SPECT Flashcards
What does SPECT stand for?
Single Photon Emission Computed Tomography
What kind of camera is used in SPECT?
a dual headed gamma camera
How much rotation is used for general SPECT scans?
360 degrees
How much rotation is used for cardiac SPECT scans?
180 degrees
What is the difference between SPECT and PET?
The main difference between SPECT and PET scans is the type of radiotracers used. While SPECT scans measure gamma rays, the decay of the radiotracers used with PET scans produce positrons.
What factors can corrupt image quality in SPECT?
photon attenuation
scatter
depth-dependent collimator (spatial resolution) response
What is used to compensate for bad image quality in SPECT?
Software corrections
What is important before starting the scan?
To identify and correct the alignment, an experimental center of rotation procedure is performed.
What processes are used for image reconstruction in SPECT?
Filtered back projection
Iterative reconstruction
(same as CT)
Why might iterative reconstruction be preferred to FBP?
Quantitatively more accurate as it can model various corrections including the collimator, scatter,
system geometry & detector resolution
A disadvantage of iterative recosntruction
Slow and requires a large computing power
What results in attenuation in SPECT images?
the interaction of photons via photoelectric absorption and Compton scatter within the patient results in attenuated projections
How to correct for attenuation of emitted photons?
Using a hybrid SPECT-CT system
Scatter results in…
loss of contrast and loss of quantitative accuracy
How is the scatter component estimated?
Using data acquired in auxiliary energy windows, and the Triple energy window (TEW) method
What does scatter correction require?
Scatter correction requires both estimating the scatter component of the projection data combined with a compensation method.
How long does each projection take with the gamma camera?
20 seconds
What is the full scan time?
20 minutes
What is a major factor in SPECT?
Quantum mottle
due to the low number of photons used to reconstruct each voxel
What is the major benefit of SPECT?
better contrast due to the elimination of overlapping structures. This leads to better lesion conspicuity
What is the most common use of SPECT CT
Myocardial perfusion imaging
What else can result in artefacts?
The SPECT scan and the CT scan do not occur at once. This can result in misregistration artifacts if any organ moves between scans
