Radiology

Question 1

What is imaging?

Answer 1

All the tests that doctors use to see things inside the body that they can’t see or feel from the outside.

Question 2

What tests are imaging tests?

Answer 2

Xrays

• plain radiography
• contrast studies (barium enema, arthrography)
• computed tomography (CT)

Ultrasound

Magnetic resonance imaging (MRI)

Nuclear medicine

Question 3

What are x-rays?

Answer 3

Electromagnetic radiation produced by an electrical source which pass through body tissue to a degree dependent on its density.

Question 4

What are the mechanics of producing an X-ray?

Answer 4

• Electric current heats filament cathode
• electrons are emitted and strike anode
• generated X-rays exit window in casing and beam is collimated (so we can aim where we want to see)
• x-rays penetrate patient and scatter
• only 1% of x-rays reach the film and contribute to the image

Question 5

Why does scattering lead to concerns for imaing safety with X-rays?

Answer 5

We want to minimise the dose to the patient and staff so need to use precautions such as led lined rooms and aprons, etc.

Question 6

Why are x-rays increasingly taken digitally?

Answer 6

• When on film they often went missing
• over and under exposure meant repeats often required
• post-exposure manipulation reduces the need for repeats
• PACS (picture archive and communication system) allows easier storage, access and retrieval of digital images (x-ray, CT, etc)
• This can also be used by different people at the same time, allows sharing of expertise etc.

Question 7

The _______ a tissue the fewer X-rays pass through it.

Answer 7

Denser

Question 8

Due to their relative densities how many X-rays can pass through air, soft tissue and cortical bone?

Answer 8

• Air lets all X-rays pass through
• Soft tissue lets some X-rays pass through
• Cortical bone lets no X-rays pass through

Question 9

What is the picture produced in an X-ray dependent upon?

Answer 9

X-ray film is blackened when x-rays hit it, so the picture is produced depending on what the x-rays have to pass through.

Question 10

What are X-rays good at showing?

Answer 10

• Things surrounded by black air e.g. lung cancer
• Things surrounded by white bone e.g. fractures
• Things that destroy white bone e.g. bone cancer

Question 11

What is the main weakness of X-rays?

Answer 11

• To be visible on a simple x-ray, an abnormality must be of very different density to the tissue that surrounds it
• A lot of pathology, especially that effecting soft tissues, is of similar density to its surroundings and isn’t shown by simple x-rays
• if two things are the same density you cannot tell where one starts and the other stops
• 2D representation of a 3D strutcure so when there are many structures overlying x-rays will have weakness.

Question 12

What is a contrast study and the theory behind it?

Answer 12

• contrast studies- application of an additional substance which is more or less dense than the substance adjacent to it.
• liquids containing dense elements like barium or iodine can block x-rays
• by putting them in the spaces between tissues, the tissue outlines become visible because the difference in density between two adjacent stuctures has been increased.

Question 13

Give two examples of contrast studies

Answer 13

• Barium enema in the colon
• Arthrogram- direct injection of iodine rich fluid in a joint

Question 14

Why can X-rays be dangerous?

Answer 14

X-rays are radiation so can damage cell DNA leading to mutations which may kill the cell or make it turn cancerous.

Question 15

What is the risk of X-rays related to?

Answer 15

X-ray dose

Question 16

What does the IRMER (ionising radiation medical exposure regulation) 2000 state?

Answer 16

• the benefit to patients must always outweigh the risk

Also hospital staff have no benefit from x-rays so must be protected

Question 17

Radiographs have limited ________ resolution and struggle to resolve different ____ tissue structures.

Answer 17

• contrast
• soft

Question 18

Describe why CT is better than radiographs

Answer 18

• sophisticated way of using X-rays to produce images
• More able than radiographs to distinguish between tissues of similar density and is often used to show tissue pathology
• superior contrast resolution conpared to a radiograph

Question 19

How does a CT scan work?

Answer 19

• Rotating x-ray source which moves around the patient coupled with a detector
• x-rays are passed through the patient at various angles and picked up at various angles
• advanced computer algorithm reconstructs the image to allow a cross sectional image

Question 20

Why are radiographs not sufficient to diagnose illness?

Answer 20

When obtaining a radiograph, the x-rays are ‘fired’ from only one direction producing an image where all structures between their source and the film are superimposed.

Question 21

How does CT overcome the issues with superimposition on a radiograph?

Answer 21

With CT, x-rays are ‘fired’ from all around the body and processed by a computer which produces a set of cross sectional pictures with no superimposition.

Question 22

Why does everyone not just automatically get a CT scan over a radiograph?

Answer 22

• Gives large doses of ionising radiation (chest CT = 250 CXR)
• soft tissues of very similar density cannot be distinguished by CT
  
  • pelvic organs (uterus, ovaries, prostate)
  • joint cartilage and ligaments
  • some areas of the brain
• CT cannot resolve bone marrow disease

Question 23

What are the benefits of ultrasound and MRI over CT and X-ray?

Answer 23

• neither employ ionising radiation
• both can show pelvic organs
• both can show muscles and tendons
• MRI can show joints and bone marrow disease
• MRI can show all areas of the brain
• ultrasound is quick to do, easy for patients, completely safe and doesn’t rely on a £1.5million scanner to generate images.

Question 24

How does an ultrasound work?

Answer 24

• piezoelectic crystals can convert electrical energy to acoustic energy
• these crystals are housed in a transducer which has an electrical supply
• the transducer produces pulses of sound waves
• the skin is coated with jelly to assist sound transmission into the body
• the transducer alternately transmits sound pulses and then listens for reflected sound returning
• the returning accoustic energy is converted back into an electrical impulse and fed into a computer.
• the computer ‘knows’ where the sound has come from by the time taken for it to return to the transducer
• it uses this to create a cross-sectional picture of the soft tissues invisible to x-rays

Question 25

On what principle do ultrasounds work?

Answer 25

Body tissues have different accoustic properties- some tend to transmit sound while others tend to reflect it.

Question 26

How do fluid and soft tissues appear on US and what is this to do with their accoustic properties?

Answer 26

Fluid appears very black and allows sound to go all the way through. Soft tissues reflect sound back to transducer and appear lighter.

Question 27

Ultrasound images are obtained \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_. During US, the diagnosis is made durig the scan, not afterwards.

Answer 27

intantaneously

Question 28

How can US scanner produce a complete survey?

Answer 28

By moving the trasnducer over the skin, the sonographer 'sweeps' the US beam thorugh the body tissues allowing for a complete survey.

Question 29

What makes a good ultrasound exam?

Answer 29

* tissues that allow sound transmission * lots of sound reaches the target and returns to the transducer * good skin-transducer contact * superficial structures * slim patients * correct transducer selection * Tissues which have different accoustic properties (reflect different amounts of sound) * a well trained and experienced sonographer * modern equipment

Question 30

What makes a poor ultrasound exam?

Answer 30

* tissues that prevent sound transmission (gas, bone) * sound can't reach the target or return to the transducer * poor skin-transducer contact (not enough jelly, hairy) * tissues which have identical accoustic properties (reflect the same amount of sound) * an incompetent operator * antique equipment

Question 31

State 4 ultrasound strengths

Answer 31

1. **High spacial resolution**, useful in imaging MSK soft tissue sturtcures- tendons and muscles 2. body **fluids readily transmit** ultrasound whereas **solid structures** within the fluid **reflect** it. 3. **abnormal fluid collections are well shown** e.g. pleural effusion, ascites, abscess, cytsts. 4. **soft tissues** with **different accoustic properties** are **well differentiated**- soft tissue tumors

Question 32

What are 3 weaknesses of ultrasounds?

Answer 32

1. **bone blocks US**, so it can't see the brain, the spinal canal, inside joints or ascess bone marrow 2. **Gas blocks** US, so 'windy' patients are difficult to assess and gas containing structures like the lungs or bowel can't be assessed. 3. **Very fat patients make poor US subjects**

Question 33

What happens in an MRI?

Answer 33

* MRI creates a strong magnetic field * the scanner produces a burst of radio signal (RF pulse), which energises the body's protons * the scanner waits * scanner listens for a return signal, produced by the protons * the amount of signal produced depends on the molecular movement of these protons * using the returned signal, the scanners computer peforms some amazingly complex calculations and creates an image.

Question 34

How is the magnetic fields in an MRI produced?

Answer 34

Magnetic field results from electrucal current passed through coiled metal wire surrounding the bore and relies on superconduction of current which occurs at very low temperatures, maintained by liquid He

Question 35

What are the dangers of an MRI scanner?

Answer 35

* superconducting magnet * Very low temperature helium * frostbite and thermal burns * deafness * disturbance of surgical and non-surgical ferrous material * pacemakers * heart valves * mobile ferrous material eg shrapnel, intra-ocular foreign bodies * missile injuries

Question 36

What are the 4 rules around staff and MRI equipment?

Answer 36

1. security keypad lock at entrance to MR suite 2. all staff are vetted before entry to MR scanner room is permitted 3. only MR approved cleaners, engineers, anaesthatists and equipment are allowed into the MR suite 4. staff must remove watches, credit cards, metal keys etc before entering MR room

Question 37

How is patient injury prevented around MRI scanners?

Answer 37

* request card safety questionnaire * patients must remove all ferrous metal, including dental plates, ear rings, belly button studs, belts, keys, etc

Question 38

What are the 4 strengths of MRI?

Answer 38

1. MRI provides the most complete assessment of the brain of any modality 2. It is a sensitive way to assess acute muscle and tendon tears, especially in deep tissues where US is less accurate. 3. Provides excellent detail of spinal canal disease 4. Allows the interiors of joints to be imaged, so injuries to cartilage and ligaments can be seen.

Question 39

What are some (5) weaknesses of MRI scanning?

Answer 39

1. Expensive 2. could harm some patients and so is contraindicated 3. some patients find MRI too claustraphobic 4. MRI scans take a long time so patients who are in pain or are restless, or those who are unstable and need monitoring can't be scanned 5. Poor at showing detail of the lungs

Question 40

What does imaging often provide even if immediate symptoms have been treated in a patient?

Answer 40

A diagnosis

Question 41

What is the role of clinical imaging?

Answer 41

* To make or confirm a diagnosis * To help narrow a differential diagnosis * To 'stage' a known disease e.g. cancer to inform treatment * To monitor the effects of treatment and follow up a known disease * To aid intervention/deliver treatment e.g. image guided procedures or interventional radiology *