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Chap 2 Proc. Concept
Imaging 2 - digital
Question | Answer |
---|---|
Images obtained can be represented in 2 domains, based on how they are acquired. What are they | spatial location and spatial frequency domain |
"often the X location is referred to as the pixel number and the Y location as the line number." Such an image is said to be in which domain? | spatial location |
The FT converts a function in the time domain to a function in _____ domain. | frequency. (time domain.... location domain?) |
Small structures within an object (patient) produce ____ frequencies that represent the ___ in an image. Large structures produce _____ frequencies and represent ____ info in the image. | small is high frequencies and detail, large are low frequencies and contrast. |
Radiologists and techs would prefer to see images in which domain? | spatial location |
Five fundamental classes of operations: | image enhancement, image restoration, image analysis, image compression, image synthesis. |
Image enhancement- purpose of this class is to | generate an image that is more pleasing to the observer. |
Image enhancement* certain characteristics can be enhanced such as: | contours and shapes |
Image analysis class purpose? | allows measurements and statistics to be performed |
Image compression class purpose? | reduce the size of the image in order to decrease transmission time and reduce storage space |
Two forms of image compression? | lossy and lossless |
In _____ compression there is no loss of any information in the image when it is decompressed. In _______ compression there is some loss image detail. | lossless, lossy |
Lossless is aka? | wavelet? |
image synthesis purpose is | "create images from other images or non image data" example: basis of CT and MR images made 3D |
Pixels calculated : | FOV/Matrix |
The number of bits per pixel is the | bit depth |
M x N x k bits. "k bits" implies that....... | every pixel in the digital image matrix M x N is represented by k binary digits. ex) a bit depth of 8 implies each pixel will have 2^8 gray levels or shades of gray |
A bit depth of 8 implies that each pixel will have... | 2^8 (or 256) gray levels/shades of gray |
FOV decreases, no change in matrix size, what happens to pixels? | decrease in size |
bit depth has an effect on the what? | number of shades of gray |
3 steps to digitizing an image. | scanning, sampling, quantization. |
In the first stage of digitizing, _______, the image is first divided into what? | Scanning. An array of pixels |
The second step of digitizing, _____, involves measuring | sampling. The brightness level of each pixel using a device such as a photomultiplier tube |
the third step in digitizing, _________, is a process whereby the brightness levels obtained from sampling are... | Quantization. Are assigned an integer called a gray scale. |
Image quality is _____ with higher bit ADCs. | better |
A histogram is a graph of the number of pixels in the image having... | the same gray levels plotted as a function of the gray levels. |
A wide histogram implies ____ contrast and a narrow histogram will show ___ contrast. | more, less |
LUT. A steep slope results in an image with what kind of contrast? | high |
windowing can change the _____ and _____ of an image | contrast and brightness |
A digital image is made up of numbers, and by definition the range of numbers is defined as _______, and the center of the range is defined as the ______. | window width, window level |
window width controls | contrast |
window level controls | brightness |
A narrow WW provides what kind of image? | high contrast (narrow histogram shows less contrast..) |
When the WL is increased, what happens to the image? | becomes darker |
Sampling frequency and pixel pitch have what kind of relationship? | Inverse. |
Low resolution has more _____ but its faster. ____ speed. High resolution you need more ____ and its slower, but has less penumbra. ____ speed. | penumbra. 200 speed. High needs more mAs, 100 speed |
LUT is used to ___, ______, _____ contrast. | refine, evaluate, correct |
What do you do to mAs when you go up in speed class? | go down in mAs |
Speed class and mAs are ____. | inverse |
How can the relationship between mAs and speed class be solved mathematically? | old mAs/new mAs = new speed/old speed |
Matrix is composed of | DELs |