RNI Equipment

Question 1

which RNI procedure would be best imaged using a low energy ultra-high resolution collimator?.

Answer 1

MDP Bone scan

Question 2

what is responsible for converting gamma energy into light photons?.

Answer 2

the scintillation crystal

Question 3

In Pet/CT radionuclides produce…

Answer 3

2 Gamma photons of 511 keV

Question 4

physical properties of Technetium 99m that make it ideal for radionuclide imaging.

Answer 4

• relatively short half life
• relatively short biological half life
• relatively short effective half- life
• non-toxic
• can be administered to patient
• gives off gamma radiation - 140kV
• inert in patient’s body
• stable in situ-

Question 5

Requirements for transporting radionuclide when injecting patient on the ward

Answer 5

• radiographer wears PPE
• needs to be transported via a syringe tube (surrounded in tungsten) or lead lined cradle
• syringe needs to be labelled - patient’s details, radionuclide being used, Activity of radionuclide
• Take something to store everything after you have used it
• trained member of staff
• never leave cradle unattended

Question 6

safety requirements needed to perform injections

Answer 6

• ID justifications
• giving information about when the patient will be injected and what time the scan will occur
• ensuring they avoid contact with children and pregnant women.
• perhaps isolate patient - due to radioactivity
• bringing spill kit and yellow bags for radioactive disposal for storage and spill clean
• geiger counters to monitor any residual doses on our hands/ body

Question 7

Why do we use RNI?

Answer 7

• to look at the area and whole functions of organs - can observe radiation uptake
• monitor treatment i.e cancer treatment
• can cater to those who cannot receive contrast. E.g. those who cannot have a CT IVU can have a MAG3 renogram
• can be combined with 3D imaging - PET/SPECT
• Selective uptake of radiopharmaceuticals by various bodily systems

Question 8

how does SPECT work

Answer 8

• camera is set up to focus on a specific piece of anatomy
• individual pictures are taken at 3 degree rotations
• this is done until it reaches a 360 degree rotation
• radiographer will overlay the images- creating a 3D image

Question 9

components of a gamma camera (bottom to top)

Answer 9

• collimators
• scintillation crystals
• photomultiplier tube
• the amplifier

Question 10

collimators are made of….

Answer 10

• a Lead plate

- septa

Question 11

why are lead plates used for collimators?

Answer 11

• they are inexpensive
• have a high density
• high attenuation coefficient

Question 12

Septa in collimators

Answer 12

• a series of small holes perpendicular to the face of the collimator
• the smaller the holes and the more often they are, increases resolution - however, the scans take longer

Question 13

function of the collimators

Answer 13

• to produce an accurate correlation between the emission of a gamma photon from the source and the position of the photon striking the crystal detector

Question 14

collimators are dependent on the type of radionuclide used

Answer 14

• low energy collimators (<150 keV) use Tc99m, TI201, I1213 ) - most commonly used
• Medium energy (< 375 keV use In111,Ga67)
• high energy (<500 keV use I131)

Question 15

types of low energy collimators

Answer 15

LEAP - low Energy All Purpose - used for MAG3 renogram
LEHR - Low Energy High Resolution
LEUHR - Low Energy Ultra High Resolution - used for bone imaging (metastes)

Question 16

types of medium energy collimators

Answer 16

MEAP - Medium Energy all purpose

Question 17

types of high energy collimators

Answer 17

HEAP - high energy all purpose collimators

Question 18

if we increase the hole diameter in the collimator, what happens to the resolution and sensitivity?

Answer 18

resolution decreases

sensitivity increases - allowing more gamma rays through with a steeper angle

Question 19

if we increase the number of holes in the collimator, what happens to the resolution and sensitivity?

Answer 19

• no change to resolution

- sensitivity improves

Question 20

if we increase the length of the holes in the collimator, what happens to the resolution and sensitivity?

Answer 20

• resolution increases - rays are able to travel in straight lines
• sensitvity decreases

Question 21

if we increase the septal thickness in the collimator, what happens to the resolution and sensitivity?

Answer 21

• no change to resolution

- sensitivity decreases

Question 22

if we increase the object distance from the collimator, what happens to the resolution and sensitivity?

Answer 22

• resolution decreases

- no changes to sensitivity

Question 23

collimators: spatial resolution

Answer 23

• the ability of the imaging system to distinguish between 2 small points of activity positioned close together
• the smaller the holes, the greater the spatial resolution

Question 24

collimators: Sensitivity

Answer 24

• the proportion of photon icidents on the collimator, which passes theoght the detector
• the larger the holes in the collimator, the greater the sensitivity (needed for function/uptake)

Question 25

scintillation crystal

Answer 25

- sodium iodide activated with thallium NaI(Tl) - no self absorption - coated with a thin layer of aluminium: crystal is air-tight and light proof - transparent- so no self absorption - sensitive to rapid temperature changes - no more than 3 degrees per hour, or crystal will crack - 50cms in diameter

Question 26

what does the scintillation crystal do?

Answer 26

- convert absorbed energy to light flashes

Question 27

scintillation length

Answer 27

- short- to prevent overlap | - the intensity of light builds up quickly and then dies away in <1µs (decrease dead-time effect)

Question 28

crystal thickness

Answer 28

modern crystals are usually 9.3mm thick - thicker crystals may reduce resolution -

Question 29

crystal detection and absorption

Answer 29

- 50 - 300keV range - if smaller than 50 keV, then the crystal wont have enough energy to scintillate - if higher than 300keV, then the photons will pass through the crystal without being absorbed, thus no scintillation

Question 30

function of a photomultiplier tube

Answer 30

- converts the light from the scintillation event into electrical energy - they determine the location of each scintillation event as it occurs in the crystal electronic logic circuit

Question 31

dynode

Answer 31

an electrode in an electron tube that functions to produce secondary emission of electrons.

Question 32

Science behind PMT's

Answer 32

- light from the scintillation spreads in many directions and the nearest PM tube receives the most light - PMT's all communicate in array - together, these signals give x and Y co-ordinates of the scintillation event - the x and y give the computer the plot to mark as an event on the image matrix - this process takes about 1 minute, however during this time the PMT cannot process another event - (dead-time)

Question 33

How does the Pulse Height Analyzer (PHA) work?

Answer 33

- analyze the frequency distribution of the spectrum of photon energies that are captured by a gamma camera. - comes after PMT - exclude scatter rays

Question 34

PHA consists of.....

Answer 34

circuits which compare the relative pulse heights from individual tubes - uses a window of 15-20% of the peak energy value