Acquiring Hyperpolarized ¹²⁹Xe Magnetic Resonance Images of Lung Ventilation

Our research seeks to establish Xenon MRI as a clinical tool for characterizing lung function. Xenon MRI allows us to directly visualize ventilation defects in patients with obstructive lung diseases like COPD, asthma, and cystic fibrosis. It offers information that can be obtained from standard MRI and pulmonary function test.

Xenon MRI was recently approved by the FDA for clinical evaluation of lung ventilation. This represents a combination of a huge amount of effort by the people in our field and it's an exciting opportunity to show how Xenon MRI can improve patient care and outcomes in pulmonary disease. Xenon MRI is still a relatively new family of techniques and standardization is still an ongoing process.

This protocol distills the existing standards for Xenon ventilation MRI into a form that we hope will be useful to research and clinical sites who are trying to perform these scans for the first time. Common clinical readouts of lung function like pulmonary function tests only give a single number for the entire lung with no spatial information included. Xenon MRI can make regional assessments of several aspects of lung health and function, which we believe will be very useful in the clinic.

Only a few institutions are currently performing Xenon MRI, but we expect there will be many more sites soon considering the recent FDA approval. We hope that this Xenon ventilation MRI protocol will serve as a blueprint for new sites and help em to ramp up their Xenon MRI operations more quickly. To begin, prepare one or more Tedlar bags containing air for the subject to practice outside the scanner.

Use an air volume that matches the total volume of xenon and buffer gas to be inhaled from the bag during the actual study. Prepare nose clips for the subject to wear during breath hold scanning. Fit the nose clips onto the subject's nose before the start of breath holds.

Use one air-filled bag for each attempt to coach the subject. Before producing the bag, ask the subject to breathe in and breathe out regularly several times. During the procedure, monitor the subject's chest to confirm that they are executing the instructions properly.

Next, place the tube attached to the Tedlar bag into the subject's mouth. Hold the bag such that the subject can inhale from it and open the valve. Ask the subject to breathe in.

Then ask the subject to hold their breath by saying, Hold your breath. When practicing, wait for a count of 10 to 15 seconds, which is the approximate amount of time required for a typical xenon 129 scan to elapse. After that, ask the subject to exhale at this point and breathe.

Coach the subject to take several deep breaths in and out for a quicker clearance of xenon 129 from the lungs and a quicker return to normal oxygen saturation levels. Verify that the subject is able to carry out the instructions reliably and consider excluding subjects who cannot do so during practice runs. To begin, ensure anyone entering the MRI scanner room has removed all metallic and electronic objects from their body or pockets.

Prepare the xenon 129 vest coil by plugging it into the scanner and placing it on the MRI scanner patient table. Instruct the subject to lie on the patient table in a feet first or headfirst supine position depending on the layout of the scanner room. Place pillows under the subject's head, knees, et cetera as needed to ensure comfort during the procedure.

Secure the xenon 129 vest coil around the subject's chest while keeping the coil midline in the head foot direction as close as possible to the expected midline of the subject's lungs when the subject is at a comfortable inflation level. Placing the coil too low on the subject may result in undesirable signal reductions at the periphery of the lungs. Set up an MRI safe pulse oximeter next to the patient table in the MRI scanner room and connect the pulse oximeter probe to the subject.

Verify that the pulse oximeter is reading correctly. Place a nasal cannula in the subject's nose and connect it to an oxygen source to be used after dose inhalation if needed. Place the oxygen tank and regulator in an MRI safe manner based on local safety policy within reachable distance.

Advance the patient table into the MRI scanner, aligning the midline of the coil or the subject's lungs to the scanner's isocenter. The images shown here represent the ventilation images from a study that was unknowingly performed using a xenon 129 vest coil with a damaged cable. The right lung displays a lower signal to noise ratio than the left lung.

The ventilation images from a study that was performed with the xenon 129 vest coil placed too far toward the subject's feet are shown here. Artificially low, xenon 129 signal is observed in both lung apices due to the lack of receiver sensitivity there. After making the final xenon 129 pre-scan adjustments and ensuring the subject is ready for the xenon 129 dose, proceed to perform the xenon 129 ventilation scan.

First, load the xenon 129 ventilation sequence from the prepared protocol. Ensure all pulse sequence parameters are as desired and set proper scan execution settings. Select the field of view or FOV size and center location based on the localizer results.

Aim for the center of the FOV to coincide with the center of the lungs in all three dimensions and the FOV to be large enough to comfortably contain the entire chest cavity, including the entirety of both lungs. Bring the xenon 129 dose bag intended for the ventilation scan from the polarization measurement station into the scanner room. Hold or place the dose bag near the subject.

Avoid regions near the bore opening where the magnetic field strength changes rapidly. Assist the subject in inhaling the xenon 129 dose from the bag following the already coached inhalation procedure. Execute the scan immediately upon hearing the signal Go"from the individual assisting the subject.

Monitor the subject while the scan proceeds. Following the scan, monitor the subject's heart rate and SpO2 using the pulse oximeter and monitor for transient central nervous system effects via verbal communication with the subject. If no significant deviations from baseline occur, then after waiting for at least two minutes, another xenon 129 dose can be administered.

The ventilation images from a healthy individual are shown here. A high xenon 129 signal can be observed throughout the lungs in these images and no ventilation impairment is evident in this individual. This figure depicts an individual with alpha-1 antitrypsin deficiency in which severe ventilation impairment can be easily detected by observing the patchy appearance of the xenon 129 images.

Similarly, severe ventilation impairment can be seen in this figure depicting an individual with severe cystic fibrosis. The images shown here depicts an individual with chronic obstructive pulmonary disease in which more subtle ventilation defects can be noted.