Flashcards in L43. Radiology: Xrays Deck (17):
How do X-rays work?
High voltage Xray beams are aimed at the body to be examined and a film on the other side of the object (silver halide film) detects the beams scattered off the body.
The more electrons passing through the more conversion of the silver halide and the darker the X-ray appears and the less electrons are in the path.
What is meant by the phrase: "shadow of the xray image is collapsed"
The image is a shadow because the body gets in the way of the Xray path forming a shadow.
The 3D object is also collapsed onto a 2D object (no depth perception) and from an X-ray you cannot tell from a big white blob what individual structures lying on top of each other are.
what determines how many X-rays get through an object?
Depends on the electron density of the object:
Atomic number and concentration of the atoms
The more electrons, the more interactions of the X-rays and the fewer passing straight through it
What is the detection scale for X-rays?
Black = air
White = metal (bone if only looking at organic material)
Anything in between = different shades of grey (air
How do you separate different anatomical structures in an xray?
By a SILHOUETTE SIGN
An interface will only be seen if there are tissues of differing electron densities next to one another. Tissues cannot be separated if they are of he same densities
What are the three things to look for in an xray before examining results?
1. Patient position
2. Quality of the image?
3. Recognition of major anatomical structures you know to be in the area
How is a routine chest X-ray expected to appear?
On full inspiration
posterior to anterior view (PA): the patient is facing the detector such that X-rays pass from the back of the chest to the front
Scapulae moved away from the chest wall (told to hug the xray cassette)
Person is erect: helps with blood flow distribution
Why is it important to take an X-ray image PA?
To ensure that the heart is closer to the film so that the edges are less blurry and less magnified. Because it is a dense object, it will tend to divert the beams away causing more blurry readings
What specific things should you look for in a chest X-ray before examining the results?
Full inspiration: 7 anterior ribs and 11 posterior ribs
Lung bases and costs phrenic angles: important for fluid accumulation
Alignment: front matches the back (eg. Space between Clavicular heads and the spinous processes)
Exposure quality by the image of the structures on either side of the vertebral column
What is the cardio thoracic ratio?
The maximum transverse diameter of the cardiac counter vs the maximum transverse length of the thoracic cavity
If the cardiac contour is >50% then it is abnormal (hypertrophy)
What are the three radiological (CXR) divisions of the lung?
Which is further subdivided into the apex, upper, middle, lower and base of the lung
Where is the "lawyers zone" and why is it named that?
The scapula and shoulder region where the joints alIgn into a relatively amorphous white patch. It is termed so because it is difficult to diagnose fractures in the area because the e densities are so closely related.
Where is the angle of Louis?
The manubriosternal junction. Just in front of the T4-5 junction
What structures are in the mediastinum?
SUPERIOR: aortic arch, SVC + branches (great vessels), upper oesophagus, trachea, vagus nerves and lymph nodes
ANTERIOR: thymus, fat, lymph nodes
MIDDLE: heart, great vessels, phrenic nerve, lymph nodes
POSTERIOR: oesophagus, descending aorta, azygous vein, thoracic duct, lymph nodes
What is the difference between the abnormalities of the pleural spaces: fluid vs air
Fluid sinks to the bases while air rises to the apices
How can you the difference between normal serous pleural cavity fluid and other fluid or abnormalities?
Normally the intrapleural pressure is subatmospheric and hence no meniscus is found. If there is contact with the outside space, this pressure rises and a meniscus is formed indicating an abnormality with the cavity.