Article sheds light on PET-CT problems
Standard helical PET-CT cardiac imaging produces false-positives 40 percent of the time, according to findings published this month in the Journal of Nuclear Medicine. Most of the errors, however, can be identified and corrected before inappropriate treatment.

The authors said that the dual modality continues to expand despite the recognized problems with artifacts and false-positives from misregistration of PET and CT attenuation correction data.

Although fused images are corrected by cine CT PET protocols or commercial software, investigators said, the frequency and the degree to which the defects could be corrected remained unknown prior to this study conducted at the University of Texas in Houston. 

Of 259 consecutive patients who had diagnostic PET-CT perfusion imaging, misregistration of helical PET-CT images led to artifactual PET defects in 103 (40 percent). The defects were moderate or severe in 59 cases but corrected in each instance by cine or shifted cine PET-CT imaging.

Quantitative misregistration was a strong predictor of artifact size and severity, representing a "real" defect.

The researchers objectively measured misregistration of PET-CT fusion images in millimeters and correlated the findings with the size and severity of the associated defect. They defined misregistration artifacts as PET defects with corresponding misregistration on helical PET-CT fusion images that resolved after correct coregistration. They established this by using a repeat CT scan, cine CT averaged attenuation during normal breathing, or shifted cine CT data that coregistered with PET data.

The authors acknowledged that the lack of coronary arteriography to document the absence of stenosis could be viewed as a limitation of their study. However, they argued that arteriography is not justified for a defect in a region of PET-CT misregistration that disappears after reconstruction using correctly coregistered CT attenuation data.