Dynamic Magnetic Resonance Imaging and Nuclear Imaging

a large-field-of-view gamma camera. The anal canal axis is defined by a line drawn through the middle of the balloon image of the anal canal. The rectal axis is defined by a line drawn parallel to the most inferior portion of the rectal image, just cephalad to the anal canal. The location of the anorectal junction is measured as the perpendicular distance from a line drawn between the pubococcygeal line to the most caudal aspect of the rectal image. In healthy persons, rectal evacuation is associated with widening of the anorectal angle and perineal descent (Fig. 12.2). In patients with symptoms of a functional defecation disorder, scintigraphy may reveal either reduced motion (i.e., anorectal angle change or descent), or increased perineal descent (i.e., descending perineum syndrome). To quantify rectal emptying, the rectum is filled with a 7.5% colloidal dispersion of aluminium magnesium silicate labeled with 1 mCi of Tc with patients in the left lateral decubitus position. Images are obtained before evacuation (3-minute acquisition), during evacuation (2-second dynamic images over 4 minutes), and after evacuation (3-minute acquisition) on a commode. The percentage and rate of total Tc evacuation is calculated; less than 37% evacuation (i.e., 2 standard deviations below mean) is considered abnormal (Fig. 12.3). The median evacuation time for seven asymptomatic subjects was 40 seconds.