Assessment of lung ventilation by MR imaging: current status and future perspectives

Abstract

The aim of this paper is to review the present status of novel MRI techniques as a new important instrument for functional ventilation imaging. The current status and future perspectives in research and clinical applications are summarized. Morphological lung imaging is based on chest radiography and computed tomography, whereas scintigraphy is used for ventilation imaging. During recent years, MRI has emerged as a new means for functional imaging of ventilation. Aerosolized contrast agents and oxygen are used in proton imaging, whereas non-proton imaging relies on fluorine compounds, such as sulfur hexafluoride and perfluorcarbons, or on hyperpolarized noble gases, such as helium-3 or xenon-129. All the gases are administered as inhaled "contrast agents" for imaging of the airways and airspaces. In general, straightforward images demonstrate the homogeneity of ventilation in a breath-hold and allow for determination of ventilated lung. The different properties of the different compounds enable the measurement of additional functional parameters. They comprise airspace size, regional oxygen partial pressure, and analysis of ventilation distribution, ventilation/perfusion ratios, and gas exchange, including oxygen uptake. Novel MRI techniques provide the potential for functional imaging of ventilation. The next steps include definition of the value and the potential of the different contrast mechanisms as well as determination of the significance of the functional information with regard to physiological research and patient management in chronic obstructive pulmonary disease and others.

Aerosol Delivery in Ventilated Newborn Pigs: An MRI Evaluation

“…The aerosol particle size for both PGE 1 and Gd-DTPA favors alveolar deposition; therefore, these results predict pulmonary drug deposition for PGE 1 following jet nebulization in a neonatal ventilator circuit. Second, inhaled molecular oxygen has been shown to be an effective MR contrast agent in MR ventilation imaging because of its paramagnetic properties (27,32,33). Although animals in this study received the same flow rate of oxygen during baseline and aerosolized Gd-DTPA administration to avoid the confounding effect of oxygen on SI changes, it is possible that enhancement of signal intensity after administration of aerosolized Gd-DTPA may be attenuated.…”

Measurement of hyperpolarized gas diffusion at very short time scales

“…Zielinski and Sen explored this issue analytically [25], and found that for gradient pulses with a square profile and δ = Δ (in maximal violation of the narrow-pulse criterion), the time-dependent diffusivity curve still approaches D 0 linearly as Δ goes to zero (confer Eq. [1]), but with a steeper slope than for narrow gradient pulses, and that accurate S/V values can be obtained from this slope if the correct proportionality constant α is used. This result was confirmed by Miller et al in a recent study of simulated 2-D diffusion [12], in which the appropriate proportionality constants α sine and α triangle for sinusoidal and triangular pulse shapes were also determined.…”

“…have derived a quantitative relationship between the short-time behavior of the diffusion coefficient in a restricted environment and the surface-to-volume ratio of the surrounding structure [9]: (1) Thus for short diffusion times D(t) varies linearly with √t, with a slope proportional to S/V, and approaches D 0 as t approaches zero. This result can be used to extract S/V from two or more measurements of D in the short-time-scale regime.…”

“…Magnetic resonance imaging of the hyperpolarized noble gases 129 Xe and 3 He is a powerful technique for studying aspects of lung structure and function not accessible with conventional 1 H MRI [1]. In particular, measurements of the apparent diffusion coefficient of inhaled 3 He have shown sensitivity to the enlargement of alveolar and acinar airspaces due to emphysema [2][3][4][5][6][7][8].…”

A broadband ytterbium-doped tunable fiber laser for 3He optical pumping at 1083�nm

“…For laser manufacturers, the main technical challenge now lies in the cost-effective production of robust, reliable and very powerful fiber sources for production of large quantities of polarized gas to support the wide dissemination of established applications of hyperpolarized 3 He gas and the emergence of new ones [45,46,47,48,49,50,51,52,53,54,55].…”