Question

In reference to panoramic radiography, what is a "focal trough"?
How does this influence the resultant image of a panoramic radiograph?
Give three examples of how improper patient positioning within the focal trough can lead to a less than ideal diagnostic image.

Answer 1

Panoramic radiography is done for the facial bones. It shows a view of the maxilla, mandible, temporomandibular joints, teeth and their supporting structures in one film. The 'focal trough' is a three dimensional area within which structures appear accurately and more sharply and clearly.

Positioning the patient within the focal trough is extremely important for obtaining a clear image of the oral structures in a panoramic radiograph.Those anatomical structures which fall in front of or behind the 'focal trough' can be distorted by being magnified or reduced.

Examples of not getting an ideal diagnostic image by wrong positioning of the patient could be -

* Lower jaw image - The lower jaw is a curved structure, almost 'U'- shaped. Wrong positioning can lead to a distorted image of the bones of the lower jaw and its joint with the upper jaw which will make accurate diagnosis difficult.

* Position of the teeth on the lower and upper jaws - Proper analysis of the positioning of the teeth on the jaws can be affected if an ideal diagnostic image is not obtained. This can affect dental treatment like implants and cosmetic dentistry.

* Temporomandibular disorder - A wrong positioning during panoramic radiograph will not give an accurate image of any type of disorders like compromised movement of the jaw joint and the surrounding muscles. This can make proper treatment difficult.