and chondromalacia patellae . When iodinated contrast media is introduced into the joint during an arthrogram, the articular surfaces can be visualized quite clearly using CT. The arthrogram can be performed as a single- or double-contrast procedure. A single-contrast examination is performed with air or radiographic contrast; a double-contrast examination is performed by injecting a small amount of radiographic contrast followed by room air. Personal preference and experience dictate which procedure is performed. Detection of loose bodies and evaluation of articular cartilage may be better with the double-contrast technique; however, improvements in CT image quality and the ability to interactively change the image window and level settings have minimized the differences between single- and double-contrast CTA.
A conventional arthrogram should be performed before the CT study to obtain scout radiographs in order to look for loose bodies, metal hardware, chon-drocalcinosis, and other calcific densities such as calcium hydroxyapatite. Radiographs from the arthrogram help to verify the findings on the subsequent CT study. The CT examination should begin immediately following the ar-throgram, because contrast injected into the joint will begin to diffuse from the joint, degrading the quality of the examination. Some authors have proposed the use of dimeric contrast agents rather than conventional monomeric contrast agents to improve retention of iodinated contrast media within the joint ; at the author's institution, 0.3 mL of 1:1000 epinephrine in every 20 mL of a conventional monomeric iodinated contrast mixture is used to achieve a similar effect.
The CT examination is performed using overlapping submillimeter (nominally 0.5 to 0.8-mm-thick) sections through the joint of interest. Technique is adjusted for thicker body regions such as the shoulders and hips; very large patients usually require higher milliampere seconds (mAs) settings to achieve diagnostic image quality through these body regions. Images are targeted to the region of interest to maximize detail of the affected joint; a medium-sharp algorithm is used to reconstruct the images. At the termination of the examination, multiplanar reformatted images are created using 1-mm-thick slices to view the joint surfaces in anatomic planes. These usually are created at the CT console to facilitate work flow.
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