Principles of Computerized Tomography (CT)

Abstract

While computerized tomography (CT) urography has been a mainstay for the imaging of the genitourinary (GU) tract in adults, it has been used less frequently in children due to concerns for the radiation dosages and the differing disease processes. Plain x-ray imaging, ultrasonography, voiding cystourethrography (VCUG), nuclear scintigraphy, and magnetic resonance (MR) urography continue to be the most commonly utilized diagnostic imaging methods for assessment of the pediatric genitourinary tract. However, as CT techniques have become more refined and the associated radiation dosages have continued to decrease, the use of CT urography in children appears to be expanding as well.

Common indications for CT urography in children include the evaluation of urinary tract stones, tumors, urinary tract infections/inflammation, trauma, and hydronephrosis. In addition, the use of CT urography has been used to delineate anatomic variations associated with GU anomalies that are unable to be adequately assessed by the other modalities. Although functional assessment of the kidneys is possible with CT urography, its usage in children continues to be low due to the relatively high radiation dosages and because of MR urography’s ability to evaluate the anatomy in a radiation-free manner. However, there remain a small number of infants and children who cannot be safely sedated for MR urography where CT urography may be a good alternative due to its excellent spatial resolution and short scan time requirements. In general, CT urography protocols in infants and children are based on body mass index, age, and weight to calculate contrast amounts and radiation dosages that are as low as possible in adherence to the “As Low As Reasonably Achievable” (ALARA) principles and “Image Gently” guidelines and the minimal use of multi-series imaging [1].