Studying Metabolic Brain Connectivity Using 2-Deoxy-2-[¹⁸F]Fluoro-D-Glucose Dynamic Positron Emission Tomography at the Single-subject Level

We're investigating how an intracerebral hemorrhage affects metabolic brain connectivity, which reflects the relationships between metabolic activities, like glucose uptake, across brain regions. Changes in these networks could explain the heightened risk for developing brain disorders like epilepsy, providing insight into brain dysfunction and recovery. Currently, the analysis of metabolic brain connectivity is based on static PET images, and the connectivity is calculated for a group of subjects, rather than within the single subject.

The use of dynamic PET images allows us to extract time-activity curves for each volume of interest per subject, further allowing us to calculate correlation-based connectivity on a single subject level. This facilitates tracking changes in metabolic brain connectivity within a subject over time. As a core facility, Infinity supports researchers from different application fields.

These researchers work with a broad range of animal models, going from stroke model to different kind of oncology models. With these models, the researchers evaluate diseases and also evaluate new treatment strategies. To begin, turn the anesthetized animal onto its left or right side, and use a heating lamp to warm its tail, inducing vasodilation for tracer injection.

Using a needle holder, break off the shaft of a 30-gauge needle and insert one to two millimeters of its backend into a BTPE-10 tubing. Fill a one-milliliter insulin syringe with saline and insert the needle tip three to five millimeters into the BTPE-10 tubing. Pre-fill the tubing with saline from the filled syringe and keep the saline syringe connected to the tubing afterwards.

Next, use a compress or paper tissue to thoroughly clean the animal's tail with ethanol for site disinfection. Then, remove the heating lamp. Insert the needle tip of the BTPE-10 tubing into a lateral tail vein.

Observe blood entering the tubing when the plunger is pulled back. Note the absence of resistance during injection and ensure no subcutaneous bleb forms at the injection site. If successful, secure the needle with a drop of instant glue at the penetration site and tape the tubing to the tail.

Insert the needle of the BTPE-10 tubing already prefilled with medetomidine two to three millimeters subcutaneously between the shoulder blades. Secure the needle with a drop of instant glue at the penetration site, and gently tape the tubing to the animal's back. To position the animal and prepare the scanner bed, place a pressure sensor and paper tissues on the bed.

Carefully transfer the animal onto the scanner bed, ensuring that the medetomidine line and tail vein catheter remains secure. Position the animal's head as straight as possible using a nose cone if necessary, and secure the head with tape once aligned properly. Now, turn on the heating pad to warm the animal.

Verify that the respiratory rate monitoring system is functioning correctly, adjusting the pressure sensor positioning as necessary. Before initiating the PET scan, confirm proper placement in the vein by aspirating and injecting a small amount of saline as described previously. Then, replace the saline syringe with the radiotracer syringe, ensuring the needle doesn't puncture the PE tubing.

Start the scan using the scanner software. Once the acquisition begins, inject the radio tracer as a bolus over approximately 0.5 to two seconds. Immediately replace the empty radio tracer syringe with the saline syringe, and flush the PE tubing with 0.1 milliliters of saline.

Use a tissue to catch any drops of radio tracer that may escape during the syringe swap. Reconstruct the acquired data into 30 two-minute timeframes using the dynamic reconstruction settings. To begin, obtain the PET data of the rat brain.

Load the DICOM file of the dynamic reconstruction into the software by dragging and dropping the file into the canvas. Use the general image display controls in the top right to navigate through slices and timeframes and adjust the color bar. If necessary, adjust the image orientation to standard orientation using the Change Input Image Orientation button on the right sidebar.

To load the reference image, click the Select normalization template button. Choose the Rat FDG W.Schiffer template as the reference image. Click the Input matching, Input Adjust manually button in the right sidebar to match the input image to the template.

Drag and rotate the input image to roughly align with the template. Ensure that rat is selected as the species and the registration method is set to deform. And click the Match Current button to proceed to the next sub-page.

On the Matching Results sub-page, verify the alignment result and adjust manually, if necessary. Click Apply Current Transformation to All to ensure all timeframes match the template. Click the green VOIs button to proceed to the next step.

In the Template tab, Select Px Rat W.Schiffer in the Atlas tab or load an atlas to choose the desired volumes. To apply the selected volumes of interest, click the Outline button at the bottom. Then, click the button above the Template tab to calculate time-activity curves, or TACs.

Send the TACs to PKIN tools for further analysis. In the bottom right of the software interface, select TACs for the display type to visualize the time-activity curves in kilo-becquerels per milliliter for the previously selected volumes of interest. Right-click on the canvas displaying the TACs and select value table of visible curves.

Copy the value table to a spreadsheet for further analysis. High standard uptake values were observed in the animal's eyes in both the time-weighted average images and the single two-minute timeframe, with color intensity ranging from blue to red.