MRI_Cross_sectional_imaging__2_-_Part_2

Page 1: Introduction to MRI

• MRI as a Complex Subject

  • MRI requires an understanding of various underlying physical principles.

  • Key topics include:

    • Signal Generation

    • Introduction to weightings

    • Basics of Equipment

    • Hardware and Safety

• Source: Siemens

Page 2: MRI Signal and Imaging

• Key Concepts

  • B0: Main magnetic field strength.

  • ω = γ: Relationship involving angular frequency based on the gyromagnetic ratio.

• Challenges

  • Resonance time can cause confusion in understanding signal intensity.

Page 3: Components of the MRI System

• Key Components

  • Radio Frequency Coil: Responsible for transmitting and receiving RF signals.

  • Magnetic Coil: Main magnet creating the B0 field.

  • Gradient Coils: Adjust the magnetic field for spatial encoding.

  • Computer: Processes imaging data.

  • Operator Keyboard: Used to control the imaging process.

  • Image Reconstruction: Processing and displaying the MR images.

Page 4: Signal Detection in MRI

• Signal Localization

  • Gradients: Linear variations of the magnetic field strength (B0) allow for localization.

  • Changes in Precessional Frequency: Occurs in the region of interest (ROI).

  • Types of Gradients: Different orientations based on the imaging axis.

Page 5: Magnetic Fields and Gradients

• Magnetic Field Conditions

  • (a) Constant field

  • (b) Constant field + Gx: Introduces gradient in the x-direction.

• Effects on Spin: Slow and fast precession changes dependent on different magnetic field conditions.

Page 6: Imaging Axes and Gradients

• Imaging Planes

  • X-Axis

  • Y-Axis

  • Z-Axis

  • Gradient Types:

    • X-Gradient

    • Y-Gradient

    • Z-Gradient

• Imaging Directions:

  • Coronal

  • Axial for body and head imaging

  • Sagittal

Page 7: Slice Selection in MRI

• Selects Sections for Imaging

  • RF Excitation Pulse: Key in defining the target slice.

  • Factors Affecting Selection:

    • RF amplitude

    • Bandwidth

    • RF carrier frequency

Page 8: Phase Encoding

• Phase Shift Mechanism

  • Affects the spinning protons and can be detected and encoded by the MRI system.

• Importance of Phase Encoding: Allows more accurate imaging.

Page 9: Frequency Encoding

• Frequency Shift Mechanism

  • Shift indicates location of spinning nuclei detected by the system during echo read.

• Significance: Essential for localization.

Page 10: MRI Cycle Overview

• Encoding Process

  • Slice Selection

  • Phase Encoding

  • Frequency Encoding

  • Represents one full imaging cycle.

Page 11: K-Space in MRI

• K-Space Functionality

  • Stores frequency and phase information of spins.

  • Contains:

    • Exact location of signal

    • Amplitude of signal

  • Components of K-Space:

    • Matrix of voxels for raw imaging data.

Page 12: Information in K-Space

• Spatial Resolution

  • Periphery contains details and definitions of edges.

  • Center contains gross forms and tissue contrast information.

Page 13: Fourier Transformation

• Image Acquisition

  • K-Space data must be Fourier transformed to obtain a visual image.

Page 14: Pulse Sequences in MRI

• Definition

  • Waveforms of gradients and RF pulses applied in MR acquisitions.

  • Each diagram corresponds to RF pulse and gradient types.

• Types of Sequences:

  • Spin Echo

  • Gradient Echo

  • Can be 2D or 3D applications.

Page 15: Pulse Timing in MRI

• Key Timing Parameters

  • TR: Repetition Time

  • TE: Echo Time

  • Gradient Pulses: Responsible for slice selection and encoding.

Page 16: Parameters Adjusting Contrast

• Contrast Emphasis

  • Adjustments: TR and TE modify contrast types during imaging.

  • Key Pulses:

    • 90° RF pulse changes NMV into the transverse plane

    • 180° pulse at TE rephases spinning nuclei.

Page 17: Spin Echo Timing

• Conventional Spin Echo

  • Long durations, less common in practice.

  • Faster SE techniques are routinely implemented.

Page 18: TR and TE Influence on Contrast

• Typical MRI Values at 1.5T

  • Short TR: 250-700 ms

  • Long TR: > 2000 ms

  • Short TE: 10-25 ms

  • Long TE: > 60 ms

Page 19: Clinical Techniques

• MR Cholangiopancreatography

  • Sequentially increasing TE enhances T2 weighting.

Page 20: Echo Train Formation

• Echo Train

  • Constructed from multiple 180° RF pulses, creating subsequent echoes.

  • Total Echo Train Length (ETL): Impacts acquisition time, reducing it significantly.

Page 21: Signal Acquisition Overview

• Signal Acquisition Components

  • Graphical representation indicating key timings and gradients, including RF and Echo events.

Page 22: Inversion Recovery in MRI

• Inversion Recovery

  • Longitudinal Magnetization: Showcases null point for fat and water signals during imaging.

Page 23: STIR Technique

• Short Tau Inversion Recovery (STIR)

  • Nulled fat signal enhances water signal contrast in imaged areas.

Page 24: FLAIR Imaging

• Fluid-Attenuated Inversion Recovery (FLAIR)

  • Selective nulling based on TI to suppress unwanted tissue signals, notably CSF and fats.

• Example TI values for suppression of specific tissues.

Page 25: Contrast Imaging Techniques

• T2W and FLAIR: Focus on various tissue contrasts impacting signal detection.

Page 26: Variable Flip Angle Techniques

• Advanced Imaging Techniques

  • Use of variable flip angles for NMV manipulation, with gradient adjustments for dephasing and rephasing.

Page 27: Gradient Sensitivity

• Gradient Adaptation

  • TR and TE adjustments sensitive to B0 inhomogeneities, critical for tissue contrast.

Page 28: T2* Imaging Effects

• Susceptibility Weighted Imaging

  • Unique measures of transverse relaxation due to variations in magnetic susceptibility utilized for hemorrhage detection.

Page 29: PWI Techniques

• Perfusion Weighted Imaging

  • T2* effects from gadolinium enhance imaging response and color overlay mapping.

Page 30: GRE Sequences Overview

• Gradient Echo (GRE)

  • Can be coherent or incoherent; both aim to maintain a steady state during imaging.

Page 31: Various Gradient Echo Sequences

• Equipment Variability

  • Different implementations by various manufacturers ensuring optimized imaging via GRE.

Page 32: Diffusion Weighted Imaging (DWI)

• DWI Explanation

  • Measures water diffusion within tissues to identify pathologies.

Page 33: DWI Signal Interaction

• Variation in b-value

  • Affects imaging brightness; higher b-values indicate restricted diffusion, lower values may indicate unobstructed diffusion.

Page 34: DWI Effects

• Applications of DWI

  • Detected changes in signal intensity indicate areas of restricted diffusion due to pathological changes.

Page 35: Rapid Diffusion Interpretation

• Unrestricted Proton Movement

  • High signal levels correspond to rapid proton diffusion.

Page 36: Slow Diffusion Characteristics

• Restricted Proton Movement

  • Slower diffusion indicates signs of potential pathologies.

Page 37 to 42: Ischemia and Angiography Techniques

• MRI Evolving Imaging Features

  • Stages of imaging in stroke assessment.

  • Angiography Techniques: Differences in contrast-enhanced methods and limitations.

Page 43: Basic Signal Generation

• Process Overview

  • Magnet creates NMV; RF pulses applied at Larmor frequency.

Page 44: Flip Angle Assessment

• Factors Affecting Flip Angle

  • Various magnetic and RF conditions influence the necessary flip angle.

Page 45: Signal Localization Responsibility

• Key Components

  • Signal localization heavily depends on gradient coils for accuracy.

Page 46: Weighting Strategies

• Short vs Long TR and TE

  • Contrast determination based on TR and TE values for different modalities.

Page 47: MRI Magnet Characteristics

• Operating Conditions

  • MRI magnets must typically remain on continuously; operates at critical cryogenic temperatures.

Page 48: Safety Considerations of MRI

• Biological and Mechanical Hazards

  • Identifies projectile risks associated with ferromagnetic objects and patient stimulations caused by RF pulses.

Page 49: Importance of MRI Safety

• Safety Procedures

  • Detailed guidelines aimed at minimizing both direct and indirect hazards in MRI environments.

Page 50: Hazard Control Measures

• Control Strategies

  • Includes authorized personnel training and clearly marked guidelines for safety.

Page 51: Directed Study Areas

• Key Topics for Further Learning

  • MRI safety, contrast media, specific absorption rate, and in-phase/out-of-phase imaging overview.

Page 52: MRI System Overview

• MRI Components

  • Overview of essential static and dynamic magnetic components.

Page 53: Static Magnetic Field Details

• Characteristics of B0

  • Biological effects and interference risks with medical devices.

Page 54: Continued Insights on B0

• Radiographic Impacts

  • Effects on safety and device compatibility within the MRI environment.

Page 55: Operational Standards for B0

• Consistency and Safety Requirements

  • Recognizes that constant monitoring of magnetic field strength is essential for safe operation.

Page 56: Safety Issues with B0

• Common Hazards

  • Outlining potential biological effects and risks of magnetic field exposure.

Page 57: Fringe Field Effects

• Field Extent and Strength

  • Variance in magnetic field strength based on scanner design and shielding effectiveness.

Page 58: Spatial Gradient Understanding

• Field Gradients' Effects

  • Informs decisions on implant positioning and compatibility issues based on magnetic field changes.

Page 59: Testing Implants in MRI Fields

• Safety Testing of Implants

  • Emphasizes importance of thorough testing for implants used near MRI machines to ensure safety.

Page 60: Biological Effects of B0

• Physiological Effects on Patients

  • Detailed descriptions of movement-induced sensations that may affect patients in an MRI environment.

Page 61: Guidelines on Biological Effects

• Public Health England's Guidelines

  • Recommendations for minimizing patient discomfort and risk through careful operational guidelines.

Page 62: Projectile Effect Explanation

• Hazard Potential

  • Danger posed by ferromagnetic objects under high magnetic force, discussing implications for patient and staff safety.

Page 63: Lenz Effect Considerations

• Impact on Heart Valves

  • Addresses potential mechanical risks associated with magnets disrupting heart valve function.

Page 64: Risks for Implanted Medical Devices

• Device Interaction with B0

  • Safety precautions that must be taken when scanning patients with implanted devices.

Page 65: MRI Safety Protocols for Patients

• Patient Guidelines

  • Establishes clear protocols for managing patients with known implantable devices.

Page 66: MRI Conditional Implants Overview

• Emerging Technologies

  • Importance of understanding and verifying implant conditions before MRI scans.

Page 67: Pacemaker Patient Protocols

• Patient Safety Procedures

  • Defined steps necessary to ensure the safety of patients with pacemakers during MRI scans.

Page 68: Active vs. Passive Implants

• Different Categories of Implants

  • Contrasts the implications of having passive implants versus active devices like pacemakers or insulin pumps.

Page 69: Patient Workflow for MRI with Pacemakers

• Clinical Regulations

  • Detailed flow of pre-scan considerations involving pacemaker patients to ensure safety during procedures.

Page 70: Implant Programming Considerations

• Operational Mode Analysis

  • Defines how operational modes of active implants can affect MRI safety and scanning techniques.

Page 71: Dislodgement Risks

• Potential Implant Disruption

  • Provides insights on the risks associated with magnetic field interactions and implanted devices.

Page 72: Scanning Protocol Adaptations

• Practical Guidelines for Scanning

  • Emphasizes necessary adaptations to scanning techniques when patients have specific implants.

Page 73: Monitoring Equipment in MRI

• Importance of Safety Monitoring

  • Outlines necessary precautions when using equipment around the MRI environment.

Page 74: IOFB Detection Hazards

• Safety Concerns in Imaging

  • Identifying foreign bodies that could interfere adversely with MRI scanning.

Page 75: Eye Safety in the MRI Environment

• Potential Injuries from Imaging

  • Graphics illustrating various eye structures at risk during MRI scans involving IOFBs.

Page 76: Time-Varying Magnetic Field Gradients

• Overview of Gradients (dB/dt)

  • Discusses the rate and its impacts on methodical scanning.

Page 77: Time-Varying Field Concerns

• Potential Biological Effects

  • Highlights electrical currents induced by movement in magnetic fields, affecting nerve and muscle function.

Page 78: Biological Effects of Electrical Currents

• Impacts on Patients

  • Definition of potential risks associated with exposure to magnetic gradients, including stimulation-related symptoms.

Page 79: Peripheral Nerve Stimulation Risks

• Induced Current Risks

  • Overview of how body sensitivity could lead to severe patient reactions, particularly in certain individuals.

Page 80: Acoustic Noise in MRI

• Noise Levels and Risks

  • Discussion of acceptable limits of noise and their relation to MRI device strength.

Page 81: Interaction with Implants

• Mechanical and Heating Risks

  • Potential interactions between time-varying magnetic fields and implanted devices including heating and vibration.

Page 82: RF Magnetic Fields

• Effects of RF Radiation

  • Overview of how RF radiation interacts with tissues leading to heating phenomena.

Page 83: ICNIRP Safety Guidelines

• Constitution of Safe Temperature Increases

  • Sets regulation for safe levels of temperature change relating to RF exposure.

Page 84: Localized Heating Effects

• Guidelines for Localized Heating

  • Levels of heat limits intended to protect specific body regions affected during MRI.

Page 85: Estimation of RF Deposition

• SAR Measurement Fundamentals

  • Discussion on methods to measure energy deposition following specified protocols in MRI environments.

Page 86: Specific Absorption Rate (SAR)

• Evaluation Techniques

  • Averages based on body type, influencing patient safety during scans.

Page 87: Categorization of SAR Levels

• Defined Modes for SAR Levels

  • Categorizes exposure standards depending on various operational demands and compliance.

Page 88: Mitigation of RF Deposition

• Control Techniques

  • Strategies to manage RF levels within safe limits while conducting scans.

Page 89: Practical Mitigation Measures

• Operator Adjustments

  • Techniques employed by staff to mitigate risks associate with scanning patients at high SAR values.

Page 90: Environmental Adjustments for SAR Control

• Scanning Techniques

  • Suggestions on how to adjust imaging parameters to maintain low SAR.

Page 91: B1+ RMS and Its Relevance

• Understanding B1 Variables

  • Importance of monitoring RMS measurement during MR procedures.

Page 92: B1+ RMS Monitoring Necessities

• Clinical Implications

  • Highlights the need for ongoing monitoring of B1+ RMS values throughout procedures.

Page 93: Patient Data Monitoring

• Continuous B1 Monitoring by Staff

  • Ensures real-time tracking of RF levels and exposure for patient safety.

Page 94: Induced Current Burns Risks

• Patient Positioning Effects

  • Advisories on proper patient positioning to avoid circuit loops causing burns.

Page 95: Contact Burn Causes

• Potential Burn Sources

  • Various mechanisms via contact with metallic items leading to patient harm.

Page 96: Metal in Clothing Risks

• Patient Safety Recommendations

  • Suggests changing to hospital garb to reduce risks during MRI.

Page 97: Risks from Tattoos and Makeup

• Iron-based Makeup Concerns

  • Identifies risks associated with specific cosmetic products during MRI.

Page 98: MR Imaging-related Electrical Thermal Injury

• Overview of Patient Injury Risks

  • Discusses potential procedural complications leading to thermal injuries during scans.

Page 99: Makeup, Piercing, and Tattoo Guidelines

• Safety Precautions

  • Advisories about how cosmetics can react adversely in MRI environments.

Page 100: Cryogen Handling Considerations

• Safety Measures

  • Emphasizes the need for certified personnel in handling cryogenic materials.

Page 101: Superconducting Magnet Specifications

• Helium Usage in Cooling

  • Details on superconductors and their operational temperatures.

Page 102: Risks Associated with Cryogens

• Potential Hazards

  • Discusses asphyxiation, cold burns, and other emergency procedures during cryogen handling.

Page 103: Quench Pipe Maintenance Requirements

• Safety Standards

  • Outlines the importance of maintaining quench pipes for operational safety.

Page 104: Complication Management Strategies

• Authoritative Controls

  • Best practices for managing hazards in MRI environments through various operational guidelines.

Page 105: Hazard Management Overview

• Operational Protocols

  • Outlines how to effectively manage safety protocols in MRI departments to reduce risk.

Page 106: Responsibility Assignment in MRI

• Defined Roles for Safety

  • Identifies key personnel responsible for MRI safety management.

Page 107: Roles of the MRI Responsible Person

• Main Responsibilities

  • Outlines the necessary qualifications and responsibilities of the MRI responsible person.

Page 108: Duties of the Responsible Person

• Operational Regulations

  • Emphasizes safety through the establishment of written procedures and ethical standards.

Page 109: MRI Safety Expert Roles

• Credentialing in MRI Safety

  • Elaborates on potential qualifications for MRI safety experts.

Page 110: Authorised Person Specifications

• Training and Access Rights

  • Details the selection and training of personnel with access to MR environments.

Page 111: Staff Access Limitations

• Categories for Staff Access

  • Specifies various staff categories permitted inside MRI-controlled areas.

Page 112: MR Operator Responsibilities

• Staff Obligations

  • Importance of appropriate training in handling MRI operations safely.

Page 113: Staff Categorization for MRI Environment

• Distinguishing Staff Groups

  • Identifies access rights and categories for various staff groups within the MR environment.

Page 114: Control of MRI Environment Access

• Access Regulations

  • Establishes rules for maintaining a safe MR environment through controlled access.

Page 115: Role of Safety in MRI Access Areas

• Critical Safety Protocols

  • Ensures safety for individuals entering MRI areas and stringent guidelines for those with implants.

Page 116: MR Environment Definition

• Space Boundaries

  • Defines the magnetic field zones and their safety implications on various personnel and equipment.

Page 117: Signage in MRI Controlled Areas

• Safety Sign Standards

  • Importance of clear signage to indicate safety guidelines and site restrictions within the MR environment.

Page 118: Equipment Labelling Necessities

• Labeling Standards

  • Requirement for all MRI equipment to conform to safety labeling standards set by governing bodies.

Page 119: Conditional Safety Labelling Requirements

• Detailed Equipment Labelling

  • Importance of specifying safety conditions for MRI compatible devices.

Page 120: Complete Hazard Identification Labelling

• Critique of Hazard Potential

  • Establishes clear categorization of equipment based on their risk levels in MRI environments.

Page 121: Comprehensive Hazard Control Guidelines

• Safety Protocol Recap

  • Overview of controlling hazards in an MRI department via trained personnel and effective signage.

Page 122: Safety Guidelines and Legislation Overview

• Current Regulatory Framework

  • Lists important legislative activities governing MRI equipment and processes.

Page 123: Public Health Guidelines Overview

• Standards for MRI Operation

  • Important guidelines focused on patient and volunteer safety.

Page 124: Manufacturer Standards Compliance

• IEC Standards for Safety

  • Outlines the necessity for manufacturers to follow prescribed safety limits in MRI design.

Page 125: ICNIRP Guidelines Summary

• Occupational and Public Health Guidelines

  • Provides framework for exposure guidelines and safety conditions in MRI.

Page 126: Latest Legislative Updates

• New 2016 Regulations

  • Introduces 2016 Health and Safety regulations effective for MRI practices.

Page 127: CEMFAW Overview

• Short-term Exposure Management

  • Highlights MRI's exemption from limits when conditions are met.

Page 128: Sensory Effects Reduction Strategies

• Best Practices for MRI Staff

  • Recommendations to minimize sensory effects for MR personnel during procedures.

Page 129: Staff Safety Measures

• High-risk Staff Screening

  • Guidelines for assessing personnel for vulnerability regarding EMF exposure.