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

Overview

This article describes multimodality imaging of cancerous tissues with PET and CT diagnostic imaging by using a radiotracer ¹⁸F-FDG. Cancerous tissue with high glycolytic activity uptakes more ¹⁸F-FDG.

Protocol

All procedures involving animals have been reviewed by the local institutional animal care committee and the JoVE veterinary review board.

1.¹⁸F-FDG PET and CT Imaging in Mice

CAUTION: Use protective equipment when handling radioactivity. Follow all applicable regulatory procedures when handling radioactivity.

1. Place the cage with the mice to be imaged on a warm bed at 37 °C 1 h prior to the ¹⁸F-FDG injection to reduce the brown fat consumption of ¹⁸F-FDG.
   NOTE: Fasting the mice for 4 - 16 h can help reduce the myocardial consumption of ¹⁸F-FDG.
2. Weigh the mouse and record its weight.
3. Anesthetize the mouse using 2 - 3% isoflurane in oxygen at 0.5 - 2 L/min for 2 - 3 min using an anesthesia chamber kept at 37 °C. Ensure that mouse has been anesthetized by pinching the toe; no reaction will be observed if the mouse has been anesthetized. Apply ophthalmic ointment to the eyes to prevent any dryness during the anesthesia.
4. Dilute ¹⁸F-FDG (109 min radioactive half-life) in sterile saline at an adjusted decay-corrected injection concentration of 70 - 75 µCi/100 µL.
   NOTE: Follow the PET scanner manufacturer's recommended ¹⁸F dose for optimal scanner imaging.
5. Draw 70 - 75 µCi with an insulin syringe with a 28 G needle, measure the radioactivity dose using a dose calibrator, and record the measurement and time. Place the syringe in a lead syringe holder.
   NOTE: The amount of ¹⁸F-FDG radioactivity in each dose is measured with a dose calibrator, which is calibrated against a standard reference material, such as cesium-137, according to the manufacturer's protocols. The time of the reading is also recorded to determine the decay correction.
6. Prick the distal end of the mouse tail and measure the mouse's blood glucose with a glucometer.
7. Warm the tail for 1 - 2 min with a gauze soaked in warm water. Wipe the tail with 70% isopropanol to dilate the tail vein just prior to the injection. Administer 100 µL of ¹⁸F-FDG (the entire volume in the syringe) with a bolus injection via the lateral tail vein and record the time of injection. Measure the remaining dose in the syringe using the dose calibrator and record the measurement and time.
   NOTE: There will be some amount of probe left in the syringe. The use of insulin syringes is preferred over syringes connected to needles via Luer locks due to the decreased amount of the dose trapped in the syringe/needle after the injection has been administered.
8. Place the injected mouse in the anesthesia chamber kept under 1.5 - 2% isoflurane at 37 °C to allow the probe to be distributed via the mouse's systemic circulation for 1 h prior to the PET scan.
   NOTE: It might be beneficial to void the bladder prior to the scanning to allow for an easier ¹⁸F-FDG PET visualization of the tumors implanted in the lower flanks of the mouse.
9. After 1 h, place the mouse in an imaging chamber under nose-cone isoflurane anesthesia and at 37 °C, and secure its limbs in place with medical tape in a supine position.
10. Place the imaging chamber in the PET/CT scanner.
11. Acquire the PET and CT scans as described in the PET/CT scanner manual.
    NOTE: The PET images are acquired for 600 s with an energy window of 150 - 650 keV, reconstructed using maximum-likelihood expectation maximization with corrections for photon attenuation, detector normalization, and radioisotope decay (a scatter correction was not applied). The CT images are acquired in a continuous mode for 50 s using a 50 kVp, 200 µA X-ray source and a flat-panel detector, and they are reconstructed using the Feldkamp algorithm.
12. After the PET/CT is completed, remove the mouse from the imaging chamber and allow it to recover in its cage.

Materials

Name	Company	Catalog Number	Comments
G8 PET/CT	Perkin Elmer	CLS139564	Used for 18F-FDG PET and CT imaging of mice