Diagnostic imaging

Question 1

how does computed x-ray tomography work?

Answer 1

Uses x-rays to make cross sectional images through the body.

Can be used to rebuild transverse section/3D images

Question 2

What do CT images show?

Answer 2

Bone=white

Variations in physical density

Question 3

What is Scintigraphy

Answer 3

Using radioactive gamma rays that become incorporated into bone metabolism and can be detected with a gamma camera

Question 4

Why is scintigraphy useful?

Answer 4

Can detect bone cancer earlier than with x-rays as bone metabolism alters before bone damage

Question 5

What can you see with Scintigraphy?

Answer 5

Metabolic activity

darker = more activity

Question 6

What is MRI?

Answer 6

making images by applying pulsed magnetic energy to the patient and collecting the radiowaves that are emitted between pulses

Question 7

What is is MRI good?

Answer 7

More soft tissue detail, good for neurological exams.

Bone = black

Question 8

How does ultrasonography work?

Answer 8

Making images by firing pulses of high frequency sound and collecting the returning echos

Question 9

What can ultrasonography be used for?

Answer 9

Organs etc near the surface

Question 10

What do you need to do before ultrasound exam?

Answer 10

Clip hair and use jelly to get good skin contact

Question 11

What else can diagnostic imaging be used for?

Answer 11

To guide biopsy and facilitate treatment

Question 12

What is radiography?

Answer 12

making images representing the shadow of an object placed in an xray beam

Question 13

What is tomography?

Answer 13

making images that represent a section through the body

Question 14

What are x-rays?

Answer 14

Short wavelength, high energy electromagnetic radiation

Question 15

What type of imaging do we normally use with x-rays?

Answer 15

Negative imaging - bones white where few xrays reach the plate

Question 16

How do we make x-rays?

Answer 16

Fast electrons released from a filment in an aluminium filter when its heated by a low voltage curent. The tungsten target attached to copper (to deal with the heat) then has a high voltage passed through it so the electrons are drawn to the tungsten. The electrons are slowed by the positive tungsten nucleus and the loss of energy causes the x-ray beam. This takes place in a vacuum.

Question 17

What is the point of the aluminium filter?

Answer 17

absorbs low energy non-penetrable x-rays to reduce exposure to patient
(also non intentionally reduces contrast)

Question 18

What do you need to make x-rays?

Answer 18

A source of electrons
way to accelerate them
target to collide with

Question 19

What does x-ray absorption depend on?

Answer 19

tissue density
atomic no of elements in tissue (big atoms absorb more)
thickness of tissue

Question 20

How does something appear that x-rays pass through easily?

Answer 20

Black/lucent e.g air

Question 21

How does something apper that absorbs x-rays?

Answer 21

Pale/opaque e.g metal

Question 22

Three types of contrast media?

Answer 22

-ve : lucent (gas) - to examine organ wall
+ve: opaque (high atomic no) - barium (GI) / iodine(angio)
doube: distend using gas, add small vol of positive to coat inner surface

Question 23

What is mAs?

Answer 23

Milliampere seconds - current passing through tube and duration of current
mAs = mA x s (so can trade off)

Question 24

What does high mAs do?

Answer 24

more electrons so more x-rays = darker radiograph

Question 25

What is kVp?

Answer 25

Kilovoltage peak - voltage applied across the x-ray tube

Question 26

What does high kVp do?

Answer 26

High kVp = more xrays and higher energy = more penetrating (for thicker parts)

Question 27

What does film look like if kVp too high/low?

Answer 27

too low - all white (exaggerated contrast)

too high - all black (poor contrast)

Question 28

What does too high mAs do?

Answer 28

Thin parts appear black as overexposed

Question 29

What is scattered radiation?

Answer 29

x-rays that have been deflected from the primary beam by interacting with the patient/table etc

Question 30

Problem with scattered radiation?

Answer 30

• make radiographs look indistinct and grey

- safety of handlers

Question 31

How do we minimise effects of scattered radiation?

Answer 31

• minimise vol of tissue irradiated (collimate primary beam with the diaphragm)
• lead-rubber between casette and table top
• high kVp so need less mAs so less scatter

Question 32

What is an x-ray grid?

Answer 32

A series of fine lead strips parallel to the direction of the primary beam, between patient and film so absorbs any scattered radiation.

Question 33

When to use an x-ray grid?

Answer 33

With bigger animals as more scattered radiation

Question 34

What is the unit for measuring the ability of radiation to ionise air?

Answer 34

Roentgen = 2.58x10-4 C/Kg (electrical charge/ionisation energy per kg of air)

Question 35

What unit is used for measuring radioactive decay?

Answer 35

Becquerel = 1 radiation disintergration /second

Question 36

Unit for measuring absorbed radiation?

Answer 36

Gray = 1joule/kg

used for radiation doses

Question 37

unit for measuring dose of effective radiation?

Answer 37

Sievert = gray x q.f (quality factor - varies with type of radiation, for x-rays q.f.=1)

Question 38

What does ALARA mean?

Answer 38

As low as reasonably achievable

Question 39

What is the maximum permissable dose (MPD) at work? and how is it detected?

Answer 39

20 mSV/year. Use a film badge or thermoluminescent detector (TLD)

Question 40

Three way to protect form radiation?

Answer 40

1) Time - minimise time in radiation if possible
2) Distance - stay away from patient (inverse square rule)
3) Barriers - absorb scatter - lead aprons + gloves, mobile barriers, walls

Question 41

Define the controlled area

Answer 41

2m radius of primary beam

Question 42

Define the designated peron

Answer 42

Named in local rules as permitted to take x-rays

Question 43

Radiation protection advisor (RDA) ?

Answer 43

Doesnt work at practice but inspects and advises. provides the local rules.

Question 44

Radiation protection supervisor (RPS)?

Answer 44

normally a partner of the practice, notifies health and safety executive that radiography is performed, administers local rules, monitors exposure, informed about broken equipment.