CT- Exam 1
What is a CT number - Answer-numerical value for each pixel, directly related to the x-ray linear
attenuation coefficient for the tissue contained in the voxel
Hounsfield Unit (HU) - Answer-relative value assigned to each pixel to quantify the degree that a
structure attenuates an x-ray beam
HU is a grey scale of - Answer-images from air being -1000 to bone +1000
Bone has a high - Answer-attenuation= high HU
High HU means - Answer-lighter shad on the image
Air is shown in _____ with low HU - Answer-black
it also has low attenuation
1 HU is a - Answer-1% difference in linear attenuation
How can HU help determine an unknown structure - Answer-dropping a ROI
, Beam attenuation - Answer-the degree to which an x-ray beam is reduced by an object "shades to gray"
Beam attenuation depends on - Answer-tissue thickness and atomic number
low attenuation= - Answer-objects where x-rays pass through uninterrupted, show up black on image
High attenuation= - Answer-objects that have the ability to absorb most of the x-ray; show up white on
image
Number of photons that interact depend on - Answer-tissue thickness
atomic # of tissue
tissue density
Tissue thickness - Answer-the thicker the tissue, the more photons will interact with its atoms
atomic number of the tissue - Answer-elements with a higher atomic number provide more opportunity
for photon interaction
Tissue density - Answer-mass of substance per unit volume
Image data - Answer-raw data that has been processed so that each pixel is assigned a HU and an image
is created
Scan data is also known as - Answer-raw data
Scan data - Answer-computer data waiting to be processed to create an image
What is a CT number - Answer-numerical value for each pixel, directly related to the x-ray linear
attenuation coefficient for the tissue contained in the voxel
Hounsfield Unit (HU) - Answer-relative value assigned to each pixel to quantify the degree that a
structure attenuates an x-ray beam
HU is a grey scale of - Answer-images from air being -1000 to bone +1000
Bone has a high - Answer-attenuation= high HU
High HU means - Answer-lighter shad on the image
Air is shown in _____ with low HU - Answer-black
it also has low attenuation
1 HU is a - Answer-1% difference in linear attenuation
How can HU help determine an unknown structure - Answer-dropping a ROI
, Beam attenuation - Answer-the degree to which an x-ray beam is reduced by an object "shades to gray"
Beam attenuation depends on - Answer-tissue thickness and atomic number
low attenuation= - Answer-objects where x-rays pass through uninterrupted, show up black on image
High attenuation= - Answer-objects that have the ability to absorb most of the x-ray; show up white on
image
Number of photons that interact depend on - Answer-tissue thickness
atomic # of tissue
tissue density
Tissue thickness - Answer-the thicker the tissue, the more photons will interact with its atoms
atomic number of the tissue - Answer-elements with a higher atomic number provide more opportunity
for photon interaction
Tissue density - Answer-mass of substance per unit volume
Image data - Answer-raw data that has been processed so that each pixel is assigned a HU and an image
is created
Scan data is also known as - Answer-raw data
Scan data - Answer-computer data waiting to be processed to create an image
