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Updated: Jul 28, 2025
Author Spotlight: Standardization and Best Practices for Advancing Lung Imaging Using 129Xe MRI
Published on: November 21, 2023
Establishing a hemoglobin adjustment for 129 Xe gas exchange MRI and MRS
Aryil Bechtel1, Junlan Lu2, David Mummy1
1Radiology, Duke University Medical Center, Durham, North Carolina, USA.
Purpose:
129 Xe MRI and MRS signals from airspaces, membrane tissues (M), and red blood cells (RBCs) provide measurements of pulmonary gas exchange. However, 129 Xe MRI/MRS studies have yet to account for hemoglobin concentration (Hb), which is expected to affect the uptake of 129 Xe in the membrane and RBC compartments. We propose a framework to adjust the membrane and RBC signals for Hb and use this to assess sex-specific differences in RBC/M and establish a Hb-adjusted healthy reference range for the RBC/M ratio.
Methods:
We combined the 1D model of xenon gas exchange (MOXE) with the principle of TR-flip angle equivalence to establish scaling factors that normalize the dissolved-phase signals with respect to a standard (14 g/dL). 129 Xe MRI/MRS data from a healthy, young cohort (n = 18, age = 25.0 3.4 years) were used to validate this model and assess the impact of Hb adjustment on M/gas and RBC/gas images and RBC/M.
Results:
Adjusting for Hb caused RBC/M to change by up to 20% in healthy individuals with normal Hb and had marked impacts on M/gas and RBC/gas distributions in 3D gas-exchange maps. RBC/M was higher in males than females both before and after Hb adjustment (p < 0.001). After Hb adjustment, the healthy reference value for RBC/M for a consortium-recommended acquisition of TR = 15 ms and flip = 20° was 0.589 0.083 (mean SD).
Conclusion:
MOXE provides a useful framework for evaluating the Hb dependence of the membrane and RBC signals. This work indicates that adjusting for Hb is essential for accurately assessing 129 Xe gas-exchange MRI/MRS metrics.
Insights
This study introduces a new method to adjust 129-xenon MRI/MRS gas exchange measurements for hemoglobin levels. Adjusting for hemoglobin is crucial for accurate pulmonary gas exchange assessment and reveals sex-specific differences.
Area of Science:
- Pulmonary Medicine
- Medical Imaging
- Physiology
Background:
- 129-xenon MRI and MRS measure pulmonary gas exchange via airspace, membrane (M), and red blood cell (RBC) signals.
- Current methods do not account for hemoglobin (Hb) concentration, which influences 129-xenon uptake in M and RBC compartments.
Purpose of the Study:
- To develop a framework for adjusting M and RBC signals for Hb concentration.
- To assess sex-specific differences in the RBC/M ratio.
- To establish an Hb-adjusted healthy reference range for the RBC/M ratio.
Main Methods:
- Combined the 1D model of xenon gas exchange (MOXE) with TR-flip angle equivalence.
- Developed scaling factors to normalize dissolved-phase signals to a standard Hb of 14 g/dL.
- Validated the model using 129-xenon MRI/MRS data from 18 healthy young adults.
Main Results:
- Hb adjustment altered RBC/M by up to 20% in healthy individuals.
- Hb adjustment significantly impacted M/gas and RBC/gas distributions.
- Males exhibited higher RBC/M than females both before and after Hb adjustment (p < 0.001).
- The Hb-adjusted healthy reference range for RBC/M was 0.589 ± 0.083.
Conclusions:
- The MOXE framework effectively evaluates Hb dependence of M and RBC signals.
- Adjusting for Hb is essential for accurate 129-xenon gas-exchange MRI/MRS metrics.
- This study provides a foundation for more precise pulmonary gas exchange analysis.
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