Imaging the soft tissues of the musculoskeletal system Flashcards
imaging the soft tissue
CT
MRI
Ultrasound
what does the CT do
Uses multiple x-ray beams at different angles to build up a cross section of the body’s organs and tissues
what are the advantages of the CT
Images acquired in transverse plane - But can be reconstructed into 3D and other planes Cross-sectional images and other planes Good high contrast bone detail Well tolerated Readily available not as catsrophobic as the MRI
what are disadvantages of CT
Ionising radiation dose
Metallic artefacts cause loss of detail
Soft tissue surrounded closely by bone difficult to image
Respiratory movement artefact
what do metal artefacts do in CT
Metal artefacts give dark and white streaks. Although there are algorithms to reduce their effect and interpolate values from similar tissue regions
how does MRI work
Uses non-ionising radiation
10,000 – 30,000 times the earth magnetic field
Very high soft tissue contrast
Can get both structural and functional information
Does not image bone directly
what is the image plane in MRI
Images acquired in transverse plane
- Patient goes through the machine supine
- But can be reconstructed into any plane
what are contraindications for MRI
Cardiac Pacemaker
- Does not apply to new models, and even old models with special arrangements
Aneurysm Clips
Metallic foreign bodies
- shrapnel
- (particularly in the eyes)
Cochlear Implants
Neurostimulators
Not in early pregnancy (1st trimester)
- Most modern implants including joint prostheses are non-ferromagnetic
- Surgical clips, sternal wires are ferromagnetic but deemed safe if after 6 weeks and fixed by fibrous tissue
what is T1
T1 – normal anatomy
in the brain gives good gray/white matter contrast (fat - white = myelin, yellow bone marrow etc)
what is T2
T2 – pathology
Very sensitive for the water content of a tissue
Inflammation or oedema in damaged tissue means higher water content
what are the colours of T1 and T2
T1 CSF appears dark.
T2 CSF appears white
T1 weighted = yellow bone marrow = white
Reduction in signal around the fracture
Fluid is darker lower signal intensity
T2 weighted = water (odema) = white
Hyperintense around the fracture – oedema and bleeding
what can reduce scattering caused by artefacts
alogorthims
how does an ultrasound work
Diagnostic range 3.5 -10MHz
Produced by piezo-electric principles
what are the advantages of ultrasound
Quick readily available, accurate technique
Can visualise movement in real time
what are the disadvantages of ultrasound
But more difficult to interpret the image
