Magnetic Exchange (MEX)
Magnetic resonance imaging (MRI) is mostly performed on protons associated with freely moving water molecules, as they are highly abundant in biological tissues yielding high signals. Nonetheless, much signal information originates from the non-aqueous species in the tissue, such as proteins and lipids. We aim to implement a novel MRI technique that allows the acquisition of signal generated by the protons adjacent to the semi-solid components of the tissue and combine it with quantitation analysis to extract the volumetric fraction of proteins or lipids. The proposed MRI sequence, MEX (magnetization exchange), can provide an insight into the content of species with restricted motion.
An illustration of MEX sequence:
Magnetic Resonanse Elastography (MRE)
Magnetic Resonance Elastography (MRE) is an MRI modality that probes tissue stiffness. MRE is performed in conjunction with the application of mechanical vibrations in typical frequencies of up to 100 Hz (in clinical scanners). The MRE pulse sequence includes application of motion encoding gradients (on top of the imaging gradients) that are switched on and off and in their polarity, in synchronization with the applied waves. The waves create sub-micron displacements in the probed object (e.g. a tissue) and the application of the gradients creates a localized phase shift in each voxel. The maps of complex phase shifts are than used to quantify the complex shear modulus: G* = G′ + iG″ that is composed of the shear storage modulus (G′) and the shear loss modulus (G″).
MRE has proven its diagnostic value across various clinical conditions such as neurodegeneration and liver and kidney fibrosis or cancer. Importantly, for our matter, brain MRE has demonstrated significant changes in the aging brain, in which aging and neurodegenerative diseases are correlated with a reduction in the shear modulus.
Beyond the prolonged effects associated with aging, alterations in the stiffness of brain tissue are also linked to dynamic events, such as brain function. Functional MRE (fMRE) experiments have demonstrated that stimulation leads to immediate changes in the tissue stiffness.
The experiments are composed of distinct phases, with stimulation activated during the 'on' stage and withheld during the 'off' state. The mechanical vibration that facilitates the acquisition of phase images that correspond to the viscoelastic changes is operated throughout the entire experiment. It was found that stimulation leads to significant changes in the stiffness.
Stray Field NMR
Osteoporosis is a disease in which the density and quality of bone are reduced, affecting mainly post-menopausal women. For now, there is no easy method to monitor early changes in bone mineral density to assess hormonal treatment efficacy in osteoporotic patients. The goal of this is to develop a small, simple, affordable, MR-based table-top scanner to detect Osteoporosis-related cellular changes in the bone marrow as an early indicator of treatment efficacy.
The scientific foundation of our project is that bone marrow adiposity (BMD) escalates in postmenopausal women with osteoporosis. Hormonal changes associated with the postmenopausal phase trigger cellular pathways that alter the differentiation of mesenchymal stem cells into adipocytes, disrupting the balance between adipocyte and osteoblast differentiation. This process starts long before changes in BMD are noticeable and exhibits rapid responsiveness to hormonal treatment.
Experiments conducted by our group have shown that alterations in the bone marrow associated with the onset of osteoporosis, can be detected by using a mobile stray field NMR. Based on these findings, we are developing a specialized mobile stray-field NMR device for monitoring bone marrow adiposity.
An axial MRI (Dixon) scan of an arm, showing the Radius (top) and the Ulna (bottom) bones