Name: cardiac magnetic resonance imaging at 7 tesla
Uploaded: 2019-01-06T13:00:00.000+00:00
Duration: 9 min 14 s
Description: Watch this Scientific Journal Video about Cardiac Magnetic Resonance Imaging at 7 Tesla at JoVE.com

The authors acknowledge the facilities, and the scientific and technical assistance of the National Imaging Facility at the Centre for Advanced Imaging, University of Queensland. We would also like to thank Graham Galloway and Ian Brereton for their help to obtain a CAESIE grant for Thoralf Niendorf.

The study is approved by the ethics committee of the University of Queensland, Queensland, Australia and informed consent has been obtained from all subjects included in the study.
1. Subjects
<ol>
	<li>Recruit volunteer subjects over 18 years of age internally at the University of Queensland.</li>
	<li>Informed consent
	<ol>
		<li>Inform each subject about potential risks of undergoing the examination before entering the magnetic resonance imaging (MRI) safety zone. Specifically, discuss the ultra-high magnetic field exposure and possible contraindications for undergoing an MRI examination. Inform the subject that participating in the examination is voluntary and that at all times he/she may abort the examination. Obtain informed consent in writing.</li>
		<li>Explain the procedure to the participant. Since imaging is performed during breath hold at end expiration and consistent breath holding is integral to image quality, coach the subject on breathing technique prior to scanning.</li>
		<li>Perform MR safety screening on all subjects before entering the MRI safety zone in writing and again before entering the scanner room. Exclude subjects with contraindications for undergoing an MRI examination (e.g., pacemakers, implanted defibrillators, other unsafe medical implants or claustrophobia).</li>
	</ol>
	</li>
	<li>Ask the subject to change into scrubs before entering the scanner room.</li>
</ol>
2. Preparation
<ol>
	<li>Set up the additional hardware required to operate the dedicated 32 channel 1H cardiac transceiver (Tx/Rx) RF coil26 on the patient table as outlined in Figure 1a and b. Apart from a small power splitter box (Figure 1c), the auxiliary coil equipment comprises one power splitter box and phase shifter box (Figure 1d) and one Tx/Rx interface box (Figure 1e) for each of the two RF coil sections that will be placed below and on top of the subject. The greater part it accommodates the local transmit electronics, which is required for signal excitation at 7 Tesla, since traditional birdcage body coils as commonly employed at 1.5 T and 3.0 T are not available.</li>
	<li>Place the additional RF coil hardware at the top end of the patient table as outlined in Figure 1b and link the individual boxes together with the Bayonet Neill-Concelman (BNC) cables. Since the distance that the patient table can be driven into the MRI bore is limited, ensure to leave sufficient space on the patient table for the coil infrastructure to guarantee that the subject&#39;s heart can be positioned with the center of the coil at the isocenter of the magnet.</li>
	<li>Connect the Tx/Rx interface boxes to the four coil plugs on the patient table.</li>
	<li>Place the center of the posterior coil array 147 cm away from top end of the patient table (Figure 1b). This spot defines where the posterior coil array has to be placed to ensure that the subject&#39;s heart is at the isocenter of the magnet if the patient table is maximally driven into the bore. The placement on the predefined coil spot is crucial, to ensure optimal operation. Determine the optimal position of the posterior coil array as well as the positioning of the auxiliary equipment in preliminary tests including several volunteers of different body height.</li>
	<li>Connect the four cables of the posterior coil array into the appropriate sockets of the Tx/Rx interface box for the posterior array.</li>
	<li>Connect the four modules of the anterior coil array are with the Tx/Rx interface box for the top array and flip the array over the auxiliary coil equipment to allow for subject positioning.</li>
	<li>Attach the three ECG electrodes to the body of the subject. Follow the vendor guidelines for electrode placement to ensure optimal operation of the system&#39;s trigger algorithm.</li>
	<li>Position the subject on the patient table (Figure 1f). Critically, make sure that the subject&#39;s heart is positioned central to the posterior coil in order to guarantee scanning within the isocenter of the magnet. As, depending on the subject&#39;s height, the head will have to be placed on top of the coil/interface box connectors, place the cables carefully and use appropriate cushioning to ensure the subject&#39;s comfort and compliance.</li>
	<li>Connect the trigger device to the ECG electrodes.</li>
	<li>Attach the pulse trigger device to the subject&#39;s index finger. Use this second device for triggering in the event of severe distortions of the ECG signal introduced by the MHD effect.</li>
	<li>Hand the safety squeeze ball to the subjects.</li>
	<li>Equip the subject with headphones and earbuds to reduce the noise exposure and to allow communication with the subject.</li>
	<li>Place the anterior coil on the subject&#39;s chest, such that the cables that connect to the plugs E-F and G-H are located to the right and left of the subject&#39;s head, respectively.</li>
	<li>Drive the subject into the scanner bore. Perform the driving operation manually and ensure that the speed button of the table controls is in the off-position to guarantee the subject&#39;s safety during the driving process. Do not use the automatic mode as the variable table speed in this mode is optimized for neuro imaging and the distance the table can be driven automatically into the bore is limited by the scanner hardware.</li>
	<li>Check if communication to the subject through the intercom is possible and if the subject is feeling well.</li>
	<li>MR imaging
	<ol>
		<li>Run basic localizer (scout) scans along the three physical gradient axes for slice planning and B0-shimming.</li>
		<li>Use an ECG-triggered fast low angle shot (FLASH) sequence with the following acquisition parameters: field of view (FOV) = 400 mm, matrix = 192 x 144, slices per gradient axis = 1, thickness = 8 mm, echo time (TE) = 1.24, repetition time (TR) = 298 ms, flip angle = 10&#176;.</li>
		<li>Apply parallel MRI with acceleration factor = 2, reference lines = 24 and generalized autocalibrating partially parallel acquisitions (GRAPPA) reconstruction.</li>
		<li>Use the localizer images to verify that the subject&#39;s heart is positioned in the isocenter of the magnet. Reposition the subject if necessary.</li>
	</ol>
	</li>
	<li>3rd order B0-shimming
	<ol>
		<li>Open the 3rd order shim tool (Figure 2a) and reset all 3rd order shim currents (Figure 2b).</li>
		<li>Prescribe the shim volume for proper shimming over a region covering the heart (Figure 2c).</li>
		<li>Run a non-triggered advanced flow compensated 2D multi-echo FLASH shim sequence for the calculation of the 3rd order shim currents. Use the following parameters: FOV = 400 x 400 mm, matrix = 80 x 80, slices = 64, thickness = 5.0 mm, TE1 = 3.06, TE2 = 5.10, TR = 7 ms, flip angle = 20 &#176;, parallel MRI (GRAPPA), acceleration factor = 2, reference lines = 24.</li>
		<li>To calculate and apply the 3rd order shim currents, open the next protocol and copy the above-mentioned shim volume. Execute the SetShim program in the start menu (Figure 2a). Next, open the Manual Adjustments window in the Options menu (Figure 2d). In the 3D Shim tab, click Calculate | Apply to set the shim currents for the 2nd order (Figure 2e). Finally, set the shim currents by clicking Set Shim_3rd in the 3rd order shim tool (Figure 2b).</li>
		<li>Close the Manual Adjustments window. Keep the shim volume and the shim currents fixed throughout the remainder of the examination. Note that the shimming procedure can be highly system specific.</li>
	</ol>
	</li>
	<li>Acquire further localizers to support double-oblique slice planning. Unless stated otherwise, use a breath held and ECG-triggered 2D FLASH sequence with the following parameters for all localizer measurements: FOV = 360 x 290 mm, matrix = 256 x 206, thickness = 6.0 mm, TE = 1.57, TR = 3.9 ms, flip angle = 35 &#176;, parallel MRI (GRAPPA), acceleration factor: 2, reference lines: 24. Advise the patient to hold the breath in expiration. Employ high flip angles or use a segmented cine protocol (see below) to achieve improved contrast.
	<ol>
		<li>Acquire the 2 chamber localizer (1 slice), planned perpendicular on the axial scout parallel to the septal wall (Figure 3a).</li>
		<li>Acquire the 4 chamber localizer (1 slice), planned perpendicular on the 2 chamber localizer slice through the mitral valve and the apex of the left ventricle (Figure 3b).</li>
		<li>Acquire the short axis localizer (7 slices, FOV = 360 x 330 mm), planned perpendicular on the 4 chamber localizer parallel to the mitral valve and perpendicular to the septal wall (Figure 3c).</li>
	</ol>
	</li>
	<li>Perform the CINE acquisitions. Use a high resolution breath held ECG-triggered segmented 2D FLASH sequence with the following parameters: FOV = 360 x 270 mm, matrix = 256 x 192/264 x 352, thickness = 4.0 mm, TE = 3.14, TR = 6.3 ms, flip angle = 35-55 &#176;, segments = 7, parallel MRI (GRAPPA), acceleration factor = 2/3, temporal resolution = 42.6/44.3 ms.
	<ol>
		<li>Start with the left ventricular 4 chamber view (horizontal long axis, HLA) slices. Plan the central slice through the center of the mitral and tricuspid valves and the apex of the left ventricle (Figure 3d). Acquire each slice within an individual breath hold in expiration.</li>
		<li>Next, acquire the left ventricular short axis slices. Plan them perpendicular to the HLA and parallel to the mitral valve so that it covers the whole left ventricle from the base to the apex (Figure 3e). To ensure accurate function testing, position the first slice accurately at the mitral valve leaflet insertions, so that the center of the slice is within the ventricle. Again, acquire each slice within an individual breath hold in expiration.</li>
	</ol>
	</li>
</ol>

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Kieran O'Brien and Jonathan Richer are employed by Siemens Ltd. Australia. Jan Rieger and Thoralf Niendorf are founders of MRI.TOOLS GmbH, Berlin, Germany. Jan Rieger was CTO and an employee of MRI.TOOLS GmbH. Thoralf Niendorf is CEO of MRI.TOOLS GmbH.

Functional CMR examinations could be conducted successfully at 7 Tesla. Based on the field strength driven SNR gain, CINE images of the human heart could be acquired with significantly higher spatial resolution compared to 1.5 or 3 T. While a slice thickness of 6 to 8 mm and in-plane voxel edge lengths of 1.2 to 2.0 mm are commonly used at lower clinical field strengths1,30, the measurements at 7 Tesla could be conducted with a slice thickness of 4 mm and an isot...

Cardiovascular magnetic resonance (CMR) is of proven clinical value with a growing range of clinical indications1,2. In particular, the evaluation of cardiac morphology and function is of major relevance and typically realized by tracking and visualizing the heart motion throughout the entire cardiac cycle using segmented breath-held two-dimensional (2D) cinematograpic (CINE) imaging techniques. While a high spatio-temporal resolution, high blood-myocardium contrast and high signal-to-noise ratio (SNR) are required, the data acquisition is highly constrained by the cardiac and respiratory motion and the use of multiple breath-holds as well as the need for whole heart or left-ventricular coverage often leads to extensive scan times. Parallel imaging, simultaneous multi-slice imaging or other acceleration techniques help to address the motion related constraints3,4,5,6.
Moreover, to benefit from the inherent SNR gain at higher magnetic fields, high field systems with B0 = 3 Tesla are increasingly employed in clinical routine7,8. The development has also encouraged investigations into ultra-high field (B0&#8805;7 Tesla, f&#8805;298 MHz) CMR9,10,11,12,13,14. The gain in SNR and blood-myocardium contrast inherent to the higher field strength holds the promise to be transferrable into enhanced functional CMR using a spatial resolution that exceeds today&#39;s limits15,16,17. In turn, new possibilities for magnetic resonance (MR) based myocardial tissue characterization, metabolic imaging and microstructure imaging are expected13. So far, several groups have demonstrated the feasibility of CMR at 7 Tesla and specifically tailored ultra-high field technology has been introduced17,18,19,20,21,22. Regarding these promising developments, the potential of ultra-high field CMR can be considered to be yet untapped13. At the same time, physical phenomena and practical obstacles such as magnetic field inhomogeneities, radio frequency (RF) excitation field non-uniformities, off-resonance artifacts, dielectric effects, localized tissue heating and field strength independent RF power deposition constraints make imaging at ultra-high field challenging10,17. The latter are employed to control RF induced tissue heating and to ensure safe operation. Moreover, electrocardiogram (ECG) based triggering can be significantly impacted by the magneto-hydrodynamic (MHD) effect19,23,24. To address the challenges induced by the short wavelength in tissue, many-element transceiver RF coil arrays tailored for CMR at 7 Tesla were proposed21,25,26,27. Parallel RF transmission provides means for transmission field shaping, also known as B1+ shimming, which allows to reduce the magnetic field inhomogeneities and susceptibility artefacts18,28. While at the current stage, some of these measures might increase the experimental complexity, the concepts have proven helpful and may be translated to the clinical field strengths of CMR 1.5 T or 3 T.
Currently, 2D balanced steady state free precession (bSSFP) CINE imaging is the standard of reference for clinical functional CMR at 1.5 T and 3 T1. Recently, the sequence was successfully employed at 7 Tesla, but a large number of challenges remain19. Patient specific B1+ shimming and extra RF coil adjustments were applied to manage RF power deposition constraints and careful B0 shimming was performed to control the sequence typical banding artifacts. With an average scan time of 93 minutes for left-ventricular (LV) function assessment, the efforts prolonged the examination times beyond clinically acceptable limits. Here, spoiled gradient echo sequences provide a viable alternative. At 7 Tesla, total examination times of (29 &#177; 5) min for LV function assessment were reported, which corresponds well to clinical imaging protocols at lower field strengths21. Thereby, spoiled gradient echo based CMR benefits from the prolonged T1 relaxation times at ultra-high field that result in an enhanced blood-myocardium contrast superior to gradient echo imaging at 1.5 T. This renders subtle anatomic structures such as the pericardium, the mitral and tricuspid valves as well as the papillary muscles well identifiable. Congruously, spoiled gradient echo based cardiac chamber quantification at 7 Tesla agrees closely with LV parameters derived from 2D bSSFP CINE imaging at 1.5 T20. Apart from that, accurate right-ventricular (RV) chamber quantification was recently demonstrated feasible using a high resolution spoiled gradient echo sequence at 7 Tesla29.
Recognizing the challenges and opportunities of CMR at ultra-high field, this work presents a setup and protocol customized for functional CMR acquisitions on an investigational 7 Tesla research scanner. The protocol outlines the technical underpinnings, shows how impediments can be overcome, and provides practical considerations that help to keep the extra experimental overhead at a minimum. The proposed imaging protocol constitutes a four-fold improvement in the spatial resolution versus today&#39;s clinical practice. It is meant to provide a guideline for clinical adaptors, physician scientists, translational researchers, application experts, MR radiographers, technologists and new entrants into the field.

<table><tbody><tr><td>7 Tesla MRI system</td><td>Siemens</td><td></td><td>Investigational Device</td></tr><tr><td>32-Channel -1H-Cardiac Coil</td><td>MRI.Tools GmbH</td><td></td><td>Transmit/Receive RF Coil for MR Imaging and Spectroscopy at 7.0 Tesla</td></tr><tr><td>ECG Trigger Device</td><td>Siemens</td><td></td><td></td></tr><tr><td>Pulse Trigger Device</td><td>Siemens</td><td></td><td></td></tr></tbody></table>

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.

Representative results of cardiac CINE examinations derived from volunteers are depicted in Figure 4. Shown are diastolic and systolic time-frames of short axis and a four-chamber long axis views of the human heart. The significantly higher spatial resolution for the short axis views (Figure&#160;4a, 4b, 4e, 4f) compared to the long axis views (Figure&#160;4c...

Watch this Scientific Journal Video about Cardiac Magnetic Resonance Imaging at 7 Tesla at JoVE.com

Cardiac Magnetic Resonance Imaging 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 ...

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11.2K Views.  The University of Queensland, Brisbane, Australia. 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. 

Video: Cardiac Magnetic Resonance Imaging at 7 Tesla

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 ...

Quantitative Magnetic Resonance Imaging of Skeletal Muscle Disease

Quantitative magnetic resonance imaging (qMRI) describes the development and use of MRI to quantify physical, chemical, and/or biological properties of living systems. Neuromuscular diseases often exhibit a temporally varying, spatially heterogeneous, and multi-faceted pathology. The goal of this protocol is to characterize this pathology using qMRI methods. The MRI acquisition protocol begins with localizer images (used to locate the position of the body and tissue of interest within the MRI system), quality control measurements of relevant magnetic field distributions, and structural imaging for general anatomical characterization. The qMRI portion of the protocol includes measurements of the longitudinal and transverse relaxation time constants (T1 and T2, respectively). Also acquired are diffusion-tensor MRI data, in which water diffusivity is measured and used to infer pathological processes such as edema. Quantitative magnetization transfer imaging is used to characterize the relative tissue content of macromolecular and free water protons. Lastly, fat-water MRI methods are used to characterize fibro-adipose tissue replacement of muscle. In addition to describing the data acquisition and analysis procedures, this paper also discusses the potential problems associated with these methods, the analysis and interpretation of the data, MRI safety, and strategies for artifact reduction and protocol optimization.

Neuromuscular diseases often exhibit a temporally varying, spatially heterogeneous, and multi-faceted pathology. The goal of this protocol is to characterize this pathology using non-invasive magnetic resonance imaging methods.

Quantitative magnetic resonance imaging (qMRI) describes the development and use of MRI to quantify physical, chemical, and/or biological properties of ...

Assessing Cortical Cerebral Microinfarcts on High Resolution MR Images

Cerebral microinfarcts are frequent findings in the post-mortem human brain, and are related to cognitive decline and dementia. Due to their small sizes it is challenging to study them on clinical MRI scans. It was recently demonstrated that cortical microinfarcts can be depicted with MRI scanners using high magnetic field strengths (7T). Based on this experience, a proportion of these lesions is also visible on lower resolution 3T MRI. These findings were corroborated with ex vivo imaging of post-mortem human brain tissue, accompanied by histopathological verification of possible cortical microinfarcts.
Here an ex vivo imaging protocol is presented, for the purpose of validating MR observed cerebral microvascular pathology with histological evaluation. Furthermore, guidelines are provided for the assessment of cortical microinfarcts on both in vivo 7T and 3T MR images. These guidelines provide researchers with a tool to rate cortical microinfarcts on in vivo images of larger patient samples, to further unravel their clinical relevance in cognitive decline and dementia, and establish these lesions as a novel biomarker of cerebral small vessel disease.

A high resolution ex vivo 7T MR imaging protocol is presented, to perform MR-guided histopathological validation of microvascular pathology in post-mortem human brain tissue. Furthermore, guidelines are provided for the assessment of cortical microinfarcts on in vivo 7T as well as 3T MR images.

Cerebral microinfarcts are frequent findings in the post-mortem human brain, and are related to cognitive decline and dementia. Due to their small sizes ...

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.

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 ...

Functional Magnetic Resonance Spectroscopy at 7 T in the Rat Barrel Cortex During Whisker Activation

Nuclear magnetic resonance (NMR) spectroscopy offers the opportunity to measure cerebral metabolite contents in vivo and noninvasively. Thanks to technological developments over the last decade and the increase in magnetic field strength, it is now possible to obtain good resolution spectra in vivo in the rat brain. Neuroenergetics (i.e., the study of brain metabolism) and, especially, metabolic interactions between the different cell types have attracted more and more interest in recent years. Among these metabolic interactions, the existence of a lactate shuttle between neurons and astrocytes is still debated. It is, thus, of great interest to perform functional proton magnetic resonance spectroscopy (1H-MRS) in a rat model of brain activation and monitor lactate. However, the methyl lactate peak overlaps lipid resonance peaks and is difficult to quantify. The protocol described below allows metabolic and lactate fluctuations to be monitored in an activated brain area. Cerebral activation is obtained by whisker stimulation and 1H-MRS is performed in the corresponding activated barrel cortex, whose area is detected using blood-oxygen-level-dependent functional magnetic resonance imaging (BOLD fMRI). All steps are fully described: the choice of anesthetics, coils, and sequences, achieving efficient whisker stimulation directly in the magnet, and data processing.

After checking by blood-oxygen-level-dependent functional magnetic resonance imaging (BOLD fMRI) that the corresponding somatosensory barrel field cortex area (called S1BF) is correctly activated, the main goal of this study is to quantify lactate content fluctuations in the activated rat brains by localized proton magnetic resonance spectroscopy (1H-MRS) at 7 T.

Nuclear magnetic resonance (NMR) spectroscopy offers the opportunity to measure cerebral metabolite contents in vivo and noninvasively. Thanks to ...

Neuroscience

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 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 ...

Magnetic Resonance Imaging of Multiple Sclerosis at 7.0 Tesla

The overall goal of this article is to demonstrate a state-of-the-art ultrahigh field (UHF) magnetic resonance (MR) protocol of the brain at 7.0 Tesla in multiple sclerosis (MS) patients. MS is a chronic inflammatory, demyelinating, neurodegenerative disease that is characterized by white and gray matter lesions. Detection of spatially and temporally disseminated T2-hyperintense lesions by the use of MRI at 1.5 T and 3 T represents a crucial diagnostic tool in clinical practice to establish accurate diagnosis of MS based on the current version of the 2017 McDonald criteria. However, the differentiation of MS lesions from brain white matter lesions of other origins can sometimes be challenging due to their resembling morphology at lower magnetic field strengths (typically 3 T). Ultrahigh field MR (UHF-MR) benefits from increased signal-to-noise ratio and enhanced spatial resolution, both key to superior imaging for more accurate and definitive diagnoses of subtle lesions. Hence, MRI at 7.0 T has shown encouraging results to overcome the challenges of MS differential diagnosis by providing MS-specific neuroimaging markers (e.g., central vein sign, hypointense rim structures and differentiation of MS grey matter lesions). These markers and others can be identified by other MR contrasts other than T1 and T2 (T2*, phase, diffusion) and substantially improve the differentiation of MS lesions from those occurring in other neuroinflammatory conditions such as neuromyelitis optica and Susac syndrome. In this article, we describe our current technical approach to study cerebral white and grey matter lesions in MS patients at 7.0 T using different MR acquisition methods. The up-to-date protocol includes the preparation of the MR setup including the radio-frequency coils customized for UHF-MR, standardized screening, safety and interview procedures with MS patients, patient positioning in the MR scanner and acquisition of dedicated brain scans tailored for examining MS.

Here, we present a protocol to acquire magnetic resonance (MR) images of multiple sclerosis (MS) patient brains at 7.0 Tesla. The protocol includes preparation of the setup including the radio-frequency coils, standardized interview procedures with MS patients, subject positioning in the MR scanner and MR data acquisition.

The overall goal of this article is to demonstrate a state-of-the-art ultrahigh field (UHF) magnetic resonance (MR) protocol of the brain at 7.0 Tesla in ...

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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 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 ...

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Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) is a noninvasive medical imaging technique based on a phenomenon of nuclear physics discovered in the 1930s, in which matter exposed to magnetic fields and radio waves was found to emit radio signals. In 1970, a physician and researcher named Raymond Damadian noticed that malignant (cancerous) tissue gave off different signals than normal body tissue. He applied for a patent for the first MRI scanning device in clinical use by the early 1980s. The early MRI scanners were crude, but advances in digital computing and electronics led to their advancement over any other technique for precise imaging, especially in discovering tumors. Compared to other diagnostic imaging techniques like computed tomography and X-ray, MRI does not expose patients to radiation.
The drawbacks of MRI scans include their much higher cost and patient discomfort with the procedure. The MRI scanner subjects the patient to such powerful electromagnets that the scan room must be shielded. The patient must be enclosed in a metal tube-like device for the duration of the scan, sometimes as long as thirty minutes, which can be uncomfortable and impractical for ill patients. The machine is also so noisy that, even with earplugs, patients can become anxious or fearful. These problems have been overcome somewhat with the development of &#34;open&#34;&#160;MRI scanning, which does not require the patient to be entirely enclosed in a metal tube. Patients with iron-containing metallic implants (internal sutures, some prosthetic devices, pacemakers and so on) cannot undergo MRI scanning because it can dislodge these implants.
Different images are formed depending on the time taken between the sequence of magnetic pulses and the receipt and interpretation of the signal. A T1-weighted image has fatty tissues appearing brighter due to their enhanced signal while suppressing water signals, making it appear darker. In contrast, the T2-weighted image shows an enhanced water signal. Further, using MRI contrast media or dyes, like gadolinium, helps improve the quality of the images. Usually injected into the patient&#39;s vein, the gadolinium contrast dyes contain strongly paramagnetic gadolinium (Gd), which has positive magnetic susceptibility. When placed in a magnetic field, it is not directly seen in the MRI result but helps shorten the T1 values in tissues, where it accumulates, which allows the tissues to appear brighter in T1-weighted images.
Functional MRIs (fMRI), which detect the concentration of blood flow in certain body parts, are increasingly being used to study the activity in parts of the brain during various body activities. This has helped scientists learn more about the locations of different brain functions and more about brain abnormalities and diseases. More recently, 4D flow MRI provides 3D blood flow images and hemodynamics, with the fourth dimension being time, allowing cardiovascular disease assessment through the 3D coverage of the anatomy and velocity.
This content is derived from <a href="https://openstax.org/books/anatomy-and-physiology/pages/1-7-medical-imaging">Openstax, Anatomy and Physiology, Section 1.7: Medical Imaging</a>

Magnetic resonance imaging (MRI) is a noninvasive medical imaging technique based on a phenomenon of nuclear physics discovered in the 1930s, in which ...