Thoracic Imaging Flashcards
Why do we limit x-rays
X-rays are a form of ionising radiation which can damage tissue, cells and DNA
Damage to DNA may lead to uncontrolled cell division (cancer)
What safety precautions must staff take when using x-rays/CT scans
Staff required to wear lead aprons
Regulated by Ionising Radiation (medical Exposure) regulations
What structures appear white on x-ray film
Dense body parts eg bone
What structures appear almost black on x-ray film
Less dense structures eg lungs
Soft tissues appear… on x-ray film
Different shades of grey depending on how dense they are
Why is diaphragm higher on the right
Presence of the liver
AP x-rays (anterior-posterior)
from front to back (the detector is behind the patient).
These are often performed when the patient is very unwell and may not be able to get into the ideal position.
As the heart is at the front of the thorax, the x-ray beams diverge after hitting the heart, creating a larger ‘shadow’ on the detector. Therefore, the heart may appear large and less crisp on an AP image.
PA x-rays (posterior-anterior)
opposite, x-ray is directed at the back of the patient and detected at the front. The heart is closer to the detector so less x-ray divergence after hitting it means it produces a more accurate size on the image, and less blurry.
• Also, the scapulae can be protracted for a PA x-ray by having the patient put their arms around the detector, so that the scapulae are not overlying the lung fields.
Pneumonia on x-ray
Causes a patchy opacification in the lung fields
Pneumothorax x-ray
Air in between the parietal and visceral pleura
• On the x-ray you may be able to see where the normal lung markings stop, and there may be a rim of very clear black around the lung field, indicating air in the pleural space.
• Normally there is a very small amount of fluid between the pleura to provide surface tension so that they stick together.
• If air gets in the pleural space (between the pleura), that ‘sticky’ surface tension is lost, so breathing is compromised.
Pleural effusion x-ray
collection of excess fluid in the pleural space. It is often caused by infection, cancer, or heart failure.
• As blood and inflammatory/pleural fluid are the same colour on an x-ray, it is difficult to tell if a unilateral (single-sided) pleural effusion is just pleural fluid, or if it could be blood (known as a ‘haemothorax’).
Rib fractures x-ray
can be seen on a chest x-ray but are often difficult to see unless displaced. Rib fractures can damage the pleura and cause a pneumothorax. If multiple rib fractures and/or significant tissue damage is suspected, a CT scan may be performed to better visualise the thorax.
Heart failure x-ray
Features of heart failure can be seen on the chest x-ray and include an enlarged heart, small bilateral pleural effusion, alveolar oedema (fluffy image), and fluid in the lung fissures.
CT scans
consists of many individual x-rays directed through the patient from all sides. The data from the x-rays detectors is then analysed to produce the 3D images.
• CT scans therefore consist of a much higher dose of ionising radiation but produce much more useful 3D images.
• As with x-rays, the left side of the image is the patient’s right.
• Axial CT images are viewed as if you are standing at the patient’s feet as they’re lying down and you’re looking up at the axial image.
Why use a lead apron
Lead absorbs ionising radiation
