Systems & Components (3)

Question 1

CT views

Answer 1

“projections”

Question 2

7 Steps of CT image production

Answer 2

1: X-ray tube directs x-ray beam toward patient
2: X-ray beam attenuated by patient
3: Remnant photons collected by radiation detectors
4: Detectors create electrical radiation readings
5: Radiation readings are converted to digital signal
6: Raw digital signal processed into digital images
7: Digital image sent to monitor or storage device

Question 3

Gantry Components (5)

Answer 3

X-ray tube
Detector Array
Collimators
High-voltage generator
Analog-to-Digital (analog to binary) Converter (ADC)

Question 4

Anode Temp

Answer 4

3600 deg F

Question 5

Gantry generator output (V)

Answer 5

140K volts of electricity

Question 6

Total gantry weight

Answer 6

In excess of 4K #

Question 7

mA influences the _______ of the beam

Answer 7

Intensity

Question 8

Max kVp

Answer 8

140

Question 9

kVp controls the _______ of the beam but also influences the _______.

Answer 9

Energy, Intensity

Question 10

kVp should be increased only with ______ ______ in part thickness

Answer 10

Significant increase

Question 11

Mottle

Answer 11

Image noise

Question 12

Increase in mA and/or kVp results in

Answer 12

increased patient dose, decreased mottle

Question 13

Generator

Answer 13

Supplies high-voltage to x-ray tube
Supplies variable kVp and mA per protocol

Question 14

Range of Variability of Tube Potential

Answer 14

Specific kVp stations: usually 80, 100, 120, 140

Question 15

Range of Variability of (Tube) Current

Answer 15

Specific stations b/w 20-500 mA

Question 16

Step-Down Transformer (for conversion of 220V, AC)

Answer 16

Used (for the filament circuit) to create the high-amp necessary for thermionic emission

Question 17

Step-up Transformer

Answer 17

Used (for x-ray tube circuit) to create high-voltage needed for x-ray production

Question 18

Rectifiers

Answer 18

Convert AC to DC to ensure electrons flow only from cathode to anode (in tube)

Question 19

Detectors

Answer 19

Mounted inside gantry to spiral around patient

Question 20

Detector Array

Answer 20

Whole assembly of detectors

Question 21

Detector Purpose

Answer 21

Collect photons (which have passed thru patient) and convert them to measurable electrical signal

Question 22

Detector Signal is Proportional to

Answer 22

Number of photons that passed thru patient (at that particular area)

Question 23

Detector Signal

Answer 23

(Transmission Reading) “Attenuation Measurement” which represent number of transmitted photons compared to number of attenuated photons

Question 24

Increased attenuation (e.g., from bone) creates _______ detector signal, while decreased attentuation (e.g., from lungs/fat) creates ________ detector signal

Answer 24

lower, higher

Question 25

Curve of detector array improves alignment with…

Answer 25

divergence of x-ray beam

Question 26

Large arrangement of detectors (typical of today’s scanners) are organized into

Answer 26

“Detector Rows,”
“Slices,”
“Detector Channels”

Question 27

4-slice v. 16-slice

Answer 27

4 rows of detectors v. 16 rows of detectors (in z-axis of patient) (generally resulting in 4x the information collected per rotation)

Question 28

Uniform v. Non-Uniform

Answer 28

Detector configuration which is ‘consistent’ v. ‘variable’ (with increasing thickness towards the outer rows) within a single array

Question 29

Beam Width

Answer 29

(“Collimation”) describes width of beam in z-axis

Question 30

Equation for calculating beam-width

Answer 30

Rows x [Detector thickness within given rows in mm/row] = # mm

Question 31

CT Collimators

Answer 31

Resize x-ray beam to match desired exposure field (and prescribed detector width)

Question 32

Pre-patient Collimators

Answer 32

Shape beam as it exits x-ray tube, ensuring width (“geometry”) is only as wide as detectors

Question 33

Detector Collimators (4)

Answer 33

Cover detectors not in use
Reduce scatter
Increases subject contrast
Improve image quality

Question 34

Series of devices thru which anatomic info–collected by CT scanner–passes

Answer 34

Detectors
–>DAS
–>Computer System & Array Processor
–>Output Devices

Question 35

DAS: 3 major functions

Answer 35

Measures transmitted radiation from detectors
Converts electrical signal to digital signal
Transmits digital (binary) signal to main computer

Question 36

Raw (DAS) data

Answer 36

“Unprocessed” (binary) attenuation readings in the form of a digital matrix that can’t be view by tech

Question 37

Reconstruction

Answer 37

Process by which raw data is changed into usable info that can be viewed, reprocessed, stored

Question 38

Array Processor

Answer 38

(CPU) Dedicated electronic circuit (including microprocessors/storage devices) through which the computer system operates at high speeds

Question 39

Image Data

Answer 39

Data leaving computer/array processor which can be viewed, archived, post-processed

Question 40

Couch

Answer 40

Gantry table

Question 41

Detectors capture & convert x-ray photons into _______ _______ signals: _______ _______

Answer 41

analog electrical signals: “radiation readings”

Question 42

DAS

Answer 42

“Data Acquisition System”
Measures analog electrical signals and converts to digital raw data