Single-exposure conventional and computed radiography. The hybrid cassette revisited.

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.