Non-resonance Electron Spin Imaging - Project Summary /Abstract Traditional magnetic resonance imaging methods, such as MRI, use radiofrequency (RF) waves to manipulate the spin, a quantum-mechanical property of subatomic particles. These particles include various types of nuclei and the electron. Constant magnetic fields are used in experiments, the strength of which must match the RF to observe resonance phenomena. The spins are very sensitive reporters of their local molecular environment. They can report the concentration, dynamics, and interactions of the surrounding molecules. However, the current resonance approach has its limitations that stem from the use of radio waves. When RF propagates through the sample, only an infinitesimally small amount of power contributes to the observable signals. Most of the energy is absorbed by the imaged object. RF energy dissipates as heat. Associated with this very inefficient use of power are multiple problems such as sample heating, limited penetration depth, power saturation of signal amplifiers, spin system saturation (distorts data), and increased noise. These problems are especially critical for electron-based paramagnetic resonance imaging. An alternative to traditional EPR, RF-free non-resonance electron spin imaging (NESI) method is proposed. This technology overcomes the limitations associated with the use of RF power. The key concept behind NESI is relatively simple. In the traditional methods, RF is used to rotate spin magnetization relative to the constant magnetic field. In NESI, the magnetic field is rotated with respect to the magnetization vector. Both experiments measure the precession of the magnetization vector around the constant magnetic field. Several innovative mathematical and engineering solutions are proposed to transform the described above concept into a fully functional imaging system. The NESI instrument will be built and rigorously tested using a wide range of samples (phantoms) with pre-determined geometry. A several-fold increase in sensitivity is expected compared to the standard EPR imaging method when traditional classical detection methods are used. Recent developments of quantum sensing promise unprecedented sensitivity for the detection of electron spin signals. These novel technologies are incompatible with the traditional EPR. Several standard types of spin probes will be used to image oxygen partial pressure (pO2) and acidity (pH) distribution in these phantoms. In future studies, NESI will be used in pre-clinical and clinical studies. Imaging of chemical microenvironment in bio-printed tissue and organ models is another important application of this technology.
