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Wu Q, Qi Y, Gong P, Huang B, Cheng G, Liang D, Zheng H, Sun PZ, Wu Y. Fast and robust pulsed chemical exchange saturation transfer (CEST) MRI using a quasi-steady-state (QUASS) algorithm at 3 T. Magn Reson Imaging 2024; 105:29-36. [PMID: 37898416 DOI: 10.1016/j.mri.2023.10.009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2023] [Revised: 10/21/2023] [Accepted: 10/22/2023] [Indexed: 10/30/2023]
Abstract
Chemical exchange saturation transfer (CEST) has emerged as a powerful technique to image dilute labile protons. However, its measurement depends on the RF saturation duration (Tsat) and relaxation delay (Trec). Although the recently developed quasi-steady-state (QUASS) solution can reconstruct equilibrium CEST effects under continuous-wave RF saturation, it does not apply to pulsed-CEST MRI on clinical scanners with restricted hardware or specific absorption rate limits. This study proposed a QUASS algorithm for pulsed-CEST MRI and evaluated its performance in muscle CEST measurement. An approximated expression of a steady-state pulsed-CEST signal was incorporated in the off-resonance spin-lock model, from which the QUASS pulsed-CEST effect was derived. Numerical simulation, creatine phantom, and healthy volunteer scans were conducted at 3 T. The CEST effect was quantified with asymmetry analysis in the simulation and phantom experiments. CEST effects of creatine, amide proton transfer, phosphocreatine, and combined magnetization transfer and nuclear Overhauser effects were isolated from a multi-pool Lorentzian model in muscles. Apparent and QUASS CEST measurements were compared under different Tsat/Trec and duty cycles. Paired Student's t-test was employed with P < 0.05 as statistically significant. The simulation, phantom, and human studies showed the strong impact of Tsat/Trec on apparent CEST measurements, which were significantly smaller than the corresponding QUASS CEST measures, especially under short Tsat/Trec times. In comparison, the QUASS algorithm mitigates such impact and enables accurate CEST measurements under short Tsat/Trec times. In conclusion, the QUASS algorithm can accelerate robust pulsed-CEST MRI, promising the efficient detection and evaluation of muscle diseases in clinical settings.
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Affiliation(s)
- Qiting Wu
- Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen, Guangdong, China; Medical AI Lab, School of Biomedical Engineering, Medical School, Shenzhen University, Shenzhen, Guangdong, China
| | - Yulong Qi
- Department of Medical Imaging, Peking University Shenzhen Hospital, Shenzhen, Guangdong, China
| | - Pengcheng Gong
- Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen, Guangdong, China
| | - Bingsheng Huang
- Medical AI Lab, School of Biomedical Engineering, Medical School, Shenzhen University, Shenzhen, Guangdong, China
| | - Guanxun Cheng
- Department of Medical Imaging, Peking University Shenzhen Hospital, Shenzhen, Guangdong, China
| | - Dong Liang
- Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen, Guangdong, China
| | - Hairong Zheng
- Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen, Guangdong, China
| | - Phillip Zhe Sun
- Department of Radiology and Imaging Sciences, Emory University School of Medicine, Atlanta, GA, USA
| | - Yin Wu
- Paul C. Lauterbur Research Center for Biomedical Imaging, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen, Guangdong, China.
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Abbasi-Rad S, Norris DG. Adiabatic null passage for on-resonance magnetization transfer preparation. Magn Reson Med 2024; 91:133-148. [PMID: 37598419 DOI: 10.1002/mrm.29835] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2023] [Revised: 07/08/2023] [Accepted: 08/01/2023] [Indexed: 08/22/2023]
Abstract
PURPOSE We propose a novel RF pulse providing an adiabatic null passage (ANP) for magnetization transfer preparation with improved insensitivity toB 1 + $$ {\mathrm{B}}_1^{+} $$ and B0 inhomogeneities and mitigated direct saturation and T2 effects. METHOD The phase modulation function of a 6-ms time-resampled frequency offset-corrected pulse was modified to achieve zero flip angle at the end of the pulse. The spectral response was simulated, and its insensitivity to B0 andB 1 + $$ {\mathrm{B}}_1^{+} $$ was investigated and compared with a phase-inverted (12 ¯ $$ \overline{2} $$ 1-1 ¯ $$ \overline{1} $$ 21 ¯ $$ \overline{1} $$ ) binomial pulse. The proposed pulse was implemented in a 2D-EPI pulse sequence to generate magnetization transfer (MT) contrast and MT ratio (MTR) maps. In vivo experiments were performed on 3 healthy participants with power-matched settings for ANP and the binomial pulse with the following parameters: 6-ms binomial pulse with a flip angle of 107° (shortest element) and pulse repetition period (PRP) of TRslice = 59 ms, three experiments with 6-ms ANP and constant MT used overdrive factor (OF)/PRP values of 1/TRslice ,2 $$ \sqrt{2} $$ /2TRslice , and3 $$ \sqrt{3} $$ /3TRslice . RESULTS At gray matter (white matter) in vivo, the MTR decreased from 61% (64%) at OF = 1 to 38% (42%) applying ANP with an OF =3 $$ \sqrt{\mathsf{3}} $$ and PRP = 3 TRslice , demonstrating the mitigation of T2 /direct effect by 22% (22%). Bloch-McConnell simulations gave similar values. In vivo experiments showed significant improvement in the MTR values for areas with high B0 inhomogeneity. CONCLUSION ANP pulse was shown to be advantageous over its binomial counterpart in providing MT contrast by mitigating the T2 effect and direct saturation of the liquid pool as well as reduced sensitivity toB 1 + $$ {\mathrm{B}}_1^{+} $$ and B0 inhomogeneity.
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Affiliation(s)
- Shahrokh Abbasi-Rad
- Donders Institute for Brain, Cognition and Behaviour, Donders Centre for Cognitive Neuroimaging, Radboud University Nijmegen, Nijmegen, Netherlands
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany
- Department of Radiology, Harvard Medical School, Boston, Massachusetts, USA
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts, USA
| | - David G Norris
- Donders Institute for Brain, Cognition and Behaviour, Donders Centre for Cognitive Neuroimaging, Radboud University Nijmegen, Nijmegen, Netherlands
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany
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Sun PZ. Numerical simulation-based assessment of pH-sensitive chemical exchange saturation transfer MRI quantification accuracy across field strengths. NMR IN BIOMEDICINE 2023; 36:e5000. [PMID: 37401645 DOI: 10.1002/nbm.5000] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/16/2023] [Revised: 04/27/2023] [Accepted: 06/12/2023] [Indexed: 07/05/2023]
Abstract
Chemical exchange saturation transfer (CEST) MRI detects dilute labile protons via their exchange with bulk water, conferring pH sensitivity. Based on published exchange and relaxation properties, a 19-pool simulation was used to model the brain pH-dependent CEST effect and assess the accuracy of quantitative CEST (qCEST) analysis across magnetic field strengths under typical scan conditions. First, the optimal B1 amplitude was determined by maximizing pH-sensitive amide proton transfer (APT) contrast under the equilibrium condition. Apparent and quasi-steady-state (QUASS) CEST effects were then derived under the optimal B1 amplitude as functions of pH, RF saturation duration, relaxation delay, Ernst flip angle, and field strength. Finally, CEST effects, particularly the APT signal, were isolated with spinlock model-based Z-spectral fitting to evaluate the accuracy and consistency of CEST quantification. Our data showed that QUASS reconstruction significantly improved the consistency between simulated and equilibrium Z-spectra. The residual difference between QUASS and equilibrium CEST Z-spectra was, on average, 30 times less than that of the apparent CEST Z-spectra across field strengths, saturation, and repetition times. Also, the spinlock fitting of the QUASS CEST effect significantly reduced the residual errors 9-fold. Furthermore, the isolated APT amplitude from QUASS reconstruction was consistent and higher than the apparent CEST analysis under nonequilibrium conditions. To summarize, this study confirmed that QUASS reconstruction facilitates accurate determination of the CEST system under different scan protocols across field strengths, with the potential to help standardize CEST quantification.
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Affiliation(s)
- Phillip Zhe Sun
- Primate Imaging Center, Emory National Primate Research Center, Emory University, Atlanta, Georgia, USA
- Department of Radiology and Imaging Sciences, Emory University School of Medicine, Atlanta, Georgia, USA
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4
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Radke KL, Kamp B, Adriaenssens V, Stabinska J, Gallinnis P, Wittsack HJ, Antoch G, Müller-Lutz A. Deep Learning-Based Denoising of CEST MR Data: A Feasibility Study on Applying Synthetic Phantoms in Medical Imaging. Diagnostics (Basel) 2023; 13:3326. [PMID: 37958222 PMCID: PMC10650582 DOI: 10.3390/diagnostics13213326] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2023] [Revised: 10/18/2023] [Accepted: 10/25/2023] [Indexed: 11/15/2023] Open
Abstract
Chemical Exchange Saturation Transfer (CEST) magnetic resonance imaging (MRI) provides a novel method for analyzing biomolecule concentrations in tissues without exogenous contrast agents. Despite its potential, achieving a high signal-to-noise ratio (SNR) is imperative for detecting small CEST effects. Traditional metrics such as Magnetization Transfer Ratio Asymmetry (MTRasym) and Lorentzian analyses are vulnerable to image noise, hampering their precision in quantitative concentration estimations. Recent noise-reduction algorithms like principal component analysis (PCA), nonlocal mean filtering (NLM), and block matching combined with 3D filtering (BM3D) have shown promise, as there is a burgeoning interest in the utilization of neural networks (NNs), particularly autoencoders, for imaging denoising. This study uses the Bloch-McConnell equations, which allow for the synthetic generation of CEST images and explores NNs efficacy in denoising these images. Using synthetically generated phantoms, autoencoders were created, and their performance was compared with traditional denoising methods using various datasets. The results underscored the superior performance of NNs, notably the ResUNet architectures, in noise identification and abatement compared to analytical approaches across a wide noise gamut. This superiority was particularly pronounced at elevated noise intensities in the in vitro data. Notably, the neural architectures significantly improved the PSNR values, achieving up to 35.0, while some traditional methods struggled, especially in low-noise reduction scenarios. However, the application to the in vivo data presented challenges due to varying noise profiles. This study accentuates the potential of NNs as robust denoising tools, but their translation to clinical settings warrants further investigation.
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Affiliation(s)
- Karl Ludger Radke
- Department of Diagnostic and Interventional Radiology, Medical Faculty, University Dusseldorf, 40225 Dusseldorf, Germany (G.A.); (A.M.-L.)
| | - Benedikt Kamp
- Department of Diagnostic and Interventional Radiology, Medical Faculty, University Dusseldorf, 40225 Dusseldorf, Germany (G.A.); (A.M.-L.)
| | - Vibhu Adriaenssens
- Department of Diagnostic and Interventional Radiology, Medical Faculty, University Dusseldorf, 40225 Dusseldorf, Germany (G.A.); (A.M.-L.)
| | - Julia Stabinska
- F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD 21205, USA
- Division of MR Research, The Russell H. Morgan Department of Radiology and Radiological Science, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Patrik Gallinnis
- Department of Diagnostic and Interventional Radiology, Medical Faculty, University Dusseldorf, 40225 Dusseldorf, Germany (G.A.); (A.M.-L.)
| | - Hans-Jörg Wittsack
- Department of Diagnostic and Interventional Radiology, Medical Faculty, University Dusseldorf, 40225 Dusseldorf, Germany (G.A.); (A.M.-L.)
| | - Gerald Antoch
- Department of Diagnostic and Interventional Radiology, Medical Faculty, University Dusseldorf, 40225 Dusseldorf, Germany (G.A.); (A.M.-L.)
| | - Anja Müller-Lutz
- Department of Diagnostic and Interventional Radiology, Medical Faculty, University Dusseldorf, 40225 Dusseldorf, Germany (G.A.); (A.M.-L.)
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Nagar D, Vladimirov N, Farrar CT, Perlman O. Dynamic and rapid deep synthesis of chemical exchange saturation transfer and semisolid magnetization transfer MRI signals. Sci Rep 2023; 13:18291. [PMID: 37880343 PMCID: PMC10600114 DOI: 10.1038/s41598-023-45548-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2023] [Accepted: 10/20/2023] [Indexed: 10/27/2023] Open
Abstract
Model-driven analysis of biophysical phenomena is gaining increased attention and utility for medical imaging applications. In magnetic resonance imaging (MRI), the availability of well-established models for describing the relations between the nuclear magnetization, tissue properties, and the externally applied magnetic fields has enabled the prediction of image contrast and served as a powerful tool for designing the imaging protocols that are now routinely used in the clinic. Recently, various advanced imaging techniques have relied on these models for image reconstruction, quantitative tissue parameter extraction, and automatic optimization of acquisition protocols. In molecular MRI, however, the increased complexity of the imaging scenario, where the signals from various chemical compounds and multiple proton pools must be accounted for, results in exceedingly long model simulation times, severely hindering the progress of this approach and its dissemination for various clinical applications. Here, we show that a deep-learning-based system can capture the nonlinear relations embedded in the molecular MRI Bloch-McConnell model, enabling a rapid and accurate generation of biologically realistic synthetic data. The applicability of this simulated data for in-silico, in-vitro, and in-vivo imaging applications is then demonstrated for chemical exchange saturation transfer (CEST) and semisolid macromolecule magnetization transfer (MT) analysis and quantification. The proposed approach yielded 63-99% acceleration in data synthesis time while retaining excellent agreement with the ground truth (Pearson's r > 0.99, p < 0.0001, normalized root mean square error < 3%).
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Affiliation(s)
- Dinor Nagar
- School of Electrical Engineering, Tel Aviv University, Tel Aviv, Israel
| | - Nikita Vladimirov
- Department of Biomedical Engineering, Tel Aviv University, 6997801, Tel Aviv, Israel
| | - Christian T Farrar
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Charlestown, MA, USA
| | - Or Perlman
- Department of Biomedical Engineering, Tel Aviv University, 6997801, Tel Aviv, Israel.
- Sagol School of Neuroscience, Tel Aviv University, Tel Aviv, Israel.
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6
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Igarashi T, Kim H, Sun PZ. Detection of tissue pH with quantitative chemical exchange saturation transfer magnetic resonance imaging. NMR IN BIOMEDICINE 2023; 36:e4711. [PMID: 35141979 PMCID: PMC10249910 DOI: 10.1002/nbm.4711] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/08/2021] [Revised: 02/03/2022] [Accepted: 02/05/2022] [Indexed: 05/12/2023]
Abstract
Chemical exchange saturation transfer (CEST) magnetic resonance imaging (MRI) has emerged as a novel means for sensitive detection of dilute labile protons and chemical exchange rates. By sensitizing to pH-dependent chemical exchange, CEST MRI has shown promising results in monitoring tissue statuses such as pH changes in disorders like acute stroke, tumor, and acute kidney injury. This article briefly reviews the basic principles for CEST imaging and quantitative measures, from the simplistic asymmetry analysis to multipool Lorentzian decoupling and quasi-steady-state reconstruction. In particular, the advantages and limitations of commonly used quantitative approaches for CEST applications are discussed.
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Affiliation(s)
- Takahiro Igarashi
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA
| | - Hahnsung Kim
- Department of Radiology and Imaging Sciences, Emory University School of Medicine, Atlanta, GA
- Yerkes Imaging Center, Yerkes National Primate Research Center, Emory University, Atlanta, GA
| | - Phillip Zhe Sun
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA
- Department of Radiology and Imaging Sciences, Emory University School of Medicine, Atlanta, GA
- Yerkes Imaging Center, Yerkes National Primate Research Center, Emory University, Atlanta, GA
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7
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Zaiss M, Jin T, Kim SG, Gochberg DF. Theory of chemical exchange saturation transfer MRI in the context of different magnetic fields. NMR IN BIOMEDICINE 2022; 35:e4789. [PMID: 35704180 DOI: 10.1002/nbm.4789] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/25/2021] [Revised: 05/31/2022] [Accepted: 06/10/2022] [Indexed: 06/15/2023]
Abstract
Chemical exchange saturation transfer (CEST) magnetic resonance imaging (MRI) is a versatile MRI method that provides contrast based on the level of molecular and metabolic activity. This contrast arises from indirect measurement of protons in low concentration molecules that are exchanging with the abundant water proton pool. The indirect measurement is based on magnetization transfer of radio frequency (rf)-prepared magnetization from the small pool to the water pool. The signal can be modeled by the Bloch-McConnell equations combining standard magnetization dynamics and chemical exchange processes. In this article, we review analytical solutions of the Bloch-McConnell equations and especially the derived CEST signal equations and their implications. The analytical solutions give direct insight into the dependency of measurable CEST effects on underlying parameters such as the exchange rate and concentration of the solute pools, but also on the system parameters such as the rf irradiation field B1 , as well as the static magnetic field B0 . These theoretical field-strength dependencies and their influence on sequence design are highlighted herein. In vivo results of different groups making use of these field-strength benefits/dependencies are reviewed and discussed.
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Affiliation(s)
- Moritz Zaiss
- High-field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tuebingen, Germany
- Institute of Neuroradiology, University Hospital Erlangen, Friedrich-Alexander University Erlangen-Nürnberg (FAU), Erlangen, Germany
| | - Tao Jin
- NeuroImaging Laboratory, Department of Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Seong-Gi Kim
- Center for Neuroscience Imaging Research, Institute for Basic Science (IBS), Suwon, South Korea
- Department of Biomedical Engineering, Sungkyunkwan University, Suwon, South Korea
- Department of Intelligent Precision Healthcare Convergence, Sungkyunkwan University, Suwon, South Korea
| | - Daniel F Gochberg
- Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, Tennessee, USA
- Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, Tennessee, USA
- Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee, USA
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8
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Lorentzian-Corrected Apparent Exchange-Dependent Relaxation (LAREX) Ω-Plot Analysis-An Adaptation for qCEST in a Multi-Pool System: Comprehensive In Silico, In Situ, and In Vivo Studies. Int J Mol Sci 2022; 23:ijms23136920. [PMID: 35805925 PMCID: PMC9266897 DOI: 10.3390/ijms23136920] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2022] [Revised: 06/05/2022] [Accepted: 06/20/2022] [Indexed: 12/14/2022] Open
Abstract
Based on in silico, in situ, and in vivo studies, this study aims to develop a new method for the quantitative chemical exchange saturation transfer (qCEST) technique considering multi-pool systems. To this end, we extended the state-of-the-art apparent exchange-dependent relaxation (AREX) method with a Lorentzian correction (LAREX). We then validated this new method with in situ and in vivo experiments on human intervertebral discs (IVDs) using the Kendall-Tau correlation coefficient. In the in silico experiments, we observed significant deviations of the AREX method as a function of the underlying exchange rate (kba) and fractional concentration (fb) compared to the ground truth due to the influence of other exchange pools. In comparison to AREX, the LAREX-based Ω-plot approach yielded a substantial improvement. In the subsequent in situ and in vivo experiments on human IVDs, no correlation to the histological reference standard or Pfirrmann classification could be found for the fb (in situ: τ = −0.17 p = 0.51; in vivo: τ = 0.13 p = 0.30) and kba (in situ: τ = 0.042 p = 0.87; in vivo: τ = −0.26 p = 0.04) of Glycosaminoglycan (GAG) with AREX. In contrast, the influence of interfering pools could be corrected by LAREX, and a moderate to strong correlation was observed for the fractional concentration of GAG for both in situ (τ = −0.71 p = 0.005) and in vivo (τ = −0.49 p < 0.001) experiments. The study presented here is the first to introduce a new qCEST method that enables qCEST imaging in systems with multiple proton pools.
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Perlman O, Ito H, Herz K, Shono N, Nakashima H, Zaiss M, Chiocca EA, Cohen O, Rosen MS, Farrar CT. Quantitative imaging of apoptosis following oncolytic virotherapy by magnetic resonance fingerprinting aided by deep learning. Nat Biomed Eng 2022; 6:648-657. [PMID: 34764440 PMCID: PMC9091056 DOI: 10.1038/s41551-021-00809-7] [Citation(s) in RCA: 22] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2020] [Accepted: 07/07/2021] [Indexed: 12/17/2022]
Abstract
Non-invasive imaging methods for detecting intratumoural viral spread and host responses to oncolytic virotherapy are either slow, lack specificity or require the use of radioactive or metal-based contrast agents. Here we show that in mice with glioblastoma multiforme, the early apoptotic responses to oncolytic virotherapy (characterized by decreased cytosolic pH and reduced protein synthesis) can be rapidly detected via chemical-exchange-saturation-transfer magnetic resonance fingerprinting (CEST-MRF) aided by deep learning. By leveraging a deep neural network trained with simulated magnetic resonance fingerprints, CEST-MRF can generate quantitative maps of intratumoural pH and of protein and lipid concentrations by selectively labelling the exchangeable amide protons of endogenous proteins and the exchangeable macromolecule protons of lipids, without requiring exogenous contrast agents. We also show that in a healthy volunteer, CEST-MRF yielded molecular parameters that are in good agreement with values from the literature. Deep-learning-aided CEST-MRF may also be amenable to the characterization of host responses to other cancer therapies and to the detection of cardiac and neurological pathologies.
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Affiliation(s)
- Or Perlman
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Charlestown, MA, USA.
| | - Hirotaka Ito
- Department of Neurosurgery, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, USA
| | - Kai Herz
- Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
- Department of Biomedical Magnetic Resonance, University of Tübingen, Tübingen, Germany
| | - Naoyuki Shono
- Department of Neurosurgery, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, USA
| | - Hiroshi Nakashima
- Department of Neurosurgery, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, USA
| | - Moritz Zaiss
- Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
- Department of Neuroradiology, Friedrich-Alexander Universität Erlangen-Nürnberg (FAU), University Hospital Erlangen, Erlangen, Germany
| | - E Antonio Chiocca
- Department of Neurosurgery, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, USA
| | - Ouri Cohen
- Memorial Sloan Kettering Cancer Center, New York, NY, USA
| | - Matthew S Rosen
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Charlestown, MA, USA
- Department of Physics, Harvard University, Cambridge, MA, USA
| | - Christian T Farrar
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Charlestown, MA, USA.
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Perlman O, Zhu B, Zaiss M, Rosen MS, Farrar CT. An end-to-end AI-based framework for automated discovery of rapid CEST/MT MRI acquisition protocols and molecular parameter quantification (AutoCEST). Magn Reson Med 2022; 87:2792-2810. [PMID: 35092076 PMCID: PMC9305180 DOI: 10.1002/mrm.29173] [Citation(s) in RCA: 17] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2021] [Revised: 01/04/2022] [Accepted: 01/07/2022] [Indexed: 12/28/2022]
Abstract
Purpose To develop an automated machine‐learning‐based method for the discovery of rapid and quantitative chemical exchange saturation transfer (CEST) MR fingerprinting acquisition and reconstruction protocols. Methods An MR physics‐governed AI system was trained to generate optimized acquisition schedules and the corresponding quantitative reconstruction neural network. The system (termed AutoCEST) is composed of a CEST saturation block, a spin dynamics module, and a deep reconstruction network, all differentiable and jointly connected. The method was validated using a variety of chemical exchange phantoms and in vivo mouse brains at 9.4T. Results The acquisition times for AutoCEST optimized schedules ranged from 35 to 71 s, with a quantitative image reconstruction time of only 29 ms. The resulting exchangeable proton concentration maps for the phantoms were in good agreement with the known solute concentrations for AutoCEST sequences (mean absolute error = 2.42 mM; Pearson’s r=0.992, p<0.0001), but not for an unoptimized sequence (mean absolute error = 65.19 mM; Pearson’s r=‐0.161, p=0.522). Similarly, improved exchange rate agreement was observed between AutoCEST and quantification of exchange using saturation power (QUESP) methods (mean absolute error: 35.8 Hz, Pearson’s r=0.971, p<0.0001) compared to an unoptimized schedule and QUESP (mean absolute error = 58.2 Hz; Pearson’s r=0.959, p<0.0001). The AutoCEST in vivo mouse brain semi‐solid proton volume fractions were lower in the cortex (12.77% ± 0.75%) compared to the white matter (19.80% ± 0.50%), as expected. Conclusion AutoCEST can automatically generate optimized CEST/MT acquisition protocols that can be rapidly reconstructed into quantitative exchange parameter maps.
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Affiliation(s)
- Or Perlman
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Charlestown, MA, USA
| | - Bo Zhu
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Charlestown, MA, USA
| | - Moritz Zaiss
- Magnetic Resonance Center, Max Planck Institute For Biological Cybernetics, Tübingen, Germany.,Department of Neuroradiology, University Hospital Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany
| | - Matthew S Rosen
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Charlestown, MA, USA.,Department of Physics, Harvard University, Cambridge, MA, USA
| | - Christian T Farrar
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Charlestown, MA, USA
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11
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Lankford CL, Louie EA, Zu Z, Does MD, Gochberg DF. A hybrid numeric-analytic solution for pulsed CEST. NMR IN BIOMEDICINE 2022; 35:e4610. [PMID: 34636458 PMCID: PMC9045009 DOI: 10.1002/nbm.4610] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/23/2020] [Revised: 07/23/2021] [Accepted: 08/12/2021] [Indexed: 05/08/2023]
Abstract
Chemical exchange saturation transfer (CEST) methods measure the effect of magnetization exchange between solutes and water. While CEST methods are often implemented using a train of off-resonant shaped RF pulses, they are typically analyzed as if the irradiation were continuous. This approximation does not account for exchange of rotated magnetization, unique to pulsed irradiation and exploited by chemical exchange rotation transfer methods. In this work, we derive and test an analytic solution for the steady-state water signal under pulsed irradiation by extending a previous work to include the effects of pulse shape. The solution is largely accurate at all offsets, but this accuracy diminishes at higher exchange rates and when applying pulse shapes with large root-mean-squared to mean ratios (such as multi-lobe sinc pulses).
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Affiliation(s)
- Christopher L. Lankford
- Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, TN, USA
| | - Elizabeth A. Louie
- Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, TN, USA
| | - Zhongliang Zu
- Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, TN, USA
- Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN, USA
| | - Mark D. Does
- Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, TN, USA
- Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN, USA
- Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, USA
- Department of Electrical Engineering, Vanderbilt University, Nashville, TN, USA
| | - Daniel F. Gochberg
- Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, TN, USA
- Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN, USA
- Department of Physics and Astronomy, Vanderbilt University, Nashville, TN, USA
- Corresponding author. Vanderbilt University Institute of Imaging Science, 1161 21 Ave. S, MCN AAA–3112, Nashville, TN 37232–2310, USA.
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12
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Lam B, Wendland M, Godines K, Shin SH, Vandsburger M. Accelerated multi-target chemical exchange saturation transfer magnetic resonance imaging of the mouse heart. Phys Med Biol 2021; 66. [PMID: 34167100 DOI: 10.1088/1361-6560/ac0e78] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2021] [Accepted: 06/24/2021] [Indexed: 12/21/2022]
Abstract
Cardiac chemical exchange saturation transfer-magnetic resonance imaging (CEST-MRI) has been used to probe levels of various metabolites that provide insight into myocardial structure and function. However, imaging of the heart using CEST-MRI is prolonged by the need to repeatedly acquire multiple images for a full Z-spectrum and to perform saturation and acquisition around cardiac and respiratory cycles. Compressed sensing (CS) reconstruction of sparse data enables accelerated acquisition, but reconstruction artifacts may bias subsequently derived measures of CEST contrast. In this study, we examine the impact of CS reconstruction of increasingly under-sampled cardiac CEST-MRI data on subsequent CEST contrasts of amine-containing metabolites and amide-containing proteins. Cardiac CEST-MRI data sets were acquired in six mice using low and high RF saturation for single and dual contrast generation, respectively. CEST-weighted images were reconstructed using CS methods at 2-5× levels of under-sampling. CEST contrasts were derived from corresponding Z-spectra and the impact of accelerated imaging on accuracy was assessed via analysis of variance. CS reconstruction preserved myocardial signal to noise ratio as compared to conventional reconstruction. However, greater absolute error and distribution of derived contrasts was observed with increasing acceleration factors. The results from this study indicate that acquisition of radial cardiac CEST-MRI data can be modestly, but meaningfully, accelerated via CS reconstructions with little error in CEST contrast quantification.
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Affiliation(s)
- Bonnie Lam
- Department of Bioengineering, UC Berkeley, Berkeley CA, United States of America
| | - Michael Wendland
- Berkeley Pre-clinical Imaging Core, UC Berkeley, Berkeley CA, United States of America
| | - Kevin Godines
- Department of Bioengineering, UC Berkeley, Berkeley CA, United States of America
| | - Soo Hyun Shin
- Department of Bioengineering, UC Berkeley, Berkeley CA, United States of America
| | - Moriel Vandsburger
- Department of Bioengineering, UC Berkeley, Berkeley CA, United States of America
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13
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Sun PZ. Quasi-steady-state CEST (QUASS CEST) solution improves the accuracy of CEST quantification: QUASS CEST MRI-based omega plot analysis. Magn Reson Med 2021; 86:765-776. [PMID: 33749052 DOI: 10.1002/mrm.28744] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2020] [Revised: 01/27/2021] [Accepted: 01/31/2021] [Indexed: 12/11/2022]
Abstract
PURPOSE CEST MRI omega plot quantifies the labile proton fraction ratio (fr ) and exchange rate (ksw ), yet it assumes long RF saturation time (Ts) and relaxation delay (Td). Our study aimed to test if a quasi-steady-state (QUASS) CEST analysis that accounts for the effect of finite Ts and Td could improve the accuracy of CEST MRI quantification. METHODS We modeled the MRI signal evolution using a typical CEST EPI sequence. The signal relaxes toward its thermal equilibrium following the bulk water relaxation rate during Td, and then toward its CEST steady state following the spin-lock relaxation rate during Ts from which the QUASS CEST effect is derived. Both fr and ksw were solved from simulated conventional apparent CEST and QUASS CEST MRI. We also performed MRI experiments from a Cr-gel phantom under serially varied Ts and Td times from 1.5 to 7.5 s. RESULTS Simulation showed that, although ksw could be slightly overestimated (3%-15%) for the range of Ts and Td, fr could be substantially underestimated by as much as 67%. In contrast, the QUASS solution provided accurate ksw and fr determination within 2%. The CEST MRI experiments confirmed that the QUASS solution enabled robust quantification of ksw and fr , superior over the omega plot analysis based on the conventional apparent CEST MRI measurements. CONCLUSIONS The QUASS CEST MRI algorithm corrects the effect of finite Ts and Td times on CEST measurements, thereby allowing robust and accurate CEST quantification.
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Affiliation(s)
- Phillip Zhe Sun
- Yerkes Imaging Center, Yerkes National Primate Research Center, Emory University, Atlanta, Georgia, USA.,Department of Radiology and Imaging Sciences, Emory University School of Medicine, Atlanta, Georgia, USA
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14
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Shin SH, Wendland MF, Vandsburger MH. Delayed urea differential enhancement CEST (dudeCEST)-MRI with T 1 correction for monitoring renal urea handling. Magn Reson Med 2020; 85:2791-2804. [PMID: 33180343 DOI: 10.1002/mrm.28583] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2020] [Revised: 10/12/2020] [Accepted: 10/13/2020] [Indexed: 12/12/2022]
Abstract
PURPOSE We demonstrate a method of delayed urea differential enhancement CEST for probing urea recycling action of the kidney using expanded multi-pool Lorentzian fitting and apparent exchange-dependent relaxation compensation. METHODS T1 correction of urea CEST contrast by apparent exchange-dependent relaxation was tested in phantoms. Nine mice were scanned at 7 Tesla following intraperitoneal injection of 2M 150 μL urea, and later saline. T1 maps and Z-spectra were acquired before and 20 and 40 min postinjection. Z-spectra were fit to a 7-pool Lorentzian model for CEST quantification and compared to urea assay of kidney homogenate. Renal injury was induced by aristolochic acid in 7 mice, and the same scan protocol was performed. RESULTS Apparent exchange-dependent relaxation corrected for variable T1 times in phantoms. Urea CEST contrast at +1 ppm increased significantly at both time points following urea injection in the inner medulla and papilla. When normalizing the postinjection urea CEST contrast to the corresponding baseline value, both urea and saline injection resulted in identical fold changes in urea CEST contrast. Urea assay of kidney homogenate showed a significant correlation to both apparent exchange-dependent relaxation (R2 = 0.4687, P = .0017) and non-T1 -corrected Lorentzian amplitudes (R2 = 0.4964, P = .0011). Renal injury resulted in increased T1 time in the cortex and reduced CEST contrast change upon urea and saline infusion. CONCLUSION Delayed urea enhancement following infusion can provide insight into renal urea handling. In addition, changes in CEST contrast at 1.0 ppm following saline infusion may provide insight into renal function.
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Affiliation(s)
- Soo Hyun Shin
- Department of Bioengineering, University of California, Berkeley, Berkeley, California, USA
| | - Michael F Wendland
- Berkeley Preclinical Imaging Core (BPIC), University of California, Berkeley, Berkeley, California, USA
| | - Moriel H Vandsburger
- Department of Bioengineering, University of California, Berkeley, Berkeley, California, USA
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15
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Demetriou E, Kujawa A, Golay X. Pulse sequences for measuring exchange rates between proton species: From unlocalised NMR spectroscopy to chemical exchange saturation transfer imaging. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2020; 120-121:25-71. [PMID: 33198968 DOI: 10.1016/j.pnmrs.2020.06.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2019] [Revised: 06/27/2020] [Accepted: 06/30/2020] [Indexed: 06/11/2023]
Abstract
Within the field of NMR spectroscopy, the study of chemical exchange processes through saturation transfer techniques has a long history. In the context of MRI, chemical exchange techniques have been adapted to increase the sensitivity of imaging to small fractions of exchangeable protons, including the labile protons of amines, amides and hydroxyls. The MR contrast is generated by frequency-selective irradiation of the labile protons, which results in a reduction of the water signal associated with transfer of the labile protons' saturated magnetization to the protons of the surrounding free water. The signal intensity depends on the rate of chemical exchange and the concentration of labile protons as well as on the properties of the irradiation field. This methodology is referred to as CEST (chemical exchange saturation transfer) imaging. Applications of CEST include imaging of molecules with short transverse relaxation times and mapping of physiological parameters such as pH, temperature, buffer concentration and chemical composition due to the dependency of this chemical exchange effect on all these parameters. This article aims to describe these effects both theoretically and experimentally. In depth analysis and mathematical modelling are provided for all pulse sequences designed to date to measure the chemical exchange rate. Importantly, it has become clear that the background signal from semi-solid protons and the presence of the Nuclear Overhauser Effect (NOE), either through direct dipole-dipole mechanisms or through exchange-relayed signals, complicates the analysis of CEST effects. Therefore, advanced methods to suppress these confounding factors have been developed, and these are also reviewed. Finally, the experimental work conducted both in vitro and in vivo is discussed and the progress of CEST imaging towards clinical practice is presented.
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Affiliation(s)
- Eleni Demetriou
- Brain Repair & Rehabilitation, Institute of Neurology, University College London, United Kingdom.
| | - Aaron Kujawa
- Brain Repair & Rehabilitation, Institute of Neurology, University College London, United Kingdom.
| | - Xavier Golay
- Brain Repair & Rehabilitation, Institute of Neurology, University College London, United Kingdom.
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16
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Detection of early cartilage degeneration in the tibiotalar joint using 3 T gagCEST imaging: a feasibility study. MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE 2020; 34:249-260. [PMID: 32725359 PMCID: PMC8018923 DOI: 10.1007/s10334-020-00868-y] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/31/2020] [Revised: 07/10/2020] [Accepted: 07/14/2020] [Indexed: 02/07/2023]
Abstract
OBJECTIVE To establish and optimize a stable 3 Tesla (T) glycosaminoglycan chemical exchange saturation transfer (gagCEST) imaging protocol for assessing the articular cartilage of the tibiotalar joint in healthy volunteers and patients after a sustained injury to the ankle. METHODS Using Bloch-McConnell simulations, we optimized the sequence protocol for a 3 T MRI scanner for maximum gagCEST effect size within a clinically feasible time frame of less than 07:30 min. This protocol was then used to analyze the gagCEST effect of the articular cartilage of the tibiotalar joint of 17 healthy volunteers and five patients with osteochondral lesions of the talus following ankle trauma. Reproducibility was tested with the intraclass correlation coefficient. RESULTS The mean magnetization transfer ratio asymmetry (MTRasym), i.e., the gagCEST effect size, was significantly lower in patients than in healthy volunteers (0.34 ± 1.9% vs. 1.49 ± 0.11%; p < 0.001 [linear mixed model]). Intra- and inter-rater reproducibility was excellent with an average measure intraclass correlation coefficient (ICC) of 0.97 and a single measure ICC of 0.91 (p < 0.01). DISCUSSION In this feasibility study, pre-morphological tibiotalar joint cartilage damage was quantitatively assessable on the basis of the optimized 3 T gagCEST imaging protocol that allowed stable quantification gagCEST effect sizes across a wide range of health and disease in clinically feasible acquisition times.
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17
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Anemone A, Consolino L, Arena F, Capozza M, Longo DL. Imaging tumor acidosis: a survey of the available techniques for mapping in vivo tumor pH. Cancer Metastasis Rev 2020; 38:25-49. [PMID: 30762162 PMCID: PMC6647493 DOI: 10.1007/s10555-019-09782-9] [Citation(s) in RCA: 98] [Impact Index Per Article: 24.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Cancer cells are characterized by a metabolic shift in cellular energy production, orchestrated by the transcription factor HIF-1α, from mitochondrial oxidative phosphorylation to increased glycolysis, regardless of oxygen availability (Warburg effect). The constitutive upregulation of glycolysis leads to an overproduction of acidic metabolic products, resulting in enhanced acidification of the extracellular pH (pHe ~ 6.5), which is a salient feature of the tumor microenvironment. Despite the importance of pH and tumor acidosis, there is currently no established clinical tool available to image the spatial distribution of tumor pHe. The purpose of this review is to describe various imaging modalities for measuring intracellular and extracellular tumor pH. For each technique, we will discuss main advantages and limitations, pH accuracy and sensitivity of the applied pH-responsive probes and potential translatability to the clinic. Particular attention is devoted to methods that can provide pH measurements at high spatial resolution useful to address the task of tumor heterogeneity and to studies that explored tumor pH imaging for assessing treatment response to anticancer therapies.
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Affiliation(s)
- Annasofia Anemone
- Molecular Imaging Center, Department of Molecular Biotechnology and Health Sciences, University of Turin, Via Nizza 52, Turin, Italy
| | - Lorena Consolino
- Molecular Imaging Center, Department of Molecular Biotechnology and Health Sciences, University of Turin, Via Nizza 52, Turin, Italy
| | - Francesca Arena
- Institute of Biostructures and Bioimaging (IBB), Italian National Research Council (CNR), Via Nizza 52, Turin, Italy.,Center for Preclinical Imaging, Department of Molecular Biotechnology and Health Sciences, University of Turin, Via Ribes 5, Colleretto Giacosa, Italy
| | - Martina Capozza
- Center for Preclinical Imaging, Department of Molecular Biotechnology and Health Sciences, University of Turin, Via Ribes 5, Colleretto Giacosa, Italy
| | - Dario Livio Longo
- Molecular Imaging Center, Department of Molecular Biotechnology and Health Sciences, University of Turin, Via Nizza 52, Turin, Italy. .,Institute of Biostructures and Bioimaging (IBB), Italian National Research Council (CNR), Via Nizza 52, Turin, Italy.
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18
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Tripepi M, Ferrauto G, Bennardi PO, Aime S, Delli Castelli D. Multilamellar LipoCEST Agents Obtained from Osmotic Shrinkage of Paramagnetically Loaded Giant Unilamellar Vescicles (GUVs). Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.201912327] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Affiliation(s)
- Martina Tripepi
- Department of Molecular Biotechnology and Health SciencesUniversity of Torino Via Nizza 52 10126 Torino Italy
| | - Giuseppe Ferrauto
- Department of Molecular Biotechnology and Health SciencesUniversity of Torino Via Nizza 52 10126 Torino Italy
| | - Paolo Oronzo Bennardi
- Department of Molecular Biotechnology and Health SciencesUniversity of Torino Via Nizza 52 10126 Torino Italy
| | - Silvio Aime
- Department of Molecular Biotechnology and Health SciencesUniversity of Torino Via Nizza 52 10126 Torino Italy
| | - Daniela Delli Castelli
- Department of Molecular Biotechnology and Health SciencesUniversity of Torino Via Nizza 52 10126 Torino Italy
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19
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Tripepi M, Ferrauto G, Bennardi PO, Aime S, Delli Castelli D. Multilamellar LipoCEST Agents Obtained from Osmotic Shrinkage of Paramagnetically Loaded Giant Unilamellar Vescicles (GUVs). Angew Chem Int Ed Engl 2020; 59:2279-2283. [PMID: 31803970 DOI: 10.1002/anie.201912327] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2019] [Indexed: 12/16/2022]
Abstract
Moving from nano- to micro-systems may not just be a matter of scale, but it might imply changes in the properties of the systems that can open new routes for the development of efficient MRI contrast agents. This is the case reported in the present paper, where giant liposomes (giant unilamellar vesicles, GUVs) loaded with LnIII complexes have been studied as chemical exchange saturation transfer (CEST) MRI contrast agents. The comparison between nanosized liposomes (small unilamellar vesicles, SUVs) and GUVs sharing the same formulation led to differences that could not be accounted for only in terms of the increase in size (from 100-150 nm to 1-2 μm). Upon osmotic shrinkage, GUVs yielded a saturation-transfer effect three order of magnitude higher than SUVs consistent with the increase in vesicles volume. Confocal microscopy showed that the shrinkage of GUVs resulted in multilamellar particles whereas SUVs are known to yield asymmetrical, discoidal shape.
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Affiliation(s)
- Martina Tripepi
- Department of Molecular Biotechnology and Health Sciences, University of Torino, Via Nizza 52, 10126, Torino, Italy
| | - Giuseppe Ferrauto
- Department of Molecular Biotechnology and Health Sciences, University of Torino, Via Nizza 52, 10126, Torino, Italy
| | - Paolo Oronzo Bennardi
- Department of Molecular Biotechnology and Health Sciences, University of Torino, Via Nizza 52, 10126, Torino, Italy
| | - Silvio Aime
- Department of Molecular Biotechnology and Health Sciences, University of Torino, Via Nizza 52, 10126, Torino, Italy
| | - Daniela Delli Castelli
- Department of Molecular Biotechnology and Health Sciences, University of Torino, Via Nizza 52, 10126, Torino, Italy
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20
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Chen L, Wei Z, Cai S, Li Y, Liu G, Lu H, Weiss RG, van Zijl PCM, Xu J. High-resolution creatine mapping of mouse brain at 11.7 T using non-steady-state chemical exchange saturation transfer. NMR IN BIOMEDICINE 2019; 32:e4168. [PMID: 31461196 DOI: 10.1002/nbm.4168] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2019] [Revised: 07/27/2019] [Accepted: 07/31/2019] [Indexed: 06/10/2023]
Abstract
The current study aims to optimize the acquisition scheme for the creatine chemical exchange saturation transfer weighted (CrCESTw) signal on mouse brain at 11.7 T, in which a strong magnetization transfer contrast (MTC) is present, and to further develop the polynomial and Lorentzian line-shape fitting (PLOF) method for quantifying CrCESTw signal with a non-steady-state (NSS) acquisition scheme. Studies on a Cr phantom with cross-linked bovine serum albumin (BSA) as well as on mouse brain demonstrated that the maximum CrCESTw signal was reached with a short saturation time determined by the rotating frame relaxation time of the MTC pool instead of the steady-state saturation. The saturation power for the maximal signal was around 1-1.5 μT for Cr with 20% cross-linked BSA and in vivo applications, but 2 μT was found to be most practical for signal stability. For the CrCEST acquisition with strong MTC interference, the optimal saturation power and length are completely different from those on Cr solution alone. This observation could be explained well using R1ρ theory by incorporating the strong MTC pool. Finally, a high-resolution Cr map was obtained on mouse brain using the PLOF method with the NSS CEST acquisition and a cryogenic coil. The Cr map obtained by CEST showed homogenous intensity across the mouse brain except for regions with cerebrospinal fluid.
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Affiliation(s)
- Lin Chen
- Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
- F. M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Research Institute, Baltimore, Maryland, USA
| | - Zhiliang Wei
- Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
- F. M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Research Institute, Baltimore, Maryland, USA
| | - Shuhui Cai
- Department of Electronic Science, Fujian Provincial Key Laboratory of Plasma and Magnetic Resonance, Xiamen University, Xiamen, China
| | - Yuguo Li
- Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
- F. M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Research Institute, Baltimore, Maryland, USA
| | - Guanshu Liu
- Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
- F. M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Research Institute, Baltimore, Maryland, USA
| | - Hanzhang Lu
- Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
- F. M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Research Institute, Baltimore, Maryland, USA
| | - Robert G Weiss
- Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
- Division of Cardiology, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Peter C M van Zijl
- Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
- F. M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Research Institute, Baltimore, Maryland, USA
| | - Jiadi Xu
- Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
- F. M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Research Institute, Baltimore, Maryland, USA
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21
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Stabinska J, Neudecker P, Ljimani A, Wittsack H, Lanzman RS, Müller‐Lutz A. Proton exchange in aqueous urea solutions measured by water‐exchange (WEX) NMR spectroscopy and chemical exchange saturation transfer (CEST) imaging in vitro. Magn Reson Med 2019; 82:935-947. [DOI: 10.1002/mrm.27778] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2018] [Revised: 03/06/2019] [Accepted: 03/28/2019] [Indexed: 12/30/2022]
Affiliation(s)
- Julia Stabinska
- Department of Diagnostic and Interventional Radiology, Medical Faculty Heinrich Heine University Düsseldorf Dusseldorf Germany
| | - Philipp Neudecker
- Institute of Physical Biology Heinrich Heine University Düsseldorf Dusseldorf Germany
- Institute of Complex Systems: Structural Biochemistry (ICS‐6), Forschungszentrum Jülich Julich Germany
| | - Alexandra Ljimani
- Department of Diagnostic and Interventional Radiology, Medical Faculty Heinrich Heine University Düsseldorf Dusseldorf Germany
| | - Hans‐Jörg Wittsack
- Department of Diagnostic and Interventional Radiology, Medical Faculty Heinrich Heine University Düsseldorf Dusseldorf Germany
| | - Rotem Shlomo Lanzman
- Department of Diagnostic and Interventional Radiology, Medical Faculty Heinrich Heine University Düsseldorf Dusseldorf Germany
| | - Anja Müller‐Lutz
- Department of Diagnostic and Interventional Radiology, Medical Faculty Heinrich Heine University Düsseldorf Dusseldorf Germany
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22
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Gochberg DF, Does MD, Zu Z, Lankford CL. Towards an analytic solution for pulsed CEST. NMR IN BIOMEDICINE 2018; 31:e3903. [PMID: 29460973 PMCID: PMC5935132 DOI: 10.1002/nbm.3903] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/12/2017] [Revised: 12/26/2017] [Accepted: 01/05/2018] [Indexed: 05/10/2023]
Abstract
Chemical exchange saturation transfer (CEST) is an imaging method based on magnetization exchange between solutes and water. This exchange generates changes in the measured signal after off-resonance radiofrequency irradiation. Although the analytic solution for CEST with continuous wave (CW) irradiation has been determined, most studies are performed using pulsed irradiation. In this work, we derive an analytic solution for the CEST signal after pulsed irradiation that includes both short-time rotation effects and long-time saturation effects in a two-pool system corresponding to water and a low-concentration exchanging solute pool. Several approximations are made to balance the accuracy and simplicity of the resulting analytic form, which is tested against numerical solutions of the coupled Bloch equations and is found to be largely accurate for amides at high fields, but less accurate at the higher exchange rates, lower offsets and typically higher irradiation powers of amines.
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Affiliation(s)
- Daniel F Gochberg
- Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, TN, USA
- Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN, USA
- Department of Physics and Astronomy, Vanderbilt University, Nashville, TN, USA
| | - Mark D Does
- Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, TN, USA
- Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN, USA
- Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, USA
- Department of Electrical Engineering, Vanderbilt University, Nashville, TN, USA
| | - Zhongliang Zu
- Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, TN, USA
- Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN, USA
| | - Christopher L Lankford
- Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, TN, USA
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23
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Demetriou E, Tachrount M, Zaiss M, Shmueli K, Golay X. PRO-QUEST: a rapid assessment method based on progressive saturation for quantifying exchange rates using saturation times in CEST. Magn Reson Med 2018; 80:1638-1654. [PMID: 29504144 DOI: 10.1002/mrm.27155] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2017] [Revised: 02/05/2018] [Accepted: 02/06/2018] [Indexed: 11/10/2022]
Abstract
PURPOSE To develop a new MRI technique to rapidly measure exchange rates in CEST MRI. METHODS A novel pulse sequence for measuring chemical exchange rates through a progressive saturation recovery process, called PRO-QUEST (progressive saturation for quantifying exchange rates using saturation times), has been developed. Using this method, the water magnetization is sampled under non-steady-state conditions, and off-resonance saturation is interleaved with the acquisition of images obtained through a Look-Locker type of acquisition. A complete theoretical framework has been set up, and simple equations to obtain the exchange rates have been derived. RESULTS A reduction of scan time from 58 to 16 minutes has been obtained using PRO-QUEST versus the standard QUEST. Maps of both T1 of water and B1 can simply be obtained by repetition of the sequence without off-resonance saturation pulses. Simulations and calculated exchange rates from experimental data using amino acids such as glutamate, glutamine, taurine, and alanine were compared and found to be in good agreement. The PRO-QUEST sequence was also applied on healthy and infarcted rats after 24 hours, and revealed that imaging specificity to ischemic acidification during stroke was substantially increased relative to standard amide proton transfer-weighted imaging. CONCLUSION Because of the reduced scan time and insensitivity to nonchemical exchange factors such as direct water saturation, PRO-QUEST can serve as an excellent alternative for researchers and clinicians interested to map pH changes in vivo.
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Affiliation(s)
- Eleni Demetriou
- Brain Repair & Rehabilitation, Institute of Neurology, University College London, United Kingdom
| | - Mohamed Tachrount
- Brain Repair & Rehabilitation, Institute of Neurology, University College London, United Kingdom
| | - Moritz Zaiss
- High Field Magnetic Resonance, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
| | - Karin Shmueli
- Department of Medical Physics and Biomedical Engineering, University College London, United Kingdom
| | - Xavier Golay
- Brain Repair & Rehabilitation, Institute of Neurology, University College London, United Kingdom
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24
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Arena F, Irrera P, Consolino L, Colombo Serra S, Zaiss M, Longo DL. Flip-angle based ratiometric approach for pulsed CEST-MRI pH imaging. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2018; 287:1-9. [PMID: 29272735 DOI: 10.1016/j.jmr.2017.12.007] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/07/2017] [Revised: 11/14/2017] [Accepted: 12/09/2017] [Indexed: 06/07/2023]
Abstract
Several molecules have been exploited for developing MRI pH sensors based on the chemical exchange saturation transfer (CEST) technique. A ratiometric approach, based on the saturation of two exchanging pools at the same saturation power, or by varying the saturation power levels on the same pool, is usually needed to rule out the concentration term from the pH measurement. However, all these methods have been demonstrated by using a continuous wave saturation scheme that limits its translation to clinical scanners. This study shows a new ratiometric CEST-MRI pH-mapping approach based on a pulsed CEST saturation scheme for a radiographic contrast agent (iodixanol) possessing a single chemical exchange site. This approach is based on the ratio of the CEST contrast effects at two different flip angles combinations (180°/360° and 180°/720°), keeping constant the mean irradiation RF power (Bavg power). The proposed ratiometric approach index is concentration independent and it showed good pH sensitivity and accuracy in the physiological range between 6.0 and 7.4.
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Affiliation(s)
- Francesca Arena
- Dipartimento di Biotecnologie Molecolari e Scienze per la Salute, Università degli Studi di Torino, Torino, Italy
| | - Pietro Irrera
- Dipartimento di Biotecnologie Molecolari e Scienze per la Salute, Università degli Studi di Torino, Torino, Italy
| | - Lorena Consolino
- Dipartimento di Biotecnologie Molecolari e Scienze per la Salute, Università degli Studi di Torino, Torino, Italy
| | | | - Moritz Zaiss
- Department of High-field Magnetic Resonance, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
| | - Dario Livio Longo
- Dipartimento di Biotecnologie Molecolari e Scienze per la Salute, Università degli Studi di Torino, Torino, Italy; Consiglio Nazionale delle Ricerche (CNR), Istituto di Biostrutture e Bioimmagini, Torino, Italy.
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Zaiss M, Angelovski G, Demetriou E, McMahon MT, Golay X, Scheffler K. QUESP and QUEST revisited - fast and accurate quantitative CEST experiments. Magn Reson Med 2017; 79:1708-1721. [PMID: 28686796 DOI: 10.1002/mrm.26813] [Citation(s) in RCA: 76] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2016] [Revised: 05/17/2017] [Accepted: 06/03/2017] [Indexed: 01/24/2023]
Abstract
PURPOSE Chemical exchange saturation transfer (CEST) NMR or MRI experiments allow detection of low concentrated molecules with enhanced sensitivity via their proton exchange with the abundant water pool. Be it endogenous metabolites or exogenous contrast agents, an exact quantification of the actual exchange rate is required to design optimal pulse sequences and/or specific sensitive agents. METHODS Refined analytical expressions allow deeper insight and improvement of accuracy for common quantification techniques. The accuracy of standard quantification methodologies, such as quantification of exchange rate using varying saturation power or varying saturation time, is improved especially for the case of nonequilibrium initial conditions and weak labeling conditions, meaning the saturation amplitude is smaller than the exchange rate (γB1 < k). RESULTS The improved analytical 'quantification of exchange rate using varying saturation power/time' (QUESP/QUEST) equations allow for more accurate exchange rate determination, and provide clear insights on the general principles to execute the experiments and to perform numerical evaluation. The proposed methodology was evaluated on the large-shift regime of paramagnetic chemical-exchange-saturation-transfer agents using simulated data and data of the paramagnetic Eu(III) complex of DOTA-tetraglycineamide. CONCLUSIONS The refined formulas yield improved exchange rate estimation. General convergence intervals of the methods that would apply for smaller shift agents are also discussed. Magn Reson Med 79:1708-1721, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Moritz Zaiss
- High Field Magnetic Resonance, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
| | - Goran Angelovski
- MR Neuroimaging Agents, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
| | - Eleni Demetriou
- Brain Repair & Rehabilitation, Institute of Neurology, University College London, United Kingdom
| | - Michael T McMahon
- Division of MR Research, The Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University, Baltimore, Maryland, USA
- F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, Maryland, USA
| | - Xavier Golay
- Brain Repair & Rehabilitation, Institute of Neurology, University College London, United Kingdom
| | - Klaus Scheffler
- High Field Magnetic Resonance, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
- Department of Biomedical Magnetic Resonance, Eberhard Karl's University of Tübingen and University Hospital, Tübingen, Germany
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Stabinska J, Cronenberg T, Wittsack HJ, Lanzman RS, Müller-Lutz A. Quantitative pulsed CEST-MRI at a clinical 3T MRI system. MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE 2017; 30:505-516. [PMID: 28569374 DOI: 10.1007/s10334-017-0625-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/16/2017] [Revised: 04/28/2017] [Accepted: 05/12/2017] [Indexed: 11/27/2022]
Abstract
OBJECTIVES The goal of this study was to quantify CEST related parameters such as chemical exchange rate and fractional concentration of exchanging protons at a clinical 3T scanner. For this purpose, two CEST quantification approaches-the AREX metric (for 'apparent exchange dependent relaxation'), and the AREX-based Ω-plot method were used. In addition, two different pulsed RF irradiation schemes, using Gaussian-shaped and spin-lock pulses, were compared. MATERIALS AND METHODS Numerical simulations as well as MRI measurements in phantoms were performed. For simulations, the Bloch-McConnell equations were solved using a two-pool exchange model. MR experiments were performed on a clinical 3T MRI scanner using a cylindrical phantom filled with creatine solution at different pH values and different concentrations. RESULTS The validity of the Ω-plot method and the AREX approach using spin-lock preparation for determination of the quantitative CEST parameters was demonstrated. Especially promising results were achieved for the Ω-plot method when the spin-lock preparation was employed. CONCLUSION Pulsed CEST at 3T could be used to quantify parameters such as exchange rate constants and concentrations of protons exchanging with free water. In the future this technique might be used to estimate the exchange rates and concentrations of biochemical substances in human tissues in vivo.
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Affiliation(s)
- Julia Stabinska
- Department of Diagnostic and Interventional Radiology, Medical Faculty, University Dusseldorf, Moorenstr. 5, 40225, Düsseldorf, Germany.
| | - Tom Cronenberg
- Department of Diagnostic and Interventional Radiology, Medical Faculty, University Dusseldorf, Moorenstr. 5, 40225, Düsseldorf, Germany
| | - Hans-Jörg Wittsack
- Department of Diagnostic and Interventional Radiology, Medical Faculty, University Dusseldorf, Moorenstr. 5, 40225, Düsseldorf, Germany
| | - Rotem Shlomo Lanzman
- Department of Diagnostic and Interventional Radiology, Medical Faculty, University Dusseldorf, Moorenstr. 5, 40225, Düsseldorf, Germany
| | - Anja Müller-Lutz
- Department of Diagnostic and Interventional Radiology, Medical Faculty, University Dusseldorf, Moorenstr. 5, 40225, Düsseldorf, Germany
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Schuenke P, Koehler C, Korzowski A, Windschuh J, Bachert P, Ladd ME, Mundiyanapurath S, Paech D, Bickelhaupt S, Bonekamp D, Schlemmer HP, Radbruch A, Zaiss M. Adiabatically prepared spin-lock approach for T1ρ-based dynamic glucose enhanced MRI at ultrahigh fields. Magn Reson Med 2016; 78:215-225. [DOI: 10.1002/mrm.26370] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2016] [Revised: 07/12/2016] [Accepted: 07/14/2016] [Indexed: 12/23/2022]
Affiliation(s)
- Patrick Schuenke
- German Cancer Research Center (DKFZ); Division of Medical Physics in Radiology; Heidelberg Germany
| | - Christina Koehler
- German Cancer Research Center (DKFZ); Division of Radiology; Heidelberg Germany
| | - Andreas Korzowski
- German Cancer Research Center (DKFZ); Division of Medical Physics in Radiology; Heidelberg Germany
| | - Johannes Windschuh
- German Cancer Research Center (DKFZ); Division of Medical Physics in Radiology; Heidelberg Germany
| | - Peter Bachert
- German Cancer Research Center (DKFZ); Division of Medical Physics in Radiology; Heidelberg Germany
| | - Mark E. Ladd
- German Cancer Research Center (DKFZ); Division of Medical Physics in Radiology; Heidelberg Germany
| | | | - Daniel Paech
- German Cancer Research Center (DKFZ); Division of Radiology; Heidelberg Germany
| | | | - David Bonekamp
- German Cancer Research Center (DKFZ); Division of Radiology; Heidelberg Germany
| | | | - Alexander Radbruch
- German Cancer Research Center (DKFZ); Division of Radiology; Heidelberg Germany
| | - Moritz Zaiss
- German Cancer Research Center (DKFZ); Division of Medical Physics in Radiology; Heidelberg Germany
- Max-Planck-Institute for Biological Cybernetics; Tübingen Baden-Württemberg Germany
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Müller-Lutz A, Cronenberg T, Schleich C, Wickrath F, Zaiss M, Boos J, Wittsack HJ. Comparison of glycosaminoglycan chemical exchange saturation transfer using Gaussian-shaped and off-resonant spin-lock radiofrequency pulses in intervertebral disks. Magn Reson Med 2016; 78:280-284. [PMID: 27484469 DOI: 10.1002/mrm.26362] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2016] [Revised: 07/06/2016] [Accepted: 07/08/2016] [Indexed: 12/14/2022]
Abstract
PURPOSE To investigate, if a train of spin-lock pulses (chemical exchange saturation transfer with spin-lock pulses = CESL) improves biochemical glycosaminoglycan imaging compared with conventional chemical exchange saturation transfer with Gaussian-shaped pulses (CEST) in lumbar intervertebral discs. METHODS T2 , CEST, and CESL imaging was performed in lumbar intervertebral discs of 15 healthy volunteers at 3 Tesla. Mean and standard deviation of the asymmetric magnetization transfer ratio (MTRasym ), the asymmetric spin-lock ratio (SLRasym ) and T2 values were calculated for nucleus pulposus (NP) and annulus fibrosus (AF). Wilcoxon test was used to analyze differences between MTRasym and SLRasym . Pearson correlation was used to determine the relationship between MTRasym , SLRasym and T2 . RESULTS Data showed no significant difference between MTRasym and SLRasym (NP: P = 0.35; AF: P = 0.34). MTRasym and SLRasym values differed significantly between NP and AF (MTRasym : P = 0.014, SLRasym : P = 0.005). T2 values correlated significantly with MTRasym (NP: ρ = 0.76, P < 0.001; AF: ρ = 0.60, P < 0.001) and SLRasym (NP: ρ = 0.73, P < 0.001; AF: ρ = 0.47, P < 0.001). CONCLUSION CESL does not improve the chemical exchange asymmetry effect compared with conventional CEST, but leads to comparable results. Magn Reson Med 78:280-284, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Anja Müller-Lutz
- University Dusseldorf, Medical Faculty, Department of Diagnostic and Interventional Radiology, Dusseldorf, Germany
| | - Tom Cronenberg
- University Dusseldorf, Medical Faculty, Department of Diagnostic and Interventional Radiology, Dusseldorf, Germany
| | - Christoph Schleich
- University Dusseldorf, Medical Faculty, Department of Diagnostic and Interventional Radiology, Dusseldorf, Germany
| | - Frithjof Wickrath
- University Dusseldorf, Medical Faculty, Department of Diagnostic and Interventional Radiology, Dusseldorf, Germany
| | - Moritz Zaiss
- Department of Medical Physics in Radiology, Deutsches Krebsforschungszentrum (DKFZ), Heidelberg, Germany
| | - Johannes Boos
- University Dusseldorf, Medical Faculty, Department of Diagnostic and Interventional Radiology, Dusseldorf, Germany
| | - Hans-Jörg Wittsack
- University Dusseldorf, Medical Faculty, Department of Diagnostic and Interventional Radiology, Dusseldorf, Germany
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Schuenke P, Windschuh J, Roeloffs V, Ladd ME, Bachert P, Zaiss M. Simultaneous mapping of water shift and B 1 (WASABI)-Application to field-Inhomogeneity correction of CEST MRI data. Magn Reson Med 2016; 77:571-580. [PMID: 26857219 DOI: 10.1002/mrm.26133] [Citation(s) in RCA: 90] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2015] [Revised: 12/18/2015] [Accepted: 12/27/2015] [Indexed: 12/18/2022]
Abstract
PURPOSE Together with the development of MRI contrasts that are inherently small in their magnitude, increased magnetic field accuracy is also required. Hence, mapping of the static magnetic field (B0 ) and the excitation field (B1 ) is not only important to feedback shim algorithms, but also for postprocess contrast-correction procedures. METHODS A novel field-inhomogeneity mapping method is presented that allows simultaneous mapping of the water shift and B1 (WASABI) using an off-resonant rectangular preparation pulse. The induced Rabi oscillations lead to a sinc-like spectrum in the frequency-offset dimension and allow for determination of B0 by its symmetry axis and of B1 by its oscillation frequency. RESULTS Stability of the WASABI method with regard to the influences of T1 , T2 , magnetization transfer, and repetition time was investigated and its convergence interval was verified. B0 and B1 maps obtained simultaneously by means of WASABI in the human brain at 3 T and 7 T can compete well with maps obtained by standard methods. Finally, the method was applied successfully for B0 and B1 correction of chemical exchange saturation transfer MRI (CEST-MRI) data of the human brain. CONCLUSION The proposed WASABI method yields a novel simultaneous B0 and B1 mapping within 1 min that is robust and easy to implement. Magn Reson Med 77:571-580, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Patrick Schuenke
- German Cancer Research Center (DKFZ), Medical Physics in Radiology, Im Neuenheimer Feld 280, D-69120, Heidelberg, Germany
| | - Johannes Windschuh
- German Cancer Research Center (DKFZ), Medical Physics in Radiology, Im Neuenheimer Feld 280, D-69120, Heidelberg, Germany
| | - Volkert Roeloffs
- Biomedizinische NMR Forschungs GmbH am Max-Planck-Institut für biophysikalische Chemie, Am Fassberg 11, D-37077, Göttingen, Germany
| | - Mark E Ladd
- German Cancer Research Center (DKFZ), Medical Physics in Radiology, Im Neuenheimer Feld 280, D-69120, Heidelberg, Germany
| | - Peter Bachert
- German Cancer Research Center (DKFZ), Medical Physics in Radiology, Im Neuenheimer Feld 280, D-69120, Heidelberg, Germany
| | - Moritz Zaiss
- German Cancer Research Center (DKFZ), Medical Physics in Radiology, Im Neuenheimer Feld 280, D-69120, Heidelberg, Germany
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Meissner JE, Goerke S, Rerich E, Klika KD, Radbruch A, Ladd ME, Bachert P, Zaiss M. Quantitative pulsed CEST-MRI using Ω-plots. NMR IN BIOMEDICINE 2015; 28:1196-208. [PMID: 26278686 DOI: 10.1002/nbm.3362] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/01/2015] [Revised: 06/18/2015] [Accepted: 06/19/2015] [Indexed: 05/24/2023]
Abstract
Chemical exchange saturation transfer (CEST) allows the indirect detection of dilute metabolites in living tissue via MRI of the tissue water signal. Selective radio frequency (RF) with amplitude B1 is used to saturate the magnetization of protons of exchanging groups, which transfer the saturation to the abundant water pool. In a clinical setup, the saturation scheme is limited to a series of short pulses to follow regulation of the specific absorption rate (SAR). Pulsed saturation is difficult to describe theoretically, thus rendering quantitative CEST a challenging task. In this study, we propose a new analytical treatment of pulsed CEST by extending a former interleaved saturation-relaxation approach. Analytical integration of the continuous wave (cw) eigenvalue as a function of the RF pulse shape leads to a formula for pulsed CEST that has the same structure as that for cw CEST, but incorporates two form factors that are determined by the pulse shape. This enables analytical Z-spectrum calculations and permits deeper insight into pulsed CEST. Furthermore, it extends Dixon's Ω-plot method to the case of pulsed saturation, yielding separately, and independently, the exchange rate and the relative proton concentration. Consequently, knowledge of the form factors allows a direct comparison of the effect of the strength and B1 dispersion of pulsed CEST experiments with the ideal case of cw saturation. The extended pulsed CEST quantification approach was verified using creatine phantoms measured on a 7 T whole-body MR tomograph, and its range of validity was assessed by simulations.
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Affiliation(s)
- Jan-Eric Meissner
- Division of Medical Physics in Radiology, Deutsches Krebsforschungszentrum (DKFZ) [German Cancer Research Center], Heidelberg, Germany
- Division of Radiology, Deutsches Krebsforschungszentrum (DKFZ) [German Cancer Research Center], Heidelberg, Germany
| | - Steffen Goerke
- Division of Medical Physics in Radiology, Deutsches Krebsforschungszentrum (DKFZ) [German Cancer Research Center], Heidelberg, Germany
| | - Eugenia Rerich
- Division of Medical Physics in Radiology, Deutsches Krebsforschungszentrum (DKFZ) [German Cancer Research Center], Heidelberg, Germany
| | - Karel D Klika
- Molecular Structure Analysis, Deutsches Krebsforschungszentrum (DKFZ) [German Cancer Research Center], Heidelberg, Germany
| | - Alexander Radbruch
- Division of Radiology, Deutsches Krebsforschungszentrum (DKFZ) [German Cancer Research Center], Heidelberg, Germany
- Department of Neuroradiology, Medical Faculty, University of Heidelberg, Heidelberg, Germany
| | - Mark E Ladd
- Division of Medical Physics in Radiology, Deutsches Krebsforschungszentrum (DKFZ) [German Cancer Research Center], Heidelberg, Germany
| | - Peter Bachert
- Division of Medical Physics in Radiology, Deutsches Krebsforschungszentrum (DKFZ) [German Cancer Research Center], Heidelberg, Germany
| | - Moritz Zaiss
- Division of Medical Physics in Radiology, Deutsches Krebsforschungszentrum (DKFZ) [German Cancer Research Center], Heidelberg, Germany
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Kunth M, Witte C, Schröder L. Continuous-wave saturation considerations for efficient xenon depolarization. NMR IN BIOMEDICINE 2015; 28:601-606. [PMID: 25900330 DOI: 10.1002/nbm.3307] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/16/2015] [Revised: 03/06/2015] [Accepted: 03/18/2015] [Indexed: 06/04/2023]
Abstract
The combination of hyperpolarized Xe with chemical exchange saturation transfer (Hyper-CEST) is a powerful NMR technique to detect highly dilute concentrations of Xe binding sites using RF saturation pulses. Crucially, that combination of saturation pulse strength and duration that generates the maximal Hyper-CEST effect is a priori unknown. In contrast to CEST in proton MRI, where the system reaches a steady-state for long saturation times, Hyper-CEST has an optimal saturation time, i.e. saturating for shorter or longer reduces the Hyper-CEST effect. Here, we derive expressions for this optimal saturation pulse length. We also found that a pulse strength, B1, corresponding to five times the Xe exchange rate, k(BA) (i.e. B1 = 5 k(BA)/γ with the gyromagnetic ratio of (129)Xe, γ), generates directly and without further optimization 96% of the maximal Hyper-CEST contrast while preserving spectral selectivity. As a measure that optimizes the amplitude and the width of the Hyper-CEST response simultaneously, we found an optimal saturation pulse strength corresponding to √2 times the Xe exchange rate, i.e. B1=√2k(BA)/γ. When extremely low host concentration is detected, then the expression for the optimum saturation time simplifies as it approaches the longitudinal relaxation time of free Xe.
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Affiliation(s)
- Martin Kunth
- ERC Project BiosensorImaging, Leibniz-Institut für Molekulare Pharmakologie (FMP), 13125, Berlin, Germany
| | - Christopher Witte
- ERC Project BiosensorImaging, Leibniz-Institut für Molekulare Pharmakologie (FMP), 13125, Berlin, Germany
| | - Leif Schröder
- ERC Project BiosensorImaging, Leibniz-Institut für Molekulare Pharmakologie (FMP), 13125, Berlin, Germany
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Windschuh J, Zaiss M, Meissner JE, Paech D, Radbruch A, Ladd ME, Bachert P. Correction of B1-inhomogeneities for relaxation-compensated CEST imaging at 7 T. NMR IN BIOMEDICINE 2015; 28:529-37. [PMID: 25788155 DOI: 10.1002/nbm.3283] [Citation(s) in RCA: 158] [Impact Index Per Article: 17.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/16/2014] [Revised: 01/20/2015] [Accepted: 02/05/2015] [Indexed: 05/17/2023]
Abstract
Chemical exchange saturation transfer (CEST) imaging of endogenous agents in vivo is influenced by direct water proton saturation (spillover) and semi-solid macromolecular magnetization transfer (MT). Lorentzian fit isolation and application of the inverse metric yields the pure CEST contrast AREX, which is less affected by these processes, but still depends on the measurement technique, in particular on the irradiation amplitude B1 of the saturation pulses. This study focuses on two well-known CEST effects in the slow exchange regime originating from amide and aliphatic protons resonating at 3.5 ppm or -3.5 ppm from water protons, respectively. A B1-correction of CEST contrasts is crucial for the evaluation of data obtained in clinical studies at high field strengths with strong B1-inhomogeneities. Herein two approaches for B1-inhomogeneity correction, based on either CEST contrasts or Z-spectra, are investigated. Both rely on multiple acquisitions with different B1-values. One volunteer was examined with eight different B1-values to optimize the saturation field strength and the correction algorithm. Histogram evaluation allowed quantification of the quality of the B1-correction. Finally, the correction was applied to CEST images of a patient with oligodendroglioma WHO grade 2, and showed improvement of the image quality compared with the non-corrected CEST images, especially in the tumor region.
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Affiliation(s)
- Johannes Windschuh
- Deutsches Krebsforschungszentrum (DKFZ) [German Cancer Research Center], Division of Medical Physics in Radiology, Heidelberg, Germany
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Zaiss M, Windschuh J, Paech D, Meissner JE, Burth S, Schmitt B, Kickingereder P, Wiestler B, Wick W, Bendszus M, Schlemmer HP, Ladd ME, Bachert P, Radbruch A. Relaxation-compensated CEST-MRI of the human brain at 7T: Unbiased insight into NOE and amide signal changes in human glioblastoma. Neuroimage 2015; 112:180-188. [PMID: 25727379 DOI: 10.1016/j.neuroimage.2015.02.040] [Citation(s) in RCA: 153] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2014] [Revised: 02/05/2015] [Accepted: 02/18/2015] [Indexed: 11/30/2022] Open
Abstract
Endogenous chemical exchange saturation transfer (CEST) effects of protons resonating near to water protons are always diluted by competing effects such as direct water saturation and semi-solid magnetization transfer (MT). This leads to unwanted T2 and MT signal contributions that contaminate the observed CEST signal. Furthermore, all CEST effects appear to be scaled by the T1 relaxation time of the mediating water pool. As MT, T1 and T2 are also altered in tumor regions, a recently published correction algorithm yielding the apparent exchange-dependent relaxation AREX, is used to evaluate in vivo CEST effects. This study focuses on CEST effects of amides (3.5ppm) and Nuclear-Overhauser-mediated saturation transfer (NOE, -3.5ppm) that can be properly isolated at 7T. These were obtained in 10 glioblastoma patients, and this is the first comprehensive study where AREX is applied in human brain as well as in human glioblastoma. The correction of CEST effects alters the contrast significantly: after correction, the CEST effect of amides does not show significant contrast between contrast enhancing tumor regions and normal tissue, whereas NOE drops significantly in the tumor area. In addition, new features in the AREX contrasts are visible. This suggests that previous CEST approaches might not have shown pure CEST effects, but rather water relaxation shine-through effects. Our insights help to improve understanding of the CEST effect changes in tumors and correlations on a cellular and molecular level.
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Affiliation(s)
- Moritz Zaiss
- Division of Medical Physics in Radiology, Deutsches Krebsforschungszentrum (DKFZ), Heidelberg, Germany.
| | - Johannes Windschuh
- Division of Medical Physics in Radiology, Deutsches Krebsforschungszentrum (DKFZ), Heidelberg, Germany
| | - Daniel Paech
- Department of Neuroradiology, University of Heidelberg Medical Center, Heidelberg, Germany; Neurooncologic Imaging, Department of Radiology, Deutsches Krebsforschungszentrum (DKFZ), Heidelberg, Germany
| | - Jan-Eric Meissner
- Division of Medical Physics in Radiology, Deutsches Krebsforschungszentrum (DKFZ), Heidelberg, Germany; Neurooncologic Imaging, Department of Radiology, Deutsches Krebsforschungszentrum (DKFZ), Heidelberg, Germany
| | - Sina Burth
- Department of Neuroradiology, University of Heidelberg Medical Center, Heidelberg, Germany; Neurooncologic Imaging, Department of Radiology, Deutsches Krebsforschungszentrum (DKFZ), Heidelberg, Germany
| | | | - Philip Kickingereder
- Department of Neuroradiology, University of Heidelberg Medical Center, Heidelberg, Germany
| | - Benedikt Wiestler
- University of Heidelberg Neurology Clinic, Heidelberg, Germany; Clinical Cooperation Unit Neuro-oncology, Deutsches Krebsforschungszentrum (DKFZ), Heidelberg, Germany
| | - Wolfgang Wick
- University of Heidelberg Neurology Clinic, Heidelberg, Germany; Clinical Cooperation Unit Neuro-oncology, Deutsches Krebsforschungszentrum (DKFZ), Heidelberg, Germany
| | - Martin Bendszus
- Department of Neuroradiology, University of Heidelberg Medical Center, Heidelberg, Germany
| | - Heinz-Peter Schlemmer
- Department of Radiology, Deutsches Krebsforschungszentrum (DKFZ), Heidelberg, Germany
| | - Mark E Ladd
- Division of Medical Physics in Radiology, Deutsches Krebsforschungszentrum (DKFZ), Heidelberg, Germany
| | - Peter Bachert
- Division of Medical Physics in Radiology, Deutsches Krebsforschungszentrum (DKFZ), Heidelberg, Germany
| | - Alexander Radbruch
- Department of Neuroradiology, University of Heidelberg Medical Center, Heidelberg, Germany; Neurooncologic Imaging, Department of Radiology, Deutsches Krebsforschungszentrum (DKFZ), Heidelberg, Germany
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