Gastric emptying on a rat model using planar μSPECT overlays on μCT scout images

Objectives Develop a translational quantitative method for solid-food gastric emptying (GE) studies in control and bariatric surgery rat models. Prior pre-clinical GE studies have not used solids and used clinical scanners and awake, restrained animals or animals anesthetized for study duration1,2,3. Our goal is to adapt a μCT/μSPECT to acquire co-registered 2D images for a high resolution GE study in rodents. As rats (and humans) primarily eat solid foods, we aim to show this improved method will harness the advantages of the pre-clinical imaging systems and minimize methodological effects on gastric motility.

Methods Rats were trained to eat ~5 gms of rat food in <10 min4. Study meal was soaked with 1 mCi (37 MBq) 99mTc sulfur colloid (SC). Under light isoflurane, planar images were acquired with a LEAP collimator, followed by a CT scout without moving the animal or bed. Process was repeated at 30 min intervals for 2 hrs. The animal woke between time points to reduce effects on GE caused by lack of movement or as a result of sustained anesthesia. Planar and scout image matrices were resized and aligned. ROIs were drawn over SC in the stomach at each time point. GE was calculated via decay corrected time activity curves.

Results Trained animals ate all food in <10 min and ingested the full dose of SC, providing optimal statistics for high resolution planar images and time-activity data. The matrix re-sizing and alignment of the CT scout provided successful co-registration with the scintigraphic image. The intermittent, short-duration anesthesia improved image quality and reduced motility impact.

Conclusions Solid-food method is valid in control rats;simulates current clinical protocols4; and adds high-resolution CT. It can be utilized in new studies of mechanisms responsible for weight loss and metabolic improvements of bariatric surgery. This method enhances data analysis for interpreting this research and is a quantitative, in vivo technique that does not involve animal sacrifice, the current standard for assessing solid food gastric emptying in rodents.

Research Support R01 DK093848-01 NIH/NIDDK