Adaptable 3D-Printed MRI Cradle for Ferret Brain Magnetic Resonance Imaging with Integrated Anesthesia and Commercial Coil Support

Introduction: : Species-specific cradles are an essential tool for animal imaging by standardizing the process and satisfying the needs and challenges that each species presents. 3D printed custom-made cradles have already been used as a cost-effective solution for animal models ranging from rodents to marmosets. However, there is not an open source or commercially available solution for ferret brain imaging. The ferret is the smallest gyrencephalic animal and has a larger white matter to grey matter ratio compared to its rodent counterpart. Although the ferret’s brain is a promising MR imaging model, their anatomy and physiology also come with some challenges to make the imaging process suitable. Ferret sex differences in body and brain size – males are ~1.5 times as large as females – present a challenge to studies that seek to include both sexes in their experimental design or that explicitly study sexual dimorphisms (See Fig.1). In this abstract, we highlight our current female ferret physical setup that incorporates a commercial rat cardiac coil adapted with custom made anesthesia device and their adaption of the design to accommodate the male ferret. Our new cradle model integrates an anesthesia piece that can slide and rotate (see Fig.2) to adapt for the largest and smallest subject housed in-lab minimizing preparation time and consequently animal anesthesia time for both male and female ferrets for future imaging studies. Our cradle proposes a modular design using a lock-and-twist mechanism to assemble (see Fig.2), an alternative to the prong-style connections commonly used in available cradle designs.

Materials and

Methods: : Requirements were determined based on the size of the largest ferret, available MRI equipment, and feedback from the veterinary staff. Physiological measurements of the ferrets revealed that the female cohort are smaller than the males, most notably in weight (94% smaller; p< 0.05), body diameter (41% smaller, p< 0.05), head width (34% smaller, p< 0.05), and body length (28% smaller)(see Fig.1). The Computer Aided Design model was created on SolidWorks and printed with Fused Deposition Modeling for fast prototyping and final product creation, using PLA filament. The cradle was used for the imaging of four male ferrets with the veterinary staff setting up the animal in place and monitoring its state as usual. Four females were imaged using the previous setup to compare the system performance. T2 Imaging was conducted using Rapid Acquisition with Refocusing Echoes (RARE) sequence to obtain multiple echo times at 0.4x0.4x0.6 mm resolution. A single echo time of TE=35ms was used for all subsequent processing for this study. Three 3x3x3 voxel size regions of interest were created in white matter, grey matter, and noise (in the nostril no tissue signals existed). An SNR analysis was then performed on the 3rd T2 echo weighted image for each ferret to evaluate the performance of the system in white matter and grey matter as shown in Fig.3. Male and female SNR was then compared and visualized in a boxplot (see Fig.3). An unpaired t-test was then performed to compare the SNR from the female ferret setup compared to the male cradle setup.

Results, Conclusions, and Discussions:: Our prototype was able to integrate with a rat head surface receiving coil (placed ventrally to allow for supine imaging) and fit in the center of our 86 mm transmitting coil. The SNR comparison from the in-vivo imaging between the new cradle and the previous female setup show that there is no significant difference (p >0.05). We concluded that the performance of the new setup is suitable to image male ferrets. We have worked closely with our veterinary staff to improve our MR setup for ferret imaging, which included making it feasible for imaging male ferrets, improving integration of anesthesia placement, integration of a commercially available surface coil to fit closely to the head, and adjustable locations for placing physiological monitoring. We aim to apply the cradle to longitudinal imaging of the ferret and evaluate how well the custom cradle adapts to age-related changes in the ferret (e.g. weight and body size fluctuations). The design of the cradle will be made publicly available, and its modular features facilitate the adaptation to different imaging applications.

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