Introduction While the embryonic zebrafish has been widely used for basic cardiac research the adult zebrafish has been used less partly due to difficulties in evaluating the hearts structure and function in-vivo. Currently available cardiac imaging techniques are limited by the hearts small size and rapid rate. Successful development of cardiac MRI for the adult zebrafish could have significant scientific, ethical and economic benefits for cardiac research.
Methods We have developed a novel magnetic resonance imaging (MRI) scanning system, designed to study cardiac structure and function in the live adult zebrafish. This has involved the development of an integrated zebrafish life support and monitoring system with an internal custom MRI solenoid microimaging coil – the ‘flow cell’ (Figure 1). Zebrafish are anesthetised (MS222) and held in position within a flow chamber that intersects the MRI coil for scanning (internal diameter 6.9 mm, SNR >130). Water flows through the system via a non-pulsatile pump from outside the scanner room (2.00 ml min–1). Water temperature and oxygenation of the flow cell is monitored using in line MRI compatible optical sensors (FirestingO2, PyroScience) to provide continuous monitoring of the fish while it is in the scanner.
Scanning is performed on a 7T preclinical MRI scanner (Bruker BioSpec). FLASH and RARE based sequences are used for locator and structural information, while functional images are obtained using a retrospective cardiac gated gradient echo imaging sequence (IntragateFLASH). All scans are at <80μm resolution in plane with individual scan times typically <10 mins. The Intragate sequence also enables a pseudo-ECG signal to be extracted from the MRI data in order to reconstruct “gated” MRI images.
Results We have created a working flow cell for obtaining cardiac MRI images from zebrafish (Figure 2). Zebrafish scanned under our current in vivo protocol have all successfully recovered from the experimental procedure (up to 40 mins) with no obvious signs of distress or injury allowing for longitudinal imaging studies.
Conclusion Our aim is to deliver in vivo MRI images with spatial and temporal quality matching rodent MRI. While we have already met with significant success generating anatomical images further refinement is required, in terms of image contrast, quality and reproducibility, before deployment in full cardiac studies.
Acknowledgement This work is funded by a BHF New Horizons grant.
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