Nuclear Medicine Flashcards
what is the main radionuclide used in nuclear medicine
Technetium (Tn)
how is technetium produced
Tn is produced in a generator from Molybdenum
what process is involved in Tn production
isomeric transition
what is isomeric transition
the production of a gamma ray without any change in atomic mass or number
In Nuclear Medicine, what does the generator consist of
the generator is a lead lined container with the parent radionuclide
how is the carrier free daughter eluted from the generator
this is done by passing a solvent like saline over the column
the eluate from a technetium generator is called?
sodium pertechnetate
what are some advantages of technetium
6hr half life
pure gamma emitter
easy to shield
combines well with other chemicals used in bone scans and renal imaging
non-toxic
what is molybdenum breakthrough
tiny amounts of molybdenum in solution of sodium pertechnetate
how is Mo breakthrough measured?
comparing eluate activity with and without Pb shielding
what is the main imaging device in NM
gamma camera
what is the gamma camera combined with
a collimator
what is the purpose of the collimator
the purpose of the collimator is to establish a relationship between the distribution of the isotope in the patient and the position at which the gamma rays are detected in the crystal
what is the gamma camera made of
sodium iodide doped with thalium
what effect does crystal thickness have on detector efficiency and spatial resolution
thicker the crystal, greater detector efficiency but lower spatial resolution
the amplitude of the signal detected in the PM tube is proportional to what?
the amplitude of the signal detected is proportional to the amount of light emitted
the light emitted is proportional to what?
the light emitted is proportional to the energy of the gamma ray
what is the Z pulse?
the summation of the PM tube outputs provides an energy, which is proportional to the total light produced in the crystal
where does the Zpulse go
to the pulse height analyser
what does the pulse height analyser do
PHA selects the isotope peak
what is the Z pulse proportional to
the z pulse is proportional to the total light output from one scintillation
what happens if z pulse is accepted
the positional circuitry is triggered to locate the gamma ray interaction
what is the PHA purpose
choice of photo peak
exclude compton scatter
what is the energy spectrum
the number of measured events with a given energy plotted as a function of energy
what is the goal of NM
To map the distribution of radiotracers
what renders gamma rays not useful for accurate measurement of radionuclide location?
when gamma rays scatter in the body first and change direction
what does the collimator design effect
spatial resolution
sensitivity
size of FOV
magnification/minification
what does spatial resolution depend on
diameter of holes in the collimator
length of holes
septal thickness
distance of pt from collimator surface
intrinsic resolution of detector
what is the point spread function (PSF)
a profile of measured counts as a function of position across a point source
line spread function
profile of measured counts as a function of position across a line source
what is the modulation transfer function
MTF is one way to more completely characterise the ability of a system to reproduce spatial frequencies
how is the MTF calculated
it is calculated as the fourier transform of the PSF or LSF and is a plot of the response of a system to different spatial frequencies
what is the relationship between resolution and sensitivity
if resolution is increased by a factor of 2, the sensitivity is decreased by a factor of 4
`what is the unit of radioactive decay?
Becquerel (in NM, we use MBq)
what has replaced lung perfusion with technetium
CT pulmonary angiography
what is the annual whole body dose limit for a member of the public
1mSv
what is the limit for the lens of the eye
15mSv
what is the whole body dose limit for a category B worker?
6mSv
How is Tc predominantly excreted?
via urine
what is encouraged to lower body dose?
frequent bladder emptying
what is the typical whole body dose in a bone scan
5mSv
