Brian Timothy Saam

Dynamic echo planar MR imaging of lung ventilation with hyperpolarized 3 He in normal subjects and patients with severe emphysema

We applied the rapid imaging capability of echo planar MR pulse sequences and hyperpolarized 3He ventilation imaging to observe the dynamic distribution of gas in the lungs during breathing. Findings in five normal volunteers (age 19–53 years) and four patients with severe smoking‐related emphysema (age 56–71 years) were compared. All studies were performed on a 1.5u2005T whole body scanner using a 30u2005cm Helmholtz surface coil and 0.5 l of 20–40% polarized 3He mixed with 1–2 l nitrogen. Our echo planar imaging pulse sequence allowed acquisition of each image in 0.04u2005s, with a pixel size of 7u2005mm2 (TRu2005=u200540.5u2005ms, TEu2005=u200512.1u2005ms, flip angleu2005=u200522°, echo train lengthu2005=u200532, matrixu2005=u200532u2005×u200564, field of viewu2005=u2005225u2005×u2005450u2005mm, slice thicknessu2005=u200510u2005mm). Imaging was performed in the transaxial plane repeatedly at 3, 10 or 20 evenly spaced levels, immediately before and during breathing of the gas mixture. In normal subjects during the first breath, 3He appeared throughout each slice first in the mid lungs, then in the lower lungs, then in the upper lungs, with slightly greater signal in the dependent posterior regions. In patients with emphysema, sequential filling of different lung regions was seen during the first breath, with delayed filling of other regions observed during rebreathing and room air washout. We conclude that subsecond dynamic 3He MR ventilation imaging can reveal normal and abnormal ventilation phenomena not seen with conventional scintigraphic methods, and offers another approach to the study of ventilation physiology and pathophysiology. Copyright

Optically Polarized He3

This article reviews the physics and technology of producing large quantities of highly spin-polarized 3He nuclei using spin-exchange (SEOP) and metastability-exchange (MEOP) optical pumping. Both technical developments and deeper understanding of the physical processes involved have led to substantial improvements in the capabilities of both methods. For SEOP, the use of spectrally narrowed lasers and K-Rb mixtures has substantially increased the achievable polarization and polarizing rate. For MEOP nearly lossless compression allows for rapid production of polarized 3He and operation in high magnetic fields has likewise significantly increased the pressure at which this method can be performed, and revealed new phenomena. Both methods have benefitted from development of storage methods that allow for spin-relaxation times of hundreds of hours, and specialized precision methods for polarimetry. SEOP and MEOP are now widely applied for spin-polarized targets, neutron spin filters, magnetic resonance imaging, and precision measurements.