18 Introduction To Medical Imaging Flashcards
What is the sagital plane?
If you were to cut from front to back down spine
What is the coronal plane?
If you were to cut from side to side, with front and back separate
What is the transverse plane?
If you were to cut and now see cross section of body
What are the two types of plain film imaging?
X-rays
Fluoroscopy
How do x-rays give an image?
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)
What are the 5 principle densities?
Black - air
- fat
- soft tissue
- bone
White - metalWhat gives a lighter appearance on x-rays?
More attenuation
More dense/higher atomic number
How to read a CXR using ABCDE
Airways Breathing Circulation Disability (bones) Everything else
How to read an AXR using ABDO
Air
Bowel (small and large)
Densities (bones)
Organs
What are the advantages of x-rays?
Quick
Portable
Cheap
Simple
What are the disadvantages of x-rays?
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
What are the uses of x-ray?
Chest (infection, pneumothorax, trauma) Bowel (dilation, perforation) Orthopaedic Post-procedure (tubes, pacemaker) Dentist
What is fluoroscopy?
Examination of anatomy and motion
Uses constant stream of x-rays to give moving picture
Often enhanced by contract (barium, iodine, gadolinium)
What are the uses of fluoroscopy?
Angiography Contrast GI studies Therapeutic joint infections Arthrograms (joints) Screening in theatre
What are the advantages of fluoroscopy?
Dynamic studies (show how tissues work)
Cheap
Interventional procedures
What are the disadvantages of fluoroscopy?
Clinician exposure must be minimised
Radiation
How does computed tomography (CT) work?
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
What are the advantages of CT?
Quick
Good spatial resolution
Can scan most areas
What are the disadvantages of CT?
Radiation Lower contrast resolution Affected by artefact Requires breath holding Overuse (fishing for diagnosis) Incidental findings
What are the uses of CT?
Diagnosis - cancer, stroke, bone injury, blood flow
Guide further tests or treatment
Monitor conditions
Who does MRI work?
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
MRI weighting
T1 weighting - fat is white, water is black
T2 weighting - water is white, fat is black
What are the uses of MRI?
CNS - brain and spinal cord scans
Bones and joint
Heart and blood vessels
Internal organs
What are the advantages of MRI?
No radiation
Good contrast resolution
What are the disadvantages of MRI?
Expensive Time consuming Availability Claustrophobic Some patients won’t fit Loud Need to lie still Metalwork
What is scintigraphy?
Nuclear medicine Injection of radio pharmaceuticals Emit gamma rays Highly sensitive Functional and anatomical information
What is positron emission tomography (PET)?
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
What is ultrasound?
High frequency sound waves from transducer probe
Sound wave reflected back by tissues where density differs
Probe detects reflected sound waves
What is acoustic shadowing?
Great differences in tissue density means sound is completely reflected therefore can’t see behind bone, air and stones
What are the uses of ultrasound?
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
What are the advantages of ultrasound?
Lack of ionising radiation Low cost Portable Can be inserted into body cavities Babies Dynamic (blood flow)
What are the disadvantages of ultrasound?
Operator dependent
No bone or gas penetration
Body habit us (more fat restricts view)
