Medical Image Visual Noise
Outline and Learning Guide
1. Introduction and Overview
1.1. Noise is a fundamental characteristic that is present, to some extent, in all images.
1.2. Noise reduces the visibility of some structures and objects, especially those that have relatively low contrast.
1.3. In medical imaging the objective is not to eliminate the noise, but to reduce it to a clinically acceptable level.
Optimizing an imaging procedure with respect to noise requires a
compromise with patient exposure (x-ray imaging) and acquisition time (MRI and
2. Visual Noise in Images
2.1. What does it look like
2.2. Other names for visual noise
2.3. Recognizing noise in clinical images
2.3.1. It is easiest to see in uniform areas within an image that does not contain anatomical structures.
Observe and judge the effect of noise on visibility of structures
3. Effect of Noise on Visibility
3.1. Relationship to object contrast
Relationship to object size
4. Sources of Image Noise
4.1. Receptor structure (crystals and film grains)
4.2. Random distribution of x-ray and gamma photons (Quantum Noise)
Electronic (Video and MRI)
5. The Statistics of Radiation Photons
5.1. Random nature of photons in time and space
5.2. Statistical distributions
5.3. Standard deviations
Relationship of standard deviation to number of photons and
6. Quantum Noise
6.1. Concept of quantum noise
6.2. Relationship to concentration of photons
Concept and significance of quantum sink
7. Relationship of Noise to Exposure
7.1. Relationship to receptor sensitivity (speed)
7.2. Optimizing noise with patient exposure
7.3. Characteristics of screen/film receptors that determine noise
7.4. Characteristics of digital radiographic receptors and digital imaging procedures that determine noise
Fluoroscopic receptor input exposure values and effects on noise
8. Relationship of Noise to Image Detail
8.1. General effect of image blurring on noise
8.2. Effect of digital image pixel size
The tradeoff between detail and noise in imaging systems.
9. Receptor Sensitivity and Exposure Requirements for the Different X-ray Imaging Systems
9.1. Why does mammography require relatively high exposures?
Why is the exposure per image relatively low in fluoroscopy?
10. Effect of Image Display Contrast on Visibility of Noise
10.1. Film contrast characteristics
Digital image windowing
11. Image Processing to Reduce Noise
11.1. Blurring and pixel averaging
Averaging or integrating a series of images