Problems and Objectives for Learning, Discussion, Review, and Self Assessment

Image Noise

Resources and References
The Physical Principles of Medical Imaging
Online Module
Online Textbook
Visuals for Discussion

• Describe the general appearance of visual noise in clinical images.

• When looking at clinical images recognize visual noise.

• Give at least two alternate names that are sometimes used for visual noise in images.

• Identify and name the major source of visual noise in x-ray images.

• Describe and illustrate the general random nature of x-ray photons within an area of an image.

• Explain how the random distribution of x-ray photons produces image noise.

• Draw a simple graph showing the distribution of the number of x-ray photons within an area and explained the concept of standard deviation.

• Describe the relationship of standard deviation to the mean or average number of photons within an area.

• Describe the general relationship of quantum noise to x-ray receptor exposure.

• Briefly describe the concept of the quantum sink.

• Describe the disadvantage of using radiographic receptors with very high sensitivity or speeds that would require low exposures.

• Explain why quantum noise might be more of a problem with digital radiography than  with film screen radiography.

• Describe the general relationship of image noise to image detail.

• Explain in general terms how blurring reduces image noise.

• Describe the general relationship between digital image pixel size and noise and explain why, especially for x-ray imaging.

• Briefly describe how digital image processing can be used to reduce image noise and its potential adverse effects on image quality.

• Briefly describe how the process of averaging a series of images can be used to reduce noise.  Identify at least three (3) applications of it in clinical imaging.

• Explain why  image display contrast has an effect on the visibility of noise.