Hp 83Kr MRI of canine lung tissue using stopped-flow optical pumping. (A) Micrograph of lung tissue demonstrating that the drying process preserves the alveolar structure. That microscopic anatomic structure is maintained as evidenced by the intact alveolar septum walls (long arrows) and alveolar epithelium (short arrows). (B) 83Kr MRI of canine lung tissue obtained by using krypton stopped-flow optical pumping. The time needed for each of the 16 individual measurements is 10 min for the optical pumping process, ≈3 s for the krypton transfer, and 103 ms for rf pulse, gradient pulse, and acquisition at 9.4-T field strength. The resolution is 480 × 655 μm (raw data) with no slice selection applied. (C) 83Kr MRI of a lung sample using only one krypton stopped-flow optical pumping cycle. The measurement takes 15 min for the pumping process, 3 s for the gas transfer, and 0.46 s for the rf pulses, gradient pulses, and signal acquisition. The small flip angle excitation (FLASH) image was produced by using sixteen 12° flip angle pulses. The resolution is 1,080 × 655 μm (raw data) with no slice selection.