Medical Imaging Flashcards by Aarav Patel

Main difference between X-ray and fluoroscopy

X-ray: single pulse of X-rays with one imagine created
Fluoroscopy : continuous/pulsed X-rays with real time moving images created

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Explain how you produce an image using X-rays (4)

Electrons accelerated towards a metal target and interaction with the metal produces photons (x-rays)
Some X-rays pass through the patient to a detector
Some are attenuated (absorbed,scattered,lose energy) as they pass through - appear brighter on an X-ray e.g bone, metal
Detected imagine digitised and process then uploaded to PACS

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What does the attenuation in X-rays depend on? (2)

Density and atomic number of tissue/material - e.g. bone attenuates X-rays more than soft tissues
Energy of the X-ray beam

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View of materials on an X-ray

Air = black = no attenuation
Fat = dark grey = some attenuation
Soft tissue = grey
Bone = very light grey = less X-rays are hitting detector
Metal = white = most X-rays attenuated

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Systematic analysis to approach a chest X-ray

A - airways, is everything in the right place?
B - breathing - left and right lung same size?
C - circulation - normal size heart, correct border between heart and lungs?
D - disability - any bone fractures or metastasis?
E - everything else - breast shadow, gastric bubble

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Systemic analysis approach to interpret an AXR (abdominal x-ray)

A- air - normal bowel gas pattern, no loops or air outside of bowel
B - bowel - small and large bowel
D - densities - bones, strones, tubes
O - organs - liver, spleen, kidneys, bladder

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Clinical use of X-rays

Chest - shortness of breath, infection, tube positioning, cancer
Abdomen - pain, bowels not opening, obstruction ]
MSK - trauma, pain, swelling, fracture, dislocation, infection

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4 advantages of X-rays

Quick
Portable
Cheap
Simple

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4 disadvantages of X-rays

Radiation (relatively low)
One plane, 2D
Cannot see all pathology
Poor soft tissue imaging

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Process of fluoroscopy X-rays

Process similar to normal X-rays but pulsed or continuous X-ray used, creating moving images

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How are fluoroscopy images enhanced?

Using contrast - usually barium/iodine
High atomic number = good X-ray absorber = dense on image

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4 clinical uses of fluoroscopy

Vascular/angiography
GI
GU
MSK - joint injections, orthopaedic surgery ( surgeons can see where placing metal work)

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2 advantages of fluoroscopy

Dynamic studies in real time - assess function or carry out intervention
Quick (using X-rays)

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5 disadvantages of fluoroscopy

Higher radiation dose than single X-ray
Radiation exposure to clinical e.g. hand is close to area of patient, X-rays reflect and hit
One plane, 2D
Cannot see all pathology
Poor soft tissue imaging

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How do computed tomography (CT) scans work?

X-rays produced as described earlier
X-ray tube on one side of a rotating gantry, and detectors on the opposite side
Patient table moves through gantry
Same principle of X-ray attenuation
Cross sectional slices of patient imaged and detected signal processed by computer to make cross sectional images

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3 clinical uses of CT

Diagnosis/ guiding further investigation/ management
Directly guiding and intervention - radiotherapy
Monitor conditions - cancer treatments, intestinal lung disease

3 advantages of CT scan

Quick
Good spatial resolution
Can scan most part of the body well

8 disadvantages of CT scan

Radiation
Lower contrast resolution
Not best for some areas e.g. Gynae
Affected by artefact e.g. patient moves, has metal in them
Requires holding breath
Overuse
Incidental findings
Contrast reactions

Explain how PET works

Radionucleotide emit positrons during decay (positron emission)
Emitted positrons collide with nearby electrons in patient (annihilation)
two annihilation gamma photons are produced, which are detected by gamma camera

How are radionucleotides administered?

Taken into the tissue by the pharmaceutical and the radionuclide creates the image. Radionuclide decays in tissues and emits gamma radiation,detected by gamma camera

What does the gamma camera do in PET?

Contains a scintillator which converts signal into light, then this light is amplified and processed by computers to produce images

Common pharmaceutical used in PET

Flurorodeoxyglucose - glucose analogue so taken up by areas of high glucose metabolism e.g tumours

4 clinical uses of PET

Oncology - detection, staging, response to treatment
Neurological
Cardiac
Infection/inflammation

2 advantages of PET

Good contrast and spatial resolution
Can analyse anatomy and function

5 disadvantages of PET

Physiological uptake of radiopharmaceutical - some tissues take up glucose anyway Radiation dose to patient Risk of radiation to others e.g. no public transport after PET Radioactive waste produced Very expensive and time consuming`

Explain how magnetic resonance imaging works (MRI)

1. Patient placed in strong magnetic field which aligns the hydrogen ions longitudinally 2. Radio frequency pulse applied to patient, 'tipping' hydrogen atoms 3. This creates a detectable magnetic field perpendicular to main MRI magnetic field, which induces electric current in nearby coils 4. Signal processed to create images

How is the contrast in MRI images produced?

Hydrogen atoms relax back into alignment with the longitudinal magnetic field of MRI magnet Contrast is due to different relaxation times of hydrogen atoms in different tissues as there is a difference in signal strength

Clinical uses of MRI

Good for imaging of: CNS, bones and joins, soft tissue lesions , heart and blood vessels, gynaecological tumours In paediatrics/pregnancy to avoid radiation from CT

2 advantages of MRI

No radiation Good contrast resolution, especially of soft tissues

6 disadvantages of MRI

Expensive Time consuming Fewer machines, fewer radiographers Contradictions : claustrophobia, lack of mental capacity Contrast reaction

How does ultrasound work?

Crystal in transducer oscillates, creating high frequency sound waves Sound waves travel through tissues and are reflected back at boundaries between tissues of different densities (acoustic impedance mismatch) Probe detects reflected sound waves and converts them into electrical signal, creating images

How do you calculate how deep a tissue is in ultrasound?

Time taken for echo to return

Hyperechoic and hypoechoic in ultrasound

Hyperechoic = more reflection = white on image Hypoechoic = less reflection = dark on image

What is acoustic shadowing?

Sound waves completely reflected back so none pass through to tissue below, creating a shadow and leaving behind a dark area

What is Doppler ultrasound?

If something is moving towards or away from sound wave e.g. blood flow in vessels Moving towards sound waves : increased frequency of echo wave Moving away from sound waves : decreased frequency of echo wave

5 clinical uses of ultrasound

Solid organs - tissue, masses, bleeding Hollow structures - tubes, ducts, bladders, chambers Obstetrics Musculoskeletal Interventional - guided injections and biopsies

4 advantages of ultrasound

Lack of radiation Low cost Portable Dynamic (can see movement)

4 disadvantages of ultrasound

Operator dependent No bone or gas penetration Difficult with obese/frail/unwell patients Theoretical risk of overheating foetus