importance of CT in patient care pathways + ct image manipulation

Question 1

what is the dose of a ct scan, what is this value comparable to

Answer 1

10mSv
3 yrs background radiation

Question 2

what are some issues concerned with contrast safetu

Answer 2

• 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

Question 3

emergency CT pathways:

• trauma, head, body limbs
• stroke
• acute abdomen
• sepsis

Question 4

what is the process of performing CT (from patient administration to …)

Answer 4

• request form
• check patient ID
• safety questionnaire done
• vetting authorisation

Question 5

what 5 things are asked for during patient pre scan

Answer 5

ID
previous imaging
pregnancy
contraindication
consent

Question 6

what is a scout view

Answer 6

• 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.

Question 7

what are some potential adverse events post CT scan

Answer 7

• extravasation
• anusea
• allergic reaction
• vasovagal (fall in bp with fainéant, sweating etc)
• postural hypotension
• bleeding

Question 8

what is DICOM and what is it used for

Answer 8

digital imaging and communications in medicint

• international standard for medical image storage
• patient info for metadata

Question 9

what are the specifications range that images in DICOM can be stored with

Answer 9

• often greyscale (12-16bit)
• colour as well (24 bit)

Question 10

what 3 type of compressions can be found in DICOM

Answer 10

• non compresses
• lossless compression
• lossy compression

Question 11

what is Jpeg

Answer 11

joint photographics experts group

• most common file format for digital photos
• photo/camera info metadata

Question 12

what size bit can jpeg hold

Answer 12

colour (24 bit)

Question 13

what type of compression is used in jpeg

Answer 13

lossy compression

Question 14

what is the resolution range in DICOM vs Jpeg

Answer 14

DICOM =
- 3 MP for DR/CR
- 5MP for mamma
- 0.25 MP for CT

Jpeg =
- up to 75 MP

Question 15

what is windowing

Answer 15

grey level mapping to radiographic density

• affects contrast of image viewed
• affects brightness of image

Question 16

manipulation of windowing allows visualisation of undetected findings or makes them more conspicious

Question 17

with a large window width, you get a very washed out image (faded grey look)

Question 18

what are window presents useful for

Answer 18

• 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

Question 19

note that image pixels are 3D with an x,y,z axis

• you can assign voxels colour and transparency

Question 20

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

Answer 20

reconstruct a small field of view

Question 21

if a 50cm scanning diameter is represented with a 512 x 512 pixel then 1 pixel = 1mm x 1mm in axial plane

Question 22

if a pixel is isotropic what does this mean

Answer 22

the lengths of the x,y,z axis of a singular pixel are equal

Question 23

what is the average slice thickness in CT scanss

Answer 23

0.5 - 5mm

Question 24

why would a thin slice be thickened dynamically on workstaiton

Answer 24

• to reduce image noise
  ( original thin slice increments during scrolling will still remain)

Question 25

you can only thicken slices, cant break voxels down

Question 26

what are the 3 methods for thickening slices

Answer 26

• average
• maximum intensity projection (MIP)
• minium intestin projection (MinIP)

Question 27

What is average method of thickening slices

Answer 27

you average the signal/instensity from the same area/pixel in all the slices

Question 28

what is MIP method of thickening slices

Answer 28

you select the largest signal of a certain area/pixel out of all the slices and use that to represent

Question 29

thicker slices = less noise + improved contrast

thinner slices = better resolution BUT noisier

Question 30

MIP would be useful for emphasising dense contrast filled vessels