Neuroimaging 2 - 1 MRI Flashcards
What is each pixel worth in an MRI scan image? What does it NOT represent
What is the size of the pixel/voxel known as? Why?
What is average size of pixel?
-each pixel respresent a number not an image!!
-its called spatial resolution because there are other type of resolution eg. temporal resolution in MRI scans
-1mmx1mm
What does it mean when pixel/voxel values are arbitrary?
they are only worth a certain value relative to eachother
What is voxel aka?
What is the difference between a voxel and a pixel?
Why are all pixels technically voxels?
-volumetric pixel
-pixel is 2D and voxel is 3D
-because a 2D pixel slice of a brain will always have some sort of volume/thickness
higher resolution = x pixels?
smaller resolution MRI images take longer or shorter?
higher res = smaller pixels
the smaller the pixel, the longer the scan will take
Do MRI scans rely on contrast?
What is the contrast made from? (how does it differ from a camera)
MRI relies on contrast to produce an image but MRI contrast is created by different tissue types exhibiting different magnetic properties/behaviour
What are the deep grey matter structures?
Are they a part of the cortex?
-basal ganglia,
-no
What is quantitative imaging in MRI?
What is an example of quantitative MRI imaging?
-not arbitrary values of pixels and voxels
-scans which show the actual TIMES of T1 magnetisation or T2 relaxation
What is the difference in the image produced scanning for T1 and T2 signals?
in terms of:
grey matter
white matter
CSF
T1
white= very bright
grey= medium bright
CSF= dark
T2
white= darker grey
grey= lighter grey
CSF= bright
white and grey matter intensities swapped and CSF is opposite
What is the advantage of using quantitative MRI scans? (actual time values of T1 and T2)
-can help emphasise certain features like evidence of stroke in brain
What are T1 and T2?
-different signals MRI can separately scan
(the contrast comes from differences in tissues T1/T2 relaxation times)
What is the purpose of using T1 weighted MRI images?
What is the benefit of using T1 over T2?
-T1 weighted has good tissue contrast
-faster than T2!
gold standard for observing healthy anatomy
good for seeing first signs of disease?/modest ability to show pathology
What are FLAIR images?
What does FLAIR stand for?
FLAIR is T2 weighted scans BUT with an additional radio frequency pulse which cancels out CSF signal making CSF dark
-Fluid-Attenuated Inversion Recovery
What are FLAIR images good for?
good for picking out specific types of brain pathology
What are perivascular spaces?
What are white matter lesions?
What is the difference in their effect on the brain?
-where brain tissue has detached from traversing blood vessels which creates CSF-filled holes
-damage to white matter tissue
-perivascular spaces are naturally occurring due to ageing but WML are tissue damage/disease
What is the advantage of using a T2 weighted image over T1 or FLAIR images ?
T2 is much better at distinguishing white matter lesions from separate from perivascular space
How is what is the advantage of using DWI imaging over other types of scan?
What does DWI stand for?
-shows recent strokes before damage becomes visible on other scans
-diffusion weighted imaging
What is scanner drift?
scanners getting older makes scans from same subject, done on same day look different
What is partial volume?
How do you reduce this effect?
the transitionary voxels between white and gray matter
increase resolution
What are the three points of views for all scans?
What is the radiological convention in coronal and axial scans?
sagittal coronal axial(horizontal)
L and R are opposite of what you think because coronal: its like you are imaging the subject looking at you and axial: its like you are imaging form feet up
How does MRI work?
magnetic field = X = X
magnetic field = frequency = position
