Anselm Deninger

Assessment of a single-acquisition imaging sequence for oxygen-sensitive 3He-MRI

MRI of the lungs using hyperpolarized helium‐3 (3He) allows the determination of intrapulmonary oxygen partial pressures (pO2). The need to separate competing processes of signal loss has hitherto required two different imaging series during two different breathing maneuvers. In this work, a new imaging strategy to measure pO2 by a single series of consecutive scans is presented. The feasibility of the method is demonstrated in three healthy human volunteers. Maps and histograms of intrapulmonary pO2 are calculated. Changes in the oxygen concentration of the inhaled gas mixture are well reproduced in the histograms. Monte Carlo (MC) simulations of the temporal evolution of 3He hyperpolarization within the lungs were performed to evaluate the accuracy of this measurement technique, and its limitations. Magn Reson Med 47:105–114, 2002.

3He-MRI-based measurements of intrapulmonary pO2 and its time course during apnea in healthy volunteers: first results, reproducibility, and technical limitations

We applied a recently developed method of following the time course of the intrapulmonary oxygen partial pressure pO2(t) during apnea by 3He MRI to healthy volunteers. Using two imaging series with different interscan times during two breathholds (double acquisition technique), relaxation of 3He due to paramagnetic oxygen and depolarization by RF pulses were discriminated. In all four subjects, the temporal evolution of pO2 was found to be linear, and was described by an initial partial pressure p0 and a decrease rate R. Also, regional differences of both p0 and R were observed. A correlation between p0 and R was apparent. Finally, we discuss limitations of the double acquisition approach. Copyright

Provision of hyperpolarized 3H⃗e and its application in MRI

Magnetic Resonance Imaging (MRI) usually relies on magnetization of hydrogen nuclei (protons) in water or molecules in tissue as source of the signal. Biological environments with low proton content, notably the lungs, are difficult to image. Inhaling of hyperpolarized 3He gas opens the possibility to investigate ventilated spaces by MRI. To overcome the loss in signal due to the low density of the gas the nuclear polarization of the 3He spins is greatly enhanced by laser Optical Pumping. For more than three decades Optical Pumping of noble gases has been investigated, using spin exchange scattering (SE) or metastability exchange scattering (ME). Since powerful resonant laser light is available for Optical Pumping, large quantities of 3He gas can be operated. The original interest was the development of dense spin polarized targets for fundamental research in physics. As a spin off, the possibility of MRI of lung tissue filled with hyperpolarized 129Xenon was demonstrated in 1994. Later 3He was used for M...