ESTRO 2024 - Abstract Book

S4963

Physics - Radiomics, functional and biological imaging and outcome prediction

ESTRO 2024

Minea Jokivuolle 1,2 , Henrik Lundell 3,4 , Kristoffer Madsen 3,5 , Faisal Mahmood 1,2

1 Odense University Hospital, Laboratory of Radiation Physics, Department of Oncology, Odense, Denmark. 2 University of Southern Denmark, Department of Clinical Research, Odense, Denmark. 3 Copenhagen University Hospital - Amager and Hvidovre, Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Copenhagen, Denmark. 4 Technical University of Denmark, Department of Health Technology, Copenhagen, Denmark. 5 Technical University of Denmark, Department of Applied Mathematics and Computer Science, Copenhagen, Denmark

Purpose/Objective:

Local recurrence is a problem for many types of cancer [1]. Biologically adapted radiotherapy may improve local control, but accurate non-invasive methods to assess tumor heterogeneity are currently lacking [2, 3].

Diffusion-weighted MRI (DW-MRI) measures diffusion of water molecules in tissue, estimated by the apparent diffusion coefficient (ADC), which makes it a powerful tool to probe tissue microstructure [4]. Standard DW-MRI assumes ADC to be constant over the diffusion time ( t d ). However, this assumption holds only for free diffusion, which requires that the diffusion is not affected by obstacles. Water molecules in vivo interact with several obstacles, mainly the cell membranes, which makes the diffusivity dependent on the diffusion time (ADC = ADC( t d )). The cell membranes can either restrict the water molecules (restricted diffusion) or let them pass through (exchange) (Figure 1). The change in ADC as a function of t d (ΔADC) reveals the dominant interaction between the water molecules and the cell membranes; a negative ΔADC implies that diffusion is restricted, and provides information about the restricting structures (e.g. cell sizes and cell density), whereas a positive ΔADC implies substantial water exchange (i.e. membrane permeability). Time-dependent diffusion MRI (TDD-MRI) measures diffusion as a function of t d , thus characterizing tissue microstructure with higher specificity than standard DW-MRI [5]. Clinical translation of TDD-MRI requires investigations on clinically available systems. The aim of this study was to explore the ability of TDD-MRI to assess tumor heterogeneity in the brain on a clinical 1.5 T MR sim system with clinical gradient strengths. To our knowledge, this is the first demonstration of TDD-MRI on a 1.5 T MR sim in brain lesions.