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 1
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: Exams: Total: 200 pts 400 pts 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/ar chive 2
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! 3
Questions? Career Busters MRI Safety 4
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. 5
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 6
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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. 8
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) 9
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) 10
Permanent Magnets: Resistive Magnets: 11
Superconducting Magnets: Superconducting Magnets: Most common magnet. Only one with Cryogens. Why? It allows conduction of electricity with no resistance. Most expensive. 12
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) 13
Gradient Coil: (secondary magnets) Gradient coils are smaller (secondary) magnetic fields that: 1. Select imaging planes. 2. Localize data spatially. 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. 14
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Imaging Planes Gradients 16
Gradient Amplitude and Rise Time Gradient Amplitude: Strength of the gradients. Measured in millitesla 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 17
Questions? 18