Mosby Wrong Answers chapter 4

Question 1

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

Answer 1

increases

Question 2

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

Answer 2

Decrease

Question 3

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?

Answer 3

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

Question 4

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

Answer 4

Radon

Question 5

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

Answer 5

Section Width

Question 6

spacial resolution is affected by this factor:

Answer 6

geometric

Question 7

2 types of geometric factors include:

Answer 7

focal spot size and slice thickness

Question 8

Contrast resolution may be altered by (3)

Answer 8

slice thickness, algorithm selection, and noise

Question 9

The human Eye can see how many shades of gray?

Answer 9

60-80

Question 10

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

Answer 10

segmented images

Question 11

1 HU is equivalent to a tissue density of:

Answer 11

0.1

Question 12

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

Answer 12

effective mAs

Question 13

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

Answer 13

Threshholding

Question 14

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

Answer 14

faithfully reproduce the area of anatomy

Question 15

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

Answer 15

Compton effect

Question 16

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

Answer 16

longitudinal spatial resolution

Question 17

the slice sensitivity profile represents:

Answer 17

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

Question 18

the full width at half maximum of the SSP.

Answer 18

Effective Section width

Question 19

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

Answer 19

ray

Question 20

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?

Answer 20

2.15mm 44/512*2.2

Question 21

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

Answer 21

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

Question 22

Controlling factors of temporal resolution: (2)

Answer 22

gantry rotation speed and reconstruction method.

Question 23

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

Answer 23

beam hardening

Question 24

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

Answer 24

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

Question 25

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

Answer 25

calibration

Question 26

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

Answer 26

high spatial frequencies

Question 27

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

Answer 27

noise

Question 28

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

Answer 28

Beam Hardening

Question 29

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

Answer 29

0.1%

Question 30

Range of CT numbers to be displayed:

Answer 30

Width

Question 31

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

Answer 31

beam hardening

Question 32

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

Answer 32

ray

Question 33

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

Answer 33

view

Question 34

the grainy image is refered to as:

Answer 34

noise

Question 35

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

Answer 35

60-80

Question 36

the typical range of pixel values in a CT system:

Answer 36

-1024HU and 3070 HU

Question 37

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

Answer 37

linearity

Question 38

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:

Answer 38

cross-field uniformity.

Question 39

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

Answer 39

180 degree interpolation.

Question 40

a increase in sampling frequency will result in a:

Answer 40

increase in spacial resolution.