K-edge digital subtraction arthrography of the painful hip prosthesis: a feasibility study.

K-edge energy subtraction radiography is a method for detecting the presence of iodinated contrast material by subtracting two digital radiographs produced by X-ray beams with energies above and below the iodine K edge. We performed a feasibility study on the application of K-edge energy digital subtraction arthrography (KEDSA) to painful hip prostheses. During arthrography, loosening of the prosthesis is implied if contrast material is seen dissecting around the prosthesis, an often difficult detection task because of adjacent prosthesis metal or cement. In conventional arthrography a preliminary mask image is thus used from which films obtained after injection of iodinated contrast material are subtracted. Movement by the patient during this process may preclude subsequent subtraction. With KEDSA, since multiple image pairs may be obtained after the injection of contrast material, the problem of patient motion is virtually eliminated. A conventional X-ray tube operating between 55 and 65 kVp was alternately filtered by iodine and cerium filters to produce the KEDSA images. The apparatus was capable of producing a subtracted image within 3 sec. The technique was applied to phantoms and to six patients immediately after hip arthrography that had been positive for prosthesis loosening. Although of lower spatial resolution, the KEDSA images were, in all cases, positive for loosening in a pattern consistent with the conventional arthrographic images. KEDSA was shown to be successful in detecting extraarticular contrast material. During a single study, subtraction in various imaging planes as well as postexercise subtraction imaging can be accomplished-techniques not heretofore possible in routine subtraction arthrography.