Traditional Posters: Body Imaging

Helen Marshall¹, Salma Ajraoui¹, James M. Wild<sup>1

1</sup>Academic Unit of Radiology, University of Sheffield, Sheffield, South Yorkshire, United Kingdom

The study of ventilation dynamics with hyperpolarised ³He requires a fast imaging sequence to capture the flow of contrast into the lungs. Radial acquisition, among other sequences, has previously been demonstrated for this purpose. However, images from a standard radial acquisition are constrained to a fixed resolution determined at the acquisition stage. Here golden angle radial sampling was used to image the inhalation of hyperpolarised ³He and compared to a standard, sequential radial acquisition. Golden angle radial imaging enabled reconstruction of the dynamic dataset at any chosen spatio-temporal resolution, providing improved visualisation of the initial stages of inhalation.

2537. On the Relationship Between 3He ADC and Lung Morphometrical Parameters

Alexander L. Sukstanskii¹, James D. Quirk¹, Jason C. Woods^1,2, David S. Gierada¹, Barbara A. Lutey³, Mark S. Conradi², Dmitriy A. Yablonskiy<sup>1,2

1</sup>Radiology, Washington University, St. Louis, Misssouri, United States; ²Physics, Washington University, St. Louis, MO, United States; ³Internal Medicine, Washington University, St. Louis, MO, United States

The apparent diffusion coefficient (ADC) of hyperpolarized 3He gas in lungs increases in emphysema and can serve as a biomarker of the disease progression. It is not clear, however, how ADC relates to lung microstructure. In the present communication, using 3He-based in vivo lung morphometry technique, we demonstrate that ADC and a standard histological parameter – mean chord length (Lm) reflect lung microstructure parameters in different ways. As a result, a there is no unique relationship between ADC and Lm. At the same time, 3He-based lung morphometry allows quantification of the lung microstructure in terms of Lm, surface-to-volume ratio and other standard histological parameters.

2538. Modelling Non-Gaussian 3He Diffusion Signal Behaviour Using a Fractional Dynamics Approach

Juan Parra-Robles¹, Salma Ajraoui¹, Jim M. Wild<sup>1

1</sup>University of Sheffield, Sheffield, United Kingdom

Diffusion of 3He gas in the lung has been shown to deviate from Gaussian behaviour. Cylinder model and diffusional kurtosis have been previously used to quantify non-Gaussian signals. In this work the diffusion stretched-exponential model is used as a new approach to model the non-Gaussian behaviour. The results obtained demonstrate that the anomalous diffusion stretched-exponential model fits well the behaviour of the 3He lung MR signal. This model can potentially provide valuable information about lung microstructure at different length scales.

2539. Experimental Investigation of the Limits of Validity of the Physical Basis of a Method for in Vivo Lung Morphometry with ³He Diffusion MRI

Juan Parra-Robles¹, Salma Ajraoui¹, Martin H. Deppe¹, Steven R. Parnell¹, Jim M. Wild<sup>1

1</sup>Unit of Academic Radiology, University of Sheffield, Sheffield, South Yorkshire, United Kingdom

In this work, the limits of validity of physical basis of a model of ³He MR lung diffusion are investigated experimentally in simple geometric models. The experimental results have highlighted limitations of the cylinder model. Breakdown of the Gaussian phase approximation was experimentally demonstrated for gradient strengths commonly used in lung ADC experiments, as the localized diffusion regime is approached. The physical assumptions of the cylinder model are only valid if the localized diffusion regime and its neighboring intermediate regimes are avoided.

2540. Exact Results for Diffusion Weighted MR on Branched Structures