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Introduction to Image Processing, Visualization, and Analysis
1
What is a digital image?
A digital image is an image discretized in spatial coordinates and in brightness. It can be represented by a multidimensional array of integers.
2
What is the difference between a pixel and a voxel?
A pixel, or picture element, is the smallest element of a 2D digital image that can be individually processed, whereas a voxel, or volume element, is the smallest element of a 3D digital image that can be individually processed. A voxel that is the same length in all three dimensions is called an isotropic voxel.
3
What is image reconstruction?
Image reconstruction is a mathematical technique implemented in computers within scanners to reconstruct tomographic or volumetric images from acquired projectional data of a patient. For example, filtered back projection (FBP) and iterative reconstruction (IR) methods are commonly used to create tomographic images in CT.
4
What is the field of view (FOV) of an image?
FOV is the width of an image, which tends to represent the width of the body region that is imaged by the scanner.
5
What is the matrix size of an image?
Matrix size is the number of pixels along the length and width of a digital image. This can be the same in both directions (e.g., 512 × 512 in CT) or can differ between the two directions (e.g., 256 × 192 in MRI).
6
What is signal-to-noise ratio (SNR)?
SNR is the ratio of the mean intensity (i.e., signal) of an object on an image to the standard deviation of the background noise on an image and is a rough measure of image quality.
7
What is contrast-to-noise ratio (CNR)?
CNR is the difference in SNR between two objects or tissue regions on an image that are adjacent to one another and is another commonly used measure of image quality to indicate the measureable contrast between the two regions.
8
What is spatial resolution?
Spatial resolution is the ability to portray two separate but adjacent objects as distinct on an image. It is a function of pixel (or voxel) size, is calculated as FOV/matrix size, and is typically measured in line pairs per millimeter (lp/mm), referring to the ability of an imaging technique to distinguish two closely placed line objects as separate.
9
What is contrast resolution?
Contrast resolution is the ability to portray tissues with different intensities in different shades of gray on an image.
10
What is temporal resolution?
Temporal resolution is the ability to acquire multiple images in a short amount of time. This factor becomes important when imaging moving objects such as the heart, lungs, and joints.
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