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RAD413 > nuclear medicine > Flashcards

nuclear medicine Flashcards

1
Q

what type of camera is used in nuclear medicine

A

gamma camera

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2
Q

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

A

collimator, NaI crystals, photomultiplier tubes, computer

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3
Q

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

A
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4
Q

what position would the gamma camera be for a cardiac scan

A

L mode

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5
Q

what is the L mode of the gamma camera

A
  • camera rotates through 180 degrees from right anterior oblique to left posterior oblique when imaging the heart
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6
Q

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

A
  • collimator
  • lead or tungsten (high density)
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7
Q

what is the purpose of the collimator

A
  • acts as a filter (composed of thousands of precisely ligned holes)
  • only allows gamma photons parallel to collimator
  • helps with spacial mapping
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8
Q

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

A

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

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9
Q

what is spacial mapping

A

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

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10
Q

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

A
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11
Q

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

A

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

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12
Q

the higher the photon energy, the thicker the septum

A
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13
Q

what is the 2nd layer of the gamma camera

A

scintillator

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14
Q

what material is the scintillator made of

A

sodium iodide with thallium doping

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15
Q

what is the role of the scintillator

A

converts gamma photons into visible light scintillation

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16
Q

how does a scintillator produce light

A
  • 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
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17
Q

what is the 3rd layer of the gamma camera

A

photomultiplier tube

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18
Q

what are the 3 components of the photomultiplier tube

A
  • photocathode
  • focusing grid
  • anodes and dynodes (in evacuated glass tube)
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19
Q

explain how to photocathode works to produce a signal

A
  • 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)
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20
Q

define electron avalanche

A

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’
21
Q

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

A
  • uses anger logic to determine the position of each detection and forms an image
22
Q

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

A

every morning

23
Q

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

A
24
Q

what are the 3 types of radioactive decay

A

alpha, beta, gamma

25
Q

most scans use gamma emitters, which molecule is most used

A

technetium-99m

26
Q

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

A

radium-223
iodine-131

27
Q

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

A
28
Q

compare nuclear medicine to MRI

A

MRI
- great detail

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

29
Q

what are 3 forms of nuclear medicine therapy

A
  • bone (secondary metastasis)
  • thyroid ablation (carcinoma or benign)
  • neuroendocrine tumour
30
Q

what radioactive molecule is used for bone cancer therapy

A

radium-223

31
Q

what radioactive molecule is used for thyroid ablation

A

iodine-131

32
Q

what radioactive molecule is used for neuroendocrine tumour

A

lutetium-177

33
Q

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

A
34
Q

radioactive material can be spilled, or excreted by patients

A

w

35
Q

what are the 2 forms of radiation protection in nuclear medicine

A

gloves
syringe shields

36
Q

what material are the syringe shields made of

A

tungsten

37
Q

be aware that there are machines for contamination monitoring

A
38
Q

what properties are needed in a suitable isotope for diagnostic imaging

A
  • 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
39
Q

practice aseptic technique when working in the radiopharmacy

A
40
Q

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

A
  • 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
41
Q

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

A

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

42
Q

what is an elute

A

fluid used to wash through another substance to remove something

  • extracting one material from another by washing with a solvent
43
Q

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

A

significant levels of AL3+ ions

  • this can interfere with pharmaceutical synthesis
44
Q

allowable levels of parent radionuclides and alumina are set by regulations

A
45
Q

what does an alumina assessment test use

A

semiquantitative colorimetrical test with standard solution of Al3+

  • performed first elution, if generator is moved and required for some pharmaceuticals
46
Q

how do you test for radionuclide purity

A
  • 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
47
Q

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

A

0.15 uCi per mCi of Tc-99m

48
Q
A

RAD413 (24 decks)

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