A Spinal Cord Window Chamber Model for In Vivo Longitudinal Multimodal Optical and Acoustic Imaging in a Murine Model

Abstract

In vivo and direct imaging of the murine spinal cord and its vasculature using multimodal (optical and acoustic) imaging techniques could significantly advance preclinical studies of the spinal cord. Such intrinsically high resolution and complementary imaging technologies could provide a powerful means of quantitatively monitoring changes in anatomy, structure, physiology and function of the living cord over time after traumatic injury, onset of disease, or therapeutic intervention. However, longitudinal in vivo imaging of the intact spinal cord in rodent models has been challenging, requiring repeated surgeries to expose the cord for imaging or sacrifice of animals at various time points for ex vivo tissue analysis. To address these limitations, we have developed an implantable spinal cord window chamber (SCWC) device and procedures in mice for repeated multimodal intravital microscopic imaging of the cord and its vasculature in situ. We present methodology for using our SCWC to achieve spatially co-registered optical-acoustic imaging performed serially for up to four weeks, without damaging the cord or induction of locomotor deficits in implanted animals. To demonstrate the feasibility, we used the SCWC model to study the response of the normal spinal cord vasculature to ionizing radiation over time using white light and fluorescence microscopy combined with optical coherence tomography (OCT) in vivo. In vivo power Doppler ultrasound and photoacoustics were used to directly visualize the cord and vascular structures and to measure hemoglobin oxygen saturation through the complete spinal cord, respectively. The model was also used for intravital imaging of spinal micrometastases resulting from primary brain tumor using fluorescence and bioluminescence imaging. Our SCWC model overcomes previous in vivo imaging challenges, and our data provide evidence of the broader utility of hybridized optical-acoustic imaging methods for obtaining multiparametric and rich imaging data sets, including over extended periods, for preclinical in vivo spinal cord research.

A Procedure for Implanting a Spinal Chamber for Longitudinal <em>In Vivo </em>Imaging of the Mouse Spinal Cord

“…Recently, another approach similar to our own using a polycarbonate chamber has been demonstrated 32 . The use of polycarbonate is advantageous since it is compatible with X-ray and acoustic imaging modalities, which is not the case for our stainless steel parts.…”

Intravital Imaging Techniques for Biomedical and Clinical Research

“…Early studies performed either single imaging sessions, or repeatedly exposed the cord with a surgery per imaging session . In response, chronic imaging windows were developed that allow repeated access to this tissue for intravital imaging for periods up to months …”

Intraoperative ultrasound in spine surgery: history, current applications, future developments

“…IoUS is now widely available and relatively inexpensive compared to other imaging modalities, but it suffers from major limitations such as the lack of orientation and panoramic view; to overcome these shortcomings, fusion of preoperative MRI and IoUS images has been proposed (44). In fact, the intrinsically high resolution of IoUS, associated with complementary imaging technologies, could provide a powerful means of quantitatively monitoring changes in anatomy, structure, physiology and function of the living cord over time after onset of disease, or therapeutic intervention (45). Protocols for fusion of IoUS images are the same used for intraoperative acquisition of CT images and their fusion on preoperative MRI: in both cases the imaging modality adopted intraoperatively serves to recalibrate the navigated MRI imaging, and by continuously updating the two modalities to adjust for artifacts and distortions due to technical issues or anatomic structures (i.e., adjacent bone, hemosiderin, etc.)…”