Other imaging modalities Flashcards
in CT, CBCT and MRI the patient is divided into ?
each ? is given a ? according to the amount it has attenuated (reduced) the beam
Different CT numbers give different shades of ?
- Bone = ?
- soft tissue = ?
- air = ?
voxels
voxel
CT (Hounsfield) number
grey
white
grey
black
voxels can be different sizes
how does the size of the voxels affect resolution?
smaller voxel = higher resolution
voxels can be different sizes
how does the size of the voxels affect scan time and radiation dose?
Smaller voxels = longer scan time so higher dose
what is windowing?
manipulate the image to allow better visualisation of more subtle changes between tissues
this image shows
Changing the windowing of a blow out fracture
Blow out fracture - fracture of orbital floor where orbital contents can herniate into the sinus
LHS - soft tissue windowing to see muscles of the eye
RHS - hard tissue windowing to see bone more clearly
remember that all images taken need to be evaluated
when looking at CT, CBCT, MRI images the data is reconstructed into what?
planes - axial, coronal, sagittal and other
what plane is this?
axial
what plane is this?
sagittal
what plane is this?
coronal
MRI - how it works
Involves ?, ? and ?
Patient is placed in ?
? align in this field
Another magnetic field is applied at an ? & then ?
The protons ? back to their original position
This ? is measured by the ?
Cortical bone and dental hard tissues appear ? as not much ? present
Various sequences show different tissues as ? or ?
protons (water)
magnetic field
radiofrequency pulses
magnetic field
water protons
angle
removed
oscillate/resonate
resonance
computer
black
water
dark
bright
this is an MRI
in MRI with T1 weighted sequences water appears what colour?
dark
T1 weighted MRI sequences are used to view what?
anatomy
in MRI with T2 weighted sequences water appears what colour?
bright
T2 weighted MRI sequences are used to view what?
pathology
advantages of MRI
No ionising radiation
Excellent for viewing soft tissues, cancellous bone, changes in marrow, infection, infiltration, cortex breach
Multi-planar
disadvantages of MRI
Multiple contraindications
○ Pacemakers, artificial heart valves, surgical clips, 1st trimester of pregnancy
FB (foreign bodies) within the eyes and orbits
Danger of strong magnetic field
Units need to be away from car parks and other facilities
Availability and cost -> long waitlists
Scan times can be long and noisy
Claustrophobia
what MRI view is this?
axial view of submandibular region
what MRI view is this?
coronal
what MRI view is this? what can be seen?
TMJ
disc can be seen
what is MRI used for in dundee dental hospital?
TMJ disorders - particularly disc problems
Salivary gland pathology
Assessing early bone changes in patients suspected of having MRONJ - medical related osteonecrosis of the jaw
how does ultrasound work?
High frequency sound waves bounce off tissues and back to the probe
Cannot travel beyond hard tissues
remember there is limited use for ultrasound around the jaws
advantages of ultrasound
No ionising radiation
No harmful effects
Ideal for superficial soft tissue structures
Multi-planar
Operator dependant
Real time images
Blood flow
disadvantages of ultrasound
Operator dependant
Difficult to interpret
Superficial tissues
Cannot penetrate bone
uses of ultrasound
Neck swelling
- Tissue of origin
- Solid/cystic
- Characteristic (benign/malignant)
Salivary glands
- Intra-glandular lesion
- Neoplasm
- Sjogren’s syndrome
- HIV
- Calculi within the salivary glands and ducts
Blood flow
- Carotid artery disease
- Relationship to lesion and lesion supply
- Guidance for biopsy/drainage
what is radioisotope scanning?
Inject isotopes which are unstable and decay emitting radioactive particles or gamma radiation
in radioisotope scanning the isotope chosen is dependant on what?
the tissue being imaged
name a substance used for radioisotope scanning
technitium
why is technitium used for radioisotope scanning?
Short half life - reduced exposure
Can be easily bound to different substances e.g. red blood cells
Taken up by thyroid and salivary glands
in radioisotope scanning radioactive compounds concentrate more in more or less active tissues?
more active tissues
in radioisotope scanning what detects radioactive emission?
Gamma camera
uses of radioisotope scanning in the head and neck
Salivary gland function
Condylar growth in mandibular asymmetry
Thyroid
Bone metastases
Osteomyelitis (inflammation of bone or bone marrow)
problems with nuclear medicine imaging (radioisotope scanning)
Poor resolution
Difficult to distinguish between different pathological processes
Radiation dose
what is PET CT
Positron emission tomography combined with CT
PET scan and CT scan images superimposed on each other
in PET CT how does it show areas where cells are more active than normal?
radioactive contrast given (orally, IV, inhaled)
contrast concentrates in more active areas
compare PET CT to CT alone
PET CT has less detail than CT alone
uses of PET CT
Diagnose and stage cancer
Radiotherapy planning
Assess effectiveness of treatment
Distinguish between active disease and scarring following treatment
