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CT Exam Prep > Mosby Wrong Answers chapter 4 > Flashcards

Mosby Wrong Answers chapter 4 Flashcards

1
Q

any decrease in voxel dimensions will do what to overall noise?

A

increases

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2
Q

any decrease in voxel dimensions will do what to the SNR?

A

Decrease

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3
Q

how would you find the CT number of a pixel, when the linear coefficient of a voxel of tissue is 0.4 and the linear attenuation coefficient of water is 0.2?

A

take tissue (0.4)-Water(0.2)=.2/0.2*1000=+1000

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4
Q

Austrian Mathematician that proved you produce a 3-D image with an infinite amount of projections.

A

Radon

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5
Q

The volume of a voxel may be calculated by multiplying the pixel dimension (mm^2) by the:

A

Section Width

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6
Q

spacial resolution is affected by this factor:

A

geometric

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7
Q

2 types of geometric factors include:

A

focal spot size and slice thickness

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8
Q

Contrast resolution may be altered by (3)

A

slice thickness, algorithm selection, and noise

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9
Q

The human Eye can see how many shades of gray?

A

60-80

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10
Q

images reconstructed from a partial rotation to reduce appearance of pt motion

A

segmented images

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11
Q

1 HU is equivalent to a tissue density of:

A

0.1

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12
Q

the calculated mAs applied to each reconstructed slice may be referred to as:

A

effective mAs

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13
Q

the technique that allows the user to select the range of pixel values used in a 3D Ct reformat is termed:

A

Threshholding

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14
Q

The modular Transfer Function measures the ability of a system to:

A

faithfully reproduce the area of anatomy

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15
Q

The Interaction between x-ray and matter that is responcible for the production of scatter radiation absorbed by the PT and detector is “

A

Compton effect

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16
Q

Describes the degree to which PT movement during volumetric acquisition can negatively affect image detail:

A

longitudinal spatial resolution

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17
Q

the slice sensitivity profile represents:

A

the degree of broadening, or point of spread that occurs along the z-axis during volumetric data acquisition.

18
Q

the full width at half maximum of the SSP.

A

Effective Section width

19
Q

The portion of the primary beam interacting with a single detector is known as:

A

ray

20
Q

an mdct image is reconstructed using a 512*512 matrix and a display field of view of 44cm. if the detector collimation is set to a section width of 2.5mm, what is the volume of each voxel?

A

2.15mm 44/512*2.2

21
Q

A Ct scanner with a limiting resolution of 15 il/cm can resolve an object as small as?

A

0.3 1/15 is equivalent to 10/15 cm to mm =0.6/2

22
Q

Controlling factors of temporal resolution: (2)

A

gantry rotation speed and reconstruction method.

23
Q

Phantom measurements of uniformity of a CT system is performed primarily to assess the negative affects of:

A

beam hardening

24
Q

A voxel’s dimensions may be decreased by: (3)

A

decreasing section width, decrease in pixel size, and decrease in dov

25
Q

the process of scanning a phantom device of known density to improve the accuracy of CT attenuation measurements is called:

A

calibration

26
Q

areas of a CT image containing abrupt changes in tissue density are electronically represented by:

A

high spatial frequencies

27
Q

A Ct image of homogeneous material contains variations in CT number from pixwl to pixwl. this image is said to have:

A

noise

28
Q

The increase in average photon energy of a HETEROGENEOUS x-ray beam

A

Beam Hardening

29
Q

two ajacent pixels are measured to have a difference of 1 HU. this amounts to tissue density difference of approximately:

A

0.1%

30
Q

Range of CT numbers to be displayed:

A

Width

31
Q

Phantom Measurement of the uniformity of a CT system is performed primarily to assess the negative effects of:

A

beam hardening

32
Q

The portion of the primary beam interacting with a single detector is known as:

A

ray

33
Q

During a CT scan, each sample of a ray sum measurments made by the data aquisition system is called:

A

view

34
Q

the grainy image is refered to as:

A

noise

35
Q

the human eye is capable of differentiating approximately how many shades of grey?

A

60-80

36
Q

the typical range of pixel values in a CT system:

A

-1024HU and 3070 HU

37
Q

The process of scanning a Phantom device of a known density to improve the accuracy of CT attenuation measurement may be referrred to as:

A

linearity

38
Q

A test phantom containing water is scanned and five ROI measurments are performed. the subsquent density measurments are compared and demostrate a maximum deviation of less than 2 HU. This quality assurance test was perfomed to evaluate the scanners:

A

cross-field uniformity.

39
Q

what is commonly used for current MDCT imager reconstruction of a volumetric MDCT?

A

180 degree interpolation.

40
Q

a increase in sampling frequency will result in a:

A

increase in spacial resolution.

CT Exam Prep (12 decks)

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