The z-spectrum from human blood at 7T

Shah, Simon; Mougin, Olivier; Carradus, Andrew J.; Geades, Nicolas; Dury, Richard; Morley, William; Gowland, Penny

doi:10.1016/j.neuroimage.2017.10.053

Cited by 33 publications

(53 citation statements)

References 41 publications

(61 reference statements)

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“…injection of 10 mg/kg LPS) was dramatically decreased to 61% of the baseline level . As blood has been shown to possess CEST signals at both 3.5 and − 3.5 ppm, this significant decrease of blood level in the kidney parenchyma can significantly lessen both APT and rNOE effects in the AKI kidneys. Finally, the mitochondrial biogenesis of tubular cells is suppressed in AKI kidneys, resulting in down‐regulated metabolism .…”

Section: Discussionmentioning

confidence: 90%

CEST MRI of sepsis‐induced acute kidney injury

et al. 2018

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Sepsis-induced acute kidney injury (SAKI) is a major complication of kidney disease associated with increased mortality and faster progression. Therefore, the development of imaging biomarkers to detect septic AKI is of great clinical interest. In this study, we aimed to characterize the endogenous chemical exchange saturation transfer (CEST) MRI contrast in the lipopolysaccharide (LPS)-induced SAKI mouse model and to investigate the use of CEST MRI for detecting such injury. We used a SAKI mouse model that was generated by i.p. injection of 10 mg/kg LPS. The resulting kidney injury was confirmed by the elevation of serum creatinine and histology. MRI assessments were performed 24 h after LPS injection, including CEST MRI at different B strengths (1, 1.8 and 3 μT), T mapping, T mapping and conventional magnetization transfer contrast (MTC) MRI. The CEST MRI results were analyzed using Z-spectra, in which the normalized water signal saturation (S /S ) is measured as a function of saturation frequency. Substantial decreases in CEST contrast were observed at both 3.5 and - 3.5 ppm frequency offset from water at all B powers, with the most significant difference obtained at a B of 1.8 μT. The average S /S differences between injured and normal kidneys were 0.07 (0.55 ± 0.04 versus 0.62 ± 0.04, P = 0.0028) and 0.07 (0.50 ± 0.04 versus 0.57 ± 0.03, P = 0.0008) for 3.5 and - 3.5 ppm, respectively. In contrast, the T and T relaxation times and MTC contrast in the injured kidneys did not show a significant change compared with the normal control. Our results showed that CEST MRI is more sensitive to the pathological changes in injured kidneys than the changes in T , T and MTC effect, indicating its potential clinical utility for molecular imaging of renal diseases.

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Section: Discussionmentioning

confidence: 90%

CEST MRI of sepsis‐induced acute kidney injury

et al. 2018

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“…The NOE(−3.5) signal was assigned to be from dipolar interactions between water protons and mobile macromolecular protons . More recently, a negative NOE‐mediated saturation transfer effect centered at around −1.6 ppm from water (NOE(−1.6)) was also reported, and hypointense NOE(−1.6) signals were found in brain tumors and ischemic stroke lesions . Preliminary experiments on reconstituted choline phospholipids suggest that this NOE(−1.6) signal may arise from dipolar interactions between membrane choline phospholipid protons and water protons .…”

Section: Introductionmentioning

confidence: 94%

“…4 More recently, a negative NOE-mediated saturation transfer effect centered at around −1.6 ppm from water (NOE(−1.6)) was also reported, and hypointense NOE(−1.6) signals were found in brain tumors and ischemic stroke lesions. [43][44][45][46][47] Preliminary experiments on reconstituted choline phospholipids suggest that this NOE(−1.6) signal may arise from dipolar interactions between membrane choline phospholipid protons and water protons. 44 However, no studies on the quantification of the NOE coupling rate and/or the solute transverse relaxation rate have been performed.…”

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confidence: 99%

Ratiometric NOE(−1.6) contrast in brain tumors

2018

NMR in Biomedicine

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Recently, a new nuclear Overhauser enhancement (NOE)‐mediated saturation transfer effect at around −1.6 ppm from water, termed NOE(−1.6), was reported to show hypointense signals in brain tumors. Similar to chemical exchange saturation transfer or magnetization transfer (MT) effects, which depend on the solute pool concentration, the exchange/coupling rate, the solute transverse relaxation rate, etc., the NOE(−1.6) effect should also depend on these factors. Since the exchange rate is relevant to tissue pH, and the coupling rate and the solute transverse relaxation rate are relevant to the motional property of the coupled molecules, further studies to quantify the contribution from only the exchange/coupling rate and the solute transverse relaxation rate are always interesting. The purpose of this paper is to apply a ratiometric approach to the NOE(−1.6) effect to obtain a metric that is more specific to the NOE coupling rate and the solute transverse relaxation rate than the NOE(−1.6) signal amplitude. Simulations indicate that the ratiometric approach allows us to rule out nearly all of the non‐specific factors including the solute pool concentration, solute and water longitudinal relaxation rates, direct water saturation, and semi‐solid MT effects, and provides a more specific NOE coupling rate‐ and solute transverse relaxation rate‐weighted signal. Animal studies show that the ratiometric NOE(−1.6) decreases dramatically in brain tumors, which suggests that the change in the NOE(−1.6) coupling rate and/or the solute transverse relaxation rate are major contributors to the previously observed hypointense NOE(−1.6) signal in tumors.

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“…35 The literature, however, is still scarce on T * 2 values at ultrahigh fields, and there are significant discrepancies in values reported at 7 T, depending on the methodology used. [35][36][37] We used the values from Ivanov et al, 35 as they yielded simulated VASO curves best matching the experimental values measured in human VASO at 7 T. 10,12 Moreover, we found no experimental measurements of blood T * 2 for B 0 > 7 T. For that reason, we extrapolated blood T * 2 values at ultrahigh magnetic fields as presented in Table 2. This extrapolation of unknown reliability leads to an important limitation on the interpretation of the exact quantitative results at ultrahigh fields obtained within this framework.…”

Section: Signal Contributions and Sources Of Variationmentioning

confidence: 99%

Modeling of vascular space occupancy and BOLD functional MRI from first principles using real microvascular angiograms

Genois

Gagnon

Desjardins

2020

Magnetic Resonance in Med

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The vascular space occupancy (VASO) is a functional MRI technique for probing cerebral blood volume changes noninvasively, including during neuronal activation in humans. An important consideration when implementing VASO is the BOLD effect in the signal. Assessing the physical origin of this BOLD contamination and the capabilities of correction methods could improve the quantification of cerebral blood volume changes with VASO. Methods: Given the heterogeneity of cerebral microvascular architecture, the vascular geometry within an MRI voxel can influence both BOLD and VASO signals. To investigate this effect, 3D high-resolution images of mouse cerebral vasculature measured with two-photon microscopy were used to model BOLD and VASO signals from first principles using Monte Carlo diffusion of water protons. Quantitative plots of VASO together with intravascular and extravascular BOLD signals as a function of TE at B 0 fields 1.5 T to 14 T were obtained. Results: The BOLD contamination of the VASO response was on the order of 50% for gradient echo and 5% for spin echo at 7 T and TE = 6 ms and significantly increased with TE and B 0. Two currently used correction schemes were shown to account for most of this contamination and recover accurate relative signal changes, with optimal correction obtained using TEs as short as possible. Conclusion: These results may provide useful information for optimizing sequence parameters in VASO and BOLD functional MRI, leading the way to a wider application of these techniques in healthy and diseased brain. K E Y W O R D S blood oxygen level-dependent, cerebral blood volume, functional magnetic resonance imaging, Monte Carlo modeling, two-photon microscopy, vascular space occupancy | 457 GENOIS Et al.

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The z-spectrum from human blood at 7T

Cited by 33 publications

References 41 publications

CEST MRI of sepsis‐induced acute kidney injury

CEST MRI of sepsis‐induced acute kidney injury

Ratiometric NOE(−1.6) contrast in brain tumors

Modeling of vascular space occupancy and BOLD functional MRI from first principles using real microvascular angiograms

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