Imaging the body - (excluding microscopy) 2025 Flashcards
Describe what X-rays are and how thry are used in imaging.
type of elecromagnetic radiation, with very short wavelengths. when passed through the body, they strike a photographic film, creating radiographs (shadow images).
describe the radiographs produced from X rays
denser strustures in the body absorb more x rays, and appear white on the iamge like bones and the softer tissues llike muscles appear different shades of grey.
how are hollow or fluid filled structures viewed with x rays.
- give an example of how an oesophagus is viewed.
they have to be first filled with a contrast mediumwhich absorbs the x rays, eg - for an x ray of the oesophagus, the patient swallows barium (which is insoluble)
give examples of different X-ray scans
angiographs, MRI and CT scans.
How is an angiogram done
usually use contrast medium - or dyes (usually iodine based) that is injected into the body,
then a radiograph or ct scan is taken.
what are angiographs used for.
for enhanced visualisation of the inside blood vessels - to detect blockages, aneurysms or vascular malformations.
- noslty with a dye for contrast.
Describe the 3 types of angiographs and mention which ones don’t require contrast dyes.
magnetic resonance angiography - MRA - uses MR techniques like TOF MRI to produce images of vessels. (no contrast dye needed)
computed topography angiography - CTA - method combines CT scanning with the injectiong of a contrast agent. again this contrast is only used to enhance contrast but isnt always neccessary.
catheter angiography - when a catheter is inserted into a artery - an invasive procedure.
why is contrast necceassry for some angiograph scans and why is is sometimes better without.
it does increase visualisation and is needed for specific scans for the brain and heart. it is sometimes better without as it reduces risks in patients who are allergic to the dye or have kidney problems.
name the 3 types of angiographs
MRA, CTA and catheter angiographs.
How do CT scans work
- using weak levels of x rays
- x ray scanner rotates around the patient, then a computer records the levels of electromagnetic energy absorbed at different intensities, depending on the density of different tissues.
- the computer then recontrusts the x ray images taken at different angles to create a cross sectional 3D image.
(- using a dye can enhance the images.)
Describe how MRI scans work
- a strong magnetic field causes the aligment of the hydrogen atoms in the body.
- a pulse of radiofrequency waves is released, throwing the atoms out of alignment, when the pulse is turned off, they retun the original magnetic field alignment (their relaxed low-energy state), as this happens they emit radio signals which where picked up (absorbed) and then turned into detailed images.
what property of hydrogen atoms allows them to be affected by magnetic resonance, specifically in NMR and MRI
becuase of their nuclear spin property.
describe how the nuclear spin arises in hydrogen atoms and why the nucleus reacts when influenced by magnetic resonance as a result.
arises from the quantum spin of a nucleus with an odd number of nucleons, like H so = non-zero spin (spin -1/2)
- this gives the nucleus a mangetic moment making it act like a tiny bar magnet - and making it very sensitive to manetic resonance.
How does hydrogens nucleus react when placed in a strong external magnetic field like MRI machine.
the protons align with or against the direction of that field. these orientations are referred to as low energy (aligned) and high-energy (opposed) states.
in MRI - they align with the field.
Desribe the resonacne in magnetic resonacne
when radio waves flip the spins
If you hit hydrogen nuclei with radiofrequency (RF) energy at just the right frequency (called the Larmor frequency, specific to hydrogen and the magnetic field strength), the protons absorb that energy and flip to the high-energy state.
why are the hydrogen atoms, the preferred choice of atoms for magnetic resonacne technologies
- most abundant isotope - in water and fat
- has a high magentic moement - making it sensitive to magnetic resonacne.
- its simple structure makes it ideal for clean and strong signals.
Why are MRIs used over X -rays
x-rays visualise bones and denser tissues and their limitations, however MRI scans are used to provide detail of soft tissues and organs like the brain.
List the applications of using CT scans
- detecting bone injuries, fractures and trauma
- ideal for chest, lung and abdominal imaging.
- usually used in emergency settings cos they are very fast.
- detects cancers, internal leeding and organ damage.
list the applications of X ray imaging
- bone and joint problems.
- chest and lung issues and infections.
- dental and oral issues.
- orthopeadic surgery follow ups.
eg - evaulating hardware implants (plaes, screws and prosthesis).
if the uses of x rays and CT scans are so similar then why are they chosen over each other.
compare -
- intitial screening
- radiation preferecne
- cost and availability
intial assessment - X rays are preffered as they are quick and good for spotting broken bone and infections.
radiation - X rays offer lower radiation exposure
Cost and availabilty - x-rays are cheaper and more widely available.
compare the detail aspects and the specific images that differentiate between CT scans and X-rays.
CT offers better visualisation, especially when injuries are deeper and more complex - like internal bleeding and multiple fractures.
- better for softer tissues as well cos x rays can’t clearly show soft organs like the brain, liver and kidneys.
- CT scans can also spot cancers/tumoours and monitor their sixe and spread. they are also essential for fast detailed enough images for urgent desicion making.
- but x-rays are enough for teeth, lungs, ribs and heart outlines.
list the practical applications of MRI scans
- ideal for soft tissue evaluation - like brain, spinal cord, muscles, ligaments and joints.
- for neurological and musculoskeletal imaging.
- used for strokes, tumours and multiple sclerosis.
- detects cartilage and ligament tears.
compare the following between CT scans and MRI scans.
- availabilty.
- contrast detail
- sensitiviy to patient movement
- radiation
- resolution
- speed
- functional imaging
availability - CT scans are cheaper and available in more areas than MRI
contrast detail - MRI has a better contrast detail than CT in the brain and spinal cord. the iodine dye used in CT for contrast isnt always preferred.
- overall CT has less contrast differentiation than MRI.
resolution - MRI gives highly detailed images for soft tissues whilst CT has a higher detail for bones and calcified tissues.
Sensitiviy to patient movement - CT scans are less sensitive to patient movement - so images aren’t affected.
radiation - CT scans use ionisation radiation, which can cause potntial harm in the long run, but MRIs can be repeated in the long term without any adverse effects on the patients.
speed - CT scans are a lot faster, MRIs can take about 30-60 mins.
functional availability - available with MRIs only.
what is functional imaging.
a technique used to visualise and mesaure brian activity by detecting changes in blood flow, metabolism and electrical activity withing the brain. can be used to see how different areas work together during various tasks and cognitive processes.
- available in fMRI, PET and EEG imaging.
