Week 1 Part 3

Question 1

function of collimator

Answer 1

ensures gamma ray collection is from 1 orientation only

Question 2

components of gamma camera

Answer 2

• collimator
• photomultiplier tubes
• arithmetic circuits
• scintillation crystal of sodium iodide

Question 3

what are the outputs of arithmetric circuits to a CRO display

Answer 3

3-D coordinates for photon position

Question 4

arithmetic circuits combine ___ with that of its neighbour so that ___ for each point on the crystal can be obtained

Answer 4

output of each photomultiplier tube; electrical equivalent of light output

Question 5

size of scintillation crystal of sodium iodide

Answer 5

250 - 400mm

Question 6

function of photomultiplier

Answer 6

changes light into electrical energy

Question 7

What is NOT a type of collimator used in gamma cameras?

Answer 7

reflective

Question 8

shape of single detector gamma cameras

Answer 8

circular / rectangular

Question 9

how many detectors in mult-detectors

Answer 9

dual / triple

Question 10

types of dual detector systems

Answer 10

• fixed and 180 degrees apart
• fixed and 90 degrees apart
• variable angles between 75 & 180 degrees apart

Question 11

Ri increases when crystal thickness ___ and gamma ray energy __

Answer 11

decreases; increases

Question 12

Rc is dependent on __

Answer 12

length of collimator holes & crystal thickness

Question 13

non uniformity is a measure of __

Answer 13

slightly different response of diff areas of detector to irradiation by uniform source

Question 14

intrinsic uniformity is dependent on __

Answer 14

PM tube balance, crystal, electronics

Question 15

extrinsic uniformity is dependent on __

Answer 15

PM tube balance, crystal, electronics and collimator integrity

Question 16

extrinsic uniformity is imaged with __

Answer 16

collimator using flood source

Question 17

intrinsic uniformity is imaged __

Answer 17

w/o collimator

Question 18

The purpose of the NaI(Tl) crystal is to

Answer 18

convert the gamma rays to light

Question 19

differential uniformity is the measurement of __

Answer 19

worst case rate of change of uniformity over a limited distance (~5 pixels)

Question 20

what are the typical integral & differential uniformity values after correction

Answer 20

1.5 - 3.5%; 1 - 2.5%

Question 21

What material is typically used to make collimators in gamma cameras?

Answer 21

Lead

Question 22

extrinsic uniformity test is performed with __

Answer 22

Co-57 flood source

Question 23

flood source is placed between ___

Answer 23

2 detector heads & acquired for 6,000,000 counts per detector

Question 24

energy resolution is ___

Answer 24

how well energy analyser of gamma camera is able to reject scattered photons and photons from other radioisotopes

Question 25

analyser ensures that only gamma irradiation within ___ passes through

Answer 25

20% energy window

Question 26

FWHM

Answer 26

full width at half maximum; measure of energy resolution & represents minimum difference necessary between energies of 2 gamma rays

Question 27

if FWHM = 20keV, 2 gamma rays with a difference in energy of ___ cannot be distinguished by detector

Answer 27

< 20 KeV

Question 28

the lower the FWHM, the __ the energy resolution

Answer 28

better

Question 29

How would you select the correct window width for a particular radionuclide on a scintillation counter?

Answer 29

Plot a spectrum and set window width centred on photopeak and limits to exclude scatter and background.

Question 30

count rate is the __

Answer 30

number of detected gamma photons per unit time

Question 31

count rate characteristics refers to __

Answer 31

camera's response to varying count rate

Question 32

gamma cameras are unable to work in high count rate environments due to ___

Answer 32

dead time

Question 33

dead time refers to ___

Answer 33

time duration in micro seconds during which camera is unable to respond to another gamma irradiation

Question 34

sensitivity refers to ___

Answer 34

detector's ability to use all gamma irradiation from patient efficiently

Question 35

sensitivity can be improved by using a high sensitive collimator but __

Answer 35

SR with degrade

Question 36

pulse height analysis and uniformity is tested __

Answer 36

daily

Question 37

center of rotation is tested __

Answer 37

weekly

Question 38

quadrant bar phantom followed by uniformity map creation is tested __

Answer 38

every 3 months

Question 39

center of rotation test is used to ensure __

Answer 39

check accuracy of mechanical and electronic alignment of gamma camera's detector heads for accurate image reconstruction

Question 40

any error in COR alignment leads to __

Answer 40

image artifacts or spatial distortion

Question 41

What does a COR offset of more than the acceptable limit indicate?

Answer 41

The rotation axis does not match the detector center

Question 42

what are the improved replacements for conventional PMTs

Answer 42

- position sensitive PMT - avalanche photodiode - silicon PMT

Question 43

why are semiconductor detector precision of gamma signal detection better ___

Answer 43

no need for light electrical signal conversion = improved energy resolution

Question 44

CdTe

Answer 44

cadmium telluride

Question 45

CZT

Answer 45

cadmium zinc telluride

Question 46

CZT and CdTe are better than HPGe in terms of __

Answer 46

energy resolution, better scatter rejection, compact and rugged package

Question 47

In solid-state gamma cameras, what is the role of CZT detectors?

Answer 47

Convert gamma photons directly to electrical signals

Question 48

What is commonly used in solid-state gamma cameras?

Answer 48

CZT

Question 49

What is the main advantage of a solid-state gamma camera over an Anger-type gamma camera?

Answer 49

Improved spatial resolution and sensitivity

Question 50

A consequence of attenuation in NM imaging is the improved appearance of ___

Answer 50

deep lesions.

Question 51

Scintillation is a process that results in an emission of beta particles by a substance (scintillator) when it is bombarded by gamma rays. True or False

Answer 51

False

Question 52

A disadvantage of sodium Iodide (Nal) crystal is that it is ___

Answer 52

hygroscopic & fragile.