PET/CT Artifacts
As with all imaging modalities, there are several artifacts inherent to PET/CT imaging that are commonly encountered. Familiarity with their appearance and their limitations on interpretation are required.
Beam Hardening Artifact:
This is classically seen as streak artifact traversing the CT images, usually resulting from positioning the patient’s arms alongside the body within the gantry (in cases where the patient is unable to raise the arms for proper positioning).
Diaphragmatic Mismatch Artifacts:
Mismatch of the position of the diaphragm between CT and PET imaging can result in curvilinear photopenic defects at both lung bases (“Banana Sign”). In the event that a lung nodule or other pathology is located in this region, its metabolic activity may be grossly underestimated.
Diaphragmatic mismatch can also result in elongated soft tissue projecting within the lung bases (“Double Diaphragm Sign” or “Mushroom Effect”), limiting evaluation of these areas.
Linear Hand Motion Artifact:
When a patient is imaged with his arms at his sides, it is not uncommon for motion of the fingers or hands to result in a significant linear photopenic artifact extending horizontally across the pelvis, limiting PET evaluation of structures in this region.
Attenuation Correction (AC) Artifacts:
On occasion (typically in older PET/CT machines), attenuation correction of PET images can result in falsely elevated metabolic activity in regions of high CT density (e.g. metallic devices, oral contrast, calcification). In such cases, these areas must be reviewed on the NAC (non-attenuation correction) images. If these regions are not also hypermetabolic on the NAC images, then their apparent increased FDG-uptake on the AC images is artifactual (addressed in detail, here).
Differing Fields of View (FOV):
The PET and CT components of the hybrid machine have different fields of view. Typically, the PET field of view is 70 cm, while the CT field of view is only 50 cm.
This difference in fields of view results in several effects:
- Portions of the body (typically the arms, if scanned in the down position), may only be seen on the PET images, without CT image correlation.
- The lack of co-registered CT images may result in artifactually decreased SUV values for lesions imaged only on the PET study (as there are no CT images for attenuation correction).
- The truncated CT images can cause streak artifact at the margin of the CT images (“Truncation Artifact”).
