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Body logistics > Intro to medical imaging > Flashcards

Intro to medical imaging Flashcards

1
Q

how is an image produced using X-rays

A
  • within an X-ray tube, electrons are accelerated towards a metal target
  • interaction of electrons with the target produces photons (X-rays)
  • some of the X-rays pass through the patient then hit a detector behind the patient
  • some are attenuated by the patient (absorbed, scattered, lose energy)
  • amount of attenuation depends on density and atomic number of tissue/material and energy of the X-ray beam
  • detected X-rays are digitised and processed, creating an image
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2
Q

imaging techniques with X-rays

A
  • x-ray single pulse of X-rays passes through patient to detector creating one image
  • fluoroscopy continuous/pulsed X-rays, creating real-time moving images
  • CT X-ray tube and detectors move around patient creating cross-sectional images
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3
Q

how does angiography work to generate an image of CVS

A
  • intial X-ray image taken of anatomical region of interest
  • second image taken of same region after iodinated contrast agent injected into the blood vessels
  • the two images are digitally subtracted leaving only the iodinated contrast outlining the blood vessels
  • radiologist compares the image to normal anatomical images
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4
Q

clinical use of X-ray

A

chest
- indications: dyspnoea, cough, haemoptysis, chest pain, post-procedure
- diagnoses: infection, pulmonary oedema, pleural effusion, pneumothorax, pericardial effusion, cancer

abdomen/pelvis
- indications: neonatal, urinary tract calculi, location of foreign bodies
- diagnoses: obstruction, volvulus, perforation, colitis, AAA

MSK
- indications: trauma, pain, deformity, swelling, post joint relocation, post reduction
- diagnoses: fracture, dislocation, effusion, soft tissue injury, tumour, infection

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5
Q

advantages of X-ray

A
  • quick
  • portable
  • cheap
  • simple
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6
Q

advantages of X-ray

A
  • quick
  • portable
  • cheap
  • simple
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7
Q

disadvantages of X-ray

A
  • radiation (relatively low)
  • one plane, two dimensional
  • cannot see all pathology
  • poor soft tissue imaging
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8
Q

how does fluoroscopy work

A
  • pulsed or continuous X-rays are used which creates moving images
  • can examine anatomy, pathology, motion and function
  • images enhanced using contrast (barium/iodine)
  • high atomic number = good absorber of X-rays so dense on image
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9
Q

clinical use of fluoroscopy

A
  • diagnostic and interventional
  • vascular (angiography) eg. cerebral, cori=onary, embolisation, angioplasty
  • GI eg. barium swallow, barium meal, barium enema
  • GU eg. urogram, hysterosalpinogram, nephrostomy, insertion
  • MSK eg. arthrogram, therapeutic joint injections, orthopaedic surgery
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10
Q

advantages of fluoroscopy

A
  • dynamic studies, can assess in real time and carry out intervention
  • quick
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11
Q

disadvantages of fluoroscopy

A
  • higher radiation dose than single X-ray
  • radiation exposure to interventional clinician
  • one plane, two dimensional
  • cannot see all pathology
  • poor soft tissue imaging
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12
Q

how does CT (computed tomography) work

A
  • X-rays produced
  • X-ray tube on one side of a rotating gantry and detectors on opposite side
  • patient table moves through gantry
  • cross-sectional slices of patient imaged
  • detected signal processed by computer
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13
Q

clinical uses of CT

A
  • diagnosis/further investigations/management trauma, bleeding, clots, ischaemia, pain, cancer, obstruction, calculi, weight loss, fever
  • monitor conditions cancer, ILD
  • interventional radiotherapy, CT guided biopsies, drains
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14
Q

advantages of CT

A
  • quick
  • good spatial resolution
  • can scan most parts of body well
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15
Q

disadvantages of CT

A
  • radiation
  • does not delineate soft tissues well
  • affected by artefact
  • requires breath-holding
  • overuse
  • incidental findings
  • contrast reactions
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16
Q

how does PET (positron emission tomography) work

A
  • radionuclides used emit positrons during decay
  • emitted positrons collide with nearby electrons in patient producing two annihilation gamma photons which are detected by gamma camera
  • radiopharmaceutical used commonly is 18F-FDG
  • often combined with CT or MRI
17
Q

how does nuclear medicine work

A
  • administration of radiopharmaceutical (pharmaceutical part takes compunt to tissue of interest and radionuclide part sends signal from tissue of interest)
  • nuclear decay of radionuclide occurs within tissues of interest, emitting gamma radiation which is detected by a gamma camera
  • gamma camera contains a scintillator which converts to signal to light
  • light signal is amplified and processed by computers to produce an image giving functional and anatomical info
  • different type: planar, SPECT, PET
18
Q

clinical uses of PET

A
  • oncology detection, staging, response to treatment
  • neurological early diagnosis of Alzheimer, localisation of seizure focus
  • cardiac identification of poorly perfused myocardium
  • infection/inflammation pyrexia of unknown origin, vasculitis
19
Q

advantages of PET

A
  • good contrast and spatial resolution
  • can analyse anatomy and function
20
Q

disadvantages of PET

A
  • physiological uptake of radiopharmaceutical
  • radiation dose to patient
  • risk of radiation to others
  • radioactive waste produced
  • expensive and time consuming
  • radionuclide shortages
21
Q

what is the natural background radiation in the UK

A

~2.3mSv/year

22
Q

how does MRI (magnetic resonance imaging) work

A
  • MRI scanner creates strong magnetic field, aligning hydrogen atoms within the patient
  • radiofrequency pulse is applied, tipping the aligned hydrogen atoms which creates a detectable magnetic field
  • this field induces an electric current in nearby coils in the MRI machine
  • varying signal intensities are produced by different tissues
  • signals are processed to create images
  • after the radiofrequency pulse ends the hydrogen atoms relax back into alignment with the magnetic field of the MRI machine
  • can adjust the settings to exploit differences between varying tissues through weighting
23
Q

weighting in MRI

A
  • T1 weighting fat is bright, water is dark
  • T2 weighting water is very bright, fat is quite bright
24
Q

images produced by MRI

A
  • bright ‘hyperintense’ = high signal
  • dark ‘hypointense’ = low signal
25
Q

clinical uses of MRI

A
  • central nervous system brain and spinal cord
  • head and neck imaging
  • MSK imaging bone, joints, soft tissue
  • GI eg. MRCP, MRI liver
  • cardiac MRI, MR angiogrpahy
  • gynaecological imaging, prostate imaging
  • in paediatrics/pregnancy to avoid radiation
26
Q

advantages of MRI

A
  • no radiation
  • good contrast resolution especially on soft tissues
27
Q

disadvantages of MRI

A
  • expensive
  • time consuming
  • fewer machines, fewer radiographers
  • contraindications (pacemakers etc), claustrophobia, lack of mental capacity
  • contrast reactions
  • other risks eg. overheating
  • image quality relies on magnetic field strength
  • risk of magnetic objects becoming missiles in room
28
Q

how does ultrasound work

A
  • utilises soundwaves
  • crystal in the transducer probe oscillates, creating high frequency sound waves
  • sound waves travel through tissues and are reflected back from boundaries between tissues of different density (acoustic impedence mismatch)
  • probe detects reflected sound waves (echoes) and converts them into electrical signals
  • time taken for echo to return is used to calculate where it was reflected from
  • proportion of reflected waves is used to calculate acoustic impedence mismatch in that place
29
Q

features of images produced by ultrasound

A
  • white on image = more reflection (hyperechoic)
  • dark on image = less reflection (hypoechoic)
  • acoustic shadowing = large acoustic impedence mismatch so sound waves completely reflected back (dark area behind bone, air, stones)
30
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 increases frequency of echo wave
  • moving away from soundwave decreases frequency of soundwave
31
Q

what is a duplex ultrasound

A

normal 2D imaging + doppler

32
Q

clinical uses of ultrasound

A
  • solid organs appearance of tissue/organ, masses, bleeds
  • hollow structures function, stones, flow, obstruction, masses
  • breast assessing lumps, abnormalities on mammogram
  • obstetrics pregnancy dating, fetal anomaly, placental location, fetal growth
  • musculoskeletal assessing muscles, tendons. ligaments, joints, nerves, soft tissue masses
  • interventional guided injections, biopsies, drains, aspirations

transvaginal, transrectal, transoesophageal ultrasounds

33
Q

advantages of ultrasound

A
  • lack of radiation
  • low cost
  • portable
  • dynamic so can see movement and assess blood flow
34
Q

disadvantages of ultrasound

A
  • operator dependent
  • no bone or gas penetration
  • difficult with obese, frail, unwell patients
  • theoretical risk of overheating if misused

Body logistics (20 decks)

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