Quantitative and qualitative comparison of two microfocus-tube imaging systems.

Two microfocus-tube magnification systems were compared: one used an RSI tube (stationary anode, Pierce-gun cathode) and the other used a GE tube (rotating anode, biased cathode). Imaging parameters for body parts of three thicknesses, the hand (low), knee (medium), and hip (high), were considered at a magnification of 2. The focal-spot MTF was measured on and off the central ray of the beam, as well as beam quality and the intensity of scatter in the image plane. Patient exposures were also determined. While both systems gave high-quality images at acceptable exposure levels, the RSI unit was judged superior for body parts up to 15 cm thick. For thicker parts, scatter degraded contrast with the RSI unit, making the GE unit superior.