CT Flashcards
CT stands for
computerized tomography
Tomos
to cut or section in Greek
Tomography
a special technique to show in detail, images of structures lying in a predetermined plane of tissue while blurring or eliminating detail in images or structures in other planes
Focal plane or region of interest
section or layer at which minimal blurring occurs
ROI is
a fixed point in the anatomy of the patient
Fulcrum
central point/ pivot point. Can be moved up and down to change the level at which the anatomy is blurred
Blur
distortion or blurring of the anatomy above and below the ROI
CT was invented in 1971 by
Sir Godfrey Hounsfield
CT also known as
CAT (computerized axial tomography)
CT used an x-ray machine that acquires images that look like
slices of a loaf of bread
An xray tube emitting a fan shaped beam of X-rays rotates _ degrees around a gantry (opening of the center of the machine) and the patient within it
360
Voxel
volume measurement in 3D imaging
Each voxel in a CT image is also calculated into a density measurement called a
Hounsfield unit (HU) or CT number
The scale is based on attenuation with pure water assigned a CT number of
0
HUs also affect
how images are displayed in terms of brightness and contrast
HUs can also be measured with a cursor to help the DVM determine
the nature of a lesion
50 HU lesion may be
fat
160 HU lesion is
calcium
Two types of field of view (the area seen in the image)
scan field of view (SFOV): number of detectors covered by x-ray beam
display field of view (DFOV): will either be equal to or smaller than the SFOV
_ and _ typically tend to be higher than standard radiography
kV and MAs
Methods of scanning
spiral or conventional
ALARA
As least as reasonably achievable
Original scanners acquired images in slices _ mm thick but these missed small lesions
10
Multislice scanners are able to acquire images slices thinner than
1mm
Scout view (scanogram)
looks like a radiograph and allows the operator to choose the regions included in a scan
conventional scanning
refers to the table motion as done by the original CT scanners
spiral or helical scanning
X-ray tube and detectors rotate continuously which saves a delay between scans
pitch
the ratio between table movement (in mm) and CT slice thickness
CT scanners allow technologists to
make any changes to a setup as needed
some protocols may require
IV contrast, angiography, abdominal scans with contrast, injecting contrast into the spinal canal via lumbar puncture (myelogram)
Modern multi slice scanners have up to _ detectors in the width of their array
256
CT remains an excellent diagnostic for
assessing trauma, broken bones, abdominal injuries, images of brain and sinus if MRI not available
CT used to be primary modality for imaging the head and spine, but _ is now the gold standard
MRI
