DCE-MRI of Orthotopic Pancreatic Tumor Xenografts: A Method to Assess Microvasculature in a Target Tumor Tissue

- An extensive network of highly disorganized and abnormal blood vessels supports tumor growth and metastasis. To assess this microvasculature, take an anesthetized tumor-bearing mouse and dilate its tail vein under a heat lamp. Intravenously insert a medical-grade microtubing assembly attached to a syringe carrying an appropriate MRI contrast agent. Secure the tail on a plastic board.

Place the mouse on a warm bed to regulate body temperature. Apply an orthogonally bent plastic board into the abdominal area and pull down to capture the tumor and secure it. Fix probes to monitor vital signs. Place a surface coil over the tumor region and slide the animal into a Dynamic Contrast-Enhanced Magnetic Resonance Imaging, or DCE-MRI scanner. Inject the contrast agent and initiate the scan.

Owing to the hyper permeable morphology of tumor vasculature, the introduction of contrast agents results in their rapid leakage and accumulation within the extracellular space of the tumor tissue. The surface coil captures variation in MR signal intensity emitted from the tissue, dependent on the distribution of contrast agents, and helps quantify the extent of tumor vasculature. In the following protocol, we will perform DCE-MRI of a mouse bearing an orthotopic pancreatic tumor xenograft.

- When the tumor reaches 5 to 7 millimeters in diameter, insert a sharp 30 gauge needle into one end of a micro polyethylene tube and a blunt 30 gauge needle tip into the other. Connect the 1-milliliter syringe containing freshly prepared MRI contrast agent to the blunt needle tip and slowly depress the plunger to fill the entire tube. Then, dilate the animal's tail veins under a heat lamp and use Kelly forceps to grab the shaft of the sharp 30 gauge needle. Carefully insert the needle into one of the dilated tail veins and tape both the tail and the tube onto a piece of 10 x 100 millimeter plastic to keep the tail straight.

Next, place the mouse supine in an animal bed equipped with circulating warm water to regulate the animal's body temperature during imaging. Insert a rectal temperature probe at this time as well. When the animal is in position, apply an orthogonally bent plastic board into the abdominal area, making sure the tumor is located behind the upper end of the board, and then pull the board down about 2 millimeters to ensure that the tumor is caught.

Firmly tape the board to the animal bed, then, tape a respiration pad transducer onto the chest area to monitor the animal's respiration during imaging. Now, place the surface coil on the top of the tumor region, securely taping it to the animal bed. Then, push the animal bed into the MR scanner until the tumor region is at the center of the volume coil. Apply T2 weighted MRI to locate the tumor, followed by T1 weighted MRI with various flip angles for T1 mapping.

Then, for the DCE-MRI imaging, apply T1 weighted MRI with a fixed flip angle continuously before, during, and after injection of the gadolinium-based MR contrast. Monitor the animal's breathing and body temperature continuously during the imaging. At the end of the imaging, remove the needle and other probes and place the animal under a heat lamp while softly massaging the lower abdominal area until the animal wakes.