Lecture 3

Question 1

How is radiation harmful?
Nature of damage dept on what?
Cells most susceptible?

Answer 1

Ionising radiation harmful to living tissues – interferes with molecular chemistry of cells.
Doses of radiation are cumulative.

Tissue irradicated, characteristics of radiation, dose of radiation, exposure time.

Rapidly dividing cells most susceptible.

Question 2

What can radiation cause?

Answer 2

Inflammation, slowed cell growth, necrosis, potential malignant change, genetic mutation.

Question 3

What does ALARA / ALARP principle stand for?

Answer 3

As Low As Reasonably Achievable / Practicable.

Question 4

Inverse square law. – Take home message?

Answer 4

Double distance from radiation beam quarters the radiation dose.
– KEEP YOUR DISTANCE!

Question 5

What will stop scattered radiation but not necessarily a primary beam?
What can be added to stop the primary beam?

Answer 5

Stone or brick wall (cavity wall usually adequate).
Add lead or barium plaster to stop primary beam.

Question 6

What can be worn by staff to protect against scatter radiation (not primary beam)?

Answer 6

Lead aprons and gloves and neck guards and sleeves.

Question 7

Other method of protection?

Answer 7

Reduce time spent around radiation.

Question 8

Legislation to regulate and direct?

Answer 8

Ionising Radiation Regulations 2017.

BVA Guidance notes for the safe use of ionising radiations in veterinary practice.

Question 9

What do practices have to do by law?

Answer 9

Has to notify Health and Safety Executive if working with ionising radiation.
Must have ‘Local Rules’ in place that detail specific info about personnel and working practices. (must specify and radiation protection advisor – external – and a radiation protection protection supervisor – internal)

Question 10

What must a local rules document define?

Answer 10

A controlled area. With advice from RPA.
An area where radiation dose may exceed 7.5 microsievert/hr. Effectively 2m from a vertical beam. When x ray machine connected to mains supply. Restricted access. Warning signs/lights in place. can be temporary eg in stables.

Question 11

Define a sievert

Answer 11

Unit of dose equivalence, equal to an effective dose of one joule of energy per kg of recipient mass.

Question 12

What must also be specified in the local rules document?

Answer 12

X-ray equipment being used.
Servicing and fault reporting arrangements.
PPE incl. safe storage checks.
Personal dosimetry (incl. dose at which investigation triggered) eg badges.
Contingency plan (if emergency fault develops).
Record keeping.
Written system of work.

Question 13

Positioning aids for SA x-rays.
Ways of maintaining distance in equine radiography?

Answer 13

Sand bags and foam wedges/pads.
Cassette in cassette holder.

Question 14

At what age should personnel not be involved in radiography?
What type of personnel should risk assessments be produced for?

Answer 14

Under 16s.
Pregnant members of staff.

Question 15

Rules regarding personal dosimeters?

Answer 15

Should be individual.
Should be changed regularly (3 monthly).
Should be worn under any PPE.
Stored carefully avoid washing machines, sunlight and airport x ray machines.
Document any potential doses and issue another monitor.

Question 16

Legal dose limits for…
General public
Trainees
Occupational

Answer 16

General public – 1mSv
Trainees (16-18) – 6mSv
Occupational (18+) – 20 mSv

CAN’T EXCEED 3/10 OF THESE LIMITS WITHOUT BECOMING A ‘CLASSIFIED’ WORKER.

Question 17

What could lead to prosecution?

Answer 17

X-raying a person – either self or someone else. Even if consented.

Question 18

What type of imaging technique is MRI?
What does MRI use?

Answer 18

Cross-sectional.
Uses strong magnet and radiowaves.

Question 19

How does MRI work?

Answer 19

Detection and analysis of the radio signals emitted by the patient gives info about the chemical composition of the tissues. Appearance of tissues depend on timing of pulses (inputs of radiowaves) and echoes (signals from tissue).

Question 20

Advantages of MRI.

Answer 20

Very good anatomical detail, particularly of soft tissues eg nerves etc.
Does not use ionising radiation (safer).
Good for imaging areas which are not very accessible to other techniques.
Particularly useful for the brain and spinal cord.
Useful for accurate assessment of extent of spread of a lesion.

Question 21

Disadvantages of MRI.

Answer 21

Not widely av in practice.
Expensive (equipment and installation, maintenance, time – every sequence or plane take extra time).
Animals must be perfectly still throughout exam – usually under GA. (risk and cost).
NO metallic object around.

Question 22

What patients should not get an MRI?
What patients should there be care taken with if need MRI?

Answer 22

Patients with pacemakers.
Patients with implants (esp ortho).

Question 23

How can a microchip affect MRI?

Answer 23

Local distortion of magnetic field

Question 24

What has been developed and is used in equine medicine?

Answer 24

‘Standing’ MRI –used to image distal limbs. A ‘C’ shaped magnet positioned around leg. – not same strength as fixed machines.

Question 25

Advantage of 'standing' MRI

Answer 25

Good anatomical detail

Question 26

Disadvantages of standing MRI

Answer 26

Only practical for distal limbs. Need software to correct for motion during acquisition. But severe cases of motion could cause distortions.

Question 27

What does CT stand for? What imaging technique is this? How does it differ to MRI?

Answer 27

Computed tomography. Cross-sectional. Ionising radiation used.

Question 28

How does CT work?

Answer 28

Patient placed inside ring containing x-ray detectors. X-ray source rotates around patient and image is picked up by the detectors in the ring opposite the source for 360 view.

Question 29

Advantage of CT over x-ray.

Answer 29

Degree of computer manipulation that can be done with the data. eg CT windowing to optimise certain tissues.

Question 30

Advantages of CT

Answer 30

Gives detailed anatomical reconstructions esp good for bony structures. Scanning time shorter than MRI. Availability increasing.

Question 31

Why is CT chosen over radiographs for the imaging of elbows? What other areas of the body would CT be advantageous for imaging?

Answer 31

Avoids superimposition of on the radiograph. Nasal, aural, LNs, lungs (masses and metastases)

Question 32

How can CT facilitate surgical planning?

Answer 32

3D reconstruction, rotate 3D image on computer, 3D printing for a life model.

Question 33

Disadvantages of CT

Answer 33

Not widely av in practice and tends to be expensive compared to radiography. Scan time is several seconds -- slower than x ray. Uses ionising radiation -- higher patient doses than radiography.

Question 34

What does scintigraphy use?

Answer 34

Uses a radioisotope (commonly technetium 99m) bound to another substance which determines where in the body it will localise eg hydroxymethylene diphosphonate which binds to bone. Technetium 99m decays to give a gamma ray with energy ~ 140KV. Increased binding with increased metabolism.

Question 35

Procedure of scintigraphy?

Answer 35

Bound isotope injected into patient (usually IV). Time allowed for isotope to reach tissue of interest. Pattern of radiation emitted from the patients recorded.

Question 36

Main uses of scintigraphy in vet medicine.

Answer 36

Look at skeletal injury in horses esp areas difficult to radiograph (eg pelvis, spine) Used in SA and LA where difficult to localise source of lameness. Used to look for ectopic tissue in hyperthyroid cats.

Question 37

Advantages of scintigraphy.

Answer 37

Increasing availability in larger equine centres - less so in sa. Uptake of bound isotope dept on metabolism/activity and not just anatomy, so element functional assessment.