nuclear medicine

Question 1

what type of camera is used in nuclear medicine

Answer 1

gamma camera

Question 2

what are the 4 main components of radiation detection in nuclear medicine

Answer 2

collimator, NaI crystals, photomultiplier tubes, computer

Question 3

the gamma camera is capable of multiple different imaging techniques- SPECT
(dynamic, static)

Question 4

what position would the gamma camera be for a cardiac scan

Answer 4

L mode

Question 5

what is the L mode of the gamma camera

Answer 5

• camera rotates through 180 degrees from right anterior oblique to left posterior oblique when imaging the heart

Question 6

what is the first layer of the gamma camera and what material is it made of

Answer 6

• collimator
• lead or tungsten (high density)

Question 7

what is the purpose of the collimator

Answer 7

• acts as a filter (composed of thousands of precisely ligned holes)
• only allows gamma photons parallel to collimator
• helps with spacial mapping

Question 8

what happens to the stray photons that cannot pass through the collimator as they are not parallel to ti

Answer 8

they get absorbed by septa (the walls between the holes)

Question 9

what is spacial mapping

Answer 9

implemented to magnify the image of the zero kinetic energy ions with different scale factors.

Question 10

be aware that different types of collimators are used based on radionuclide used

Question 11

what photon energy level in KeV is consider low, medium or high eenrgy + its associated septal thickness

Answer 11

low energy = 150 (0.3mm)
medium energy = 300 (1mm)
high energy = 400 (2mm)

Question 12

the higher the photon energy, the thicker the septum

Question 13

what is the 2nd layer of the gamma camera

Answer 13

scintillator

Question 14

what material is the scintillator made of

Answer 14

sodium iodide with thallium doping

Question 15

what is the role of the scintillator

Answer 15

converts gamma photons into visible light scintillation

Question 16

how does a scintillator produce light

Answer 16

• incoming photo energy absorbed by crystal
• excites electron up from valence band into conduction band
• electron de-excites and gets trapped briefly in activation centres (impurities)
• when it de-excites from the activation centre, a photon of visible light is emitted

Question 17

what is the 3rd layer of the gamma camera

Answer 17

photomultiplier tube

Question 18

what are the 3 components of the photomultiplier tube

Answer 18

• photocathode
• focusing grid
• anodes and dynodes (in evacuated glass tube)

Question 19

explain how to photocathode works to produce a signal

Answer 19

• photocathode (-ve) converts light into electron via photoelectric effect
• focussing grid focuses electrons onto the first dynode
• dynodes emit electrons when struck by an electron (process known as electron avalanche)
• anode receives signal (in form of electron avalanche)

Question 20

define electron avalanche

Answer 20

amplified original signal reducing the effect of scatter photon

• as the dynode gets hit with an electron from the photocathode, it begins to emit electrons itself causing an ‘avalanche’

Question 21

how does the computer form an image after the signal is received from the photomultiplier tube

Answer 21

• uses anger logic to determine the position of each detection and forms an image

Question 22

how often is quality control carried out on all gamma cameras to confirm they are working within specification

Answer 22

every morning

Question 23

peak and uniformity ( measure of how close to peak intensity the emission is over the entire area to be cured, ) are also checked,

if outside the limit, patients image would eb affected and corrective long QC can be performed to recalibrate the camera

Question 24

what are the 3 types of radioactive decay

Answer 24

alpha, beta, gamma

Question 25

most scans use gamma emitters, which molecule is most used

Answer 25

technetium-99m

Question 26

most therapies use alpha or beta emitters, which molecules are most likely used

Answer 26

radium-223 iodine-131

Question 27

nuclear medicine produces functional images which show the physiology of an organ or system, hence compared to an MRI scan of a freshly dead person, the nuclear medicine brain scan can show if they are alive or not

Question 28

compare nuclear medicine to MRI

Answer 28

MRI - great detail Nuclear medicine - less detail - can see physiological state (if organs are working etc)

Question 29

what are 3 forms of nuclear medicine therapy

Answer 29

- bone (secondary metastasis) - thyroid ablation (carcinoma or benign) - neuroendocrine tumour

Question 30

what radioactive molecule is used for bone cancer therapy

Answer 30

radium-223

Question 31

what radioactive molecule is used for thyroid ablation

Answer 31

iodine-131

Question 32

what radioactive molecule is used for neuroendocrine tumour

Answer 32

lutetium-177

Question 33

know that the radiation source in nuclear medicine cant be 'switched off' as it moves around in syringes and pateints

Question 34

radioactive material can be spilled, or excreted by patients

Answer 34

w

Question 35

what are the 2 forms of radiation protection in nuclear medicine

Answer 35

gloves syringe shields

Question 36

what material are the syringe shields made of

Answer 36

tungsten

Question 37

be aware that there are machines for contamination monitoring

Question 38

what properties are needed in a suitable isotope for diagnostic imaging

Answer 38

- half life of 6hrs (long enough for imaging, short enough to reduce radiation dose) - energy level of gamma emittion around 140 KeV, ideally suitable for efficient detection by scintillation instrument (gamma camera) - suitable chemical properties, chemically incorporated into small molecule ligands and proteins that concentrate in specific organs or tissues when injected - non-toxic - parent nuclide half life of 66hrs (long enough to be transported), short enough for Tc99m formation

Question 39

practice aseptic technique when working in the radiopharmacy

Question 40

how is technetium-99m generated from molybdenum-99 in the radiopharmacy

Answer 40

- 0.9% saline solution (eluant) passed thru molybdenum absorbed alumina column - daughter of molybdenum 99 decay is eluted (removed) from the column due to almost total lack of affinity for alumina

Question 41

why is there a safety concern with the breakthrough of the parent nuclide into the eluent

Answer 41

If the parent nuclide is introduced into the patient, it will decay and produce extra radiation dose and degrade image

Question 42

what is an elute

Answer 42

fluid used to wash through another substance to remove something - extracting one material from another by washing with a solvent

Question 43

if there is breakdown of the column structure, what can happen to the generator eluate produced

Answer 43

significant levels of AL3+ ions - this can interfere with pharmaceutical synthesis

Question 44

allowable levels of parent radionuclides and alumina are set by regulations

Question 45

what does an alumina assessment test use

Answer 45

semiquantitative colorimetrical test with standard solution of Al3+ - performed first elution, if generator is moved and required for some pharmaceuticals

Question 46

how do you test for radionuclide purity

Answer 46

- Tc-99m placed inside special 7mm thick lead shield - shielded solution placed in dose calibrator - any presence of measure activity from shielded solution must be Mo-99m due to high energy emission

Question 47

what is the maximum allowed breakthrough of molybdenum-99m for the Tc-99m sample to still be considered as pure

Answer 47

0.15 uCi per mCi of Tc-99m