MRI Definition: Magnetic Resonance Imaging is a medical imaging technique that non-invasively visualizes the internal structures of the body. Basic Concept: MRI uses powerful magnetic fields and radio waves to create detailed images of tissues and organs. Importance: MRI is valuable in diagnosing a wide range of medical conditions and provides excellent soft tissue contrast.

1. Physical Principle of MRI
Presenter: Dr. Dheeraj Kumar
MRIT, Ph.D. (Radiology and Imaging)
Assistant Professor
Medical Radiology and Imaging Technology
School of Health Sciences, CSJM University, Kanpur

2. What is MRI?
MRI Definition: Magnetic Resonance Imaging is a medical imaging
technique that non-invasively visualizes the internal structures of the body.
• Basic Concept: MRI uses powerful magnetic fields and radio waves to
create detailed images of tissues and organs.
• Importance: MRI is valuable in diagnosing a wide range of medical
conditions and provides excellent soft tissue contrast.
Thursday, 26 October 2023 Physical Principle of MRI By- Dr. Dheeraj Kumar 2

3. MRI Machine
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4. Historical Perspective
Early Developments: The concept of NMR and MRI was first introduced in
the mid-20th century.
• Key Milestones: Significant developments, including the work of Paul
Lauterbur and Peter Mansfield, which led to the Nobel Prize in Physiology
or Medicine in 2003.
• Continuous Evolution: MRI technology has evolved since its inception.
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6. The Magnetic Field
Introduction to Magnetism: The fundamental principles of
magnetism, including magnetic poles and magnetic fields.
• MRI's Strong Magnetic Fields: The high-strength magnets used in
MRI machines and their impact on the surrounding environment.
• Effects on the Human Body: The magnetic field affects the human
body, including contraindications and safety measures.
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8. Nuclear Magnetic Resonance (NMR)
• Introduction to NMR: The
concept of Nuclear Magnetic
Resonance and its applications in
chemistry and physics.
• NMR in MRI: NMR principles are
adapted for use in MRI, focusing
on the interaction with hydrogen
nuclei (protons).
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9. The Hydrogen Atom
• Importance of Hydrogen: Hydrogen is the most commonly imaged
element in MRI due to its abundance in the body.
• Proton Magnetic Properties: The magnetic properties of protons,
specifically the property of "spin" that makes them suitable for MRI.
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11. Magnetic Resonance
Overview of Magnetic Resonance: Explain the
resonance phenomenon in MRI, where protons
align with the external magnetic field.
• Proton Alignment: Describe how protons
align themselves with the magnetic field and
the energy transitions associated with this
process.
• Role of RF Signals: Introduce the role of
Radiofrequency (RF) pulses in perturbing the
proton alignment and causing resonance.
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12. Proton Alignment
• In the human body, the majority
of MRI imaging focuses on the
hydrogen nuclei (protons). When
placed within the strong magnetic
field, these protons align
themselves parallel or antiparallel
to the magnetic field lines.
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13. Radiofrequency (RF) Pulse
• To produce images, the
protons' alignment is
temporarily disturbed by the
application of an RF pulse.
This pulse is transmitted in the
form of a specific frequency of
electromagnetic radiation.
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14. Resonance and Energy Absorption:
• When the RF pulse matches the resonant
frequency of the protons, it causes them to
absorb energy and flip from their aligned
positions.
• The protons are excited to a higher energy
state. When the RF pulse ends, they relax
back to their original alignment, releasing
the absorbed energy.
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15. Signal Emission
• During relaxation, the protons
release the absorbed energy as
radiofrequency signals. These
signals contain information
about the tissue properties and
the spatial distribution of
protons within the body.
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16. Signal Detection
• A receiver coil within the
MRI machine detects the
emitted RF signals. This coil
acts as an antenna and
captures the signals, which
are then processed and
converted into digital data.
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17. Gradient Coils
• Gradient coils within the MRI machine
create varying magnetic fields in
precise spatial gradients. These
gradients are used to distinguish the
location of protons in the body. By
altering the magnetic field strength in
different regions, the MRI machine can
encode spatial information.
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18. Radiofrequency (RF) Signals
• Introduction to RF Signals: Explain the use of
RF signals in MRI for exciting protons and
generating detectable signals.
• Role of RF Pulses: Detail how RF pulses are
applied to alter the proton alignment, causing a
shift from low-energy to high-energy states.
• Resonance Frequency and Excitation:
Mention the importance of using the correct RF
frequency to match the magnetic field strength
for efficient excitation.
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19. Image Formation
• Introduction to Image Formation: the core
concept of how MRI generates images from the
signals emitted by excited protons.
• Signal Generation Process: the steps involved in
signal generation, including precession, signal
detection, and data acquisition.
• Basics of Fourier Transform: the concept of the
Fourier Transform, which is used to convert raw
data into a visual MRI image, highlighting its role
in creating the final image.
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20. Types of MRI Sequences
• T1-weighted Imaging:
• T1-weighted images that emphasize differences in tissue relaxation times (T1).
• Clinical applications, e.g., visualizing anatomy and distinguishing fat from other
tissues.
• T2-weighted Imaging:
• T2-weighted images that emphasize differences in tissue relaxation times (T2).
• Clinical applications, e.g., detecting edema, inflammation, and pathology.
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21. • Proton Density Imaging:
• Proton density-weighted images that focus on the density of protons in tissues.
• Clinical applications, e.g., evaluating the composition of tissues.
• Diffusion-Weighted Imaging (DWI):
• DWI, which measures the random motion of water molecules within tissues.
• Clinical applications, e.g., detecting acute stroke and assessing cellular density
in tumors.
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22. Gradient Echo Imaging
• Gradient echo sequences, which provide fast imaging with various
contrast options.
• Clinical applications, e.g., cardiac imaging and functional MRI
(fMRI).
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23. Contrast in MRI
• Definition of Contrast: the concept of contrast in MRI, which is the ability
to distinguish between different tissues in an image.
• Factors Influencing Contrast: how MRI contrast is influenced by tissue
relaxation times (T1 and T2), pulse sequences, and the choice of imaging
parameters.
• Clinical Applications: Examples of how contrast is used in clinical
practice, such as detecting pathology and characterizing lesions.
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24. Artifacts in MRI
• Common MRI Artifacts:
• Common artifacts in MRI images, including motion artifacts, magnetic
susceptibility artifacts, and aliasing artifacts.
• The causes of these artifacts and their impact on image quality.
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25. Minimizing Artifacts
• Strategies for minimizing artifacts, such as patient cooperation to
reduce motion artifacts and optimizing scan parameters to mitigate
susceptibility artifacts.
• The importance of quality control in MRI.
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26. Safety Considerations
• MRI Safety Guidelines:
• The safety guidelines and precautions that must be followed in MRI, including the
screening of patients for contraindications.
• The importance of non-ferromagnetic equipment and patient monitoring.
• Potential Risks:
• Potential risks, such as the heating of metallic implants, projectile hazards, and the
effects of strong magnetic fields on pacemakers and other electronic devices.
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27. Clinical Applications
• Overview of Clinical Applications:
• an overview of the wide range of medical specialties where MRI is essential,
including neurology, cardiology, orthopedics, oncology, and more.
• The ability of MRI to diagnose, monitor, and guide treatment in various conditions.
• Examples in Various Specialties:
• Specific examples of how MRI is used in different medical fields, such as brain
imaging for neurological disorders, cardiac MRI for assessing heart function, and
breast MRI for breast cancer detection.
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28. Advancements in MRI
• Recent Innovations and Developments:
• Recent advancements in MRI technology, including higher field strengths,
improved imaging sequences, and innovative contrast agents.
• Developments have enhanced diagnostic capabilities.
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29. Future Trends
• Potential future trends in MRI, such as real-time MRI, artificial
intelligence integration for image analysis, and the expansion of
functional MRI applications.
• These trends can further improve patient care and diagnostics.
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30. Thank You
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31. Any Question?
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32. References
1. Haacke, E. M., Brown, R. W., Thompson, M. R., & Venkatesan, R. (1999). Magnetic resonance imaging:
Physical principles and sequence design. Wiley-Liss.
2. Bushberg, J. T., Seibert, J. A., Leidholdt, E. M., & Boone, J. M. (2011). The essential physics of medical
imaging. Lippincott Williams & Wilkins.
3. Huda, W., & Slone, R. M. (2001). Review of radiologic physics. Lippincott Williams & Wilkins.
4. Chen, D. Q., & Ider, Y. Z. (2012). Principles of magnetic resonance imaging. Inverse Problems, 28(7), 075012.
5. Lee, S. C., Kim, M., Kim, Y. B., & Kim, E. (2018). Recent advances in magnetic resonance imaging. Journal of
Magnetic Resonance Imaging, 48(3), 589-604.
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