Nuclear Med Flashcards
Regions of chamber response graph
(V vs current)
Recombination
Ion saturation
Proportional
Limited proportional
Geiger Muller
Use ion saturation so small variations in voltage don’t affect current
4 types of nuclear medicine acquisition and examples
Static / whole body - bone
Dynamic - renogram
Gated imaging - MUGA or gated MPS
Tomographic imaging - DaTSCAN
Parameters used in gamma camera protocol
Image matrix - higher, increased resolution but lower, more counts and reduced noise
Collimator - higher res, better resolution but higher sens, more counts
Imaging time - longer, reduced noise and more counts but patient might move
Energy window - narrower, less noise but less counts too
Examples of quantitative analysis in NM
Regions of interest: relative renal function DMSA, striatal uptake DaTSCAN
Time activity curve: uptake and drainage MAG3, LV ejection fraction MUGA
What tests are perfumed on eluate post elution
Radionuclide purity - molybdenum breakthrough test
Chemical purity - aluminium breakthrough test
Energy of PE event and compton scatter for Tc99m
140keV PE
~40keV is upper energy event
Why use NaI
Efficient absorber of gamma rays
Signal proportional to energy deposited in crystal
High output of photons per keV - good energy res
Lifetime of excited state is short so high count rate
Transparent to own light
Equation for energy of photoelectron
E = (hv-w)eV
(v is frequency and w is work function)
What is effective half life
Takes into account physics half life and biological half life
What is CoV
Opposite of SNR - 1/root n
What three things can collimator geometry effect
Sensitivity, resolution, magnification
What is the result of low radiochemical purity of Tc99m
Free pertechtenate - taken up by thyroid and stomach. Could mask something else or cause confusion - also irradiates organs that wouldn’t have been otherwise.
Advantages of SPECT
Depth information
Increases contrast - removes effect of overlying tissues
Can do hybrid imaging
Compensation with attenuation and scatter possible
What compensations can be applied to SPECT
Main compensations are for:
Attenuation (use map of change due to attenuation - counts in centre are boosted)
Scatter (photons scattered more than absorbed, some in photopeak is scatter. Can use multiple energy windows to estimate amount, best done using CT information)
Collimator resolution (model effect of collimator parameters and take this into account)
Two brain scans
DaTSCAN - function of neurons in striata
HMPAO - brain perfusion scan
Advantages and disadvantages of FBP and OSEM
FBP: + computationally quick and okay for visual interpretation. - streaking/noise, difficult to apply image compensators - not qualitative technique, only view images
OSEM + physics can be modelled into iterative process, use of subsets speeds up process - can be slow and relies on accurate models, optimal number of iterations varies
HMPAO brain scan
99mTc-HMPAO.
Crosses BBB and binds in proportion to regional cerebral perfusion
Doesn’t measure absolute flow: reference to unaffected area
Used in neurodegredation and epilepsy
DaTSCAN
123I - cocaine analogue
Binds to dopamine transporters in striata
Doperminergic neurons reduced in parkinsons and dementia with lewy-bodies - low signal on scan
Can use automated software to compare to norm - ROIs
Geometric mean equation
C1 = root (CA1 x CP1)
Takes into account posterior and anterior counts so depth shouldn’t matter as much
How is Mo99 generate?
Fission of U235 (which produces other products which could contaminate)