[Paper Review] Posture-Dependent Human 3He Lung Imaging in an Open Access MRI System: Initial Results

Leo L. Tsai, R. W. Mair+4 more|ArXiv.org|Jul 23, 2007

Atomic and Subatomic Physics Research56 references4 citations

TL;DR

This study investigates posture-dependent ventilation in human lungs using hyperpolarized 3He MRI in an open-access MRI system that allows imaging in both supine and upright positions. Initial results demonstrate feasible 2D (4 mm in-plane resolution) and 3D (1.5 cm slice thickness) lung imaging with observable posture-related ventilation changes, highlighting gravity's role in lung function heterogeneity.

ABSTRACT

The human lung and its functions are extremely sensitive to orientation and posture, and debate continues as to the role of gravity and the surrounding anatomy in determining lung function and heterogeneity of perfusion and ventilation. However, study of these effects is difficult. The conventional high-field magnets used for most hyperpolarized 3He MRI of the human lung, and most other common radiological imaging modalities including PET and CT, restrict subjects to lying horizontally, minimizing most gravitational effects. In this paper, we briefly review the motivation for posture-dependent studies of human lung function, and present initial imaging results of human lungs in the supine and vertical body orientations using inhaled hyperpolarized 3He gas and an open-access MRI instrument. The open geometry of this MRI system features a "walk-in" capability that permits subjects to be imaged in vertical and horizontal positions, and potentially allows for complete rotation of the orientation of the imaging subject in a two-dimensional plane. Initial results include two-dimensional lung images acquired with ~ 4 mm in-plane resolution and three-dimensional images with ~ 1.5 cm slice thickness. Effects of posture variation are observed.

Motivation & Objective

• To investigate the impact of body posture on lung ventilation and perfusion heterogeneity using hyperpolarized 3He MRI.
• To overcome limitations of conventional high-field MRI systems that restrict subjects to horizontal positioning.
• To evaluate the feasibility of using an open-access MRI system for posture-dependent pulmonary imaging in humans.
• To assess the influence of gravity and anatomical constraints on regional lung function using non-invasive imaging.
• To establish initial imaging protocols for upright and supine lung imaging with hyperpolarized 3He gas.

Proposed method

• Utilized an open-access MRI system with a 'walk-in' design enabling vertical and horizontal subject positioning.
• Performed hyperpolarized 3He gas ventilation in human subjects to enable functional lung imaging.
• Acquired 2D lung images with approximately 4 mm in-plane resolution and 3D images with ~1.5 cm slice thickness.
• Imaged subjects in both supine and upright orientations to compare ventilation distribution.
• Employed standard MRI sequences optimized for 3He gas signal detection in lung parenchyma.
• Used a single-shot EPI sequence for rapid 2D imaging and 3D gradient-echo sequences for volumetric data acquisition.

Experimental results

Research questions

• RQ1 How does body posture affect regional ventilation distribution in the human lung as measured by 3He MRI?
• RQ2 To what extent does gravity influence ventilation heterogeneity in the lungs during upright versus supine positioning?
• RQ3 Can an open-access MRI system reliably acquire high-resolution 3He lung images in non-supine positions?
• RQ4 What are the technical and physiological challenges in performing posture-dependent 3He lung imaging?
• RQ5 How do anatomical constraints and gravitational forces alter ventilation patterns across lung regions?

Key findings

• The open-access MRI system successfully acquired 2D hyperpolarized 3He lung images with ~4 mm in-plane resolution in both upright and supine positions.
• Three-dimensional 3He lung images were obtained with a slice thickness of approximately 1.5 cm, enabling volumetric assessment.
• Posture-dependent changes in ventilation distribution were visually observed, indicating gravity's influence on ventilation heterogeneity.
• The system's open design allowed for stable imaging in vertical and horizontal orientations, supporting future studies of posture effects.
• Initial results demonstrate the feasibility of using open-access MRI for functional lung imaging across multiple body positions.
• The study provides a foundation for future investigations into gravity-dependent lung function using non-invasive, high-resolution 3He MRI.