Imaging modalities Flashcards
How do radiodense and radiolucent structures appear on medical images?
radiodense structures appear bright e.g bone
radiolucent structures appear dark
what are some advantages and disadvantages of x-rays?
ADV:
- quick
- accessible
- low cost
- low radiation dose
DIS:
- not as good
- uses radiation
- single 2D views
What is digital tomosynthesis?
three-dimensional mammogram that uses X-rays to obtain sectional images of the breast, which are then reconstructed into a 3D volume.
What is fluoroscopy cerebral anagram?
contrast injected into the carotid artery (major brain vessels that provide brains blood supply), which specified the cerebral arterial vessels
What does RF stand for and what does it do?
Radiography fluroscopy
continuous or pulsed x-rays produce a series of images
What imaging modality is used with fluoroscopy?
movable c-arm (may vary)
Discuss what happens when fluoroscopy contrast is swallowed
- contrast is swallowed whilst pulsed X-ray taken
- equipment may vary from c-arm
-multiple angles taken
-contrast followed down to stomach and traced through the bowels with static images
give some ADV and DIS of radiographic fluoroscopy
ADV:
- records multiple images
- can measure element of function
- guide for therapeutic procedures
- versatile
DIS:
- variable radiation dose
- 2D images usually
- most applications require contrast
- therapeutic procedure take time
Give some examples of why you might undergo a fluoroscopy
- evaluation of GI tract
- vessel angiography
- sialography (tear ducts/salivary glands)
- evaluate where contrast is injected
- evaluate movement
What does US stand for?
Ultrasound
How does an ultrasound work?
sound waves reflected by changed in soft tissue density.
They originate from the probe and reflections also picked up
When will a high frequency or low frequency probe be better during an ultrasound?
high frequency probes excellent resolution at skin surface
lower frequency probes better depth penetration
Why is gel used in an ultrasound?
eliminates air interface with probe
Give ADV and DIS of ultrasounds
ADV:
- accessible than some
- mobile
- lowish cost
- no radiation
- view images in real time
- measure blood flow
DIS:
- reliant on operator skill
- only operator determined images saved
- air/bone interfaces limit deeper visibility
- reduced resolution of deeper structures
Why might an ultrasound be used?
- antenatal evaluation
- image abdominal organs/ vessels in abdominal symptoms
- elevate musculoskeletal problems
- soft tissue lumps and bumps
- echocardiography (cardiac evaluation)
What does CT stand for?
Computed tomography
How does a CT work?
- x-ray source rotates count the patient
- x-rays pass through the patient and are picked up by an array of detectors opposite the source
- patient moves progressively though the scanner
- cross sectional image data calculated from acquired raw data
How many slices can a CT take in 350ms?
What pixels is it?
350ms for 16-320 slices
512x512 matrix
What can 3D reconstruction from CT scans provide an advantage for?
- provide useful info for operative planning
- show medical imaging to those unfamiliar with it
- used to create bespoke prosthetic implants and 3D printing
What are some ADV and DIS of CT?
ADV:
- increasingly accessible
- large amount of info obtained quickly
- versatile
- 3D representation of anatomical areas
- visualise large number of anatomical structures well
- guide for interventional procedures
DIS:
- radiation dose
- other tests more accessible/quicker
- more expensive than some
- over utilised as a diagnostic test
Give some examples of when you would use CT
- Trauma
- abdominal pain
- chest pain
- vasular pain
- cancer staging
What does MR stand for?
Magnetic resonance
How does MR work?
- patient placed in bore of scanner via motorised table
- strong magnetic field permanently active
- radiofrequency waves interact with protons within body
Protons spin on their axis, radio frequency waves are used to flip the aligned protons or align their spin.
The net magnetic moment can be measures.
T1 effects relate to proton flip.
T2 effects relate to proton spin alignment.
What is MRI great for screening?
soft tissue or areas of inflammation/water content
Give ADV and DIS of MRI
ADV:
- no radiation
- multiplayer imaging of any body part
- provides info on soft tissue that other modalities cannot
- wide variety of specialised use e.g blood flow
DIS:
- long scan time
- large magnet
- heating effects
- noise
- calustrophobia
- image artefacts common
- low accessibility and expensive
When might you use an MRI?
- neurological signs e.g brain or spine
- assessing ‘lesions’ within various body organs
- assessing joint soft tissue/ bones
- evaluating heart
`How is nuclear medicine imaging undergone?
- preprepared radioactive tracer injected into patient
- tracer accumulates in body system/anatomical regions based on tracer type
- tracer emits gamma rays which are detected on gamma camera
What does PET stand for?
positron emission tomography
What is the tracer used in PET scans?
FDG, fluro deoxyglucose
What is the half life of FDG
2 hours
Why is FDG used as tracer?
its taken up by areas of high metabolic activity e.g cancer cells
Why are PET and CT scans fused?
to add anatomical detail
Give ADV and DIS of nuclear medicine scans
ADV:
- large scan coverage
- provides functional/metabolic aspect
- well tolerated
- wide ranging application
DIS:
- long scan times + multiple visits
- limited anatomical detail
- radioactive patient
- radiopharmaceutical prep
When might you use NM scans?
- blood clots in lungs
- malignant spread to organs/systems
- evaluating fractures
- looking for infection
- blood flow to organs
- therapeutic use
