Lecture 18- An Introduction To Medical Imaging

Question 1

What type of images do X-Rays produce ?

Answer 1

2D images

Question 2

Where are X-Rays often used on the body ?

Answer 2

• chest X-rays which help detect pneumonia , lung cancer or pulmonary oedema.
• abdominal x -rays : detect bowel/intestinal obstruction , free air and free fluid in the abdomen.
• Kidney stings or gallstones
• evaluating an orthopaedic Implant such as a knee , hip or shoulder replacement.
• dentistry : problems resulting from tooth decay

Question 3

Where are X-rays not used to study the body ?

Answer 3

• two fat tissues such as the brain and muscle.

Question 4

What structures in the body have high density and what colour do they appear in an X ray image ?

Answer 4

• bones
• metal
• they absorb a lot of the X-day radiation , preventing the X ray beams from reaching the films , this results in a white colour on the image.

Question 5

Which are examples of low density structures ? and what colours do they appear on an X ray image ?

Answer 5

• fat
• air
• skin
• internal organs
• they appear black.

Question 6

How do X-rays give an image ?

Answer 6

Focused beam of high energy electrons

• these can pass through the body onto receiver
• some beams of electrons are absorbed or scattered
• absorption of electrons depends on the density And atomic number of structure

Question 7

How to read a chest x ray

Answer 7

A - airways

B- breathing

C- circulation ( heart width )

D- disability

E- everything else eg gastric bubble , breast shadow

Question 8

What are the advantages of X-rays

Answer 8

• quick
• portable
• cheap
• simple

Question 9

What are the disadvantages of x-rays

Answer 9

• radiation ( but low dosage(
• 2D
• would not see all pathology eg brain
• poor soft tissue imaging

Question 10

What is fluoroscopy

Answer 10

Examination of anatomy and motion

• uses constant stream of x rays
• often enhanced by contrast media such as barium , iodine , gadolinium
• provides moving projection radiographs

Question 11

What is angiography

Answer 11

The use of fluoroscopy to view the cardiovascular system.

• an iodine based contrast is injected into the bloodstream and watched as it travels around the body into the cardiac vessels.

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Question 12

What can fluoroscopy be used for ?

Answer 12

• angiography

- therapies joint injections

Question 13

What are the advantages of fluoroscopy

Answer 13

• dynamic studies
• cheap

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Question 14

What are disadvantages of fluoroscopy

Answer 14

• clinicians exposure must be minimised

- radiation

Question 15

CT scan

Answer 15

• patient placed into a rotating gantry
• x ray tubes on one side and detectors on the other side
• images put together by computer

Question 16

The more dense a structure the more NEGATIVE OR POSITIVE the hounsfield unit is

Answer 16

Positive

Eg metal is the most positive

Then bone

Then soft tissue

Then blood

Question 17

What structure has 0 HU

Answer 17

Water

Question 18

The less dense the structure the more NEGATIVE/POSITIVE the HU value

Answer 18

Negative eg fat and air

• air being the most negative

Question 19

What type of anatomical plane is used for CT scans ?

Answer 19

Transverse plane

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Question 20

What are advantages of CT scans ?

Answer 20

• quick
• good spatial resolution : can distinguish between two tissues adjacent to eachother
• can scan most areas

Question 21

What are the disadvantages of CT scans ?

Answer 21

• radiation exposure
• lower contrast resolution ( distinguishing between different densities )
• affected by artefact
• requires breath holding ( some patients cannot manage )

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Question 22

How does an MRI work ?

Answer 22

1) atoms spin in random directions in their magnetic field
2) in the magnetic field produced by the MRI , atoms line up either south or north - there are a few unmatched atoms
3) when radio frequency pulse is applied , the unmatched atoms spin the other way
4) when the radio frequency is turned off , the extra atoms return to normal position - emitting energy.
5) the energy sends a signal to computer which converts the signal into an image.

Question 23

What does an MRI rely on?

Answer 23

• magnetic field

Question 24

What can we use MRI for ?

Answer 24

• CNS
• bones and joints
• heartand blood vessels
• internal organs

Question 25

What are the advantages of MRI scans ?

Answer 25

• no radiation

- good contrast resolution ( can distinguish well between different densities )

Question 26

What are the disadvantages of MRI

Answer 26

• expensive
• time consuming
• claustrophobic
• some patients won’t fit
• loud
• need to lie still
• not suitable for patients with metal work in them

Question 27

Nuclear medicine

Answer 27

Injection of radio pharmaceuticals which emit gamma rays

Question 28

How does an ultrasound work ?

Answer 28

• it transmits high frequency sound pulses into your body using a probe.
• the sound waves travel into your body and hit a boundary between tissues where density differs eg soft tissue and bone)
• the reflected waves are picked up by the probe and relayed back to machine.

Question 29

Hyperechoic

Answer 29

• more reflective = white eg fat tissue or stones

Question 30

Hypoechoic

Answer 30

Less reflective= dark grey

Eg lymph node , tumour

Question 31

Anechoic

Answer 31

Not reflective ( pure fluid)= black

Question 32

Advantages of ultrasounds

Answer 32

Low cost

Lack of ionising radiation

Portable

Babies

Dynamic ( blood flow - Doppler ultrasound )

Question 33

Disadvantages of ultrasounds

Answer 33

• operator dependant

- no bone or gas penetration