1
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:
Phone:
435.770.2643 (cell)
801.626.8122 (office)
Address:Radiology Sciences
Weber State University
3925 University Circle
Ogden, UT 84408-3925
2
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
3
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!
4
Questions?
Career Busters
MRI Safety
5
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.
6
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
7
8
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.
9
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)
10
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)
11
Permanent Magnets:
Resistive Magnets:
12
Superconducting Magnets:
Superconducting Magnets:
• Most common magnet.
• Only one with Cryogens. Why?
It allows conduction of electricity with no resistance.
• Most expensive.
13
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)
14
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.
15
16
Imaging Planes
Gradients
17
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
18
Questions?