Limitations of the lead oxide vidicon for dual-energy digital subtraction angiography.
Dual-energy digital subtraction angiography (DSA) can be performed, with some modifications, using existing systems designed for conventional DSA work. However, the video camera generally found in such installations, the lead oxide vidicon, places significant limitations on the image quality of dual-energy DSA. If the video camera is operated in a 60 Hz, 266 line progressive scanning mode to maintain a nominal 30 subtraction images/s frame rate, the maximum available X-ray pulse width is limited to 5 ms. The resulting required increase in low-energy kVp reduces the dual-energy signal-to-noise ratio by approximately 40% for cardiac dual-energy DSA imaging. In addition, the performance of the video camera with respect to read-out lag is much more important for dual-energy DSA than conventional single-energy imaging. Measurements show that lag reduces the iodine contrast in dual-energy DSA by up to 20% when a 30 Hz vertical scan mode is used, and by up to 27% when a 60 Hz vertical scan mode is employed. Replacement of the lead oxide vidicon with a CCD camera removes these limitations.
Van Lysel
M S
MS
Dept. of Med., Wisconsin Univ. Sch. of Med., Madison, WI.