An Introduction to Medical Imaging: Flashcards
Describe what is meant by the coronal, sagittal and transverse body plane?
Sagittal plane - from the side of someone.
Coronal plane - looking straight ahead.
Transverse plane - looking from feet up/head down.
How do you produce an X ray image?
- Electrons accelerates towards a metal target, produces photons (X rays) (single pulse of X rays).
- Some X rays pass through the patient to a detector.
- Some are attenuated by the patient (e.g. absorbed or scattered).
- an image is created.
What does the amount of attenuation of X rays depend on?
- density and atomic number of tissue/material.
- energy of the X-ray beam.
What are the advantages of X rays?
They are quick, portable, cheap and simple.
What are some disadvantages of X-rays?
- radiation omitted (risk relatively low).
- poor soft tissue imaging.
- cannot see all pathology.
- one plane, two dimensional.
What are the clinical uses of X-rays?
- chest (for chest pain, pneumothorax, infection etc).
- abdomen/pelvis (obstruction, pain or perforation)
- MSK (for trauma, pain, fracture or tumours).
How do you carry out a fluoroscopy?
- similar process to an X-ray.
- instead pulsed/continuous X rays are used to create moving images.
What are the clinical uses of fluoroscopy?
- vascular/angiography (e.g. coronaries)
- GI
- GU (genitourinary - genital/urinary systems).
- MSK (orthopaedic surgery, therapeutic joint infections).
What are the advantages of fluoroscopy?
- real-time moving images created.
- can assess function or carry out intervention in real-time.
- quick
What are the disadvantages of fluoroscopy?
- Higher radiation dose than a single X ray.
- radiation exposure to clinician.
- poor soft tissue imaging.
- cannot see all pathology.
- one plane, two dimensional.
How is a CT scan produced?
- X rays produced in standard way.
- X ray tube on one side of a rotating gantry (ring), detectors on the opposite side.
- patient moves through gantry.
- same principle of X ray attenuation as before.
- cross sectional slices of the patient imaged and processed by computer.
- cross sectional images produced.
What are the clinical uses of CT?
- diagnosing/guiding further investigation/management (e.g. infection, bleed, cancer etc).
- directly guiding an intervention (e.g. biopsy, radiotherapy).
- monitoring conditions (e.g. cancer treatment).
What does CT stand for?
Computed tomography (CT)
What are the advantages of CT?
- quick
- good spacial resolution
- can scan most parts of the body well (but not all)
What are the disadvantages of CT?
- radiation
- lower contrast resolution
- affected by artefacts
- requires breath holding (not all patients can do this).
- not the best for some areas (e.g. gynae)
What is the full name for a PET scan?
Positron emission tomography scan
How does a PET scan work?
- uses radionuclides to emit positrons during decay.
- emitted positrons collide with nearby electrons in patient (annihilation).
- two annihilation gamma photons are produced which are detected by the gamma camera.
- gamma camera contains a scintillator (converts signal into light).
- light sample amplified and processed by computers to produce images.
What type of rays from the electromagnetic spectrum are used in a PET scan?
Gamma rays (NOT X-rays)
What are some clinical uses of PET scans?
- oncology (detection of tumours, staging and response to treatment).
- neurological (localisation of seizure focus, and diagnosis of Alzheimers disease).
- cardiac
- infection/inflammation (pyrexia of unknown origin).
What are the advantages of a PET scan?
- good contrast and spatial resolution.
- can analyse anatomy and function.
What are the disadvantages of a PET scan?
- physiological uptake of radiopharmaceutical
- radiation dose to patient
- risk of radiation to others
- radioactive waste produced
- very expensive and time consuming.
When is a radiopharmaceutical used and what do both parts of it do?
- Used in a PET scan.
- pharmaceutical (takes compound to tissues of interest)
- radionuclide (creates the image)
What does MRI stand for?
Magnetic resonance imaging
How does MRI work?
- Atoms spin in random directions around their individual magnetic fields.
- in the magnetic field produced by the MRI, atoms line up either north or south. Roughly half the atoms go each way, but there are a few unmatched atoms.
- when radio frequency pulse is applied, the unmatched atoms spin the other way.
- when the radio frequency is turned off the extra atoms return to normal position, emitting energy.
- the energy sends a signal to a computer which uses a mathematical formula to convert the signal into an image.
How is the contrast in MRI images created?
- From different relaxation times of the hydrogen atoms back to their normal positions in different tissues.
What are the advantages of MRI?
- no radiation used.
- good contrast resolution (especially of soft tissues).
What are the disadvantages of MRI?
- expensive
- time consuming
- not many machines/radiographers
- can be a claustrophobic process
- risk of magnetic objects becoming missiles in the room.
- risk of overheating
What are the clinical uses of MRI?
- CNS (brain and spinal cord).
- bones and joints
- soft tissue lesions
- heart and blood vessels
- gynaecological (female reproductive system) tumours.
- used in pregnancy/paediatrics to avoid radiation from CT.
How is an ultrasound produced?
- uses sound waves (not part of electromagnetic spectrum).
- high frequency sounds waves are released.
- sound waves travel through tissues and are reflected back at boundaries between tissues of different densities.
- probe detects reflected sound waves and converts them into electrical signal to create an image.
What does hyperechoic and hypoechoic mean in relation to an ultrasound?
- hyperechonic = more reflection (white on image)
- hypoechomic = less reflection (dark on image)
What is the time taken for the echo to return used to calculate in an ultrasound?
Where it was reflected from.
How would something moving towards or away from the sound wave be affected during an ultrasound?
- moving towards the wave - increase frequency of echo wave.
- moving away from the wave - decreased frequency of echo wave.
What are the clinical uses of ultrasound?
- look at solid organs (e.g. liver, pancreas, kidney etc.)
- look at hollow structures (tubes, ducts, bladders).
- obstetrics (pregnancy, fetal growth/placental location).
- musculoskeletal (assessing muscles, tendons, ligaments, joints, nerves etc).
What are the advantages of ultrasounds?
- lack of radiation
- low cost
- portable
- dynamic (can see movement and assess blood flow).
What are the disadvantages of ultrasounds?
- operator dependent (must be experienced at them).
- no bone/gas penetration.
- difficult with obese/fragile/unwell patients.
- theoretical risk of overheating foetus if misused.
What is not visible on a chest X ray?
Air
In T1 and T2 weighting what colours would fat and water be?
T1- Fat is bright, water is dark.
T2 - Fat is quite bright, water very bright.
