Introduction
It is well known that by using an intensifying
screen in the cassette in combination with X-ray film, the phosphor generally used such as calcium tungstate absorb incident X-ray energy and emit visible light of high intensity in the blue and violet continuous spectrum, which gives an advantage of intensification resulting in the use of lesser X-ray energy in imaging.1 When screens containing phosphors like gadolinium or lanthonium disulphide activated by terbrium, which emits a line spectrum of green light, it is expected that the X-ray film used in the cassette in combination should be a green sensitive one or an orthochromatic type. In other words there is need for film phosphor compatibility.2 It may be possible that this compatibility is lost when an X-ray film is loaded in a wrong cassette or vice versa or when a film is packed and labelled wrongly. The end result shall be disastrous in getting a useless image.

Material and Methods
Generally, our hospital uses blue sensitive X-ray films supplied by one of the leading manufacturer for their X-ray imaging work loaded in compatible cassette fixed with a blue sensitive phosphor and the images used to be excellent. Recently during our routine work the 17 x 14 inch size film was found to be requiring more factors than normal and the resulting radiographs were extremely of bad quality. This attracted a lot of criticism during our weekly quality audit meeting as well as from referring consultants.

We were puzzled to find out what exactly was the problem for the poor quality of the image. Later we noticed that this is not happening with other size films. This had been reported to the local supplier and they in turn replaced with another packet of 17 x 14 films, but appear to be the same batch. Unfortunately this packet of films also had the same problem. We have tried many alternative techniques, which did not help to solve the problem, and finally we cut one of these 17 x 14 films and loaded in a green sensitive cassette and exposed by normal factors. To our surprise this picture came out extremely well (Fig. 1). We also loaded another cut film in blue sensitive cassette and exposed with normal factors, which was very much under exposed (Fig. 2).

Thus, it was proved that the packet containing green sensitive film had been wrongly labelled. This was confirmed by more than one trial.

Fig. 1 : Green sensitive film in combination with green sensitive screen.	Fig. 2 : Green sensitive film in combination with blue sensitive screen.

Discussion
In our first trial using 17 x 14 inch film in a blue sensitive cassette, our picture was defective and when a similar film loaded in a green sensitive cassette the image was fine. This gave us the clue that the original film supplied was a green sensitive one packed in a packet wrongly labelled as blue sensitive. The error of incompatibility erupt in was not noticed at the supplier level or manufacturing and packing level of the company. It is noted that such errors created tension in the X-ray department of the hospital causing unnecessary repetition of X-ray, inconvenience to the clinician and more radiation dose to the patient.

Conclusion
It is the duty of quality control department of the film manufacturing company to verify and confirm that the packed films are correctly labelled before dispatching to the customer. Due to such incidents the patient will receive unnecessary radiation and the resultant image is of no use, which will cause lot of inconvenience to the treating clinician and embarrassment to the radiologist. Hence a periodical quality auditing will help to minimize the radiation dose to the patients and also to get good quality radiograph.

The packing and quality control section of the film manufacturer must also think of possibility of incompatibility error as explained when films are packed and check the label of outer cover are proper. Such errors create problems at the user end where clinicians make use of X-ray images for their diagnostic purpose in the course of treatment of their patients.

References

1. Farr RF, Allisy - Roberts PJ. "Physics for Medical Imaging". Published by Margaret Macdonald and WB Saunders, Elsevier Science. Robert Stevenson House, Edinburgh, reprinted in 2002, page 66.
2. Joseph Selman. Fundamentals of X-ray and Radiation Physics' Page 282. Published by Charles C. Thomas USA 8th Edition 1994.