importance of CT in patient care pathways + ct image manipulation Flashcards
what is the dose of a ct scan, what is this value comparable to
10mSv
3 yrs background radiation
what are some issues concerned with contrast safetu
- extravasation ( leakage of blood, lymph, or other fluid, such as an anticancer drug, from a blood vessel or tube into the tissue around it.)
- contrast induced nephropathy
- allergic reaction / anaphylaxis
emergency CT pathways:
- trauma, head, body limbs
- stroke
- acute abdomen
- sepsis
what is the process of performing CT (from patient administration to …)
- request form
- check patient ID
- safety questionnaire done
- vetting authorisation
what 5 things are asked for during patient pre scan
ID
previous imaging
pregnancy
contraindication
consent
what is a scout view
- a mode of operating a CT system. It is generally used to prescribe CT slices and to display slice locations rather than for direct diagnosis.
- taken to help the CT technologist appropriately position the patient so that the correct anatomic structures are imaged.
what are some potential adverse events post CT scan
- extravasation
- anusea
- allergic reaction
- vasovagal (fall in bp with fainéant, sweating etc)
- postural hypotension
- bleeding
what is DICOM and what is it used for
digital imaging and communications in medicint
- international standard for medical image storage
- patient info for metadata
what are the specifications range that images in DICOM can be stored with
- often greyscale (12-16bit)
- colour as well (24 bit)
what 3 type of compressions can be found in DICOM
- non compresses
- lossless compression
- lossy compression
what is Jpeg
joint photographics experts group
- most common file format for digital photos
- photo/camera info metadata
what size bit can jpeg hold
colour (24 bit)
what type of compression is used in jpeg
lossy compression
what is the resolution range in DICOM vs Jpeg
DICOM =
- 3 MP for DR/CR
- 5MP for mamma
- 0.25 MP for CT
Jpeg =
- up to 75 MP
what is windowing
grey level mapping to radiographic density
- affects contrast of image viewed
- affects brightness of image
manipulation of windowing allows visualisation of undetected findings or makes them more conspicious
with a large window width, you get a very washed out image (faded grey look)
what are window presents useful for
- quicker when viewing CT images
- more consistent apperance across serial imaging
- optimised specific attenuation ranges and structures (soft tissue, bone, lung, angiographic etc)
may require manual tweaking based on preference and display
note that image pixels are 3D with an x,y,z axis
- you can assign voxels colour and transparency
CT axial image are output at 512 x 512 pixels and predetermined slice thickness, if you were only interested in smaller structures than say an abdomen, what would you do
reconstruct a small field of view
if a 50cm scanning diameter is represented with a 512 x 512 pixel then 1 pixel = 1mm x 1mm in axial plane
if a pixel is isotropic what does this mean
the lengths of the x,y,z axis of a singular pixel are equal
what is the average slice thickness in CT scanss
0.5 - 5mm
why would a thin slice be thickened dynamically on workstaiton
- to reduce image noise
( original thin slice increments during scrolling will still remain)
you can only thicken slices, cant break voxels down
what are the 3 methods for thickening slices
- average
- maximum intensity projection (MIP)
- minium intestin projection (MinIP)
What is average method of thickening slices
you average the signal/instensity from the same area/pixel in all the slices
what is MIP method of thickening slices
you select the largest signal of a certain area/pixel out of all the slices and use that to represent
thicker slices = less noise + improved contrast
thinner slices = better resolution BUT noisier
MIP would be useful for emphasising dense contrast filled vessels
