Computers in Imaging Q & A Robert Metzger, Ph.D.

Raphex General Question 2002 G83-G85: Match the following prefizes with the correct power of 10: A. 10 –12 B. 10 –6 C D E G83: micro G84: mega G85: giga

RAPHEX Answer to 2002 Questions G83-85 G83: B. G84: C. G85: D.

RAPHEX General Question 2003 G77: The computational speed of a computer is measured in units of: A. MB B. MIPS C. RVU D. BAUD E. BPI

RAPHEX Answer to 2003 Question G77 B. MIPS MIPS stands for Millions of Instructions Per Second

RAPHEX General Question 2003 G79: Parallel processing refers to: A. Running multiple tasks simultaneously B. Using multiple processors to increase speed C. Computer networking D. Sharing peripheral devices between computers

RAPHEX Answer to 2003 Question G79 B. Using parallel processors to increase speed. Parallel processors divide a task into pieces, with each pieces being solved on a separate processor to increase speed.

RAPHEX General Question 2003 G80: There are approximately ____ bits in a megabyte. A B C D. 2,000,000 E. 8,400,000

RAPHEX Answer for 2003 Question for G80 E. 8,400,000 1 byte = 8 bits 1 Mbyte = 1024 X 1024 = 1,044,448,575 bytes = 8,388,608 bits

RAPHEX Diagnostic Question 2001 D37-D41: Concerning digital subtraction angiography: (Answer A for True and B for False) D37: X-rays exiting the patient are normally captured in a cesium iodide II tube to produce a visible image. D38: The TV cameras used for DSA normally have a signal-to- noise ratio of about 100:1. D39: The video signals form the TV camera are processed in a digital-to-analog converter to obtain a matrix of numbers corresponding to the image. D40: Systems with the greatest capability for artifact correction for re-masking are those which store the subtracted image in analog form on a video disk. D41: Compared with film subtraction images, electronically subtracted images normally have somewhat poorer spatial resolution, but better iodine contrast resolution.

RAPHEX Answer for 2001 Question D37-D41 D37: TRUE – The x-ray image is captured in high resolution with a CsI input phosphor. D38: FALSE – Because the differences signal contains noise determined by the sum of the noise in the mask and the angiogram, a very low noise TV camera (SNR 500:1 or higher) is normally employed in order to prevent additional noise from being added to the image. D39: FALSE – The analog video signals go to an analog-to-digital converter (ADC) D40: FALSE – Image manipulation and enhancement is bets achieved with systems which store the mask and angiogram separately in digital form D41: TRUE – The resolution is limited by the II (4 1p/mm), which has lower resolution than screen-film (6-10 1p/mm) systems. However, contrast enhancement (window/level) is easily achieved.

RAPHEX Diagnostic Question 2002 D47: Concerning computed radiography (CR), which of the following is true? A. Numerous, small solid-state detectors are used to capture the x-ray exposure patterns B. It has better spatial resolution than film C. It is ideal for portable x-ray examinations, when phototiming cannot be used D. It is associated with high reject/repeat rates E. The image capture, storage, and display are performed by the receiver

RAPHEX Answer to 2002 Question D47 C. It is ideal for portable x-ray examinations, when phototiming cannot be used. Computer radiography has a wide dynamic range, in effect wide latitude. It produces acceptable films with sub-optimal technique, such as those obtained with portable x-ray units. It uses image plages covered with photostimulable phosphor (Europium activated Barium Fluoride) as a receiver. Resolution with screen-film systems (5 to 10 1p/mm) is better than that obtained with CR (2.5 to 5 1p/mm). The reject rate in CR is low due to post processing techniques available electronically. Unlike film, CR image capture, storage, and display are all performed by different component fo the system.

RAPHEX Diagnostic Question 2002 D48: In picture archiving and communications systems (PACS), large-matrix display stations (for digitalized radiographs and CR) have all of the following EXCEPT: A. A magnification function B. Interactive window and level functions C. Ability to measure the linear attenuation coefficient accurately D. Ability to invert eh gray-scale values of the image E. Ability to rotate and flip the image

RAPHEX Answer for 2002 Question for D48 C. Ability to measure the linear attenuation coefficient accurately Unlike the case with CT, where CT number measured in Hounsfield numbers represent linear attenuation coefficient values relative to water, in general radiography imaging pixel values are not referenced to value associated with any particular tissue or material.

RAPHEX Diagnostic Question 2003 D51: A flat panel digital radiographic detector has a square 20 X 20 cm image receptor field. The full filed of the detector is coupled to a nominal 2048 X 2048 CCD array. The relative spatial resolution ( expressed as line pair per mm) when going from a 20 X 20 to a 10 X 10 filed of views is: A. Four times better B. Twice as good C. The same D. Half as good E. One fourth as good

RAPHEX Answer for 2003 Question D51 C. The same Digital radiographic (DR) detectors use a fixed number of pixels to image the entire field of view (2048 X 2048 for 20 X 20 cm in this example). Only some of the pixels are used when the image is coned down (1024 X 1024 for 10 X 10 in this example). Since the pixel size is fixed, spatial resolution does not change with collimation.

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