IRM et la TEP dans les modèles de souris de l'infarctus du myocarde
Summary
We describe how to perform MRI and PET imaging of the mouse heart. The protocol is tailored to assess treatment efficacy in models of myocardial infarction and heart failure.
Abstract
L'infarctus du myocarde est une des principales causes de décès dans le monde occidental. La similitude du cœur de la souris pour le cœur humain en a fait un modèle idéal pour tester de nouvelles stratégies thérapeutiques.
Dans l'imagerie par résonance magnétique in vivo (IRM) donne une vue imprenable sur le cœur de manière non invasive avec le détail anatomique claire, qui peut être utilisé pour l'évaluation fonctionnelle précise. Les agents de contraste peuvent fournir des mesures de base de la viabilité des tissus, mais ceux-ci ne sont pas spécifiques. Tomographie par émission de positons (TEP) est une technique complémentaire qui est hautement spécifique pour l'imagerie moléculaire, mais il lui manque le détail anatomique de l'IRM. Utilisés ensemble, ces techniques offrent un outil sensible, spécifique et quantitative pour l'évaluation du cœur dans la maladie et la récupération après le traitement.
Dans cet article, nous expliquons comment ces méthodes sont effectuées dans des modèles murins de l'infarctus du myocarde aigu. Les procédures décrites havant ont été conçus pour l'évaluation des traitements médicamenteux de protection putatifs. Nous avons utilisé l'IRM pour mesurer la fonction systolique et la taille de l'infarctus avec gadolinium en retard, et la TEP avec FDG (FDG) pour évaluer la fonction métabolique dans la région infarcie. Le document met l'accent sur les aspects pratiques tels que la planification de la tranche, ouverture de porte précis, l'administration de médicaments, la segmentation d'images, et recalage multimodal. Les méthodes présentées ici obtenir une bonne répétabilité et la précision de maintenir un débit élevé.
Introduction
In order to measure the efficacy of new treatment strategies for myocardial infarction (MI) in preclinical studies, the assessment of the acute stage as well as long-term outcome is required1. Methods such as histopathology, intracardiac catheters2, and ex vivo heart models3 are commonly used for preclinical studies in mice. It is impossible, however, to follow up treatment with ex vivo or highly invasive methods. Noninvasive measurement techniques as in vivo magnetic resonance imaging (MRI) and positron emission tomography (PET) allow longitudinal experimental designs for disease staging in single subjects. Cine-MRI is used to derive global functional parameters such as left ventricular mass (LVM), ejection fraction (EF) and cardiac output (CO). In addition, after the injection of a gadolinium contrast agent, due to impaired perfusion and washout in the infarction, tissue viability can be assessed with late gadolinium enhancement (LGE) MRI. Complementarily, PET offers a sensitive measure of radiolabeled molecules in order to assess tissue metabolism. The high accuracy of these techniques permits significant reductions in the number of animals required for testing new drugs targeting MI.
The PET and MRI procedures are involved, and without a carefully designed protocol reproducibility is hard to maintain. Procedures established in the clinic for patients require substantial modification for use in mice, due to their considerably faster heart rate and smaller dimensions of the heart4. There is wide variation between individual subjects, both at baseline and in response to induced injury, so a considerable number of mice are needed to establish treatment efficacy.
In this report, we describe our method for sequential PET/MRI imaging of the mouse heart. Both modalities use intravenous contrast agents, which are delivered through the tail vein. MRI consists of standard assessment with Cine-MRI5 with an optimal protocol for LGE as described in our previous work6. The entire MRI procedure lasts 30 min. We have obtained consistent fittings for the beds of our instruments so it is possible to transfer the animal on a platform with the same monitoring and anesthetic delivery apparatus between the machines. The PET scan lasts 45 min with in situ injection once the scan is started. The final step is to measure the parameters from both MRI and PET images following coregistration.
Protocol
Representative Results
Discussion
PET/MRI is a comprehensive measurement method for the noninvasive and longitudinal evaluation of systolic function, tissue viability and specific metabolic markers in mouse models of myocardial infarction. Here we have described a protocol for performing MRI and PET sequentially, where coregistration is simplified by the transfer of the same bed between systems. This strategy, also adopted by manufacturers of clinical systems11, does not require a combined PET/MRI scanner and can be performed with standard equ…
Divulgazioni
The authors have nothing to disclose.
Acknowledgements
We are grateful for funding from the British Heart Foundation to TK and to the UK Medical Research Council for a postgraduate research studentship to GB.
Materials
| Material name | Company | Catalogue number | Comments |
| Gadovist | Bayer Schering Pharma | PL 00010/0535 | |
| FDG | IBA Molecular | ||
| Equipment | |||
| Material name | Company | Catalog number | Comments |
| Bruker BioSpec 47/40 | Bruker | ||
| Bruker mouse bed | Bruker | This bed includes tubing for anesthesia delivery and scavenging. | |
| 12 cm diameter birdcage transmitter | Bruker | T5346 | |
| 2 cm diameter surface coil receiver | Bruker | T7027 | |
| Red Dot Neonatal monitoring electrodes | 3M | P/N: 2330 | |
| Monitoring equipment | SA Systems | The monitoring kit includes respiratory pillow and rectal probe for temperature measurements. | |
| Anesthesia equipment | General Anesthetic Services | ||
| Induction box | Vet Tech Solutions LTD | ||
| Cambridge split-magnet PET/MRI scanner | University of Cambridge | A custom built PET/MRI scanner22 was used to perform the PET, its PET performance similar to an F120 micropet scanner23 | |
| Segment software | Medviso, Lund University | Freely available | |
| SPM-mouse | University of Cambridge | Freely available |
Riferimenti
- Borst, O., et al. Methods employed for induction and analysis of experimental myocardial infarction in mice. Cell. Physiol. Biochem. 28, 1-12 (2011).
- Pacher, P., Nagayama, T., Mukhopadhyay, P., Bátkai, S., Kass, D. A. Measurement of cardiac function using pressure-volume conductance catheter technique in mice and. 3, 1422-1434 (2008).
- Larsen, T. S., et al. The isolated working mouse heart: methodological considerations. Pflügers Arch. 437, 979-985 (1999).
- Epstein, F. H. MR in mouse models of cardiac disease. NMR Biomed. 20, 238-255 (2007).
- Schneider, J. E., Wiesmann, F., Lygate, C. A., Neubauer, S. How to perform an accurate assessment of cardiac function in mice using high-resolution magnetic resonance imaging. J. Cardiov. Magn. Reson. 8, 693-701 (2006).
- Buonincontri, G., Methner, C., Krieg, T., Carpenter, T. A., Sawiak, S. J. A fast protocol for infarct quantification in mice. J. Magn. Reson. Imaging. , (2013).
- Methner, C., Schmidt, K., Cohen, M. V., Downey, J. M., Krieg, T. Both A2a and A2b adenosine receptors at reperfusion are necessary to reduce infarct size in mouse hearts. Am. J. Physiol. 299, 1262-1264 (2010).
- Methner, C., et al. Protection through postconditioning or a mitochondria-targeted S-nitrosothiol is unaffected by cardiomyocyte-selective ablation of protein kinase. , (2013).
- Heiberg, E., et al. Design and validation of Segment–freely available software for cardiovascular image analysis. BMC Med. Imaging. 10, 1 (2010).
- Sawiak, S. J., Wood, N. I., Williams, G. B., Morton, A. J., Carpenter, T. A. Voxel-based morphometry in the R6/2 transgenic mouse reveals differences between genotypes not seen with manual 2D morphometry. Neurobiol. Dis. 33, 20-27 (2009).
- Zaidi, H., et al. Design and performance evaluation of a whole-body Ingenuity TF PET-MRI system. Phys. Med. Biol. 56, 3091-3106 (2011).
- Thomas, D., et al. T1-weighted cine FLASH is superior to IR imaging of post-infarction myocardial viability at 4.7T. J. Cardiov. Magn. Reson. 8, 345-352 (2006).
- Protti, A., Sirker, A., Shah, A. M., Botnar, R. Late gadolinium enhancement of acute myocardial infarction in mice at 7T: cine-FLASH versus inversion recovery. J. Magn. Reson. Imaging. 32, 878-886 (2010).
- Bohl, S., et al. Advanced methods for quantification of infarct size in mice using three-dimensional high-field late gadolinium enhancement MRI. Am. J. Physiol. 296, 1200-1208 (2009).
- Chapon, C., Herlihy, A. H., Bhakoo, K. K. Assessment of myocardial infarction in mice by late gadolinium enhancement MR imaging using an inversion recovery pulse sequence at 9.4T. J. Cardiov. Magn. Reson. 10, 6 (2008).
- Price, A. N., et al. Cardiovascular magnetic resonance imaging in experimental models. The open cardiov medicine journal. 4, 278-292 (2010).
- Hiba, B., Richard, N., Thibault, H., Janier, M. Cardiac and respiratory self-gated cine MRI in the mouse: comparison between radial and rectilinear techniques at 7T. Magn. Reson. Med. 58, 745-753 (2007).
- Buonincontri, G., et al. PET/MRI in the infarcted mouse heart with the Cambridge split magnet. Nucl. Instrum. Methods Phys. Res. A. , (2012).
- Büscher, K., et al. Isochronous assessment of cardiac metabolism and function in mice using hybrid PET/MRI. J. Nucl. Med. 51, 1277-1284 (2010).
- Berr, S. S., et al. Images in cardiovascular medicine. Serial multimodality assessment of myocardial infarction in mice using magnetic resonance imaging and micro-positron emission tomography provides complementary information on the progression of scar formation. Circulation. 115, 428-429 (2007).
- Lee, W. W., et al. PET/MRI of inflammation in myocardial infarction. J. Am. Coll. Cardiol. 59, 153-163 (2012).
- Lucas, A. J., et al. Development of a combined microPET-MR system. Technol. Cancer Res. Treat. 5, 337-341 (2006).
- Hawkes, R. C., Fryer, T. D., Siegel, S., Ansorge, R. E., Carpenter, T. A. Preliminary evaluation of a combined microPET-MR system. Technol. Cancer Res. Treat. 9, 53-60 (2010).
