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Alan Connelly - One of the best experts on this subject based on the ideXlab platform.
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perfusion precision in Bolus Tracking mri estimation using the wild bootstrap method
Magnetic Resonance in Medicine, 2009Co-Authors: Fernando Calamante, Alan ConnellyAbstract:Bolus-Tracking MRI involves the Bolus injection of contrast agent, and the resultant concentration time course can be used to calculate perfusion by deconvolution analysis. However, most deconvolution methods do not provide a measure of precision. Precision could be estimated from many repeated measurements; however, this would involve a series of successive Bolus injections, which is not a feasible option in practice due to contrast agent dose constraints. In this work, a method is presented to estimate precision in Bolus-Tracking MRI using the wild-bootstrap method. This approach is able to estimate the uncertainty in perfusion measurements from the data acquired during a single Bolus of contrast agent injection. The methodology was assessed using numerical simulations and applied to real data with a range of image qualities. The method is shown to provide useful estimates of precision, and the results from real data were consistent with the underlying MRI data quality. The methodology provides an important complementary tool in clinical and research applications of Bolus-Tracking MRI.
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minimising the effects of Bolus dispersion in Bolus Tracking mri
NMR in Biomedicine, 2008Co-Authors: Lisa Willats, Alan Connelly, Fernando CalamanteAbstract:Bolus-Tracking perfusion measurements in patients with vascular abnormalities are often unreliable, because delay and/or dispersion of the Bolus within the vessels distorts the measured arterial input function (AIF). Erroneous measurements of perfusion can be identified by examining the measured response function, the shape of which is determined by both the tissue and arterial retention. In this work, an accurate response function is extracted by combining maximum-likelihood expectation-maximisation deconvolution, regularised using an oscillation index, with subsequent wavelet thresholding. Simulations show that this method recovers both the smooth-dispersed and the sharp-delayed response functions. This enables regions where the Bolus is delayed and/or dispersed to be identified when the methodology is applied to data from patients with vascular abnormalities. Simulations also demonstrate robust and accurate perfusion estimates when there is no Bolus delay and/or dispersion. The presence of delay and/or dispersion in the response function suggests that the perfusion measurements are erroneous, and that the global AIF is an inaccurate approximation to the true AIF in these regions. Perfusion measurements are corrected within the affected regions by defining a regional AIF from the independent component analysis of the dynamic susceptibility contrast MRI data. The regional AIF is shown to remove the delay and dispersion, improving the accuracy of the perfusion maps. Copyright © 2008 John Wiley & Sons, Ltd.
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quantification of Bolus Tracking mri improved characterization of the tissue residue function using tikhonov regularization
Magnetic Resonance in Medicine, 2003Co-Authors: Fernando Calamante, David G Gadian, Alan ConnellyAbstract:Quantification of cerebral blood flow (CBF) and the tissue residue function (R) using Bolus-Tracking MRI requires deconvolution of the arterial input function (AIF). Currently, the most commonly used deconvolution method is singular value decomposition (SVD), which has been shown to produce accurate estimations of CBF. However, this method introduces unwanted oscillations in the time course of R, and there are situations in which the actual shape is of interest (e.g., in calculating flow heterogeneity and assessing Bolus dispersion). In such cases, the conventional SVD method may no longer be suitable, and an alternative approach may be required. This work describes the implementation of Tikhonov regularization with the L-curve criterion to quantify CBF and obtain a better characterization of R. The methodology is tested on simulated and patient data, and the results are compared to those found using the conventional SVD approach. Although both methods produce similar CBF values, the deconvolved R shape obtained using SVD is dominated by oscillations and fails to characterize the shape in the presence of dispersion. On the other hand, the use of the proposed regularization method improves the characterization of the tissue residue function.
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quantification of perfusion using Bolus Tracking magnetic resonance imaging in stroke assumptions limitations and potential implications for clinical use
Stroke, 2002Co-Authors: Fernando Calamante, David G Gadian, Alan ConnellyAbstract:Background — MR techniques have been very powerful in providing indicators of tissue perfusion, particularly in studies of cerebral ischemia. There is considerable interest in performing absolute perfusion measurements, with the aim of improving the characterization of tissue “at risk” of stroke. However, some important caveats relating to absolute measurements need to be taken into account. The purpose of this article is to discuss some of the issues involved and the potential implications for absolute cerebral blood flow measurements in clinical use. Summary of Comment — In Bolus Tracking MRI, deconvolution of the concentration-time course can in theory provide accurate quantification. However, there are several important assumptions in the tracer kinetic model used, some of which may be invalid in cerebral ischemia. These can introduce significant errors in perfusion quantification. Conclusions — Although we believe that Bolus Tracking MRI is a powerful technique for the evaluation of perfusion in cerebral ischemia, interpretation of perfusion maps requires caution; this is particularly true when absolute quantification is attempted. Work is currently under way in a number of centers to address these problems, and with appropriate modeling they may be overcome in the future. In the interim, we believe that it is necessary for users of Bolus Tracking perfusion data to be aware of the current technical limitations if they are to avoid misinterpretation or overinterpretation of their findings.
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is quantification of Bolus Tracking mri reliable without deconvolution
Magnetic Resonance in Medicine, 2002Co-Authors: Joanna E Perthen, Fernando Calamante, David G Gadian, Alan ConnellyAbstract:Bolus Tracking data obtained with paramagnetic intravascular tracers are commonly analyzed and quantified by the direct measurement of properties of the tissue concentration-time curve (e.g., time to peak (TTP)). The measurement of these “summary parameters” is used as an accessible alternative approach to the complex deconvolution procedure, and provides indirect measures of perfusion. However, summary parameters do not take into account differences in arterial input functions (AIFs) or residue functions (R(t)) between patients or studies. Simulations were performed to assess the variability of summary parameters over a realistic range of AIFs and for differing R(t), to establish whether they can be used as reliable measures of tissue perfusion status. Results showed that the value of each summary parameter investigated is highly dependent upon both the AIF and R(t). The referencing of summary parameters to their corresponding value in the AIF or in normal tissue is a method commonly used to normalize results, but this approach did not lead to any measures that were independent of both the AIF and R(t) in this study. The results presented here show that the use of summary parameters requires considerable caution, since tissue or patient types can easily be incorrectly classified due to the effect of variations in patient AIF and R(t). Magn Reson Med 47:61‐67, 2002. © 2002 Wiley-Liss, Inc.
Leif Ostergaard - One of the best experts on this subject based on the ideXlab platform.
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inferring origin of vascular supply from tracer arrival timing patterns using Bolus Tracking mri
Journal of Magnetic Resonance Imaging, 2008Co-Authors: Soren Christensen, Stephen M Davis, Fernando Calamante, Niels Hjort, Anne Dorte Blankholm, Patricia Desmond, Leif OstergaardAbstract:Purpose To investigate the potential of novel postprocessing and visualization techniques to distinguish presence of collateral flow using Bolus Tracking MRI. Collateral blood supply is believed to be of paramount importance in acute stroke, yet clinical evaluation is challenging as the gold standard digital subtraction angiography is often not feasible in the acute scenario. Materials and Methods In principle, Bolus arrival delay data contains information about the route of blood supply into tissue and hereby presence of collateral flow patterns. We first examined the potential of current clinical Bolus Tracking protocols to accurately characterize Bolus arrival delay. Using the simulation results, we analyzed Bolus Tracking data from one normal volunteer and one acute stroke patient. Results The Bolus arrival patterns in the volunteer and in the normal hemisphere of the patient were found to be qualitatively similar and in good agreement with physiology. The Bolus was seen to spread from the larger arteries toward the periphery. The stroke hemisphere in the patient indicated a retrograde direction of flow on the cortical mantle consistent with leptomeningeal vessels. Conclusion Bolus Tracking MRI can likely be used to distinguish collateral flow patterns from normal flow patterns. J. Magn. Reson. Imaging 2008;27:1371–1381. © 2008 Wiley-Liss, Inc.
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principles of cerebral perfusion imaging by Bolus Tracking
Journal of Magnetic Resonance Imaging, 2005Co-Authors: Leif OstergaardAbstract:The principles of cerebral perfusion imaging by the method of dynamic susceptibility contrast magnetic resonance imaging (DSC-MRI) (Bolus Tracking) are described. The MRI signals underlying DSC-MRI are discussed. Tracer kinetics procedures are defined to calculate images of cerebral blood volume (CBV), cerebral blood flow (CBF), and mean transit time (MTT). Two general categories of numerical procedures are reviewed for deriving CBF from the residue function. Procedures that involve deconvolution, such as Fourier deconvolution or singular value decomposition (SVD), are classified as model-independent methods because they do not require a model of the microvascular hemodynamics. Those methods in principle also yield a measure of the tissue impulse response function and the residue function, from which microvascular hemodynamics can be characterized. The second category of methods is the model-dependent methods, which use models of tracer transport and retention in the microvasculature. These methods do not yield independent measures of the residue function and may introduce bias when the physiology does not follow the model. Statistical methods are sometimes used, which involve treating the residue function as a deconvolution kernel and optimizing (fitting) the kernel from the experimental data using procedures such as maximum likelihood. Finally, other hemodynamic indices that can be measured from DSC-MRI data are described.
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cerebral perfusion imaging by Bolus Tracking
Topics in Magnetic Resonance Imaging, 2004Co-Authors: Leif OstergaardAbstract:Cerebral perfusion may be visualized by the dynamic imaging of an intravenously injected Bolus (a few milliliters) of clinically approved gadolinium-containing contrast media. During its passage through the vasculature of the brain, the contrast agent induces magnetic field disturbances, which can be seen as signal loss on appropriately weighted dynamic MRI. This article deals with the quantitative analysis of such signal changes, first in terms of tracer concentration and then, via the mathematical approach of deconvolution, in terms of tissue microvascular physiology, culminating in quantitative estimates on a pixel-by-pixel basis of physiologic parameters, such as cerebral blood volume, mean transit time, and cerebral blood flow.
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comparison of gradient and spin echo imaging cbf cbv and mtt measurements by Bolus Tracking
Journal of Magnetic Resonance Imaging, 2000Co-Authors: Claus Z Simonsen, Leif Ostergaard, Peter Vestergaardpoulsen, Donald F Smith, Carsten GyldenstedAbstract:The authors measured cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT) in pigs by gadodiamide Bolus injections and the Bolus Tracking technique. Two different pulse sequences were applied and compared: gradient-echo (GE) and spin-echo (SE) echoplanar imaging (EPI). After normalization of CBF and CBV values to the area under the arterial input function (AIF), a linear relation between the two methods was found, suggesting that a previous normalization approach for determining absolute CBF by SE EPI may be extended to GE EPI measurements. The ratio between CBV values measured with GE and SE [CBV (GE)/CBV (SE)] was 2.96. Assuming that the GE acquisition reflects total CBV, our findings suggest that SE is sensitive to 34% (1/2.96) of the total vasculature. The corresponding ratio for CBF was 2.53. There was no significant difference in these two ratios, suggesting that MTT estimates derived from GE and SE EPI measurements are comparable. The findings suggest that SE and GE are equally useful in clinical measurements of functional parameters such as CBF, CBV, and MTT in the brain. J. Magn. Reson. Imaging 2000;12:411-416.
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cerebral blood flow and blood volume measured by magnetic resonance imaging Bolus Tracking after acute stroke in pigs comparison with 15 o h 2 o positron emission tomography
Stroke, 2000Co-Authors: Masaharu Sakoh, Carsten Gyldensted, Lisbeth Rohl, Albert Gjedde, Leif OstergaardAbstract:Background and Purpose—Early and accurate assessments of cerebral ischemia allow therapy to be tailored to individual stroke patients. We examined the feasibility of using a novel method for measuring cerebral blood flow (CBF) of ischemic tissue based on MRI after middle cerebral artery occlusion (MCAO). Moreover, the regional correlations between CBF and cerebral blood volume (CBV) were investigated in the regions with acute ischemic stroke. Methods—CBF and CBV were measured before and after MCAO or reperfusion by positron emission tomography (PET) in 13 pigs. Just after the PET scans, CBF and CBV were measured by MR Bolus Tracking and were compared with results obtained by PET at 6 hours after permanent MCAO or reperfusion. The infarction was verified histologically. Results—The MR method yielded parametric CBF and CBV maps with tissue contrast in good agreement with parametric PET images, which demonstrated hypoperfused and hyperperfused areas after MCAO or reperfusion. Both MRI and PET technology show...
Fernando Calamante - One of the best experts on this subject based on the ideXlab platform.
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perfusion precision in Bolus Tracking mri estimation using the wild bootstrap method
Magnetic Resonance in Medicine, 2009Co-Authors: Fernando Calamante, Alan ConnellyAbstract:Bolus-Tracking MRI involves the Bolus injection of contrast agent, and the resultant concentration time course can be used to calculate perfusion by deconvolution analysis. However, most deconvolution methods do not provide a measure of precision. Precision could be estimated from many repeated measurements; however, this would involve a series of successive Bolus injections, which is not a feasible option in practice due to contrast agent dose constraints. In this work, a method is presented to estimate precision in Bolus-Tracking MRI using the wild-bootstrap method. This approach is able to estimate the uncertainty in perfusion measurements from the data acquired during a single Bolus of contrast agent injection. The methodology was assessed using numerical simulations and applied to real data with a range of image qualities. The method is shown to provide useful estimates of precision, and the results from real data were consistent with the underlying MRI data quality. The methodology provides an important complementary tool in clinical and research applications of Bolus-Tracking MRI.
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minimising the effects of Bolus dispersion in Bolus Tracking mri
NMR in Biomedicine, 2008Co-Authors: Lisa Willats, Alan Connelly, Fernando CalamanteAbstract:Bolus-Tracking perfusion measurements in patients with vascular abnormalities are often unreliable, because delay and/or dispersion of the Bolus within the vessels distorts the measured arterial input function (AIF). Erroneous measurements of perfusion can be identified by examining the measured response function, the shape of which is determined by both the tissue and arterial retention. In this work, an accurate response function is extracted by combining maximum-likelihood expectation-maximisation deconvolution, regularised using an oscillation index, with subsequent wavelet thresholding. Simulations show that this method recovers both the smooth-dispersed and the sharp-delayed response functions. This enables regions where the Bolus is delayed and/or dispersed to be identified when the methodology is applied to data from patients with vascular abnormalities. Simulations also demonstrate robust and accurate perfusion estimates when there is no Bolus delay and/or dispersion. The presence of delay and/or dispersion in the response function suggests that the perfusion measurements are erroneous, and that the global AIF is an inaccurate approximation to the true AIF in these regions. Perfusion measurements are corrected within the affected regions by defining a regional AIF from the independent component analysis of the dynamic susceptibility contrast MRI data. The regional AIF is shown to remove the delay and dispersion, improving the accuracy of the perfusion maps. Copyright © 2008 John Wiley & Sons, Ltd.
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inferring origin of vascular supply from tracer arrival timing patterns using Bolus Tracking mri
Journal of Magnetic Resonance Imaging, 2008Co-Authors: Soren Christensen, Stephen M Davis, Fernando Calamante, Niels Hjort, Anne Dorte Blankholm, Patricia Desmond, Leif OstergaardAbstract:Purpose To investigate the potential of novel postprocessing and visualization techniques to distinguish presence of collateral flow using Bolus Tracking MRI. Collateral blood supply is believed to be of paramount importance in acute stroke, yet clinical evaluation is challenging as the gold standard digital subtraction angiography is often not feasible in the acute scenario. Materials and Methods In principle, Bolus arrival delay data contains information about the route of blood supply into tissue and hereby presence of collateral flow patterns. We first examined the potential of current clinical Bolus Tracking protocols to accurately characterize Bolus arrival delay. Using the simulation results, we analyzed Bolus Tracking data from one normal volunteer and one acute stroke patient. Results The Bolus arrival patterns in the volunteer and in the normal hemisphere of the patient were found to be qualitatively similar and in good agreement with physiology. The Bolus was seen to spread from the larger arteries toward the periphery. The stroke hemisphere in the patient indicated a retrograde direction of flow on the cortical mantle consistent with leptomeningeal vessels. Conclusion Bolus Tracking MRI can likely be used to distinguish collateral flow patterns from normal flow patterns. J. Magn. Reson. Imaging 2008;27:1371–1381. © 2008 Wiley-Liss, Inc.
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quantification of Bolus Tracking mri improved characterization of the tissue residue function using tikhonov regularization
Magnetic Resonance in Medicine, 2003Co-Authors: Fernando Calamante, David G Gadian, Alan ConnellyAbstract:Quantification of cerebral blood flow (CBF) and the tissue residue function (R) using Bolus-Tracking MRI requires deconvolution of the arterial input function (AIF). Currently, the most commonly used deconvolution method is singular value decomposition (SVD), which has been shown to produce accurate estimations of CBF. However, this method introduces unwanted oscillations in the time course of R, and there are situations in which the actual shape is of interest (e.g., in calculating flow heterogeneity and assessing Bolus dispersion). In such cases, the conventional SVD method may no longer be suitable, and an alternative approach may be required. This work describes the implementation of Tikhonov regularization with the L-curve criterion to quantify CBF and obtain a better characterization of R. The methodology is tested on simulated and patient data, and the results are compared to those found using the conventional SVD approach. Although both methods produce similar CBF values, the deconvolved R shape obtained using SVD is dominated by oscillations and fails to characterize the shape in the presence of dispersion. On the other hand, the use of the proposed regularization method improves the characterization of the tissue residue function.
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quantification of perfusion using Bolus Tracking magnetic resonance imaging in stroke assumptions limitations and potential implications for clinical use
Stroke, 2002Co-Authors: Fernando Calamante, David G Gadian, Alan ConnellyAbstract:Background — MR techniques have been very powerful in providing indicators of tissue perfusion, particularly in studies of cerebral ischemia. There is considerable interest in performing absolute perfusion measurements, with the aim of improving the characterization of tissue “at risk” of stroke. However, some important caveats relating to absolute measurements need to be taken into account. The purpose of this article is to discuss some of the issues involved and the potential implications for absolute cerebral blood flow measurements in clinical use. Summary of Comment — In Bolus Tracking MRI, deconvolution of the concentration-time course can in theory provide accurate quantification. However, there are several important assumptions in the tracer kinetic model used, some of which may be invalid in cerebral ischemia. These can introduce significant errors in perfusion quantification. Conclusions — Although we believe that Bolus Tracking MRI is a powerful technique for the evaluation of perfusion in cerebral ischemia, interpretation of perfusion maps requires caution; this is particularly true when absolute quantification is attempted. Work is currently under way in a number of centers to address these problems, and with appropriate modeling they may be overcome in the future. In the interim, we believe that it is necessary for users of Bolus Tracking perfusion data to be aware of the current technical limitations if they are to avoid misinterpretation or overinterpretation of their findings.
Michael E Kelly - One of the best experts on this subject based on the ideXlab platform.
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mdma ecstasy increases cerebral cortical perfusion determined by Bolus Tracking arterial spin labelling btasl mri
British Journal of Pharmacology, 2013Co-Authors: J Rouine, Oliviero L Gobbo, Matthew Campbell, Valentina Gigliucci, I Ogden, Mchugh K Smith, P Duffy, Brendan Behan, D Byrne, Michael E KellyAbstract:Background and Purpose The purpose of this study was to assess cerebral perfusion changes following systemic administration of the recreational drug 3,4-methylendioxymethamphetamine (MDMA ‘ecstasy’) to rats. Experimental Approach Cerebral perfusion was quantified using Bolus-Tracking arterial spin labelling (btASL) MRI. Rats received MDMA (20 mg·kg−1; i.p.) and were assessed 1, 3 or 24 h later. Rats received MDMA (5 or 20 mg·kg−1; i.p.) and were assessed 3 h later. In addition, rats received MDMA (5 or 10 mg·kg−1; i.p.) or saline four times daily over 2 consecutive days and were assessed 8 weeks later. Perfusion-weighted images were generated in a 7 tesla (7T) MRI scanner and experimental data was fitted to a quantitative model of cerebral perfusion to generate mean transit time (MTT), capillary transit time (CTT) and signal amplitude. Key Results MDMA reduces MTT and CTT and increases amplitude in somatosensory and motor cortex 1 and 3 h following administration, indicative of an increase in perfusion. Prior exposure to MDMA provoked a long-term reduction in cortical 5-HT concentration, but did not produce a sustained effect on cerebral cortical perfusion. The response to acute MDMA challenge (20 mg·kg−1; i.p.) was attenuated in these animals indicating adaptation in response to prior MDMA exposure. Conclusions and Implications MDMA provokes changes in cortical perfusion, which are quantifiable by btASL MRI, a neuroimaging tool with translational potential. Future studies are directed towards elucidation of the mechanisms involved and correlating changes in cerebrovascular function with potential behavioural deficits associated with drug use.
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quantitative functional magnetic resonance imaging of brain activity using Bolus Tracking arterial spin labeling
Journal of Cerebral Blood Flow and Metabolism, 2010Co-Authors: Michael E Kelly, Christoph W Blau, K M Griffin, Oliviero L Gobbo, James F X Jones, Christian KerskensAbstract:Blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) is the most widely used method for mapping neural activity in the brain. The interpretation of altered BOLD signals is problematic when cerebral blood flow (CBF) or cerebral blood volume change because of aging and/or neurodegenerative diseases. In this study, a recently developed quantitative arterial spin labeling (ASL) approach, Bolus-Tracking ASL (btASL), was applied to an fMRI experiment in the rat brain. The mean transit time (MTT), capillary transit time (CTT), relative cerebral blood volume of labeled water (rCBVlw), relative cerebral blood flow (rCBF), and perfusion coefficient in the forelimb region of the somatosensory cortex were quantified during neuronal activation and in the resting state. The average MTT and CTT were 1.939±0.175 and 1.606±0.106 secs, respectively, in the resting state. Both times decreased significantly to 1.616±0.207 and 1.305±0.201 secs, respectively, during activation. The rCBVlw, rCBF, and perfusion coefficient increased on average by a factor of 1.123±0.006, 1.353±0.078, and 1.479±0.148, respectively, during activation. In contrast to BOLD techniques, btASL yields physiologically relevant indices of the functional hyperemia that accompanies neuronal activation.
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Bolus Tracking arterial spin labelling theoretical and experimental results
Physics in Medicine and Biology, 2009Co-Authors: Michael E Kelly, Christoph W Blau, Christian KerskensAbstract:Arterial spin labelling (ASL) is a magnetic resonance imaging (MRI) technique that can be used to provide a quantitative assessment of cerebral perfusion. Despite the development of a number of theoretical models to facilitate quantitative ASL, some key challenges still remain. The purpose of this study is to develop a novel quantitative ASL method based on a macroscopic model that reduces the number of variables required to describe the physiological processes involved. To this end, a novel Fokker?Planck equation consisting of stochastically varying macroscopic variables was derived from a general Langevin equation. ASL data from the rat brain was acquired using a Bolus-Tracking ASL protocol where a Bolus of labelled spins flowing from an inversion plane in the neck into an imaging plane in the brain can be observed. Bolus durations of 1.5 s, 2.0 s and 3.0 s were used and the solution to the Fokker?Planck equation for the boundary conditions of Bolus-Tracking ASL was fitted to the experimental data using a least-squares fit. The mean transit time (MTT) and capillary transit time (CTT) were calculated from the first and second moments of the resultant curve respectively and the arterial transit time (ATT) was calculated by subtracting the CTT from the MTT. The average MTT, CTT and ATT values were 1.75 ? 0.22 s, 1.43 ? 0.12 s and 0.32 ? 0.04 s respectively. In conclusion, a new ASL protocol has been developed by combining the theoretical model with ASL experiments. The technique has the unique ability to provide solutions for varying Bolus volumes and the generality of the new model is demonstrated by the derivation of additional solutions for the continuous and pulsed ASL (CASL and PASL) techniques.
Peder E Z Larson - One of the best experts on this subject based on the ideXlab platform.
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a regional Bolus Tracking and real time b _1 calibration method for hyperpolarized 13 c mri
arXiv: Medical Physics, 2020Co-Authors: Shuyu Tang, Robert Bok, Daniel B Vigneron, Eugene Milshteyn, Galen D Reed, Jeremy W Gordon, Xucheng Zhu, Zihan Zhu, Peder E Z LarsonAbstract:Purpose: Acquisition timing and B$_1$ calibration are two key factors that affect the quality and accuracy of hyperpolarized $^{13}$C MRI. The goal of this project was to develop a new approach using regional Bolus Tracking to trigger Bloch-Siegert B$_1$ mapping and real-time B$_1$ calibration based on regional B$_1$ measurements, followed by dynamic imaging of hyperpolarized $^{13}C$ metabolites in vivo. Methods: The proposed approach was implemented on a system which allows real-time data processing and real-time control on the sequence. Real-time center frequency calibration upon the Bolus arrival was also added. The feasibility of applying the proposed framework for in vivo hyperpolarized $^{13}$C imaging was tested on healthy rats, tumor-bearing mice and a healthy volunteer on a clinical 3T scanner following hyperpolarized [1-$^{13}$C]pyruvate injection. Multichannel receive coils were used in the human study. Results: Automatic acquisition timing based on either regional Bolus peak or Bolus arrival was achieved with the proposed framework. Reduced blurring artifacts in real-time reconstructed images were observed with real-time center frequency calibration. Real-time computed B$_1$ scaling factors agreed with real-time acquired B$_1$ maps. Flip angle correction using B$_1$ maps results in a more consistent quantification of metabolic activity (i.e, pyruvate-to-lactate conversion, k$_{PL}$). Experiment recordings are provided to demonstrate the real-time actions during the experiment. Conclusion: The proposed method was successfully demonstrated on animals and a human volunteer, and is anticipated to improve the efficient use of the hyperpolarized signal as well as the accuracy and robustness of hyperpolarized $^{13}$C imaging.
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a regional Bolus Tracking and real time b 1 calibration method for hyperpolarized 13 c mri
Magnetic Resonance in Medicine, 2019Co-Authors: Shuyu Tang, Robert Bok, Daniel B Vigneron, Eugene Milshteyn, Galen D Reed, Jeremy W Gordon, Xucheng Zhu, Zihan Zhu, Peder E Z LarsonAbstract:Author(s): Tang, Shuyu; Milshteyn, Eugene; Reed, Galen; Gordon, Jeremy; Bok, Robert; Zhu, Xucheng; Zhu, Zihan; Vigneron, Daniel B; Larson, Peder EZ | Abstract: PurposeAcquisition timing and B1 calibration are two key factors that affect the quality and accuracy of hyperpolarized 13 C MRI. The goal of this project was to develop a new approach using regional Bolus Tracking to trigger Bloch-Siegert B1 mapping and real-time B1 calibration based on regional B1 measurements, followed by dynamic imaging of hyperpolarized 13 C metabolites in vivo.MethodsThe proposed approach was implemented on a system which allows real-time data processing and real-time control on the sequence. Real-time center frequency calibration upon the Bolus arrival was also added. The feasibility of applying the proposed framework for in vivo hyperpolarized 13 C imaging was tested on healthy rats, tumor-bearing mice and a healthy volunteer on a clinical 3T scanner following hyperpolarized [1-13 C]pyruvate injection. Multichannel receive coils were used in the human study.ResultsAutomatic acquisition timing based on either regional Bolus peak or Bolus arrival was achieved with the proposed framework. Reduced blurring artifacts in real-time reconstructed images were observed with real-time center frequency calibration. Real-time computed B1 scaling factors agreed with real-time acquired B1 maps. Flip angle correction using B1 maps results in a more consistent quantification of metabolic activity (i.e, pyruvate-to-lactate conversion, kPL ). Experiment recordings are provided to demonstrate the real-time actions during the experiment.ConclusionsThe proposed method was successfully demonstrated on animals and a human volunteer, and is anticipated to improve the efficient use of the hyperpolarized signal as well as the accuracy and robustness of hyperpolarized 13 C imaging.
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a 2drf pulse sequence for Bolus Tracking in hyperpolarized 13c imaging
Magnetic Resonance in Medicine, 2015Co-Authors: Shuyu Tang, Wenwen Jiang, Hsinyu Chen, Robert Bok, Daniel B Vigneron, Peder E Z LarsonAbstract:Purpose A novel application of two-dimensional (2D) spatially selective radiofrequency (2DRF) excitation pulses in hyperpolarized imaging is proposed for monitoring the Bolus injection with highly efficient sampling of the initially polarized substrate, thus leaving more polarization available for detection of the subsequently generated metabolic products. Methods A 2DRF pulse was designed with a spiral trajectory and conventional clinical gradient performance. To demonstrate the ability of our 2DRF Bolus Tracking pulse sequence, hyperpolarized [1- ]pyruvate in vivo imaging experiments were performed in normal rats, with a comparison to 1DRF excitation pulses. Results Our designed 2DRF pulse was able to rapidly and efficiently monitor the injected Bolus dynamics in vivo, with an 8-fold enhanced time resolution in comparison with 1DRF in our experimental settings. When applied at the pyruvate frequency for Bolus Tracking, our 2DRF pulse demonstrated reduced saturation of the hyperpolarization for the substrate and metabolic products compared to a 1DRF pulse, while being immune to ±0.5 ppm magnetic field inhomogeneity at 3T. Conclusion 2DRF pulses in hyperpolarized imaging can be used to efficiently monitor the Bolus injection with reduced hyperpolarization saturation compared to 1DRF pulses. The parameters of our design are based on clinical scanner limits, which allows for rapid translation to human studies. Magn Reson Med 74:506–512, 2015. © 2014 Wiley Periodicals, Inc.