CT Powerpoint

what type of scanning is CT

3-dimensional

how does the tube rotate around the patient in CT

360 degree rotation

CT takes away what in the imaging

superimposition

who was the first successful person to demonstrate a CT scan

sir godfrey housenfield

what year did sir godfrey housefield first successfully demonstrated a CT

1970

what year had shorter scans (more detail), and CT was widely available

1980w

what year was CT heart images acquired

2008

what is a set number of slices that it can acquire per 360 degree rotation

multi-slice

what year was multi slice images created

2000+

what are 4 things that CT is used for

1. procedures

2. biopsy

3. ablations

4. nuclear medicine

what are the common/routine CT scans

head and abdomen

what is a CT number

it is a number assigned to each pixel

what is our means of reference on the CT number scale

water

what number is water on the CT number scale

0

why is water our means of reference of 0

the human body is 70% water and water is very abundant in our bodies

what are positive numbers on the CT number scale

means they are thicker and more dense than water

example of a positive number

bone

what is a negative number on the CT scale

thinner than water, less densee

example of a negative number

air

what is the name of a grid of pixels

matrix

what is the single square of a matrix

pixel

what does each pixel have

a hounsfield unit number

what is the volume element of the matrix

voxel

what does a voxel produce

the pixel area and slice thickness

what can determine the amount of data we can see on the monitor

field of view

list the 5 parts of the CT machine

1. couch

2. bore

3. set up lasers

4. control panel

5. gantry

what is the part where the pt lays and has a weight limit

the couch

what is the name of the machine where the couch goes into

the bore

what is used for positioning and centering the pts/helps as a guide to line up the pt

set up lasers

what part of the ct machine has the detector and tube inside of it

the gantry

what is a slip ring

electricity that takes away the detectors from having to rotate back

what is on both sides and helps move up/down and in/out

the control panel

Ct can handle ____ heat than regular x-ray machines

more

the couch is linked to the _, which is linked to the _

gantry; computer

what is indexing the couch mean

how fast/slow the couch goes into the bore

what. is the compostion of the couch

wood or low density carbon (so it does not show up on the scan)

accessories for the pt in the scan

• head and foot boards

• head craddle

• straps

  • sponges and pillows

can you tilt the gantry

yes, forward or backwards

Parameters of the CT board

-Usually unchanged
-technique factors, slice rate, etc.

images produced are seen in what scale

gray scale

after the image is produced, how is it manipulated

in gray scale using window width and window level

a narrow window width produces what

few shades of grey, higher contrast

a wide window width produces what

more shades of grey, less contrast

what is the window level used for

to adjust the brightness and set the housfield number that is related to the part

CT images are only taken in what slice cuts

axial

what are the three phases of CT image formation

1. scan and data acquisition

2. image reconstructions

3. digital conversion/display control

list the 5 things under scan and data acquistion

1. kv

2. ma

3. time

4. pitch

5. beam wid

can you change the 5 things under scan and dad acquisition after the image has been taken

NO

what are the 4 things under image reconstruction

slice thickness, FOV, matrix, filter

can you change the 4 things under image reconstruction after the image has been taken

YES

what are the 3 things under digital conversion/display control

window width, window level, zoom

what are the 5 artifacts in CT

motion, ring, noise, metal artifacts, beam harding artifacts

what is MPR

multiplanar reconstruction; makes sagittal and coronal after the axial cut

3D

not used in diagnostic, tech dependent

Ring artifact is caused by

a defected detector

noise artifact is caused by

not enough signal is getting to the detector to make the image

beam harding artifacts are caused by what

very dense tissues; ex: when pt leaves arm done for a chest

how is beam hardening artifacts created

when low energy photons are attenuated and it only leaves the high energy photons, the energy of the beam is now increased/harden

what causes motion artifact

motion of the ptw

what can be used to help with motion artifact

making sure the pt is comfortable

what are two ways to fix metal artifacts

increase the KVP to reduce the glare, and using the metal reduction software button

DLP stands for what

dose length product

what is CTDI

CT dose x length of scan

CTDI is impacted with what

impact with thickness, pitch

Term

what is pitch

ratio of distance that the table moves around 360 rotation

when would you lower the radiation dose for a ct scan

1. a peds patient

   1. if the pt has had more than 10 CTs in a calendar year

what is the goal of contrast

it gives different tissues with the same attenuation, to have a different attenuation

how to be successful with contrast

it has to change Housenfield number by at least 10

how is contrast given on ct

intravenously, rectally, orally, air

3 types of contrast given

barium, air, iodinated (most freq used)

who goes first

CT with contrast and then MRI with contrast

(mri contrast will show up on a ct and dilutes the image)

what are the two ways to give contrast

mechanically and manually

pros of a mechanical way to give contrast

allows contrast to be given during a time frame

pros of a CT image

detailed 3d images, painless and precise, few restrictions

cons of CT images

dose, reactions with contrast, misinterpretation on the radiologist part