MAP.15 Medical Imaging Using X-rays
Medical Imaging Using X-rays
Presenter Information
Presenter: Dr. Andy Ma
Learning Outcomes
Recall: Understanding the formation of simple x-ray photographic images.
Describe: The physical principles underlying Digital Subtraction Angiography (DSA).
Define: The term tomography.
Describe: Key principles of how x-ray computerized tomography (CT) is conducted.
Outline: Basic principles of x-ray CT image reconstruction.
X-Ray Imaging
2-D (Traditional) X-Ray Images
Basic Principle: X-rays are absorbed differently by various materials.
Production: 'Shadow pictures' created when an object is between an x-ray source and photographic film.
Attenuation of X-Ray Beam
Air: Negligible absorption.
Bone: Significant absorption due to high density (Calcium has a high atomic mass).
Soft Tissue: Similar absorption properties to water.
Fat Tissue: Less absorption compared to water.
Lungs: Weaker due to low density.
Contrast Agents: Iodine and barium used to visualize body cavities.
X-Ray Production Mechanics
Creation of X-Rays
Electrons are accelerated to excite a tungsten target, producing X-rays.
Diaphragm: Narrows the x-ray beam before it reaches the patient.
Photographic Film: Used for capturing x-ray images.
Applications of 2-D X-Rays
Commonly applied for detecting bone fractures.
Digital Subtraction Angiography (DSA)
Principles of DSA
Contrast Media: Selected for their K-edge matching x-ray energies for optimal absorption.
Injection: Contrast media is injected into blood vessels being studied.
Imaging Process: Two x-ray images taken (before and after contrast), one is subtracted from the other for clarity.
Steps in DSA Imaging
Initial X-Ray: Normal image is captured.
Contrast Injection: Media introduced into bloodstream.
Second X-Ray: Taken in the same area post-contrast.
Digital Subtraction: The first image is digitally subtracted from the second to clarify blood vessels' details.
DSA Advantages
Provides detailed imaging of blood vessel networks, invaluable for studying organ blood supply.
Tomography
Definition
Tomography: The technique of producing images of a slice or section through a solid object.
Mechanism: Based on gathering information from multiple absorption characteristics along various paths to reconstruct an image.
Computerized Tomography (CT)
Overview of CT
Also known as Computer Axial Tomography (CAT).
Basic Principle: Structures are reconstructed from a series of x-ray projections taken uniformly from all around.
CT Imaging Process
Thin Pencil Beams: X-ray beams pass through the tissue from various angles.
Common Volume: All beams pass through the same area, collecting data on tissue absorption.
Data Processing: Modern CT uses rapid projections to get detailed absorption data from numerous small areas in seconds.
Image Reconstruction in CT
Mathematical Manipulation
Absorption Data: Linear attenuation coefficients (LACs) calculated from all x-ray projections.
3-D Array Construction: Computer builds a 3D matrix representing the absorption data.
Image Visualization
Colour Coding: Specific colours assigned to ranges of absorption values to construct the final image.
Challenges: Image reconstruction is complicated mathematically but crucial for effective imaging.
CT Applications
Resolution of Tissue Types: CT can differentiate among soft tissues, blood, and bones.
3-D Imaging: Allows complex visual reconstructions beneficial for surgery planning.
Advanced CT Techniques
3-D CT Imaging: Enables manipulation and analysis of digital images for treatment plans.
Clinical Cases: Supports prosthetic design and surgical reconstruction, such as for facial fractures.
Conclusion
Learning Outcomes Recap
Students should be able to recall formation of x-ray images, understand DSA principles, define tomography, and describe CT principles and reconstruction methods.
Further Contact
Thank You for the Attention
For More Information: Contact Dr. Andy Ma
Email: ama@rcsi.com