Diffusion Microstructure Models in the Body and Tumor
Sungheon Gene Kim1
1Weill Cornell Medicine, United States

Synopsis

Keywords: Contrast mechanisms: Diffusion, Body: Body, Cross-organ: Cancer

This lecture provides an overview of how diffusion MRI has been used to measure tissue microstructural properties in various tissues and organs outside the brain. We will focus on (i) diffusion microstructure models in the body that have been used to measure the tissue microstructural properties in specific examples including muscle, breast, and prostate; and (ii) diffusion microstructure models for tumor that can be used to measure cancer cell properties, such as cell size and transcytolemmal water exchange rate. The need and challenges for validation will also be discussed.

Diffusion microstructure models in the body

Diffusion MRI has become the modality of choice to study brain microstructural properties non-invasively in recent years [1]. However, its potential use for other tissues and organs outside the brain has not been explored as much. Conducting diffusion MRI in the body comes with increased challenges for data acquisition, in general, due to motion and anatomical size and location. In addition, it often requires a careful consideration of the tissue microstructural properties specific to a target tissue that are closely related to adequate selection of a proper diffusion microstructure model as well as data acquisition parameters, such as diffusion time, diffusion weighting directions and strengths. In this lecture, we will discuss this more in depth for several cases, including muscle [2-4], prostate [5], and breast [6]. We will consider both signal representation and biophysical models in terms of their strengths, limitations, and unmet need for validation.

Diffusion microstructure models for tumor

Diffusion MRI is a unique imaging tool to probe tumor microstructural and functional properties without using an exogenous contrast agent [7, 8]. A number of studies have demonstrated that diffusion MRI parameters, primarily diffusion coefficient D, are highly sensitive to treatment-induced changes [9, 10]. In addition, the diffusional kurtosis coefficient K, a non-Gaussian diffusion measure that complements D [11], has been suggested as a promising empirical biomarker of cell microstructure and for evaluation of early treatment response.[12, 13] While both D and K are biomarkers sensitive to microstructures, they are not specific to microstructural properties. This is partly because D and K are not fixed constants, but rather functions of the diffusion time t, D(t) and K(t); their t-dependency is determined by tissue properties, such as cell size, extracellular volume, and plasma membrane permeability [14-17]. In this lecture, we will discuss how to harness diffusion strength and diffusion time to quantify tumor tissue microstructural properties. It will include both signal representation and biophysical models that have been successfully used to provide specific information about the tissue microstructural changes induced by tumor growth or treatment. We will also discuss challenges in validation of tumor microstructural parameters.

Acknowledgements

This work was supported by NIH grants R01CA160620, R01CA219964, and UH3CA228699.

References

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Proc. Intl. Soc. Mag. Reson. Med. 31 (2023)