Information in this chapter is arranged anatomically from superior to inferior. It would not be feasible to include all available imaging tests in one chapter in a book of this size, but we have attempted to summarize the essential features of those examinations that are most frequently ordered in modern clinical practice or those that may be associated with difficulty or risk. Indications, advantages and disadvantages, contraindications, and patient preparation are presented. Costs of the studies are approximate and represent averages reported from several large medical centers.
$ = <$250
$$ = $250–$750
RISKS OF IODINATED CT INTRAVENOUS CONTRAST AGENTS
Although iodinated CT intravenous contrast is an important tool in radiology, it is not without risks. Minor reactions (nausea, vomiting, hives) occur with an overall incidence between 1% and 12%. Major reactions (laryngeal edema, bronchospasm, cardiac arrest) occur in 0.16–1 cases per 1000 patients. Deaths have been reported in 1:40,000 to 1:170,000 cases. Patients with an allergic history (asthma, hay fever, allergy to foods or drugs) have a slightly increased risk. A history of allergic-type reaction to contrast material is associated with an increased risk of a subsequent severe reaction. Prophylactic measures that may be required in such cases include corticosteroids and H1 and H2 blockers.
In addition, there is a risk of iodinated contrast-induced nephropathy, which is usually mild and reversible. Recent data suggests the risk of contrast-induced nephropathy is lower than previously estimated. Persons at increased risk for potentially irreversible renal damage include patients with preexisting renal disease (particularly diabetics with renal dysfunction), multiple myeloma, and severe hyperuricemia. Iodinated CT contrast materials are generally contraindicated in patients with severe renal insufficiency (ie, estimated glomerular filtration rate < 30 mL/min/1.73 m2). In patients with mild to moderate renal insufficiency (ie, estimated glomerular filtration rate between 30 and 60 mL/min/1.73 m2), minimizing the dose of contrast and increasing hydration are suggested.
RISKS OF GADOLINIUM-BASED MRI INTRAVENOUS CONTRAST AGENTS
Contrast agents used in MRI are different from those used in most other radiology studies. Most MRI contrast agents are gadolinium-based and are teratogenic and thus contraindicated in pregnancy. Rarely, patients with severe renal dysfunction, particularly if on dialysis, or those with acute renal failure may develop irreversible nephrogenic systemic fibrosis after receiving gadolinium-based intravenous contrast. Gadolinium-based contrast is contraindicated in these patients. In patients with mild to moderate renal insufficiency, the dose of gadolinium-based contrast material should be minimized. Immediate contrast reactions are rare (minor reactions in approximately 0.07% and major reactions in 0.001%). Contrast-induced renal failure is generally not associated with MRI intravenous contrast.
In summary, intravenous contrast agents should be viewed in the same manner as other medications—that is, risks and benefits must be balanced before any examination using these pharmaceuticals is ordered.
DIAGNOSTIC IMAGING: TEST ...