Abstract and Introduction
The widespread availability and diagnostic capabilities of ultrasound (US) and computed tomography (CT) have made these tools invaluable in triaging patients with abdominal pain in busy emergency departments. Given the variety of diagnostic possibilities in patients with abdominal pain and their sometimes urgent ensuing treatments, a rapid and accurate diagnosis is of paramount importance. For example, emergent abdominal surgical procedures account for approximately 53% of all nontrauma-related surgical interventions performed in the acute care setting.
The American College of Radiology (ACR) rates US and CT with a high priority score of 6 to 9 for acute abdominal and pelvic conditions in nonpregnant adults (1=least appropriate; 9=most appropriate). However, in pregnant or young patients, the appropriateness of CT drops to 4 to 6, depending on the indication. Although US yields high sensitivities and specificities in abdominal and pelvic pathology in the hands of an expert, it is highly operator and patient dependent. For example, obesity can affect the ability of the ultrasound beam to penetrate the soft tissues, and patient motion and bowel gas can prevent visualization of underlying organs. The main disadvantage of CT is exposure of the patient to ionizing radiation. In younger patients, the radiation dose considerably increases the risk of developing a radiation-induced cancer.
With advances in magnetic resonance imaging (MRI) sequences, protocols, and coil technology, as well as growing familiarity with the modality on both the part of technologists and radiologists, MRI has become a viable alternative to CT. MRI can assess the entire abdomen within minutes, yielding diagnostic sensitivities and specificities similar to those of CT and without the operator dependence encountered in US. Acute abdominal and pelvic conditions that can be rapidly diagnosed with MRI include choledocholithiasis, acute cholecystitis, acute pancreatitis, bowel inflammation in the setting of inflammatory bowel disease (Crohn's disease and ulcerative colitis) and appendicitis.[6,7] In addition, MRI is critical in the characterization of indeterminate CT and US findings. The ACR, however, rates MR imaging of nonpregnant patients in acute abdominal and pelvic conditions with a medium appropriateness score of 4 to 6 because of its limited availability, longer acquisition times, higher cost and lack of incremental diagnostic gain compared with CT. The appropriateness score for evaluation of a pregnant woman with fever, leukocytosis and suspected appendicitis jumps to 7, just below the appropriateness score of 8 for US.
MRI provides several notable advantages over US and CT in the assessment of abdominal pathologies. The first is its lack of ionizing radiation. This feature is of particular benefit to pediatric patients and, by extension, to pregnant women.[5,8] Another subset of patients who undergo numerous CT scans for recurring abdominal pain are patients with inflammatory bowel disease. A second advantage of MRI is the ability to image patients who have allergies to CT contrast agents. Third, MRI can delineate certain disease entities better than US or CT, such as choledocholithiasis, where bowel gas and patient body habitus can obscure acoustic windows on US exams and many stones can go undetected on CT. Last, MRI provides superior contrast resolution and excellent characterization of pathologic tissue.
Disadvantages of MR imaging in evaluating acute gastrointestinal conditions include its high cost, limited availability, longer examination times compared to US and CT, and its incompatibility with equipment used for intensive care and patient monitoring. In addition, MR imaging also has poorer spatial resolution and higher sensitivity to motion-related artifacts than does CT.
Appl Radiol. 2012;41(11):9-15. © 2012 Anderson Publishing, Ltd.