Magnetic Resonance Imaging (MRI)

True or false,
Quenching is dangerous and prohibitively expensive

True

how is Data localization in MRI accomplished

a gradient magnetic field is superimposed on a static external magnetic field.

what is the primary variable in the data collection procedure during MRI

the sequence

True or false,
Two electromagnetic coils are required to produce magnetic field gradients corresponding to the axis to be imaged

False

determines the section thickness, resolution and plane of the image in MRI

Gradients coils

Repetition time (TR)

the interval between pulse sequences

The frequency of a given type element is called the

Larmor Frequency

the longer the wave is applied to the patient,

the greater the angle of precession

The higher the proton density

the higher the MRI signal

True or false,
a 380 degree pulse is most effective in MRI

False,

90 degrees or 180 degrees pulse are more effective in MRI

Higher strength magnetic field

stronger RF signal

CSF will appear as dark signal on

T1 weighted images

CSF will appear as bright signal on

T2 wieghted images

true or false,
A free magnet will move to align itself in a magnetic field

true, this is called a magnetic moment

nuclei used in MRI

are found in abundance in the human body, (Hydogen)
have and odd number of protons and neutrons, and
affect external magnetic field.

Part of the scanning procedure controlled by the MRI operator

RF pulse sequencing,
, and it is user dependent

type of bone that MR does not image as clearly as seen in CT

Cortical bone

Higher magnetic strengths produce stronger RF signals and

higher resolution images

what special problem in MRI is caused by the extremely long scan times that must be used

Motion

Contraindications to the contrast media most commonly used for MRI procedures

Renal failure and pregnancy

What type of magnet produces a strong field up to 4T

Superconductive

MR images are viewed in a

Monitor

a unit of magnetic field strength

Telsa

The protons of this element gives rise to the signal used in clinical MR imaging

Hydrogen

The ability to differentiate adjacent tissues

contrast

A measurement of smallest object that we can visualize in the image

pixel

The tiny MR signal which results from applying the radio waves to the patient

echo

The MR system component that makes the "knocking" noise during an exam.

gradient

Energy used in MR imaging

Radio frequency

An extremely cold liquid used in a superconducting magnet

cryogen

The grid of rows and columns of pixels which make the digital image

matrix

a plane which is perpendicular to the axis which runs from head to foot in the patient

Transverse

This property is exhibited by a spinning proton

magnetism

a type of image which can be stored on a computer and viewed on a monitor

Digital

This type of radiation is not used in MRI

ionizing

The digital processor used at the heart of an MR system

computers (arrays)

the "R" in MRI

Resonance

Lying face up

Supine

an MR image, representing a slice through the patient is called

section

the sub-atomic particular which gives the MR signal

proton

The loop of wire used to measure the MR signal

coil

The smallest unit of matter that still behaves like a particular substance

atom

TE, or time to echo

Time period between the excitation and sampling of induced signal

T1 weighted image

demonstrates anatomy

T2 weighted image

demonstrates pathology

resistive magnets

high electrical current ,
Ideal for severe claustrophobia

Resistive Magnets Advantages:

Good uniform field,
Can be turned off,
Good for implants, orthopedic imaging,
Inexpensive

Resistive Magnets disadvantages:

Low magnetic field strength,
Longer imaging time,
High electrical bill

Permanent Magnets (no used today)

vertical magnetic field, and temperature sensitive, unable to turn off

Permanent Magnets advantages

Easy to site,
Good for implants, and orthopedic imaging,
Inexpensive

Permanent Magnets Disadvantages:

Low magnetic field strength,
Longer imaging time,
Unable to turn off,
Temperature sensitive

Superconducting Magnets

Electromagnet,
Property of superconductivity, 
Cryogens used to reduce resistance,
Up to 3.0 Tesla

Superconductive Magnets adventages

High magnetic field strength,
Shorter imaging time

Superconductive Magnets Disadvantages:

Expensive,
Cannot be turned off (safety concerns)

ramping

bringing magnet to proper temperature

Quenching

abnormal termination of magnet operation,
cryogens cools the magnet coils boil off rapidly

FONAR

Upright MRI Scanner, used for back and extremity imaging)

World's Most Powerful MRI scanner
9.4 Tesla (T)

at the University of Illinois at Chicago

Gradient Coils

Resistive electromagnets that create magnetic fields that vary in intensity,
Located in the bore of the magnet

RF Coils

Attachment coils that surround the part that is being imaged,
Serve as transmitter and/or receiver of MRI signal

Shim Coils

Corrective magnetic coils,
Located in the bore of the magnet,
Means of magnetic field homogeneity

Spin echo (SE) (FSE)

Most common pulse sequence

Gradient recalled echo (GRE)

rapid acquisition imaging

Inversion recovery

longest pulse sequence

Gadolinium DTPA

Paramagnetic agent,
Shortens T1 relaxation times, appears bright,
Used in neurology imaging, MRA

Safety Areas

Zone 1: outside of scanner environment,
Zone 2 : greeting area, MRI technologist supervises area,
Zone 3: control area, Access controlled and limited by MRI technologist,
Zone 4 : Room housing scanner, MRI technologist must supervise everyone entering room

1 Tesla=

10,000 gauss

T1 relaxation time-

time that 63% of net, longitudinal magnetization has recovered

T2 relaxation time-

time that 63% of transverse net magnetization has decayed

the 1st MRI Image (1977) was

Dr. Larry Minkoff's chest,
and it happend in Stoneybrook, N.Y

precess

protons wobble

Radio Frequency Pulse

Short burst of electromagnetic wave used to excite proton,