The effect of dissolved oxygen on the susceptibility of blood

MR Imaging Techniques for Microenvironment Mapping of the Glioma Tumors: A Systematic Review

RATIONALE AND OBJECTIVES

The tumor microenvironment (TME) is a critical regulator of cancer progression, metastasis, and treatment response. Currently, various imaging approaches exist to assess the pathophysiological features of the TME. This systematic review provides an overview of magnetic resonance imaging (MRI) methods used in clinical practice to characterize the pathophysiological features of the gliomas TME.

METHODS

This review involved a systematic comprehensive search of original open-access articles reporting the clinical use of MR imaging in glioma patients of all ages in the PubMed, Scopus, and Web of Science databases between January 2010 and December 2023. We restricted our research to papers published in the English language.

RESULTS

A total of 1137 studies were preliminarily identified through electronic database searches. After duplicate studies were removed, 44 studies met the eligibility criteria. The glioma TME was accompanied by alterations in metabolism, pH, vascularity, oxygenation, and extracellular matrix components, including tumor-associated macrophages, and sodium concentration.

CONCLUSION

Multiparametric MRI is capable of noninvasively assessing the pathophysiological features and tumor-supportive niches of the TME, which is in line with its application in personalized medicine.

MR-oximetry with fat DESPOT

PURPOSE

The R₁ relaxation rate of fat is a promising marker of tissue oxygenation. Existing techniques to map fat R₁ in MR-oximetry offer limited spatial coverage, require long scan times, or pulse sequences that are not readily available on clinical scanners. This work addresses these limitations with a 3D voxel-wise fat R₁ mapping technique for MR-oximetry based on a variable flip angle (VFA) approach at 3 T.

METHODS

Varying levels of dissolved oxygen (O₂) were generated in a phantom consisting of vials of safflower oil emulsion, used to approximate human fat. Joint voxel-wise mapping of fat and water R₁ was performed with a two-compartment VFA model fitted to multi-echo gradient-echo magnitude data acquired at four flip angles, referred to as Fat DESPOT. Global R₁ was also calculated. Variations of fat, water, and global R₁ were investigated as a function of the partial pressure of O₂ (pO₂). Inversion-prepared stimulated echo magnetic resonance spectroscopy was used as the reference technique for R₁ measurements.

RESULTS

Fat R₁ from Fat DESPOT was more sensitive than water R₁ and global R₁ to variations in pO₂, consistent with previous studies performed with different R₁ mapping techniques. Fat R₁ sensitivity to pO₂ variations with Fat DESPOT (median O₂ relaxivity r_{1, O2} = 1.57× 10^-3 s^-1 mmHg^-1) was comparable to spectroscopy-based measurements for methylene, the main fat resonance (median r_{1, O2}= 1.80 × 10^-3 s^-1 mmHg^-1).

CONCLUSION

Fat and water R₁ can be measured on a voxel-wise basis using a two-component fit to multi-echo 3D VFA magnitude data in a clinically acceptable scan time. Fat and water R₁ measured with Fat DESPOT were sensitive to variations in pO₂. These observations suggest an approach to 3D in vivo MR oximetry.

Mapping oxidative metabolism in the human brain with calibrated fMRI in health and disease

Conventional functional MRI (fMRI) with blood-oxygenation level dependent (BOLD) contrast is an important tool for mapping human brain activity non-invasively. Recent interest in quantitative fMRI has renewed the importance of oxidative neuroenergetics as reflected by cerebral metabolic rate of oxygen consumption (CMR_O2) to support brain function. Dynamic CMR_O2 mapping by calibrated fMRI require multi-modal measurements of BOLD signal along with cerebral blood flow (CBF) and/or volume (CBV). In human subjects this "calibration" is typically performed using a gas mixture containing small amounts of carbon dioxide and/or oxygen-enriched medical air, which are thought to produce changes in CBF (and CBV) and BOLD signal with minimal or no CMR_O2 changes. However non-human studies have demonstrated that the "calibration" can also be achieved without gases, revealing good agreement between CMR_O2 changes and underlying neuronal activity (e.g., multi-unit activity and local field potential). Given the simpler set-up of gas-free calibrated fMRI, there is evidence of recent clinical applications for this less intrusive direction. This up-to-date review emphasizes technological advances for such translational gas-free calibrated fMRI experiments, also covering historical progression of the calibrated fMRI field that is impacting neurological and neurodegenerative investigations of the human brain.

Helminth Eggs as a Magnetic Biomaterial: Introducing a Recognition Probe

Parasitic helminths, despite their known negative impact (biomaterial) on human health and animal production, have fascinating features. In this study, we find fantastic magnetic properties in several forms: inductor [between 20.10 and 58.85 (±2.50) H], source of detectable electrical voltage [from +0.5 to 7.3 (±0.1) V, vs. the ground, GND, measured by an AVO meter] and different inductor magnitude [between 3.33 and 41.23 (±0.76)] μH, detected by electrochemical impedance spectroscopy as well as frequency scannable electromagnetic wave horn) in several frequencies (including 100, 120, Hz, and 1, 10, 100 kHz) in “Fasciola hepatica”, “Parascaris equorum” (with and without larvae), “Dicrocoelium dendriticum,” “Taenia multiceps”, and “Moniezia expansa” eggs. This claim is attributed to some surprising characteristics, including superior inductance and intrinsic magnetic susceptibility. This feature along with a close relationship to helminth egg structure, is a novel probe with acceptable reproducibility (RSD > 8.0%) and high enough trustworthiness for adequate differentiation in their magnitudes, relatively. These traits were measured by the “Single Cell Rrecording” methodology using a three-microelectrode system, implanted to each egg at the Giga ohm sealed condition (6.08 ± 0.22 GΩ cm−1, n = 5). The reliability of these results was further confirmed using multiple calibrated instruments such as a high-resolution inductance analyzer, LCR meter, impedance spectrometer, potentiometer, and an anomalous Hall effect (Magnetic field density) sensor. In addition, the critical role played (Synergistic Effect) by water-like molecules as the intermediate medium, besides the partial influence of other compounds such as dissolved oxygen, are investigated qualitatively, and specific relation between these molecules and magnetic field creation in helminth eggs was proved. These intrinsic characteristics would provide novel facilitators for efficient arriving at the researchable bio-based magnetic biomaterials, besides innovative and real-time identification probes in the “Parasitology” fields.

Lesion magnetic susceptibility response to hyperoxic challenge: A biomarker for malignant brain tumor microenvironment?

BACKGROUND AND PURPOSE

Quantitative susceptibility mapping has been previously used to differentiate lesions in patients with brain tumors. The aim of this work was to characterize the response of magnetic susceptibility differences in malignant brain tumors and surrounding edema to hyperoxic and hypercapnic respiratory challenges.

METHODS

Images of malignant brain tumor patients (2 glioblastoma multiforme, 2 anaplastic astrocytoma, 1 brain metastasis) with clinical MRI exams (contrast-enhanced T1w) were acquired at 3T. 3D multi-gradient-echo data sets were acquired while the patients inhaled medical-air (21% O2), oxygen (100% O2), and carbogen (95% O2, 5% CO2). Susceptibility maps were generated from real and imaginary data. Regions of interest were analyzed with respect to respiration-gas-induced susceptibility changes.

RESULTS

Contrast-enhancing tumor regions with high baseline magnetic susceptibility exhibited a marked susceptibility reduction under hyperoxic challenges, with a stronger effect (-0.040 to -0.100ppm) under hypercapnia compared to hyperoxia (-0.010 to -0.067ppm). In contrast, regions attributed to necrotic tissue and to edema showed smaller changes of opposite sign, i.e. paramagnetic shift. There was a correlation between malignant tumor tissue magnetic susceptibility at baseline under normoxia and the corresponding susceptibility reduction under hypercapnia and - to a lesser degree - under hyperoxia.

CONCLUSION

In this small cohort of analysis, quantification of susceptibility changes in response to respiratory challenges allowed a complementary, functional differentiation of tumorous sub-regions. Those changes, together with the correlations observed between baseline susceptibility under normoxia and susceptibility reduction with challenges, could prove helpful for a non-invasive characterization of local tumor microenvironment.

Transverse signal decay under the weak field approximation: Theory and validation

PURPOSE

To derive an expression for the transverse signal time course from systems in the motional narrowing regime, such as water diffusing in blood. This was validated in silico and experimentally with ex vivo blood samples.

METHODS

A closed-form solution (CFS) for transverse signal decay under any train of refocusing pulses was derived using the weak field approximation. The CFS was validated via simulations of water molecules diffusing in the presence of spherical perturbers, with a range of sizes and under various pulse sequences. The CFS was compared with more conventional fits assuming monoexponential decay, including chemical exchange, using ex vivo blood Carr-Purcell-Meiboom-Gill data.

RESULTS

From simulations, the CFS was shown to be valid in the motional narrowing regime and partially into the intermediate dephasing regime, with increased accuracy with increasing Carr-Purcell-Meiboom-Gill refocusing rate. In theoretical calculations of the CFS, fitting for the transverse relaxation rate (R₂ ) gave excellent agreement with the weak field approximation expression for R₂ for Carr-Purcell-Meiboom-Gill sequences, but diverged for free induction decay. These same results were confirmed in the ex vivo analysis.

CONCLUSION

Transverse signal decay in the motional narrowing regime can be accurately described analytically. This theory has applications in areas such as tissue iron imaging, relaxometry of blood, and contrast agent imaging. Magn Reson Med 80:341-350, 2018. © 2017 International Society for Magnetic Resonance in Medicine.