2b. MRI - Head Radiology Flashcards
what are the 7 advantages of MRI
no ionizing radiation
versatile with multiple modes/sequence types
good for prenatal brain
contrast can be manipulated
acute ischaemia demonstrated ealy when CT is normal
Angiography with/without contrast
multiplanar
what are the 8 disadvantages of MRI
long acquisition time (10-120min) poorer access expensive motion sensitive need high level of expertise to acquire complex examinations = substantial post-processing times safety issues artifacts from metals
what is the safety concern for MRI
magnet on all the time and metal objects near it could be turned into a projectile
how does the MRI work in terms of the nuclei
body placed in powerful magnetic field and some proton nuclei align with direction of field and act as tiny bar magnets
how does the MRI work in terms of how the radiofrequency pulse is applied and what results from this
radiofrequency pulse is applied perp to main field which flips direction of aligned nuclei
how does the MRI work in terms of what happens once the RF pulse is removed
nuclei realign with the main magnetic field and lose energy as they do so and they emit their own signal
what 2 factors vary the signal produced by the nuclei in MRI
tissue type
pulse sequence used
what can be done to the energy produced in MRI production
energy manipulated and collected in a number of ways resulting in designed image contrast/info
what are the 2 most basic types of MRI sequences
T1 weighted and T2 weighted
what is CSF and fat intensity on T1 MRI
CSF = hypointense (dark) fat = hyper intense (bright)
what is CSF and fat intensity on T2 MRI
CSF = hyperintense (bright) fat = hypointense (dark)
after administering contrast the areas with compromised BBB does what on T1W imaging
it enhances
what does bone look like in terms of intensity MRI
why is it like that
bone is black as it has few mobile protons and so not much signal
what does scalp look like in terms of intensity MRI
why is it like that
scalp is bright and white as its high signal from the fat etc
what does eyeball look like in terms of intensity MRI
eyeball is bright and white as its high signal
malignant tumors in MRI has what intensity for the rim and what does the border look like
enhancing from contrast so is bright
rim is irregular
tumor is always affected by contrast in which MRI T type
always affected by contrast in T1
not T2
what does multiple metastases look like in MRI
multiple lesions and enhanced with contrast media and lot of oedema around them
if the MRI image looks like metastases but weren’t metastases or cancer what else could it be
infection due to bacteria/fungi/parasite
what can you see in DWI MRI imaging
get sequences from MRI and process in different ways to get different info out of it
can see direction of nerve fibres and produce white matter tract maps using DWI data
what is DWI MRI imaging
diffusion west image
within mins of a stroke the DWI signal is bright due to what reason
restriction of movement of water out of the cell caused by cytotoxic oedema
what 3 feature identifies abscesses on MRI
enhancing round lesion
uniform rim
what does meningitis look like on a MRI T1
how enhancing is it and why
Lots of bright areas in the brain and basal cisterns is where blood goes if you have a subarachnoid haemorrhage
Meninges have swollen and lots of leaky blood vessels so enhancing with contrast agent -> hugely enhancing
what does tapeworm look like on a MRI in terms of appearance and location
Multiple bilateral lesions throughout all lobes of brain and also in soft tissues
Very extensive , at least 50% of brain is replaced by cysts by tape worm and in other soft tissue of body
what does TB look like in a T1&2W MRI image and what features signify it in the image
2 features
Vertebral body destroyed
anterior collection of fluid - pus with Tb bacteria in it
when TB in the spine is more advanced you get what to the spine and what is this called
When its more advance you get angulation of spine due to collapse of vertebrae - gibous
what does multiple sclerosis look like on a MRI in terms of appearance
enhancing lesions in the brain
what does Alzheimer’s look like on a MRI in terms of appearance and location
3 features
gross atrophy in brain (could be global/whole brain)
reduced tissue and ventricles are huge
could have focal tissue loss in hippocampus
what does functional MRI do and what is it useful for
locates brain activity
useful for surgical planning
what can be demonstrated and done with anatomy with FMRI for surgical planning
reconstruction from MRI and functional activation
demonstrates location of tumor in relation to cortex responsible for hand and foot control (ie can tell if remove tumor from this location in cortex, could lead to loss of hand/foot function)
what is the difference between the machine appearance for MRI and CT
CT is like a donut
MRI head coil is longer
is CT or MRI better for stroke imaging
MRI
is CT or MRI better for tumor imaging
MRI
is CT or MRI better for bony reconstruction
CT
is CT or MRI better for angiography
MRI (doesnt need contrast) or CT (needs contrast)
