Name: fat-water phantoms for magnetic resonance imaging validation: a flexible and scalable protocol
Uploaded: 2018-09-07T13:45:00.000+00:00
Duration: 7 min 59 s
Description: Watch this Scientific Journal Video about Fat-Water Phantoms for Magnetic Resonance Imaging Validation: A Flexible and Scalable Protocol at JoVE.com

Funding support for this research was provided the National Institutes of Health (NIH) and National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)/NIH R01-DK-105371. We thank Dr. Houchun (Harry) Hu for advice and suggestions on fat water phantom creation.

1. Prepare the Workstation and Materials
<ol>
	<li>Adhere to all laboratory safety rules. Wear eye protection and gloves. Read the material safety data sheet for each of the reagents used and take appropriate precautions. Review the materials and equipment list, chemical handling procedures, and glassware precautions. 
	Caution: This protocol requires the use of a hotplate at high temperatures. Use caution and wear heat resistant gloves when interacting with hot containers and do not touch the surface of the hotplate.</li>
	<li>Clear the workspace and clean the surfaces with disinfectant. Wash your hands and put gloves on.</li>
	<li>Sterilize all instruments and the inside of all glass jars to reduce the potential risk of contamination and increase the longevity of the phantom. 
	NOTE: If the phantom will be used for more than a couple of days, periodically clean the surface of the completed phantom with ethanol to prevent bacterial growth.</li>
</ol>
2. Prepare the Water Solution
<ol>
	<li>Prepare the workspace for the&#160;water solution. Position the following materials and equipment on the bench: graduated cylinder, 400 mL beaker, stir bar, scale, 2x weigh boats, spatula, 2x 1.0 mL syringes with needle, distilled water, gadolinium-diethylenetriaminepentacetate (DTPA) contrast agent, water-soluble surfactant, agar, and sodium benzoate. 
	NOTE: Syringes can be used with or without needles. However, using needles will improve the accuracy of the measurement and help prevent splatter when the contents are being added to the water or oil solutions.</li>
	<li>Place a stir bar into a 400 mL beaker. Use a 100 or 200 mL graduated cylinder to measure 300 mL of distilled water and pour the water into the beaker. Place the beaker on the hotplate and set at 90 &#176;C with a stir rate of 100 rpm. 
	NOTE: High temperatures are used in this protocol to achieve quick results. Because the solutions are not left on the hotplate for long periods of time, the set-point temperature for the hotplate does not reflect the temperature of the solution.</li>
	<li>Use a calibrated scale to measure 0.30 g of sodium benzoate into a weigh boat. Add sodium benzoate to the water solution.</li>
	<li>Use a syringe to measure 0.6 mL of the water-soluble surfactant. Make sure that there are no air bubbles. Hold the needle a few millimeters over the center of the solution, and slowly release the water-soluble surfactant to avoid splatter on the walls of the beaker.</li>
	<li>Using a clean syringe, measure 0.24 mL of the gadolinium-DTPA contrast agent. Add it to the beaker, using the same technique as in step 2.4. 
	NOTE: Gadolinium-DTPA is used to adjust the phantom&#39;s MRI relaxation properties to match those of the tissue of interest. The reader can adjust the volume of added gadolinium-DTPA to better match the relaxation properties of the tissue of interest.</li>
	<li>Measure 9.0 g of agar into a weigh boat. Slowly spoon the agar with a spatula into the beaker with water.</li>
	<li>Once everything has been added to the water solution, increase the hotplate temperature to 350 &#176;C and stir bar speed to 1100 rpm for 5-10 min to melt the agar.
	<ol>
		<li>To check if the agar is melted, briefly remove the water solution from the hotplate, stop stirring, and check the color of the solution. Melted agar should be clear (no streamers or clumps) and yellow or amber in color.</li>
	</ol>
	</li>
	<li>Once the agar is fully melted, use a syringe or pour about 3.5 mL of the water solution into a small vial. If the test solution does not set or separates after 5-10 min, the agar is not melted. Increase the hotplate temperature back to 350 &#176;C and continue heating the solution.</li>
	<li>Repeat step 2.8 until water solution in the test vial sets properly.</li>
	<li>Leave the water solution on the hotplate at 50 &#176;C and 100 rpm. Clean the work space and prepare for the oil solution.
	<ol>
		<li>Remove the following materials from the bench: scale, 2x weigh boats, spatula, 2x 1.0 mL syringes with needle (used), distilled water, gadolinium-DTPA contrast agent, water-soluble surfactant, agar, and sodium benzoate.</li>
		<li>Position the following materials and equipment on the bench: 400 mL beaker (clean), stir bar (clean), 2.0 mL syringe with needle, peanut oil, and oil-soluble surfactant.</li>
	</ol>
	</li>
</ol>
3. Oil Solution
<ol>
	<li>Place a new stir bar into a clean 400 mL beaker. Use a graduated cylinder to measure 300 mL of peanut oil and pour into the beaker. Remove the beaker containing the water solution and place the oil solution beaker on the hotplate. Set to 90 &#176;C with a stir rate of 100 rpm for 1 min. 
	NOTE: Peanut oil is used because it has a similar nuclear magnetic resonance spectrum compared to triglycerides in human adipose tissue15.
	<ol>
		<li>Do not leave the oil on the hotplate unattended. If the oil gets too hot and begins to smoke, remove it from the hotplate and reduce the temperature before returning the oil to the hotplate.</li>
	</ol>
	</li>
	<li>Measure 3.0 mL of the oil-soluble surfactant with a clean syringe. Using the same technique described in step 2.4, add the oil-soluble surfactant to the beaker. Set the hotplate to 150 &#176;C and 1100 rpm for 5 min to fully mix the oil solution.</li>
	<li>Take the oil solution off the hotplate and clean the workspace in preparation for creating the phantom.
	<ol>
		<li>Remove the following materials from the bench: 2.0 mL syringe with needle (used), peanut oil, and oil-soluble surfactant.</li>
		<li>Position the following materials and equipment on the bench: 250 mL Erlenmeyer flask, stir bar (clean), volumetric pipettes, volumetric pipette holder, and 5x 120 mL glass jars.</li>
	</ol>
	</li>
</ol>
4. Create Phantom Emulsion
<ol>
	<li>Prepare volumetric pipettes for the water and oil solutions. Pipettes should only be used with their respective solution to prevent cross-contamination.
	<ol>
		<li>Match the size of the pipette to the volume being used in the protocol. For example, use 2x 50 mL volumetric pipettes (50 mL water solution + 50 mL oil solution) to create a 100 mL phantom with a target FF of 50% fat.</li>
	</ol>
	</li>
	<li>Place the water solution on the hotplate and set the hotplate to 300 &#176;C and 1100 rpm. After 4-5 min, turn the stirrer off.</li>
	<li>Using a volumetric pipette, check if the water solution is ready for extraction by partially filling the pipette with a small amount (5-10 mL) of the solution and releasing back into the beaker. If the water solution can be easily removed and released without excessive remnants in the pipette, move on to next step, otherwise, leave it on the hotplate and check again in 2-3 min. 
	NOTE: The components of the water solution are more susceptible to setting and separating, so it is best to keep the water solution stirring and/or warm as often as possible. If the water solution is not warmed and stirred before transferring, it will be very difficult to measure accurate volumes due to the tendency of agar to congeal when cooled.</li>
	<li>Carefully add a clean stir bar to a 250 mL Erlenmeyer flask. Take the water solution off the hotplate, measure the proper volume (Table 2), and transfer it to the Erlenmeyer flask.</li>
	<li>Place the oil solution on the hotplate and set at 90 &#176;C and 1100 rpm to ensure the solution is homogeneous. After 1-2 min, remove the oil solution from the hotplate and replace it with the Erlenmeyer flask.</li>
	<li>Measure proper amount of the oil solution (Table 2) and slowly add to the water solution in the Erlenmeyer flask.</li>
	<li>Once all oil solution has been added, increase the temperature to 300 &#176;C and maintain the stirring at 1100 rpm. Stir the combined solutions for 4-5 min (there should be vortex from the stir bar). The emulsion should be white, with a creamy texture.</li>
	<li>Use a magnetic stir bar retriever to remove the stir bar. 
	NOTE: The stir bar retriever should be used to remove the stir bars from all future emulsions. Clean it thoroughly between each use.</li>
	<li>Use heat resistant gloves to carefully pour the mixture in the Erlenmeyer flask into a clean 120 mL glass jar. Slowly pour the mixture down the side of the glass jar to prevent bubbles in the mixture as it cools.</li>
	<li>Clean the Erlenmeyer flask and stir bar, then repeat steps 4.2-4.8, adjusting the amounts of water and oil solutions, until all phantoms are created. 
	NOTE: Make sure the glass is cool before cleaning.</li>
</ol>

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Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=NMR+imaging+estimates+of+muscle+volume+and+intramuscular+fat+infiltration+in+the+thigh:+variations+with+muscle,+gender,+and+age.">NMR imaging estimates of muscle volume and intramuscular fat infiltration in the thigh: variations with muscle, gender, and age.</a> Age (Omaha). 37 (3), 1-11 (2015).</li><li>Hoskins, P. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Simulation+and+Validation+of+Arterial+Ultrasound+Imaging+and+Blood+Flow.">Simulation and Validation of Arterial Ultrasound Imaging and Blood Flow.</a> Ultrasound Med Biol. 34 (5), 693-717 (2008).</li><li>Hu, H. H., Perkins, T. G., Chia, J. 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F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantification+of+pancreatic+lipomatosis+and+liver+steatosis+by+MRI:+comparison+of+in/opposed-phase+and+spectral-spatial+excitation+techniques.">Quantification of pancreatic lipomatosis and liver steatosis by MRI: comparison of in/opposed-phase and spectral-spatial excitation techniques.</a> Invest Radiol. 43 (5), 330-337 (2008).</li><li>Wokke, B. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantitative+MRI+and+strength+measurements+in+the+assessment+of+muscle+quality+in+Duchenne+muscular+dystrophy.">Quantitative MRI and strength measurements in the assessment of muscle quality in Duchenne muscular dystrophy.</a> Neuromuscul Disord. 24 (5), 409-416 (2014).</li><li>Fischer, M. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Liver+Fat+Quantification+by+Dual-echo+MR+Imaging+Outperforms+Traditional+Histopathological+Analysis.">Liver Fat Quantification by Dual-echo MR Imaging Outperforms Traditional Histopathological Analysis.</a> Acad Radiol. 19 (10), 1208-1214 (2012).</li><li>Hayashi, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Influence+of+Gd-EOB-DTPA+on+proton+density+fat+fraction+using+the+six-echo+Dixon+method+in+3+Tesla+magnetic+resonance+imaging.">Influence of Gd-EOB-DTPA on proton density fat fraction using the six-echo Dixon method in 3 Tesla magnetic resonance imaging.</a> Radiol Phys Technol. , (2017).</li><li>Hines, C. D. G., Yu, H., Shimakawa, A., McKenzie, C. A., Brittain, J. H., Reeder, S. 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The authors declare that the research was conducted in the absence of any commercial or financial relationship that could be construed as a potential conflict of interest.

We describe a robust method to create fat water phantoms suitable for validating the medical imaging techniques used to quantify adipose tissue and triglyceride content in vivo. By creating two reservoirs (one for the oil solution and one for the water solution), stable phantoms with a variety of FF values &#8211; including values exceeding 50% &#8211; were constructed without the need for expensive equipment. High FF phantoms (&#62;50%) provide the utility to ensure imaging techniques for adipose quantification...

Interest in quantifying adipose tissue and triglyceride content using imaging modalities, such as magnetic resonance imaging (MRI), extends across many fields. Research areas include the investigation of white and brown adipose tissue depots and ectopic storage of lipid in organs and tissues such as the liver1, pancreas2, and skeletal muscle3. As these novel techniques for adipose quantification are developed, methods are needed to confirm that imaging parameters are valid for research and clinical applications.
Phantoms, experimental replicas of a tissue or organ, provide a low-cost, flexible, and controlled tool to develop and validate imaging techniques4. Specifically, phantoms can be constructed to consist of fat and water in a volume ratio or fat fraction (FF) comparable to that of the tissue of clinical interest. Clinically, FF values in tissues and organs can vary widely: FF in brown adipose tissue falls between 29.7% and 93.9%5; the average liver FF in steatosis patients is 18.1 &#177; 9.0%6; the pancreatic FF in adults at risk for type 2 diabetes ranges between 1.6% and 22.2%7; and in some cases of advance disease, patients with Duchenne muscular dystrophy can have FF values of almost 90% in some muscles8.
Because non-polar molecules such as lipids do not dissolve well in solutions composed of polar molecules such as water, creating stable phantoms with a high target FF remains challenging. For FF up to 50%, many existing methods can be used to create fat water phantoms9,10,11,12. Other methods that achieve higher FFs typically require expensive equipment such as a homogenizer or an ultrasonic cell disruptor13,14. Although these techniques provide a roadmap for high FF phantoms, equipment constraints and varying amounts of experimental details limit the efforts to create reproducible and robust fat water phantoms.
Building upon these previous techniques, we developed a method to construct cost-effective and stable fat water phantoms across a customizable range of FF values. This protocol details the steps needed to make 5x 100 mL of fat phantoms with FF values of 0%, 25%, 50%, 75%, and 100% using a single hotplate. It can easily be adjusted to create various volumes (10 to 200 mL) and fat percentages (0 to 100%). The efficacy of the phantom technique was evaluated in the feasibility study comparing fat-water MRI FF values to the target FF values in the constructed phantoms.

<table><tbody><tr><td>Distilled Water</td><td>Amazon</td><td>B000P9BY38</td><td>Base of water solution</td></tr><tr><td>Agar</td><td>Sigma Aldrich Incorporated</td><td>A1296-100G</td><td>Gelling agent</td></tr><tr><td>Water-Soluble Surfactant</td><td>Sigma Aldrich Incorporated</td><td>P1379-500ML</td><td>Surfactant/emulsifying agent</td></tr><tr><td>Gadolinium-DTPA Contrast Agent</td><td>Bayer Healthcare</td><td>50419-0188-01</td><td>Magnetic Resonance Imaging Contrast Agent.</td></tr><tr><td>Sodium Benzoate</td><td>Sigma Aldrich Incorporated</td><td>71300-250G</td><td>Preservative</td></tr><tr><td>Peanut Oil</td><td>Amazon</td><td>54782-LOU</td><td>Base of oil solution</td></tr><tr><td>Oil-Soluble Surfactant</td><td>Sigma Aldrich Incorporated</td><td>S6760-250ML</td><td>Surfactant/emulsifying agent</td></tr><tr><td>Hotplate w/ Stirrer</td><td>Fisher Scientific</td><td>07-770-152</td><td></td></tr><tr><td>Stir bars (Egg-Shaped)</td><td>Sigma Aldrich Incorporated</td><td>Z127116-1EA</td><td></td></tr><tr><td>400 mL Beaker</td><td>Sigma Aldrich Incorporated</td><td>CLS1003400-48EA</td><td></td></tr><tr><td>250 mL Erlenmeyer Flask</td><td>Sigma Aldrich Incorporated</td><td>CLS4450250-6EA</td><td></td></tr><tr><td>25 mL Glass Volumetric Pipette</td><td>Fisher Scientific</td><td>13-650-2P</td><td>Quantity = 2</td></tr><tr><td>50 mL Glass Volumetric Pipette</td><td>Fisher Scientific</td><td>13-650-2S</td><td>Quantity = 2</td></tr><tr><td>75 mL Glass Volumetric Pipette</td><td>Fisher Scientific</td><td>13-650-2T</td><td>Quantity = 2</td></tr><tr><td>3.0 mL Syringe</td><td>Sigma Aldrich Incorporated</td><td>Z248002-1PAK</td><td></td></tr><tr><td>1.0 mL Syringe</td><td>Sigma Aldrich Incorporated</td><td>Z230723-1PAK</td><td></td></tr><tr><td>Spatula</td><td>Sigma Aldrich Incorporated</td><td>S3897-1EA</td><td></td></tr><tr><td>Scale (100g X 0.01g Resolution)</td><td>Amazon</td><td>AWS-100-BLK</td><td></td></tr><tr><td>Weigh Boats</td><td>Sigma Aldrich Incorporated</td><td>Z740499-500EA</td><td></td></tr><tr><td>120 mL Glass Jars</td><td>McMaster Carr Supply Co</td><td>3801T73</td><td></td></tr><tr><td>Heat Resistant Gloves (pair)</td><td>Amazon</td><td>B075GX43MN</td><td></td></tr><tr><td>Syringe Needles</td><td>Sigma Aldrich Incorporated</td><td>Z192341-100EA</td><td></td></tr><tr><td>18&quot; stir bar retriver</td><td>Fisher Scientific</td><td>14-513-70</td><td></td></tr><tr><td>1 Dram Clear Glass Vial</td><td>Fisher Scientific</td><td>03-339-25B</td><td></td></tr></tbody></table>

fat-water phantoms for magnetic resonance imaging validation: a flexible and scalable protocol

As new techniques are developed to image adipose tissue, methods to validate such protocols are becoming increasingly important. Phantoms, experimental replicas of a tissue or organ of interest, provide a low cost, flexible solution. However, without access to expensive and specialized equipment, constructing stable phantoms with high fat fractions (e.g., &#62;50% fat fraction levels such as those seen in brown adipose tissue) can be difficult due to the hydrophobic nature of lipids. This work presents a detailed, low cost protocol for creating 5x 100 mL&#160;phantoms with fat fractions of 0%, 25%, 50%, 75%, and 100% using basic lab supplies (hotplate, beakers, etc.) and easily accessible components (distilled water, agar, water-soluble surfactant, sodium benzoate, gadolinium-diethylenetriaminepentacetate (DTPA) contrast agent, peanut oil, and oil-soluble surfactant). The protocol was designed to be flexible; it can be used to create phantoms with different fat fractions and a wide range of volumes. Phantoms created with this technique were evaluated in the feasibility study that compared the fat fraction values from fat-water magnetic resonance imaging to the target values in the constructed phantoms. This study yielded a concordance correlation coefficient of 0.998 (95% confidence interval: 0.972-1.00). In summary, these studies demonstrate the utility of&#160;fat phantoms for validating adipose tissue imaging techniques across a range of clinically relevant tissues and organs.

If the water solution has been prepared correctly, a small amount of the solution should congeal quickly in a test vial (Figure 1, left). If the solution separates (Figure 1, right), the solution should be prepared again (as instructed in step 3.8 of the protocol). If the emulsion separates (examples in Figure 2, left and right), the phantom is not v...

Watch this Scientific Journal Video about Fat-Water Phantoms for Magnetic Resonance Imaging Validation: A Flexible and Scalable Protocol at JoVE.com

Fat-Water Phantoms for Magnetic Resonance Imaging Validation: A Flexible and Scalable Protocol

The purpose of this work is to describe a protocol for creating a practical fat-water phantom that can be customized to produce phantoms with varying fat percentages and volumes.

As new techniques are developed to image adipose tissue, methods to validate such protocols are becoming increasingly important. Phantoms, experimental ...

fat-water-phantoms-for-magnetic-resonance-imaging-validation-flexible

Research

JoVE Journal

Medicine

11.2K Views.  Vanderbilt University Medical Center. Het doel van dit werk is voor het beschrijven van een protocol voor het maken van een praktische vet-waterfantoom die kan worden aangepast om te spoken met verschillende vet percentages en volumes produceren.

Video: Fat-Water Phantoms for Magnetic Resonance Imaging Validation: A Flexible and Scalable Protocol

Use of a Multi-compartment Dynamic Single Enzyme Phantom for Studies of Hyperpolarized Magnetic Resonance Agents

Imaging of hyperpolarized substrates by magnetic resonance shows great clinical promise for assessment of critical biochemical processes in real time. Due to fundamental constraints imposed by the hyperpolarized state, exotic imaging and reconstruction techniques are commonly used. A practical system for characterization of dynamic, multi-spectral imaging methods is critically needed. Such a system must reproducibly recapitulate the relevant chemical dynamics of normal and pathological tissues. The most widely utilized substrate to date is hyperpolarized [1-13C]-pyruvate for assessment of cancer metabolism. We describe an enzyme-based phantom system that mediates the conversion of pyruvate to lactate. The reaction is initiated by injection of the hyperpolarized agent into multiple chambers within the phantom, each of which contains varying concentrations of reagents that control the reaction rate. Multiple compartments are necessary to ensure that imaging sequences faithfully capture the spatial and metabolic heterogeneity of tissue. This system will aid the development and validation of advanced imaging strategies by providing chemical dynamics that are not available from conventional phantoms, as well as control and reproducibility that is not possible in vivo.

A multi-compartment dynamic phantom is used to simulate some biology of interest for metabolic studies using hyperpolarized magnet resonance agents.

Imaging of hyperpolarized substrates by magnetic resonance shows great clinical promise for assessment of critical biochemical processes in real time. Due ...

Engineering

Tracking the Mammary Architectural Features and Detecting Breast Cancer with Magnetic Resonance Diffusion Tensor Imaging

Breast cancer is the most common cause of cancer among women worldwide. Early detection of breast cancer has a critical role in improving the quality of life and survival of breast cancer patients. In this paper a new approach for the detection of breast cancer is described, based on tracking the mammary architectural elements using diffusion tensor imaging (DTI). 
The paper focuses on the scanning protocols and image processing algorithms and software that were designed to fit the diffusion properties of the mammary fibroglandular tissue and its changes during malignant transformation. The final output yields pixel by pixel vector maps that track the architecture of the entire mammary ductal glandular trees and parametric maps of the diffusion tensor coefficients and anisotropy indices. 
The efficiency of the method to detect breast cancer was tested by scanning women volunteers including 68 patients with breast cancer confirmed by histopathology findings. Regions with cancer cells exhibited a marked reduction in the diffusion coefficients and in the maximal anisotropy index as compared to the normal breast tissue, providing an intrinsic contrast for delineating the boundaries of malignant growth. Overall, the sensitivity of the DTI parameters to detect breast cancer was found to be high, particularly in dense breasts, and comparable to the current standard breast MRI method that requires injection of a contrast agent. Thus, this method offers a completely non-invasive, safe and sensitive tool for breast cancer detection.

We describe how to obtain parametric and vector maps of the diffusion tensor of the breast using magnetic resonance imaging. The protocol and final output following imaging processing are tailored for tracking breast architectural features and detecting breast malignancy.

Breast cancer is the most common cause of cancer among women worldwide. Early detection of breast cancer has a critical role in improving the quality of ...

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 ...

Human Brown Adipose Tissue Depots Automatically Segmented by Positron Emission Tomography/Computed Tomography and Registered Magnetic Resonance Images

Reliably differentiating brown adipose tissue (BAT) from other tissues using a non-invasive imaging method is an important step toward studying BAT in humans. Detecting BAT is typically confirmed by the uptake of the injected radioactive tracer 18F-Fluorodeoxyglucose (18F-FDG) into adipose tissue depots, as measured by positron emission tomography/computed tomography (PET-CT) scans after exposing the subject to cold stimulus. Fat-water separated magnetic resonance imaging (MRI) has the ability to distinguish BAT without the use of a radioactive tracer. To date, MRI of BAT in adult humans has not been co-registered with cold-activated PET-CT. Therefore, this protocol uses 18F-FDG PET-CT scans to automatically generate a BAT mask, which is then applied to co-registered MRI scans of the same subject. This approach enables measurement of quantitative MRI properties of BAT without manual segmentation. BAT masks are created from two PET-CT scans: after exposure for 2 hr to either thermoneutral (TN) (24 &#176;C) or cold-activated (CA) (17 &#176;C) conditions. The TN and CA PET-CT scans are registered, and the PET standardized uptake and CT Hounsfield values are used to create a mask containing only BAT. CA and TN MRI scans are also acquired on the same subject and registered to the PET-CT scans in order to establish quantitative MRI properties within the automatically defined BAT mask. An advantage of this approach is that the segmentation is completely automated and is based on widely accepted methods for identification of activated BAT (PET-CT). The quantitative MRI properties of BAT established using this protocol can serve as the basis for an MRI-only BAT examination that avoids the radiation associated with PET-CT.

The method presented here uses 18F-Fluorodeoxyglucose (18F-FDG) positron emission tomography/computed tomography (PET-CT) and fat-water separated magnetic resonance imaging (MRI), each scanned following 2 hr exposure to thermoneutral (24 &#176;C) and cold conditions (17 &#176;C) in order to map brown adipose tissue (BAT) in adult human subjects.

Reliably differentiating brown adipose tissue (BAT) from other tissues using a non-invasive imaging method is an important step toward studying BAT in ...

Manufacturing Abdominal Aorta Hydrogel Tissue-Mimicking Phantoms for Ultrasound Elastography Validation

Ultrasound (US) elastography, or elasticity imaging, is an adjunct imaging technique that utilizes sequential US images of soft tissues to measure the tissue motion and infer or quantify the underlying biomechanical characteristics. For abdominal aortic aneurysms (AAA), biomechanical properties such as changes in the tissue's elastic modulus and estimates of the tissue stress may be essential for assessing the need for the surgical intervention. Abdominal aortic aneurysms US elastography could be a useful tool to monitor AAA progression and identify changes in biomechanical properties characteristic of high-risk patients.
A preliminary goal in the development of an AAA US elastography technique is the validation of the method using a physically relevant model with known material properties. Here we present a process for the production of AAA tissue-mimicking phantoms with physically relevant geometries and spatially modulated material properties. These tissue phantoms aim to mimic the US properties, material modulus, and geometry of the abdominal aortic aneurysms. Tissue phantoms are made using a polyvinyl alcohol cryogel (PVA-c) and molded using 3D printed parts created using computer aided design (CAD) software. The modulus of the phantoms is controlled by altering the concentration of PVA-c and by changing the number of freeze-thaw cycles used to polymerize the cryogel. The AAA phantoms are connected to a hemodynamic pump, designed to deform the phantoms with the physiologic cyclic pressure and flows. Ultra sound image sequences of the deforming phantoms allowed for the spatial calculation of the pressure normalized strain and the identification of mechanical properties of the vessel wall. Representative results of the pressure normalized strain are presented.

Here we describe a method to manufacture aneurysmal, aortic tissue-mimicking phantoms for the use in testing ultrasound elastography. The combined use of computer-aided design (CAD) and 3-dimensional (3D) printing techniques produce aortic phantoms with predictable, complex geometries to validate the elastographic imaging algorithms with controlled experiments.

Ultrasound (US) elastography, or elasticity imaging, is an adjunct imaging technique that utilizes sequential US images of soft tissues to measure the ...

Bioengineering

Preparation and In Vitro Characterization of Magnetized miR-modified Endothelial Cells

To date, the available surgical and pharmacological treatments for cardiovascular diseases (CVD) are limited and often palliative. At the same time, gene and cell therapies are highly promising alternative approaches for CVD treatment. However, the broad clinical application of gene therapy is greatly limited by the lack of suitable gene delivery systems. The development of appropriate gene delivery vectors can provide a solution to current challenges in cell therapy. In particular, existing drawbacks, such as limited efficiency and low cell retention in the injured organ, could be overcome by appropriate cell engineering (i.e., genetic) prior to transplantation. The presented protocol describes the efficient and safe transient modification of endothelial cells using a polyethyleneimine superparamagnetic magnetic nanoparticle (PEI/MNP)-based delivery vector. Also, the algorithm and methods for cell characterization are defined. The successful intracellular delivery of microRNA (miR) into human umbilical vein endothelial cells (HUVECs) has been achieved without affecting cell viability, functionality, or intercellular communication. Moreover, this approach was proven to cause a strong functional effect in introduced exogenous miR. Importantly, the application of this MNP-based vector ensures cell magnetization, with accompanying possibilities of magnetic targeting and non-invasive MRI tracing. This may provide a basis for magnetically guided, genetically engineered cell therapeutics that can be monitored non-invasively with MRI.

Preparation and In Vitro Characterization of Magnetized miR-modified Endothelial Cells

This manuscript describes the efficient, non-viral delivery of miR to endothelial cells by a PEI/MNP vector and their magnetization. Thus, in addition to genetic modification, this approach allows for magnetic cell guidance and MRI detectability. The technique can be used to improve the characteristics of therapeutic cell products.

To date, the available surgical and pharmacological treatments for cardiovascular diseases (CVD) are limited and often palliative. At the same time, gene ...

Viscoelastic Characterization of Soft Tissue-Mimicking Gelatin Phantoms using Indentation and Magnetic Resonance Elastography

Characterization of biomechanical properties of soft biological tissues is important to understand the tissue mechanics and explore the biomechanics-related mechanisms of disease, injury, and development. The mechanical testing method is the most straightforward way for tissue characterization and is considered as verification for in vivo measurement. Among the many ex vivo mechanical testing techniques, the indentation test provides a reliable way, especially for samples that are small, hard to fix, and viscoelastic such as brain tissue. Magnetic resonance elastography (MRE) is a clinically used method to measure the biomechanical properties of soft tissues. Based on shear wave propagation in soft tissues recorded using MRE, viscoelastic properties of soft tissues can be estimated in vivo based on wave equation. Here, the viscoelastic properties of gelatin phantoms with two different concentrations were measured by MRE and indentation. The protocols of phantom fabrication, testing, and modulus estimation have been presented.

This article presents a demonstration and summary of protocols of making gelatin phantoms that mimic soft tissues, and the corresponding viscoelastic characterization using indentation and magnetic resonance elastography.

Characterization of biomechanical properties of soft biological tissues is important to understand the tissue mechanics and explore 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 ...

A Comprehensive 3D-Liver Fat Function Distribution Model Using Dixon MRI

A 3D Quantification Technique for Liver Fat Fraction Distribution Analysis Using Dixon Magnetic Resonance Imaging

This study presents a 3D quantification methodology for the distribution of liver fat fraction (LFF) through the utilization of Dixon MRI image analysis. The central aim is to offer a highly accurate and non-invasive means of evaluating liver fat content. The process involves the acquisition of In-phase and Water-phase images from a Dixon sequence. LFF maps are then meticulously computed voxel by voxel by dividing the Lipid Phase images by the In-phase images. Simultaneously, 3D liver contours are extracted from the In-phase images. These crucial components are seamlessly integrated to construct a comprehensive 3D-LFF distribution model. This technique is not limited to healthy livers but extends to those afflicted by hepatic steatosis. The results obtained demonstrate the remarkable effectiveness of this approach in both visualizing and quantifying liver fat content. It distinctly discerns patterns that differentiate between normal and steatotic livers. By harnessing Dixon MRI to extract the 3D structure of the liver, this method offers precise LFF assessments spanning the entirety of the organ, thereby holding great promise for the diagnosis of hepatic steatosis with remarkable effectiveness.

Author Spotlight: A Non-Invasive Tool to Assess and Differentiate Fat Patterns in Liver Using 3D Dixon MRI 

This study introduces a unique 3D quantification method for liver fat fraction (LFF) distribution using Dixon Magnetic Resonance Imaging (Dixon MRI). LFF maps, derived from in-phase and water-phase images, are integrated with 3D liver contours to differentiate LFF patterns between normal and steatotic livers, enabling precise assessment of liver fat content.

This study presents a 3D quantification methodology for the distribution of liver fat fraction (LFF) through the utilization of Dixon MRI image analysis. ...

Using 23Na Magnetic Resonance Imaging to Measure Sodium in Muscle Tissues

This video demonstrates the quantification of sodium content in human tissues using sodium magnetic resonance imaging (23Na-MRI). The patient&#39;s lower leg is placed within the radiofrequency (RF) coil of the machine, and a three-dimensional gradient-echo sequence is performed. Multinuclear MRI images are generated using hydrogen and sodium nuclei to quantify sodium levels in various tissues.

All procedures involving human participants have been performed in compliance with the institutional, national, and international guidelines for human ...

Fat-Water Phantoms for Magnetic Resonance Imaging Validation: A Flexible and Scalable Protocol

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