ABSTRACT
I. Introduction 325
II. Basic Physiology of Regional Oxygen Balance 327
III. Methods Based on Hyperpolarized Helium-3 329
A. Physical Principles 329
B. Techniques of Measurement 330
C. Validation Studies 334
D. Studies in Humans 336
IV. Methods Based on Fluorine-19 336
A. MRI Techniques Using Fluorinated Gases 337
B. MRI Techniques Using Liquid PFCs 340
V. Comparison of Methods 343
A. Helium-3 vs. Fluorine-19 343
B. Other Nuclei 343
Hyperpolarized Xenon-129 343
O2-Sensitive 1H MRI 345
C. Specific Uses and Current Limitations 346
VI. Summary 349
Acknowledgments 349
References 350
I. Introduction
The local ratio between ventilation ( _VA) and perfusion ( _Q) and its distribution throughout the lung is one of the most important defining factors of alveolar
gas composition (1). Until recently, direct and simultaneous regional mea-
surement of alveolar and capillary gas concentrations has not been possible.
Information about the regional pO2 distribution within the pulmonary bio-
compartments would (i) add to the understanding of _VA= _Q distribution and heterogeneity in the normal lung, for example, with regard to species differences,
maturation, structural, gravitational, exertional, and many other effects; (ii) con-
tribute to diagnosis and monitoring of obstructive, interstitial, inflammatory, and
embolic pulmonary diseases; and (iii) help to monitor the effects of drugs upon
the pulmonary vasculature or the airways.
