Quality Control Of MPI Flashcards
Energy peaking
Daily
Ensure camera is counting photons using the correct energy
Perform intrinsically- point source should be placed at least 1.5 m away from the surface of camera detector.
Perform extrinsically- a sheet source should be used
Either way, source should be enough to flood entire field of view (fov)
Repeat if for any reason camera is powered down during the day
No greater than a 2% energy window
Uniformity
Daily
Performed by exposure of detector surface to a radioactive source
Use Tc-99m point source of ~100-509 microcurie in less than or equal to 0.5 ml of volume
Point source placed in center and at a distance of about 5 use five FOV from detector surface. Acquisition performed for 2-5 million counts using a 20% energy window.
May use cobalt-57 sheet source
Sensitivity
Daily
Resolution and linearity
Weekly
Should be performed intrinsically using a radioactive point source and a test phantom
Should not be performed extrinsically because the patterns of the lead bars in the phantom and the lead septa of the collimator may interfere with one another causing artifacts
Center of rotation
Weekly
If a cor error occurs, may produce what has been characterized as a “doughnut”-shaped or “tuning fork” artifact
SPECT phantom evaluation
Quarterly
Plexiglas and water filled SPECT phantoms have attenuation and scattering properties similar to tissue
Common causes of artifacts
Soft tissue attenuation
Extracardiac activity
Patient motion
Irregular heart rate (R-R interval) with gated SPECT
To-201 energy peak
78 keV
Tc-99m energy peak
140 keV
Diaphragm attenuation
Decreased activity in inferior wall
Breast attenuation
Decreased activity in the anterior wall
Extracardiac activity
Increased liver or bowel activity, most common with Tc-99m
Encourage some type of exercise with pharmacologic stress to help stimulate liver clearance
Motion artifact
Always review raw image to ensure no motion
Overfiltering
Mask lesion or defect
Under filtering
Create lesion or defect
