Clinical history
The cat was first presented for 'being off colour for the past few days'. On clinical exam- ination it was found that there was a solid mass on the right medial hock. On being questioned the owner reported that the mass had be growing over the last few months. Several lymph nodes were enlarged, but no other abnormal clinical symptoms were found. The mass appeared to be a tumour and the owner was advised that the cat would need radiography and a biopsy to determine the extent and type of tumour. The owner signed a consent form for a general anaesthetic, radiography and a biopsy. The cat was starved overnight with access to water until 2 hours prior to premedication.

Restraint for radiography
This was achieved with general anaesthesia. 

Choice of film/screen/grid
Agfa CP B Blue 100 NIF film was used with calcium tungstate screens. This is a blue light sensitive film to compliment the blue light emitting screen. No grid was necessary as the tissue depth was not greater than 10 cms.

Positioning for RH distal limb
Lateral
The cat was laid in right lateral recumbency with the RH placed on the cassette. The left hind limb was abducted, pulled caudally and tied, to avoid superimposition of the left limb on the radiograph. The right limb was tied in partial extension. A visual check was made to ensure that the hock was not rotated. Sometimes a foam pad will be need to be used to bring the hock to the true lateral position. A right marker was placed next to the limb.

Craniocaudal
The cat was laid in dorsal recumbency with the right hind extended and placed on the unexposed part of the cassette. The right hind was extended and tied. The body is rotated axially until the hock is straight. Sand bags can be used along the body, and also one placed over the femur helps bring the hock parallel to the cassette. This is possible with cats but sometimes difficult with dogs to bring the hock down onto the cassette. A right marker was placed by the limb.

All safety precautions taken during radiography are described in Appendix 1.

Centering
An overall view of the distal limb was requested by the clinician, so the hock was used as the centring point for both projections.

Collimation
For both projections the collimation included the distal half of the tibia and fibula to the distal phalanges.

Exposures
The following exposures were used:

Radiographic appraisal
Positioning
Lateral The positioning of this projection is very nearly straight. The metatarsals are quite well superimposed. The hock is slightly rotated. The positioning is good enough in this case to enable a diagnosis.

Craniocaudal
This projection is slightly rotated - the metatarsals do not appear in true cranoicaudal projection. It is difficult when trying to position broken limbs, as the bones proximal to the fracture may be in true position but not distal to the fracture. Positioning was adequate to enable a diagnosis to be made.

The most prominent fault in positioning is that the cassette was not turned so that both projections were similarly distally/proximally aligned. This is distracting when viewing a radiograph, as one projection appears upside down and the radiograph has to be turned around to view each projection properly.

Centering
Lateral
An overall view of the distal limb was required so the primary beam was centred over the hock. In this projection the centre of the beam is at the level of the hock, just cranial to it. This could be improved by better palpation of the bones.

Craniocaudal
Again the distal limb was required so the beam was centred over the hock. In fact it is actually centred just lateral to the hock.

Collimation
Lateral
All four edges of the film are unexposed which demonstrates the extent of the primary beam. This is important for personal safety and to produce a better quality radiograph. The area of interest was actually the distal tibia and fibula. For normal projections of this area the collimation should be closer to the area of interest. In this case the whole of the distal limb was required, so collimation is acceptable.

Craniocaudal
As above.

Exposure
Both projections are slightly overexposed. Particularly in this case assessment of the soft tissues is important, although the soft tissue mass can be seen. Perhaps halving the time of the exposure would have produced a better result - too much mAs blackens the whole film, which is what appears to be happening here. Detail is reasonably good despite over exposure and the definition is also good. There is still a fairly large range of densities around the hock area. This is a diagnostic radiograph.

Processing
An automatic processor was used for this radiograph and it appears to be processed correctly. Labelling Labelling should be done at the time of exposure or before processing, with a light marker, to ensure permanent labelling and also to avoid radiographs being labelled with the wrong animal details. There are presently neither of these in use at this practice.

Artefacts
There are roller marks caused by the processor which do not respond to repeated cleaning of the rollers. There are also finger prints caused after processing during examination of the radiograph.

Diagnosis
The diagnosis in this case was osteosarcoma. The thorax was radiographed and examined under a bright light due to overexposure. No metastasis was evident but the owner was warned that metastasis could still have occurred. The owner opted for amputation of the limb and this has been done, despite advice that it might be better to put the cat to sleep.

General comments on radiography
Radiography was a good diagnostic tool in this case as it enabled sight of both soft tissue and bone, as a non evasive procedure. Heavy sedation and analgesia could probably have been used to obtain diagnostic radiographs rather than general anaesthesia, as the cat was quite ill. A radiograph of the right lateral thorax was also taken but not included as a case here. See Radiographic Case no. 4 with reference to radiography of the thorax. 

References
Small Animal Diagnostic Imaging, BSAVA 1995
Diploma Notes 1999