Textbook 5 + 6 Flashcards
high-contrast reconstruction algorithms are also known as?
bone or detail filters
localizer scans
digital image acquisitions done by the tube being stationary and the bed is moving through the scan field
localizer scans aka?
scout, surview, tomogram, scanogram, preview, and pilot
z axis in terms of patient positioning?
head-foot direction
y axis in terms of patient positioning?
whether the table in the gantry is too high or too low
x axis in terms of patient positioning?
patient lying more to one side or not
axial scans programmed for contiguous slices result in what?
when one slice abuts the next
cine or dynamic methods
when scanners are programmed to repeat scans at the same slice location
when are gapped slices used?
high-resolution chest studies
overlapping slices
acquiring data in a noncontiguous way
what are some disadvantages to the axial method?
- increased examination time
- delays in imaging can be significant
- motion artifacts
- reconstruction limitations
misregistration
occurs when the patient breaths differently with each data acquisition
when are axial scans preferred?
- acquisition speed isn’t a concern
- optimal resolution needed
- gapped slices needed
- interruption in exposure
what are the key “ingredients” to a helical scan?
- x-ray tube is constantly moving
- constant x-ray output
- uninterrupted table movement
what are some advantages to helical scans?
- improved image resolution with iodinated contrast concentration
- decreased motion artifacts due to resp. and cardiac motion
- superior multiplayer or 3D reformation capabilities
- improved scanning speed
slip rings
allows for the tube to move continually in the same direction
- cuts out interscan delays
interpolation
statistical methods to remove slants or blur of helical images
what are the disadvantages to interpolation?
more interpolation required, the decrease of image resolution and effective slice thickness
pitch
distance the table travelled per 360 rotation of the x-ray tube divided by the x-ray beam collimation width
when pitch is less than 1, what does it mean?
scans are overlapping because the table feed is less than the beam collimation
in SDCT systems, the width of the collimator is what?
the sole determinator of slice thickness
pitch expressed as a ratio
table speed:slice thickness
↑pitch = ___ slice angle
as pitch increases, so does the slice angle
↑slice angle = ____ ?
as slice angle increases, so does the interpolation which will decrease the image resolution
↑pitch = ___ data acquisition for each table position
as pitch increases, fewer data is acquired for each table position
overall, increasing pitch does what to acquisition time?
it will cover more anatomy for a given total acq. time which reduces radiation dose
overall, decreasing pitch does what?
it’ll slow down the table speed which decreases the amount of anatomy covered per unit time, which increases the radiation dose
