Other imaging modalities

Question 1

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 = ?

Answer 1

voxels

voxel
CT (Hounsfield) number

grey

white
grey
black

Question 2

voxels can be different sizes

how does the size of the voxels affect resolution?

Answer 2

smaller voxel = higher resolution

Question 3

voxels can be different sizes

how does the size of the voxels affect scan time and radiation dose?

Answer 3

Smaller voxels = longer scan time so higher dose

Question 4

what is windowing?

Answer 4

manipulate the image to allow better visualisation of more subtle changes between tissues

Question 5

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

Question 6

remember that all images taken need to be evaluated

Question 7

when looking at CT, CBCT, MRI images the data is reconstructed into what?

Answer 7

planes - axial, coronal, sagittal and other

Question 8

what plane is this?

Answer 8

axial

Question 9

what plane is this?

Answer 9

sagittal

Question 10

what plane is this?

Answer 10

coronal

Question 11

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 ?

Answer 11

protons (water)
magnetic field
radiofrequency pulses

magnetic field

water protons

angle
removed

oscillate/resonate

resonance
computer

black
water

dark
bright

Question 12

this is an MRI

Question 13

in MRI with T1 weighted sequences water appears what colour?

Answer 13

dark

Question 14

T1 weighted MRI sequences are used to view what?

Answer 14

anatomy

Question 15

in MRI with T2 weighted sequences water appears what colour?

Answer 15

bright

Question 16

T2 weighted MRI sequences are used to view what?

Answer 16

pathology

Question 17

advantages of MRI

Answer 17

No ionising radiation

Excellent for viewing soft tissues, cancellous bone, changes in marrow, infection, infiltration, cortex breach

Multi-planar

Question 18

disadvantages of MRI

Answer 18

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

Question 19

what MRI view is this?

Answer 19

axial view of submandibular region

Question 20

what MRI view is this?

Answer 20

coronal

Question 21

what MRI view is this? what can be seen?

Answer 21

TMJ

disc can be seen

Question 22

what is MRI used for in dundee dental hospital?

Answer 22

TMJ disorders - particularly disc problems

Salivary gland pathology

Assessing early bone changes in patients suspected of having MRONJ - medical related osteonecrosis of the jaw

Question 23

how does ultrasound work?

Answer 23

High frequency sound waves bounce off tissues and back to the probe

Cannot travel beyond hard tissues

Question 24

remember there is limited use for ultrasound around the jaws

Question 25

advantages of ultrasound

Answer 25

No ionising radiation No harmful effects Ideal for superficial soft tissue structures Multi-planar Operator dependant Real time images Blood flow

Question 26

disadvantages of ultrasound

Answer 26

Operator dependant Difficult to interpret Superficial tissues Cannot penetrate bone

Question 27

uses of ultrasound

Answer 27

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

Question 28

what is radioisotope scanning?

Answer 28

Inject isotopes which are unstable and decay emitting radioactive particles or gamma radiation

Question 29

in radioisotope scanning the isotope chosen is dependant on what?

Answer 29

the tissue being imaged

Question 30

name a substance used for radioisotope scanning

Answer 30

technitium

Question 31

why is technitium used for radioisotope scanning?

Answer 31

Short half life - reduced exposure Can be easily bound to different substances e.g. red blood cells Taken up by thyroid and salivary glands

Question 32

in radioisotope scanning radioactive compounds concentrate more in more or less active tissues?

Answer 32

more active tissues

Question 33

in radioisotope scanning what detects radioactive emission?

Answer 33

Gamma camera

Question 34

uses of radioisotope scanning in the head and neck

Answer 34

Salivary gland function Condylar growth in mandibular asymmetry Thyroid Bone metastases Osteomyelitis (inflammation of bone or bone marrow)

Question 35

problems with nuclear medicine imaging (radioisotope scanning)

Answer 35

Poor resolution Difficult to distinguish between different pathological processes Radiation dose

Question 36

what is PET CT

Answer 36

Positron emission tomography combined with CT PET scan and CT scan images superimposed on each other

Question 37

in PET CT how does it show areas where cells are more active than normal?

Answer 37

radioactive contrast given (orally, IV, inhaled) contrast concentrates in more active areas

Question 38

compare PET CT to CT alone

Answer 38

PET CT has less detail than CT alone

Question 39

uses of PET CT

Answer 39

Diagnose and stage cancer Radiotherapy planning Assess effectiveness of treatment Distinguish between active disease and scarring following treatment