CT applications

Question 1

what is the choice of modality dependent on

Answer 1

• clinical indications
• pathology diagnosed
• stage of disease
• pre/post treatment
• follow up patient management options

Question 2

name the scanning parameters of CT

Answer 2

• mA
• kVp
• scan time
• slice thickness
• pitch
• RFOV
• tube rotation speed
• patient positioning

Question 3

what does ‘pitch’ refer to

Answer 3

the ratio of table movement to slice thickness during single rotation of CT scanner
- the faster the table moves, the higher the pitch

Question 4

when is a lower kVp used

Answer 4

soft tissue imaging

Question 5

when is a higher kVp used

Answer 5

bone imaging

Question 6

longer scan time results in …

Answer 6

more detailed images
increased exposure

Question 7

what does thin slices do to an image

Answer 7

• higher spatial resolution
• more radiation
• more data to process
• sharper images (mA must also be increased to avoid grainy images)

Question 8

what does a thicker slice require

Answer 8

more flattening
- this is because to create an image the system must flatten the scan thickness

Question 9

what is windowing

Answer 9

allows to find right balance between contrast and brightness to see details of interest within a CT image

Question 10

what is window level?

Answer 10

brightness control
- move it up and image becomes brighter
- move it down = darker

Question 11

what is window width

Answer 11

contrast control
- increase window width and the range of grey shades become broader - broader range of tissues
- decreasing it narrows range - easier to focus on specific density range like blood vessels

Question 12

3d reconstruction

Answer 12

turns 2d images to 3d

Question 13

MPR

Answer 13

• multi-planar reconstruction
• allows you to view same structure from different angles

Question 14

MIP

Answer 14

• maximum intensity projection
• highlights brightest areas in CT scan eg blood vessels with contrast

Question 15

volume rendering

Answer 15

• creates 3D images that includes both internal and external surfaces of structures
• assigns opacities of colour/grey scale to different types of tissue

Question 16

how is legislation of required doses kept in line with ALARP

Answer 16

• dose efficient equipment
• equipment QA programmes
• optimizing scans
• training
• diagnostic reference levels

Question 17

positive oral contrast

Answer 17

• iodinated agents (gastrografin) but can obscure lesions
• water soluble iodinated agents safe if bowel pathology or perforation

Question 18

negative oral contrasts

Answer 18

• water
• effective in depicting stomach lining and bowel
• will not obscure blood vessels

Question 19

positive bowel contrast

Answer 19

• iodinated gastrograffin
• water soluble iodinated agents safe if bowel pathology or perforation

Question 20

negative rectal contrast

Answer 20

• air/ co2 via foley catheter

Question 21

aim of IV contrast agents

Answer 21

• label blood vessels and organs
• iodinated agents

Question 22

factors affecting IV contrast

Answer 22

• age
• weight
• cardiovascular status
• rate, volume and concentration of contrast agents
• pump inject for reliability and reproducibility

Question 23

what is triple phase

Answer 23

• no contrast
• arterial contrast
• venous contrast

Question 24

difference between CTA and angio

Answer 24

CTA provides detailed cross-sectional images of blood vessels throughout the body using CT technology and contrast material, while angiography involves X-ray and fluoroscopy-guided imaging of specific vascular regions via direct injection of contrast agents for diagnostic and interventional purposes