SPECT Flashcards
What does SPECT stand for?
Single proton emission computed tomography
In simple terms what is SPECT?
Tomographic imaging method that generates a 3D representation of radiopharmecutical distribution in the body
How are SPECT images acquired?
Using rotating gamma camera
What’s the main application of SPECT?
To give 3D distribution of radio pharmaceuticals
What is H-mode?
The 2 cameras are opposite each other
What is L-mode?
The 2 cameras are next to each other at a right angle
What is H and L modes used for?
H - Bone, oncology
L- cardiac
What is the matrix of SPECT?
64x64 or 128x128
How are spect studies acquired?
Using multiple projections at different angles
Over 360° around 128 projections are acquired - each covers roughly a 3° angle.
Why does raw data of SPECT not covey much info?
This is due to the imaging time for each projection only being 20 to 30 seconds
Typical planar you would have the patient sit for 10 minutes and get an image? Where as in SPECT it’s a lot faster.
The power of SPECT study comes from combining the information from each projection during processing.
Are SPECT patients given higher or lower activities?
Higher - to counteract the speed of the scan
What are the 2 methods of gamma camera acquisition? And what are they used for?
Step and shoot - brain
( 3-4 degrees per movement)
Continuous motion - lung
(Quicker - but at risk from motion artefact )
What’s a sinogram?
Its displayed each image angle and each activity positions of all the projections in one
What are the 2 methods for image reconstruction?
Filtered back projection
Iterative reconstruction
How does Filtered back projection work?
Each projection acquired consist of pixels which are the sum of counts along a line through he patient.
What is attenuation correction?
It corrects for absorption of gamma rays inside the body giving an apparently lower activity for deep tissues compared to more superficial ones.
FBP - AC (attenuation correction) has to be applied either before or after reconstruction.
Iterative methods - can be incorporated into the reconstructions
What is scatter correction?
Gamma rays can be scattered rather than absorbed by the body.
Scattered grey can become part of the image, but during the scattering process they lose energy and fall outside of the accepted energy window.
Gamma rays at high scatter angles even 30 to 45° only lose around 5 to 10 kv can still be included in the image
A simple way of applying scatter correction is to measure the scattered photons in a separate low activity window and subtracting contribution
