Thoracic imaging: perception, positioning and technology (Proceedings)

Radiograhic image

The radiographic image is a compilation of black, gray and white areas.

With convention film/screen technology, the radiograph is placed on a lighted view box, light penetrates the film/emulsion in varying degrees; the light strikes your eyes, goes to the brain and an image is formulated based on your prior knowledge/perception.

With digital technology, the image is generated, displaced on monitor, the light from the image strikes your eyes, goes to your brain and an images is formulated based on your prior knowledge/perception.

Image perception

     • You tend to see what you have seen before.

     • The larger your data base, the greater your list of differentials.

     • The greater your experience, the more realistic is your most probable diagnosis.

Radiographic definition

If the radiographic image is of diagnostic quality, you are able to perceive objects/structures because of their atomic composition and the state of the matter in those objects/structures.

The terms used to compare objects of different darkness or whiteness are radiolucent (dark, less opaque) and radiopaque (white, more opaque).

The opacities seen and the jargons used when viewing and describing a radiographic image are:

The opacities of these objects vary from black (gas) to white (bone) and this, in turn, is related to their density, atomic configuration, and volume.

An object can be seen as a distinct entity if it is surrounded by, or contains something of a different opacity.

Straight interpretation

     • Take as many radiographs as required to answer the questions you need to answer or to satisfy yourself the lesion is not definable to the degree you desire.

     • View the radiographs in a consistent fashion; you can follow the international conventions or have your own convention but be consistent!

     • During conventional radiographic studies, equipment and patient motion should be kept to a minimum. A wobbly tube head, a moving table or cassette, patient torso motion or excessive respiratory motion will all result in a loss of image detail.

     • The most accurate anatomic information is usually obtained when the x-ray beam is centered on the area of interest.

     • Proper radiographic techniques are required to help define a lesion. The smaller the lesion, the better the technique required to define the lesion.

     • Overhead lights should be off and the room should be darkened; for convention film/screen imaging, only the viewers required to see the radiographs should be on. You can use "masks" to block off unwanted light from a viewer where the radiograph does not occupy the entire panel; this will improve your ability to see the image. The bulbs in the radiographic viewer should all be the same; the bulbs should not be flickering, and the viewing panel should be clean. A hot light should be available. A ruler should be available. A marking pen should be available.

          o For digital radiology, the quality of the monitor does determine the size of the lesion that can be detected-the better the quality of the monitor the smaller the lesion that can be detected

     • All radiographs should be labeled with

          o Hospital/veterinarian's name

          o Date and time of day if sequential evaluations are performed on the same day.

          o Patient ID

          o Side-Left/Right

          o Position – VD/DV/Right Lateral/Left Lateral.

     • Be aware of artifacts which can be mistaken for lesions:

          o Debris in or on cassette/table/grid

          o Debris on patient

          o Defects in table

          o Film/screen technology: pressure marks and water marks on the film

          o Digital technology: x-ray to electronic conversion artifacts, electronic artifacts

Digital imaging:

     • Type and Quality of the radiographic equipment-single phase vs. high frequency.

     • Type and Quality of the digital detector-CR, Flat Panel DR, CCD

     • Type and Quality of the computer equipment and software

     • Type and Quality of the computer monitors

There is variation in the appearance and prominence of viscera as influenced by inspiration and expiration especially:

     • Lung

     • Heart

     • Mediastinum

     • Diaphragm

     • Liver

     • Vessels

Final comments

     • The good interpreters look in the area of the radiograph where they expect the lesion to be; the great interpreters look at the entire radiograph.

     • Look at the radiograph when you are not rushed, harassed or tired.

     • Avoid constant interruptions when reviewing the radiograph.

     • Try to review the radiographs before the client calls or returns to your hospital to discuss the case with you.

     • When reviewing the radiographs, do the following:

          o List your radiographic findings

          o List your differentials/diagnosis

          o State your comments and methods for further evaluation