High spatial resolution hyperpolarized ³He MRI of the rodent lung using a single breath X‐centric gradient‐recalled echo approach

Abstract

The x-centric method significantly reduces diffusion weighting, allowing high spatial and temporal resolution HP He gas density-weighted rodent lung MRI. Magn Reson Med 78:2334-2341, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

Accelerated 129Xe MRI morphometry of terminal airspace enlargement: Feasibility in volunteers and those with alpha‐1 antitrypsin deficiency

“…The signal void observed on the b = 0 long‐TE image (Figure C, yellow arrow) corresponds to a short (3–5 ms) lung region. We have calculated the b‐value corresponding to the readout gradient (0.26 s/cm 2 ) following the method of Ouriadov et al to check if the induced diffusion signal attenuation because of the imaging gradient contributes to the signal void. This b‐value can cause only a 5% signal decay for the case of freely diffusion xenon (0.21 cm 2 /s).…”

19F MRI of the Lungs Using Inert Fluorinated Gases: Challenges and New Developments

“…Each image in the washout series was acquired using a 2D x-centric pulse sequence, which provides the advantages of having both a short TE and a Cartesian kspace sampling approach. 61 Figure 5 shows three representative series of preclinical 19 F washout images obtained in a control rat, a rat instilled with lipopolysaccharide (LPS, to produce inflammation), and a rat instilled with bleomycin (to produce fibrosis). 30 The rat instilled with LPS has washout images that are similar to the control rat, while the rat instilled with bleomycin shows more ventilation heterogeneity and a slower SF 6 washout.…”

High Resolution3He Pulmonary MRI

“…Coupled with the issues of high-resolution imaging are the effects of fast diffusion of 3 He ($2cm 2 /s) through strong spatial encoding gradients, which can completely destroy the MRI signal in the airways and significantly attenuate the signal in the lung parenchyma [24][25][26]. There is a need for an imaging method which incorporates specific hardware and novel rapid image acquisition approaches that minimize the signal loss due to all of these mitigating factors and permit fast and high spatial resolution 3 He MR imaging of small animal airways and lung microstructure [27]. Such imaging modalities can be used for observation of ventilation heterogeneity, such as in an ovalbumin asthmatic mouse model [22,27], as well as for pediatric lung applications [28] often requiring much smaller field-of-view (FOV).…”

“…The projection-reconstruction (PR) approach is the well-known [29] acquisition method that minimizes 3 He diffusion-induced signal decay, as it acquires the k-space center immediately following the excitation pulse and before the imaging gradient starts which avoids significant signal loss occurs [27]. Both PR and spiral/ cones acquisitions belong to free induction decay based or apparent transverse relaxation time (T 2 *) based methods, acquiring k-space in a non-Cartesian fashion.…”

“…In addition, they ensure very short echo-times ((TE) < 200 μs) which minimizes T 2 *-weighting, leading to pure gas density weighting [35]. Unfortunately, PR uses a significant number of RF pulses (50,640 views for a 128 Â 128 Â 128 matrix size and 204,196 for a 256 Â 256 Â 256 matrix size [36]) or radial projections to sufficiently sample k-space and this naturally leads to reduction of the available SNR from the non-renewable hyperpolarized state [27]. Cones [34] and spiral [28] k-space trajectories normally do not require a significant number of RF tipping or interleaves to fill k-space, but this should still be compensated by using an elongated readout-window which can be difficult to achieve due to the short T 2 *of 3 He gas in small animal lungs (T 2 * < 3 ms, at high field [37]).…”