Week 4 Lecture 1

Question 1

6 basic ct equipment

Answer 1

1. couch/table
2. operating console
3. workstation
4. contrast media injector
5. accessory equipment
6. gantry

Question 2

describe some characteristics of the table.

Answer 2

it is made of carbon fibre to provide it with rigidity
it is controlled by electrical and mechanical controls
there are attachment areas for accessory equipments
it is narrow and concave

Question 3

2 planes the table can move in

Answer 3

1. vertical (y axis)
2. horizontal (z axis)

Question 4

incrementation

Answer 4

when the table moves to a specified distance in the z axis plane

Question 5

why is table motion important?

Answer 5

it can affect consistency of the scanning and pathology localization

Question 6

why is table referencing important?

Answer 6

it will help maintain scan consistency between followup exams

Question 7

scan point

Answer 7

table’s position relative to the gantry; gives you the location of irradiation

Question 8

scan point should be manually set to _____ by technologist

Answer 8

zero

Question 9

limitations to the table

Answer 9

• weight restrictions
• scannable range* (must be considered to prevent patient repositioning)

Question 10

*exceeding the weight limits of the table can…?

Answer 10

affect precision of pitch

Question 11

operating console

Answer 11

pieces of equipment that allow technologists to input factors prior to acquisition that affect the scan

Question 12

what are the monitors called at the operating console?

Answer 12

scan monitors & display monitors

Question 13

what makes up the operating console?

Answer 13

1. computer
2. keyboard
3. multiple monitors

Question 14

the keyboard at the operating console enables?

Answer 14

• communication with scan room
• manipulation of gantry tilt
• table movement
• irradiation

Question 15

scan monitors

Answer 15

enables the selection of various factors prior to acquisition (ex. patient’s demographics, scan protocols and parameters)

Question 16

display monitors

Answer 16

enables image viewing and post-processing functions

Question 17

what type of data is stored at the operators console?

Answer 17

RAW data

Question 18

workstation

Answer 18

**access and manipulate IMAGE DATA; post-process images

Question 19

what is the key difference between the keyboard’s control on the operators console vs. workstation?

Answer 19

keyboard at operators console allows for communication with scan room, gantry tilts, table movement and irradiation

keyboard at workstation only communicates with the computer (*focus here is on image manipulation)

Question 20

contrast media injector

Answer 20

mechanical device to safely administer large amounts of contrast media through an IV

Question 21

contrast media injectors can be programmed for?

Answer 21

• to ensure precise volumes and injection rates
  *this allows for consistency of image appearance

Question 22

syringes on the contrast media injectors keep contrast and saline separate. contrast syringes need what special considerations?

Answer 22

a “warming sleeve”

Question 23

contrast media injectors have audible and visual alerts. why?

Answer 23

to help identify potential problems

Question 24

warming sleeves

Answer 24

*to maintain the desired temperature of contrast media

Question 25

what does the contrast media injector comprise of?

Answer 25

1. syringes (one or two) 2. warming sleeves 3. console

Question 26

consoles on the contrast media injection devices are for?

Answer 26

allows for selection and monitoring - selection of pre-programmed protocols and other administration factors

Question 27

accessory equipments

Answer 27

designed to improve patient care and image quality

Question 28

what are some accessory equipment commonly used in ct?

Answer 28

- specialized headrest - sponges - immobilization straps - shielding

Question 29

gantry

Answer 29

houses the x-ray tubes + detectors - opening the patient moves through

Question 30

what is the average diameter of the gantry aperture?

Answer 30

~70-90 cm

Question 31

what is the max gantry tilt?

Answer 31

30 degrees

Question 32

cephalad

Answer 32

towards the head/anterior

Question 33

caudad

Answer 33

towards the back/posterior

Question 34

what are the lights on the gantry for?

Answer 34

enables accurate patient positioning -- isocenter

Question 35

what are the components you can find in the gantry?

Answer 35

x-ray tube, detectors, collimators, filtration, das, slip ring

Question 36

DAS

Answer 36

digital acquisition system measures the transmitted radiation beam (ex. radiation flux at the detectors)

Question 37

what is sampling?

Answer 37

how DAS reduces the creation of image artifacts

Question 38

DAS converts measurements into? with what?

Answer 38

digital signals by using a ADC

Question 39

converted digital signals are sent to the computer by the ADC for?

Answer 39

reconstruction

Question 40

slip rings

Answer 40

electromagnetic devices that provides continuous electrical power and electronic communication across rotating surfaces

Question 41

what type of generators do conventional units use?

Answer 41

3-phase generators

Question 42

3 phase generators are found (inside/outside) the gantry

Answer 42

outside of the gantry

Question 43

what type of generators do the modern units use?

Answer 43

high frequency generators

Question 44

high frequency generators are found (inside/outside) the gantry

Answer 44

inside the gantry

Question 45

high-frequency inverter circuit

Answer 45

- enables high kV settings - produces less voltage ripple (consistent power levels)

Question 46

what generator has better efficiency?

Answer 46

high frequency generators

Question 47

what are the two common sizes of focal spots?

Answer 47

0.5mm & 1mm

Question 48

how are the x-ray tube components designed in order to decrease heat loads?

Answer 48

- higher anode rotation speeds - larger and thicker anodes - metal envelope - dual focal spots

Question 49

power supplied by high frequency generators (increase/decrease) heat loading.

Answer 49

decreases

Question 50

what is the common range for the high frequency generators?

Answer 50

120-140 kVp

Question 51

higher kVps = (fewer/more) electrons boiling off the filament

Answer 51

higher kVps = fewer electrons boiling off

Question 52

filtration

Answer 52

shapes the x-ray beam by absorbing low energy photons

Question 53

filtration results in (homogeneous/heterogenous) beam

Answer 53

homogenous beam

Question 54

by increasing the average energy of the beam, what does it do to the patient's dose?

Answer 54

reduces it (less to be absorbed by the patient)

Question 55

a consistent, uniform beam is good for?

Answer 55

increasing the accuracy of HU measurements

Question 56

**increasing the accuracy of HU measurements results in?

Answer 56

**minimizing the appearance of artifacts caused by beam hardening

Question 57

what are the two classification of filtration?

Answer 57

1. inherent 2. added (aka compensating)

Question 58

what are the 3 factors to inherent filtration?

Answer 58

1. built into the system 2. can't be changed 3. applied to all exams

Question 59

what are the 3 factors to compensating filtration?

Answer 59

1. located between the tube and patient 2. applied anatomically specific exams 3. have special shapes to match beam divergence and patient shape

Question 60

collimators

Answer 60

small, thin pieces of lead that resemble shutters

Question 61

where are the collimators located?

Answer 61

1. pre-patient (source) 2. post-patient (pre-detector)

Question 62

why is the collimator needed post-patient?

Answer 62

- to maintain beam width at the detector - decrease scatter that reaches the detector

Question 63

what does "narrowing the x-ray beam" mean?

Answer 63

restricting the x-ray beam to anatomy of interest, which allows for the controlling of the voxel length (z-axis)

Question 64

***collimators contribute to slice thickness in (SDCT/MDCT) collimators control slice thickness in (SDCT/MDCT)

Answer 64

contribute - mdct controls - sdct

Question 65

detectors

Answer 65

absorb transmitted radiation photons

Question 66

**detectors convert absorbed x-ray energy into _______

Answer 66

electrical signals

Question 67

radiation intensity (≠/=) electrical energy

Answer 67

radiation intensity = electrical energy

Question 68

detectors count the quantity of photons but not quality

Answer 68

quality = energy of the photons