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
What are the uses of PET scans?
Heavily used in Oncology
- Tumour staging
- Assessment of treatment
- differentiating between benign and malignant
- detects tumour recurrence
How does ultrasound work?
- High frequency sound waves from transducer probe
- This sound wave is reflected back by tissues where density (impedance) differs
- Probe detects reflected sound waves
Creates electrical signals:
- Determined distance - time to come back
- Determined impedance - proportion of reflected waves
How are waves seen on ultrasounds?
- Hyperchoic = more reflective = white
- Hypoechoic = Less Reflective = Dark grey
- Anechoic = Not Reflective (pure fluid) = Black
What are the specifics of Doppler Ultrasound?
Moving objects influence sound waves
Therefore flowing blood can affect ultrasound signal
- Coming towards - Increased Frequency
- Going Away - Decreased Frequency
Uses of ultrasound
Solid organs
Obs and gynae
Urinary tract
Musculoskeletal
Advantages and disadvantages of Ultrasound
Advantages
- Lack of ionising radiation
- Low cost
- portable
- Dynamic flow
Disadvantages
- Operator dependant
- no bone or gas penetration
- Body habitus - harder to use on patients with more fat
Why is contrast media needed?
Helps in better differentiation of tissues
Various different types based on modality of examination
Most commonly used in:
- Fluroscopy
- CT
- MRI
- Arteriograms
- Ultrasound
Types of contrast media
- Positive: Barium, iodine, Gadolinium
- Negative: water, air and CO2
Sodium iodide is only used in contrast agent
Barium sulphate is used in GI Imaging
What is the Ideal contrast media?
- Low osmolality and viscosity
- High water solubility
- Biologically inert
- Safe
- Heat and chemical stability
- Cost effective
What are the different ways Contrast media can be administered?
- Oral
- Rectal
- IV
- IA
- Filling a space or cavity (cavity, bladder, gall bladder)
What is the important aspect of excretion of contrast media?
- the patient needs to have good kidneys and the kidneys have to be functioning well because contrast media could cause risks (renal failure or complications).
- Glomerular filtration - 95%
- Tubular excretion and protein binding negligible
- Half life: 30-60 minutes - it doesn’t last long, it needs to be done in appropriate time
What are the side effects of contrast media?
- Reactions due to osmolality
- Endothelial damage - occasionally causes below
- Thrombosis and thrombophlebitis
Which can lead to
- Vasodilation
- Vascular pain
Disadvantages of contrast media
Idiosyncratic reactions - within 20 minutes - unpredictable
- mild
- moderate
- severe - 0.03% -true allergic reactions are extremely rare
Non idiosyncratic reactions - predictable
- Cardiac
- Nephrogenic
- Extravasations
- delayed reactions - beyond 30 min - 7 days
