Name: high-resolution cardiac positron emission tomography/computed tomography for small animals
Uploaded: 2022-12-16T13:00:00
Description: Watch this Scientific Journal Video about High-Resolution Cardiac Positron Emission Tomography/Computed Tomography for Small Animals at JoVE.com

This research was supported in part by the JPI-HDHL-INTIMIC &#34;GUTMOM&#34; Project: Maternal obesity and cognitive dysfunction in the offspring: Cause-effect role of the GUT MicrobiOMe and early dietary prevention (project no. INTIMIC-085, Italian Ministry of Education, University and Research Decree no. 946/2019).

Animal experiments were performed in accordance with the recommendations in the Guide for the Care and Use of Laboratory Animals of the International Guidelines on Handling of Laboratory Animals, demanded by the European Directive (Directive 86/609/EEC of 1986 and Directive 2010/63/UE) and Italian laws (D.Lgs. 26/2014).
1. Setup of the PET/CT imaging protocols and workflow
NOTE: The protocol presented here is specifically designed for cardiac imaging ...

The protocol presented in this paper focuses on a typical experimental procedure for translational cardiovascular research on small animal models of cardiac injury by using high-resolution PET/CT imaging. The presented results are indicative of the high quantitative and qualitative value of PET and Cine-CT images, providing both functional and structural information of the whole heart regarding its glucose metabolism, shape, and the dynamics of its contraction. Moreover, all the images obtained are 3D, time-resolved, and...

Small animal models are extremely important for the advancement of the understanding of cardiovascular diseases1,2. Non-invasive, diagnostic imaging tools have revolutionized the way we look at cardiac function in the last decades, both in clinical and preclinical settings. As far as small animal models of cardiac diseases are concerned, specific imaging tools have been developed with very high spatiotemporal resolution. Thus, such instruments can match the need for accurate quantification of the relevant metabolic and kinetic myocardial parameters on the very small and very fast-moving hearts of mice and rats in specific disease models, such as heart failure (HF)3 or myocardial infarction (MI)4. Several modalities are available for this purpose, each with their own strengths and weaknesses. Ultrasound (US) imaging is the most widely used modality due to its great flexibility, very high temporal resolution, and relatively low cost. The adoption of US cardiac imaging in small animals has increased considerably since the advent of systems using probes with ultra-high frequency5,6, featuring spatial resolutions below 50 &#181;m.
Among the main disadvantages of US for fully 3D cardiac imaging is the need for linear scans along the heart axis by mounting the probe on a motorized translation stage to create a full stack of dynamic B-mode images of the whole heart7. Eventually, this procedure gives rise (after accurate spatial and temporal registration of the images acquired in each probe position) to a 4D image with different spatial resolutions between the in-plane and out-of-plane directions. The same problem of non-uniform spatial resolution occurs in cardiac MR (CMR),8 which still represents the gold standard in the functional imaging of the heart. Real isotropic 3D imaging can be instead obtained using both computed tomography (CT) and positron emission tomography (PET)9. PET provides a very sensitive tool in terms of image signal per quantity of injected probe (in the nanomolar range), even though it suffers from a reduced spatial resolution compared to CT, MR, or US. The main advantage of PET is its ability to display the cellular and molecular mechanisms underlying the organ&#39;s pathophysiology. For instance, a PET scan following the injection of [18F]FDG allows the reconstruction of a 3D map of the glucose metabolism in the body. By combining this with dynamic (i.e., time-resolved) data acquisition, tracer kinetic modeling can be used to calculate parametric maps of the metabolic rates of glucose uptake (MRGlu), which will provide important information about myocardial viability10.
CT requires significant volumes of external contrast agents (CA) at high concentrations (up to 400 mg of iodine per mL) to provide a measurable enhancement of the relevant tissue components (e.g., blood vs. muscle), but it excels in spatial and temporal resolution, especially when using state-of-the-art micro-CT scanners designed for small animal imaging.11 A typical disease model in which the cardiac PET/CT can be applied is the experimental evaluation of myocardial infarction and heart failure and related response to therapy. A common way of inducing MI in small animals is by surgical ligation of the left anterior descending (LAD) coronary artery12,13 and then longitudinally evaluating the progression of the disease and the cardiac remodeling in the subsequent days4. Nevertheless, the quantitative morphofunctional evaluation of the heart in small animals is largely applicable also for other disease models, such as the evaluation of the effect of aging on cardiac function14 or altered receptor expression in models of obesity15. The presented imaging protocol is not restricted to any given disease model and, hence, could be of the widest interest in several contexts of preclinical research with small rodents.
In this paper, we present a start-to-end experimental protocol for cardiac imaging using small animal integrated PET/CT. Even though the presented protocol is designed for a specific bimodal integrated scanner, the PET and CT parts of the described procedure could be performed independently on separate scanners from different manufacturers. In the PET/CT scanner in use, the sequence of operations is organized in a preprogrammed workflow. The main branches of each workflow are one or more acquisition protocols; each acquisition protocol can have one or more branches for specific preprocessing protocols, and in turn, each preprocessing protocol can have one or more branches for specific reconstruction protocols. Both the preparation of the animal on the imaging bed and the preparation of the external agents to be injected during the imaging procedures are described. After the completion of the image acquisition procedure, example procedures for quantitative image analysis based on commonly available software tools are provided. The main protocol is specifically designed for mouse models; even though the mouse remains the most used species in this field, we also show an adaptation of the protocol for rat imaging at the end of the main protocol. Representative results are shown for both mice and rats, demonstrating the type of output that might be expected with the described procedures. A thorough discussion is made at the end of this paper to emphasize the pros and cons of the technique, critical points, as well as how different PET radiotracers could be used with almost no modification to the preparatory and acquisition/reconstruction steps.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>0.9% sterile saline</td>
			<td>Fresenius Kabi</td>
			<td></td>
			<td>0.9% sodium chloride for injection</td>
		</tr>
		<tr>
			<td>1025L Physiological Monitoring</td>
			<td>Small Animal Instruments</td>
			<td></td>
			<td>Physiological monitoring system for small animal imaging</td>
		</tr>
		<tr>
			<td>5 mL syringes</td>
			<td>Artsana</td>
			<td></td>
			<td>Syringes with needle for injection of PET tracer</td>
		</tr>
		<tr>
			<td>Atomlab 500</td>
			<td>Else Nuclear</td>
			<td></td>
			<td>PET Dose calibrator</td>
		</tr>
		<tr>
			<td>Atrium software</td>
			<td>Inviscan</td>
			<td>Version 1.5.5</td>
			<td>PET/CT operating software</td>
		</tr>
		<tr>
			<td>Butterfly catheters</td>
			<td>Delta Med</td>
			<td></td>
			<td>27.5 G needle</td>
		</tr>
		<tr>
			<td>Carimas software</td>
			<td>Turku PET Center</td>
			<td>Version 2.10</td>
			<td>Image analysis software</td>
		</tr>
		<tr>
			<td>Fenestra VC</td>
			<td>Medilumine</td>
			<td></td>
			<td>Lipid emulsion iodinated contrast agent for small animals</td>
		</tr>
		<tr>
			<td>Heat lamp</td>
			<td></td>
			<td></td>
			<td>Heat lamp with clamp and switch</td>
		</tr>
		<tr>
			<td>Insulin syringes</td>
			<td>Artsana</td>
			<td></td>
			<td>Syringes with needle for injection of CT CA</td>
		</tr>
		<tr>
			<td>Iomeron 400 mgI/mL</td>
			<td>Bracco</td>
			<td></td>
			<td>Iomeprol, vascular contrast agent</td>
		</tr>
		<tr>
			<td>IRIS PET/CT</td>
			<td>Inviscan</td>
			<td></td>
			<td>PET/CT scanner for small animals</td>
		</tr>
		<tr>
			<td>Isoflurane</td>
			<td>Zoetis</td>
			<td></td>
			<td>Inhalation anesthetic, 250 mL</td>
		</tr>
		<tr>
			<td>OneTouch Glucometer</td>
			<td>Johnson&#38;Johnson Medical</td>
			<td></td>
			<td>Glucose meter kit</td>
		</tr>
		<tr>
			<td>Osirix MD software</td>
			<td>Pixmeo</td>
			<td>Version 11</td>
			<td>Image analysis software</td>
		</tr>
		<tr>
			<td>Oxygen</td>
			<td>Air liquide</td>
			<td></td>
			<td>Compressed gas</td>
		</tr>
		<tr>
			<td>Rectal probe for 1025L</td>
			<td>Small Animal Instruments</td>
			<td></td>
			<td>Rectal probe with cable for SAII 1025L systems</td>
		</tr>
		<tr>
			<td>Respiratory sensor for 1025L</td>
			<td>Small Animal Instruments</td>
			<td></td>
			<td>Respiratory pillow with tubings for SAII 1025L systems</td>
		</tr>
		<tr>
			<td>TJ-3A syringe pump</td>
			<td>Longer</td>
			<td></td>
			<td>Motorized syringe pump for CT CA injection</td>
		</tr>
	</tbody>
</table>

high-resolution cardiac positron emission tomography/computed tomography for small animals

Positron emission tomography (PET) and computed tomography (CT) are among the most employed diagnostic imaging techniques, and both serve in understanding cardiac function and metabolism. In preclinical research, dedicated scanners with high sensitivity and high spatio-temporal resolution are employed, designed to cope with the demanding technological requirements posed by the small heart size and very high heart rates of mice and rats. In this paper, a bimodal cardiac PET/CT imaging protocol for experimental mouse and/or rat models of cardiac diseases is described, from animal preparation and image acquisition and reconstruction to image processing and visualization.
In particular, the 18F-labeled fluorodeoxyglucose ([18F]FDG)-PET scan allows for the measurement and visualization of glucose metabolism in the different segments of the left ventricle (LV). Polar maps are convenient tools to display this information. The CT part consists of a time-resolved 3D reconstruction of the entire heart (4D-CT) using retrospective gating without electrocardiography (ECG) leads, allowing the morphofunctional evaluation of the LV and the subsequent quantification of the most important cardiac function parameters, such as ejection fraction (EF) and stroke volume (SV). Using an integrated PET/CT scanner, this protocol can be executed within the same anesthesia induction without the need to reposition the animal between different scanners. Hence, PET/CT can be seen as a comprehensive tool for the morphofunctional and metabolic evaluation of the heart in several small animal models of cardiac diseases.

In this section, typical results are shown for both PET and CT analysis following the procedures described so far. Figure 6 shows the results of the automatic myocardial and LV cavity segmentation of the [18F]FDG PET scan of a control (healthy) CD-1 mouse. Even though the right ventricle is not always visible in the reconstructed images, the orientation axes based on the DICOM header can be used to correctly discriminate the interventricular septum from the other LV walls, as requ...

Watch this Scientific Journal Video about High-Resolution Cardiac Positron Emission Tomography/Computed Tomography for Small Animals at JoVE.com

High-Resolution Cardiac Positron Emission Tomography/Computed Tomography for Small Animals

Here, we present an experimental imaging protocol for the quantification of cardiac function and morphology using high-resolution positron emission tomography/computed tomography for small animals. Both mice and rats are considered, discussing the different requirements of computed tomography contrast agents for the two species.

Positron emission tomography (PET) and computed tomography (CT) are among the most employed diagnostic imaging techniques, and both serve in understanding ...

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