Flip-angle measurement by magnetization inversion: Calibration of magnetization nutation angle in hyperpolarized (3) He magnetic resonance imaging lung experiments.

The aim of this work was to establish a new, fast, and robust method of flip-angle calibration for magnetic resonance imaging of hyperpolarized (3) He. The method called flip-angle measurement with magnetization inversion is based on acquiring images from periodically inverted longitudinal magnetization created using the spatial modulation of magnetization technique. By measuring the width of the area where the magnetization was inverted by the spatial modulation of magnetization preparation in phase images, the flip angle can be generated using a simple equation. To validate and establish the limits of the proposed method, flip-angle measurement with magnetization inversion acquisitions were simulated and applied to proton and hyperpolarized (3) He phantoms. Then, the calibration procedure was applied during hyperpolarized (3) He magnetic resonance imaging in a healthy volunteer. The advantage of the flip-angle measurement with magnetization inversion method compared with the conventional method based on the assessment of radiofrequency-decay is that it is free of errors induced by relaxation due to oxygen, by imperfect excitation slice profile and by any diffusion of (3) He into and out of the slice. Another advantage is that it does not require image processing with external software and therefore can be performed using the implemented tools on the magnetic resonance workstation.

Magnetic resonance imaging of dissolved hyperpolarized 129Xe using a membrane-based continuous flow system.

A technique for continuous production of solutions containing hyperpolarized (129)Xe is explored for MRI applications. The method is based on hollow fiber membranes which inhibit the formation of foams and bubbles. A systematic analysis of various carrier agents for hyperpolarized (129)Xe has been carried out, which are applicable as contrast agents for in vivo MRI. The image quality of different hyperpolarized Xe solutions is compared and MRI results obtained in a clinical as well as in a nonclinical MRI setting are provided. Moreover, we demonstrate the application of (129)Xe contrast agents produced with our dissolution method for lung MRI by imaging hyperpolarized (129)Xe that has been both dissolved in and outgassed from a carrier liquid in a lung phantom, illustrating its potential for the measurement of lung perfusion and ventilation.