4/13/2023 0 Comments Gas inhale mr contrastFirst, pulmonary Helium content may simply be quantified, a test that is no different from a gadolinium enhanced MRI- or iodine enhanced CT-scan. There are three particular approaches to the use of hyperpolarised helium imaging. No adverse effects have thus been reported with its use. While Xenon has known anaesthetic properties due to its significant solubility in biological tissues, Helium is chemically inert and absorbed only in negligible quantities. Owing to the decay characteristics of the polarised gas, as well as the need to consider cardiac pulsation and respiratory motion artefacts, fast low flip-angle (gradient echo) sequences (fast 3-D coronal FLASH, dynamic transverse-axial 2-D FLASH) are employed. MR system requirements for He-lung MR imaging (He-MRI) include a broadband radio-frequency system, such as that used in MR spectroscopy applications and dedicated receiver coils operating at the He-frequency. The resulting gas may be compressed, making it storable in low gradient magnetic fields for several hours (up to six days), also allowing transporting it to remote sites for imaging applications. Polarisation is transferred from polarised laser light when Helium principally absorbs the polarised light. the spins of the gas atoms, which act as small dipoles, align into one direction, causing ‘macroscopic’ magnetisation. Polarisation using so-called optical pumping methods produces spin alignments, i.e. This allows fast breath hold imaging and holds the promise of enhanced sensitivity and contrast in pulmonary imaging, a new technique that was first experimentally explored by US researchers in guinea pigs (Middleton H et al., Magn Reson Med 1995 33:271-5). While the nuclear density of these gases in their unprocessed state is too low to produce a useful signal, polarisation techniques can increase nuclear spin polarisation by 4-5 orders of magnitude, yielding a proportionally spectacular signal on dedicated MRI examination. The non-radioactive noble gas isotopes 3Helium (He) and 129Xenon, for example, may be inhaled and serve as contrast media in the determination of air space distribution within the lungs. Nonetheless, while hydrogen is the most frequently imaged nucleus in MRI, due to its great abundance in virtually all other biological tissues, any nucleus with a net nuclear spin may principally be explored by MRI. In addition, the innumerable air-soft tissue interfaces in pulmonary parenchyma do cause considerable susceptibility artefacts. However, the possibility to combine imaging of both structure and function in a non-invasive magnetic resonance imaging (MRI) examination, as performed anywhere else in the body, is hindered by the lack of free water, which renders the lungs signal deficient on conventional proton MRI. ![]() All of the aforementioned techniques also carry a radiation penalty. In contrast, scintigraphy techniques allow imaging of ventilation and perfusion, but lack spatial resolution. Given the inherent density differences in lung parenchyma, computed tomography (CT) permits high contrast resolution in lung imaging, although the assessment of very peripheral airways remains limited.
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