Helical (spiral) CT of the retroperitoneum.

Helical CT promises to improve imaging of the retroperitoneum through the elimination of respiratory misregistration and the minimization of partial volume averaging. The speed of acquisition enables the entire abdomen and pelvis to be imaged in less than 2 minutes with standard collimator widths. This is a distinct advantage in critically ill patients, particularly in the case of trauma. Selective intravenously administered contrast enhancement is made possible with helical CT. Rapid scanning allows imaging in an arterial, renal cortical, renal medullary, or delayed collecting system phase. This property of helical CT enables CT angiography to emerge as a powerful minimally invasive alternative to conventional arteriography for imaging the abdominal aorta and its branches. After 4 years of investigating the use of volumetric CT, the clinical settings described herein remain the only clear indications for using helical CT in the kidney and retroperitoneum. These studies took advantage of the single most important feature of helical CT--the elimination of respiratory misregistration. Two broad diagnostic advantages result: (1) the ability to search and characterize a region thoroughly, such as in the evaluation of a small renal mass, or to search for the needle-tip during an interventional procedure; and (2) the ability to create multiplanar and 3-D images that are of sufficient quality to be useful in clinical practice, such as in imaging the vasculature (CT angiogram), and in surgical planning.