Advanced Oral and Maxillofacial Imaging Flashcards
What are the indications for Computing Tomography? (4)
- Excellent for fine bone detail so very useful in mid-facial trauma
- Cranio-facial reconstruction planning
- Assessment of bony expansion or destruction caused by large cysts or tumours
- Assessment of intra-cranial trauma or disease
What is a Cone Beam CT? (7)
- Sometimes known as digital volume tomography
- Uses a cone shaped x-ray beam
- Scan time ranges from 20-40 seconds
- Larger field of view results in greater radiation dose
- Dose is much lower than a “medical” CT
- Gives excellent bony detail but very poor for soft tissue (unlike medical CT)
- Several machines available with different field sizes
What are the indications for a Cone Beam CT? (7)
- Implants
- Cysts and tumours in the jaws
- Trauma
- TMJ
- Sinuses
- Orthodontics
- 3rd molar – ID nerve relationship
What are contrast techniques? (2)
- Contrast agents are radiopaque substances that when introduced into the body alter subject contrast artificially
- Many contain iodine so allergic reactions are possible
What contrast techniques are used in the head and neck? (5)
- Sialography
- TMJ arthrography
- Angiography
- Investigation of fistulae
- As an adjunct to CT or MRI
What is Sialography? (3)
- This involves the introduction of contrast into the ductal system of the parotid or submandibular salivary glands
- Indicated when there is a history suggestive of obstruction
- Also used to investigate patients with suspected Sjögren’s syndrome
What are the contraindications for Sialography? (3)
- Acute salivary gland infection
- Allergy to iodine
- Discrete salivary gland swelling … other techniques are more informative
What is TMJ arthrography? (3)
- This involves the introduction of contrast into, usually, the inferior, joint space of the TMJ to determine disc position and detect disc perforations and adhesions
- Still used in some centres to investigate longstanding TMJ “dysfunction”
- In Sheffield MRI is used instead
What are the advantages of TMJ arthography? (2)
- May reveal perforations of
the disc - Can produce a truly dynamic study of joint movement
What are the disadvantages of TMJ arthography? (4)
- Unpleasant … quite invasive
- Technically demanding … few Radiologists are trained to do it
- Involves ionizing radiation
- Does not image the disc directly
What is Angiography? (2)
- Involves the injection of contrast directly into blood vessels via a catheter, usually inserted into the femoral artery, followed by selective catheterization of carotid branches
- Done under fluoroscopic control
What are the indications for Angiography? (2)
- To show the vascular anatomy and feeder vessels associated with haemangiomas
- Investigation of arteriovenous malformations and suspected intracranial bleeds
What does MRI stand for? (1)
- Magnetic Resonance Imaging
What is MRI? (7)
- Involves placing the patient in a very strong magnetic field
- Radiowaves are pulsed into the patient
- This induces resonance of hydrogen protons
- A radiowave signal is emitted and then converted into a visual tomographic image
- Ionizing radiation is not involved at all
- In contrast to CT, with MRI, bone does not emit a signal and so appears dark
- T1 weighted images show normal anatomy well whilst T2 weighted images are good for showing disease
What are the indications for an MRI? (3)
- Excellent for tumour staging … provides good soft tissue detail … in any plane
- Excellent for intracranial disease
- Can be used to directly image the disc position within the TMJ
What are the disadvantages of MRI? (3)
- Expensive and not widely available - yet
- Claustrophobic, noisy and time-consuming
- Contra-indicated in patients with ferro-magnetic surgical clips, pacemakers, cochlear implants and in first 3m of pregnancy
What is Ultrasonography? (4)
- Uses high frequency (1.5-10MHz) sound waves from a transducer against the skin
- Sound reflected by tissue interfaces … echoes
- Echoes detected by transducer and converted to an electrical signal … image
- Non-invasive, safe and cheaper than CT/MRI
What are the uses of Ultrasonography? (3)
- Excellent for assessment of superficial swellings eg parotid, thyroid, cervical lymph nodes
- In some centres it is possible to do a fine needle aspiration of swellings under US guidance
- Doppler US may help in assessing vascularity of lesions
What is Digital Imaging? (1+2, 1)
- Uses conventional x-ray machine but traditional x-ray film is replaced by either:
(1) a charge coupled device (CCD) or
(2) a photostimulable phosphor plate - In both cases the image receptors convert received information into digital data
How is Digital Imaging stored and used/assessed? (5)
- The digital data is stored on a computer
- Converted to a grey-scale visual image
- Image displayed on a monitor
- Possible to alter contrast and resolution
- A hard copy can be produced
What is Direct Digital Imaging? (4)
- Uses the CCD image receptor
- Produces instant images
- With some systems the sensor is quite bulky making it awkward to position in the mouth
- Examples include: Trophy’s Radiovisiography and Schick’s CDR
What is Indirect Digital Imaging? (5)
- Uses the photostimulable phosphor plate
- After exposure the plate has to be placed in a “reader”
- Digital info. then stored and manipulated
- The plate can be cleared and reused
- Example is the Soredex Digora system
What are the advantages of Digital Imaging? (5)
- Lower radiation dose
- No need for conventional film processing
- Possible to alter contrast and resolution and enhance images
- Possible to transfer images between departments in a hospital or between hospitals
- Storage of patient info - no lost x-ray films!
What are the disadvantages of Digital Imaging? (4)
- Expensive
- Need large disc space for storage
- Some loss of image definition and resolution compared with film
- Image manipulation can be misleading and could be misused. Hard copy images may fade with time
What is Radionuclide Imaging? (5)
- Involves injection of radioactive agent which emits gamma rays … detected by gamma camera
- The agents used have an affinity for the target tissue
- Provides info. regarding function and/or structure of target tissue
- Technetium 99m commonly used
- Possible to attach this to other substances that are concentrated in different organs eg MDP (methylene diphosphonate) …bone
What are the indications for Radionuclide Imaging? (6)
- Detection of bony metastases
- Detection of bony invasion by tumours
- Investigation of salivary gland function
- Condyle hyperplasia - assessment of continued growth
- Evaluation of bone grafts
- Thyroid investigations
What are the disadvantages of Radionuclide Imaging? (5)
- Limited image resolution
- Images not usually disease specific
- Radiation dose can be high
- Difficult to localize exact anatomical site of source of emissions
- Can be time consuming
What are the further developments in Radionuclide Imaging? (3)
- Single photon emission computed tomography (SPECT) … produces a cross-sectional image … good for localisation
- Positron emission tomography (PET) also produces cross-sectional images … well localised. Can investigate disease at a molecular level and possible to superimpose the PET scan on a CT scan
- See BJOMFS Feb 2005 page 1-6
What sort of Imaging would you use for a Dental implant assessment? (1)
- Cone Beam CT
What sort of Imaging would you use for a Complex bony detail with soft tissue? (1)
- CT
What sort of Imaging would you use for a Salivary gland obstruction / Sjögren’s? (1)
- Sialography
What sort of Imaging would you use for a Complex soft tissue detail? (1)
- MRI
What sort of Imaging would you use for a Haemangioma/AVM? (1)
- Angiography
What sort of Imaging would you use for a Superficial soft tissue swelling? (1)
- Ultrasound
What sort of Imaging would you use for Condyle hyperplasia? (1)
- Radionuclide Scan
What sort of Imaging would you use to Search for bony metastases? (1)
- Radionuclide Scan
