10. MR Physics & Imaging

B0

________ is the magnet by itself, and the magnet is always on.

RF cage

________ has to be in the MRI room to absorb any signals from outside, otherwise FM radio frequencies would be measured.

T2

________ is the transvese relaxation time (spin minus spin relaxation)

Z directional coils

________ are called Maxwell pairs.

NMR

________ is nuclear magnetic resonance, but is not related to radioactive decay (the nucleus is spinning, but theres no radioactivity)

Resonance

________ comes from B1 (the additional force) being at the same frequency as B0 (𝜔0) to make sure there is maximum energy being delivery.

Protons

________ and neutrons are spinning inside the atom, which act like magnets.

Larmor frequency

________ depends only on the material (𝛾) and the main magnetic field strength (B0)

vector 𝜇

The ________ precesses (spins) around the z axis st an angular frequency 𝜔 (radians per second)

M

As ________ returns to equilibrium, an RF signal is produced by energy releasing from the absorbed energy that was given to the material from B1.

Relaxation

________: The process by which M returns to steady state configuration after a B1 is done being applied.

𝜔0

While oscilating at ________, the RF pulse can have three shapes, rectangular, sinc, and triangular.

angular momentum

Spinning nuclei possess ________ (J) called spin.

Α

________ (always in radians) is the integration from 0 to 𝜏 over B1 (t) with respect to t (in seconds)

Gradients

________ are localized in x, y, and z directions.

TR

________ is the repetition time.

max

For the ________ transverse component Mxy, α is set to pi /2 radians.

MRI

________ offers images of the same object in different contrasts to bring attention to different areas.

B1

Since the spins and ________ field are both rotating, you can image from a spinning reference.

z axis

If M tips away from the ________ (during excitation), a component in the x- y plane is generated.

coil

The ________ with current running through it acts as the magnet, and is surrounded by liquid Helium to keep the ________ cool (decreasing resistance and energy lost to heat)

Mz^0

________ is the steady state of Mz.

Mxy

________ decays at a faster rate (T2* instead of T2) because of signal desync.

TE

________ is the echo time.

X directional coils

________ are called Golay coils.

Y directional coils

________ are called Golay- type coils.

signal component

The ________ is always in the transverse x- y plane.

signal intensity

The difference in ________ is used to discriminate different tissues by representing them as brightness.

MR signal

________ is always recorded in the xy plane.

gyromagnetic ratio

The ________ can also be gamma divided by 2pi.

nuclei

If a(n) ________ has an even atomic number, the magnetic fields cancel out.

transverse plane

The ________ (xy) is rotating at 𝜔, which is equal to 𝜔0, so it can be considered a rotating plane (x- y)

K

________ is the scaling factor.

equilibrium

At ________, the net magnetization vector M precesses about the z- axis.

Mz

________ (0+) is transverse magnetization Mxy immediately after the RF pulse.

longitudinal Mz

The ________ and transverse Mxy components vary as time changes, and are descibed by Bloch Equations.

Hydrogen

________ has the highest gyromagnetic ratio.

15T magnet

A(n) ________ is about 30, 000 times stronger than Earths magnetic field.

Spin echo

________ makes the slower spins catch up with faster oens to sync the signal.

rectangular pulse

For a(n) ________ after 𝜏 seconds, the vector M has rotated at an angle α.

T2 weighting

________: We want ta long TR (minimize T1 differences) and an intermediate TE.

external magnetic field

The net (bulk) magnetization vector with a(n) ________ is nonzero.

Larmor Frequency

The angular frequency at which the bulk magnetization factor precesses around the z-axis

Relaxation

The process by which M returns to steady state configuration after a B1 is done being applied

Pulse sequence

Carefully timed set of scanner operations used to generate images

Proton density weighting

We want a long TR and a short TE

T1 weighting

We want an intermediate TR and a short TE (becomes a constant scaling factor, less noise)

T2 weighting

We want ta long TR (minimize T1 differences) and an intermediate TE