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Purpose: The purpose of this work is to apply multi‐echo spin‐ and gradient‐echo (SAGE) echo‐planar imaging (EPI) combined with a navigator‐based (NAV) prospective motion compensation method for a quantitative liver blood oxygen level dependent (BOLD) measurement with a breath‐hold (BH) task. Methods: A five‐echo SAGE sequence was developed to quantitatively measure T2 and T2* to depict function with sufficient signal‐to‐noise ratio, spatial resolution and sensitivity to BOLD changes induced by the BH task. To account for respiratory motion, a navigator was employed in the form of a single gradient‐echo projection readout, located at the diaphragm along the inferior–superior direction. Prior to each transverse imaging slice of the spin‐echo EPI‐based readouts, navigator acquisition and fat suppression were incorporated. Motion data was obtained from the navigator and transmitted back to the sequence, allowing real‐time adjustments to slice positioning. Six healthy volunteers and three patients with liver carcinoma were included in this study. Quantitative T2 and T2* were calculated at each time point of the BH task. Parameters of t value from first‐level analysis using a general linear model and hepatovascular reactivity (HVR) of Echo1, T2 and T2* were calculated. Results: The motion caused by respiratory activity was successfully compensated using the navigator signal. The average changes of T2 and T2* during breath‐hold were about 1% and 0.7%, respectively. With the help of NAV prospective motion compensation whole liver t values could be obtained without motion artifacts. The quantified liver T2 (34.7 ± 0.7 ms) and T2* (29 ± 1.2 ms) values agreed with values from literature. In healthy volunteers, the distribution of statistical t value and HVR was homogeneous throughout the whole liver. In patients with liver carcinoma, the distribution of t value and HVR was inhomogeneous due to metastases or therapy. Conclusions: This study demonstrates the feasibility of using a NAV prospective motion compensation technique in conjunction with five‐echo SAGE EPI for the quantitative measurement of liver BOLD with a BH task. [ABSTRACT FROM AUTHOR]

Background Purpose Methods Results Conclusions Perfusion magnetic resonance imaging (MRI)s plays a central role in the diagnosis and monitoring of neurovascular or neurooncological disease. However, conventional processing techniques are limited in their ability to capture relevant characteristics of the perfusion dynamics and suffer from a lack of standardization.We propose a physics‐informed deep learning framework which is capable of analyzing dynamic susceptibility contrast perfusion MRI data and recovering the dynamic tissue response with high accuracy.The framework uses physics‐informed neural networks (PINNs) to learn the voxel‐wise TRF, which represents the dynamic response of the local vascular network to the contrast agent bolus. The network output is stabilized by total variation and elastic net regularization. Parameter maps of normalized cerebral blood flow (nCBF) and volume (nCBV) are then calculated from the predicted residue functions. The results are validated using extensive comparisons to values derived by conventional Tikhonov‐regularized singular value decomposition (TiSVD), in silico simulations and an in vivo dataset of perfusion MRI exams of patients with high‐grade gliomas.The simulation results demonstrate that PINN‐derived residue functions show a high concordance with the true functions and that the calculated values of nCBF and nCBV converge towards the true values for higher contrast‐to‐noise ratios. In the in vivo dataset, we find high correlations between conventionally derived and PINN‐predicted perfusion parameters (Pearson's rho for nCBF: 0.84±0.03$0.84 \pm 0.03$ and nCBV: 0.92±0.03$0.92 \pm 0.03$) and very high indices of image similarity (structural similarity index for nCBF: 0.91±0.03$0.91 \pm 0.03$ and for nCBV: 0.98±0.00$0.98 \pm 0.00$).PINNs can be used to analyze perfusion MRI data and stably recover the response functions of the local vasculature with high accuracy. [ABSTRACT FROM AUTHOR]

Remodeling of tissue microvasculature commonly promotes neoplastic growth; however, there is no imaging modality in oncology yet that noninvasively quantifies microvascular changes in clinical routine. Although blood capillaries cannot be resolved in typical magnetic resonance imaging (MRI) measurements, their geometry and distribution influence the integral nuclear magnetic resonance (NMR) signal from each macroscopic MRI voxel. We have numerically simulated the expected transverse relaxation in NMR voxels with different dimensions based on the realistic microvasculature in healthy and tumor‐bearing mouse brains (U87 and GL261 glioblastoma). The 3D capillary structure in entire, undissected brains was acquired using light sheet fluorescence microscopy to produce large datasets of the highly resolved cerebrovasculature. Using this data, we trained support vector machines to classify virtual NMR voxels with different dimensions based on the simulated spin dephasing accountable to field inhomogeneities caused by the underlying vasculature. In prediction tests with previously blinded virtual voxels from healthy brain tissue and GL261 tumors, stable classification accuracies above 95% were reached. Our results indicate that high classification accuracies can be stably attained with achievable training set sizes and that larger MRI voxels facilitated increasingly successful classifications, even with small training datasets. We were able to prove that, theoretically, the transverse relaxation process can be harnessed to learn endogenous contrasts for single voxel tissue type classifications on tailored MRI acquisitions. If translatable to experimental MRI, this may augment diagnostic imaging in oncology with automated voxel‐by‐voxel signal interpretation to detect vascular pathologies. [ABSTRACT FROM AUTHOR]

Purpose Since quantitative susceptibility mapping (QSM) quantifies magnetic susceptibility relative to a reference value, a suitable reference tissue has to be available to compare different subjects and stages of disease. Methods To find such a suitable reference tissue for QSM of the brain, melanoma patients with and without brain metastases were measured. Twelve reference regions were chosen and assessed for stability of susceptibility values with respect to multiple intra-individual and inter-individual measurements, age, and stage of disease. Results Cerebrospinal fluid (CSF), the internal capsule and one region in the splenium of the corpus callosum are the regions with the smallest standard deviations of the mean susceptibility value. The mean susceptibility is 0.010 ± 0.014 ppm for CSF in the atrium of the lateral ventricles (csfpost), −0.060 ± 0.019 ppm for the posterior limb of the internal capsule (ci2), and −0.008 ± 0.019 ppm for the splenium of the corpus callosum. csfpost and ci2 show nearly no dependence on age or stage of disease, whereas some other regions, e.g., the red nucleus, show moderate dependence on age or disease. Conclusion The internal capsule and CSF appear to be the most suitable reference regions for QSM of the brain in the melanoma patients studied. Both showed virtually no dependence on age or disease and small variations among patients. Magn Reson Med 78:204-214, 2017. © 2016 International Society for Magnetic Resonance in Medicine [ABSTRACT FROM AUTHOR]

Purpose: A method for the quantification of perfusion in murine myocardium is demonstrated. The method allows for the reconstruction of perfusion maps on arbitrary time points in the heart cycle while addressing problems that arise due to the irregular heart beat of mice. Methods: A flow-sensitive alternating inversion recovery arterial spin labeling method using an untriggered FLASH-read out with random sampling is used. Look-Locker conditions are strictly maintained. No dummy pulses or mechanism to reduce deviation from Look-Locker conditions are needed. Electrocardiogram and respiratory data are recorded for retrospective gating and triggering. A model-based technique is used to reconstruct missing k-space data to cope with the undersampling inherent in retrospectively gated methods. Acquisition and reconstruction were validated numerically and in phantom measurements before in vivo experimentation. Results: Quantitative perfusion maps were acquired within a single slice measurement time of 11 min. Perfusion values are in good accordance to literature values. Myocardial infarction could be clearly visualized and results were confirmed with histological results. Conclusion: The proposed method is capable of producing quantitative perfusion maps on arbitrary positions in the heart cycle within a short measurement time. The method is robust against irregular breathing patterns and heart rate changes and can be implemented on all scanners. [ABSTRACT FROM AUTHOR]

Purpose The quantification of myocardial perfusion using a Look-Locker flow-sensitive alternating inversion recovery- arterial spin labeling experiment is considered. Due to the anatomy of the heart, a substantial but unintended partial inversion of the inflowing blood occurs during the slice-selective inversion. Both, the partial inversion as well as the Look-Locker pulse train, influence the myocardial perfusion quantification and are addressed in this work. Methods The mean relaxation time approximation is used to calculate the monoexponential relaxation time of the signal in perfused tissue under Look-Locker readout. The left ventricular blood serves as an approximation of the inflowing blood in the description of FAIR-ASL measurements with global and slice-selective inversion to correctly quantify the myocardial perfusion. Results The analysis shows that the myocardial perfusion can be overestimated if the T1-based quantification method is not adapted respecting the Look-Locker pulse train explicitly. Additionally, it turns out that without correction for the partial inversion of the blood pool during the slice-selective inversion the myocardial perfusion is underestimated. Conclusion It is shown that the Look-Locker readout as well as the nonideal slice-selective inversion experiment have a considerable influence and have to be included properly to correctly quantify myocardial perfusion. Magn Reson Med 71:1784-1797, 2014. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

This study reports the T1 and T2 relaxation rates of rhodamine-labeled anionic magnetic nanoparticles determined at 7, 11.7, and 17.6 T both in solution and after cellular internalization. Therefore cells were incubated with rhodamine-labeled anionic magnetic nanoparticles and were prepared at decreasing concentrations. Additionally, rhodamine-labeled anionic magnetic nanoparticles in solution were used for extracellular measurements. T1 and T2 were determined at 7, 11.7, and 17.6 T. T1 times were determined with an inversion-recovery snapshot-flash sequence. T2 times were obtained from a multispin-echo sequence. Inductively coupled plasma-mass spectrometry was used to determine the iron content in all samples, and r1 and r2 were subsequently calculated. The results were then compared with cells labeled with AMI-25 and VSOP C-200. In solution, the r1 and r2 of rhodamine-labeled anionic magnetic nanoparticles were 4.78/379 (7 T), 3.28/389 (11.7 T), and 2.00/354 (17.6 T). In cells, the r1 and r2 were 0.21/56 (7 T), 0.19/37 (11.7 T), and 0.1/23 (17.6 T). This corresponded to an 11- to 23-fold decrease in r1 and an 8- to 15-fold decrease in r2. A decrease in r1 was observed for AMI-25 and VSOP C-200. AMI-25 and VSOP exhibited a 2- to 8-fold decrease in r2. In conclusion, cellular internalization of iron oxide nanoparticles strongly decreased their T1 and T2 potency. Magn Reson Med, 2010. © 2010 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

Background: A recent innovation in computed tomography (CT) imaging has been the introduction of photon-counting detector CT (PCD-CT) systems, which are able to register the number and the energy level of incoming x‑ray photons and have smaller detector elements compared with conventional CT scanners that operate with energy-integrating detectors (EID-CT)., Objectives: The study aimed to evaluate the potential benefits of a novel, non-CE certified PCD-CT in detecting myeloma-associated osteolytic bone lesions (OL) compared with a state-of-the-art EID-CT., Materials and Methods: Nine patients with multiple myeloma stage III (according to Durie and Salmon) underwent magnetic resonance imaging (MRI), EID-CT, and PCD-CT of the lower lumbar spine and pelvis. The PCD-CT and EID-CT images of all myeloma lesions that were visible in clinical MRI scans were reviewed by three radiologists for corresponding OL. Additionally, the visualization of destructions to cancellous or cortical bone, and trabecular structures, was compared between PCD-CT and EID-CT., Results: Readers detected 21% more OL in PCD-CT than in EID-CT images (138 vs. 109; p < 0.0001). The sensitivity advantage of PCD-CT in lesion detection increased with decreasing lesion size. The visualization quality of cancellous and cortical destructions as well as of trabecular structures was rated higher by all three readers in PCD-CT images (mean image quality improvements for PCD-CT over EID-CT were +0.45 for cancellous and +0.13 for cortical destructions)., Conclusions: For myeloma-associated OL, PCD-CT demonstrated significantly higher sensitivity, especially with small size. Visualization of bone tissue and lesions was considered significantly better in PCD-CT than in EID-CT. This implies that PCD-CT scanners could potentially be used in the early detection of myeloma-associated bone lesions., (© 2024. The Author(s), under exclusive licence to Springer Medizin Verlag GmbH, ein Teil von Springer Nature.)

Purpose: To apply velocity selective arterial spin labeling (VSASL) combined with a navigator-based (NAV) prospective motion compensation method for a free-breathing liver perfusion measurement without contrast agent., Methods: Sinc-modulated Velocity Selective Inversion (sinc-VSI) pulses were applied as labeling and control pulses. In order to account for respiratory motion, a navigator was employed in the form of a single gradient-echo projection readout, located at the diaphragm along the inferior-superior direction. Prior to each transverse imaging slice of the spin-echo EPI based readouts, navigator and fat suppression were incorporated. Motion data was obtained from the navigator and transmitted back to the sequence, allowing real-time adjustments to slice positioning. The sinc-VSI without velocity-selective gradients during the control condition but with velocity-selective gradients along all three directions during labeling was chosen for the VSASL. The VSASL was compared with pseudo-continuous ASL (pCASL) methods, which selectively tagged the moving spins using a tagging plane placed at the portal vein and hepatic artery., Results: The motion caused by respiratory activity was effectively computed using the navigator signal. The coefficients of variation (CoV) of average liver voxel in NAV were significantly decreased when compared to breath-hold (BH), with an average reduction of 29.4 ± 18.44% for control images, and 29.89 ± 20.83% for label images (p < 0.001). The resulting maps of normalized ASL signal (normalized to M 0 ) showed significantly higher perfusion weightings in the NAV-compensated VSASL, when compared to the NAV-compensated pCASL techniques., Conclusions: This study demonstrates the feasibility of using a navigator-based prospective motion compensation technique in conjunction with VSASL for the measurement of liver perfusion without the use of contrast agents while allowing for free-breathing., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier GmbH.. All rights reserved.)

Microscopically small magnetic field inhomogeneities within an external static magnetic field cause a free induction decay in magnetic resonance imaging that generally exhibits two transverse components that are usually summarized to a complex entity. The Fourier transform of the complex-valued free induction decay is the purely real and positive-valued frequency distribution which allows an easy interpretation of the underlying dephasing mechanism. Typically, the frequency distribution inside a cubic voxel as caused by a spherical magnetic field inhomogeneity is determined by a histogram technique in terms of subdivision of the whole voxel into smaller subvoxels. A faster and more accurate computation is achieved by analytical expressions for the frequency distribution that are derived in this work. In contrast to the usually assumed simplified case of a spherical voxel, we also consider the tilt angles of the cubic voxel to the external magnetic field. The typical asymmetric form of the frequency distribution is reproduced and analyzed for the more realistic case of a cubic voxel. We observe a splitting of frequency distribution peaks for increasing tilt of the cubic voxel against the direction of the external magnetic field in analogy to the case for dephasing around cylindrical, vessel-like objects inside cubic voxels. These results are of value, e.g., for the analysis of susceptibility-weighted images or in quantitative susceptibility imaging since the reconstruction of these images is performed in cubic-shaped voxels., (Copyright © 2021. Published by Elsevier GmbH.)

This study reports the T(1) and T(2) relaxation rates of rhodamine-labeled anionic magnetic nanoparticles determined at 7, 11.7, and 17.6 T both in solution and after cellular internalization. Therefore cells were incubated with rhodamine-labeled anionic magnetic nanoparticles and were prepared at decreasing concentrations. Additionally, rhodamine-labeled anionic magnetic nanoparticles in solution were used for extracellular measurements. T(1) and T(2) were determined at 7, 11.7, and 17.6 T. T(1) times were determined with an inversion-recovery snapshot-flash sequence. T(2) times were obtained from a multispin-echo sequence. Inductively coupled plasma-mass spectrometry was used to determine the iron content in all samples, and r(1) and r(2) were subsequently calculated. The results were then compared with cells labeled with AMI-25 and VSOP C-200. In solution, the r(1) and r(2) of rhodamine-labeled anionic magnetic nanoparticles were 4.78/379 (7 T), 3.28/389 (11.7 T), and 2.00/354 (17.6 T). In cells, the r(1) and r(2) were 0.21/56 (7 T), 0.19/37 (11.7 T), and 0.1/23 (17.6 T). This corresponded to an 11- to 23-fold decrease in r(1) and an 8- to 15-fold decrease in r(2) . A decrease in r(1) was observed for AMI-25 and VSOP C-200. AMI-25 and VSOP exhibited a 2- to 8-fold decrease in r(2) . In conclusion, cellular internalization of iron oxide nanoparticles strongly decreased their T(1) and T(2) potency., (Copyright © 2010 Wiley-Liss, Inc.)