Imaging description

The CT in an integrated PET/CT scanner is optimized for PET imaging. The CT is converted to provide attenuation correction and to lend structural data to the fused PET/CT image. Accurate co-registration between the CT and PET images is optimal for both attenuation correction and fusion. The CT images are generally acquired at mid-inspiration and PET images are acquired during quiet respiration. Careful patient coaching and cooperation is required to prevent a mismatch between the two datasets. Pulmonary nodules, particularly in the lung bases, have modest motion even with quiet breathing. The net result is that “hot spot” on the PET image does not match the lung nodule on the CT image. Review of the CT slices above and below the hot focus allows confident identification of this artifact (Figure 75.1). The frequency of misregistration is lessened when PET/CT is performed on scanners with six or more rows of CT detectors [1, 2].

Importance

Incorrect localization of a pulmonary FDG “hot spot” in the lungs could have several adverse consequences. At a minimum, the error is confusing, since there will be no anatomic correlate for the foci of increased FDG uptake in the lungs on CT. Worse, a patient may be incorrectly assumed to have low FDG uptake in the pulmonary nodule so that the nodule is not reported as having high malignant potential.