Diffusion Magnetic Resonance Imaging for Cancer Treatment Response Assessment
Martin G. Pomper, Juri G. Gelovani, Benjamin Tsui, Kathleen Gabrielson, Richard Wahl, S. Sam Gambhir, Jeff Bulte, Raymond Gibson, William C. Eckelman in Molecular Imaging in Oncology, 2008
Magnetic resonance imaging (MRI) can be used to obtain information related to biophysical, physiological, metabolical, anatomical, or functional properties of tissues. This chapter will highlight the application of diffusion MRI as a molecular imaging approach for oncological imaging. Applications of diffusion MRI range from assessment of cellular status (1), cellular density (2), diagnostic screening (3), and microstructural organization (4,5), all of which are used in clinical and research studies. Specific attention will be given to the application of this imaging approach for assessment of cancer treatment response. The overall concept for this application in cancer imaging is that diffusion MR can be used to quantify the mobility or diffusion of water molecules within tissue. Because the diffusion of individual water molecules relies on interactions which occur at the cellular level, subtle alterations in, for example, cellular density results in a corresponding change in the diffusion rate of water molecules which makes diffusion MRI a sensitive imaging biomarker (6,7). The goal of this chapter will be to provide the reader with an up to date summary of the basic methods and applications of applying diffusion MRI in oncological research and clinical practice.
Mapping the Injured Brain
Yu Chen, Babak Kateb in Neurophotonics and Brain Mapping, 2017
Diffusion MRI has long been used as an important tool in studying neurological disorders because it provides in vivo measurements of tissue microstructure changes that are unable to be detected using conventional CT or MR imaging. Diffusion tensor imaging (DTI) entails measuring water diffusion in at least six directions to obtain an appropriate representation of a diffusion tensor, describing the preferential diffusion direction and an ellipsoidal diffusivity profile. Briefly speaking, common measurements in DTI include mean diffusivity (MD) and apparent diffusion coefficient, which both measure the average magnitude of diffusivity, and fractional anisotropy (FA), which measures the disproportion of diffusion along the three principal axes of the diffusion ellipsoid. The diffusion properties of different brain tissues (GM, WM, CSF) exhibit unique structural properties. Diffusion in CSF is similar to free diffusion in water, so MD is extremely high (~3 × 10−3 mm2/s) and FA is almost 0. Diffusion in GM is generally nondirectional or isotropic because it is mostly composed of neurons and glial cells (FA < 0.2). On the other hand, in WM, diffusion is highly anisotropic due to the myelinated axons, which restrict water diffusion in the direction perpendicular to the axon. Therefore, axial diffusivity (AD, diffusion measured along the axon) can be as much as seven times the radial diffusivity (RD, diffusion measured perpendicular to the axon averaged across two axes) (FA ~ 0.45–0.8) (Song et al., 2003). Figure 14.1 shows an example of water diffusion in WM axons and the effect of axon membrane injury to water diffusion, which leads to increased RD and reduced FA.
Acquisition Strategies
Luisa Ciobanu in Microscopic Magnetic Resonance Imaging, 2017
Besides the three basic types of contrast discussed in the previous section, MR images can be sensitized to other physical processes such as molecular diffusion, perfusion, oxygenation level, etc. Among these, diffusion imaging is often used in magnetic resonance microscopy. The evolution of magnetization in a magnetic field in the presence of molecular diffusion is described by the Bloch‐Torrey equation, which is obtained by including an additional diffusion term to the Bloch equation:
Cellular and extracellular white matter alterations indicate conversion to psychosis among individuals at clinical high-risk for psychosis
Published in The World Journal of Biological Psychiatry, 2021
Felix L. Nägele, Ofer Pasternak, Lisa V. Bitzan, Marius Mußmann, Jonas Rauh, Marek Kubicki, Gregor Leicht, Martha E. Shenton, Amanda E. Lyall, Christoph Mulert
The diffusion MRI-based free-water imaging technique addresses these limitations by decomposing the diffusion signal into two compartments (Pasternak et al. 2009). The first compartment models the fractional volume of isotropic, unrestricted diffusion in the extracellular space (free-water, FW) which can be responsive to pathologies such as edoema and atrophy (Pasternak et al. 2012; Lyall et al. 2018). The second compartment models hindered/restricted diffusion in close proximity to cellular membranes, from which FA of the tissue (FAT) is derived, reflecting more closely changes in myelination and axonal membrane health than the conventional DTI metric FA (Pasternak et al. 2009). By differentiating these compartments this model has proven to be successful in providing new insights to potential biological mechanisms underlying the observed FA reductions in schizophrenia (Pasternak et al. 2012, 2015; Lyall et al. 2018).
Impact of Amblyopia on the Central Nervous System
Published in Journal of Binocular Vision and Ocular Motility, 2020
Nathaniel P. Miller, Breanna Aldred, Melanie A. Schmitt, Bas Rokers
However, in recent decades, advances in magnetic resonance imaging (MRI) methods have enabled more precise in vivo assessment of the structure and function of the brain beyond the retina. Functional integrity can be assessed using functional MRI (fMRI) in which neural activity is estimated based on metabolic demand via blood oxygen level-dependent (BOLD) signals.35 Structural integrity can be assessed with voxel-based morphometry (VBM) or diffusion MRI (dMRI). VBM is based on MRI intensity differences produced by different kinds of brain tissue and can assess local gray and white-matter volume. Diffusion MRI measures the diffusion of water molecules in tissue, enabling the identification of white-matter pathways in the brain and the estimation of their structural integrity.
Comparison between CT and MRI in detection of metastasis of the retroperitoneum in testicular germ cell tumors: a prospective trial
Published in Acta Oncologica, 2020
Marjut Laukka, Susanna Mannisto, Annette Beule, Mauri Kouri, Carl Blomqvist
MRI of the abdomen from the level of thoracic vertebra 10 to the groins without contrast medium was performed using a 1.5 T GE machine, Optima MR450w (2011). To improve the detection of small lymph nodes, we used DWI, but no quantitative ADC measurements were carried out. The machine was updated in 2014, and at that time, three b-value DWI was introduced in addition into the protocol. Because of this technical development, 21 of patients examined in 2015–2017 underwent both diffusion imaging protocols. Imaging of the abdomen: coronal and axial T1-weighted images, 4.4- to 5-mm slice, overlap 2.2–2.5 mm, FOV 42 × 33.6–42 (LAVA flex); axial T2-weighted images, 5-mm slice, gap 1 mm, FOV 42 × 29.4 respiratory triggering. Axial diffusion-weighted images were with two p values 0 and 600 (all patients). Due to system update at the end of 2014, three p value diffusion-weighted images were added to the protocol using p values 50, 200 and 800. Imaging of the pelvis: axial T1-weigted images 5-mm slice, 0 gap, FOV 42 × 42 and axial T2-weighted images 5-mm slice, 0 gap, FOV 42 × 42. Axial diffusion-weighted images with two p values 0 and 600 and with three p values 50, 200 and 800 were performed in the same way as in the abdomen.
Related Knowledge Centers
- Contrast
- Diffusion
- In Vivo
- Macromolecule
- Tissue
- Tractography
- Mri Sequence
- Biological Membrane
- White Matter
- Spin–Lattice Relaxation