway; for example in Germany the parallel interventional society began to break free of the DR society in 2008.^[5] In the UK, interventional radiology was approved as a sub-specialty of clinical radiology in 2010.^[6][7] While many countries have an interventional radiology society, there is also the European-wide Cardiovascular and Interventional Radiological Society of Europe, whose aim is to support teaching, science, research and clinical practice in the field by hosting meetings, educational workshops and promoting patient safety initiatives. Furthermore, the Society provides an examination, the European Board of Interventional Radiology (EBIR), which is a highly valuable qualification in interventional radiology based on the European Curriculum and Syllabus for IR.

Interventional radiologists commonly perform both diagnostic and therapeutic procedures, although diagnostic angiography is becoming less common as the quality and reliability of CT and MRI angiography has allowed for alternative forms of non invasive evaluation.

• 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.^[8]
• Cholangiography: Imaging the bile ducts within the liver to look for areas of blockage.
• Biopsy: Taking of a tissue sample from the area of interest for pathological examination from a percutaneous or transvenous approach.^[9]

Vascular

• Balloon angioplasty/stent: Opening of narrow or blocked blood vessels using a balloon, with or without placement of metallic stents to aid in keep vessel patent.^[10]
• Endovascular aneurysm repair: Placement of endovascular stent-graft across an aneurysm, in order to prevent expansion or progression of the defective vessel.^[11]
• Embolization: Placement of a metallic coil or embolic substance (gel-foam, poly-vinyl alcohol) to block blood through to a blood vessel, either to stop bleeding or decrease blood flow to a target organ or tissue.^[12]
  • Uterine artery embolization (UAE) or uterine fibroid embolization (UFE)
  • Prostate artery embolization (PAE)
  • Pulmonary arteriovenous malformation (PAVM) embolization ^[13]
• Thrombolysis: Catheter-directed technique for dissolving blood clots, such as pulmonary embolism, deep venous thrombosis) with either pharmaceutical (TPA) or mechanical means.
• IVC filters: Metallic filters placed in the vena cava to prevent propagation of deep venous thrombus.
• Dialysis related interventions: Placement of tunneled hemodialysis catheters, peritoneal dialysis catheters, and revision/thrombolysis of poorly functioning surgically placed AV fistulas and grafts.^[14]
• TIPS: Placement of a Transjugular Intrahepatic Porto-systemic Shunt (TIPS) for select indications in patients with critical end-stage liver disease and portal hypertension.^[15]
• Endovenous laser treatment of varicose veins: Placement of thin laser fiber in varicose veins for non-surgical treatment of venous insufficiency.

Biliary intervention^[16]

• Placement of catheters in the biliary system to bypass biliary obstructions and decompress the biliary system.
• Placement of permanent indwelling biliary stents.
• Cholecystostomy: Placement of a tube into the gallbladder to remove infected bile in patients with cholecystitis, an inflammation of the gallbladder, who are too frail or too sick to undergo surgery.

Catheter placement

• Central venous catheter placement: Vascular access and management of intravenous devices (IVs), including both tunneled and non-tunneled catheters (e.g. PIC, Hickman, port catheters, hemodialysis catheters, translumbar and transhepatic venous lines).
• Drainage catheter placement: Placement of tubes to drain pathologic fluid collections (e.g., abscess, pleural effusion). This may be achieved by percutaneous, trans-rectal, or trans-vaginal approach. Exchange or repositioning of indwelling catheters is achieved over a guidewire under image guidance.
• Radiologically inserted gastrostomy or jejunostomy : Placement of a feeding tube percutaneously into the stomach and/or jejunum.^[17]

Ablative^[18][19]

• Chemoembolization: combined injection of chemotherapy and embolic agents into the arterial blood supply of a tumor, with the goal of both local administration of chemotherapy, slowing "washout" of the chemotherapy drug, and also decreasing tumor arterial supply.
• Radioembolization: combined injection of radioactive glass or plastic beads and embolic agents into the arterial blood supply of a tumor, with the goal of both local administration of radiotherapy, slowing "washout" of the radioactive substance, and also decreasing tumor arterial supply.
• Radiofrequency ablation (RF/RFA): local treatment which uses a special catheter to destroy tissue by using heat generated by medium frequency alternating currents.
• Cryoablation: local treatment which uses a special catheter to destroy tissue by using cold temperature generated by rapid expansion of compressed argon gas. This technique is mostly used for the treatment of small renal cancers and for the palliation of painful bone lesions.^[20]
• Microwave ablation: local treatment which uses a special catheter to destroy tissue by using heat generated by microwaves.

Genitourinary^[21]

• Percutaneous nephrostomy or nephroureteral stent placement: Placement of a catheter through the skin, directly into the kidney in order to drain from the collecting system. This is typically done to treat a downstream obstruction of urine.
• Ureteral stent exchange: indwelling double-J type ureteral stents, typically placed by urologist using cystoscopy, may be exchanged in retrograde fashion through the female urethra. The IR uses a thin wire snare under fluoroscopy to capture the distal portion of the stent. After partially extracting the distalmost stent, exchange for a new stent can be accomplished over a guidewire.

Pain management

• Vertebroplasty: Percutaneous injection of biocompatible bone cement inside a fractured spinal vertebrae in order to restore vertebral body height and relieve pain.^[22]

About 87% of all strokes are ischemic strokes, in which blood flow to the brain is blocked.^[23] A clot-busting medication such as tissue plasminogen activator (t-PA) can be used in a controlled hospital setting to dissolve the clot and help restore blood flow to the damaged area of the brain. Certain patients who are suffering from an acute ischemic stroke may be candidates for endovascular therapy.^[24] Endovascular therapy is a procedure performed by neurointerventionalists to remove or dissolve the thrombus (clot) and restore blood flow to parts of the brain. Using a catheter that is directed through the blood vessels in the arm or leg up to the brain, the interventionalist can remove the thrombus or deliver drugs to dissolve the thrombus.^[23] These procedures are referred to as mechanical thrombectomy or thrombolysis, and several factors are considered before the procedure is completed.

People who may be eligible for endovascular treatment have a “large vessel occlusion” which means the thrombus is in an artery that is large enough to reach and there are no contraindications such as, a hemorrhagic stroke (bleeding in the brain), greater than 6 hours since onset of symptoms, or greater than 24 hours in special cases. Hospitals with comprehensive stroke centers are equipped to treat patients with endovascular care.^[25]

Long term care after an ischemic stroke is focused on rehabilitation and preventing future blood clots using anticoagulant therapy. Patients will work with specialists from fields such as physical therapy, occupational therapy, and speech therapy to complete recovery.^[26]

Utilizing image guidance, local anesthetics and/or long-acting steroid medications can be directly delivered to localized sites of pain. The use of image guidance helps to confirm appropriate needle placement. ^[27] This includes common imaging modalities used in joint injections: ultrasound, fluoroscopy and computerized tomography (CT).

• Facet joints, also known as zygapophyseal joints, refer to small bony structures located between the vertebrae of the spine that promote spinal stability.
• Degeneration or damage to the facet joints can often lead to “facet joint syndrome”, which can be both diagnosed and treated by image-guided injection of anesthetics.^[28]
• Facet joint block is a minimally invasive procedure in which a physician uses fluoroscopy or CT imaging to guide the placement of an injection of medication into a facet joint to provide pain relief. ^[29]

• The sacroiliac joint is a structure that is located at the bottom of the spine, and connects the spine to hips. The purpose of this joint is to help the spine bear the weight of the upper region of the body. The sacroiliac joint also decreases the incidence of injuries by improving overall stability and restricting the torso’s range of movement.
• A sacroiliac joint injection is typically performed to decrease persistent back pain that developed due to an injured or inflamed sacroiliac joint. ^[28]

• In the spine, the epidural space is an anatomic space that is the outermost part of the spinal canal. It is the space within the canal (formed by the surrounding vertebrae) lying outside the dura mater (which encloses the arachnoid mater, subarachnoid space, the cerebrospinal fluid, and the spinal cord).
• Injection of local anesthetics is often performed to treat local pain or radiculopathy, particularly due to disc herniation or central/foraminal stenosis. ^[27]
• Usually performed under fluoroscopic guidance.

• A spinal nerve root is the initial or proximal segment of one of the thirty-one pairs of spinal nerves leaving the central nervous system from the spinal cord.
• Damage to nerve roots can cause paresis and paralysis of the muscle innervated by the affected spinal nerve. It can also cause pain and numbness in the corresponding dermatome. A common cause of damage to the nerve roots are lesions in the spine, such as prolapse of the nucleus pulposus, spinal tuberculosis, cancer, inflammation and spinal tabes. Root pain syndromes, known colloquially as radiculitis (i.e. sciatica) are one of the most common symptoms caused by damage to the nerve root.
• Used to treat patients with radicular symptoms in the cervical, thoracic, lumbar or sacral region. ^[27]
• Helps to alleviate pain by dealing with inflammation of the nerve root.

• Veins have one-way valves that help keep blood flowing toward your heart. If the valves are weak or damaged, blood can pool in your veins, which causes them to swell. When this happens near the pelvis, it is called pelvic congestion syndrome, which can lead to chronic pain beneath the level of the belly button.
• Pelvic congestion syndrome usually affects women who have previously been pregnant, because the ovarian veins and pelvic veins had widened to accommodate the increased blood flow from the uterus during pregnancy. After the pregnancy, some of these veins remain enlarged and fail to return to their previous size, causing them to weaken and allowing blood to pool. ^[30]
• An interventional radiologist can off a minimally invasive treatment option for pelvic congestion syndrome: ovarian vein embolization
• Ovarian vein embolization is a same-day treatment, which takes place in an interventional radiology suite. The interventional radiologist gains access through a large vein in the groin, called the femoral vein, by using a small catheter, which is a flexible tube like a strand of spaghetti. The catheter is moved through the vein to the enlarged pelvic veins, allowing the introduction of embolic agents, which are medications that cause the vein to seal off and relieve the painful pressure.^[31]
  • This treatment can be less expensive than surgery and is much less invasive.
• A number of diagnostic tests can be performed through minimally invasive methods, to determine whether your chronic pelvic pain is a result of pelvic varicose veins. These tests include:
  • Pelvic and Transvaginal Ultrasound
  • Pelvic Venogram
  • Computed Tomography (CT)
  • Magnetic Resonance Imaging (MRI)

• Palliative care is an interdisciplinary approach to specialized medical and nursing care for people with life-limiting illnesses. It focuses on providing relief from the symptoms, pain, physical stress, and mental stress at any stage of illness. The goal is to improve quality of life for both the person and their family. ^[32]
• The interventional radiologist may be uniquely skilled as hospice and palliative medicine providers. As an imager, the radiologist is the expert in obtaining maximum imaging value; furthermore, the radiologist has extensive experience in diagnostic image interpretation and disease prognostication. In addition, the interventional radiologist has an array of both therapeutic and palliative interventions to offer the patient coping with a life-threatening illness.^{[33] [34]}

• Injection of medication or anesthetic to decrease inflammation or "turn off" a pain signal along a specific distribution of nerve.^[29]
• “Block” vs. Ablation”: Although these terms are often used interchangeably, they differ in terms of duration of action
  • Nerve block: “temporary disruption of the disruption of pain transmission via the celiac plexus and is accomplished by injecting corticosteroids or long-acting local anesthetics”.^[35]
  • Neurolysis: “permanent destruction of the celiac plexus with ethanol or phenol”. ^[35]
• Types of blocks/neurolyses:
  • Celiac plexus block/neurolysis: A procedure performed to manage refractory cancer-related abdominal pain by modulating the celiac plexus, which is a network of nerve fibers located in the retroperitoneum along the anterolateral wall of the aorta.
    • Often used in the management of incurable pancreatic cancer.
    • Often utilizes multidetector CT for image guidance.
  • Superior hypogastric plexus block/neurolysis: A procedure performed to manage refractory abdominal/pelvis pain by modulating the superior hypogastric plexus, which is a network of nerve fibers located in the retroperitoneum that modulate pain from the bladder, vulva, vagina, uterus, urethra, penis, perineum, prostate, testes, rectum, and colon.
  • Lumbar sympathetic block: A procedure performed to manage pain originating from the lower back, buttocks or legs.^[36]
    • Common indications: complex regional pain syndrome (CRPS)/regional sympathetic dystrophy (RDS), post-herpetic neuralgia, neuropathy.
  • Pudendal nerve block: A procedure performed to manage chronic pelvic pain.
    • Common indications: pudendal neuralgia (i.e. repetitive use from cycling)^[37], cancer-related pain
  • Sphenopalatine ganglion block
    • A procedure performed to manage head and neck pain/headaches related to the trigeminal nerve, usually in the treatment of migraine headaches.^[38]

• The standard of care for local treatment of extraspinal osseous metastases is external-beam radiation therapy. Fifty percent of patients who undergo this therapy achieve complete response or resolution of symptoms. Of the remaining patients, half fail therapy (20–30% of the total), 10% require retreatment, and 1–3% experience debilitating complications such as fracture of the treated bone.
• Due to the need for multiple treatments requiring multiple transports to and from the hospital and potential disruption to treatment/therapy, minimally invasive options in the treatment of extraspinal osseous metastases have emerged as attractive options in management of symptomatic metastases. These typically take the form of three types of ablative therapy: microwave thermal ablation, radiofrequency ablation (“coblation”) and cryoablation. ^[39]
  • Microwave thermal ablation
    • Microwave ablation is a treatment that uses heat to treat tumors. An interventional radiologist makes a tiny incision in the skin to insert a special needle into the body. Using a live computed tomography (CT) scan or an ultrasound, the doctor guides the needle to the tumor. The interventional radiologist generates electromagnetic microwaves that can destroy the tumor. ^[40]
    • The advantages of microwave ablation (removal of tissue) compared to radiofrequency ablation include a generation of higher temperatures and the ability to use multiple needles to better destroy larger tumors.
    • After the treatment, patients will follow up with their physician for several months. The treatment team will also order additional imaging scans to evaluate whether the microwave ablation was successful in destroying the tumor.
  • Plasma-mediated radiofrequency ablation (“coblation”)
    • Radiofrequency ablation is a treatment that uses heat to destroy multiple small tumors. An interventional radiologist makes a tiny incision and uses either a computed tomography (CT) scan or ultrasound to guide a special needle to the site of the tumors. Next, radiofrequency (RF) electrodes are placed into the tumor. The electrodes generate an electric current (RF energy) which is transformed into heat, destroying the tumor. This technique can be repeated at multiple sites, as necessary, before the interventional radiologist removes the RF electrode.
    • After the treatment, patients will follow up with their physician for several months. The treatment team will also order additional imaging scans to evaluate whether the radiofrequency ablation was successful in destroying the tumor.^[41]
  • Cryoablation
    • Cryoablation is a treatment option that destroys cancer cells by applying extremely cold temperatures at the location of the tumor. A small cut is made in the skin and a tiny needle called a cryoprobe is inserted. Using image-guidance – either by a computed tomography (CT) scan or by ultrasound–the interventional radiologist maneuvers the cryoprobe toward the location of the tumor.
    • Next, the cryoprobes are inserted into the tumor to begin freezing it with a gas called argon, creating an “ice ball” over the entire tumor to freeze it for about ten minutes. Nitrogen gas is then used to thaw the tumor for five minutes. This cycle is repeated two or three times depending on the tumor type and size. ^{[40] [42]}

• Vertebroplasty and kyphoplasty are procedures used to treat painful vertebral compression fractures in the spinal column, which are a common result of osteoporosis. Your doctor may use imaging guidance to inject a cement mixture into the fractured bone (vertebroplasty) or insert a balloon into the fractured bone to create a space and then fill it with cement (kyphoplasty). Following vertebroplasty, about 75 percent of patients regain lost mobility and become more active.^[43]
• Vertebroplasty
  • Vertebroplasty is a minimally invasive treatment developed to treat pain caused by vertebral compression fractures, and has been safely performed since 1987. Using fluoroscopic (x-ray) imaging, an interventional radiologist precisely inserts a needle into the collapsed vertebral body through a small incision in the skin. This image-guided technique (a technique guided by live x-rays) allows the doctor to accurately access the fracture while minimizing any trauma to surrounding tissue. A medical-grade liquid cement is then injected into the center of the vertebrae. As the cement solidifies, the broken bone is stabilized. The treatment is performed with the patient face-down and sedated for their comfort. Afterwards, many patients feel immediate relief from pain, and can be discharged home the same day.^[44]
• Kyphoplasty
  • Kyphoplasty is similar to vertebroplasty and is equally effective in stabilizing compression fractures. As with vertebroplasty, a needle is inserted into the fractured vertebra, using x-ray imaging. A balloon is then positioned into the collapsed bone and inflated to create a cavity for cement injection. The cement is injected into the cavity once the balloon is removed. Many patients feel immediate pain relief and are able to resume regular activities within a few days. Your doctor will most likely schedule a follow-up visit and explain limitations, if any, on physical activity.^[44]
  • Based on Level I and II studies, balloon kyphoplasty had significantly better and vertebroplasty tended to have better pain reduction compared with non-surgical management.^[45]
• Vertebral augmentation
  • In addition to balloon kyphoplasty, vertebral body height loss can also be stabilized with insertion of a medical device/implant in a procedure known as vertebral augmentation.
  • One such example is the Kiva system, which uses a flexible implant made of a medical polymer to restore height to the vertebral body and hold the cement. Inserting the implant requires an incision about 1 cm in length, about the same size as with balloon kyphoplasty. The physician uses the incision to insert an introducer into the vertebral body. The introducer allows the operator to deploy a preshaped Nitinol guidewire coil for precise placement of the implant. The implant slides over the coil and follows its path down into the vertebral body. Once the implant has been placed, the coil is retracted and the delivery device is removed. Next, a cement needle is inserted into the back of the implant that was placed in the vertebra. The cement goes through little slots on the inside of the implant, which allows the physician to customize the amount of cement the Kiva implant delivered during the procedure to restore the vertebra to its original height.
    • Potential advantages of vertebral augmentation with implant placement are better containment of the bone cement as well as better simulation of natural bone biomechanics via the implant device as opposed to purely from bone cement. ^[46]

• Sacral insufficiency fractures are an infrequent but often disabling cause of severe low back pain. At times, the pain can be so severe that it may cause the patients to become bedridden, placing them at risk for complications of immobility such as deep vein thrombosis, pulmonary emboli, muscle atrophy, decubitus ulcers, and bone demineralization. Until the development of the sacroplasty technique, there was no definitive treatment other than bed rest.
• Sacral insufficiency fractures result from an axial loading mechanism on abnormal bone, such as osteoporosis or underlying neoplasm.
• Analogous to vertebroplasty, the purpose of sacroplasty is to provide stabilization to prevent painful micromotion at the fracture site. A needle is placed through the skin and into the bone under CT guidance and a polymethylmethacrylate mixture is injected into the sacrum under real-time fluoroscopy.
• Sacroplasty is a safe and effective procedure in the treatment of sacral insufficiency fractures that can provide substantial pain relief and lead to a better quality of life.^[32]