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

Summary

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.

Abstract

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., >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 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 fat phantoms for validating adipose tissue imaging techniques across a range of clinically relevant tissues and organs.

Introduction

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, prov....

Protocol

1. Prepare the Workstation and Materials

1. 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.
2. Clear the workspace and clean the surfaces with disinfectant. Wash your hands and put gloves on.
3. Sterilize all instruments an....

Results

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.......

Discussion

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 – including values exceeding 50% – were constructed without the need for expensive equipment. High FF phantoms (>50%) provide the utility to ensure imaging techniques for adipose quantification.......

Materials

List of materials used in this article

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