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87 Cards in this Set
- Front
- Back
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As a radiation detector, film-screen cannot show differences in tissue contrast that are less than ___%?
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10%
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What are the major components of a generic digital imaging system for use in radiology?
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Data acquisition
Image Processing Image/Display/Storage/Archiving, and Image Communication |
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What is data acquisition?
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Refers to a systematic method of collecting data from the patient
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What are the data acquisition components?
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x-ray tube and digital image detectors
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The output signal from the detectors in a/an __________ signal.
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electrical signal (an analog signal that varies continuously in time)
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Because a digital computer is used in imaging systems, the analog signal must be converted into a digital one. How is this done?
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analog-to-digital converter ADC
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Two digits are referred to as what?
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binary digits or bits
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The output of computer processing, or the output digital image, must first be converted into an analog signal before it can be displayed on the monitor for viewing. What converts the signal back to analog?
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digital-to-analog converter DAC
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Analog images are ____________ images.
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Continuous
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Digital images are _________ representations or images of objects.
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numerical
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Any information that enters the computer for processing must first be converted into _______ form, or numbers. What component does this?
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Digital
ADC |
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If both the input and output image are analog, this is referred to as ________ processing.
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analog processing
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If both the input and output image are discrete, this is referred to as _______ processing.
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digital processing
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CT is based on a reconstruction process whereby a _______ image is changed into a visible physical image.
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digital
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What is a process and who described it?
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Castleman described a process as "a series of actions or operations leading to a desired result; a series of actions or operation are performed upon an abject to alter its form in a desired manner."
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What is digital image processing and who described it?
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Castleman defined digital image processing as "subjecting numerical representations of objects to a series of operations in order to obtain a desired result."
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Images can be represented in two domains on the basis of how they were acquired. These domains are?
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Spatial Location Domain
Spatial Frequency Domain |
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All images displayed for viewing by humans are in what domain?
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Spatial Location Domain
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Radiography and CT acquire images in what domain?
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Spatial Location Domain
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What domain does MRI acquire images?
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Spatial Frequency Domain
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The structure of a digital image can be described with respect to several characteristics. What does this include?
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matrix
pixels voxels bit depth |
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What is a matrix?
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A matrix consists of columns and rows that define small square regions called picture elements or pixels.
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What imaging a patient with a digital imaging modality, the operator selects the matrix size, sometimes referred to as the __________?
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Field-of-View (FOV)
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As the image becomes larger, they require more _______ _______ and more ________ _______.
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processing time
storage space |
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What are pixels?
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picture element
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What makes up the matrix?
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pixels
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Each pixel contains a number that represents a _________ level.
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brightness
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In radiography and CT, the brightness level numbers of the pixels are related to the ______ number and ________ density of the tissues.
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atomic number
mass density |
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How is pixel size calculated?
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pixel size = FOV/matrix size
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The larger the matrix size, the ________ the pixel size. This does what to spatial resolution?
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smaller
equals better spatial resolution if the matrix is larger with a smaller pixel size. |
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What is a voxel?
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volume element
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The matrix, pixel, and bit depth all have an affect on the digital image, particularly its ______ _______ and its _______ ________.
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Spatial resolution
Density resolution |
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The larger the matrix size ( for the same FOV), the smaller pixel size, hence the better the appearance of ______.
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detail
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As the FOV decreases without a change in matrix size, the size of the pixel decreases as well, thus improving _____.
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detail
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The operator selects a ______ matrix size when image larger body parts, and a ______ matrix size and imaging smaller body parts.
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larger
smaller |
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The primary objective during image digitization is to convert a/an ______ image into _______ data for processing by the computer.
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analog
numerical |
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Bit depth has an effect on the number of shades of grey, hence the _________ resolution of the image.
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contrast
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What are the three steps in digitization? pg 66-67
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scanning
sampling quantization |
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What is scanning? pg 66-67
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The first step in digitization is the division of the picture into small regions, or scanning.
Scanning results in a grid characterized by rows and columns. |
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What does the rows and columns from scanning create? pg 67
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a matrix
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What is sampling? pg 67
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The second step in image digitization is sampling, which measures the brightness of each pixel in the entire image.
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What is quantization?
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The final step in digitization, in which the brightness value of each sampled pixel is assigned an integer (0, or a positive or negative number) called a gray level.
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The total number of gray levels is called what?
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gray scale
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The result of the quantization process is a digital image, an array of numbers representing the analog image that was ______, _______, and ________.
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scanned, sampled, and quantized.
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What does the ADC do?
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samples the analog signal at various times to measure its strength at different points.
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Two important characteristics of the ADC are ______ and ________.
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speed and accuracy.
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What does accuracy refer to?
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to the sampling of the signal
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If enough samples are not taken by the ADC, what happens to the representation of the original image? What is this error called?
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it will not be accurate after computer processing.
The error is called aliasing. |
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What is aliasing?
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An artifact that appears on the image when not enough samples are taken by the ADC. It appears as Moire patterns on the images.
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What does speed refer to in the ADC?
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the time taken to digitize the analog signal.
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In the ADC, speed and accuracy are ______ proportional.
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Inversely proportional.
The greater the accuracy, the longer it takes to digitize the signal |
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What are the five fundamental classes of operations involved in transforming an input image into an output image?
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Image enhancement
Image restoration Image analysis Image compression Image synthesis |
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What is image enhancement?
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The purpose of this class of processing is to generate an image that is more pleasing to the observer.
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What is image restoration?
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The purpose of image restoration is to improve the quality of images that have distortions or degredations.
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What is image analysis?
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This class of digital image processing allows measurements and statistics to be performed, as well as image segmentation, feature extraction, and classification of objects.
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What is image compression?
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The purpose of image compression of digital images is to reduce the size of the image to decrease transmission time and reduce storage space.
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What is image synthesis?
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These processing operations "create image from other images and non-image data. these operations are used when a desired image is either physically impossible or impractical to acquire or does not exist in a physical form at all"
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Image processing techniques are based in three types of operations:
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point operations
local operations global operations |
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What are point operations?
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The least complicated and most frequently used image processing technique.
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What is the most commonly point processing technique?
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gray-level mapping
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What is gray-level mapping also referred to as?
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contrast enhancement
contrast stretching histogram modification histogram stretching windowing |
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Gray-level mapping uses a ____-___ ______, which plots the output and input gray-levels against each other.
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look-up table (LUT)
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What do histograms indicate?
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The overall brightness and contrast of an image.
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If the histogram is modified or changed, the _______ and _______ of the image can be altered. This is referred to as histogram modification, or histogram stretching.
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brightness and contrast
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If the histogram is wide, the resulting image will have high or low contrast?
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high
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If the histogram is narrow, the resulting image will have high or low contrast?
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low
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What are local operations?
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An image processing operation in which the output image pixel value is determined from a small area of pixels around the corresponding input pixel.
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Spatial frequency filtering is an example of a _______ operation that concerns brightness information in an image.
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local
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An image with smaller pixels has higher or lower frequency information than an image with larger pixels?
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higher
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When an image changed slowly or at a constant rate, the image is said to have high or low spatial frequency?
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low
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Spatial frequency filtering can alter images in several ways such as:
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image sharpening
image smoothing image blurring noise reduction feature extraction (edge enhancement and detection) |
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What is convolution?
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A general-purpose algorithm. It is a technique of filtering in the space domain.
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The high pass filtering process, also known as ___________________, is intended to sharpen an input image in the spatial domain that appears blurred.
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edge enhancement or sharpness
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What are global operations?
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In global operations, the entire input image is used to compute the value of the pixel in the output image.
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What is a common global operation?
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Fourier domain processing, or the FT, which uses filtering in the frequency domain rather than the space domain.
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What are geometric operations?
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They are intended to modify the spatial position or orientation of the pixels in an image.
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Geometric operations can result in the ______ and ______ of images and image _______ and _______. pg. 75
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Scaling and sizing of images and image rotation and translation.
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What are the types of image data compression?
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lossless or reversible compression
Lossy or irreversible compression |
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What is lossless or reversible compression?
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There is no loss of information in the compressed image data.
It doesn't involve the process of quantization but makes use of image transformation and encoding to provide a compressed image. |
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What is lossy or irreversible compression?
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It involved at least three steps:
Image transformation Quantization Encoding |
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Which step in lossy compression make the image lose its data integrity?
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Quantization
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Is lossy compression used by radiologist? pg 78
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No
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What are the four major classes of 3D imaging?
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Preprocessing
Visualization Manipulation Analysis |
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What is surface rendering?
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A simple procedure in which the surface of an object is creatd using contour data and shading the pixels to provide the illusion of depth.
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What percentage of 3D space does surface rendering use?
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10%
It does not require a great deal of computation. |
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What is volume rendering?
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Is much more sophisticated than surface rendering. It uses all the data in 3D space to provide additional information by allowing the observer to view more details inside the object.
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What are the major components of basis image processing?
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ADC
Image storage Image display Image processor Host computer DAC |
