Which of the following are possible results of partial voluming?
1. decreased sharpness of edges
2. misleading CT numbers
3. improvement in resolution
Which of the following has the highest patient dose assuming all other parameters are the same?
CT numbers _____ would appear black if a window width of 400 and a window level of -100 are used.
If a calcification iwth a CT number of +300 appears pure white on an image, which of the following could be the window width and window level selected?
1. window level = 0, window width = 500
2. window level = +300, window width = 500
3. window level = +100, window width = 1000
Which of the following determinants of CT image quality is responsible for how grainy or speckled a CT image appears?
Whcih of the following statements is FALSE?
1. magnification requires the raw data
2. increasing magnification increases resolution
3. magnification decreases the size of displayed anatomy
If a thin slice is used, which of the following would help reduce the apparent image noise?
A CT number Calibration Test should be performed:
Which of the following is a reason to increase the pitch?
1. a greater volume of anatomy can be covered in a given time
2. a given volume of anatomy can be covered faster
3. radiation dose to the patient can be increased
Which of the following is FALSE about the spatial resolution of an image?
1. resolution is dependent on matrix size
2. resolution is dependent on reconstruction FOV
3. resolution is dependent on scanned FOV
An increase in _____ will result in hardening of an x-ray beam
1. tissue density
2. tissue thickness
If the slice thickness is changed from 5 mm to 7 mm and all other parameters are held constant, _____ % more photons will be used in making the slice.
Which of the following will result in an increased voxel size?
1. decreased reconstruction FOV
2. increased slice thickness
3. increased matrix
If a reconstruction FOV of 32 cm and a 512x512 matrix are used, the pixel size is _____ mm.
b--Pixel size is equal to reconstruction FOV divided by matrix--remember to convert to mm
Which of the following does NOT occur when reconstruction FOV is decreased?
1. spatial resolution is increased
2. pixel size is increased
3. noise in the image increases
Which of the following is the converstion equation from CT number to Hounsfield unit?
There are _____ total pixels in a 1024 x 1024 matrix.
c. more than 1 million
d. more then 2 million
c--multiply 1024 x 1024
Which of the following occurs when slice thickness is reduced?
1. appearance of noise in the image increases
2. the nubmer of photons used in making the slice decreases
3. partial volume averaging decreases
Increasing _____ results in lowering the patient dose.
3. table increment
_____ affects the CT number of water.
The smallest object that can be resolved if a reconstruction FOV of 24 cm and a 512 x 512 matrix are used is _____ mm.
a - 240 mm divided by 512
If the radiologist requires 2 mm thick contiguous slices through the pituitary, and 2.4 cm of coverage, _____ slices are necessary?
Which of the following is NOT a result of reducing the reconstruction FOV?
1. improved spatial resolution
2. increased appearance of image noise
3. anatomical structures appear smaller
Which of the following parameters affects the contrast of a CT image?
Which of the following parameters is responsible for partial volume averaging?
On MDCT, the final reconstructed slice thickness is determined by the:
The distance that the table travels between slices is called:
A set of images is reconstructed with a 150 mm reconstruction FOV. Keeping all other parameters constant, a second set of images is reconstructed with a 300 mm reconstruction FOV, and then magnified so that the anatomical structures in the first and second set appear the same size. Which of the following statements is FALSE?
1. the resolution of the second set of images is better than the first set
2. the apparent noise in the second set of images is more pronounced than the first set
3. the patient dose of the first set of images is higher than the second set
Which of the following is NOT directly proportional to mAs?
Which of the following parameters causes helical slices to be reconstructed so they overlap?
Which of the following is the expected result of a CT number Calibration Test performed on a water phantom?
On a conventional, or serial, CT scan, if we want 5 mm slices iwth 1 mm of overlap, the table increment should be _____mm.
Which of the following parameters allows adjacent slices to be overlapped without increasing the dose to the patient?
Which of the following can be changed retrospectively?
1. the slick thickness from an MDCT helical scan
2. the slick overlap from a single-row detector scanner helical scan
3. the slick thickness from a single-row detector scanner helical scan
Which of the following values for pitch would stretch the x-ray helix the most?
The _____ determines how penetrating the x-ray beam will be.
Which of the folling would be used in a high resolution study of the temporal bones?
1. reduced slick thickness
2. reduced reconstruction FOV
3. sharp reconstruction filter
Which of the following would be used to better visualize low contrast resolution?
1. decreased mAs
2. sharp reconstruction filter
3. narrow window width
For a given distance of coverage, which of the following is TRUE?
1. as reconstruction FOV increases, patient dose increases
2. as pitch increases, patient dose decreases
3. as slice thickness increases, patient dose decreases
_____ the window _____ will make the image appear darker so that bony structures can be evaluated.