Computed Radiography In Cetaceans
IAAAM Archive
Natalie Rourke1; Reimi Kinoshita1; Crista Rayner1; Paul Chan2; Lawrence Cheung2; Con Metreweli2; Fiona Brook3
1Ocean Park Corporation, Ocean Park, Aberdeen, Hong Kong; 2Prince of Wales Hospital Shatin, New Territories, Hong Kong; 3Hong Kong Polytechnic University, Kowloon, Hong Kong


Respiratory disease is a common cause of morbidity and mortality, in captive cetaceans. Regular monitoring, standardization of collection methods and establishment of normative parameters, are required for the success of a preventive medical programme.

A range of diagnostic methods is available for collection of clinical data. Cetacean thoracic parameters are commonly assessed by cross-referencing physical examination findings, blood parameters, blowhole flora and cytology, ultrasonography, radiography and bronchoscopy.

Computed radiography (CR) is now replacing conventional screen film systems, in general medical radiography. Digital radiography differs from conventional radiographic screen film systems, the x-rays exiting the patient are captured by a detector, or imaging plate, that generates a latent analogue image, rather than a standard film.

The imaging plate (IP) is then placed in a 'reader', which converts the latent image from analogue to digital data (ADC). CR images can then be viewed and stored on a workstation. Digital image processing techniques, such as edge enhancement, may then be applied to improve specific diagnostic performance.

The image may be printed on a film, or electronically transmitted. The advantage of the CR technique is that the IP has a wider exposure latitude, which compensates for exposure errors, and produces final images of very good quality- even in bad conditions. Dose reduction is theoretically possible, however a large dose reduction produces increase in quantum noise, therefore in practice the radiation dose tends to equal conventional screen/film systems. There are four technologies in use or under development, in CR. The most common system, utilizing phosphor plates, was employed here to investigate the value of this new technique for cetaceans.

CR of the thorax was performed on juvenile and mature, nongravid cetaceans, including 17 bottlenose dolphins (Tursiops truncatus [subspecies- aduncas]) and one false killer whale (Pseudorca crassidens), from July 1996 through to July 2000.

The detailed images acquired, the minimal restraint required to achieve them, and the inherent exposure compensation, of computed radiography, provide real improvements in disease surveillance in these species.


This study was made possible by kind donation of imaging plates from Fuji film; a grant from Poly Technic University, Kowloon, Hong Kong [CRG- $362], and the support of the husbandry and animal care staff at Ocean Park Corporation, Ocean Park, Aberdeen, Hong Kong.

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Natalie Rourke

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