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Background
Persistent acute severe right lower quadrant pain in children inevitability results in a trip to the emergency department. A suspicious physical examination is typically followed by an ultrasound study to confirm or exclude appendicitis. In the event of a nondiagnostic ultrasound examination, noncontrast magnetic resonance imaging (MRI) of the abdomen has replaced both noncontrast and contrast-enhanced computed tomography (CT) as the modality of choice due to the lack of ionizing radiation and proven efficacy. Sustaining this approach in a busy academic emergency department requires a high rate of successful diagnostic studies, accurate interpretation 24/7, reproducible free breathing sequences, and imaging times that are on average under 20 minutes. The major limitation of this approach has been the need to obtain the MRI study outside the emergency department increasing actual overall turn-around time and stretching nursing coverage. This remaining limitation has been eliminated by the placement of a dedicated MRI unit in the emergency department.

Educational Goals / Teaching Points
To discuss the etiology of appendicitis in children. To compare imaging modalities in the workup of appendicitis. To describe the rapid MR protocol that used free-breathing sequences. To demonstrate quick and accurate identification of the appendix. To illustrate the critical findings of uncomplicated and perforated appendicitis. To show examples of other causes of right lower quadrant pain. Review the benefits and impact of having a dedicated MRI scanner in the emergency department.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
The rapid MRI protocol consists of respiratory-gated axial, sagittal, and coronal single-shot fast spin-echo T2 with and without fat saturation and diffusion-weighted sequences. The protocol is performed without oral or IV contrast material. The imaging findings of appendiceal/periappendiceal T2 hyperintensity restricted diffusion within the appendiceal wall/periappendiceal fluid collections and increased diameter measuring more than 7 mm increase the specificity of diagnosis of acute appendicitis. Knowledge of the normal diameter of the appendix is important in assessing appendicitis in younger age groups. MRI also helps in accurately diagnosing complications such as abscess formation in cases of perforated appendicitis.

Conclusion
MRI of the abdomen and pelvis in children has become the imaging modality of choice following a nondiagnostic ultrasound examination. The MRI study is time efficient, consistently of diagnostic quality, and accurate in diagnosing appendicitis as well as other causes of acute abdominal pain in children. It provides increased confidence in ruling in or ruling out appendicitis and in some cases establishes a new diagnosis and course of therapy. The benefit of having a dedicated MRI scanner in the emergency department environment has increased the overall utilization of MRI in children having right lower quadrant pain due to faster turn-around times and maintenance of proximity to physicians and nursing staff.