14 - Medical Imaging Flashcards
What are the advantages and disadvantages of X-Rays?
Advantages - Fast - View bone - Less radiation than CT
Disadvantages - Can’t see soft tissue - Radiation - 2D
What are the advantages and disadvantages of CT scan?
+ 3D
+ Quick
+ Can see bone and high density
- Cheaper than MRI
- High radiation
- Can’t see soft tissue
What are the advantages and disadvantages of MRI scan?
+ Can see soft tissue and high detail
+ No radiation
- Expensive
- Claustrophobia/Loud
- Slow
- Not good for bones
- Patients with metal implants can’t use (e.g affects pacemaker signals)
- Tissue heating
What are the advantages and disadvantages of a PET scan?
+ Can be combined with CT for greater detail
+ 3D
+ Non-invasive diagnosis (e.g if stent worked)
- Radiation
- Expensive
What are the advantages and disadvantages of fluoroscopy?
+ Live image
+ Can be used for surgical procedures to check placing right
+ Cheap
- Radiation
What are the advantages and disadvantages of ultrasound?
+ No radiation
+ Dynamic
+ Cheap + Fast + 3D + Doppler effect
+ Patients in ICU can use rather than taking them to x-ray
- Poor detail
- Can’t see bone
- User dependable (depends who is interpreting at time)
- Can’t view past air (need jelly)
How does an X-Ray work?
Gamma rays emitted from cathode ray tube at individual. Dense tissue, e.g bone, absorb (attenuate) more x-rays emitted so they are not collected by detector. They appear white on x-ray film.
How do you generate an angiography?
Initial image of area of interest is X-rayed. Inject patient with iodine, which increases density of vessels, and take another image. Subtract the first image from the second image to see just the vessels.
How does a CT (computed tomography) work?
Emitter and receiver spin around the patient taking lots of x-ray pictures. Combined by computer to form 3D image. Most dense area is white, least dense is black.
What is attenuation measured in?
Hounsfield units, given a colour on the grey scale. Bone is white and air is black.
How does PET (positron emission tomography) work?
Radioactively labelled is eaten or injected. Glucose taken up by highly metabolic cells, e.g cancer. Scanned so areas with high radioactivity can show where glucose is. Combined with CT for 3D.
How does fluoroscopy work?
Continuous x-ray beam takes series of x-rays and combines them to form a ‘movie’. They are dynamic. Can be used with contrast to see movement of substance.
How does MRI (magnetic resonance imaging) work?
Uses hydrogen ions. Nuclei spin randomly. Magnetic field produced by MRI causes atoms to spin only north and south, in pairs. Few unmatched atom not in pairs. Radio frequency pulse applied and this gives unmatched atoms energy to flip. Pulse removed and atoms flip back to original to, releasing energy in form of radio waves. Energy sends signal to computer which uses mathematical formula to form an image.
How does an ultrasound work?
Ultrasonic frequency emitted by probe. Sound waves travel into tissue and then when they meet a change in density they are reflected. Reflections are detected and converted into image based on time taken to return.
How can you improve ultrasound resolution?
Increase the frequency of waves, more reflections. However won’t be able to reach as much depth, e.g if fetus.
What can PET be used to diagnose?
- Cancer
- Brain activity (dementia, epilepsy)
How would you interpret a chest x-ray?
- What film it is (e.g chest, abdomen)
- Orientation
- Is it adequate?
What organs can help tell orientation of X-ray and why?
Left: - Spleen - Heart - Stomach
Right: - Liver - Appendix
How would you describe orientation of x-rays?
- Superior
- Inferior
- Anterior
- Posterior
- Medial
- Lateral
What are the three planes of x-ray?
- Coronal (put crown on down middle)
- Transverse/Axial (cut me at the stomach)
- Sagittal (cut me down nose and look at from side)
What is are the two types of chest x-rays, and which is better?
AP (Anterior to Posterior)
- Poorly patients cant drape themselves
- Poor image
- Proportion of organs out
PA (posterior to anterior)
- Ideal, high detail
- Patient drapes over detector so scapula out the way
What are hounsefield units?
Measure of attenuation. Bone is most, given white 1000. Air is least, given black -1000. Everything else in between.
What plane are CT scans in?
Axial/Transverse (standing at feet looking up)
How can you improve resolution of CT, MRI and X-Ray?
Use contrast (inject dye, e.g iodine)
What are x-rays most useful for diagnosing?
- Issues with bones
- Issues of density in areas where there should be low density
- Issues of low density in areas that should be high density
- Narrowing of tubes (contrast)
E.g - Chest - Pneumonia, cancer, pulmonary oedema - Abdomen - Ascites, obstructions, stones - Metal Implants - Tooth cavities
What are CT scans most useful for diagnosing?
- Head: tumours, oedema, infarction, haemorrhage, calcification
- Lungs: emphysema, fibrosis
- Angiography: Dye can add contrast so can see vessels, obstructions in vessels are dark as vessel is white
- Cardiac: Coronary HD (contrast), Coronary Calcium (no contrast to see severity of CHD)
- Abdominal: Cancer (calcified tissues)
- Complex bone fractures (high resolution)
What is fluoroscopy most useful for diagnosing?
- Placement of stents and catheters
- Angiography (aneurysms, leaks, thromboses, new vessel growth)
What is MRI most useful for diagnosing?
- Head (oedema, tumour, haemorrhage)
- Spine (tumour and breaks)
- Joints (infection osteomyelitis, ligament damage etc)
- Cholangiopancreatography (biliary or pancreatic duct blockage or stones)
What is an ultrasound most useful for diagnosing?
- Foetal development
- Abdominal swelling
- Blood flow in vessels (Doppler effect)
- Guide drainage and fetus surgery
- Critically ill patients
What are the two phases in MRI?
Relates to colour water goes
T1 - Black
T2 - White
What is nuclear medicine and what is it used to image?
Imaging involving the administration of radiopharmaceuticals to display physiological function (PET)
- iodine-123 and 131
- gallium 67
- thallium 201
- 18F-FDG
Image: heart, brain, gallbladder, thyroid, lungs and bones
What are the main differences between PET and X-Rays?
- PET uses positrons not gamma rays
- Has higher resolution
- Can see multi planar (SPECT)
What is interventional radiography?
Minimally invasive procedures for diagnostic or treatment purposes, e.g angiography
What the positives of intervention radiography?
- Patient awake not sedated
- Decrease infection, hospital stay length
- Increase recovery time
What are some examples of positive and negative media?
Positive (white): Barium, iodine, gadolinium
Negative (black): Water, air, CO2
How would you choose a contrast media to use?
- Safe
- Cost effective
- Inert
- Highly water soluble
How would you administer contrast and how is it removed?
Administer: Oral, Rectal, IV
Removal: Excretion
What are some issues with using contrast?
- Allergic reactions
- Thrombosis
- Endothelial damage
- Vascular pain
What would you consider when using contrast with patients?
- Previous reactions to contrast
- If they have kidney disease (can’t excrete contrast)
How would you assess a chest x-ray?
A - Airway (is trachea central)
B- Breathing
C - Circulation (heart size)
D - Disability (fractures)
E - Everything else
What is contrast media commonly used for?
- Gall bladder function
- Angiography (iodine)
- DCBE (barium)
Why are CT’s chosen over MRI?
- Availability
- Cost
- Speed
