Part II (written exam) – Magnetic Resonance Imaging Physics


Examination Content Outline

Subject Weight
The Physics of Nuclear Magnetic Resonance 15
MR Imaging Theory and Image Reconstruction 15
MR Image Characteristics & Artifacts 15
Advanced Imaging Techniques & System Features 15
Contrast Enhancement, MR Angiography & Cardiac MRI 15
MR Technology and Equipment Quality Control 15
Site Planning and Safety of MR Examinations 10


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The Physics of Nuclear Magnetic Resonance (15%)

  1. Review of basic physics
    • Fundamental Properties of Magnetic Fields
    • Magnetic Dipole and its Field
    • Magnetic Moment in a Magnetic Field
  2. The nuclear magnetic resonance phenomenon
    • Quantum Description (Anomalous Zeeman Effect)
    • Equilibrium Magnetization
    • Resonant Frequency and the B0 Magnetic Field – the Larmor Equation
    • Semi-Classical Net Magnetization Vector Model
    • Descriptions of Spin Dynamics in the Rotating Frame
  3. Relaxation mechanisms, longitudinal relaxation (T1) and transverse relaxation (T2)
    • Relaxation Mechanism Physics (Physical Interactions Between Spins)
    • Molecular Dynamics (Correlation Times)
    • Relaxation Mechanisms in Biological Tissues
    • Relaxation Mechanisms and B0 Magnetic Field Strength
    • Bloch’s Phenomenological System of Equations for Relaxation
  4. Radio frequency (RF) pulses and the free induction decay (FID)
    • Nutation of Magnetization Due to Radio Frequency (RF) Pulses
    • Larmor Equation in the Rotating Frame
    • Determination of Nutation (Flip) Angle
    • On-Resonance and Off-Resonance Effects
    • Effects of Transverse Relaxation (T2) and B0 Field Inhomogeneities
    • Refocusing 180° Pulses and the Spin Echo
  5. The measurement of relaxation times
    • The Saturation Recovery Experiment
    • The Inversion Recovery Experiment
    • Hahn’s Spin Echoes, Stimulated Echoes and Diffusion Effects on the NMR Signal
    • Measuring T2 with the Carr-Purcell-Meiboom-Gill (CPMG) Experiment
    • Mechanisms for J-Coupling

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MR Imaging Theory and Image Reconstruction (15%)

  1. General methods for MR imaging
    • Properties and Limitations of the Fourier Transform in MRI
    • Reconstruction from Projections
    • Fourier Transform MR Imaging
    • Application of Sampling Theory to Magnetic Resonance Imaging
    • The Nyquist Limit
  2. Mathematics of a Fourier Transform
    • Continuous and Discrete Fourier Transforms
    • Fourier Shift Theorem
    • Convolution Theorem
    • Common Fourier Transform Pairs (Gaussian, Sinc, etc.)
  3. Signal frequencies vs. spatial frequencies
    • Definition of k-Space
    • Relationship between k-Space Sampling Interval and Image Field-of-View
    • Relationship between k-Space Sampling Range and Image Resolution
    • Truncation Artifact (Gibbs ringing)
    • Partial Sampling of k-Space and Exploiting Conjugate Symmetry
  4. Slice selection
    • Relationship Between the RF Pulse Bandwidth and the Slice Thickness
    • Relationship Between the Slice-Select Gradient and the Slice Thickness
    • Nonlinear Effects of RF Pulses on the Net Magnetization
    • Defining Slice Thickness and Location – Practical Implementation
    • Optimization of Slice Profiles (Pulse Crafting)
  5. Frequency encoding
    • Relationship between Gradient Strength and Receiver Bandwidth
    • Relationship between Gradient Strength and Digitizer Dwell Time
    • Relationship between Gradient Strength and Image Field-of-View
  6. Phase encoding
    • Relationship between Gradient Strength and Image Field of View
    • Strategies for Incrementing the Phase Encoding Gradient
    • Phase Dispersion Within and Between Voxels
  7. Other applications for magnetic field gradients
    • Strategies for Imaging in Oblique Planes
    • Selective Spoiling of Magnetization with Gradient Pulses
    • Dephasing and Rephasing Gradient Fields
  8. Specific MR imaging protocols
    • Identification of Gradient and RF pulses and Signal Digitization in Sequence Timing Diagrams
    • Relaxation Effects on the MR Signal and Pulse Sequence Timing (T1-weighting, T2-weighting, etc.)
    • Effects of Imaging Parameters on Signal-to-Noise Ratio and Spatial Resolution
  9. Image reconstruction
    • Steps in Image Reconstruction
    • Analog and Digital Filtering Processes
    • Interpolation (Zero-Filling)
    • Image Quality Trade-offs in Image Enhancement through Filtering
    • 3-Dimensional Fourier Transform Reconstruction
    • Rectangular Field of View

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MR Image Characteristics & Artifacts (15%)

  1. Fundamental relation between signal and noise in MR images
    • Imaging Parameters Affecting Image Signal-to-Noise Ratio
    • Properties of MR Image Noise (Rician Distribution)
    • Contrast-to-Noise Ratio (CNR) versus Signal-to-Noise Ratio (SNR)
    • Fractional NEX (NSA) (conjugate symmetry, 0.5 or 0.75 NEX versus 1.5 NEX with no phase wrap)
    • Clinical Utility of Image Quality obtained using Spin Echo MR Images
  2. Manipulation of MR image contrast
    • Definitions of Spin Density Weighting, T1 Weighting, and T2 Weighting
    • Relaxation Properties of Fat, CSF, Muscle and Brain
    • Signal Averaging, Partial Field-of-View, and Total Scan Time
  3. Imaging with non-stationary states
    • Fast Spin Echo (Turbo Spin Echo)
    • Magnetization Prepared Fast Sequences (Including Centric Encoding)
    • Relationship between Image Resolution and Contrast in Fast Spin Echo Imaging
    • Single-Shot Fast Spin Echo Imaging (RARE)
  4. Volume (3D) acquisition
    • Generic Pulse Sequence Timing Considerations
    • Relationship Between Resolution, Signal-to-Noise Ratio and Coverage in 3DFT MR Imaging
    • Slice Thickness and Contiguity in 3DFT MR Imaging
  5. Acquisition and MR imaging options
    • Slice Ordering, Slice Gaps, Coverage and Slice Cross-Talk
    • Sequential vs. Interleaved Acquisition of Slices
    • Concatenated Scanning and Segmented k-Space Scanning
    • Off-Center Slices (in Frequency- and Phase-Encoding Directions; Role of Post-Processing)
    • Strategies to Avoid Wrap-Around in the Readout and Phase-Encoding Directions
    • Variable Bandwidth and Signal-to-Noise Ratio
    • Fat/Water Suppression Strategies (Chemical Selective Saturation, STIR and FLAIR)
    • Fractional RF and Incrementing Partial Flip Angles
  6. Artifacts
    • Sources and Remedies for Blocking, Banding, Pixelation, and Similar Artifacts
    • Origin, Properties and Methods to Reduce, Including:
      1. Chemical Shift Artifacts
      2. Truncation Artifact
      3. Susceptibility Artifacts
      4. Motion Artifacts
      5. Wrap-around Artifacts (Aliasing)
      6. Geometric Distortion
      7. Image Ghosting

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Advanced MR Imaging Techniques & System Features (15%)

  1. Gradient Echoes (also called Field Echoes and FAST Imaging)
    • The Mechanism of Gradient Echo Formation
    • Comparison of T2- and T2*-contrast in Spin Echo and Gradient Echo Protocols
    • Imaging Magnetization in Steady State Free Precession
    • Classification of Commercial Protocols: GRASS, FLASH, FISP, true FISP, spoiled GRASS, etc.
    • Use of Variable Flip Angle Sequences
  2. Diffusion Phenomena in MRI
    • The Physics of Diffusion
    • Relationship Between Diffusion Effects and Relaxation on the Spin Echo Signal
    • Relationships of the Apparent Diffusion Coefficient to Tissue Structure
    • Diffusion Weighted Imaging and T2 “Shine Through”
    • Practical Requirements for Measuring Apparent Diffusion Coefficients
  3. MR Spectroscopy and Chemical Shift Imaging (CSI)
    • Nuclei Useful for Clinical MR Spectroscopy
    • Methods of Water Saturation for In Vivo MRS
    • Eddy Current Compensation and In Vivo MRS
    • Basic Single Volume MRS Acquisition Methods: PRESS and STEAM
    • Basic Pulse Sequence for 3DFT Chemical Shift Imaging
    • Scan Time versus Voxel Size Tradeoffs
    • Clinical Importance and Spectral Features of Brain Metabolites Containing Protons
    • Relaxation Properties of Brain Metabolites Containing Protons
  4. Blood Oxygen Level Dependent (BOLD) Imaging (sometimes called fMRI)
    • Physiological Explanation for the BOLD Contrast Effect
    • Generic Pulse Sequence for BOLD-Weighted Echo Planar Imaging
    • Methods for BOLD Data Analysis (t-Test, Correlation, etc.)
    • Typical Protocols for BOLD Imaging of Visual Cortex & Motor and Somatosensory Strips
  5. Processing and Reconstruction Options
    • Uses of Phased-Array Coils
    • SENSE and SMASH
    • Maximum Intensity Reconstructions (MIP)
    • 3-Dimensional Reconstruction
    • Multi-Planar Reformatting
    • Surface Rendering

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Contrast Enhancement, MR Angiography and Cardiac MRI (15%)

  1. The Physics of Paramagnetic Contrast Agents
    • Types of Gadolinium Contrast Agents and Their Differences
    • The Role of Dipole-Dipole Interactions in Determining the Longitudinal Relaxation Rate
    • Relationships Between Correlation Times and Relaxation Times
    • Methods and Theory of Using Gadolinium Contrast Agents to Increase Susceptibility
  2. Mechanisms of Relaxation Enhancement in Tissues
    • Contrast Effects of Blood at Various Lesion Ages and Oxygenation States
    • Extra-Cellular, Interstitial, and Intra-Vascular Contrast Agents and their Applications
    • Clinical Uses of Contrast Agents in Brain, Body and Angiography
    • Toxicity and Adverse Reactions
  3. Flow effects in MR imaging
    • Flow-Induced Changes in the Magnitude of the MRI Signal
    • Flow-Induced Changes in the Phase of the MRI Signal
    • Controlling Flow Effects through Spatial Saturation
    • Controlling Flow Effects through Gradient Moment Nulling (MAST, Flow Comp, etc.)
    • Flow Void: Flow Effects at Vessel Branches, Bifurcations and Stenoses
  4. Magnetization Transfer Contrast (MTC) in MRI
    • Theoretical Description of Bound and Free Water Compartments in Tissue
    • Tissues for Which MTC is Practical
    • Methods for Implementing MTC in Pulse Sequences
    • Magnetization Transfer Effects in Fast Spin Echo Imaging
  5. Time of Flight (TOF) Angiography
    • Differential Effects in the Saturation of Spins in Moving Blood and Stationary Tissue
    • Pulse Sequence Considerations for Optimizing TOF Angiography
    • Advantages and Limitations of 2D TOF Angiography
    • Methods to Improve Blood-Soft Tissue Contrast in TOF Angiography
    • Tilted Optimized Nonsaturating Excitation (TONE, RAMP, etc.)
    • Advantages and Limitations of 3D TOF Angiography
    • Sources of “Venetian Blind” Artifacts in MR Angiography
    • Methods for First-Pass Angiography using Intravascular Contrast Agents
  6. Phase Contrast MR imaging
    • Theory of Phase Difference and Complex Difference MR Angiography
    • Advantages and Limitations of 2D and 3D Phase-Contrast Angiography
    • Strategies for Setting the VENC and Avoiding Phase-Wrap
    • Data Processing and Interpretation Steps for Quantitative Flow Measurements
  7. Motion Suppression Techniques
    • Simple Respiratory Compensation with Bellows
    • Methods and Instrumentation for MRI Triggering using Pulsed Oximetry
    • Prospective Cardiac Gating: Heart Rate, Gating Delay and Trigger Windows
    • Advantages and Limitations of Retrospective Gating
    • Advantages and Problems with Navigator Echo Compensation Schemes
  8. Cardiac MR imaging
    • Acquisition Planning: Anatomical Locations and Cardiac Phases
    • k-Space Segmentation: Cardiac Phases, Reduced Field of View and Phase-Encoding Group Size
    • Applications of Echo-Planar Imaging in Cardiological Diagnosis
    • Methods for Black-Blood Heart Imaging
    • Approaches to Coronary Angiography

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MR Technology & Equipment Quality Control (15%)

  1. The Elements of an MRI Scanner
    • Superconducting versus Open Magnets: Engineering Constraints in Design
    • Magnetic Field Gradients: Coil Design and Power Supply Considerations
    • General Theory of Quadrature RF Coils, Surface RF Coils and Phased-Array RF Coils
    • Generic Flow Diagram of an RF Receiver and Digitization System for an MRI Scanner
    • Issues involving the Computer Control, Operator Interface, Image Display and Data Archiving
    • Laser Camera Interfaces, Network Interfaces and DICOM Data Conversion Issues
  2. Quality Control (QC) Procedures
    • Tests and Phantoms Required for the ACR MRI Accreditation Program
    • Daily QC Tasks to be Performed by the Technologist
    • Weekly QC Tasks to be Performed by the Technologist
    • Annual QC Tests and Record Reviews to be Performed by the Medical Physicist
    • Rules for Adequate Data Collection and Record Keeping
    • The Role of the Medical Physicist, Technologist, Radiologist and Service Engineer in Quality Control
  3. Acceptance Testing of the MRI unit
    • Phantoms and Phantom Materials Required for Acceptance Testing
    • Inspecting Records on Magnet Homogeneity, RF Phase Stability & Cryogen Boil-off
    • Initial Evaluation of the Magnet Subsystem
    • Initial Evaluation of the RF Subsystem
    • Initial Evaluation of the Gradient Subsystem
    • Baseline MRI System Performance Checks

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Site Planning & Safety Considerations (10%)

  1. Known and Theoretical Physiological Effects
    • Constant Magnetic Fields
    • Time-Varying Magnetic Fields
    • Radiofrequency Magnetic Fields
  2. FDA Guidelines for Patient Safety
    • Permanent Magnetic Field Strength Limitations
    • Limitations on Rapidly Switching Gradient Fields (dB/dt)
    • Factors Influencing Specific Absorption Rates (SAR) in Various MRI Scanning Procedures
    • NEMA Definition of Acoustic Noise and Methods for its Measurement
    • Safety Issues with Paramagnetic Contrast Agents (Dose and Clearance Issues)
  3. Cryogen Safety and Magnetic Field Safety Procedures
    • Handling of Special Cases – Pacemakers, Metallic Implants, Clothing
    • Methods and Policies for Patient Screening
    • Policies for Pregnant Workers and Pregnant Patients
    • Loops and ECG Leads in MRI
  4. Site Planning for MRI
    • Methods for Measuring the B0 Magnetic Fringe Fields
    • Strategies for Protecting the MR System: Policy, Signage, Personnel Restrictions & Shielding
    • Design and Testing of RF and Static Magnetic Field Shielding
    • Strategies for Measuring Instrument and Device Compatibility with the MRI System

 Sample Test Questions

Type A (one question per item):

1. The magnetic field homogeneity of a MRI magnet is specified in terms of:


a. its average value in ppm over the surface of a sphere.
b. its relative value compared to the earth’s magnetic field.
c. its change away from isocenter in mT/m.
d. the amount of current required to power the magnet.
e. the fractional variation of the resonant frequency as a function azimuthal angle


Type B (multiple questions per item):

B01. Match the physical effect with the process responsible for its occurance:


a. High RF duty cycle at high magnetic fields
b. Rapidly switching gradient fields
c. ECG triggering through hig-impedance leads
d. Inductive loading of RF coils by patients
e. Use of solenoid-type superconducting magnets


2. peripheral nerve stimulation

3. heating in patients

4. detuning of reciever coil

5. fringe fields in magnet room

Type K (one question per item):

6. Which of the following statements is true regarding functional MRI methods that use BOLD?


(1) There is a delay of seconds between the stimulus and the hemodynamic response.
(2) BOLD imaging typically uses 3D-spin echo methods with presaturation.
(3) The BOLD effect typically results in a 1%-5% change in the MRI signal.
(4) The BOLD effect is greater at lower Bo field strengths.
(5) BOLD fMRI measures changes in blood volume in mL/pixel.


A. (1),(2) and (3) only are correct
B. (1) and (3) only are correct
C. (2) and (4) only are correct
D. (4) only is correct
E. All are correct


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Suggested References

  1. Bernstein MA, King KF, Zhou XJ. Handbook of MRI Pulse Sequences. Elsevier Academic Press, Burlington, MA 2004. ISBN: 9780120928613
  2. Biederman RW, Doyle M, Yamrozik J. Cardiovascular MRI Tutorial: Lectures and Learning. Lippincott, Williams & Wilkins, 2007.  ISBN: 9780781772167
  3. Brown MA, Semelka RC. MRI: Basic Principles and Applications, 4th edition. USA. Wiley-Blackwell, 2010. ISBN: 9780470500989
  4. Brown RW, Cheng YCN, Haacke EM, Thompson MR, Venkatesan R. Magnetic Resonance Imaging: Physical Principles and Sequence Design, 2nd edition. Wiley-Blackwell, 2014. ISBN: 9780471720850
  5. Bushong, SC, Clarke, G. Magnetic Resonance Imaging: Physical and Biological Principles, 4th edition. C.V. Mosby Publishing Company. St. Louis, MO, 2015. ISBN: 9780323073547
  6. Ernst RR, Bodenhausen G, Wokaun A. Principles of Nuclear Magnetic Resonance in One and Two Dimensions, Clarendon Press, Oxford, UK, 1990. ISBN: 9780198556473
  7. Filippi M, Arnold DL, Comi (eds.) Magnetic Resonance Spectroscopy in Multiple Sclerosis, Springer-Verlag Mailand, 2001. ISBN 978-8-8470-2109-9
  8. Hahn EL. Spin Echoes. Physical Review 1950. 80(4): 580-594.
  9. Jin J. Electromagnetic Analysis and Design in Magnetic Resonance Imaging, CRC press, Boca Raton FL, 1998. ISBN 978-0-8493-9693-9
  10. Liang Zhi-Pei, Lauterbur PC. Principles of Magnetic Resonance Imaging: A Signal Processing Perspective. Wiley-IEEE Press, 1999. ISBN: 978-0-7803-4723-6
  11. McRobbie DW, Moore EA, Graves MJ, Prince MR. MRI: From Picture to Proton, 2nd edition. Cambridge University Press, 2007. ISBN: 978-0-5216-8384-5
  12. Manning WJ, Pennell DJ. Cardiovascular Magnetic Resonance, 2nd edition. Churchill Livingstone, New York, 2010. ISBN: 978-0-4430-6686-3
  13. Merbach AE, Helm L, Toth E. The Chemistry of Contrast Agents in Medical Magnetic Resonance Imaging, Wiley, 2013. ISBN: 978-1-119-99176-2
  14. Moritani T, Ekholm S, Westesson P-L. Diffusion-Weighted MR Imaging of the Brain, 2nd ed. Springer-Verlag, Berlin, 2009.  ISBN: 978-3-540-78784-6
  15. Prince MR, Grist T, Debatin JF. Three-Dimensional Contrast MR Angiography, 3rd edition. Springer-Verlag, Berlin. 2003. ISBN: 978-3-540-42874-9

17. Shellock FG, ed. Magnetic Resonance Procedures: Health Effects and Safety. CRC Press, Boca Raton, FL 2001.

18. Shellock F. Reference Manual Mri Safety Devices And Implants 2005, Biomedical Research Assoc Llc, 2005.

19. Sprawls, P. Magnetic Resonance Imaging: Principles, Methods & Techniques. Medical Physics Publishing, 2000.

20. Stark D, Bradley WG. Magnetic Resonance Imaging, 3rd edition, Vol I. Mosby Yearbook 1999.

21. Tofts, P. Quantitative MRI of the Brain, Wiley, Chicester, 2003.

22. Vlaardingerbroek MT, Den Boer JA. Magnetic Resonance Imaging: Theory and Practice. 3rd Edition, Springer 2003.

23. Westbrook C, Kaut C. MRI in Practice. Blackwell Science, 1998.

Websites Study materials for physicists and other clinical scientists learning the basics of MRI.

NMR Physics Lectures: