| 1. |
- Lehmann, Patrick M, et al.
(author)
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A numerical human brain phantom for dynamic glucose-enhanced (DGE) MRI : On the influence of head motion at 3T
- 2023
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In: Magnetic Resonance in Medicine. - : Wiley. - 1522-2594 .- 0740-3194. ; 89:5, s. 1871-1887
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Journal article (peer-reviewed)abstract
- PURPOSE: Dynamic glucose-enhanced (DGE) MRI relates to a group of exchange-based MRI techniques where the uptake of glucose analogues is studied dynamically. However, motion artifacts can be mistaken for true DGE effects, while motion correction may alter true signal effects. The aim was to design a numerical human brain phantom to simulate a realistic DGE MRI protocol at 3T that can be used to assess the influence of head movement on the signal before and after retrospective motion correction.METHODS: MPRAGE data from a tumor patient were used to simulate dynamic Z-spectra under the influence of motion. The DGE responses for different tissue types were simulated, creating a ground truth. Rigid head movement patterns were applied as well as physiological dilatation and pulsation of the lateral ventricles and head-motion-induced B 0 -changes in presence of first-order shimming. The effect of retrospective motion correction was evaluated. RESULTS: Motion artifacts similar to those previously reported for in vivo DGE data could be reproduced. Head movement of 1 mm translation and 1.5 degrees rotation led to a pseudo-DGE effect on the order of 1% signal change. B 0 effects due to head motion altered DGE changes due to a shift in the water saturation spectrum. Pseudo DGE effects were partly reduced or enhanced by rigid motion correction depending on tissue location. CONCLUSION: DGE MRI studies can be corrupted by motion artifacts. Designing post-processing methods using retrospective motion correction including B 0 correction will be crucial for clinical implementation. The proposed phantom should be useful for evaluation and optimization of such techniques.
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| 2. |
- Mohammed Ali, Sajad, et al.
(author)
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Deep learning-based Lorentzian fitting of water saturation shift referencing spectra in MRI
- 2023
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In: Magnetic Resonance in Medicine. - 1522-2594. ; 90:4, s. 1610-1624
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Journal article (peer-reviewed)abstract
- PURPOSE: Water saturation shift referencing (WASSR) Z-spectra are used commonly for field referencing in chemical exchange saturation transfer (CEST) MRI. However, their analysis using least-squares (LS) Lorentzian fitting is time-consuming and prone to errors because of the unavoidable noise in vivo. A deep learning-based single Lorentzian Fitting Network (sLoFNet) is proposed to overcome these shortcomings.METHODS: A neural network architecture was constructed and its hyperparameters optimized. Training was conducted on a simulated and in vivo-paired data sets of discrete signal values and their corresponding Lorentzian shape parameters. The sLoFNet performance was compared with LS on several WASSR data sets (both simulated and in vivo 3T brain scans). Prediction errors, robustness against noise, effects of sampling density, and time consumption were compared.RESULTS: LS and sLoFNet performed comparably in terms of RMS error and mean absolute error on all in vivo data with no statistically significant difference. Although the LS method fitted well on samples with low noise, its error increased rapidly when increasing sample noise up to 4.5%, whereas the error of sLoFNet increased only marginally. With the reduction of Z-spectral sampling density, prediction errors increased for both methods, but the increase occurred earlier (at 25 vs. 15 frequency points) and was more pronounced for LS. Furthermore, sLoFNet performed, on average, 70 times faster than the LS-method.CONCLUSION: Comparisons between LS and sLoFNet on simulated and in vivo WASSR MRI Z-spectra in terms of robustness against noise and decreased sample resolution, as well as time consumption, showed significant advantages for sLoFNet.
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| 3. |
- Seidemo, Anina, et al.
(author)
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Towards robust glucose chemical exchange saturation transfer imaging in humans at 3 T: Arterial input function measurements and the effects of infusion time
- 2022
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In: NMR in Biomedicine. - : Wiley. - 0952-3480 .- 1099-1492. ; 35:2, s. 4624-4624
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Journal article (peer-reviewed)abstract
- Dynamic glucose-enhanced (DGE) magnetic resonance imaging (MRI) has shown potential for tumor imaging using D-glucose as a biodegradable contrast agent. The DGE signal change is small at 3 T (around 1 and accurate detection is hampered by motion. The intravenous D-glucose injection is associated with transient side effects that can indirectly generate subject movements. In this study, the aim was to study DGE arterial input functions (AIFs) in healthy volunteers at 3 T for different scanning protocols, as a step towards making the glucose chemical exchange saturation transfer (glucoCEST) protocol more robust. Two different infusion durations (1.5 and 4.0 min) and saturation frequency offsets (1.2 and 2.0 ppm) were used. The effect of subject motion on the DGE signal was studied by using motion estimates retrieved from standard retrospective motion correction to create pseudo-DGE maps, where the apparent DGE signal changes were entirely caused by motion. Furthermore, the DGE AIFs were compared with venous blood glucose levels. A significant difference (p = 0.03) between arterial baseline and postinfusion DGE signal was found after D-glucose infusion. The results indicate that the measured DGE AIF signal change depends on both motion and blood glucose concentration change, emphasizing the need for sufficient motion correction in glucoCEST imaging. Finally, we conclude that a longer infusion duration (e.g. 3–4 min) should preferably be used in glucoCEST experiments, because it can minimize the glucose infusion side effects without negatively affecting the DGE signal change.
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| 4. |
- van Zijl, Peter C. M., et al.
(author)
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Hyperpolarized MRI, functional MRI, MR spectroscopy and CEST to provide metabolic information in vivo
- 2021
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In: Current Opinion in Chemical Biology. - : Elsevier BV. - 1367-5931. ; 63, s. 209-218
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Journal article (peer-reviewed)abstract
- Access to metabolic information in vivo using magnetic resonance (MR) technologies has generally been the niche of MR spectroscopy (MRS) and spectroscopic imaging (MRSI). Metabolic fluxes can be studied using the infusion of substrates labeled with magnetic isotopes, with the use of hyperpolarization especially powerful. Unfortunately, these promising methods are not yet accepted clinically, where fast, simple, and reliable measurement and diagnosis are key. Recent advances in functional MRI and chemical exchange saturation transfer (CEST) MRI allow the use of water imaging to study oxygen metabolism and tissue metabolite levels. These, together with the use of novel data analysis approaches such as machine learning for all of these metabolic MR approaches, are increasing the likelihood of their clinical translation.
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| 5. |
- Xu, Xiang, et al.
(author)
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d-glucose weighted chemical exchange saturation transfer (glucoCEST)-based dynamic glucose enhanced (DGE) MRI at 3T : early experience in healthy volunteers and brain tumor patients
- 2020
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In: Magnetic Resonance in Medicine. - : Wiley. - 1522-2594 .- 0740-3194. ; 84:1, s. 247-262
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Journal article (peer-reviewed)abstract
- PURPOSE: Dynamic glucose enhanced (DGE) MRI has shown potential for imaging glucose delivery and blood-brain barrier permeability at fields of 7T and higher. Here, we evaluated issues involved with translating d-glucose weighted chemical exchange saturation transfer (glucoCEST) experiments to the clinical field strength of 3T.METHODS: Exchange rates of the different hydroxyl proton pools and the field-dependent T2 relaxivity of water in d-glucose solution were used to simulate the water saturation spectra (Z-spectra) and DGE signal differences as a function of static field strength B0 , radiofrequency field strength B1 , and saturation time tsat . Multislice DGE experiments were performed at 3T on 5 healthy volunteers and 3 glioma patients.RESULTS: Simulations showed that DGE signal decreases with B0 , because of decreased contributions of glucoCEST and transverse relaxivity, as well as coalescence of the hydroxyl and water proton signals in the Z-spectrum. At 3T, because of this coalescence and increased interference of direct water saturation and magnetization transfer contrast, the DGE effect can be assessed over a broad range of saturation frequencies. Multislice DGE experiments were performed in vivo using a B1 of 1.6 µT and a tsat of 1 second, leading to a small glucoCEST DGE effect at an offset frequency of 2 ppm from the water resonance. Motion correction was essential to detect DGE effects reliably.CONCLUSION: Multislice glucoCEST-based DGE experiments can be performed at 3T with sufficient temporal resolution. However, the effects are small and prone to motion influence. Therefore, motion correction should be used when performing DGE experiments at clinical field strengths.
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| 6. |
- Xu, Xiang, et al.
(author)
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Dynamic Glucose-Enhanced (DGE) MRI: Translation to Human Scanning and First Results in Glioma Patients.
- 2015
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In: Tomography : a journal for imaging research. - : MDPI AG. - 2379-1381. ; 1:2, s. 105-114
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Journal article (peer-reviewed)abstract
- Recent animal studies have shown that D-glucose is a potential biodegradable MRI contrast agent for imaging glucose uptake in tumors. Here, we show the first translation of that use of D-glucose to human studies. Chemical exchange saturation transfer (CEST) MRI at a single frequency offset optimized for detection of hydroxyl protons in D-glucose (glucoCEST) was used to image dynamic signal changes in the human brain at 7T during and after infusion of D-glucose. Dynamic glucose-enhanced (DGE) image data from four normal volunteers and three glioma patients showed strong signal enhancement in blood vessels, while the enhancement varied spatially over the tumor. Areas of enhancement differed spatially between DGE and conventional Gd-enhanced imaging, suggesting complementary image information content for these two types of agents. In addition, different tumor areas enhanced with D-glucose at different times post-infusion, suggesting a sensitivity to perfusion-related properties such as substrate delivery and blood-brain barrier (BBB) permeability. These preliminary results suggest that DGE MRI is feasible to study glucose uptake in humans, providing a time-dependent set of data that contains information regarding arterial input function (AIF), tissue perfusion, glucose transport across the BBB and cell membrane, and glucose metabolism.
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