18 Alternative Imaging Modalities Flashcards
In CT, CBCT, and MRI voxels are used, what are these?
The patient is divided in voxels - pixels with volume
Each voxel is given a CT number (hounsfield unit) depending on the amount of absorption within that block of tissue
Each CT number is assigned a different degree of greyness, allowing a visual image to be constructed and displayed on the monitor
Images can be manipulated to allow better visualisation without re-exposing the patient, what is this called?
Windowing
- using window level and window width
What are the advantages of CT (computed tomography)
- imaging of hard and soft tissue
- excellent differentiation between different types od tissue
- good for head injuries (can see brain and bone)
- multi-planar (manipulate and reconstruct images)
- speed, cost and availabilty (compared to MRI)
What are the disadvantages of CT
- Patient radiation dose (dose for head - 2mSv)
- artefact (metallic objects, amalgam in head and neck)
- often required IV contrast to distinguish tissues (iodine based, allergy)
- expensive compared to plain radiography
True or false: Smaller CBCT voxel’s result in a higher dose.
True
smaller size requires a longer scan time, therefore a higher dose
What are the basics of MRI
- involves protons (water), magnetic field, and radio-frequency pulses
- patient is placed in a magnetic field
- the water protons align in this field
- another magnetic field is applied at an angle and then removed
- the protons oscillate/resonate back to their original position
- this resonance is measured by the computer
how does pathology generally appear in a MRI scan?
T2 weighted - water bright
what are the advantages to MRI?
- no ionising radiation
- excellent for viewing soft tissue and cancellous bone (changes in marrow, infection, infiltration and cortex breach)
- mutiplanar
What are the contraindications for MRI
- pacemakers
- artificial heart valves
- surgical clips particularly intra-cerebral aneurysm clips
- 1st trimester pregnancy
what are the disadvantages of MRI
- danger of strong magnetic field
- units need to be away from car parks and other facilities
- availability and cost of scanning - waiting lists
- scan times can be quite long and noisy
- claustrophobia
In DDH, when are MRI scans used?
TMJ disorders - particularly disc problems
Salivary gland pathology - including MRI sialography
Assessing early bone changes in patients suspected of having MRONJ
What are the advantages of ultrasound?
- no ionising radiation
- no known harmful effects
- ideal for superficial soft tissue structures
- multi=planar
- operator dependent
- real time images
- blood flow
- can be used to guide fine needles, aspirate or biopsies
what are the disadvantages of ultrasounds?
- operator dependent
- difficult to interpret
- superficial tissues
- cannot penetrate bone
what are the uses of ultrasounds in dentistry?
for neck swellings:
- tissue of origin
- solid/cystic
- characteristics (benign or malignant)
for salivary glands
- neoplasm
- sjogrens syndrome
- HIV
- calculi within the salivary glands and ducts
for blood flow:
- carotid artery disease
- relationship to lesion and lesion supply
- guidance for biopsy/drainage
how is radioisotope scanning used?
- inject isotopes which are unstable and decay emitting radioactive particles (a, b) and radiation (gamma)
- isotope selected according to tissue to be imaged
- radioactive compound concentrated in target tissue indicating:
- increased activity (hotspot)
- reduced/no activity (cold spot)
- radioactive emissions detected by gamma camera
