Radiology Flashcards
What type of imaging is CBCT and what is it suitable to assess?
A form of cross-sectional imaging suitable for assessing radio-dense structures
What are the benefits of CBCT over plain radiography?
- No superimposition
- Ability to view subject from any angle
- No magnification/distortion
- Allows for volumetric (3D) reconstruction
What are the downsides of CBCT over plain radiography?
- Increased radiation dose to patient
- Lower spatial resolution
- Susceptible to artefacts
- Equipment more expensive
- Images more complicated to manipulate and interpret
- Requires additional training
What are the benefits of CBCT in comparison to conventional CT?
- Lower radiation dose
- Potential for higher resolution
- Cheaper
- Smaller footprint
What are the benefits of conventional CT over CBCT?
- Able to differentiate soft tissues better
- “Cleaner” (better signal to noise ratio)
- Larger field of view possible
What are the common uses of CBCT in dentistry?
- Clarifying relationship between impacted 3rd molar and the IAN canal prior to intervention
- Measuring alveolar bone dimensions
- Visualising complex root canal morphology to aid endo treatment
- Investigating external root resorption next to impacted teeth
- Assessing large cystic jaw lesions
What are the three common orthogonal planes used for visualising CBCT?
- Axial view
- Sagittal view
- Coronal view
What is the “field of view” (FOV)?
The size of the captured volume of data
Why do you ideally want to have a small FOV?
Because a small field of view will mean less radiation given to patient (as there will be less tissues irradiated and less scatter)
What is a voxel, and what does it decipher?
A voxel is a 3D pixel and it deciphers the resolution of an image.
Why does FOV need to be as small as possible on a CBCT if investigating endodontic cases?
So that you can visualise finer details of root canals
What is a rough estimate of how much larger the radiation dose of CBCT is compared to DPT?
CBCT is roughly 2-3 x the dose of DPT
What are the two main types of artefacts that you can get on CBCT imaging?
- Movement artefacts
- Streak artefacts
What causes streak artefacts?
High-attenuation objects (e.g. amalgam metal filling)
What are the two main issues of streak artefacts?
- Can prevent caries assessment
- Can prevent assessment of perforations/missed canals in root canal treated teeth
What are the contraindications for CBCT?
- If plain radiograph is sufficient
- If soft tissue visualisation is required for pathology (malignant gland or infection spread)
- If high risk of debilitating artefacts
- Pt unable to stay still or fit in machine
What patients might have difficulty fitting in CBCT machine?
- Kyphotic patients
- Patients with unfavourable neck to body ratios (obese, bodybuilder)
What is required to be able to refer, justify, perform or interpret CBCT?
Current UK undergraduate teaching deemed inadequate. Recommended post graduate training. Some form of refresher training recommend once every 5 years.
Other than CBCT, what other imaging modalities are there?
- Conventional CT
- MRI
- Ultrasound
- Nuclear medicine
- Combination of multiple imaging modalities including PET-CT/ PET MRI
If the voxel is smaller, what does this mean in regard to resolution?
Resolution is higher
What is the value of density that CT voxels are given?
Hounsfield units
What structure has the highest hounsfield number on CT (+1000) and is therefore the most radio-opaque (white)?
Air, water, dense bone, fat.
Dense bone
What is “windowing”?
Windowing alters levels of densities visualised in CT scan to optimally look at specific tissues.
Define, window level.
The value at centre of range
Define, window width.
The range of values selected to view tissues
MRI uses ionising radiation. True or false?
False, uses a magnetic field (radio frequency pulses and hydrogen protons within body to produce images)
Why is the cortisol bone always black on MRI?
As it has very little water content
What are the advantages of MRI?
- No ionising radiation
- Very good imaging of soft tissues + early change in bone marrow
What are the disadvantages of MRI?
- Multiple contraindications
- Length scan
- Claustrophobia
- Cost + availability
What are contraindications for MRI?
- Pacemakers
- Orbital foreign bodies
- Artificial heart valves
- Surgical clips
What might MRI be used for in relation to dentistry?
- To visualise degenerative changes in the TMJ
- To visualise salivary glands
- To visualise sinuses for malignancy
How does ultrasound work?
High frequency sound waves used to produce images
What sort of structures is ultrasound good at imaging?
Superficial structures
What are the advantages of ultrasound?
- No ionising radiation
- Good for superficial structures
- Real time imaging
- Can be used as adjunct to biopsy/aspirates
- Blood flow
What are the disadvantages of ultrasound?
- operator dependant
- Can’t penetrate bone
- Can be difficult to interpret
- Only superficial structures are seen
In relation to dentistry, what is ultrasound good for imaging?
- Neck lumps
- Salivary glands
- Vascular lesions
Give three examples of nuclear medicine?
- PET (positron emission tomography)
- SPECT (single photon emission CT)
- Scintigraphy
How does nuclear medicine work?
Patient is injected within intra venous radiopharamceutical which when it decays emits particles that are picked up on a gamma camera.
What are the advantages of nuclear medicine scans?
- Can be superimposed over other cross-sectional imaging (e.g. CT)
- Highly sensitive
- Can assess function
What are the disadvantages of nuclear medicine scans?
- Poor resolution
- Poor specificity
- Very high radiation dose
Name 4 radioisotopes that can be used in nuclear medicine images?
- Technetium
- MDP
- Pertechnetate
- 18-FDG
What combination of imaging modalities is typically used for cancer diagnosis?
PET-CT
