FDG Based PET/CT Scan: A Method of Using Radiotracer for Non-invasive Imaging of Tumor Metabolism

— Tumor cells show high glycolic activity. Radio tracers such as F18 fluorodeoxyglucose– FDG– are glucose analogs used for observing cancerous tissues. First, measure the radioactivity decay of the FDG solution in a dose calibrator. Draw FDG solution in an insulin syringe and place in a lead syringe holder. Place a mouse at a warm temperature, to prevent brown adipose tissue activation. Activated brown adipose tissue leads to more FDG uptake. Anesthetize the mouse for two minutes and transfer it to a restrainer. Prick the tail and measure blood glucose level. Hyperglycemia can lead to reduced uptake of FDG by the lungs.

Under warm conditions, sanitize and dilate the tail vein of the mouse. Inject FDG solution. Transfer the mouse inside the anesthetic chamber for systemic FDG distribution. Inside the cancer cell, hexokinase converts FDG to FDG 6 phosphate, which can't metabolize further, thus accumulates inside the cell. Secure the mouse in supine position under anesthesia in an imaging chamber. Perform PET/CT imaging. After imaging, let the mouse recover in the cage. Positron emission from F18 is recorded during the PET scan, while the CT scan shows X-ray images of the tissues. The following protocol shows FDG PET/CT imaging of metabolically active lung cancer models.

— Caution. Use protective equipment and follow all applicable regulatory procedures when handling radioactivity. Begin by warming the cage of mice to be imaged at 37 degrees Celsius, for the hour prior to Fluorine18 labeled fluorodeoxyglucose injection. This reduces the brown fat consumption of the tracer. Weigh the first mouse and record it's weight. After anesthetizing the mouse using an institutionally approved method, test the depth of anesthesia by pinching the toe. If no response is seen, continue the procedure by applying ophthalmic ointment to the eyes to prevent any dryness during the anesthesia. Carefully, dilute Fluorine18 labeled fluorodeoxyglucose, which has a 109 minute radioactive half life, in sterile saline at an adjusted decay corrected injection concentration of 70 to 75 microcurie per 100 microliters.

Then, draw 100 microliters into an insulin syringe with a 28 gauge needle and measure the radioactivity dose, using a dose calibrator. Record the measurement and time of measurement to determine the decay correction. Place the syringe in a lead syringe holder. To inject, first warm the tail for 1 to 2 minutes with a gauze soaked in warm water. And then, wipe with 70% isopropanol to dilate the tail vein, just prior to the injection. Administer the entire volume in the syringe with a bolus injection via the lateral tail vein and record the time of injection. Then, measure the remaining dose in the syringe using the dose calibrator and record the measurement and time.

Finally, place the injected mouse in the anesthesia chamber with 1.5 to 2% isoflurane at 37 degrees Celsius to allow the probe to be distributed via the mouse's systemic circulation for one hour prior to the PET scan. After one hour place the first mouse in an imaging chamber set at 37 degrees Celsius, under nose cone isoflurane anesthesia and secure its limbs in place with medical tape in the supine position. Place the imaging chamber in the PET/CT scanner and acquire the PET and CT scans as described in the PET/CT scanner manual. After the PET/CT is completed, remove the mouse from the imaging chamber and allow it to recover in its cage.