Med Imaging MRI

Tesla

The Unit of the Magnetic Field

Place patient in a large uniform magnetic field

First step for an MRI

Displace the equilibrium magnetization vector with a Radio Frequency Pulse

Second step for an MRI

Observe the signal as the magnetization vector returns to equilibrium

Third step for an MRI

Z

___ axis: Foot to head (horizontal)

Y

____ axis: Back to front (Vertical)

X

___ axis: Across the shoulder (transverse plane)

Inductors

____ can create an electromagnet by running current through a coil

MRI tube

What is the uniform magnetic field in MRI?

hydrogen

By placing patient in the magnet, it will align all of their _____ in the same direction.

main

In MRI, H is the ____ magnet

second

In MRI, H1 is the ____ magnet

Larmor

H1 must be tuned at ____ frequency to displace M

hydrogen

Larmor frequency is the natural spin of ____ nuclei

90

From step 2, RF pulse must cause the M vector to rotate ___ degrees

Larmor, precessional

The ____ __or__ ______ frequency in MRI refers to the rate of precession of the magnetic moment of the proton around the external magnetic field

Strength

The frequency of precession is related to the _____ of the magnetic field

xy

At the end of RF pulse turning on, M (magnetzation vector) will be in the ____ plane

hydrogen spinning will generate tiny magnetic field and induce current to be detected

how do you detect signal from body in MRI after turning H1 off before M goes back to Mz

receive

When RF is off, it is on ___ mode

H1

Signal received in MRI is called Free Induction Decay. “Free” as in it is no longer constrained by ___

The signal is very weak compared to the RF pulse, The FID decays very fast

Two factors important in FID

spin echo sequence

Main issue is when RF pulse is turned off, we lose most of FID signal, so ___________ is used so we can get enough time to switch from send to receive mode

strength, hydrogen

For data gathering, computer uses ________ of magnetic field generated by__ ____ to create an image

Voxel

___ is 3D pixel

Gradient coils

Divide patient into voxels using ______ in MRI to produce proper image

z

Slice selection happens on ____ axis gradient

y

Phase encoding happens on ____ axis gradient

x

Frequency encoding happens on ____ axis gradient

Slice selection

What is happening in this image

ON

In Slice selection, RF pulse is ____ (ON or OFF)

ON

In Slice selection, Z gradient is ____ (ON or OFF)

Phase encoding

____ mainly involves rotating or spinning the protons/ hydrogen so that they are at different points at the initiation of the spin

Phase shift

Asking the computer to see each point of initiation of the spin of each hydrogen is the ______

Phase Encoding

What is happening in this image

OFF

In Phase Encoding, Z gradient is ____ (ON or OFF)

OFF

In Phase Encoding, RF pulse is ____ (ON or OFF)

ON

In Phase Encoding, Y gradient is ____ (ON or OFF)

frequency

X gradient coil produces a change in the ____ along x axis

Frequency encoding

____ provides a way to divide the slice into vertical columns

speed

The x gradient coil- frequency encoding-decreases or increases the magnetic field by affecting the ____of spin depending on which side the hydrogen proton lies

OFF

In Frequency Encoding, Z gradient is ____ (ON or OFF)

OFF

In Frequency Encoding, Y gradient is ____ (ON or OFF)

ON

In Frequency Encoding, X gradient is ____ (ON or OFF)

OFF

In Frequency Encoding, RF Pulse is ____ (ON or OFF)

Spin echo sequence

_____ involves assembling the RF pulses and gradients into a package that will allow the acquisition of an image

Slice Selection

In this diagram identify what should be in “A”

one of many phase encoding

In this diagram identify what should be in “B”

Prepare for Echo

In this diagram identify what should be in “C”

Echo Detection

In this diagram identify what should be in “D”

Waiting Time

In this diagram identify what should be in “E”

second slice selection

In this diagram identify what should be in “F”

next phase encoding

In this diagram identify what should be in “G”

Gy1

In this diagram identify what should be in “H”

Gy2

In this diagram identify what should be in “I”

Time of Echo

In this diagram identify what should be in “J”

Time of Repetition

In this diagram identify what should be in “K”

Receive

In this diagram identify what should be in “L”. ___ mode

Send

In this diagram identify what should be in “M”. ____ mode

hydrogen

In MRI, brightness of image part depends on the ____ density in that tissue.

Time of repetition

____ is where delay occurs in MRI spin echo sequence

efficiency

The reason x is on for a long time compared to y and z in spin echo sequence of MRI is a matter of _____. To save columns

Waiting time

What does TR depend on"?