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Body Logistics > 8.1 - Medical Imaging > Flashcards

8.1 - Medical Imaging Flashcards

1
Q

how is an image produced using x ray

A

within x ray tube…
- electrons are accelerated to metal target
- interaction of electrons with target produces photons (x rays)
- some of the x-rays pass through patient, then hit a detector behind patient
- some are attenuated by the patient (absorbed, scattered, or lose energy)

amount of attenuation depends on…
- density and atomic number of tissue/material
- energy of the x-ray beam

detected x rays are digitized and processed, creating an image which is uploaded

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2
Q

densities on x rays

A

most dense → attenuates lots of x-rays. lighter
* metal
* bone
* muscle
* blood
* liver
* lung
* fat
* air
least dense → darker/black

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3
Q

systematic interpretation of chest x-ray

A

A - airways
B - breathing
C - circulation
D - disability (bones)
E - everything else

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4
Q

systematic interpretation of abdominal x-ray

A

A - air
B - bowel
D - densities (bones, stones, tubes, foreign bodies)
O - organs

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5
Q

clinical indications for use of x rays

A

chest
dyspnoea, cough, haemoptysis, chest pain, tube/line poisioning, post procedure, cancer mets

abdomen
neonatal, passing of urinary tract calculi, presence of foreign bodies

MSK
trauma, pain, deformity, swelling, post relocation of joint

haemoptysis - coughing up blood

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6
Q

diagnoses from x-ray

A

chest
infection, pulmonary oedema, pleural effusion, pericardial effusion, pneumothorax, cancer

abdomen/pelvis
obstruction, volvulus, perforation, colitis (can see inflammation), calculi (eg calculi), abdominal aortic aneurysm (can see widening of aorta)

MSK
fracture, dislocation, effusion, soft tissue injury, tumor, infection

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7
Q

pros + cons of x ray

A

advantages
- quick
- portable
- cheap
- simple

disadvantages
- radiation (very low)
- one plane, and two dimensions only
- cannot see all pathology
- poor soft tissue imaging (particularly if they’re close together as they are difficult to distinguish)

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7
Q

pros + cons of x ray

A

advantages
- quick
- portable
- cheap
- simple

disadvantages
- radiation (very low)
- one plane, and two dimensions only
- cannot see all pathology
- poor soft tissue imaging (particularly if they’re close together as they are difficult to distinguish)

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8
Q

what is flouroscopy

A
  • similar to x ray process
  • continuous/pulsed x-rays are used
  • creates a moving image
  • can examine anatomy, pathology, motion and function
  • images often enhanced using contrast (eg barium or iodine)
  • high atomic number = good absorber of x-rays = dense on image
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9
Q

clinical use of flouroscopy

A
  • diagnostic and interventional
  • vascular (angiography) eg cerebal, coronory, embolisation, angioplasty and stenting
  • GI eg barium swallow/meal, barium enema
  • GU eg urogram, nephrostomy, hysterosalpinogram
  • MSK eg arthogram, therapeutic joint injections, orthopaedic surgery
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10
Q

pros and cons of flouroscopy

A

advantages
- dynamic studies, real time - can assess function, carry out intervention
- quick

disadvantages
- higher radiation dose than single x-ray due to it being continuous
- radiation exposure to interventional radiographer
- one plane, two dimensions, cannot see all pathology
- poor soft tissue imaging

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11
Q

how does CT scan work

A
  • x rays produced as normal
  • x ray tube on one side of rotating gantry (ring), with detectors on opposite side
  • patient table moves through gantry
  • same principle of x ray attenuation
  • cross sectional slices of the patient imaged
  • detected signal processed by computer to produce cross sectional images
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12
Q

what view is CT

A

axial / transverse view
looking from feet up

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13
Q

clinical use of CT

A

diagnosis / guiding further investigation / management
- trauma
- bleeding + clots
- ischaemia / infarcts
- cancer + staging cancer
- perforation
- obstruction
- calculi
- weight loss
- fever

monitor conditions
eg cancer and interstitial lung disease (ILD)

interventional
radiotherapy, CT guided biopsies/drains

ischaemia = when blood flow restricted

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14
Q

pros and cons of CT scan

A

advantages
- quick
- good spatial resolution
- can scan most parts of the body well

disadvantages
- significant radiation
- does not delineate soft tissues well (eg gynae)
- affected by artefact (eg movement/metal)
- requires breath holding, which not all patients can do
- overuse
- incidental findings (have to follow this up, and this causes patient anxiety)
- contrast reactions

delinate = describe or portray something precisely

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15
Q

PET scans how do they work

A

positron emission tomography
- work by gamma rays
- administration of radiopharmaceutical (more info on different card)
- nuclear decay of the radionuclide occurs within tissues of interest, emitting positrons
- positrons collide with electrons, producing gamma radiation
- this is detected by gamma camera close to patient
- gamma camera contains scintillator (converts signal to light)
- light signal amplified and processed by computers
- gives functional and anatomical infomation

16
Q

how do radiopharmaceuticals work

A

administration
- injection
- ingestion
- inhalation

two parts to radiopharmaceutical
- pharmaceutical part: takes the compound to tissues of interest
- radionuclide part: sends signal from tissue of interest

how it works
- nuclear decay of radionucleotide occurs within tissues of interest
- emit positrons during decay
- positrons collide with nearby electrons
- these produce gamma photons
- these are detected by the gamma camera

17
Q

what is a common radiopharmaceutical

A

18F-FDG

  • flourodeoxyglucose is pharmaceutical part (glucose analogue) which is taken up by areas of high glucose metabolism
  • this then releases flourine-18 (radionuclide)
  • some tissues are naturally metabolically active
  • therefore some tissues naturally glow on PET
  • other metabolically active tissues will also glow eg tumours
18
Q

clinical use of PET

A

oncology
detection, staging and response to treatment

neurological
early diagnosis of Alzheimer’s disease and localisation of seizure focus

cardiac
identification of poorly perfused myocardium

infection/inflammation
pyrexia of unknown origin and vasculitis

pyrexia = fever

19
Q

clinical use of PET

A

oncology
detection, staging and response to treatment

neurological
early diagnosis of Alzheimer’s disease and localisation of seizure focus

cardiac
identification of poorly perfused myocardium

infection/inflammation
pyrexia of unknown origin and vasculitis

pyrexia = fever

20
Q

pros + cons of PET

A

advantages
- good contrast and spatial resolution
- can analyse anatomy and function
- can identify cancers

disadvantages
- physiological uptake of radiopharmaceutical
- radiation dose to patient
- risk of radiation to others
- radioactive waste produced
- expensive and time consuming
- radionuclide shortages
- confusion: eg if patient has done heavy exercise → tissues more metabolically active + will show up on scan

21
Q

how does MRI work

A
  • MRI scanner creates strong magnetic field
  • this aligns all the hydrogen atoms in the matient
  • radiofrequency pulse is applied
  • this ‘tips’ the aligned hydrogen atoms, which then create detectable magnetic field
  • this field induces an electric current in nearby coils in MRI machine
  • varying signal intensities are produced by different tissues
  • signals then processed to create images
  • after radiofrequency pulse ends, hydrogen atoms relax back into alignment
22
Q

imaging colours / weighting

A

high signal = bright = ‘hyperintense’
low signal = dark = ‘hypointense’

→ T1 weighting = fat is bright, water is dark
→ Τ2 weighting = fat is dark, water is bright

23
Q

clinical use of MRI

A
  • central nervous system
  • head and neck imaging
  • MSK imaging (bones/joints/soft tissues)
  • GI eg liver
  • cardiac MRI, angiography
  • gynaecological imaging and prostate imaging
  • in paediatrics and pregnancy to avoid radiation (and therefore theoretical damage to DNA)
24
Q

pros and cons of MRI

A

advantages
- no radiation
- good contrast resolution, especially soft tissues

disadvantages
- expensive
- time consuming
- fewer machines and radiographers available
- contraindications (pacemakers, cochlear implants, metal, claustrophobia, inability to stay still)
- contrast reactions
- some other risks eg overheating
- magnetic field strength - need to remove all metal objects from room

25
Q

pros and cons of MRI

A

advantages
- no radiation
- good contrast resolution, especially soft tissues

disadvantages
- expensive
- time consuming
- fewer machines and radiographers available
- contraindications (pacemakers, cochlear implants, metal, claustrophobia, inability to stay still)
- contrast reactions
- some other risks eg overheating
- magnetic field strength - need to remove all metal objects from room

26
Q

how does ultrasound work

A
  • utilises soundwaves (not part of electromagnetic spectrum)
  • crystal in transducer probe oscillates
  • this creates high frequency sound waves
  • sound waves travel through tissues and are refelected back from boundaries between tissues of different density (acoustic impedence mismatch)
  • probe detects reflected sound waves and converts them into electrical signal
  • time taken for echo to return is used to calculate where it was reflected from
  • proportion of reflected waves are used to calculate acoustic impedence mismatch in that place

hyperechoic = more reflection = white on image
hypoechoic = less reflection = dark

acoustic shadowing = large acoustic impedence mismatch = sound waves completely reflected back, non pass through, dark area behind bone, air, stones

27
Q

doppler ultrasound

A
  • if something is moving towards or away from the soundwave, eg blood flow in a vessel, the frequency of the reflected wave is affected
  • moving towards the soundwave = increased frequency of echo wave
  • moving away from the soundwave = decreased frequency of echo wave
28
Q

what is duplex ultrasound

A

normal 2D imaging + doppler

29
Q

clinical use of ultrasound

A

solid organs (liver, kidneys, spleen, pancreas, thyroid, fetal brain, lymph nodes etc) can see tissue, massess and bleeds etc

hollow structures (eg heart, vessels, gallbladder, common bile duct, appendix, uterus etc) can see function, flow, obstruction, masses, stones etc

breast assess for lumps or abnormality seen on mammogram

obstetrics pregnancy dating, fetal anomaly, placental location, fetal growth

MSK assessing ligaments, tendons, joints, muscles, nerves, soft tissue masses

interventional eg guided injections, biopsies, drains and aspirations

can also have transvaginal, transrectal, transoesopageal ultrasounds

30
Q

clinical use of ultrasound

A

solid organs (liver, kidneys, spleen, pancreas, thyroid, fetal brain, lymph nodes etc) can see tissue, massess and bleeds etc

hollow structures (eg heart, vessels, gallbladder, common bile duct, appendix, uterus etc) can see function, flow, obstruction, masses, stones etc

breast assess for lumps or abnormality seen on mammogram

obstetrics pregnancy dating, fetal anomaly, placental location, fetal growth

MSK assessing ligaments, tendons, joints, muscles, nerves, soft tissue masses

interventional eg guided injections, biopsies, drains and aspirations

can also have transvaginal, transrectal, transoesopageal ultrasounds

31
Q

pros + cons of ultrasound

A

advantages
- lack of radiation
- low cost
- portable
- dynamic, eg can see blood flow
- quick

disadvantages
- operator dependent
- no bone or gas penetration
- diffiult with obese, frail and unwell patients
- risk of overheating

Body Logistics (11 decks)

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