IMAGING SYSTEM DESIGN

Question 1

3 MAJOR COMPONENTS

Answer 1

1.) Gantry
2.) Operating Console
3.) Computer

Question 2

 Largest component

Answer 2

GANTRY

Question 3

Subsystems:

Answer 3

x-ray tube, detector array, high
voltage generator, patient couch and
mechanical support

Question 4

X-RAY TUBE
 Special requirements:
o Power capacity: must be high
___ kVp
 ___ mA

Answer 4

> 120
400

Question 5

X-RAY TUBE
 Special requirements:
High speed rotors: for

Answer 5

heat
dissipation

Question 6

X-RAY TUBE
Anode heat capacity: __MHU
(Spiral CT)

Answer 6

7 MHU

Question 7

X-RAY TUBE
Heat storage capacity: _- MHU

Answer 7

8

Question 8

X-RAY TUBE
Anode cooling rates: __MHU/min

Answer 8

1

Question 9

X-RAY TUBE
Focal spot size:
Focal spot design: must be
robust or strong
 Heat dissipation

Answer 9

small

Question 10

X-ray tube life: approx.___
exposures (Conventional CT)

Answer 10

5000

Question 11

CT scanners
designed for____ imaging not for
direct projection imaging

Answer 11

high spatial
resolution

Question 12

o Design to predict the focal spot
thermal state
o To adjust the mA setting accordingly

Answer 12

Focal-Spot Cooling Algorithms:

Question 13

o The entire collection of detectors
o Group of detectors
o The image receptor in CT

Answer 13

DETECTORY ARRAY

Question 14

absorbs radiation and converts it
to electrical signal

Answer 14

Detector:

Question 15

 The ability of the detector to
capture transmitted photons and change them to electronic
signals

Answer 15

High detector efficiency

Question 16

 A brief, persistent flash of
scintillation that must be
taken into account &
subtracted before image
reconstruction

Answer 16

Low or no after glow

Question 17

Optimal Characteristics: OF DETECTOR

Answer 17

High detector efficiency
Low or no after glow
High scatter suppression
o High stability

Question 18

 Allows a system to be used
without interruption of
frequent calibration

Answer 18

High stability

Question 19

2 TYPES OF DETECTOR

Answer 19

Gas-filled detector – previously used
o Scintillation & solid-state detectors –
recently used

Question 20

o Basis: ionization of gas

o Characteristics:
 Excellent stability
 Large dynamic range
 Low quantum efficiency

Answer 20

Gas detector:

Question 21

Three types: OF DETECTOR

Answer 21

 Ionization chamber
 Proportional counter
 Geiger-Muller counter

Question 22

Scintillation detector: CRYSTAL USED

Answer 22

SODIUM IODIDE

Question 23

detector:
o Characteristic: high x-ray detection
efficiency (90%)
 Reduces patient dose
 Allows faster imaging time
 Improves image quality

Answer 23

Scintillation

Question 24

Scintillation detector: Replaced by:
 (BGO)
 (CsI)

Answer 24

Bismuth germinate
Cesium iodide

Question 25

SCINTILLATION DETECTOR Current crystal of choice:
 (CdWO4)


Answer 25

Cadmium tungstate
Special ceramics

Question 26

converts light into electrical
signal

Answer 26

Photodiode:

Question 27

Characteristics: OF PHOTODIODE


Answer 27

Small,
 Cheap
 Does not require power
supply

Question 28

THREE IMPORTANT FACTORS
CONTRIBUTING TO DETECTOR EFFICIENCY

Answer 28

GEOMETRIC EFFICIENCY
QUANTUM
CONVERSION

Question 29

 The product of geometric, quantum and
conversion efficiency

Answer 29

OVERALL/DOSE EFFICIENCY

Question 30

The product of the following factors
o

Answer 30

Stopping power of the detector
material
o Scintillator efficiency (in solid-state
types)
o Charge collection efficiency (in
xenon types)
o Geometric efficiency
o Scatter rejection

Question 31

Normal value: b/n ___

Answer 31

0.45-0.85

Question 32

Value <__: non ideal detector system
o Result: increased in patient dose to
maintain image quality

Answer 32

1

Question 33

 Refers to the ability with which the detector
obtains photons that have passed through the
patient

Answer 33

CAPTURE EFFICIENCY

Question 34

 Refers to the number of photons absorbed
by the detector
 Depends on: physical properties of the
detector face
o Thickness
o Material

Answer 34

ABSORPTION EFFICIENCY