Monday, January 26, 2009

Criteria of good radiograph, composite shadow & projection for foreign bodies

I had received the following questions from a reader. These are my answers:

Question 1: What are the criteria for good chest radiograph?
a. Well expanded chest where atleast 6 ½ anterior ribs are seen.
b. No rotation. This is assessed by measuring the distance between the medial end of clavicles and the spinous process. Both sides should be equidistant.
c. Both scapulas are outside lung fields
d. Correct exposures
e. Correct processing condition
f. ID and side marker are present
g. Vascular pattern are seen up to middle 1/3 (and not in the outer 1/3)
h. Upper 4 thoracic vertebrae are seen but not the lower ones

Question 2: What is composite shadow? Why it may mimic a cavity?
Composite shadow is a combination of many shadows such as artery and veins. When a few arteries and veins criss-cross each other, a lesion mimicking a cavity may be seen. Most often the problem arises around the hilar region when there are many structures criss-crossing each other.

Question 3: What projections do you do for foreign bodies?
To look for foreign body in a soft tissue, the best is to do 3 views: AP, lateral and tangential views. AP & lateral are standard views for extremity x-rays. Tangential refers to another projection where the x-ray beam is placed tangential to the soft tissue of interest. With these 3 views, you are less likely to miss any foreign bodies.

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