Theme 2 - Radiology Flashcards by GM Edge

What are the 3 focal trough samples from a conventional DPT?

1) Beam through TMJ, sinuses and nasal structures
2) Beam through dental arch
3) Beam through mandible

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What is the difference in focal trough width in a DPT and a CBCT?
What effect does this have?

DPT = 3cm post, 1 cm ant
CBCT = 0.4mm
Much clearer image but much higher dose of radiation

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What is the effective dose for
a) Full mouth PAs
b) DPT

a) 150 uSv
b) 15-20uSv

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What has caused the following positioning problems in a DPT?
a) Occlusal plane smiling, elongation of chin and no separation of teeth?
b) Occlusal plane frowning, shortened ramus, hard to see root apices of maxillary teeth
c) Lots of vertebral column/spine on show, teeth and jaw narrowed

a) Head inclined forward (looking down)/frankfort plane tilted down
b) Head inclined to rear (looking up)/ frankfort plane backwards
c) Pt too far forwards in machine

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What has caused the following positioning problems in a DPT?
a) No spine on image and magnified anterior teeth
b) Teeth magnified on one side, one sinus denser, ramus different sizes
c) Inclination of central line and unequal distance on each side between edge of image and TMJ
d) Wavy image

a) Pt has head too far back in machine
b) Rotation - magnified side is the side furthest from film
c) Lateral inclination of head ie tilting
d) Pt unable to keep still e.g. parkinsons or children

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Where will a ghost image be located on a DPT?

Opposite side from image of actual object
Larger than image of actual object
Projected higher on film
Less distinct
(from mandible or metal jewellry)

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How is a patient positioned for a lateral ceph?

Pt at known distance from xray source, parallel positioning of auditory meatus, ruler on nasion

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What areas should be looked at when analysing a lateral ceph?

-Frontal sinuses for pathology and development
- Base of skull and pituitary fossa to asses for expansion and erosion
- Facial bones for pathology
- Upper spine for pathology and airway spaces

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What may you see on a lateral ceph that would indicate acromegaly?

Frontal sinus large (frontal bossing)
Large pituitary fossa (can impact on optic chiasm)
Class 3

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What bone causes challenges when facial imaging because it superimposes over the facial bone?

Petrous temporal bone

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What does the undertilted occiptomental (OM) facial view show?
What does the OM 30 show?
What does the submental vertex view (SMV) show?

1) Lower orbit to look for fractures - petrous temporal bone under maxillary sinuses
2) Zygomatic arches - petrous ridge well below temporal bone
3) Zygomatic arches - taken under chin

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What is the reverse townes view (occipito-frontal 30)

Xray behind pts head (reduce dose to eyes), pt keeps mouth open, radiographic baseline 90 degrees to film. Beam angled 30 degrees up.
Captures zygomatic arches and allows condylar necks to be seen

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What is the occipitomental view (OM)?

Xray behind pt, pts facial bones close to image to avoid magnification, radiographic baseline at 45degrees to film, central ray through base of nose.
Good for mid third of face and orbital structures

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What lines are used to analyse an OM view?

Campbell lines
1 = suprorbital
2 = zygomatic arches
3 = mastoid and upper teeth
4 = lower border of mandible

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What is the PA mandible view?

Radiographic baseline 90 degrees to film, beam approaces through mandible at 90 degrees to fil.
Shows fractured condylar neck, not zygomatic arch, cervical spine tends to obscure anterior part

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What is the lateral oblique mandible?

Median saggital plane at 45degrees, beam approaches from under the mandible and the side closest to film seen most clearly

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How does the Y of Ennis help with localisation?

If no surrounding teeth and root remenent just below it is a 3
Doesn’t tell you where it is palatal/labially, but does tell you where it is anterior/posterior

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How does parallax help localise?

2 images where xray tube moves and pick reference point.
SLOB: Same direction = lingual, opposite direction = buccal

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How can foreign bodies in soft tissue be identified by a radiograph?

Taken at lower kVp (60kV rather than 70kV)
2 views at right angles needed
Use ultrasound too

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What factors influence the justification for a CBCT?

Pathology
Competence (trained in use and interpretation)
Consent
Risk/benefit
Dose of radiation

What do the following mean
a) Coronal
b) Axial
c) Sagittal

a) Through coronal suture
b) Transverse slice
c) Through saggital suture

What is the classification of CBCT units commonly used in dentistry?

Single arch 5-7cm field of view

What is the difference between CBCT/iCat and multidetector/medical CT?

See better ST planes with MDCT but higher radiation dose
Fan beam

What are the uses of CBCT?

Assess L8 and ID canal relationship
Implant planning
Endo
Ortho controversial as higher dose than lateral ceph

What is the DAP (dose area product) value for radiation?

Total energy imparted to patients and helps calculate the effective dose. Measured over an area Gym2

What is the DRL (diagnostic reference levels) for radiation?

Trigger to allow quality improvement. Identifies doses overly high. Data collected over the country

What is the dose of: a) 2 x I/O b) DPT c) CBCT full FOV max/mand

a) 5uSv b) 19 uSv c) 155 micro Sv

Does small volume always mean less dose to patient?

No it depends on the setting e.g. high resolution

What is the average cancer risk from CBCT?

6 per million

What 3 questions must a dr ask when gaining consent (IRMER)?

- Does pt know material risks of procedure? - Does pt know about reasonable alternatives? - Have I taken reasonable care to ensure patient knows this?

How would you consent someone for a CBCT?

CBCT radiation dose equivalent to around 6-30days of normal background radiation Without may not be sufficient to assess bone accurately Check pregnancy

How can we limit dose?

Access previous images Timing of the CT scan - check no gap between scan and treatment Can a different imaging modality be used e.g. ultrasound

How can risk of adverse CBCT event be reduced?

- Induction programme for new staff - Grading and review - Clinical audit - Good practice and technique applied - Investigation of near misses

What should you do if CBCT is given to the wrong patient?

Report to RPS Contact the RPA Report to CQC Must tell patient what has happened

How can we make use of CBCT S.A.F.E.R?

S= source, restrict who can refer A= audit efficacy F= forms E= ensure clear image coding R= review previous images

What are the IRMER duty roles?

Referrer = gives I.D. x3, MH, DH Practitioner = justification with requirements check Operator= takes and reports image

What is the '6 step plan' for imaging gently for children?

1) No routine views 2) Fastest image receptor 3) Collimation 4) Thyroid collars 5) Child size exposure 6) Only CBCT when necessary

How much higher is the risk of radiation to children under 10 years?

3 x higher

For a medical CT scan, what are the limitations?

- Dose - As slice thickness reduced you get increased noise, have to increase dose to reduce noise - Limited ST appreciation - Streak artefacts from metallic objects e.g. amalgam fillings

What are the following used for? a) CT angiography b) CT sialography

a) IV bolus of contrast for blood vessels/tumour b) salivary glands - rarely used as high dose for info given

What is an MRI? What are the units?

Magnets align bodies of protons, local magnet in area assessing and the change in direction of protons gives off energy. Tesla

What are the side effects of the magnet in an MRI scan?

- Increases the size of T wave on ECG - Pacemakers can malfunction - Tattoos can heat up - Dislodge surgical clips and foreign bodies - Visual disturbances - Must have no metal in room can fly into tube

How does an ultrasound record an image?

Aucoustic impedence - proportion of sound reflected dependent on material

Why is ultrasound imaging safer? What are its risks?

Non-ionising Local heating - cell membrane permeability may be addected Cavitation - can get microbubbles introduced

What is radionuclide imaging?

Gamma camera, radio-isotope labelled to vehicle for delivery. Used for salivary glands

What is a PET scan?

Annhilation radiation, radioisotope labelled with deoxyglucose. This is taken up by highly metabolic sites = tumours

When is a PET scan indicated?

- Search for primary tumour - Assess recurrent disease - Staging of pts tumour/metastasis

What frequency is used for ultrasound of head and neck?

13.5-20MHz