Medical Imaging Flashcards
What is an x-ray image?
-“shadow” on detection device
– film - originally
– detector - modern
- X-rays hit the film converts silver-halide crystals to silver (i.e. black)
– more X-rays → blacker image (more silver halide converted to silver)
– fewer X-rays → whiter image (less silver halide converted to silver)
- detector → electric signal → digital image
- “collapses” a 3D object into 2D c/w CT or MRI
– only get a 3D perspective by looking at other projections e.g. lateral
- no depth perception which can be problematic
What are some basic electron densities of things that you may see on an x-ray?
- x-rays are dependant on the amount of electrons in the body. More electrons will have more interactions.
- how many X-rays get through an object is dependent on the e-density
- atomic #
- Concentration
- air - low e-density → black
- fat
- soft tissue (muscle, viscera)
- calcium (bone)
- contrast agents (iodine, barium)
- metal - high e-density → white
How do you separate anatomical structures on an x-ray?
- “silhouette sign” - you need some tissues of different density between those of the same density in order to see it.
- interface will only be seen if there are tissues of differing e-density next to each other
- air/soft tissue
- air/bone
- soft tissue/ bone
- soft tissue/contrast agent
- bone/metal
- tissue cannot be separated if they are o the same e-density
- chambers of the heart
Here, there are various electron densities and so you are able to see them.
- nipple ring is metallic - bones are white - muscular heart can be seen however the two atria cannot be differentiated because all the muscle has the same electron density.
What is the general pattern for x-ray interpretation?
- patient position
- is examination of adequate quality?
- recognition of anatomical structures:
- “inside out” pattern is my recommendation
- you need your own way of looking at an x-ray
What are some features of an Erect PA CXR: (typical chest x-ray)?
- “routine” examination of the chest is done at full inspiration.
- PA = posterior to anterior
- x-rays pass from the posterior chest wall to the anterior (ie/patient facing away from the x-ray source)
- this is so that the heart is close to the film
- less magnified (because the x-ray process involves divergent electrons that can have a magnifying effect the further away that something is) and edges less “blurry”
- scapulae moves away from chest wall
- “hug” the x-ray cassette
- erect
- determining blood flow distribution in the lungs
- pleural fluid
What are some structures you may see on a chest x-ray?
- midline structures: heart, trachea, spine
- right cardio-mediastinal contour
- left cardio-mediastinal contour
- lungs : zones, lobes and fissures
- lungs : vessels and airways
- diaphragm, upper abdomen, lower neck
- shoulders, clavicles, ribs, breasts
How can you judge whether an x-ray is good or not?
Has the patient inspired properly?
- count the ribs - 7 ribs (ant)/11 ribs (post) indicate a full inspiratory effort
Has the image been exposed enough?
- can you see through the heart? - yes. exposed enough
Can you see the scapula?
- no. then you can see the lungs entirely
Can you see the bases of the lung?
- yes, then you are able to judge if there is fluid on the lungs.
Has the patient stood up straight?
- line up something midline at the front and the back to see if they are superimposed.
What is the first thing you should look at on a CXR?
How large is the heart?
- The maximal transverse diameter of the heart must be 50% (or less) of the maximal transverse diameter of the internal thoracic transverse diameter.
What is the second thing you should look at on a CXR?
Lungs?
You cannot see the lungs because they are filled with air.
We cannot distinguish lobes and so there are three zones: Upper, middle, lower zones.
- The top of the upper zone is the apex and the bottom of the lower zone is the base.
- Always check the entire x-ray because you may miss a fractured humorous.
What are some features of the mediastinum in a CXR?
The mediastinum cannot be easily defined on the radiograph and so the angle of Louis is used. It divides the mediastinum into inferior and superior.
- Laterally the inferior mediastinum is divided into anterior, posterior and middle.
Superior: aortic arch, SVC and branches of these great vessels, upper oesophagus & trachea, vagus nerves, LNs
Anterior: thymus, fat, LNs
Middle (pericardium): heart, great vessels, phrenic nerves, LNs
Posterior: oesophagus, descending aorta, azygos vein, thoracic duct, LNs
What are some features of the mediastinum in a CXR?
The mediastinum cannot be easily defined on the radiograph and so the angle of Louis is used. It divides the mediastinum into inferior and superior.
- Laterally the inferior mediastinum is divided into anterior, posterior and middle.
Superior: aortic arch, SVC and branches of these great vessels, upper oesophagus & trachea, vagus nerves, LNs
Anterior: thymus, fat, LNs
Middle (pericardium): heart, great vessels, phrenic nerves, LNs
Posterior: oesophagus, descending aorta, azygos vein, thoracic duct, LNs
What are some CXR features of the pleural spaces?
- If there is fluid in the pleural space then it will sink and form a meniscus
- If there is air in the lung it rises to the apices.
What is an analytical approach to understanding CXR?
- approaches are often not specific
- cannot be interpreted in isolation
- must have reasonable clinical notes!!
- patient age, sex and ethnicity (label)
- PA, erect, centred, inspiratory, exposure
- medical devices, foreign bodies
- heart size, valves (if calcified)
- mediastinal size, contour and divisions
- lungs (normal) – airspace, airways, interstitium and lobes/zones
- lungs (abnormal) – nodules, masses, scars, cavities
- pleura – effusion, pneumothorax
- diaphragm, upper abdomen, lower neck
- soft tissues (incl. breasts), bones, joints
What are some features of Pneumonia seen on a CXR?
Pneumonia: mid zone right lung (right upper lobe defined by the fissure that is giving the straight line at the base of the pathology)
- likely to be sputum, bugs, neutrophils etc.
- usually caused by Strep. pneumoniae
RIGHT UPPER LOBE PNEUMONIA
What are some features of an abscess caused by infection seen on a CXR?
Infection: likely to be immunosuppressed. Enlarged Heart: may not be abnormal if the x-ray is not reliable.
- abnormality is in the right lung upper zone (rounded mass with a cavity of fluid)
- When IV drug uses inject, they may not inject cleanly and inject bacteria etc. which get trapped in the lung capillaries.
- Usually skin organisms such as Staph. and forms an abscess in the lung.
ABSCESS IN RIGHT LUNG
