Indirect detection of lung perfusion using susceptibility‐based hyperpolarized gas imaging

Abstract

Purpose:To address the problem of inadequate signal-tonoise ratio (SNR) encountered in lung perfusion magnetic resonance imaging (MRI) by developing an indirect detection based on the strong hyperpolarized (HP) gas signal. Materials and Methods:Our model is based on detecting the effects of gadolinium (Gd) flowing through lung capillaries by recording the phase of the nearby alveolar HP gas. In a HP gas 3 He phantom we imaged gas phases before and after removing tubes containing paramagnetic solution away from the phantom. We also imaged HP gas phases in pig lungs before and after injection of Gd. Finally, parenchymal spin phase in excised lungs was measured as a function of Gd concentration. Results:In the phantom, the differential phase map displayed a pattern characteristic of a susceptibility-induced dipole field, showing the possibility of an indirect detection. In vivo, the differential phase map showed homogeneous appearance, as expected for uniform perfusion in healthy lungs. Ex vivo, the parenchymal spin phases were shown to depend linearly on Gd concentration. Conclusion:Our method should allow indirect perfusion (Q) and direct ventilation (V) to be assessed simultaneously, thus allowing for diagnosis of V/Q mismatches. The linear dependency of parenchymal spin phase vs. Gd concentration may allow for quantification of lung perfusion.

Functional lung imaging using hyperpolarized gas MRI

“…One approach that addresses the spatial misregistration problem exploits the T1-shortening due to the paramagnetic effects of Gd contrast agent as it flows through the lung vasculature. The Gd contrast causes depolarization of the HP He-3 and thus can indirectly measure perfusion (61,86).…”

Advances in bio-imaging: A survey from WWMR 2010

“…Recently Rizi and co-workers [4] have introduced a measurement technique that makes it possible to obtain ADC, pO 2 , and R from the same measurement. This makes it possible to save expensive 3 He, to apply shorter measurement times, and to assess the correlation between all the parameters related to COPD.…”

“…The newest development in this field allows the characterization of lung microstructure at the alveolar level by measurement of the apparent diffusion coefficient (ADC) using hyperpolarized 3 He [3]. ADC images, which make it possible to detect tissue destruction from chronic obstructive pulmonary disease (COPD), rely on the fact that diffusion of gases into alveoli is strongly limited relative to free diffusion.…”

“…Pathological lung structures are also described by alveolar partial pressure of oxygen (pO 2 ) and oxygen depletion rate (R). The use of hyperpolarized 3 He provides a way to measure pO 2 and R, as the relaxation rate of the polarized nucleus is increased by the presence of paramagnetic oxygen, yielding a kind of functional lung imaging using hyperpolarized gas. The correlation between pulmonary structure and oxygen exchange efficiency is particularly interesting for the early diagnosis of disease and for detection of response to treatment.…”

NMR detection using laser-polarized xenon as a dipolar sensor

“…These experiments can also be seen as a useful complement -in the sense of adding spectral information -to two recently proposed experiments which use dipolar fields for local magnetometry. In [23], 1 H and 13 C resonances of chloroform dissolved in liquid xenon were used for quantitative measurements of xenon magnetization; in [24] it is proposed to use 3 He gas in lung tissue to measure and quantify susceptibility changes in nearby blood vessels upon loading them with paramagnetic contrast agents.…”