ABSTRACT
BACKGROUND: Magnetic resonance imaging (MRI) is a noninvasive technique that provides excellent contrast for soft tissue organs. However, due to the low density of protons and many air-tissue junctions, its application in the lung is limited. Thus, Xray-based methods are often used here (with the well-known disadvantages of ionizing radiation). OBJECTIVES: In this review, we discuss pulmonary MRI with hyperpolarized xenon-129 (Xe-MRI). Xe-MRI provides unique valuable insights into lung microstructure and function, including gas exchange with red blood cells-parameters not accessible by any standard clinical methods. METHODS: By magnetic labelling, i.e. hyperpolarization, the signal from xenon-129 is amplified by up to 100,000 times. In this process, electrons from rubidium are first polarized to 100% using laser light and then transferred to xenon by collisions. Then the hyperpolarized gas is brought to the patient in a bag and inhaled shortly before the MRI scan. RESULTS: Using special programming (sequences) of the MRI, the ventilation, microstructure, or gas exchange of the lungs, can be displayed in 3D. This allows, for example, quantitative visualization of ventilation defects, alveolar size, tissue gas uptake and gas transfer to the blood. CONCLUSIONS: Xe-MRI provides unique information about the state of the lung-noninvasively, in vivo and in less than a minute.
Subject(s)
Lung , Xenon , Humans , Lung/diagnostic imaging , Magnetic Resonance Imaging/methods , RespirationABSTRACT
Sources of high-energy photons have important applications in almost all areas of research. However, the photon flux and intensity of existing sources is strongly limited for photon energies above a few hundred keV. Here we show that a high-current ultrarelativistic electron beam interacting with multiple submicrometer-thick conducting foils can undergo strong self-focusing accompanied by efficient emission of gamma-ray synchrotron photons. Physically, self-focusing and high-energy photon emission originate from the beam interaction with the near-field transition radiation accompanying the beam-foil collision. This near field radiation is of amplitude comparable with the beam self-field, and can be strong enough that a single emitted photon can carry away a significant fraction of the emitting electron energy. After beam collision with multiple foils, femtosecond collimated electron and photon beams with number density exceeding that of a solid are obtained. The relative simplicity, unique properties, and high efficiency of this gamma-ray source open up new opportunities for both applied and fundamental research including laserless investigations of strong-field QED processes with a single electron beam.
