MRI

MRI vs ct

Different modalities

Different noises

MRI measures what

Amount of hydrogen in area of interest magnetism converts into electrical energy

What does ct measure

Measures attenuation x-ray beam passing through the partient converting into electrical energy

Advantages of mri

Best contrast in soft tissues

Evaluates anatomical structures in physiology

Ability to see arteries and veins and blood flow

Disadvantage of mri

Can’t look at cortical bone

Not ideal for patients with claustrophobia

Not readily available

Higher cost

Long scanning times

MRI field strength measured in

Tesla : increasing Tesla reduces scan time

Mr angiography

Blood vessels

MRI arthorgrphy

Joints

Mr venograohy

Veins only

Mrs- spectroscopy

Measures chemical competition

FMRI

functional mri - how brain works

Imri- interventional mri

Real time image guided surgery

Mdm

Magnetic distribution movement

static is what in mri

Magnetic type - standard type in most scanners

Coils are ??

Acquiring images in different planes

Flexible coil

Close contact with patient provided best signal to noise ratio

Head coil

Helmholz coil - collects 360 data from whole head

Surface coil

Limited depth of signal

Mri signal generates ?

Presence of hydrogen. Magnetic field of hydrogen atom align with magnetic field of scanner

Magnetic field generated by

By the proton adopts additional movement

Principal of resonance

Patient need to be separated from magnetism from MR scanner to receive the image. Once separated patient can be red by MR COIL

MRI arthorgrphy

Joints

Precession:

Additional movement of an atom

Net magnetic vector

when all components come together they are known as net magnetic vector

rate of precession

Patient scanned is bombarded with rf waves at same frequency as precession

bo?

Magnetic field created by machine- needs to be separated from net magnetic vector to be same rw frequency

Exciting the net magnetic vector

Process of separating out the energy from magnetism from out patient

Pulse sequence

Set of changing magnetic gradients different pulse sequence Produce different image

Spin echo

Basic, high signal to noise ratio + resolution

different pulse sequence

Spin echo, fast spin echo , gradient echo, echo planter imaging

Time of flight phase contrast

Used for mr arthography

Where magnetism coming from the patient

Localizing mr signal recognizes where the mr signal is coming from

Gradient coils

Used to deliberately change strength of magnetic field to change rate of precession

Total signal Fourier

Identifying and representing the intensity of signal

More signals darker images

Fourier transform

Frequencies in logical order stored in virtual bay called k-space signal allows it to map into image matrix

Parameters 2 types

Te (time echo)

Tr (time repeat)

They control amount of information present in image

Te

Time echo - flips net restore movement from longitudinal to transverse plane

Tr

Time for repeat. Rf frequency flips it into the next time is applied

image contrast

Tr + te altered contrast depends on tr and te

Tr relation to t1

Tr controls how much t1 relaxation occurres

Shorter tr gives t1 weighted images

Te relation to t2

Te controls how much t2 weighted images long te gives t2 weighted images

T1

Fat is bright fluid dark

T2

Fat is dark fluid is bright