Because of the strong magnetic field, no objects that can be attracted by a magnet can be brought into the MRI room, and there are various relative and absolute contraindications for the examination. The magnet may affect devices such as cardiac pacemakers, internal defibrillators, and implanted nerve stimulators unless the devices are specifically magnetic resonance (MR) conditional. MR conditional devices allow patients to safely undergo MRI as long as the machine is correctly calibrated. However, so patients with non-MR-conditional devices are excluded from undergoing MRI exams. The same holds true for most aneurysm clips because the magnetic field may cause some of them to move or twist, an event that could prove catastrophic. Therefore, before beginning any MRI exam, patients should fill out a detailed medical history form for their protection. MRI provides detailed anatomic images, and it is excellent for the diagnosis of soft tissue abnormalities.

Patients are usually scanned while lying down or sitting adjacent to a scintillation camera. Nuclear medicine studies can detect tumors, fractures, abscesses, arthritis, bleeding points, ischemic cardiac regions, and a multitude of other problems. Importantly, besides structure, these tests usually illustrate how the organs function. For example, renal scans show the structure and function of the kidneys and may be enhanced by giving certain medications during the studies. Lung scans detect emboli and other lesions by showing perfusion, which illustrates regional blood flow to the lungs, and ventilation, which compares it to airflow. For this test, the patient inhales a radioactive gas to show ventilation and also receives an intravenous injection to outline pulmonary perfusion. Nuclear cardiology studies, in which various types of cardiac scans are performed, have become very popular. For example, the exams can show perfusion of the heart muscle before and after increased stress caused by treadmill exercise or induced by inotropic drugs. Studies are available to image the functioning of brain tissue (e.g., positron emission tomography [PET] scanning), which has become an important step in attempting to diagnose Alzheimer disease [18].

Obviously, not every patient is a candidate for an invasive procedure, no matter how minor it may be considered. Biopsies are performed using long sampling needles that are often inserted into organs deep within the body. For many reasons, patients should be evaluated before any decision is made to proceed. Blood work should be obtained and the results reviewed to assure that platelet counts, prothrombin time (PT), international normalized ratio (INR), and activated partial thromboplastin time (PTT) are within normal limits. The liver and kidney, for example, are two highly vascular organs, and patients with bleeding or clotting dysfunctions may be considered too much of a risk to undergo needle biopsy.

There are many patients with peripheral vascular disease who could benefit greatly from an interventional radiologic procedure but are on some type of anticoagulant. Many of these are inpatients who are receiving heparin drips. While most physicians feel it is adequate to stop the medication four hours before the procedure is to begin, some feel the lab work should be repeated immediately before the procedure begins. Others may believe this is unnecessary. The effective half-life of heparin is about 90 minutes, so the four-hour window seems to provide more than an adequate margin for safety [20].

As noted, the various types of x-ray contrast materials are all either ionic or nonionic when broken down to their simplest form. Both types contain iodine, which may be considered potentially nephrotoxic, as the dye has an acute osmotic effect that can further compromise function due to its dehydrating properties. Injection of a contrast medium produces an initial vasodilatation, which is followed by a reactive vasoconstriction in the renal circulation, an effect implicated in renal toxicity. X-ray dye is administered cautiously to patients with renal insufficiency; blood urea nitrogen (BUN) and creatinine levels should always be checked [23,24]. A BUN greater than 23 mg/dL or a creatinine greater than 1.2 mg/dL should signal a warning to be careful.

Patients suffering from congestive heart failure may also show adverse effects from IV contrast materials as they expand vascular volume and increase blood return to the right side of the heart [24]. The FDA warns of small but serious risks associated with iodinated contrast media including kidney damage and anaphylaxis [7]. Patients with multiple myeloma have a significant potential for kidney damage after iodinated contrast injection because the dye may potentiate the precipitation of protein in the kidney [24]. An oral diabetic agent, metformin, has been shown to have a small potential to cause renal damage if given with iodinated x-ray contrast agents due to the possibility of lactic acid formation [24]. This problem may be avoided by discontinuing the metformin for two days after the contrast material is given and being certain renal function is adequate before restarting the drug. In each case, a complete medical assessment should be completed and the decision made whether the benefit of the procedure outweighs any potential harm to the patient before any procedure using contrast materials is performed.

Nonionic iodinated CT contrast media are associated with a very low incidence of adverse reactions. A review of 298,491 doses given at a single facility over the course of four years shows that the most common adverse reactions to these agents (498 total) are hives and nausea; most required no treatment; 79 required treatment in the radiology department, and 16 of those 79 required outside treatment—one death occurred 30 minutes after media injection [25]. Additionally, 32 of the 79 incidents were in patients who had previous allergies to contrast media and had received premedication, 2 of which required further treatment in the emergency department [25]. Patients may be premedicated with diphenhydramine (Benadryl) and one of the corticosteroids (generally reserved for patients with previous moderate or severe idiosyncratic adverse reactions) [23]. Table 3 is an example of one possible premedication protocol.

Because moderate sedation (formerly called conscious sedation) is used so commonly in interventional radiology, it will be discussed briefly in this section. In 2001, the Joint Commission developed a new definition of moderate sedation that is widely accepted and used. Moderate sedation is defined as a minimally depressed level of consciousness, during which the patient retains the ability to maintain a continuously patent airway and respond appropriately to physical stimulation or verbal commands [28,29]. The objectives of moderate sedation are mood alteration, maintenance of consciousness and cooperation, elevation of the pain threshold with minimal changes in vital signs, partial amnesia, and a prompt, safe return to activities of daily living.

Respiratory depression is the main adverse effect of IV moderate sedation. Because of this, it is advisable to administer smaller doses, making certain that the total effect of the drug has been fully evaluated before any further doses are given. In addition to the required emergency equipment, it is prudent to have reversal agents directly on hand. Naloxone is a narcotic antagonist and is the drug of choice to counter effects of the opioids. Flumazenil partially or completely reverses the sedative effects of the benzodiazepines (midazolam and diazepam) [20]. Because several doses of both these reversal agents may be needed, careful titrating is necessary. It is advisable to have dosage charts available for emergency use, so valuable time is not wasted trying to calculate how much of which drug should be given.

Kidney biopsies are extremely helpful to pinpoint an exact diagnosis in a patient experiencing kidney disease. Lupus-like syndromes and types of tubular interstitial disorders may be diagnosed accurately by examination of kidney tissue. Cellular changes, atrophy, and neutrophil infiltration all may be seen by the pathologist, and these factors aid the nephrologist in treatment planning and prognosis. Renal biopsies are also performed to aid in tracking rejection after a kidney transplant. Some smaller hospitals send their renal specimens out to a laboratory that specializes in analysis of renal tissue because the care and examination of renal specimens are quite involved. The kidney biopsy itself, however, may be performed in general interventional radiology departments.

Many liters of fluid may be removed this way, although care should be taken to ensure that the sudden release of pressure in the abdomen does not cause any detrimental hemodynamic effects to the patient. At times, the radiologist may stop the procedure after a certain volume has been withdrawn to prevent any such problems. If a very large amount of abdominal fluid is drained, the radiologist or patient's referring physician may order some intravenous volume replacement with albumin or other similar solution. An immediate postprocedure image will show the size of any remaining ascitic collection.

Untreated intra-abdominal abscesses have a very high degree of mortality. Abscesses may form from various sources, such as complications of acute appendicitis, severe diverticulitis, or a perforated viscus. Abdominal abscesses may also form after disruption in a suture line or from conditions such as Crohn disease. The mass may cause partial or complete bowel obstruction.

Drainage catheter removal is based on several principles. The tube should come out when there is insignificant drainage or cessation of drainage and radiologic imaging shows proper catheter position. Removal can also take place when the patient demonstrates clinical improvement and the signs and symptoms of infection have significantly diminished. Also, if the CT scan documents the absence of residual abscess and the collection does not reaccumulate when the tube is clamped, it is time for it to be removed [50,51].

Thoracic empyema, once always drained in the operating room along with a chest decortication, now may be performed in the radiology department under CT assistance. The cross-sectional CT images allow the radiologist to have a detailed look at the precise location of the fluid collection. An already very ill and compromised patient may be spared a more invasive procedure in which general anesthesia is required. When the pleural space is drained, the indwelling catheter is most often connected to a water seal set-up, such as the Thora-Seal or Pleura vac type. This is necessary to ensure that no air enters the pleural space, as this would inhibit full expansion of the lungs.

PCN provides a less invasive means to drain the renal collecting system in cases where obstruction of the kidney and ureter has resulted in hydronephrosis. Most often used for patients with kidney stones or bladder or pelvic tumor obstructions, PCN may be used to divert urine from the renal collecting system to allow leaks and fistulas to heal [67]. The procedure is often performed after attempts at placing a ureteral stent through retrograde cystoscopy have proven unsuccessful. Hence, it is vital that the urologist and radiologist consult and work as a team. In cases of ureteral obstruction, radiographic images often show an obstructive hydronephrosis. Providing drainage for that kidney is an urgent necessity, and PCN provides an exact method of accomplishing this task.

Patients undergoing PCN should be treated with antibiotics and should receive an intravenous dose within one hour of the procedure being initiated [67]. There is a high incidence of septic shock in patients with upper urinary tract infection, even with antibiotic prophylaxis. Because kidney stones are commonly associated with infection, premedication with antibiotic therapy is commonly used when stones are thought to be present. The most common urinary pathogens are gram-negative bacteria, thus administration of the antibiotic is continued for at least 48 hours after the procedure. Nephrostomy tube placement is most often performed with local anesthesia along with IV moderate sedation. General or epidural anesthesia is indicated only if extensive tract dilatation is planned prior to stone removal.

Nephrostograms, using a dye or contrast through the nephrostomy tube to assess the condition of the ureter and implanted stent, should be performed as a follow-up procedure. When the radiologist is confident that the stent is open and urine is flowing freely, the nephrostomy tube is usually removed. The patient is left with a functioning urinary system with a ureter that will hopefully remain open for a long time. The procedure leaves no external signs of any manipulation, except the small wound that should quickly begin to heal.

Percutaneous transhepatic cholangiogram (PTC) or transhepatic cholangiogram is used to establish drainage of the biliary system. The procedure is commonly performed in the interventional radiology area and obviates the need for open major abdominal surgery. This procedure is often palliative and is frequently performed on patients with nonresectable malignant disease but may occasionally be indicated for patients obstructed with gallstones [72]. It may be contraindicated, though, for patients with diffuse hepatic metastasis, liver failure, or a life expectancy of only days to weeks.

The patient should be premedicated with intravenous antibiotics for at least one hour prior to the transhepatic cholangiogram. Special attention should be paid to PT, INR, and PTT results because patients with liver disease often will have abnormal coagulation studies [72]. The patient should understand the procedure and realize that he or she will likely have to wear a bag to drain bile following the PTC or transhepatic cholangiogram.

When the balloon is in the correct position inside the occlusion, it is inflated with a mixture of sterile saline and contrast medium. Besides allowing the procedure to be watched under fluoroscopy, this is also a safety measure because both the contrast and saline would be observed in the circulation if the balloon should break.

Pressure gradients may first be measured across the renal artery stenosis and percutaneous transluminal angioplasty accomplished in the same manner. Because vascular spasm with renal artery PCI may be a more difficult problem, these patients are more likely to be given vasodilators. Because they usually already have blood pressure problems, they should be watched closely. In addition, many of these patients have borderline kidney function and require extra hydration and diuresis to prevent any type of insult from the intravascular contrast material. Overall, patients who undergo renal artery angioplasty have lasting morphologic improvement in the lumen of the dilated vessels.

Vascular stents are commonly used to improve the result of balloon angioplasty. They act as a scaffold to hold the vessel open, preventing elastic recoil. Stents are usually made of metallic coils or tubular mesh and are introduced into the vessel by a delivery catheter. The goal is to have the endothelium of the blood vessel grow and cover the surface of the stent, which helps to protect it against low-flow thrombosis.

It is important to check the angiogram carefully to make certain that the positioning of the filter is below the renal veins. At the same time, it is possible to ascertain if the size of the filter is appropriate for the patient's anatomy. If the jugular approach is taken, the radiology staff should be alert to changes on the cardiac monitor as arrhythmias may occur as the filter is guided through the heart.

CT-guided celiac plexus block is considered to be a fairly permanent and safe method of pain control. It is primarily used for the relief of intractable pain in patients with malignant abdominal disease or for the relief of chronic, severe visceral abdominal pain in certain types of benign disease, such as chronic pancreatitis.

Embolization is a procedure that has become more common in clinical practice. It is used to form a thrombus in order to block the flow of blood in a vessel. Using the human body's natural tendency to form a clot over a foreign body in a vessel, this technique can be used to close an arteriovenous malformation (AVM) or stop a hemorrhage. It can also decrease vascularity and lessen pain caused by the bulk and position of tumors and may be indicated for some aneurysms.

Microwave ablation is an extension of RFA technology, using a higher energy segment of the electromagnetic spectrum that essentially applies the same principles as microwave cooking to treating tumors. Several limitations of RFA exist that relate to heating capability and, therefore, tumor killing ability, which are overcome by microwave ablation. First, RFA heat generation relies on conductivity between the needle-electrode and grounding pad; as the temperature of the electrode approaches 100 degrees C, soft tissue begins to vaporize and conductivity is diminished; thus, heating stops until the tissue rehydrates and the electrode can be turned back on. Second, blood circulation around the treatment area cools the tissue oftentimes faster than the RF electrode can generate heat [138]. Rather than using electrodes (i.e., needle and grounding pad), the microwave needle-antenna is self-radiant and does not rely on conductivity; additionally, microwaves are higher energy than RF and capable of the intense molecular excitation needed to overcome the circulatory cooling effect. Microwave ablation offers the promise of treating larger tumors, with higher temperatures, faster ablation time, and an improved convection profile over RFA [138,139]. A five-year review of 270 microwave ablations found the treatment to be safe and effective, with a low rate of local recurrence (2% at 36 months); tumors up to 6 cm were successfully treated [140]. A comparison of high-frequency (2450 MHz) and low-frequency (915 MHz) microwave ablation devices found that high-frequency ablations resulted in larger ablation margins and fewer local tumor progression, based on follow-up CT, than low-frequency ablations [141].

It should be noted that the risk/benefit ratio becomes unfavorable when alteplase is administered more than three hours after acute ischemic stroke; therefore, if the onset of stroke symptoms is greater than three hours or is unknown, treatment with this agent is generally not recommended [20,145,149]. The primary risk of alteplase treatment is intracerebral hemorrhage, and there are many contraindications for alteplase, including history of intracerebral hemorrhage, recent previous stroke (within three months), recent head injury, recent surgery, uncontrolled hypertension, seizures, active internal bleeding, or rapidly improving or minor stroke symptoms [146,148,149]. Despite the conventional 3-hour efficacy and safety window, the third European Cooperative Acute Stroke Study (ECASS III) has shown that, although it is optimal to begin treatment as early as possible, there are still modest benefits gained 3 to 4.5 hours after onset of a stroke if presentation is delayed [146,148,150]. While there was an increased incidence of intracerebral hemorrhage in the 3 to 4.5 hour ECASS III treatment (versus placebo) groups, the hemorrhage rate was no greater than current 3-hour treatment statistics; mortality was also not greater [150]. Other research supports extending the approved treatment window to 4.5 hours, but likewise, stresses the importance of beginning treatment as early as possible [146,148,151,152,153].

The most important side effect of papaverine is hypotension, as the vasodilation produced by the drug may cause a significant decrease in blood pressure. A patent intravenous line is essential to provide access for fluid administration. The only direct contraindication for papaverine is heart block, which can further increase conduction delays. The drug also should be used with extreme caution in patients with acute angle glaucoma. Abdominal pain and diarrhea during mesenteric infusion are common and may reflect successful reperfusion rather than the development of bowel infarction [20].

Vasopressin should be used with extreme caution in patients with coronary artery disease because the vasoconstrictive effects may systematically result in constriction of the coronary arteries [20]. In such patients, even small doses may precipitate anginal pain. With larger doses, the possibility of myocardial infarction should be considered.