Project Motivation, Needs, and Goals

My Motivation

My name is Kevin Yarnall, and I am a MEng student. I came to the idea for this project while working in a research lab studying novel imaging techniques to measure lung function. When subjects undergo magnetic resonance imaging (MRI) of the lungs, they inhale hyperpolarized xenon and I felt that there was an opportunity to improve this process. In this project, I created a device to measure the flow of the hyperpolarized xenon and purge gas from the polarizer to the dose bag that could then be used to determine the volume of gas in the bag to fill the dose bags of xenon and purge gas consistently each time.

Project Background

Hyperpolarized xenon is used as a contrasting agent for taking MR images of the lungs. Without xenon, the MR scans of the lungs are not able to show much detail, as the signal from room air in the lungs is not nearly as strong as the sign from the hydrogen atoms in the water throughout the body. HP Xe increases the gas signal from the MR by 5 orders of magnitude, allowing images shown below.  They show the difference between standard MR imaging and MR imaging enhanced with HP Xe. The image on the left is a standard MRI of the lungs, while the image on the right is a lung MRI enhanced with HP Xe [1].

Clinicians can use this improved MR image to get a better understanding of a patient’s lung function, which can be valuable information in treating many lung diseases. 

Preparation of Hyperpolarized Xenon

The process for preparing hyperpolarized xenon is shown on the right. Ultra high purity nitrogen and xenon mix are pumped into the cell of the polarizer. The cell has rubidium enclosed within it. A high powered laser is directed into the cell, which excites the valence electron from the rubidium. This electron then exchanges its momentum with the xenon, polarizing the xenon. The xenon is then pumped into the cold finger, where it is frozen in a bath of liquid nitrogen. The remainder of the purge gas is not frozen, so xenon is able to accumulate. Once the xenon has been accumulated, the technician removes the liquid nitrogen bath and thaws the xenon in a water bath. Xenon then flows out of the outflow of the polarizer into the dose bag. The subject then inhales the hyperpolarized xenon from the dose bag immediately prior to the MRI scan [1].


The image to the left depicts the current workflow of study process [1]. The filling of a hyperpolarized xenon dose bag is done manually and requires a highly trained technician. The bag must be filled with enough xenon to provide the necessary dose to the lung prior to the MRI, but if too much hyperpolarized xenon is put into the dose bag, it can pop, leading to loss of the xenon and potentially a delay in the MRI scan. This is crucial because time with the MRI scanner is difficult to schedule and is quite expensive. Even with training, it is impossible to ensure that the bags are being filled consistently each time by the technician, leading to potential for error within the study. 

Project Goal

This research project aims to develop an automated process for filling dose bags to ensure a consistent and accurate filling each time, preventing overfilling and rupturing of dose bags, losing xenon doses, and delays in MRI scans.

Learning Objectives

By completing this project, a student will gain experience in many areas including

  • Basic data acquisition
  • Pressure and flow measurements
  • CAD and 3D modeling
  • 3D printing
  • Microcontrollers
  • Programming

Completion of this project gives practical experience in each of these areas and allows for development a product to fulfill a specific need.

Fundamentals of Flow

In this section, I discuss various ways to measure flow. In my project, I based the pressure differential flow meter off of the Venturi tube. This information is important to the expert stage of this project described below.

Pressure Differential (Venturi) Meter:

Venturi meters use differential pressure measurement to measure the flow of a gas or liquid using Bernoulli’s Equation by reducing the cross sectional flow area in the flow path, thus generating a pressure difference.

Image source: [2]

Hot wire Anemometer:

This device measures the velocity and direction of fluid or gas by measuring the heat loss of a wire placed in the flow stream.

 Image source: [3]

Laminar Flow Element:

Uses Poiseuille’s equation to measure differential pressure change.  The laminar flow element works by forcing gas molecules to move in parallel along the length of the passage, minimizing flow turbulence. The differential pressure is measured within the laminar region.

Image source: [4]

Bubble Flow Meter:

Bubble flow meters can be used to measure the volumetric flow rate of gases. Bubble flow meters are comprised of a burette attached to a rubber bulb containing soap solution. The gas is passed through the burette, and the bulb containing soap solution is squeezed. This pushes a soap bubble into the burette. The time taken for the bubble to travel a known volume through the burette is used to calculate the flow rate.

Image source: [5]

Project Vision and Narrative

The vision for this project is to develop a method to measure the flow rate of xenon gas from the polarizer to the dose bag. This flow rate can then be used to determine a standardized volume of hyperpolarized xenon and purge gas to be put into each dose bag.

I developed a pressure differential flow meter to serve this purpose. This device will attach on one end to the polarizer, which releases the gas, and on the other end to the dose bag itself. The pressure differential tube is then connected to a device that is able to measure the flow based on the pressure difference inside of the tube. 

Materials Needed

  • Arduino Starter Kit
  • MPX5500DP
  • Manometer
  • BD syringe (10 mL)
  • 3/16” Inner Diameter Vinyl Tubing
  • Access to a 3D Printer

Project Stages:

The table below breaks down the project into 4 modules. 

Instructional Lecture: Final Prototype of Flow Meter

The video to the right describes the pressure differential flow meter that was designed for this project and its use in the process of filling dose bags with hyperpolarized xenon and purge gas. As the video shows, filling dose bags appropriately is a complex process. This pressure differential flow meter will allow technicians working with the polarizer to fill bags to a designated, consistent volume, preventing bags from being underfilled or overfilled and rupturing.


Pressure Differential Flow Meter Prototype

Figure 1. Flow sensor

Figure 2. Pressure Differential Tube

Figure 3. Polarizer Side Cap

Figure 4. Dose Bag Side Cap

This gallery above shows the CAD of the flow sensor coupling. The prototype was designed based on the principle of a Venturi tube in that it utilizes pressure differential to measure flow. The pieces coming off the side of the pressure differential tube will be connected to a pressure sensor so that the change in pressure can be converted into a flow rate of the gas. Connector caps were also developed so that the flow sensor is able to attach to the polarizer on one end and the dose bag on the other. The pieces were then 3D printed to create the prototype shown in the video above.

About the Author

Kevin Yarnall

I am a MEng student in MEMS at Duke’s Pratt School of Engineering. I have interests in device design and prototyping, and aspire to work as an R&D engineer at a medical device company.

Works Cited

[1] Koren, R. Polarean Imaging plc. – Home. Retrieved from

2. Textbook: Venturi image

[3] Hot Wire Anemometer Principle – Instrumentation Tools. (2019, June 20).
Retrieved from

4. Textbook: Laminar flow element

[5] Manual Bubble Flowmeter (Standard Version) 20562. (n.d.). Retrieved from®ion

Authored by: Kevin Yarnall
Last updated: May 2021