18 Introduction To Medical Imaging

Question 1

What is the sagital plane?

Answer 1

If you were to cut from front to back down spine

Question 2

What is the coronal plane?

Answer 2

If you were to cut from side to side, with front and back separate

Question 3

What is the transverse plane?

Answer 3

If you were to cut and now see cross section of body

Question 4

What are the two types of plain film imaging?

Answer 4

X-rays

Fluoroscopy

Question 5

How do x-rays give an image?

Answer 5

Focused beam of high energy electrons
Can pass through body into receiver
Some are absorbed or scattered (attenuation)
Depends upon density and atomic number (metals)

Question 6

What are the 5 principle densities?

Answer 6

Black  - air
             - fat
             - soft tissue 
             - bone
White - metal

Question 7

What gives a lighter appearance on x-rays?

Answer 7

More attenuation

More dense/higher atomic number

Question 8

How to read a CXR using ABCDE

Answer 8

Airways
Breathing 
Circulation
Disability (bones)
Everything else

Question 9

How to read an AXR using ABDO

Answer 9

Air
Bowel (small and large)
Densities (bones)
Organs

Question 10

What are the advantages of x-rays?

Answer 10

Quick
Portable
Cheap
Simple

Question 11

What are the disadvantages of x-rays?

Answer 11

Radiation but relatively low
One plane (2D)
Would not see all pathology
Can’t visualise all areas (e.g. brain due to skull)
Poor soft tissue imaging

Question 12

What are the uses of x-ray?

Answer 12

Chest (infection, pneumothorax, trauma)
Bowel (dilation, perforation)
Orthopaedic
Post-procedure (tubes, pacemaker)
Dentist

Question 13

What is fluoroscopy?

Answer 13

Examination of anatomy and motion
Uses constant stream of x-rays to give moving picture
Often enhanced by contract (barium, iodine, gadolinium)

Question 14

What are the uses of fluoroscopy?

Answer 14

Angiography 
Contrast GI studies
Therapeutic joint infections
Arthrograms (joints)
Screening in theatre

Question 15

What are the advantages of fluoroscopy?

Answer 15

Dynamic studies (show how tissues work)
Cheap
Interventional procedures

Question 16

What are the disadvantages of fluoroscopy?

Answer 16

Clinician exposure must be minimised

Radiation

Question 17

How does computed tomography (CT) work?

Answer 17

Rotating gantry with X-ray tube on one side and detectors on the other
Images put together by computer
Same principle of attenuation as x-ray

Question 18

What are the advantages of CT?

Answer 18

Quick
Good spatial resolution
Can scan most areas

Question 19

What are the disadvantages of CT?

Answer 19

Radiation
Lower contrast resolution
Affected by artefact
Requires breath holding
Overuse (fishing for diagnosis)
Incidental findings

Question 20

What are the uses of CT?

Answer 20

Diagnosis - cancer, stroke, bone injury, blood flow
Guide further tests or treatment
Monitor conditions

Question 21

Who does MRI work?

Answer 21

Strong magnetic field, aligns hydrogen atoms
Some point towards head and some towards feet (not 50/50 so unmatched ions remain)
Radio frequency pulse applied
Unmatched ions absorb energy and spin in different direction
Pulse turned off and atoms spin returns which emits energy
Computer processing to generate image

Question 22

MRI weighting

Answer 22

T1 weighting - fat is white, water is black

T2 weighting - water is white, fat is black

Question 23

What are the uses of MRI?

Answer 23

CNS - brain and spinal cord scans
Bones and joint
Heart and blood vessels
Internal organs

Question 24

What are the advantages of MRI?

Answer 24

No radiation

Good contrast resolution

Question 25

What are the disadvantages of MRI?

Answer 25

``` Expensive Time consuming Availability Claustrophobic Some patients won’t fit Loud Need to lie still Metalwork ```

Question 26

What is scintigraphy?

Answer 26

``` Nuclear medicine Injection of radio pharmaceuticals Emit gamma rays Highly sensitive Functional and anatomical information ```

Question 27

What is positron emission tomography (PET)?

Answer 27

Radionuclides that decay by positron emission Bound to glucose PET camera detects annihilations (high energy gamma rays) Hot spots - areas of high glucose metabolism Heavily used in oncology

Question 28

What is ultrasound?

Answer 28

High frequency sound waves from transducer probe Sound wave reflected back by tissues where density differs Probe detects reflected sound waves

Question 29

What is acoustic shadowing?

Answer 29

Great differences in tissue density means sound is completely reflected therefore can’t see behind bone, air and stones

Question 30

What are the uses of ultrasound?

Answer 30

Solid organs - liver, kidneys, spleen, pancreas, thyroid, tested Urinary tract - stones, dilation, volume Obs and gynae- pregnancy, uterus Musculoskeletal Use in body cavities- transvaginal, transracial, transoesophageal

Question 31

What are the advantages of ultrasound?

Answer 31

``` Lack of ionising radiation Low cost Portable Can be inserted into body cavities Babies Dynamic (blood flow) ```

Question 32

What are the disadvantages of ultrasound?

Answer 32

Operator dependent No bone or gas penetration Body habit us (more fat restricts view)