Mosby Wrong Answers chapter 4 Flashcards
any decrease in voxel dimensions will do what to overall noise?
increases
any decrease in voxel dimensions will do what to the SNR?
Decrease
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?
take tissue (0.4)-Water(0.2)=.2/0.2*1000=+1000
Austrian Mathematician that proved you produce a 3-D image with an infinite amount of projections.
Radon
The volume of a voxel may be calculated by multiplying the pixel dimension (mm^2) by the:
Section Width
spacial resolution is affected by this factor:
geometric
2 types of geometric factors include:
focal spot size and slice thickness
Contrast resolution may be altered by (3)
slice thickness, algorithm selection, and noise
The human Eye can see how many shades of gray?
60-80
images reconstructed from a partial rotation to reduce appearance of pt motion
segmented images
1 HU is equivalent to a tissue density of:
0.1
the calculated mAs applied to each reconstructed slice may be referred to as:
effective mAs
the technique that allows the user to select the range of pixel values used in a 3D Ct reformat is termed:
Threshholding
The modular Transfer Function measures the ability of a system to:
faithfully reproduce the area of anatomy
The Interaction between x-ray and matter that is responcible for the production of scatter radiation absorbed by the PT and detector is “
Compton effect
Describes the degree to which PT movement during volumetric acquisition can negatively affect image detail:
longitudinal spatial resolution
the slice sensitivity profile represents:
the degree of broadening, or point of spread that occurs along the z-axis during volumetric data acquisition.
the full width at half maximum of the SSP.
Effective Section width
The portion of the primary beam interacting with a single detector is known as:
ray
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?
2.15mm 44/512*2.2
A Ct scanner with a limiting resolution of 15 il/cm can resolve an object as small as?
0.3 1/15 is equivalent to 10/15 cm to mm =0.6/2
Controlling factors of temporal resolution: (2)
gantry rotation speed and reconstruction method.
Phantom measurements of uniformity of a CT system is performed primarily to assess the negative affects of:
beam hardening
A voxel’s dimensions may be decreased by: (3)
decreasing section width, decrease in pixel size, and decrease in dov
the process of scanning a phantom device of known density to improve the accuracy of CT attenuation measurements is called:
calibration
areas of a CT image containing abrupt changes in tissue density are electronically represented by:
high spatial frequencies
A Ct image of homogeneous material contains variations in CT number from pixwl to pixwl. this image is said to have:
noise
The increase in average photon energy of a HETEROGENEOUS x-ray beam
Beam Hardening
two ajacent pixels are measured to have a difference of 1 HU. this amounts to tissue density difference of approximately:
0.1%
Range of CT numbers to be displayed:
Width
Phantom Measurement of the uniformity of a CT system is performed primarily to assess the negative effects of:
beam hardening
The portion of the primary beam interacting with a single detector is known as:
ray
During a CT scan, each sample of a ray sum measurments made by the data aquisition system is called:
view
the grainy image is refered to as:
noise
the human eye is capable of differentiating approximately how many shades of grey?
60-80
the typical range of pixel values in a CT system:
-1024HU and 3070 HU
The process of scanning a Phantom device of a known density to improve the accuracy of CT attenuation measurement may be referrred to as:
linearity
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:
cross-field uniformity.
what is commonly used for current MDCT imager reconstruction of a volumetric MDCT?
180 degree interpolation.
a increase in sampling frequency will result in a:
increase in spacial resolution.
