PET scan for evaluation lung nodules
Dear OncoLink "Ask The Experts,"
Peeyush Bhargava MD, Chief Fellow in the Ddepartment of Nuclear Medicine at the University of Pennsylvania, responds:
PET scan is a very good modality for the evaluation of the lung nodules. The CT scan can diagnose the lung nodules but it has very low sensitivity in identifying malignancy in the lung nodule. With PET scans, we get metabolic information and the sensitivity of diagnosing malignancy or cancer in a lung nodule is very high.
The test involves giving the patient an injection (intravenous/IV) of a radioactive glucose solution (FDG- Fluoro-deoxy Glucose). The patient is asked to fast overnight and after the injection, the patient typically waits for 45 to 60 minutes. During this time, we ask the patient to minimize physical activity and not to talk. After this, the images are acquired in the PET scanner with the patient lying on the camera table. The camera is doughnut shaped, similar to the CT scan, and it takes 45 to 60 minutes for the imaging. So, from the time of injection of the radioisotope or the glucose solution, the scan typically takes two hours.
The injection does not have any side effects and the patients don't feel any different after the injection. It is NOT a contrast dye and does NOT contain any iodine. PET scan is limited in evaluation of lesions, which are less than 1 cm. in size. Some centers also like to take second set of images, of the chest, to add more information in the differentiation of cancerous and non-cancerous nodules.
Figure 3 and 4 are good examples each of non-cancerous and cancerous nodule, respectively, in the lung and the value of PET in finding cancer in the lung nodules.
Figure 3 shows images of a patient with lung nodules. Images on the left are from the CT scan and show multiple nodules in left and right lung. The images on the right are from the PET scan and none of the lesions on the CT scan were active on the PET scan. This means that these nodules did not have any cancer in them. The two prominent black areas in the PET scan are the heart and the urinary bladder.
Figure 4 shows images from another patient with lung nodules. The image on the right is the CT scan which shows a spot (a nodule) in the right lung. Images on the left are from the PET scan. Different views are seen. The top image, the transverse view, corresponds to the CT image. The intense activity (black color) in the region of the lung nodule in the CT, (red arrow), confirms the presence of cancer in the lung nodule.