This work was supported by grants from Ministry of Science and Technology, Taiwan, under grant number of MOST-105-2314-B-039-044-MY2.

The Institutional Care and Use Committees (IACUC) of the China Medical University approved all procedures.
1. Animal Preparation and Monitoring
<ol>
	<li>Leave all magnetically susceptible objects such as wallets, keys, credit card, etc. outside the scanner room prior to commencing animal preparation for MRI scanning.</li>
	<li>Initially anesthetize the rat (2-month-old male Sprague-Dawley (SD) rat, 280&#8211;350 g) in an induction box using a mixture of 5% isoflurane (ISO) and oxygen (2 L/min) for 3&#8211;5 min, as necessary.</li>
	<li>When the animal is recumbent and exhibits no response to a tail or toe pinch, discontinue ISO administration and transfer the animal to the scanning room.</li>
	<li>Place the rat in the MRI bed in a head-first prone position, and deliver 2-3% ISO through a nose cone device for maintaining anesthesia.</li>
	<li>Monitor respiration by placing a respiratory pillow sensor under the animal&#39;s torso.</li>
	<li>Connect the sensor to a respiratory system and check for respiration rate between 40-50 beats per minute (bpm).</li>
	<li>For cine-gated PC-MRI acquisition, place one electrode each on the right forepaw and the left hind paw, respectively (Figure 1a).</li>
	<li>Twist the electrocardiography (ECG) cables together.</li>
	<li>Use a head holder with ear bars and a bite bar to secure the animal to restrict head movement.</li>
	<li>Use a warm air heating system or gauze pads to maintain body temperature while in the magnet.</li>
	<li>Ensure that the R-wave is clear on the ECG monitor (Figure 1b), and place the animal in the scanner. There is no need to place the surface coil on the top of the animal&#39;s neck as images are acquired by the volume coil.</li>
</ol>
2. MRI Acquisition
<ol>
	<li>Use 2&#8211;3% ISO to maintain anesthesia during the entire imaging procedure. Continuously monitor physiological responses and keep as constant as possible.</li>
	<li>Start the MRI scans once the animal is placed inside the scanner and continues to be physiologically stable. In this study, use a 7 T small animal MRI system with a gradient strength of 630 mT/m, but other field strengths of small animal MRI systems can be used.</li>
	<li>Select the &#34;Localizer&#34; sequence from the console monitor of the MRI scanner and acquire scout images along all three orientations using any fast image acquisition sequence, e.g., the fast spin echo, to create coronal, axial, and sagittal images. The purpose of these scout images is to determine the imaging planes.</li>
	<li>Ensure that the center of the animal&#39;s head and neck is at the center of the magnet. If necessary, adjust the animal&#39;s position until the correct position is reached. If the animal is repositioned, repeat scanning to obtain scout images.</li>
	<li>Select the &#34;Time-of-flight (TOF) angiogram&#34;&#160;sequence from the console monitor of the MRI scanner and acquire a 2D TOF angiogram first to ascertain the precise anatomical location of the CCA. Use the following scanning parameters: repetition time (TR)/ echo time (TE)=22/4.87 ms, flip angle = 90&#176;, field of view (FOV) = 40 &#215; 40 mm2, matrix size = 256 &#215; 256, slice thickness 0.6 mm, with the number of excitation (NEX) = 1. 
	NOTE: The name of the TOF sequence could be vender-specific. The user can insert these parameters in the console monitor.</li>
	<li>Ensure that the saturation band is &#34;on&#34; and is placed on the top to avoid interference from venous signals. 
	NOTE: For the saturation band, it usually comes with the TOF sequence. If the saturation band does not show on the monitor, please notify the service person.</li>
	<li>After locating the CCA using the TOF angiogram, target the image plane of the PC-MRI to the center of the CCA and orient such that the slice is perpendicular to the direction of blood flow (Figure 2a).</li>
	<li>Ensure that both respiration and ECG gating are connected to the MRI system, showing the clear signal on the monitor computer (Figure 1b), and set the trigger module to be &#34;on&#34; in the &#34;Trigger Mode&#34; from the console monitor of the MRI scanner.</li>
	<li>Confirm that the animal&#39;s physiological responses are stable before initiating the PC-MRI scan from the monitoring computer (Figure 1b). Verify that gating selections are &#34;on&#34; in both the monitor computer and the console monitor of MRI scanner. 
	Note: The physiology monitoring system used in this study is provided by the vender. For most animal scanners, the similar physiology monitoring systems are provided and vender-specific.</li>
	<li>Select the sequence of PC-MRI sequence from the console monitor of the MRI scanner and perform gated PC-MRI scans using the following parameters: TR/TE=15.55/4.51 ms (minimum TR and TE), flip angle=30&#176;, FOV = 40 &#215; 40 mm2, matrix size = 192 &#215; 192, slice thickness = 2 mm, velocity encoding (VENC) = 120 cm/s, with NEX=8. Unidirectional VENC is acquired in the through-plane direction. 
	Note: The scan time is approximately 8.5 min, but the actual scan time may be slightly different among animals due to the variation in cardiac cycles.</li>
	<li>Repeat steps 2.6&#8211;2.9 of image acquisition if the region of interest (ROI) is to be changed to another location in the CCA, such as at the bifurcation&#160;4.</li>
	<li>Remove the animal from the scanner and return it to its recovery&#160;cage when the scan is complete.</li>
	<li>Warm the animal with a heating lamp to maintain body temperature. Keep the lamp at least 15 cm away from the animal to prevent overheating.</li>
	<li>When the animal starts to move and exhibits a response to a tail or toe pinch, turn off the heating lamp.</li>
</ol>
3. Data Processing
<ol>
	<li>Save MRI data in Digital Imaging and Communications in Medicine (DICOM) format or any other vender-specific format. Generate cine series with two types of images: a magnitude image (anatomy image) and a phase image (Figure 2b). 
	NOTE: In some scanners, the third type of image, which could be the magnitude image &#215; phase image or the complex-difference (the complex subtraction between the two acquisitions with different velocity-encoding gradients), is generated. The third image is vendor-dependent.</li>
	<li>Pre-process the image data. Covert the phase image into the velocity map and correct the phase-offset error&#160;5. 
	NOTE: The phase image has an arbitrary MR unit of signal intensity instead of true velocity values, but the MR signal intensity is linearly proportional to velocity. The maximum MRI signal from the phase image is typically assigned as the value of VENC, and the minimum signal is assigned the opposite value of VENC. See supplemental code file 1 for an example of the Matlab script and press the button of &#34;Run&#34;.</li>
	<li>Delineate the ROI carefully by tracing the boundary of the CCA. As the artery may dilate and construct during the various cardiac phases, delineate ROIs for each time frame. Calculate the blood flow by integrating over the artery ROI, i.e., velocity &#215; area. The resulted blood flow of each artery was in the units of mL/s. See supplemental code file 2 for an example of the Matlab script and press the button of &#34;Run&#34;.</li>
</ol>

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There is nothing to disclose.

PC-MRI is a comprehensive approach for non-invasive and longitudinal evaluation of blood flow. We present a protocol for performing PC-MRI of the rat CCA. This procedure is easy to perform in any animal MRI scanner and demonstrates good reproducibility.
The PC-MRI technique has gained increasing popularity in human 10,11 as well as animal studies 4,12. Among these studies, resu...

Magnetic resonance imaging (MRI) is a versatile approach that provides detailed information on internal body structures and physiology, and is increasingly being used for clinical diagnosis and in preclinical animal studies. Animal models are vital for better understanding of considerable clinical implication 1. As animal models considerably differ from humans with respect to anesthesia requirements and physiological parameters, optimization of MRI procedures for such animals assumes importance.
Phase contrast MRI (PC-MRI) is a specialized type of MRI that uses the velocity of flowing spins to quantify flow-related parameters such as blood flow. With PC-MRI, mapping flow patterns in the major arteries using animal models can help shed light on cardiovascular pathologies 2. Moreover, PC-MRI can non-invasively monitor the inherent alternations in blood flow in pathophysiological conditions 3. These observations suggest that PC-MRI is a valuable approach that can be used in animal models of human cardiovascular diseases.
In this report, we describe a method for the quantification of blood flow in the common carotid artery (CCA) of rats. The two CCAs supply the head and neck with oxygenated blood, and the carotid artery disease is a major cause of stroke. Therefore, detecting the early pathology in the CCA is pivotal. This procedure has a duration of approximately 15 min and can be potentially applied to conditions with hemodynamics alterations, such atherosclerosis or stroke.

<table><tbody><tr><td>7T small animal MRI system</td><td>Bruker</td><td></td><td></td></tr><tr><td>Isoflurane&amp;nbsp;</td><td>Baxter</td><td>1001936040</td><td>anesthetic</td></tr><tr><td>ECG lead&amp;nbsp;</td><td>3M</td><td>2269T</td><td></td></tr><tr><td>Matlab</td><td>MathWorks</td><td></td><td>sofeware for image processing</td></tr><tr><td>Monitoring and gating system</td><td>SA instruments, Inc</td><td>Model 1030</td><td></td></tr></tbody></table>

phase contrast magnetic resonance imaging in the rat common carotid artery

Phase contrast magnetic resonance imaging (PC-MRI) is a noninvasive approach that can quantify flow-related parameters such as blood flow. Previous studies have shown that abnormal blood flow may be associated with systemic vascular risk. Thus, PC-MRI can facilitate the translation of data obtained from animal models of cardiovascular diseases to pertinent clinical investigations. In this report, we describe the procedure for measuring blood flow in the common carotid artery (CCA) of rats using cine-gated PC-MRI and discuss relevant analysis methods. This procedure can be performed in a live, anesthetized animal and does not require euthanasia after the procedure. The proposed scanning parameters yield repeatable measurements for blood flow, indicating excellent reproducibility of the results. The PC-MRI procedure described in this article can be used for pharmacological testing, pathophysiological assessment, and cerebral hemodynamics evaluation.

Correct slice geometry is pivotal for ensuring the success of the PC-MRI experiment. The accurate image plane positioning yields a &#34;round&#34; artery shape (Figure 3a), and as angulation increases, i.e., when it is less perpendicular to the artery, the resulting artery geometry becomes ovoid, leading to larger partial volume effects (Figure 3b). Severe partial volume effects would lead to the overestimation of blood ...

Watch this Scientific Journal Video about Phase Contrast Magnetic Resonance Imaging in the Rat Common Carotid Artery at JoVE.com

Phase Contrast Magnetic Resonance Imaging in the Rat Common Carotid Artery

The overall goal of this procedure is to measure the blood flow in the rat common carotid artery by using noninvasive phase contrast magnetic resonance imaging.

Phase contrast magnetic resonance imaging (PC-MRI) is a noninvasive approach that can quantify flow-related parameters such as blood flow. Previous ...

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Research

JoVE Journal

Medicine

9.4K Views.  Chang Gung Memorial Hospital. The overall goal of this procedure is to measure the blood flow in the rat common carotid artery by using noninvasive phase contrast magnetic resonance imaging.

Video: Phase Contrast Magnetic Resonance Imaging in the Rat Common Carotid Artery

Focal Cerebral Ischemia Model by Endovascular Suture Occlusion of the Middle Cerebral Artery in the Rat

Stroke is the leading cause of disability and the third leading cause of death in adults worldwide1. In human stroke, there exists a highly variable clinical state; in the development of animal models of focal ischemia, however, achieving reproducibility of experimentally induced infarct volume is essential. The rat is a widely used animal model for stroke due to its relatively low animal husbandry costs and to the similarity of its cranial circulation to that of humans2,3. In humans, the middle cerebral artery (MCA) is most commonly affected in stroke syndromes and multiple methods of MCA occlusion (MCAO) have been described to mimic this clinical syndrome in animal models. Because recanalization commonly occurs following an acute stroke in the human, reperfusion after a period of occlusion has been included in many of these models. In this video, we demonstrate the transient endovascular suture MCAO model in the spontaneously hypertensive rat (SHR). A filament with a silicon tip coating is placed intraluminally at the MCA origin for 60 minutes, followed by reperfusion. Note that the optimal occlusion period may vary in other rat strains, such as Wistar or Sprague-Dawley. Several behavioral indicators of stroke in the rat are shown. Focal ischemia is confirmed using T2-weighted magnetic resonance images and by staining brain sections with 2,3,5-triphenyltetrazolium chloride (TTC) 24 hours after MCAO.

Surgical induction of ischemic brain damage in the rat is a widely used model for stroke research. Here we demonstrate the induction of focal cerebral ischemia by occlusion of the middle cerebral artery. Visualization of the resulting infarct by histological staining and magnetic resonance imaging is also shown.

Stroke is the leading cause of disability and the third leading cause of death in adults worldwide1. In human stroke, there exists a highly variable ...

Neuroscience

Optimized System for Cerebral Perfusion Monitoring in the Rat Stroke Model of Intraluminal Middle Cerebral Artery Occlusion

The translational potential of pre-clinical stroke research depends on the accuracy of experimental modeling. Cerebral perfusion monitoring in animal models of acute ischemic stroke allows to confirm successful arterial occlusion and exclude subarachnoid hemorrhage. Cerebral perfusion monitoring can also be used to study intracranial collateral circulation, which is emerging as a powerful determinant of stroke outcome and a possible therapeutic target. Despite a recognized role of Laser Doppler perfusion monitoring as part of the current guidelines for experimental cerebral ischemia, a number of technical difficulties exist that limit its widespread use. One of the major issues is obtaining a secure and prolonged attachment of a deep-penetration Laser Doppler probe to the animal skull. In this video, we show our optimized system for cerebral perfusion monitoring during transient middle cerebral artery occlusion by intraluminal filament in the rat. We developed in-house a simple method to obtain a custom made holder for twin-fibre (deep-penetration) Laser Doppler probes, which allow multi-site monitoring if needed. A continuous and prolonged monitoring of cerebral perfusion could easily be obtained over the intact skull.

Cerebral perfusion monitoring has been demonstrated to improve accuracy in ischemic stroke models. Technical difficulties often limit the use of this essential tool for cerebrovascular research. In this video, an optimized system is shown to obtain a single or multi-site hemodynamic monitoring during intraluminal middle cerebral artery occlusion in rats.

The translational potential of pre-clinical stroke research depends on the accuracy of experimental modeling. Cerebral perfusion monitoring in animal ...

Non-invasive Imaging and Analysis of Cerebral Ischemia in Living Rats Using Positron Emission Tomography with 18F-FDG

Stroke is the third leading cause of death among Americans 65 years of age or older1. The quality of life for patients who suffer from a stroke fails to return to normal in a large majority of patients2, which is mainly due to current lack of clinical treatment for acute stroke. This necessitates understanding the physiological effects of cerebral ischemia on brain tissue over time and is a major area of active research. Towards this end, experimental progress has been made using rats as a preclinical model for stroke, particularly, using non-invasive methods such as 18F-fluorodeoxyglucose (FDG) coupled with Positron Emission Tomography (PET) imaging3,10,17. Here we present a strategy for inducing cerebral ischemia in rats by middle cerebral artery occlusion (MCAO) that mimics focal cerebral ischemia in humans, and imaging its effects over 24 hr using FDG-PET coupled with X-ray computed tomography (CT) with an Albira PET-CT instrument. A VOI template atlas was subsequently fused to the cerebral rat data to enable a unbiased analysis of the brain and its sub-regions4. In addition, a method for 3D visualization of the FDG-PET-CT time course is presented. In summary, we present a detailed protocol for initiating, quantifying, and visualizing an induced ischemic stroke event in a living Sprague-Dawley rat in three dimensions using FDG-PET.

Non-invasive Imaging and Analysis of Cerebral Ischemia in Living Rats Using Positron Emission Tomography with 18F-FDG

Brain damage resulting from cerebral ischemia may be non-invasively imaged and studied in rats using pre-clinical positron emission tomography coupled with the injectable radioactive probe, 18F-fluorodeoxyglucose. Further, the use of modern software tools that include volume of interest (VOI) brain templates dramatically increase the quantitative information gleaned from these studies.

Stroke is the third leading cause of death among Americans 65 years of age or older1. The quality of life for patients who suffer from a stroke fails to ...

Diffusion Imaging in the Rat Cervical Spinal Cord

Magnetic resonance imaging (MRI) is the state of the art approach for assessing the status of the spinal cord noninvasively, and can be used as a diagnostic and prognostic tool in cases of disease or injury. Diffusion weighted imaging (DWI), is sensitive to the thermal motion of water molecules and allows for inferences of tissue microstructure. This report describes a protocol to acquire and analyze DWI of the rat cervical spinal cord on a small-bore animal system. It demonstrates an imaging setup for the live anesthetized animal and recommends a DWI acquisition protocol for high-quality imaging, which includes stabilization of the cord and control of respiratory motion. Measurements with diffusion weighting along different directions and magnitudes (b-values) are used. Finally, several mathematical models of the resulting signal are used to derive maps of the diffusion processes within the spinal cord tissue that provide insight into the normal cord and can be used to monitor injury or disease processes noninvasively.

The goal of this protocol is to obtain high-quality diffusion weighted magnetic resonance imaging (DWI) of the rat spinal cord for noninvasive characterization of tissue microstructure. This protocol describes optimizations of the MRI sequence, radiofrequency coil, and analysis methods to enable DWI images free from artifacts.

Magnetic resonance imaging (MRI) is the state of the art approach for assessing the status of the spinal cord noninvasively, and can be used as a ...

Simultaneous PET/MRI Imaging During Mouse Cerebral Hypoxia-ischemia

Dynamic changes in tissue water diffusion and glucose metabolism occur during and after hypoxia in cerebral hypoxia-ischemia reflecting a bioenergetics disturbance in affected cells. Diffusion weighted magnetic resonance imaging (MRI) identifies regions that are damaged, potentially irreversibly, by hypoxia-ischemia. Alterations in glucose utilization in the affected tissue may be detectable by positron emission tomography (PET) imaging of 2-deoxy-2-(18F)fluoro-&#7429;-glucose ([18F]FDG) uptake. Due to the rapid and variable nature of injury in this animal model, acquisition of both modes of data must be performed simultaneously in order to meaningfully correlate PET and MRI data. In addition, inter-animal variability in the hypoxic-ischemic injury due to vascular differences limits the ability to analyze multi-modal data and observe changes to a group-wise approach if data is not acquired simultaneously in individual subjects. The method presented here allows one to acquire both diffusion-weighted MRI and [18F]FDG uptake data in the same animal before, during, and after the hypoxic challenge in order to interrogate immediate physiological changes.

The method presented here uses simultaneous positron emission tomography and magnetic resonance imaging. In the cerebral hypoxia-ischemia model, dynamic changes in diffusion and glucose metabolism occur during and after injury. The evolving and irreproducible damage in this model necessitates simultaneous acquisition if meaningful multi-modal imaging data are to be acquired.

Dynamic changes in tissue water diffusion and glucose metabolism occur during and after hypoxia in cerebral hypoxia-ischemia reflecting a bioenergetics ...

A Magnetic Resonance Imaging Protocol for Stroke Onset Time Estimation in Permanent Cerebral Ischemia

MRI provides a sensitive and specific imaging tool to detect acute ischemic stroke by means of a reduced diffusion coefficient of brain water. In a rat model of ischemic stroke, differences in quantitative T1 and T2 MRI relaxation times (qT1 and qT2) between the ischemic lesion (delineated by low diffusion) and the contralateral non-ischemic hemisphere increase with time from stroke onset. The time dependency of MRI relaxation time differences is heuristically described by a linear function and thus provides a simple estimate of stroke onset time. Additionally, the volumes of abnormal qT1 and qT2 within the ischemic lesion increase linearly with time providing a complementary method for stroke timing. A (semi)automated computer routine based on the quantified diffusion coefficient is presented to delineate acute ischemic stroke tissue in rat ischemia. This routine also determines hemispheric differences in qT1 and qT2 relaxation times and the location and volume of abnormal qT1 and qT2 voxels within the lesion. Uncertainties associated with onset time estimates of qT1 and qT2 MRI data vary from &plusmn; 25 min to &plusmn; 47 min for the first 5 hours of stroke. The most accurate onset time estimates can be obtained by quantifying the volume of overlapping abnormal qT1 and qT2 lesion volumes, termed 'Voverlap' (&plusmn; 25 min) or by quantifying hemispheric differences in qT2 relaxation times only (&plusmn; 28 min). Overall, qT2 derived parameters outperform those from qT1. The current MRI protocol is tested in the hyperacute phase of a permanent focal ischemia model, which may not be applicable to transient focal brain ischemia.

A protocol for stroke onset time estimation in a rat model of stroke exploiting quantitative magnetic resonance imaging (qMRI) parameters is described. The procedure exploits diffusion MRI for delineation of the acute stroke lesion and quantitative T1 and T2 (qT1 and qT2) relaxation times for timing of stroke.

MRI provides a sensitive and specific imaging tool to detect acute ischemic stroke by means of a reduced diffusion coefficient of brain water. In a rat ...

Quantitative MRI of Endothelial Permeability and (Dys)function in Atherosclerosis

Cardiovascular diseases are the leading causes of death worldwide. A permeable/leaky and dysfunctional endothelium is considered the earliest marker of vascular damage and thought to drive atherosclerosis. A method to identify these changes in vivo would be desirable in the clinic. Magnetic resonance imaging (MRI)-based tools and other technologies have enabled a profound understanding of the role of the endothelium in cardiovascular diseases and risk in vivo. There is, however, a need for reproducible and simple approaches for extracting quantifiable data reflective of endothelial damage from a single imaging study. A non-invasive, easy-to-implement, and quantitative MRI workflow was developed to acquire and analyze images that allow the quantification of two imaging biomarkers of arterial endothelial damage (leakiness/permeability and dysfunction). Here, the protocol describes the application of this method in the brachiocephalic artery of atherosclerotic ApoE-/- mice using a clinical MRI scanner. First, late gadolinium enhancement (LGE) and Modified Look-Locker Inversion Recovery (MOLLI) T1 mapping protocols to quantify endothelial leakage using an albumin-binding probe are described. Second, anatomic, and quantitative blood flow sequences to measure endothelial dysfunction, in response to acetylcholine are described. Importantly, the method outlined here allows the acquisition of high-spatial-resolution 3D images with large volumetric coverage enabling accurate segmentation of vessel wall structures to improve inter- and intra-observer variability and to increase reliability and reproducibility. Additionally, it provides quantitative data without the need for high-temporal resolution for complex kinetic modeling, making it model-independent and even allowing for imaging of highly mobile vessels (coronary arteries). Therefore, the approach simplifies and expedites data analysis. Finally, this method can be implemented on different scanners, can be extended to image different arterial beds, and is clinically applicable for use in humans. This method could be used to diagnose and treat patients with atherosclerosis by adopting a precision-medicine approach.

Quantitative MRI of Endothelial Permeability and Dysfunction in Atherosclerosis

We have developed an accurate, non-invasive, and easy-to-use method to quantify endothelial permeability and dysfunction in the arteries using Magnetic Resonance Imaging (MRI), named qMETRIC. This technique enables assessing vascular damage and cardiovascular risk associated with atherosclerosis in preclinical models and humans.

Cardiovascular diseases are the leading causes of death worldwide. A permeable/leaky and dysfunctional endothelium is considered the earliest marker of ...

Bioengineering

Ferric Chloride-induced Canine Carotid Artery Thrombosis: A Large Animal Model of Vascular Injury

Occlusive arterial thrombosis leading to cerebral ischemic stroke and myocardial infarction contributes to ~13 million deaths every year globally. Here, we have translated a vascular injury model from a small animal into a large animal (canine), with slight modifications that can be used for pre-clinical screening of prophylactic and thrombolytic agents. In addition to the surgical methods, the modified protocol describes the step-by-step methods to assess carotid artery canalization by angiography, detailed instructions to process both the brain and carotid artery for histological analysis to verify carotid canalization and cerebral hemorrhage, and specific parameters to complete an assessment of downstream thromboembolic events by utilizing magnetic resonance imaging (MRI). In addition, specific procedural changes from the previously well-established small animal model necessary to translate into a large animal (canine) vascular injury are discussed.

Here, we present the modifications necessary to a well characterized and commonly used small animal ferric chloride-induced (FeCl3) carotid artery injury model for use in a large animal vascular injury model. The resulting model can be utilized for pre-clinical trial assessment of both prophylactic and thrombolytic pharmacological and mechanical interventions.

Occlusive arterial thrombosis leading to cerebral ischemic stroke and myocardial infarction contributes to ~13 million deaths every year globally. Here, ...

Cardiac Magnetic Resonance Imaging

Source: Frederick W. Damen and <a href="https://www.jove.com/author/Craig+J._Goergen">Craig J. Goergen</a>, Weldon School of Biomedical Engineering, Purdue University, West Lafayette, Indiana
In this video, high field, small-bore magnetic resonance imaging (MRI) with physiological monitoring is demonstrated to acquire gated cine loops of the murine cardiovascular system. This procedure provides a basis for assessing left-ventricular function, visualizing vascular networks, and quantifying motion of organs due to respiration. Comparable small animal cardiovascular imaging modalities include high-frequency ultrasound and micro-computed tomography (CT); however, each modality is associated with trade-offs that should be considered. While ultrasound does provide high spatial and temporal resolution, imaging artifacts are common. For example, dense tissue (i.e., the sternum and ribs) can limit imaging penetration depth, and hyperechoic signal at the interface between gas and liquid (i.e., pleura surrounding the lungs) can blur contrast in nearby tissue. Micro-CT in contrast does not suffer from as many in-plane artifacts, but does have lower temporal resolution and limited soft-tissue contrast. Furthermore, micro-CT uses X-ray radiation and often requires the use of contrast agents to visualize vasculature, both of which are known to cause side effects at high doses including radiation damage&#160; and renal injury. Cardiovascular MRI provides a nice compromise between these techniques by negating the need for ionizing radiation and providing the user with the ability to image without contrast agents (although contrast agents are often used for MRI).
This data was acquired with a triggering Fast Low Angle SHot (FLASH) MRI sequence that was gated off of the R-peaks in the cardiac cycle and expiratory plateaus in respiration. These physiological events were monitored through subcutaneous electrodes and a pressure-sensitive pillow that was secured against the abdomen. To ensure the mouse was properly warmed, a rectal temperature probe was inserted and used to control the output of a MRI-safe heating fan. Once the animal was inserted into the bore of the MRI scanner and navigation sequences were run to confirm positioning, the gated FLASH imaging planes were prescribed and data acquired. Overall, high field MRI is a powerful research tool that can provide soft tissue contrast for the study of small animal disease models.

Cardiac MRI: Principle and Imaging

Source: Frederick W. Damen and Craig J. Goergen, Weldon School of Biomedical Engineering, Purdue University, West Lafayette, Indiana
In this video, high ...

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Biomedical Engineering

 Phase Contrast Magnetic Resonance Imaging to Assess Blood Flow in the Arteries of a Rat

<a href='https://app.jove.com/v/57304/phase-contrast-magnetic-resonance-imaging-rat-common-carotid'>Source: Chiu, S., et al. Phase Contrast Magnetic Resonance Imaging in the Rat Common Carotid Artery. J. Vis. Exp. (2018).</a>This video demonstrates phase contrast magnetic resonance imaging (PC-MRI) to measure blood flow in the common carotid artery of a rat. After securing an anesthetized rat on the MRI bed and ensuring stable physiological parameters, the common carotid artery is scanned to capture images at defined intervals. Blood flow is then computed from these images to evaluate changes throughout the cardiac cycle.

Source: Chiu, S., et al. Phase Contrast Magnetic Resonance Imaging in the Rat Common Carotid Artery. J. Vis. Exp. (2018).This video demonstrates phase ...