[Clinical application of a spot filter for exposure dose reduction]

An added filter on the collimator of the X-ray tube is useful for reducing exposure dose in interventional radiology (IVR). During IVR, high-quality fluoroscopic images are needed around the target region, but the portion of the fluoroscopic image that shows catheter/guide wires need not to be of high quality. Thus, we constructed an additional filter (spot filter) consisting of a copper sheet with an open hole in the center. The spot filter is moved by a remote control technique and can be used in cases of neurological, cardiac, abdominal, and pelvic IVR. Using this filter, image quality was improved at the target region of the image intensifier, because scatter radiation was attenuated in the periphery. Although image quality was deteriorated in the periphery, there was no significant disadvantage for IVR. The spot filter would be effective in reducing exposure dose in cases where the image quality of the target region needs to be maintained and in prolonged fluoroscopy.