Our research focuses on using hyperpolarizing on 129 MRI technology to assess pulmonary function and to investigate lung diseases. The main objective is to see how this imaging technique can lead to better detection, understanding, and tracking of different lung conditions. Most hyperpolarized lung MR imaging is performed during a breath hold.
We believe that pulmonary function quantified under such an artificial condition, may not fully reflect gas exchange during regular respiration. And we are testing new free breathing measurements that do not require any breath hold. Current challenges include the optimization of the CSSR acquisition technique for consistency and accuracy in the face of physiological variation and patient compliance.
Severely ill or pediatric patients struggle with maintaining lengthy breath holds. The CSSR technique appears particularly sensitive to changes in alveolar septal wall thickness. As we and others in the field have demonstrated, alveolar wall thickening could indicate the presence of interstitial edema, inflammation, or pulmonary fibrosis.
All metrics derived from CSSR spectroscopy acquisitions are currently based on the temporal dynamics of the signal amplitudes. In the future though, we hope to include changes in peak shape and center frequency in the analysis to obtain a more complete picture of the ongoing gas exchange processes. To begin, set up the physiological monitoring system to record breathing curves and real-time gas analysis during imaging.
Connect and test the MRI room headphones with the audio signal that guides the subject using an inhale, exhale audio recording. Adjust the playback speed of the audio track.Inhale.Exhale. Based on the normal breathing rate of each subject.Inhale.Exhale.
Next, prepare the scanner bed with a clean headrest, leg support pillow, and blanket. Place the unfastened Xenon-129 chest vest coil on the table of the MRI scanner, and insert the connector plug of the coil. For a free breathing study, introduce the subject to the inhale, exhale voice recording for synchronized breathing during imaging.
Lead the subject into the MRI room, and position them on the scanner bed, lying on top of the open Xenon vest coil. Once the subject is positioned, fasten the Velcro straps so that the vest coil is closed, but does not constrict the subject's chest. For a free breathing study, place a face mask with a pneumotach over the patient's face.
Tighten the straps so the mask fits snugly over the nose and mouth without being too tight. After fitting, remove the mask and set it aside for later, leaving the straps behind the subject's head. Then place two pulse oximeters on both index fingers to continuously monitor heart rate and blood oxygen saturation during the study.
Place MRI compatible headphones over the subject's ears. Move the MRI scanner table into the magnet bore so the subject's lungs are positioned in the center of the field of view. To begin, heat up the Xenon polarizer, approximately 2.5 hours before the study starts.
Thread the connector tube of a 250 milliliter specialized polyvinyl fluoride or PVF bag through a ceiling clip. Attach the bag to one of the four available polarizer dispense ports. On the polarizer touchscreen, select the enriched Xenon tank.
Set the flow rate to Medium, and the polarization volume to 250 milliliters. Then press the Start button to initiate the polarization process. Once the polarized Xenon gas has been dispensed, the polarizer's touchscreen will display a message to remove the bag.
Pinch the connector tube of the specialized PVF bag shut with the sealing clip, and then disconnect the bag to place it inside the bore of the MRI scanner. To perform Xenon inhalation using the breath hold method, place a nose clip on the nose of the subject to facilitate breathing through the mouth. At the end of a normal exhalation to functional residual capacity, insert the mouthpiece of the Xenon bag into the subject's mouth.
Allow the subject to inhale 500 milliliters of Xenon gas from the Xenon bag, then, remove the mouthpiece, and instruct the subject to continue inhaling room air until the lungs are full. At the end of inhalation, ask the subject to raise their thumb. Request the nurse coordinator to verbally convey this information to the scanner operator to start the pulse sequence.
After the data acquisition period, instruct the subject to return to normal breathing. Move the subject out of the MRI scanner. Place a face mask over their nose and mouth, connect the hoses to the mask, and then connect the pre-fitted straps from behind the head to the mask, and secure it in place.
Move the subject to its original position inside the MRI scanner. Once the subject follows the breathing protocol, ask the nurse coordinator to inform the MRI operator to initiate data acquisition. The nurse coordinator then opens the valves on the gas delivery system, and the subject inhales 50 milliliters of hyperpolarized Xenon-129 mixed with the airflow inside the breathing mask.
Instruct the subject to continue breathing for approximately 10 breaths, until the volume of Xenon gas has been used up for the imaging protocol. Load the CSSR pulse sequence for free breathing. Set the acquisition frequency according to the hyperpolarized Xenon gas phase frequency determined during the calibration scan.
Adjust the reference voltage to match the value obtained from the calibration scan. Select the Wait for user"option or its equivalent, for sequence execution, following the system vendor's operating instructions. Start the MRI scanner sequence.
The scanner will pause for user input before data acquisition. Once the nurse coordinator switches the hyperpolarized Xenon gas or air mixture, start data acquisition. Ensure the sequence is already running before the subject inhales the first dose of Xenon gas.
After the three minute data acquisition, or exhaustion of hyperpolarized Xenon gas, remove the subject from the MRI scanner. In the young healthy female, the membrane signal increases rapidly due to the quick filling of thin walls. In the older lung transplant recipient, the membrane signal rises more gradually reflecting the longer time required to fill the thicker septal walls.
