The Use of Breathing Synchronized PET/CT Imaging In the Detection and Quantification of FDG Uptake in Lung Nodules

Positron emission tomography is now a clinically accepted imaging modality for the evaluation of pulmonary nodules as well as for the staging of patients with lung cancer. PET imaging with the radiotracer 18 Fluoro-deoxy-glucose (FDG) has a high accuracy for the differentiation between benign and malignant lung lesions and for the detection of nodal metastases. This is because malignant tumors are characterized by an increase in glucose metabolism as compared to most normal tissues. In clinical practice, PET images are interpreted visually or semiquantitatively, using a standardized uptake value (SUV). Previous studies have shown that SUV thresholds can be used with high accuracy to distinguish between benign and malignant lesions that exhibit increased uptake of FDG. In addition, the SUV is frequently used as a surrogate marker for the evaluation of a response to chemo- or radiation therapy. Unfortunately, the accuracy of SUV measurements may be affected by lesion motion during the image acquisition. This is a particular problem in PET imaging of the lung. Normal respiratory motion, and hence lesion motion, causes a smearing effect, whereby the concentration of radiotracer within a given lesion is spread out over a larger area. For the same reason small lesions and lesions with relatively low uptake of radiotracer may become undetectable during normal breathing (partial volume effect). PET images are acquired for several minutes, image acquisition during breath hold is therefore not an option for clinical scans. However recently published work from UCLA (Auerbach et al. J Nucl Med., February 2006) shows that 3 lesions per patient on average can be missed on shallow breathing scans compared to breath-hold CT scans. These lesions did not show any FDG uptake on clinical PET scans. The goal of this pilot study is to evaluate whether respiratory gating during PET image acquisition enables the detection of those lesions which are identified during the breath-hold CT scan.

Inclusion criteria

• Age ≥ 18 years old
• Patients must have at least one lung lesion or lung cancer on prior chest Xray or chest CT.
• Sign informed consent. Eligible patients should give their consent at the beginning of the clinical PET scan. Following clinical CT and PET scans, breathhold CT should follow. Then, these breath-hold CT images will be reviewed by one of the investigating physicians to determine if the patient qualifies for the study. If there is a small lesion (< 5 mm) gated PET images will be acquired.

Exclusion criteria

• Pregnant women are ineligible.
• Patients who are unable to follow breathing instructions either due to language difficulties or hearing impairment This will be determined by one of the consenting individuals when they approach the patient to ask for informed consent.
• Patients who are too ill to hold their breath.