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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 |
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Zoest35
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