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Single-exposure conventional and computed radiography. The hybrid cassette revisited
1Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, Missouri 63110.
Rationale And Objectives:
The authors constructed and evaluated a hybrid cassette for single-exposure extremity imaging with storage-phosphor plates and conventional radiographic film.
Methods:
A hybrid cassette was constructed using a fine radiographic screen and a storage-phosphor plate. Exposures of a Lucite step wedge and a line pair gauge were made with the hybrid cassette, a conventional radiographic cassette, and a storage-phosphor cassette. The spatial resolution and imaging speeds of the hybrid and standard systems were compared.
Results:
Spatial resolution loss was less than 0.5 line pairs per mm with the hybrid cassette. Speed loss was characteristic of the hybrid cassette, requiring approximately 40% greater exposure to produce the same film density as standard cassettes.
Conclusions:
The speed difference between this and a previous study is probably due to differences in film-screen choice, kilovolt peak, and storage-phosphor plate generations. The sensitivity spectrum of our film and the emission spectrum of our screens were more closely matched than were the spectra in the previous study; we used lower kilovolt peak, and our storage-phosphor plates were a later, more efficient, generation. Despite slight speed losses, the hybrid cassette appears to be a better choice for obtaining matched images for clinical trials than the alternative of two separate exposures.