Mosby CT Registry Review Questions with 100% Verified Correct Answers What is the smallest component of a digital image - Correct Answer pixel How many CT numbers are assigned to each pixel in the image matrix? - Correct Answer One In a CT image, the CT number - Correct Answer Of a material is dependent on its linear attenuation coefficient Each two-dimensional square of data that make up the CT image is called a - Correct Answer pixel What is an element of the digital image - Correct Answer pixel Which of the following influences the spatial resolution in cardiac CT imaging - Correct Answer *detector size *reconstruction interval *pitch As patient motion increases spatial resolution decreases - Correct Answer TRUE Which is an advantage of using a small focal spot - Correct Answer increased spatial resolution Increasing the CT image matrix from 256x256 to 512x512 will likely improve? - Correct Answer High- contrast spatial resolution The practical limiting spatial resolution of a CT scanner is 3.6 lp/cm. What size object does this correspond to? - Correct Answer 1.4 mm Use of a bone filter, as opposed to a soft tissue filter, to reconstruct CT images would likely improve?
- Correct Answer Spatial resolution
The spatial resolution of a typical CT scanner is on the order of? - Correct Answer 1 mm 1 / 4
A 512 x 512 matrix CT image over a 30-cm field of view could show a spatial resolution of no better than ? lp/cm? - Correct Answer 8.5 When comparing a 512x512 matrix to a 1024x1024 matrix, the 1024x1024 matrix? - Correct Answer Contains four times as many pixels: 1024 x 1024 =1048576 then 512 x 512= 262144...then divide
1048576 /262144 = 4
High contrast spatial resolution and low contrast resolution are typically measured baseline and ?thereafter - Correct Answer Biannually To improve the high contrast spatial resolution of a CT study, one would increase _____ while keeping all other factors the same. - Correct Answer Matrix size (128x128 to 512x512) A radiologist wants to improve the high-contrast spatial resolution of anatomy which he/she is examining by CT. The change which would best lead to this improvement is - Correct Answer Increase the matrix size To improve the high-contrast spatial resolution of a CT study, one could increase ? while keeping all other factors the same? - Correct Answer Matrix size A voxel contains 25% air, 50% water and 25% bone. The CT number for this voxel would be expected to be _____ HU? - Correct Answer 0 How many pixels are contained in a 1,024 matrix image? - Correct Answer D. 1,048,576
MATH 1024 X1024
It is located in a matrix and is a two dimensional representation of a voxel - Correct Answer pixel When CT numbers are calculated for voxels (volume elements) of tissue what is assigned the calculated number and a subsequent shade of gray - Correct Answer pixel What is defined as a picture element or the smallest component of the digital image - Correct Answer pixel 2 / 4
A CT scan produces a 512x512 matrix transverse image of a 30 cm diameter FOV. Each pixel is approximately _____ mm on a side. - Correct Answer 0.6 equation: 30cm/512= .058cm convert to mm and its .58 which is approximately 0.6 The ability of a system to define small objects distinctly is referred to as which of the following? - Correct Answer spatial resolution Which of the following terms is/are commonly used to describe a CT scanner's ability to differentiate objects with similar linear attenuation coeffiecents - Correct Answer *spatial resolution *sensitivity Which of the following factors have an affect on contrast resolution - Correct Answer *patient size *slice thickness *pixel size *mAs/dose As mAs/dose increases contrast resolution decreases - Correct Answer FALSE As mAs/dose increases contrast resolution INCREASES - Correct Answer TRUE The ability of a CT scanner to accurately image objects with similar densities is termed - Correct Answer *contrast resolution *sensitivity Which of the following has a direct relationship on increasing contrast resolution - Correct Answer *mAs/dose increase *Slice thickness For a particular CT scanner's beam quality, the linear attenuation coefficient for water is 0.20 cm-1 and for a certain tumor is 0.21 cm-1. What is the CT number of the tumor? - Correct Answer 50.Equation (.21-.20/.21) × 1000= 50 3 / 4
A CT scanner with poor contrast resolution or low sensitivity has difficulty separating - Correct Answer tissues whose linear attenuation coefficients are nearly equal What is the basic physical quantity being measured by a CT system - Correct Answer Linear attenuation coefficient Assume the linear attenuation coefficient is 0.20 cm-1 for water and 0.40 cm-1 for tissue within a given voxel. What is the CT number in Hounsfield units for the pixel representing this voxel? - Correct Answer +1,000....Equation { (.4-.2) /.2} x 1000 What fraction of monoenergetic x-rays will be absorbed by a 20-cm thick material having a linear attenuation coefficient of 0.05 cm-1? - Correct Answer 0.63 The contrast resolution of CT is approximately ? % - Correct Answer 0.3 to 0.6 This term describes the ability CT scanner to differentiate objects with MINIMAL differences in attenuation coefficients - Correct Answer contrast resolution What is the term for resolution of a CT scanner referred to as the system's ability to differentiate objects with SIMILAR densities. - Correct Answer contrast resolution In order to pass ACR CT accreditation, the CT scanner's adult head protocol must be within - Correct Answer 1.0 The QC test for the average CT number for water should be done - Correct Answer Daily The following are all basic tenets of a QC program for computed tomography scanner - Correct Answer *QC test must be conducted regularly *Accurate record keeping *all test results must be interpreted promptly Using the ACR CT accreditation phantom, module 3 is used to measure which of the following - Correct Answer CT number uniformity
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