NUC MED Flashcards
counts/pixel in SPECT and PET
100 counts/pixel in SPECT
1000/pixel in PET
1000 photons/mm2 is reasonable
secular equilibrium
long lived parent
parent and daugther activities meet to be equal
transient equilibrium
parent is short lived but still longer half life than daughter
-activities only proportional to each other
when does transient or secular equilibrium occur?
after 4 daughter half lives
electron capture nuclides in Nuc Med
67 Ga, III In, 123I
regulatory limit for 99Mo breathrough
5.5 kBq Mo/37 MBq 99mTc
nuc med matrix size
128x128, 1 byte/pixel, 1/64 MB
what products are carrier free?
neutron activation products are not carrier free. Cyclotron and fission products are
number of LORs in PET
n(n-1)
n is number of detectors
gamma camera system sensitivity
105 counts/MBq
PET spatial resolution
3 mm FWHM
SPECT spatial resolution
8 mm FWHM
PET effective dose
8 mSv
PET scan time
2-3 min at each detector position
uses 5 positions to cover body
system spatial resolution
square root of (intrinsic res. ^2 + collimator res. ^2)
collimator res is limiting
99mTc effective dose
4 mSv
for what organs is nuc med dose high?
thyroid, spleen, gallbladder, liver
PET administered 18F activity
600 MBq
scan time of SPECT
60-120 images
radionuclides used for therapy
P32
Sr89
Y90
I131
what causes ring artifact in SPECT
non-uniformity
energy windows for gamma cameras
-low energy counts = compton
-mi energy is from backscatter out of detector or patient
-max scatter is from backscatter in detector
-multiple scattered photons have low E
remember backscatter IN detector = max
when is NRC notified wrt uninetended dose
uninetended radiation exceeds 50 mSv or 500 mGy to an organ
typical nuc med activity administered to patient
22 mCi or 700 MBq
isomeric transition
gamma rays emitted
isobar
nuclides with same mass number
geometric efficiency for single hole collimator
1/b^2
b is distance from source to collimator
what has low acoustic impedance
air and lung
-low density and low sound velocity
what does reflection/transmission depend on?
differences in acoustic impedance
what are sound waves formed from
electrical energy converted into mechanical energy
impedance formula
Z (Rayls) = density * sound velocity
compressibility vs sound velocity
high compressability (ie bone) = high sound velocity
thickness of matching later
1/4 wavelength of sound in that material
velocity of sound in air
343 m/s
US to kill tissue?
high intensity US kills through ablation
US frequency range
> 20 kHz
1-20 MHz used in clinic
when does scattering occur
when US encounters objects that are smaller than US wavelength
what does US wavelength depend on
material compressability
velocity of sound in tissue
1540 m/s
axial resolution
1/2 the pulse length
typically = wavelenght
specular reflection
from large smooth surface
non-specular reflection
from rough surface
doesn’t contribute to image
attenuation rate
0.5 dB/cm/MHz
fluids have low attenuation
lung and bone have high attenuation
refraction
f stay sams, lamba and v change per Snell’s law,
v1/v2=sin theta1/sintheta2
material of transducer
PZT
impedance of transducer
intermediate between transducer and tissue
square root (ZtransZtiss)
trade-off between high and low frequency
low frequency = better penetration
high frequency= better axial resolution
dB
10% is 10 dB, 1% is 20dB, 0.1% is -30 dB
bladder and cysts in US
appear as black
have almost no scatter
width and height of individual elements in array
width = lambda/2
height = a few mm
transducer crystal thickness
lambda/2
issue with side lobes
yields artifacts
Side lobe artifact occurs when the beam of an off-axis side lobe encounters a structure and returns this off-axis object as coming from the main beam. This creates a duplicate structure on the screen but in a different area.
what organs have many scattering sites
-kidney, pancreas, spleen, liver
focal depth
pt at which beam is at its narrowest
range of frquency of audible sound
15 Hz - 20 kHz
how to produce short pulses
use blocks of damping material
focal zone
near field
region where US is narrow
-don’t use far zone for imaging
is pulsed or continuous US used in clinic
pulsed
size of PZT
<lambda/2 in width and a few mm high
what does Doppler US measure
change in frequency
not velocity
reverbation
large number of reflected waves, which can be perceived as continuous sound
US contrast agents
microbubbles
how to improve lateral resolution
reduce frame rate
-this also reduces temporal resolution
increase pulse repetition frequency to increase line density
-this reduces listening interval and thus reduces imaging depth
pulse repetition frequency to avoid aliasing
PRF> 2 X highest doppler delta f
how to improve axial resolution
increase transducer frequency to reduce pulse length
power doppler
more sensitive than regular doppler
-shows only magnitude, not direction
show US artifacts in image
US artifacts in image
US artifacts in image
Anger camera max non-uniformity
5%
intrinsic vs extrinsic
intrinsic looks at imager part only
extrinsic looks at total image, realistic conditions
parrallel hole collimator resolution
degraded with increasing distance from collimator
what scintillator is in Anger camera
NaI
how many counts in Anger camera
500,000
intrinsic resolution of anger camera
3-5 mm
formula for system resolution
square root (intrinsic res^2+ colli res^2)
colli is limiting
types of SPECT collimators
-parrallel hole (constant FOV)
-converging (magnified, FOV~ 1/distance)
-diverging (FOV increases with distance)
-pinhole (magnify and inver)
isotope vs isotone
isotoPe= same number of protons
isotoNe= same number of neutrons
how far does an alpha particle travel
<0.1 mm
thickness of PET detector
20-30 mm thick to efficiently detect 0.511 MeV photons
how much more sensitive is 3D PET vs 2D PET?
3D PET is 6x more sensitive than 2D PET
Equation for cumulative activity
1.44Aot1/2
S factor
absorbed dose in target organ/ unit cumulative activity in source organ
S increases as the size of the organ decreases
MIRD
medical internal radiation dose
-framework for assessing absorbed dose to organs, tissue, etc
99Mo breakthrough limit
5.5 kBq 99Mo per 37 MBq Tc 99m
-when you give it to the patient. Have to account for decay- 99Mo decays a lot slower than 99Tc so you would have to be below this limit at time of elution to be within the limit at time of treatment
ALI
annual limit on intake
-activity of radionuclide that will deliver effective dose of 20 mSv during 50 yrs after radionuclide taken in by someone over 20 yo or for period starting at intake and ending at 70 for someone < 18
does resolution degrade with depth in SPECT?
yes
holes see more photons
equation for nuc med integral uniformity
100%*(max counts - min counts)/(max counts + min counts)
What does theranostic mean
rad nuclide used for therapy and diangostics
what does Ae^-1t + Be^-bt look like on a semi-log plot
2 straight line segments
efficiency of counting system
(Cradionuclide- Cbackground)/Aradionuclode *100%
