MEDICAL IMAGE CHARACTERISTICS
and
QUALITY FACTORS
 


Outline

INTRODUCTION AND OVERVIEW
Significance of Image Characteristics
Topics to be Covered

MEDICAL IMAGE CHARACTERISTICS
Contrast
Blur
Noise
Artifacts
Spatial and Geometric

CONTRAST
Image Contrast
Concept
Visual Appearance
Object Contrast
Concept
Imaging Modality Specific
Procedure Contrast Sensitivity
Concept
Clinical Significance

BLUR

Concept
Effects On:
Visibility of Anatomical Detail
Image Sharpness
Spatial Resolution
Range of Values For:
Mammography
Radiography
Fluoroscopy
Computed Tomography
Magnetic Resonance Imaging
Ultrasound
Gamma Camera
Positron Emission Tomography

VISUAL NOISE

Concept
Visual Appearance
Effect on Visibility of Objects and Structures

 

ARTIFACTS
Concept
Visual Appearance
Imaging Modality Specific
Clinical Significance

SPATIAL AND GEOMETRIC
Concept
Imaging Views
Projection
Tomographic
Volume and 3D

Geometric Magnification
Concept
Factors Affecting Magnification
Clinical Significance
Distortion
General Concept
Size Distortion
Shape Distortion
Position Distortion
Location Distortion

IMAGE VIEWING CONDITIONS
Object Characteristics that Affect Visibility
Size
Contrast
Edge Sharpness
Background
Viewing Conditions
Image Luminance (Brightness)
Glare
Room Illumination
Distance

OBSERVER PERFORMANCE
Concept and Overview
Diagnostic Performance
Sensitivity
Specificity
True Positive
False Positive
True Negative
False Negative
Receiver Operating Characteristic (ROC) Curve
Concept
Human Operating Point
Clinical Applications

 


Mind Map


Learning Objectives

  • Identify the five basic characteristics of an image that determine its quality.

  •  Describe generally how each characteristic affects visibility of anatomical structures and signs of pathology.

  • While looking at a chest radiograph, explain the concept of object and area contrast.

  • While looking at a chest radiograph, identify areas in which object contrast appears to be reduced because the areas are either too light or too dark.

  • Explain the concept of contrast sensitivity and it's significance in medical imaging.

  •  Compare the contrast sensitivity characteristics of radiography and MRI for visualization of soft tissue.

  •  Identify the radiographic procedure that requires the highest contrast sensitivity and explain why.

  • While looking at radiographs, identify some of the objects that represent anatomical detail, estimate their sizes.

  • Describe the basic relationship between image blurring and visibility of detail.

  • Compare and rank the various medical imaging modalities with respect to blurring and visibility of detail.   NOTE: In later modules you will learn the factors in each imaging modality that have an effect on blurring and visibility of detail.

  • Describe the appearance of image noise.

  • While looking at images from each modality identify the image noise, Identify the modalities that appear to produce images with relatively low noise, with relatively high noise.

  • Describe the effect of noise on visibility of objects within an image and identify the object characteristic that makes it have reduced visibility in the presence of noise.  NOTE: In later modules you will learn the factors in each imaging modality that produce and have an effect on the noise.

  • Define and describe image artifact.

  • X Recognize common image artifacts in images from each modality.  NOTE: In later modules you will learn the factors in each imaging modality that produce and have an effect on artifacts

  • Identify and describe three possible types of medical image distortion.

  • Identify and describe three major viewing condition factors that have an effect on the visibility of objects within a medical image.

  • Describe the factors that produce optimum viewing conditions for medical images.

  • Describe the special viewing conditions required in mammography and explain how they are achieved.

  • Explain and compare the two characteristics of a diagnostic procedure: sensitivity and specificity.

  • Define and briefly describe the clinical significance of: True Positive, False Positive, True Negative, False Negative.

  • Sketch a receiver operating characteristic (ROC) curve, label the scales, and describe factors that determine the position of the human operating point.

  • Interpret the general results of a receiver operating characteristic (ROC) analysis.

  • Briefly describe the clinical application of ROC analysis.

 


Text Reference

Chapter 1
The Physical Principles of Medical Imaging, 2nd Edition
Medical Physics Publishing, http://www.medicalphysics.org
 

Image characteristics of MR images are described in detail in:
Magnetic Resonance Imaging: Principles, Methods, and Techniques
Medical Physics Publishing, http://www.medicalphysics.org