Alternative imaging modalities Flashcards
Name the 4 alternative imaging modalities.
- CT computed tomography
- MRI magnetic resonance imaging
- ultrasound
- nuclear medicine
what are the main issues with plain radiographs? 7 things
- limited use for soft tissues
- ionising radiation
- sensitivity and specificity
- only show retrospective view (active or arrested caries?)
- significant demineralisation necessary to detect change.
- 2D image = superimposition & multiple view needed for localisation
give 3 positives of plain radiographs.
- cheap
- readily available
- relatively low dose
what kind of radiation is used for CT scan?
Xray photons
how does the CT scanner move?
it rotates around the patient with an X-ray beam at one side of the ring and an X-ray receptor at the other side
what does the CT scanner do as it rotates around the patient?
splits the patient into little cubes called voxels
define a voxel
pixels with volume
what is the size range for a voxel?
0.008-0.04 mm
what is the benefit and disadvantage of using small voxel?
good = high definition bad = greater exposure time = higher dose
how is the CT number determined?
the CT scanner works out how much attenuation of the beam has occurred in each voxel
In a CT what colour is 1. bone 2. soft tissue 3. air
- white 2. grey 3. black (just like X-ray)
Define windowing?
manipulation of an image to allow bettie visualisation of more subtle changes between tissues.
what 2 types of windowing can you get?
Soft tissue windowing and bone windowing
what shows up in the soft tissue windowing?
bone is totally white
what shows up in the bone windowing?
the bone is different shades depending upon the density
what are the 4 advantages of a CT scan?
- images both bone and soft tissue
- speed - faster than MRI
- multiplanar
- low cost and more available compared to MRI
what are the 4 disadvantages of a CT scan?
- high dose to patient
- artefacts will interfere (i.e. amalgam)
- expensive in comparison to plain radiograph
- allergy to iodine based intravenous contrast commonly used to distinguish tissues
give reasons for the use of CT scans in the head and neck (6)
- intracranial bleed, infarct, tumour
- trauma (orbit, cranial base, cervical spine)
- orthognathic surgery and treatment planning
- evaluation of bony lesions
- salivary glands
- neoplasia (primary and metastases)
what does CBCT stand for?
cone-beam computer tomography
what is CBCT good for looking at?
bone (not soft tissues)
3 advantages of CBCT
- 3D
- multiplanar
- same dose as conventional CT
what is the difference between CBCT and normal CT?
normal CT = computer takes multiple slices (32 or 64) and adds together
CBCT = computer takes image as a whole volume and you split it up
what are the 4 planes that data can be reconstructed into?
- axial
- coronal
- sagittal
- specific ones e.g. panoramic
Indications for use of CBCT
- Trauma
- Pathology
- Implantology
- endodontics
- localisation of impacted teeth that affect adjacent structures
What does MRI stand for?
magnetic resonance imaging
what 3 things make give an MRI scan?
protons (water) & strong magnetic field & radio frequency pulses
what is MRI scan good at viewing?
The soft tissues and bone
what colour is bone and dental tissues on an MRI scan?
Black
what are the two types of MRI scan?
T1 and T2 weighted
what is the T1 weighted MRI used for and what colour is water in it?
good for anatomy and water is dark
what is the T2 weighted MRI used for and what colour is the water?
good for looking at pathology and bright water
why is T2 weighted MRI better for looking at pathology?
with pathology you get increased water so these areas will show up brightly
3 advantages of MRI
- no ionising radiation
- excellent for looking at soft tissues (and bone)
- multiplanar
what are the 6 diadvantages of MRI
- many contraindications
- danger associated with strong magnetic field
- availability and expense
- long scan time
- claustrophobia
- very noisy
Ultrasound is created by what?
high frequency sound waves >13MHz
what are the 4 contraindications for using an MRI scan on a patient?
- pacemakers (may switch on/off)
- heart valves (old ones moved due to magnet)
- 1st trimester of pregnancy
- aneurysm clip (will heat it up)
the benefits of ultrasound are.. (5)
- multiplanar
- no ionising radiation
- no adverse effects known
- real time images
- ideal for ST
diadvantages of ultrasound (4)
- operator dependant
- difficult to interpret
- superficial tissues only
- won’t penetrate bone
the probe for an ultrasound is the … and the …
the source and the receptor
uses for ultrasound are..
- neck swelling
- salivary glands (intraglandular lesions and calculus)
- guidance for biopsy/drainage
- blood flow testing in lesions
