The authors acknowledge support from the Department of Diagnostic Imaging at the H. Lee Moffitt Cancer Center and Research Institute.

The following protocol follows the departmental clinical guidelines and is adherent to the institution&#8217;s human research ethics guidelines.
1. Prepare for MRI Data Acquisition
<ol>
	<li>Conduct a safety screening.
	<ol>
		<li>Evaluate for renal impairment8.
		<ol>
			<li>Avoid gadolinium contrast in patients with stage 4 or 5 chronic kidney disease (estimated glomerular filtration rate &#60;30 mL/min/1.71 m2) not on chronic dialysis, patients with end-stage renal disease on chronic dialysis, and patients with known or suspected acute kidney injury due to concerns for NSF.</li>
		</ol>
		</li>
		<li>Determine necessity for sedation9. 
		NOTE: Moderate sedation or general anesthesia allows completion of the examination for patients suffering from anxiety or claustrophobia or pediatric patients.
		<ol>
			<li>Administer a lorazepam tablet up to 1 mg orally prior to scanning for patients with claustrophobia. Driving or machinery operation after medication administration is contraindicated.</li>
		</ol>
		</li>
		<li>Evaluate for implanted devices9.
		<ol>
			<li>Perform a careful review of the patient&#8217;s history and safety to identify implanted devices that may be hazardous in the CMR environment or create image artifact.</li>
			<li>Determine MR compatibility of patient implanted devices. Each case is reviewed for risks and benefits. The proper personnel are required to be present during the examination if CMR is to be performed in patients with non-MR safe devices.</li>
			<li>Obtain radiographs to assist with screening, particularly orbit radiographs when there is possible history of metal fragments within the eye. Perform posterior-anterior radiographs with eyes up, eyes down, and a lateral view.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Provide patient instructions.
	<ol>
		<li>Deliver breathing instructions10.
		<ol>
			<li>Perform breath holding at end expiration as reproducibility is higher compared to inspiratory breath holds. For CMR, use the typical breath hold command: &#8220;breathe in, breathe out, stop breathing&#8221;.</li>
			<li>Provide patient with headphones connected to the technologist microphone so commands can be efficiently conveyed.</li>
			<li>Perform free-breathing protocol when patient is unable to hold-breath for the exam due to sedation or medical condition. Free breathing protocols increase the number of averages (excitations) up to 4 and allow adequate free breathing image acquisition. Free breathing protocols can be selected from typical scanner exam libraries.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Setup physiological monitoring10.
	<ol>
		<li>Place electrocardiogram (ECG) leads in optimal positions on the left chest, and confirm adequate ECG signal.</li>
	</ol>
	</li>
	<li>Position the patient on the MRI scanner.
	<ol>
		<li>Ensure an appropriate surface coil size is chosen to maximize the signal-to-noise ratio over the heart. Often a dedicated cardiac coil is selected for optimal performance. Signal to noise correlates directly with image quality and is visually evident during scanning</li>
		<li>Reduce field of view to maintain adequate spatial resolution. FOV is changed in the scanner settings directly and is dependent on patient size</li>
	</ol>
	</li>
</ol>
2. Acquire the MRI Data [Cardiac MR without and with IV Contrast Limited] Focused Scan to Evaluated Potential Cardiac Thrombus
NOTE: Basic scan sequences are often loaded by the MRI technologist from scan libraries that are present on each MRI scanner. Standard cardiac scan prescription and orientations are also considered routine operating tasks for MRI technologists.
<ol>
	<li>Obtain the Scout T1-weighted fast spin-echo including the trans-axial localizing stack1. 
	NOTE: This constitutes the first scan for each MRI exam and allows further sequences to be prescribed using spatial localization.</li>
	<li>Obtain the Bright-blood, cine SSFP gradient-echo &#8211; axial stack with full heart coverage. This sequence offers the most consistent mass delineation and correlation with other radiology studies.
	<ol>
		<li>Obtain short axis, 2 chamber, 3 chamber, and 4-chamber planes as needed depending on clinical indications. Scan plane prescriptions are discussed in detail in Boegart11. 
		NOTE: These acquisitions are non-dependent on flow effects which allow for short TR, improve temporal resolution, and permit determination of mobility of a thrombus. SSFP provides high SNR and CNR due to intrinsic contrast properties between myocardium and blood pool.</li>
	</ol>
	</li>
	<li>Perform the tissue characterization module1,2,3,11,12.
	<ol>
		<li>Obtain the black-blood triple inversion recovery. 
		NOTE: This provides excellent contrast resolution for determining the size and the extent of the mass. It is useful for characterizing myocardial edema associated with mass or cystic component of mass and in detecting fat within the mass.
		<ol>
			<li>Obtain the black-blood double inversion recovery if there is a benefit of a bright fat signal. This is run as a separate sequence available in most CMR scanner sequence libraries where blood pool and myocardium signal are nulled while fat remains bright.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Perform the first-pass arterial perfusion module1,2,3,11,12.
	<ol>
		<li>Obtain T1-weighted fat-saturated volumetric contrast-enhanced images; the axial plane is often most universal for mass visualization.
		<ol>
			<li>Begin imaging during contrast administration of 0.05&#8211;0.1 mmol/kg injected at 3&#8211;4 mL/s.</li>
			<li>Image until the contrast passes through the LV myocardium (40&#8211;50 heart beats). 
			NOTE: A vascular tumor enhances during perfusion sequences while a thrombus does not enhance.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Perform the post gadolinium delayed viability module1,2,3,11,12.
	<ol>
		<li>Obtain phase sensitive inversion recovery (PSIR), (~10 min post injection) 6&#8211;8 mm slices with inversion time set to null thrombus, to differentiate the thrombus from the tumor or delineate the thrombus surrounding or associated with the tumor.
		<ol>
			<li>Set the scan &#8220;time to inversion&#8221; (TI time) which changes in real time based on gadolinium kinetics and is typically set at 200&#8211;450 ms at 1.5 T; 300&#8211;550 ms at 3 T. Set a new TI time into the scanner for each PSIR sequence run, which is usually higher than the previous time based on gadolinium kinetics. 
			NOTE: Serial imaging can be performed to distinguish hypo-perfused tumor necrotic core from thrombus. This is performed by repeating the PSIR sequence at multiple time points to evaluate gadolinium kinetics with the region of concern.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Consider obtaining emerging sequences13,14,15,16,17,18,19.
	<ol>
		<li>Obtain native T1 mapping (multiple protocols available). 
		NOTE: For example, use a single shot inversion recovery readout with a 5(3)3 scheme: inversion followed by 5 acquisition heartbeats, 3 recovery heartbeats, an additional inversion followed by 3 heartbeats.</li>
		<li>Obtain post contrast T1 mapping (extracellular volume fraction). 
		NOTE: Post contrast Extracellular volume (ECV) represents a gadolinium-based measurement of the size of the extracellular space which primarily reflects interstitial disease. ECV is calculated by comparing the changes in relaxivity of myocardium and blood pool prior to and following the administration of the IV contrast agent. Serum hematocrit is necessary to calculate ECV.</li>
		<li>Obtain T2 mapping. 
		NOTE: T2 mapping can be derived from bright-blood T2 prepped SSFP sequence. Accurate application of T2 mapping requires a reference range for normal T2w signal; however, large interpatient variability of myocardial T2 signal can affect interpretation of results.</li>
		<li>Obtain a cardiac triggered 3D spoiled gradient echo acquisition named 3D-QALAS (3D quantification). 
		NOTE: This sequence uses an interleaved look-locker acquisition sequence with T2-preparation and has been shown to be a feasible option for myocardial T1 and T2 mapping in a single breath hold.</li>
	</ol>
	</li>
</ol>
3. Analysis of the MRI data
<ol>
	<li>Perform post-processing2,20.
	<ol>
		<li>Use an FDA-approved software for processing data either as part of the MRI system or on a separate workstation. 
		NOTE: Post-processing is performed or supervised by the cardiac MRI physician and appropriately documented in the report.</li>
	</ol>
	</li>
	<li>Assess ventricular chambers.
	<ol>
		<li>Perform visual analysis of global and segmental function and wall motion. Look for any wall motion abnormalities in all obtained planes.</li>
		<li>Perform quantitative analysis of ventricular volumes and wall thicknesses. Ensure there is no abnormal thickening (&#62;13 mm) or thinning of the left ventricular myocardium, which could suggest underlying pathology.</li>
	</ol>
	</li>
	<li>Evaluate T2-weighted imaging.
	<ol>
		<li>Visually analyze to detect or exclude regions of increased myocardial signal intensity indicating edema. For cardiac thrombus evaluation, the thrombus can have increased T2w signal intensity in the subacute time period and low T2w signal intensity in the chronic time period.</li>
		<li>Perform semi-quantitative analysis of T2 signal intensity ratios, if needed. Using Picture Archiving and Communication Software (PACS), draw an ROI over a portion of the LV myocardium and compare the LV T2 signal to skeletal muscle ROI signal. This can be useful in ruling out myocarditis.</li>
	</ol>
	</li>
	<li>Evaluate perfusion imaging.
	<ol>
		<li>Perform visual analysis to identify regions of relative hypoperfusion. In cardiac thrombus evaluation, the mass in question is carefully analyzed for any internal post contrast increased signal, which would suggest against thrombus and signify the presence of vascular tumor.</li>
	</ol>
	</li>
	<li>Evaluate late gadolinium enhancement (LGE) imaging within myocardium and any suspected masses.
	<ol>
		<li>Perform visual analysis to assess for the presence and the pattern of LGE. No solid regions of internal LGE are expected within a thrombus. However, a thin linear component of LGE can be seen along the outer margin of thrombus.</li>
		<li>Perform visual analysis of location and extent of LGE.</li>
		<li>Perform quantitative analysis with T1 mapping. Post processing software is used. Motion corrected sequences are used for analysis. Draw a region of interest over the mass of interest and over the myocardial regions of concern and record the pertinent T1 relaxation times. 
		NOTE: This is potentially helpful in distinguishing a thrombus from a tumor by providing quantitative assessment of pre-contrast T1 relaxation times.</li>
	</ol>
	</li>
	<li>Generate the report20,21.
	<ol>
		<li>Include general study information.
		<ol>
			<li>Document the study site, scanner information including the manufacturer and the model, the field strength, and the software platform.</li>
			<li>Document patient demographics.</li>
			<li>Document the patient ID, gender, and date of birth.</li>
			<li>Document the referring physician and service.</li>
		</ol>
		</li>
		<li>Include study performance information.
		<ol>
			<li>Document the date and time of examination, the personnel involved, the indication for examination, and the list of sequences used.</li>
			<li>Document the patient history and risk factors.</li>
			<li>Document the height, the weight, the heart rate, and the electrocardiogram interpretation.</li>
			<li>Document the contrast agent administered, the route, and the dose.</li>
			<li>Document the amount, the type, the route, and the dose of sedation, if applicable.</li>
		</ol>
		</li>
		<li>Report the cardiovascular imaging features.
		<ol>
			<li>Describe the cardiac size and function based on qualitative and quantitative assessment.
			<ol>
				<li>Report the cardiac mass and describe the location, the anatomic relationships, the 3-dimensional size, and the morphology.</li>
				<li>Report the mass T1- and T2-weighted signal characteristics of the mass. Classically, a thrombus will have low T1 and T2 signals. However, the T2w signal can vary with the age of blood products.</li>
				<li>Report the first pass perfusion pattern of the mass. The thrombus should have no internal perfusion.</li>
				<li>Report the late gadolinium enhancement pattern of the mass. Thrombus generally has no internal LGE but may have thin linear LGE signal around the periphery.</li>
				<li>Report the mass motion on cine imaging and its effect on myocardial contractility.</li>
				<li>Provide concluding statements synthesizing the findings into a comprehensive impression</li>
			</ol>
			</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>

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The authors have nothing to disclose.

With the increasing quality and frequency of diagnostic imaging, it is not uncommon to discover incidental cardiac masses when performing imaging for unrelated indications. Patients with cardiac masses are often asymptomatic, and if present, symptoms are typically nonspecific.
The diagnosis of cardiac thrombus is important not only for differentiating thrombus from benign or malignant cardiac tumors, but also for determining the need for anticoagulation and prevention of embolic events<sup cla...

Cardiac magnetic resonance (CMR) imaging is an important diagnostic modality for the evaluation of cardiovascular function and pathology. Technological advances allow for reduced acquisition time, improved spatial and temporal resolution, as well as higher quality tissue characterization. These advances are particularly useful in the evaluation of cardiac masses.
Echocardiography remains the first line imaging modality for the initial evaluation of cardiac masses, specifically with respect to mass location, morphology, and physiologic impact. However, echocardiography is limited by poor tissue characterization, a restricted field of view, and operator dependent image quality. Cardiac computed tomography (CT) is often utilized as a second-line imaging modality for assessing cardiac masses. Advantages of cardiac CT over other modalities include excellent spatial resolution and a superior ability in detecting calcifications. The main disadvantage of cardiac CT is patient exposure to ionizing radiation. Additional limitations include decreased temporal resolution and soft tissue contrast resolution. CMR is emerging as a valuable tool in the characterization of cardiac masses detected on echocardiography or CT. Compared to CT, CMR does not expose patients to ionizing radiation. In addition, CMR can be useful in treatment and surgical planning1,2.
A thrombus is the most common cardiac mass. The most common locations for cardiac thrombi are the left atrium and left atrial appendage, especially in the setting of atrial fibrillation or a dysfunctional left ventricle1,3. The diagnosis of thrombus is important for the prevention of embolic events as well as establishing the need for anticoagulation. CMR can aide in determining the acuity of a thrombus. Acute thrombus typically demonstrates intermediate T1- and T2-weighted signal intensity relative to the myocardium due to high amounts of oxygenated hemoglobin. Increased methemoglobin content in the subacute thrombus results in lower T1-weighted signal intensity and intermediate or increased T2-weighted signal intensity. With a chronic thrombus, methemoglobin and water are replaced with fibrous tissue leading to decreased T1- and T2-weighted signal intensity1,2,3.
The avascular composition gives a cardiac thrombus intrinsic tissue characteristics that can be exploited by contrast enhanced CMR, to aide in the differentiation of a thrombus from other cardiac tumors4. An organized thrombus does not enhance while true cardiac lesions enhance on post contrast imaging due to the presence of intratumoral vascularity3. Arterial perfusion imaging allows real time assessment of vascularity within a mass and is critical to differentiate a thrombus from a tumor. Perfusion within a mass can also be useful in the delineation of a bland thrombus from a tumor thrombus. Cine imaging provides advantages over other modalities that can be subject to motion artifact, and the temporal resolution provided by real time gated perfusion imaging increases sensitivity in detecting enhancement5.
T1 mapping is a MR technique that allows pre-contrast native T1 relaxation times and post-contrast extracellular volume calculation to detect pathologic alterations in tissue. By adding a quantitative dimension to CMR, T1 mapping can help differentiate various disease processes from the normal myocardium. An emerging application is the characterization of cardiac masses and delineation of masses from cardiac thrombi. Previous studies performed on a 1.5 T Aera XQ scanner have reported native T1 relaxation times of a recent thrombus (911 &#177; 177 ms) and a chronic thrombus (1,169 &#177; 107 ms)6. Other pertinent native T1 relaxation times include lipoma (278 &#177; 29 ms), calcifications (621 &#177; 218 ms), melanoma (736 ms), and normal myocardium (950 &#177; 21 ms). This data suggests that T1 mapping can add quantitative information to a non-contrast exam which in the setting of contraindication to IV gadolinium could be extremely useful6,7.
Contrast-enhanced CMR has been well validated for the detection of a left ventricular thrombus. It has been shown to provide the highest sensitivity and specificity (88% and 99%, respectively) for detection of a left ventricular thrombus compared to transthoracic (23% and 96%, respectively) and transesophageal (40% and 96%, respectively) echocardiography8. Currently, there are no large-scale studies validating the utility of CMR for assessing a thrombus in other chambers of the heart3.
Despite the many advantages of CMR over other imaging modalities for evaluating cardiac masses, there are also limitations. CMR, like cardiac CT, relies on electrocardiographic gating. This can cause artifact and image degradation in patients with significant arrhythmias. Image quality can also be degraded when scanning patients who have difficulty complying with breath hold requirements. However, faster acquisition times and respiratory gating techniques allow for quality images during free breathing. The presence of certain implanted devices is a contraindication for CMR and poses as a major disadvantage, although the number of MR compatible implantable devices is increasing1,2.
In summary, specific CMR sequences can be utilized to develop a dedicated MR imaging protocol for the evaluation of a suspected cardiac thrombus. The method presented here will provide instructions for the acquisition of CMR data for evaluation of a suspected thrombus. Pre-procedure screening, sequence selection, troubleshooting, post-processing, volumetric analysis, and report generation will be discussed.

<table><tbody><tr><td>MRI Scanner</td><td>Siemens Healthcare&lt;br/&gt; Erlangen, Germany</td><td>Magnetom Aera 1.5 Tesla&amp;nbsp;</td><td>MRI scanner that will be used for the demonstration</td></tr><tr><td>Post processing software&amp;nbsp;</td><td>Medis&lt;br/&gt; The Netherlands</td><td>Qmass software</td><td>post processing software for ventricular volumetric and T1 mapping analysis</td></tr><tr><td>Scanner processing software</td><td>Siemens Healthcare&lt;br/&gt; Erlangen, Germany</td><td>Myomaps&amp;nbsp;</td><td>Scanner sequence package and post processing software</td></tr></tbody></table>

cardiac magnetic resonance for the evaluation of suspected cardiac thrombus: conventional and emerging techniques

We present the conventional cardiac magnetic resonance (CMR) protocol for evaluating a suspected thrombus and highlight emerging techniques.&#160;The appearance of a mass on certain magnetic resonance (MR) sequences can help differentiate a thrombus from competing diagnoses such as a tumor. T1 and T2 signal characteristics of a thrombus are related to the evolution of hemoglobin properties. A thrombus typically does not enhance following contrast administration, which also helps differentiation from a tumor. We also highlight the emerging role of T1 mapping in the evaluation of a thrombus, which can add another level of support in diagnosis. Prior to any CMR exam, patient screening and interviews are critical to ensure safety and to optimize patient comfort. Effective communication during the exam between the technologist and the patient promotes proper breath holding technique and higher quality images. Volumetric post processing and structured reporting are helpful to ensure that the radiologist answers the ordering services&#39; question and communicates these results effectively. Optimal pre-MR safety evaluation, CMR exam execution, and post exam processing and reporting allow for delivery of high quality radiological service in the evaluation of a suspected cardiac thrombus.

The CMR protocol designed for the evaluation and diagnosis of cardiac thrombus encompasses patient screening and preparation, data acquisition utilizing specific sequences, data post-processing, and report generation. Specific signal characteristics on given sequences can infer with high accuracy the diagnosis of a cardiac thrombus and differentiate these from the competing diagnosis of a cardiac tumor. Table 1 highlights the conventional and emerging CMR sequences that a...

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Cardiac Magnetic Resonance for the Evaluation of Suspected Cardiac Thrombus: Conventional and Emerging Techniques

The goal of this article is to describe how cardiac magnetic resonance can be used for the evaluation and diagnosis of a suspected cardiac thrombus. The method presented will describe data acquisition as well as the pre-procedure and post-procedure protocol.

We present the conventional cardiac magnetic resonance (CMR) protocol for evaluating a suspected thrombus and highlight emerging techniques.&#160;The ...

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Research

JoVE Journal

Medicine

10.2K Views.  University of South Florida. Cardiac Magnetic Resonance of CMR is belangrijk in de evaluatie voor potentiële trombus omdat CMR een definitieve diagnose van de etiologie van een hartmassa kan bieden. CMR heeft voordelen ten opzichte van andere modaliteiten, zoals echocardiografie als CMR kan bieden multi-sequenced gedetailleerde karakterisering van weke delen massa's waar echo biedt voornamelijk visualisatie en grootte metingen. Voorafgaand aan de MRI worden de patiënten gescreend op metalen of geïmplanteerde apparaten...

Video: Cardiac Magnetic Resonance for the Evaluation of Suspected Cardiac Thrombus: Conventional and Emerging Techniques

Magnetic Resonance Derived Myocardial Strain Assessment Using Feature Tracking 

Purpose: An accurate and practical method to measure parameters like strain in myocardial tissue is of great clinical value, since it has been shown, that strain is a more sensitive and earlier marker for contractile dysfunction than the frequently used parameter EF. Current technologies for CMR are time consuming and difficult to implement in clinical practice. Feature tracking is a technology that can lead to more automization and robustness of quantitative analysis of medical images with less time consumption than comparable methods.
Methods: An automatic or manual input in a single phase serves as an initialization from which the system starts to track the displacement of individual patterns representing anatomical structures over time. The specialty of this method is that the images do not need to be manipulated in any way beforehand like e.g. tagging of CMR images.
Results: The method is very well suited for tracking muscular tissue and with this allowing quantitative elaboration of myocardium and also blood flow.
Conclusions: This new method offers a robust and time saving procedure to quantify myocardial tissue and blood with displacement, velocity and deformation parameters on regular sequences of CMR imaging. It therefore can be implemented in clinical practice.

Magnetic Resonance Derived Myocardial Strain Assessment Using Feature Tracking

An accurate and practical method to measure parameters like strain in myocardial tissue is of great clinical value, since it has been shown, that strain is a more sensitive and earlier marker for contractile dysfunction than the frequently used parameter EF.

Purpose: An accurate and practical method to measure parameters like strain in myocardial tissue is of great clinical value, since it has been shown, that ...

Retrograde Perfusion and Filling of Mouse Coronary Vasculature as Preparation for Micro Computed Tomography Imaging

Visualization of the vasculature is becoming increasingly important for understanding many different disease states. While several techniques exist for imaging vasculature, few are able to visualize the vascular network as a whole while extending to a resolution that includes the smaller vessels1,2. Additionally, many vascular casting techniques destroy the surrounding tissue, preventing further analysis of the sample3-5. One method which circumvents these issues is micro-Computed Tomography (&mu;CT). &mu;CT imaging can scan at resolutions &lt;10 microns, is capable of producing 3D reconstructions of the vascular network, and leaves the tissue intact for subsequent analysis (e.g., histology and morphometry)6-11. However, imaging vessels by ex vivo &mu;CT methods requires that the vessels be filled with a radiopaque compound. As such, the accurate representation of vasculature produced by &mu;CT imaging is contingent upon reliable and complete filling of the vessels. In this protocol, we describe a technique for filling mouse coronary vessels in preparation for &mu;CT imaging.
Two predominate techniques exist for filling the coronary vasculature: in vivo via cannulation and retrograde perfusion of the aorta (or a branch off the aortic arch) 12-14, or ex vivo via a Langendorff perfusion system 15-17. Here we describe an in vivo aortic cannulation method which has been specifically designed to ensure filling of all vessels. We use a low viscosity radiopaque compound called Microfil which can perfuse through the smallest vessels to fill all the capillaries, as well as both the arterial and venous sides of the vascular network. Vessels are perfused with buffer using a pressurized perfusion system, and then filled with Microfil. To ensure that Microfil fills the small higher resistance vessels, we ligate the large branches emanating from the aorta, which diverts the Microfil into the coronaries. Once filling is complete, to prevent the elastic nature of cardiac tissue from squeezing Microfil out of some vessels, we ligate accessible major vascular exit points immediately after filling. Therefore, our technique is optimized for complete filling and maximum retention of the filling agent, enabling visualization of the complete coronary vascular network &#x2013; arteries, capillaries, and veins alike.

Visualization of the coronary vessels is critical to advancing our understanding of cardiovascular diseases. Here we describe a method for perfusing murine coronary vasculature with a radiopaque silicone rubber (Microfil), in preparation for micro-Computed Tomography (&mu;CT) imaging.

Visualization of the vasculature is becoming increasingly important for understanding many different disease states. While several techniques exist for ...

In Vivo Quantitative Assessment of Myocardial Structure, Function, Perfusion and Viability Using Cardiac Micro-computed Tomography

The use of Micro-Computed Tomography (MicroCT) for in vivo studies of small animals as models of human disease has risen tremendously due to the fact that MicroCT provides quantitative high-resolution three-dimensional (3D) anatomical data non-destructively and longitudinally. Most importantly, with the development of a novel preclinical iodinated contrast agent called eXIA160, functional and metabolic assessment of the heart became possible. However, prior to the advent of commercial MicroCT scanners equipped with X-ray flat-panel detector technology and easy-to-use cardio-respiratory gating, preclinical studies of cardiovascular disease (CVD) in small animals required a MicroCT technologist with advanced skills, and thus were impractical for widespread implementation. The goal of this work is to provide a practical guide to the use of the high-speed Quantum FX MicroCT system for comprehensive determination of myocardial global and regional function along with assessment of myocardial perfusion, metabolism and viability in healthy mice and in a cardiac ischemia mouse model induced by permanent occlusion of the left anterior descending coronary artery (LAD).

In Vivo Quantitative Assessment of Myocardial Structure, Function, Perfusion and Viability Using Cardiac Micro-computed Tomography

This method outlines the use of Quantum Micro-Computed Tomography (MicroCT) to assess cardiac morphology, function, perfusion, metabolism and viability with iodinated contrast agent in mice with experimentally-induced myocardial ischemia. The technique can be applied for non-destructive high-throughput longitudinal in vivo imaging of various animal models of human heart disease.

The use of Micro-Computed Tomography (MicroCT) for in vivo studies of small animals as models of human disease has risen tremendously due to the fact that ...

Bioengineering

Noninvasive Assessment of Cardiac Abnormalities in Experimental Autoimmune Myocarditis by Magnetic Resonance Microscopy Imaging in the Mouse

Myocarditis is an inflammation of the myocardium, but only ~10% of those affected show clinical manifestations of the disease. To study the immune events of myocardial injuries, various mouse models of myocarditis have been widely used. This study involved experimental autoimmune myocarditis (EAM) induced with cardiac myosin heavy chain (Myhc)-&#945; 334-352 in A/J mice; the affected animals develop lymphocytic myocarditis but with no apparent clinical signs. In this model, the utility of magnetic resonance microscopy (MRM) as a non-invasive modality to determine the cardiac structural and functional changes in animals immunized with Myhc-&#945; 334-352 is shown. EAM and healthy mice were imaged using a 9.4 T (400 MHz) 89 mm vertical core bore scanner equipped with a 4 cm millipede radio-frequency imaging probe and 100 G/cm triple axis gradients. Cardiac images were acquired from anesthetized animals using a gradient-echo-based cine pulse sequence, and the animals were monitored by respiration and pulse oximetry. The analysis revealed an increase in the thickness of the ventricular wall in EAM mice, with a corresponding decrease in the interior diameter of ventricles, when compared with healthy mice. The data suggest that morphological and functional changes in the inflamed hearts can be non-invasively monitored by MRM in live animals. In conclusion, MRM offers an advantage of assessing the progression and regression of myocardial injuries in diseases caused by infectious agents, as well as response to therapies.

This study demonstrates the successful establishment of magnetic resonance microscopy imaging as a non-invasive tool to assess the cardiac abnormalities in mice affected with autoimmune myocarditis. The data indicate that the technique can be used to monitor the disease-progression in live animals.

Myocarditis is an inflammation of the myocardium, but only ~10% of those affected show clinical manifestations of the disease. To study the immune events ...

A Multicenter MRI Protocol for the Evaluation and Quantification of Deep Vein Thrombosis

We evaluated a magnetic resonance venography (MRV) approach with gadofosveset to quantify total thrombus volume changes as the principal criterion for treatment efficacy&#160;in a multicenter randomized study comparing edoxaban monotherapy with a heparin/warfarin regimen for acute, symptomatic lower extremities deep vein thrombosis (DVT) treatment. We also used a direct thrombus imaging approach (DTHI, without the use of a contrast agent) to quantify fresh thrombus. We then sought to evaluate the reproducibility of the analysis methodology and applicability of using 3D magnetic resonance venography and direct thrombus imaging for the quantification of DVT in a multicenter trial setting. From 10 randomly selected subjects participating in the edoxaban Thrombus Reduction Imaging Study (eTRIS), total thrombus volume in the entire lower extremity deep venous system was quantified bilaterally. Subjects were imaged using 3D-T1W gradient echo sequences before (direct thrombus imaging, DTHI) and 5 min after injection of 0.03 mmol/kg of gadofosveset trisodium (magnetic resonance venography, MRV). The margins of the DVT on corresponding axial, curved multi-planar reformatted images were manually delineated by two observers to obtain volumetric measurements of the venous thrombi. MRV was used to compute total DVT volume, whereas DTHI was used to compute volume of fresh thrombus. Intra-class correlation (ICC) and Bland Altman analysis were performed to compare inter and intra-observer variability of the analysis. The ICC for inter and intra-observer variability was excellent (0.99 and 0.98, p &#60;0.001, respectively) with no bias on Bland-Altman analysis for MRV images. For DTHI images, the results were slightly lower (ICC = 0.88 and 0.95 respectively, p &#60;0.001), with bias for inter-observer results on Bland-Altman plots. This study showed feasibility of thrombus volume estimation in DVT using MRV with gadofosveset trisodium, with good intra- and inter-observer reproducibility in a multicenter setting.

The goal of this study is to use magnetic resonance venography with long-circulating gadolinium-based contrast agent and direct thrombus imaging for quantitative evaluation of DVT volume in a multicenter, clinical trial setting. Inter- and intra-observer variability assessments were conducted, and reproducibility of the protocol was determined.

We evaluated a magnetic resonance venography (MRV) approach with gadofosveset to quantify total thrombus volume changes as the principal criterion for ...

Combined Near-infrared Fluorescent Imaging and Micro-computed Tomography for Directly Visualizing Cerebral Thromboemboli

Direct thrombus imaging visualizes the root cause of thromboembolic infarction. Being able to image thrombus directly allows far better investigation of stroke than relying on indirect measurements, and will be a potent and robust vascular research tool. We use an optical imaging approach that labels thrombi with a molecular imaging thrombus marker&#160;&#8212; a Cy5.5 near-infrared fluorescent (NIRF) probe that is covalently linked to the fibrin strands of the thrombus by the fibrin-crosslinking enzymatic action of activated coagulation factor XIIIa during the process of clot maturation. A micro-computed tomography (microCT)-based approach uses thrombus-seeking gold nanoparticles (AuNPs) functionalized to target the major component of the clot: fibrin. This paper describes a detailed protocol for the combined in vivo microCT and ex vivo NIRF imaging of thromboemboli in a mouse model of embolic stroke. We show that in vivo microCT and fibrin-targeted glycol-chitosan AuNPs (fib-GC-AuNPs) can be used for visualizing both in situ thrombi and cerebral embolic thrombi. We also describe the use of in vivo microCT-based direct thrombus imaging to serially monitor the therapeutic effects of tissue plasminogen activator-mediated thrombolysis. After the last imaging session, we demonstrate by ex vivo NIRF imaging the extent and the distribution of residual thromboemboli in the brain. Finally, we describe quantitative image analyses of microCT and NIRF imaging data. The combined technique of direct thrombus imaging allows two independent methods of thrombus visualization to be compared: the area of thrombus-related fluorescent signal on ex vivo NIRF imaging vs. the volume of hyperdense microCT thrombi in vivo.

This protocol describes the application of combined near-infrared fluorescent (NIRF) imaging and micro-computed tomography (microCT) for visualizing cerebral thromboemboli. This technique allows the quantification of thrombus burden and evolution. The NIRF imaging technique visualizes fluorescently labeled thrombus in excised brain, while the microCT technique visualizes thrombus inside living animals using gold-nanoparticles.

Direct thrombus imaging visualizes the root cause of thromboembolic infarction. Being able to image thrombus directly allows far better investigation of ...

Cardiac Magnetic Resonance Imaging at 7 Tesla

CMR at an ultra-high field (magnetic field strength B0&#160;&#8805; 7 Tesla) benefits from the signal-to-noise ratio (SNR) advantage inherent at higher magnetic field strengths and potentially provides improved signal contrast and spatial resolution. While promising results have been achieved, ultra-high field CMR is challenging due to energy deposition constraints and physical phenomena such as transmission field non-uniformities and magnetic field inhomogeneities. In addition, the magneto-hydrodynamic effect renders the synchronization of the data acquisition with the cardiac motion difficult. The challenges are currently addressed by explorations into novel magnetic resonance technology. If all impediments can be overcome, ultra-high field CMR may generate new opportunities for functional CMR, myocardial tissue characterization, microstructure imaging or metabolic imaging. Recognizing this potential, we show that multi-channel radio frequency (RF) coil technology tailored for CMR at 7 Tesla together with higher order B0 shimming and a backup signal for cardiac triggering facilitates high fidelity functional CMR. With the proposed setup, cardiac chamber quantification can be accomplished in examination times similar to those achieved at lower field strengths. To share this experience and to support the dissemination of this expertise, this work describes our setup and protocol tailored for functional CMR at 7 Tesla.

The sensitivity gain inherent to ultrahigh field magnetic resonance holds promise for high spatial resolution imaging of the heart. Here, we describe a protocol customized for functional cardiovascular magnetic resonance (CMR) at 7 Tesla using an advanced multi-channel radio-frequency coil, magnetic field shimming and a triggering concept.

CMR at an ultra-high field (magnetic field strength B0&#160;&#8805; 7 Tesla) benefits from the signal-to-noise ratio (SNR) advantage inherent at higher ...

Quantification of Mouse Heart Left Ventricular Function, Myocardial Strain, and Hemodynamic Forces by Cardiovascular Magnetic Resonance Imaging

Mouse models have contributed significantly to understanding genetic and physiological factors involved in healthy cardiac function, how perturbations result in pathology, and how myocardial diseases may be treated. Cardiovascular magnetic resonance imaging (CMR) has become an indispensable tool for a comprehensive in vivo assessment of cardiac anatomy and function. This protocol shows detailed measurements of mouse heart left ventricular function, myocardial strain, and hemodynamic forces using 7-Tesla CMR. First, animal preparation and positioning in the scanner are demonstrated. Survey scans are performed for planning imaging slices in various short- and long-axis views. A series of prospective ECG-triggered short-axis (SA) movies (or CINE images) are acquired covering the heart from apex to base, capturing end-systolic and end-diastolic phases. Subsequently, single-slice, retrospectively gated CINE images are acquired in a midventricular SA view, and in 2-, 3-, and 4-chamber views, to be reconstructed into high-temporal resolution CINE images using custom-built and open-source software. CINE images are subsequently analyzed using dedicated CMR image analysis software.
Delineating endomyocardial and epicardial borders in SA end-systolic and end-diastolic CINE images allows for the calculation of end-systolic and end-diastolic volumes, ejection fraction, and cardiac output. The midventricular SA CINE images are delineated for all cardiac time frames to extract a detailed volume-time curve. Its time derivative allows for the calculation of the diastolic function as the ratio of the early filling and atrial contraction waves. Finally, left ventricular endocardial walls in the 2-, 3-, and 4-chamber views are delineated using feature-tracking, from which longitudinal myocardial strain parameters and left ventricular hemodynamic forces are calculated. In conclusion, this protocol provides detailed in vivo quantification of the mouse cardiac parameters, which can be used to study temporal alterations in cardiac function in various mouse models of heart disease.

This study describes a comprehensive cardiovascular magnetic resonance imaging (CMR) protocol to quantify the left ventricular functional parameters of the mouse heart. The protocol describes the acquisition, post-processing, and analysis of the CMR images as well as assessment of different cardiac functional parameters.

Mouse models have contributed significantly to understanding genetic and physiological factors involved in healthy cardiac function, how perturbations ...

Tissue Preparation Techniques for Contrast-Enhanced Micro Computed Tomography Imaging of Large Mammalian Cardiac Models with Chronic Disease

Structural remodeling is a common consequence of chronic pathological stresses imposed on the heart. Understanding the architectural and compositional properties of diseased tissue is critical to determine their interactions with arrhythmic behavior. Microscale tissue remodeling, below the clinical resolution, is emerging as an important source of lethal arrhythmia, with high prevalence in young adults. Challenges remain in obtaining high imaging contrast at sufficient microscale resolution for preclinical models, such as large mammalian whole hearts. Moreover, tissue composition-selective contrast enhancement for three-dimensional high-resolution imaging is still lacking. Non-destructive imaging using micro-computed tomography shows promise for high-resolution imaging. The objective was to alleviate sufferance from X-ray over attenuation in large biological samples. Hearts were extracted from healthy pigs (N = 2), and sheep (N = 2) with either induced chronic myocardial infarction and fibrotic scar formation or induced chronic atrial fibrillation. Excised hearts were perfused with: a saline solution supplemented with a calcium ion quenching agent and a vasodilator, ethanol in serial dehydration, and hexamethyldisilizane under vacuum. The latter reinforced the heart structure during air-drying for 1 week. Collagen-dominant tissue was selectively bound by an X-ray contrast-enhancing agent, phosphomolybdic acid. Tissue conformation was stable in air, permitting long-duration microcomputed tomography acquisitions to obtain high-resolution (isotropic 20.7 &#181;m) images. Optimal contrast agent loading by diffusion showed selective contrast enhancement of the epithelial layer and sub-endocardial Purkinje fibers in healthy pig ventricles. Atrial fibrillation (AF) hearts showed enhanced contrast accumulation in the posterior walls and appendages of the atria, attributed to greater collagen content. Myocardial infarction hearts showed increased contrast selectively in regions of cardiac fibrosis, which enabled the identification of interweaving surviving myocardial muscle fibers. Contrast-enhanced air-dried tissue preparations enabled microscale imaging of the intact large mammalian heart and selective contrast enhancement of underlying disease constituents.

Here, we present a protocol to obtain high resolution micro computed tomography images of healthy and pathological large mammalian whole hearts with collagen-selective contrast enhancement.

Structural remodeling is a common consequence of chronic pathological stresses imposed on the heart. Understanding the architectural and compositional ...

Estimating Bilateral Atrial Function by Cardiovascular Magnetic Resonance Feature Tracking in Patients with Paroxysmal Atrial Fibrillation

Atrial fibrillation (AF) is the most common form of arrhythmia. Atrial remodeling is considered the most critical mechanism for the presence and development of atrial fibrillation. Also, atrial remodeling can lead to the enlargement and dysfunction of the left atrium (LA), resulting in thrombosis and heart failure. Functional changes in left atrial strain and strain rate occur before structural alterations and are closely associated with structural remodeling and left atrial fibrosis. These parameters are sensitive biomarkers for atrial function. Cardiac magnetic resonance feature tracking (CMR-FT) is a novel, non-invasive, post-processing technique that can evaluate left atrial strain and strain rate. The CMR-FT was utilized in this investigation to assess the bilateral atrium strain rate in individuals with paroxysmal AF. Modifications in each segmental strain were evaluated using segmental analysis. The CMR-FT is recommended for non-invasive evaluations in the clinical assessment of atrial strain among existing strain imaging techniques. Further, it is a flexible parameter measurement with good reproducibility, high soft-tissue resolution, and post-processing based on standard cine balanced steady-state free precision (bSSFP) long-axis images without requiring a new sequence acquisition.

The atrial function is associated with the strain and strain rate. The cardiac magnetic resonance feature tracking (CMR-FT) technique was used in this study to quantify left and right atrial global and segmental longitudinal strain and strain rate in individuals with paroxysmal atrial fibrillation.

Cardiac Magnetic Resonance for the Evaluation of Suspected Cardiac Thrombus: Conventional and Emerging Techniques

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