X-ray Image Formation And Contrast

 

Outline and Learning Guide


 

Introduction and Overview

Contrast Types
Object Contrast
Concept
Sources of Object Contrast
Physical Density
Atomic Number
Object Thickness
Subject Contrast
Concept and Description
How It Is Expressed

Image Contrast
Concept and Description
How It Is Expressed
Film Radiography
Digital Radiography Displayed on Monitors
Fluoroscopy

Effects of Photon Energy (KV)
Factors That Affect Spectra
Anode Material
KV
Filtration
Effects on Object Penetration and Contrast
Effects on Body Penetration
Appropriate Spectra and KV Values For:
Mammography
Extremities
Pelvis and Abdomen
Skull
Chest
 

Large Area Contrast
Concept and Description
Why It Reduces Object Contrast and Visibility
Sources of Area Contrast
Variations in Density (Chest)
Variations in Thickness (Breast)
Methods For Reducing Effects of Area Contrast
High KV (Chest)
Latitude Film (Chest)
Digital Image Processing and Windowing (Chest and Breast)
Breast Compression (Breast)
Appropriate Film and Exposure Level (Breast)
 

 

 

 

Learning Objectives

While looking at a radiograph define image (radiographic) contrast and describe
how it is expressed.

Define "subject contrast" and describe how it is expressed.

Name the factors that determine the amount of subject contrast coming from a
patient's body.

While looking at a radiograph distinguish between "object" and "area" contrast.

Discuss the physical characteristics of an object within the body that determine its
contrast.

Explain why barium and iodine are particularly useful as contrast agents in
radiology.

Explain why air is an effective contrast agent even though its effective atomic
number (6.65) is near that of soft tissue (7.42).

Discuss the general relation of image contrast to KV.

Identify clinical procedures in which low KV values are used and explain why.

Describe the major disadvantages in using low KV values.

Identify the anode and filter materials used for mammography and explain why.

Sketch a typical x-ray spectrum used for mammography and explain how it is
affected by anode material, filter material, and KV values.

State the KV values which will generally give maximum contrast for iodine and
barium and explain why.

Describe the relationship of K-edge to contrast.

Identify clinical procedures in which high KV values are used and explain why.

State appropriate KV values for each general type of radiographic examination.

Describe the effects of large area contrast on object visibility.

Describe the steps taken to reduce large area contrast in mammography.

Describe the steps taken to reduce large area contrast in chest radiography.

 

 

 

Text Reference

Chapter 12
The Physical Principles of Medical Imaging, 2nd Edition
Medical Physics Publishing, http://www.medicalphysics.org
 

 

 

 

 

 

 

Mind Map