Several steps are involved in the evaluation of film quality.  Positioning, technique, and inspiration must all be evaluated.  We will look at each one of these in turn.

Positioning:  

The Frontal chest radiograph, if properly positioned, will demonstrate the spinal processes centered between the medial ends of the clavicles.   Position variation from centered, of more than about one centimeter,  will affect the appearance of the chest.  This variation will cause the density of one lung to increase, while the other decreases.  Unusual appearances to the hila will also be noted.  The Lateral chest radiograph, if properly positioned, will demonstrate near superimposition of the ribs from the left and right side.  Also the sternum will appear to have minimal thickness in the well positioned lateral.

Unlabeled frontal.  Can you visualize the relationship between the medial clavicles and the spinous process. (place mouse over image for labels)

 

Lateral, note the posterior ribs and the sternum. (place mouse over image for labels) Arrows indicate the superimposed ribs in the well positioned film

Technique: 

The evaluation of technique is a subject that could require several pages of discussion.  In general however, the quality Frontal chest radiograph will allow the observer to clearly define the lower thoracic vertebral bodies through the shadow of the heart.   In addition, lung markings should be visible throughout the visualized lung fields.  In our familiar example, a box has been drawn around one of the lower thoracic vertebrae.  Other vertebrae can also be distinctly identified through the spine.  If you are able to identify the vertebrae as well as lung markings, the study is of a good quality.  In the case of the lateral film, the bodies of the spine should all be visible.  Lung markings should also be easily seen.

Frontal view, markings are noted throughout the lungs.  Vertebrae are visible through the heart.

Lateral view, good visualization of both lung markings as well as adequate penetration of the spine

 

Inspiration: 

Inspiration evaluation is also very important in determining the quality of the radiograph.  On the frontal evaluation, in the adult, it should be possible to identify 10 posterior ribs above the diaphragm.   Without an adequate inspiration, the 'crowding' of lung markings that are caused can confuse the observer into believing that there are abnormalities in the lungs when there are not.  In addition, the cardiac shadow is not adequately evaluated in the poorly expanded chest.  The heart will appear larger than it actually is.  Counting the ribs is most easily accomplished if you start with the anterior aspect of the first rib and follow it back to the spine.  Use that as your starting point to assure that all ribs are included.

Excellent Inspiration, 11 posterior ribs

Slightly less inspiration at 10 ribs. Note increased density of lower lungs and lungs in general.  Also note the relative increase in cardiac size on the poor inspiration film.