Programmable dynamic line phantom control

Abstract

The dynamic line phantom (DLP) produces various test patterns for the qualitative assessment of gamma camera performance, by stepper motor control of the translatory movement of a radioactive rigid line source. The addition of a V24 serial interface port has allowed external control via an RS-232 connection to a personal computer. Programmability has enabled the DLP to be used as a quantitative test tool. One such program produces a variable contrast 'hot' and 'cold' bar pattern. The addition of a Quick Basic computer program modifies the line source movement to compensate for variation in line source activity. This maintains a test pattern with fixed, absolute contrast levels, giving the potential for the measurement of variations in long-term imaging performance. A modulation transfer function (MTF) pattern has been designed which encompasses a sinusoidally varying intensifying function with a changing spatial frequency component. Repeated measurements on two gamma cameras demonstrated poor reproducibility (CV of up to 50% dependent upon spatial frequency) and significant differences between the MTF obtained from line spread function measurements (percentage deviation of up to 23%, dependent upon spatial frequency). Neither test pattern has been adopted for routine quantitative assessment of gamma camera imaging characteristics. The reproducibility of results is poor (dominated by counting statistic limitations), making the techniques insensitive to small changes in camera performance.