Computed Tomography: Physical Principles, Clinical Applications, And Quality Control, 4th Edition Test Bank

Chapter 02: Digital Image Processing Seeram: Computed Tomography, 4th Edition MULTIPLE CHOICE 1. The origin of digital image processing stems from: a. the space program. b. General Electric. c. Hounsfield. d. the Mayo Clinic. ANS: A The history of digital image processing dates to the early 1960s, when National Aeronautics and Space Administration (NASA) was developing its lunar and planetary exploration program. REF: p. 29 2. Visible images include all of the following except: a. paintings. b. mathematical images. c. photographs. d. drawings. ANS: B Some examples of visible images are paintings, drawings, or photographs. REF: p. 30 3. Nonvisible physical images include all of the following except: a. temperature. b. pressure. c. elevation maps. d. holograms. ANS: D Examples of nonvisible physical images are temperature, pressure, or elevation maps. Holograms are optical images. REF: p. 30 4. A digital image: a. is a continuous image. b. is a numerical representation of an object. c. cannot be processed by a digital computer. d. is a nonvisible physical image. ANS: B Digital images are numerical representations or images of objects. REF: p. 30 5. In which of the following are numerical representations of objects subjected to a series of operations to produce a desired result? a. Digital image processing b. Pattern recognition c. Analog-to-digital conversion d. Digital to analog conversion ANS: A Digital image processing involves subjecting numerical representations of objects to a series of operations to obtain a desired result. REF: p. 30 6. Which of the following represents the logical order in digitizing an image? a. Scanning, sampling, and quantization b. Sampling, scanning, and quantization c. Quantization, scanning, and sampling d. Sampling, quantization, and scanning ANS: A Digitization consists of three distinct steps (in order): scanning, sampling, and quantization. REF: p. 35 7. The contraction for “picture element” is: a. pixel. b. voxel. c. matrix. d. address. ANS: A A digital image is made up of a two-dimensional array of numbers, called a matrix. Small square regions in a matrix are called picture elements, or pixels. REF: p. 32 8. A 10  10 matrix consists of ______ pixels. a. 10 b. 20 c. 100 d. 120 ANS: C The matrix consists of columns (M) and rows (N), and the dimension can be described as M  N = Matrix size. REF: p. 32 | p. 33 9. The process of dividing a picture into small regions called pixels is referred to as: a. sampling. b. quantization. c. analog-to-digital conversion. d. scanning. ANS: D The first step in digitization is the division of the picture into small regions, or scanning. Each small region of the picture is a picture element, or pixel. REF: p. 35 10. In which of the following is the brightness level of each pixel in a picture measured by a photomultiplier tube (PM)? a. Scanning b. Sampling c. Quantization d. Digital to analog conversion ANS: B Sampling measures the brightness of each pixel in the entire image. A small spot of light is projected onto the transparency, and the transmitted light is detected by a PM positioned behind the picture. REF: p. 35 11. Which of the following assigns integers to the brightness values measured by the PM? a. Scanning b. Sampling c. Quantization d. Analog-to-digital conversion ANS: C Quantization is the final step, in which the brightness value of each sampled pixel is assigned an integer. REF: p. 35 12. The systematic method of collecting data from the patient is called: a. image processing. b. data acquisition. c. image display. d. image communication. ANS: B The term data acquisition refers to a systematic method of collecting data from the patient. REF: p. 28 13. An 8-bit analog to digital converter (ADC) will divide a signal into: a. 8 parts. b. 8 parts. c. 64 parts. d. 256 parts. ANS: D An 8-bit ADC generates 256 (28) equal parts. REF: p. 36 14. The purpose of image enhancement is: a. to generate an image more pleasing to the observer. b. to improve the quality of images that have distortions. c. to allow measurements and statistics to be performed. d. to reduce the size of the image. ANS: A The purpose of this class of processing is to generate an image that is more pleasing to the observer. Certain characteristics such as contours and shapes can be enhanced to improve the overall quality of the image. REF: p. 37 15. Which of the following reduces the amount of data that makes up the image? a. Image enhancement b. Image restoration c. Image analysis d. Image compression ANS: D The purpose of image compression of digital images is to reduce the size of the image to decrease transmission time and reduce storage space. REF: p. 37 16. The least complicated and most frequently used image processing technique is the: a. point operation. b. local operation. c. global operation. d. geometric operation. ANS: A In general, image processing techniques are based on three types of operations: point operations (point processes), local operations (area processes), and global operations (frame processes). Point operations are perhaps the least complicated and most frequently used image processing technique. REF: p. 38 17. Contrast stretching is an example of a: a. local operation. b. global operation. c. geometric operation. d. point processing technique. ANS: D The most commonly used point processing technique is called gray-level mapping. This is also referred to as “contrast enhancement,” “contrast stretching,” “histogram modification,” “histogram stretching,” or “windowing.” REF: p. 38 18. An example of a local operation that causes image brightness to change slowly or at a constant rate is called: a. area processes. b. low spatial frequency. c. convolution. d. high spatial frequency. ANS: B Spatial frequency filtering is an example of a local operation that concerns brightness information in an image. When the brightness changes slowly or at a constant rate, the image is said to have low spatial frequency. REF: p. 39 19. A histogram in digital image processing is: a. a plot of the number of pixels as a function of the number of gray levels. b. a local operation. c. a spatial frequency filter. d. a windowing level. ANS: A A histogram is a graph of the pixels in all or part of the image plotted as a function of the gray level. REF: p. 39 | p. 40 20. Pixels in a digital image representing information contained in a volume of tissue in the patient are referred to as a: a. pixel. b. voxel. c. bit depth. d. matrix. ANS: B Pixels in a digital image represent the information contained in a volume of tissue in the patient. Such volume is referred to as a voxel (contraction for volume element). REF: p. 33 21. An increase of matrix size (with no change in field of view (FOV)) will ____________ detail. a. increase b. decrease c. not change d. have no effect on ANS: A The matrix size has an effect on the detail or spatial resolution of the image. The larger the matrix size (for the same FOV), the smaller pixel size, hence the better the appearance of detail. REF: p. 34 22. Which of the following is the final step in digitizing an image? a. Sampling b. Analog-to-digital conversion c. Quantization d. Scanning ANS: C Quantization is the final step in which the brightness value of each sampled pixel is assigned an integer, called a gray level. REF: p. 35 23. The total number of gray levels is called: a. a matrix. b. the gray scale. c. an electronic signal. d. bit depth. ANS: B The total number of gray levels is called the gray scale, such as an eight-level gray scale. The gray scale is based on the value of the gray levels; 0 represents black and 255 represents white. The numbers in-between 0 and 255 represent shades of gray. REF: p. 35 24. Which of the following converts an analog signal (voltage) into digital data (numbers)? a. An analog switch b. An ADC c. A digitizer d. A digital to analog converter (DAC) ANS: B The conversion of analog signals to digital information is accomplished by the ADC. REF: p. 28 25. Which ADC is more accurate with respect to sampling an analog signal? a. 2-bit ADC b. 4-bit ADC c. 8-bit ADC d. 16-bit ADC ANS: D The higher the number of bits, the more accurate the ADC. REF: p. 36 26. Which type of artifact will appear on a digital image as a result of poor sampling of the analog signal? a. Beam hardening b. Partial volume c. Aliasing d. Poor sampling does not create artifacts ANS: C If enough samples are not taken, the representation of the original signal will be inaccurate after computer processing. This sampling error is referred to as aliasing, and it appears as an artifact on the image. REF: p. 36 27. In which of the following is the quality improved of a digital image that has distortions or degradations? a. Image enhancement b. Image analysis c. Image restoration d. Pattern recognition ANS: B The purpose of image restoration is to improve the quality of images that have distortions or degradations. For example, blurred images can be filtered to make them sharper. REF: p. 37 28. Which type of image processing technique is intended to modify the spatial position of the pixels in an image? a. Point processing operation b. Geometric processing operation c. Local processing operation d. Global processing operation ANS: B Geometric operations are intended to modify the spatial position or orientation of the pixels in an image. These algorithms change the position rather than the intensity of the pixels, which is also a characteristic of point, local, and global operations. REF: p. 42 29. Which type of image compression results in no loss of information in the compressed image data? a. Lossless b. Lossy c. Irreversible d. Recoverable ANS: A In lossless or reversible compression, there is no loss of information in the compressed image data. REF: p. 43 30. Which image processing hardware is responsible for high-speed processing of the input digital data? a. Digitizer b. Image memory c. Internal image processor d. Host computer ANS: C The internal image processor is responsible for high-speed processing of the input digital data. REF: p. 47 TRUE/FALSE 1. Digital image processing techniques have been applied successfully in not only the space program but also in medical imaging. ANS: T The technology of digital processing has found widespread applications in medicine and particularly in diagnostic imaging, where it has been successfully applied to ultrasonography, digital radiography, nuclear medicine, computed tomography, and magnetic resonance imaging. REF: p. 29 | p. 30 2. The sine wave is an example of an analog signal. ANS: T The sine wave is an example of a continuous function (analog signal). REF: p. 30 3. A digital image is a discrete function. ANS: T A discrete function represents a digital image. REF: p. 30 4. A radiograph is an example of an analog image. ANS: T Analog images are continuous images. For example, a black-and-white photograph of a chest X-ray is an analog image because it represents a continuous distribution of light intensity as a function of position on the radiograph. REF: p. 30 5. All images displayed for viewing by humans are in the spatial frequency domain. ANS: F All images displayed for viewing by humans are in the spatial location domain. REF: p. 31 6. The output digital image must first be converted into an analog signal. ANS: T The output digital image must first be converted into an analog signal before it can be displayed on a monitor for viewing by the observer. REF: p. 28 7. Digital image processing can be defined as “subjecting numerical representations of objects to a series of operations to obtain a desired result.” ANS: T Digital image processing is defined as subjecting numerical representations of objects to a series of operations to obtain a desired result. REF: p. 30 8. Digitization consists of four steps: scanning, sampling, quantization, and digital to analog conversion. ANS: F Digitization consists of three distinct steps: scanning, sampling, and quantization. REF: p. 35 9. Aliasing results in an artifact that appears as a moiré pattern in the image. ANS: T Aliasing artifacts appear as moiré patterns on the image. REF: p. 36 10. A technique of filtering in the spatial domain rather than in the frequency domain is convolution. ANS: T Convolution, a general-purpose algorithm, is a technique of filtering in the spatial domain. REF: p. 39 11. The Fourier transform is used to transform one image domain into another image domain. ANS: T Digital image processing can transform one image domain into another image domain, which is a task completed by the Fourier transform. REF: p. 31 12. Computers operate using the binary number system which operates with a base of 10. ANS: F Computers use the binary number system (which operates with base 2, that is, 0 or 1). These two digits are referred to as binary digits or bits. Bits are not continuous but rather they are discrete units. Computers operate with binary numbers, 0 and 1, discrete units that are processed and transformed into other discrete units. REF: p. 28 13. Digital image processing was first developed for NASA’s work in lunar and planetary exploration. ANS: T The history of digital image processing dates to the early 1960s, when the NASA were developing its lunar and planetary exploration program. REF: p. 29 14. The number of bits per pixel is the bit formation. ANS: F The number of bits per pixel is the bit depth. REF: p. 34 15. A larger matrix results in a larger pixel size. ANS: F The larger the matrix size (for the same FOV), the smaller pixel size, hence the better the appearance of detail. REF: p. 34 MATCHING Please match the following digital image processing concepts for each group. Answer selections may be used more than once. a. Global operations b. Point operations c. Local operations d. Geometrical operations 1. 2. 3. 4. 5. Most frequently used image processing technique Also called area processes or group processes A common operation in this processing technique is Fourier domain processing This technique can result in the scaling and sizing of images Gray-level mapping 6. Spatial frequency filtering is an example of this operation 7. In the operation, the entire input image is used to compute the value of the pixel in the output image 1. 2. 3. 4. 5. 6. 7. ANS: B ANS: C ANS: A ANS: D ANS: B ANS: C ANS: A REF: REF: REF: REF: REF: REF: REF: p. 38 p. 39 p. 42 p. 42 p. 38 p. 39 p. 42 ESSAY 1. Explain briefly what is meant by convolution. ANS: Convolution is a digital image processing technique. It is an algorithm that filters an image in the spatial domain. The algorithm uses a kernel (matrix of pixels) to calculate a new image, the output image. Specifically, the new value of a pixel in the output image is calculated by multiplying it by each of the pixels in the kernel and then summing their values. The convolution is done by moving the kernel across the entire input image, pixel by pixel, until all output image pixels are computed. This is a time-consuming process, so special hardware (such as array processors) can be used to speed up the process. Convolution, a general-purpose algorithm, is a technique of filtering in the spatial domain. REF: p. 39 | p. 40 | p. 41 2. What are the components of a digital image processing system? ANS: A basic digital image processing system consists of several interconnected components. The major components are the ADC, image storage, image display, image processor, host computer, and DAC. The main components of a digital image processing system are the ADC, image storage, image display, image processor, host computer, and DAC. REF: p. 46 | p. 47 3. What is the purpose of the host computer in a digital image processing system? ANS: The purpose of the host computer in a digital image processing system is to perform several major tasks such as reading and writing the stored image date, store data on disks or tapes, and communicate images from one point to another. In digital image processing, the host computer is a primary component capable of performing several functions. For example, the host computer can read and write the data in the image store and provide for archival storage on tape and disk storage systems. The host computer plays a significant role in applications that involve the transmission of images to another location, such as medical imaging. REF: p. 47