Clinical applications of MRI

Question 1

what are the different parts of an MRI scanner

Answer 1

Person lies in the MRI scanner.
This is the strong magnetic field that lines up the protons.
Typically getting an image from a patient with 1mmx1mm- to get good quality spatial resolution.
Between 1mm to 5mm.
T1- 1mm to get high resolution.
T2 and diffusion need thicker slices to get more signal and to get good quality image.

Aligned magnetisation and radio frequency pulses are used to generate a signal.
And signal from image depends on many factors.
This is t1 image- where signal intensity depends on the fact that the gad allium contrast agent can leak out in the tumour.
Most signal from water and some lipids.
Signals from things that aren’t fluid die very quickly that you cannot pick them up.

Magnet is very dangerous.
There is magnetisation of protons that you can manipulate.

RF pulses generate an oscillating magnetic field within the tissue that interacts with the magnetisation to change its orientation, the closer the coils are to the tissue being imaged the stronger the MRI signal. This is used to select a slice of tissue or code the signal that comes back from there

Question 2

how does membrane damage affect T2 relaxation time

Answer 2

membrane damage increase free water (it’s very fluid like that in CSF), increase T2 due to slower decay, hence stronger the signal

Question 3

what determines brightness in a proton weighted image

Answer 3

Proton density image- how many protons will give signal, more fluid so more protons and therefore more signal and brighter

Question 4

how does grey matter change with age

Answer 4

grey matter volumes as function of age which decreases over time.
there is greatest rate of atrophy- frontal parietal and temporal lobes. This is what happens in normal brain.
AD – much greater decrease with volume

Question 5

what are the clinical applications for T1W

Answer 5

dementia, epilepsy, and PD

for research
-depression
-schizophrenia and dementia

monitoring progression of atrophy like in AD

Question 6

What causes a reduction in relaxation time?

Answer 6

Fe and gadolinium-Gd (paramagnetic ions)

Question 7

what do contrast agents allow us to see

Answer 7

tumour as it leaked into the interstitial space as its BBB is not intact, therefore can detect brain cancer