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Weber State University

Radiologic Technology 4603

MRI Physics and Instrumentation

Instructor: Rex T. Christensen MHA R.T. (R) (MR) (CT) (ARRT) CIIP

_____________________________________________

Contact Info:

E-mail:

rexchristensen@weber.edu

Phone:

435.770.2643 (cell)

801.626.8122 (office)

Address:Radiology Sciences

Weber State University

3925 University Circle

Ogden, UT 84408-3925

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Grading:

Grading Scale:

95-100 A

90-94 A-

87-89 B+

84-86 B

80-83 B-

77-79 C+

74-76 C

70-73 C-

67-69 D+

64-66 D

60-63 D-

0-59 F

Objectives: 200 pts

Exams: 400 pts

Total: 600 pts

Resources:

• http://www.fonar.com/glossary.htm

• http://www.mr-tip.com

• http://www.mrisafety.com

• http://www.e-mri.com

• http://www.radiologictechnology.org/archive

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Studying Suggestions:

• Focus on key ideas and concepts.

• Use multiple resources for learning key

concepts.

• Learn in steps (baby steps).

• Don’t be afraid to ask questions (learn

from peers).

• K.I.S.S. Keep It Simple Stupid

What makes a good MRI technologist?

• Education. Have a desire to continue to learn.

• Be a professional.

• Be a problem solver, not just a problem

identifier.

• Good communication skills with Dr’s,

technologists, and patients.

• Good attitude. (“That’s not my job.”).

• Know the language.

• Have fun!

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Questions?

Career Busters

MRI Safety

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Safety Video

Brief History:

In 1977 Dr. Raymond Damadian and

his team performed the first whole

body transaxial proton density

weighted image that took almost 5

hours to complete. He named his

scanner the Indomitable.

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Advantages: MRI vs. CT

• Non-ionizing radiation

• Non-invasive

• Multiplanar

• Better contrast resolution

MRI Equipment:

The 3 main components of an MRI:

• Gantry (magnet)

• Operating Console

• Computer

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RF Coils

• RF Transmitter

• RF Receiver (surface coils)

Surface coils:

Receives the signal from the body.

Increases image resolution.

Proper coil placement is vital to getting good images.

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Phased Array Coils:

Multiple surface coils.

High SNR low sensitivity area (single)

Shim Coil:

This coil enhances the magnetic field

homogeneity.

Homogeneity = Magnetic field uniformity.

Measured in parts per million (PPM)

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Shim Coil:

Two kinds of shim coils:

• Passive (physical way to shim)

• Active (electronic way to shim)

Types of Magnets:

• Permanent

• Resistive

• Superconducting

Measured in Tesla (T)

1 Tesla = 10,000 Gauss(Gauss is another form of measurement)

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Permanent Magnets:

Resistive Magnets:

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Superconducting Magnets:

Superconducting Magnets:

• Most common magnet.

• Only one with Cryogens. Why?

It allows conduction of electricity with no resistance.

• Most expensive.

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Shielding a Magnet Room

Items to consider:

• Magnetic field strength

• Location

• Safety

• Cost

Shielding a Magnet Room

Types of shielding:

• RF shielding (copper)

• Magnet shielding

Passive (steel)

Active (reverse magnetic field)

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Gradient coils are smaller (secondary)

magnetic fields that:

1. Select imaging planes.

2. Localize data spatially.

Gradient Coil: (secondary magnets)

Gradient Coil: (secondary magnets)

Z, X, Y Gradients:

• Z gradient coils are circular in shape. The coils are on opposite ends of the gantry.

Transverse slices are acquired by this gradient.

• X gradient coils are 4 saddle shaped coils in sets of two (located on the side of the gradient coil).

Saggital slices are acquired by this gradient.

• Y gradient coils are the same as the X gradient coils (located on the top and bottom of the gradient coil).

Coronal slices are acquired by this gradient.

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Imaging Planes

Gradients

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Gradient Amplitude and Rise Time

• Gradient Amplitude: Strength of the gradients. Measured in milli-tesla per meter (mT/m).

• Gradient Rise Time: The time it takes for the gradients to reach their maximum strength or amplitude. Measured in microseconds (ms).

• Slew Rate: The strength of the gradient over distance. Measured in milli-tesla per meter per second (mT/m/s).

Gradient Amplitude

Rise Time = Slew Rate

• Duty Cycle: The percentage of time per TR that the gradient is permitted to be at maximum amplitude, or the work time. Measured in percentage i.e. 50%.

Gradient Amplitude and Rise Time

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Questions?