In vivo MR imaging and spectroscopy using hyperpolarized ¹²⁹Xe

Hyperpolarized ¹²⁹Xe has been used to obtain gas phase images of mouse lung in vivo, showing distinct ventilation variation as a function of the breathing cycle. Spectra of ¹²⁹Xe in the thorax show complex structure in both the gas phase (-4 to 3 ppm) and tissue-dissolved (190-205 ppm) regions. The alveolar gas peak shows correlated intensity and frequency oscillations, both attributable to changes in lung volume during breathing. The two major dissolved peaks near 198-200 ppm are attributed to lung parenchyma and to blood; they reach maximum intensity in 5-10 s and decay with an apparent T₁ of 30 s. Another peak at 190 ppm takes 20-30 s to reach maximum; this must represent other well-vascularized tissue (e.g., heart and other muscles) in the thorax. The maximum integrated area of the tissue components reaches 30-80% of the maximum alveolar gas area, indicating that imaging at tissue frequencies can be achieved.