Radiology Flashcards
How does an x-ray work
Focused beam of high energy electrons
These can pass through the body onto receiver
But some are absorbed or scattered (attenuation- the higher the density and atomic number the higher the attenuation
Depends upon density and atomic number (metals)
What are the principle densities?
Air Fat Soft tissue Bone Metal
How to read a CXR
AIR Breathing Circulation Disabilities (bones Everything else
How to read a AXR?
AIR
BOWEL
DENSITIES (BONES)
ORGANS
How to read orthopaedic film
Fractures - displacement
Bony abnormality - bone quality
Advantages and disadvantages of X-ray
Advantages Quick Simple cheap Portable
Disadvantage Ionising Radiation (low) Poor soft tissue imaging One plane two dimensional Cant visualise all areas
Uses of x-ray
Chest
Bowel
Orthopaedic
What occurs in fluoroscopy?
Examination of anatomy and motion.
Uses constant steam of x-rays
Often enhanced by contrast
What are the contrast used in fluoroscopy?
Barium, iodine or gadolinium (MRI)
What are the uses of fluoroscopy?
Angiography
Contrast GI studies
Screening in theatre
What are the two cross sectional imaging?
CT
MRI
What occurs in CT ?
There is a rotating gantry
X-ray tubes on one side
Detectors on the other side
The patient lays in the trolly, then they will pass through it as the gantry spins around them.
Images put together by computer
Same principle of attenuation as x-ray
What are Hounsfield Units (HU)?
Ability to distinguish densities in CT scans
Less dense = negative HU
E.g. air (more negative) and fat
More dense = positive HU
E.g. bone and metal
Water = 0HU
Pg29
What are the advantages and disadvantages of fluoroscopy?
Advantages
Dynamic studies
Cheap interventional procedures
Disadvantages
Clinician exposure must be minimised
Radiation
Advantages and disadvantages of CT scans?
Advantages
Quick
Good spatial resolution
Can scan most areas
Disadvantage
Radiation
Affected by artefacts
Requires holding breathe
Lower contrast resolution
Uses of CT Scans
Diagnosis e.g. cancer, stroke
Guide further test or treatment e.g. biopsy and radiotherapy
Monitor condition e.g. cancer treatment
How does an MRI work?
Strong magnetic field , aligns hydrogen atoms
Some point towards the head and some towards the feet and unmatched ions remain (creating a bit of an overall polarisation).
Radio frequency pulse applied
Unmatched ions absorb energy and spin in different directions
Pulse is turned off and atoms spin returns which emits energy ( the atoms that were unmatched and absorbed the energy will release the energy again abs the computer will detect this energy and create an image.
Computer processing to generate image
What is needed in an MRI?
Image quality relies on magnetic field
Narrow gantry
What are the specifics of MRI weighting?
Relaxations (when you turn off radio frequency pulse, provides different weighting for tissue).
Different relaxations produce different weighting’s from tissues
What is T1 and T2?
T2 weighting : Fat is white, water is black
T2 weighting: Water is white, fat is black
T2 = High signal water T2 = Water White = High signal Black = Low signal
Uses of MRI’s
CNS - Brain and Spinal cord
Bones and joints
Heart and blood vessels
Internal organs
Advantages and disadvantages of MRI
Advantages
No radiation
Good contrast resolution
Disadvantages Expensive Time consuming Metalwork + artificial joints and pacemakers are now MRI safe, due to the magnetic field some things can be ripped out of the body at very high forces Claustrophobic Some patients don’t fit
What is Scintigraphy (Nuclear Medicine)
Injection of radio pharmaceuticals
Emits gamma rays - which are detected
Highly sensitive
Functional and anatomical information - often combined with MRI and CT Scans
How does Positron Emission Tomography (PET) work?
Insert radionuclides that decay by Positron emission
Bound to glucose
PET scan detect annihilations (high energy gamma rays)
- More annihilation’s the bigger the signal
- Tends to be combined with CT/MRI
Hot spots - Areas of high glucose metabolism
