# Physics and Instrumentation

 Partial volume averaging on the CT image may be decreased by D. decreasing slice thickness The loss of anatomic information between contiguous sections due to inconsistent patient breathing is called D. misregistration A CT image is formed in part by projecting back all of the attenuation values recorded during data acquisition onto a D. matrix What is the dimension of each pixel in an image with a 512x512mm matrix and a DFOV equaling 25.6cm? D. both a and c the dimension of a pixel may be calculated by dividing the FOV by the matrix size The following formula is used to calculate the linear attenauation coefficient: I= Ioe The reduction in intensity of an xray beam as it interacts with matter is termed D. attenuation The major disadvantage of the fan-shaped xray beams used in modern CT units when compared with the pencil-thin beams is B. increased patient dose Which of the following is the most common type of noise found in the CT image? D. statistical noise Scintillation crystals are used exclusively as detectors in _______CT scanners A. fourth-generation A first generation CT scanner consists of an xray tube and two detectors that translate across the patient's head while rotating in 1 degree increments for a total of B. 180 Which of the following factors does not affect the dimensions of a voxel? B. kernel the dimension of a voxel is determined by mutiplying the pixel dimension by the slice thickness Areas of a CT image that contain abrupt changes in tissue density are electronically represented by which of the following? D. high spatial frequencies Which of the following is an analytic form of image reconstruction? 1. iterative technique 2. Fourier reconstruction 3. filtered back-projection a. 1 only b. 1 and 2 only c. 2 and 3 only d. 1,2, and 3 c. 2 and 3 only The term used to describe the relation between the linear attenuation coefficients of an object and the calculated CT numbers is A. linearity The component of the CT scanner responsible for the mathematical calculations of the image reconstruction process is the B. array processor Which of the folowing statements regarding retrospective image reconstruction is false? B. the slice thickness and the SFOV may be changed Which of the following decreases the noise of a CT image? D. decrease in matrix size Increasing the pitch during a spiral CT examination adversely affects the spatial resolution along with which of the following? C. z axis When an operator reduces the SFOV for a particular body part, which of the following technical changes occurs? B. a smaller number of detectors are activated The mathematical manipulations required during the reconstruction of a CT image are accomplished using a(n) 1. algorithm 2. kernel 3. mathematical filter function a. 1 only b. 1 and 2 only c. 1 and 3 only d. 1, 2, and 3 d. 1, 2, and 3 Which of the following technical parameters would greatly improve the quality of CT studies requiring multiplanar reformats? D. overlapping scans with narrow section thickness Which of the following mathematical techniques is used exclusively for image reconstruction with spiral CT scanners? a. back-projection c. convolution c. interpolation d. iterative techniques c. interpolation Which of the following reduces scatter radiation reaching the detectors? D. both a and c A voxel may be defined as which of the following? A. a volume element Which of the following would increase spatial resolution of a CT examination using the following parameters: large focal spot size, 10mm sections, 512 X 512mm matrix? 1. change to small focal spot size 2. perform 5mm sections 3. reconstruct images in a 320 X 320mm matrix a. 1 only b. 1 and 2 only c. 1 and 3 only d. 1, 2, and 3 b. 1 and 2 only A pixel may be defined as A. a picture element The mathematical technique that involves the estimation of an unknown value from values on either side of it is known as B. interpolation When compared with conventional radiography, CT produces diagnostic images with improved A. low contrast resolution In 1917, the Austrian mathematician________ proved that it was possible tp reconstruct a three-dimensional object ftom the infinite set of all its projections D. Radon Which of the following is not commonly used as a CT scintillation detector material? C. silver halide Authorrandy794 ID5970 Card SetPhysics and Instrumentation Descriptionct, registry, physics Updated2010-02-03T16:49:44Z Show Answers