Introduction
The significance of artifacts in SPECT imaging has been recognized progressively by nuclear physicians in recent years. Since the last discussions we .had 3 years ago on this subject at a Nuclear Medicine Symposium in Seoul several studies on the ASPECT artifacts and quality control measures were ~publisheed´-". The studies on SPECT artifacts have been mainly on cardiac SPECT studies. This trend is relevant because a false positive stress cardiac
PECT result may lead to an unneccessary, expen´ve and invasive procedure.
A brief review on principal source of SPECT ifacts along with summary on recent findings will the scope of this chapter.
Cause of Artifacts
1. Quality Control Problem in Instrumentation
ld Uniformity : Non-uniform field is a frequent -;use of artifacts in SPECT. Artifact caused by non
? orm detector field may produce findings that
? mass lesion, or produce streak or ring mark
If one of multiple detectors has non-uniform field will cause various forms of artifacts which ´may
17 manifested as poor quality image.
´When non-uniform field of a detector has a focal
gh count mechanism such as a short-circuit in a ~, cuit board this may cause streak or hot spots ~: i±act(Fig. 1).
Non-uniform field may be caused by various reaNns including ; weary or worn PM tube(s),
oupled PM tube(s), weary circuit board, damaged ´llimator(s), weary detector crystal etc.
earity and Center of Rotation : The quality of
images will be degraded by distorted linearity or by error in center of rotation (COR).
Minor errors, or problem in only one of multidetector system, however, may not be recognizable. Good news is current state of art SPECT systems do have build-in automatic correction mechanism thus, as long as one adheres manufacturer´s directions of quality control procedure the COR and linearity will not become cause of SPECT artifacts.
Collimators : One of limitations inherent to SPECT system is low weight bearing capacity. Not many systems are furnished with "true high energy" collimators. SPECT imaging of I -131 performed using a medium energy collimators may cause artifacts from septal penetration and scatter.
Even Tc-99m photon may produce scatter artifact with low energry collimator if a focal activity source contains too high activity.
Damaged or "leaky" collimators) will cause field uniformity problem which can be corrected only by replacement of the collimator(s).
Imager, Image Formatter, and Printer : Printer or imagers respond to operators commands for intensity, contrast, and scale etc. Thus, majority of printing artifacts are due to operator´s neglegence. However, defective printer or imager can create significant image artifacts such as uneven image intensity, artifactitious defects, etc.
2. Attenuation and Adjacent High Count
Organ
Attenuation Artifacts : Attenuation artifacts in SPECT are most commonly seen in cardiac studies. Effect of diaphragm causing inferior wall defect or infero-septal wall defect is almost tule in male patients"´.
It has been our hope that this artifacts could be - minimized by use of Tc-99m-labeled perfusion agents instead of T1-201. When Tc-99m-Hexa-MIBI concentration in the liver equals or supasses that of
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