Measurement of x-ray image intensifier sharpness in the x-ray department.
A method is presented for determining the modulation transfer function (MTF) of an image intensifier as it is found in the x-ray department. The image of an edge input into the image intensifier tube is photographed at the television camera port with a high quality camera and the photographic image scanned with a microdensitometer. Densitometric conversion enables the determination of the edge spread function and further calculation produces the line spread function and the MTF. A correction is made for the camera/lens/film/developer response function. Results from the use of the technique on over 25 x-ray image intensifiers in New Zealand hospital x-ray departments are presented and discussed. Most of the image intensifiers had been in use for more than 7 years. The low-frequency drop values were similar to reported values with an average value of 22%, but modulation values at 1 cycle/mm (the average value was 29%) were generally lower than values previously reported, indicating that the sharpness performance in the clinical environment is inferior to claims for new or state-of-the-art intensifiers.
Le Heron
J C
JC
National Radiation Laboratory, Christchurch, New Zealand.
Poletti
J L
JL
D005069:Evaluation Studies as Topic; D006748:Hospital Departments; D006801:Humans; D009520:New Zealand; D011856:Radiographic Image Enhancement / Q000295:instrumentation; D011872:Radiology Department, Hospital; D014963:X-Ray Intensifying Screens