المؤلفون: Ece Su Sayin, Olivia Sobczyk, Julien Poublanc, David J. Mikulis, Joseph A. Fisher, James Duffin

المصدر: Frontiers in Physiology, Vol 14 (2023)

مصطلحات موضوعية: transfer function analysis, transient hypoxia, MRI, BOLD = blood oxygen level dependent, contrast agents, brain, Physiology, QP1-981

الوصف: Introduction: Use of contrast in determining hemodynamic measures requires the deconvolution of an arterial input function (AIF) selected over a voxel in the middle cerebral artery to calculate voxel wise perfusion metrics. Transfer function analysis (TFA) offers an alternative analytic approach that does not require identifying an AIF. We hypothesised that TFA metrics Gain, Lag, and their ratio, Gain/Lag, correspond to conventional AIF resting perfusion metrics relative cerebral blood volume (rCBV), mean transit time (MTT) and relative cerebral blood flow (rCBF), respectively.Methods: 24 healthy participants (17 M) and 1 patient with steno-occlusive disease were recruited. We used non-invasive transient hypoxia-induced deoxyhemoglobin as an MRI contrast. TFA and conventional AIF analyses were used to calculate averages of whole brain and smaller regions of interest.Results: Maps of these average metrics had colour scales adjusted to enhance contrast and identify areas of high congruence. Regional gray matter/white matter (GM/WM) ratios for MTT and Lag, rCBF and Gain/Lag, and rCBV and Gain were compared. The GM/WM ratios were greater for TFA metrics compared to those from AIF analysis indicating an improved regional discrimination.Discussion: Resting perfusion measures generated by The BOLD analysis resulting from a transient hypoxia induced variations in deoxyhemoglobin analyzed by TFA are congruent with those analyzed by conventional AIF analysis.

وصف الملف: electronic resource

العلاقة: https://www.frontiersin.org/articles/10.3389/fphys.2023.1167857/fullTest; https://doaj.org/toc/1664-042XTest

الوصول الحر: https://doaj.org/article/7301816458004c009d79cb51b09b77e4Test

المؤلفون: Jacob Benjamin Schulman, Ece Su Sayin, Angelica Manalac, Julien Poublanc, Olivia Sobczyk, James Duffin, Joseph A. Fisher, David Mikulis, Kâmil Uludağ

المصدر: Frontiers in Neuroimaging, Vol 2 (2023)

مصطلحات موضوعية: perfusion, DSC, gadolinium, simulations, deoxyhemoglobin, Neurology. Diseases of the nervous system, RC346-429

الوصف: IntroductionDynamic susceptibility contrast (DSC) MRI allows clinicians to determine perfusion parameters in the brain, such as cerebral blood flow, cerebral blood volume, and mean transit time. To enable quantification, susceptibility changes can be induced using gadolinium (Gd) or deoxyhemoglobin (dOHb), the latter just recently introduced as a contrast agent in DSC. Previous investigations found that experimental parameters and analysis choices, such as the susceptibility amplitude and partial volume, affect perfusion quantification. However, the accuracy and precision of DSC MRI has not been systematically investigated, particularly in the lower susceptibility range.MethodsIn this study, we compared perfusion values determined using Gd with values determined using a contrast agent with a lower susceptibility—dOHb—under different physiological conditions, such as varying the baseline blood oxygenation and/or magnitude of hypoxic bolus, by utilizing numerical simulations and conducting experiments on healthy subjects at 3T. The simulation framework we developed for DSC incorporates MRI signal contributions from intravascular and extravascular proton spins in arterial, venous, and cerebral tissue voxels. This framework allowed us to model the MRI signal in response to both Gd and dOHb.Results and discussionWe found, both in the experimental results and simulations, that a reduced intravascular volume of the selected arterial voxel, reduced baseline oxygen saturation, greater susceptibility of applied contrast agent (Gd vs. dOHb), and/or larger magnitude of applied hypoxic bolus reduces the overestimation and increases precision of cerebral blood volume and flow. As well, we found that normalizing tissue to venous rather than arterial signal increases the accuracy of perfusion quantification across experimental paradigms. Furthermore, we found that shortening the bolus duration increases the accuracy and reduces the calculated values of mean transit time. In summary, we experimentally uncovered an array of perfusion quantification dependencies, which agreed with the simulation framework predictions, using a wider range of susceptibility values than previously investigated. We argue for caution when comparing absolute and relative perfusion values within and across subjects obtained from a standard DSC MRI analysis, particularly when employing different experimental paradigms and contrast agents.

وصف الملف: electronic resource

العلاقة: https://www.frontiersin.org/articles/10.3389/fnimg.2023.1048652/fullTest; https://doaj.org/toc/2813-1193Test

الوصول الحر: https://doaj.org/article/ce71c70ddd594426a2ccf68897f08e29Test

المؤلفون: Yashesh Dasari, James Duffin, Ece Su Sayin, Harrison T. Levine, Julien Poublanc, Andrea E. Para, David J. Mikulis, Joseph A. Fisher, Olivia Sobczyk, Mir Behrad Khamesee

المصدر: Healthcare, Vol 11, Iss 16, p 2231 (2023)

مصطلحات موضوعية: blood oxygenation level-dependent magnetic resonance imaging (BOLD-MRI), cerebrovascular reactivity (CVR), convolutional neural networks (CNNs), deep learning, medical image analysis, steno-occlusive disease (SOD), Medicine

الوصف: Cerebrovascular Reactivity (CVR) is a provocative test used with Blood oxygenation level-dependent (BOLD) Magnetic Resonance Imaging (MRI) studies, where a vasoactive stimulus is applied and the corresponding changes in the cerebral blood flow (CBF) are measured. The most common clinical application is the assessment of cerebral perfusion insufficiency in patients with steno-occlusive disease (SOD). Globally, millions of people suffer from cerebrovascular diseases, and SOD is the most common cause of ischemic stroke. Therefore, CVR analyses can play a vital role in early diagnosis and guiding clinical treatment. This study develops a convolutional neural network (CNN)-based clinical decision support system to facilitate the screening of SOD patients by discriminating between healthy and unhealthy CVR maps. The networks were trained on a confidential CVR dataset with two classes: 68 healthy control subjects, and 163 SOD patients. This original dataset was distributed in a ratio of 80%-10%-10% for training, validation, and testing, respectively, and image augmentations were applied to the training and validation sets. Additionally, some popular pre-trained networks were imported and customized for the objective classification task to conduct transfer learning experiments. Results indicate that a customized CNN with a double-stacked convolution layer architecture produces the best results, consistent with expert clinical readings.

وصف الملف: electronic resource

العلاقة: https://www.mdpi.com/2227-9032/11/16/2231Test; https://doaj.org/toc/2227-9032Test

الوصول الحر: https://doaj.org/article/3bf494d5c4d945f4914ba3d42a516cf0Test

المؤلفون: Vittorio Stumpo, Ece Su Sayin, Jacopo Bellomo, Christian Hendriik Bas van Niftrik, Martina Sebök, Olivia Sobczyk, Julien Poublanc, Joseph Fisher, David Mikulis, Athina Pangalu, Zsolt Kulcsar, Michael Weller, Andrea Bink, Luca Regli, Jorn Fierstra

المصدر: Brain and Spine, Vol 3, Iss , Pp 102173- (2023)

مصطلحات موضوعية: Neurology. Diseases of the nervous system, RC346-429

وصف الملف: electronic resource

العلاقة: http://www.sciencedirect.com/science/article/pii/S2772529423004617Test; https://doaj.org/toc/2772-5294Test

الوصول الحر: https://doaj.org/article/488dc28a955d45ecb25b97b38f148d8eTest

المؤلفون: Alex A. Bhogal, Ece Su Sayin, Julien Poublanc, James Duffin, Joseph A. Fisher, Olivia Sobcyzk, David J. Mikulis

المصدر: NeuroImage, Vol 261, Iss , Pp 119523- (2022)

مصطلحات موضوعية: Hypoxia, Blood arrival time, SAO2 hemodynamics, Vascular, MRI, BOLD, Neurosciences. Biological psychiatry. Neuropsychiatry, RC321-571

الوصف: Cerebral blood arrival and tissue transit times are sensitive measures of the efficiency of tissue perfusion and can provide clinically meaningful information on collateral blood flow status. We exploit the arterial blood oxygen level dependent (BOLD) signal contrast established by precisely decreasing, and then increasing, arterial hemoglobin saturation using respiratory re-oxygenation challenges to quantify arterial blood arrival times throughout the brain. We term this approach the Step Hemoglobin re-Oxygenation Contrast Stimulus (SHOCS). Carpet plot analysis yielded measures of signal onset (blood arrival), global transit time (gTT) and calculations of relative total blood volume. Onset times averaged across 12 healthy subjects were 1.1 ± 0.4 and 1.9 ± 0.6 for cortical gray and deep white matter, respectively. The average whole brain gTT was 4.5 ± 0.9 s. The SHOCS response was 1.7 fold higher in grey versus white matter; in line with known differences in tissue-specific blood volume fraction. SHOCS was also applied in a patient with unilateral carotid artery occlusion revealing ipsilateral prolonged signal onset with normal perfusion in the unaffected hemisphere. We anticipate that SHOCS will further inform on the extent of collateral blood flow in patients with upstream steno-occlusive vascular disease, including those already known to manifest reductions in vasodilatory reserve capacity or vascular steal.

وصف الملف: electronic resource

العلاقة: http://www.sciencedirect.com/science/article/pii/S1053811922006383Test; https://doaj.org/toc/1095-9572Test

الوصول الحر: https://doaj.org/article/a356a5d8dec340f594f0363498ac4fbfTest

المؤلفون: Ece Su Sayin, Olivia Sobczyk, Julien Poublanc, David J. Mikulis, Joseph A. Fisher, Kevin H. M. Kuo, James Duffin

المصدر: Physiological Reports, Vol 10, Iss 19, Pp n/a-n/a (2022)

مصطلحات موضوعية: cerebrovascular reactivity, CO2, sickle cell disease, transfer function analysis, Physiology, QP1-981

الوصف: Abstract In patients with sickle cell disease (SCD), the delivery of oxygen to the brain is compromised by anemia, abnormal rheology, and steno‐occlusive vascular disease. Successful compensation depends on an increase in oxygen supply such as that provided by an increase in cerebral blood flow (CBF). We used magnetic resonance imaging to provide a high‐resolution assessment of the ability of SCD patients to respond to a vasoactive stimulus in middle, anterior, and posterior cerebral artery territories for both white and gray matter. Cerebrovascular reactivity (CVR) was measured as the blood oxygen level dependent signal (a surrogate for CBF) response to an increase in the end tidal partial pressure of CO2 (PETCO2). The dynamic aspect of the response was measured as the time constant of the first order response kinetics (tau). To confirm and support these findings we used an alternative examination of the response, transfer function analysis (TFA), to measure the responsiveness (gain), the speed of response (phase), and the consistency of the response over time (coherence). We tested 34 patients with SCD and compared the results to those of 24 healthy controls participants. The results from a three‐way ANOVA showed that patients with SCD have reduced CVR (p

وصف الملف: electronic resource

العلاقة: https://doaj.org/toc/2051-817XTest

الوصول الحر: https://doaj.org/article/86e3a224da09422f91535b9ccb790851Test

المؤلفون: Stéphanie Forté, Olivia Sobczyk, Julien Poublanc, James Duffin, Gregory M. T. Hare, Joseph Arnold Fisher, David Mikulis, Kevin H. M. Kuo

المصدر: Frontiers in Physiology, Vol 13 (2022)

مصطلحات موضوعية: sickle cell disease (SCD), cerebrovascular reactivity (CVR), cerebrovascular reactivity to carbon dioxide, functional magnetic resonance imaging (fMRI), cerebral hemodynamics, cerebral blood flow (CBF), Physiology, QP1-981

الوصف: Background: Despite increased cerebral blood flow (CBF), cerebral infarcts occur in patients with sickle cell disease (SCD). This suggests increased CBF does not meet metabolic demand possibly due to compromised cerebral vasodilatory response. Hypothesis: In adult SCD patients, cerebrovascular reactivity (CVR) and speed of vasodilatory response (tau) to a standardized vasodilatory stimulus, are reduced compared to normal subjects.Methods: Functional brain imaging performed as part of routine care in adult SCD patients without known large vessel cerebral vasculopathy was reviewed retrospectively. CVR was calculated as the change in CBF measured as the blood-oxygenation-level-dependent (BOLD)-magnetic resonance imaging signal, in response to a standard vasoactive stimulus of carbon dioxide (CO2). The tau corresponding to the best fit between the convolved end-tidal partial pressures of CO2 and BOLD signal was defined as the speed of vascular response. CVR and tau were normalized using a previously generated atlas of 42 healthy controls.Results: Fifteen patients were included. CVR was reduced in grey and white matter (mean Z-score for CVR −0.5 [−1.8 to 0.3] and −0.6 [−2.3 to 0.7], respectively). Tau Z-scores were lengthened in grey and white matter (+0.9 [−0.5 to 3.3] and +0.8 [−0.7 to 2.7], respectively). Hematocrit was the only significant independent predictor of CVR on multivariable regression.Conclusion: Both measures of cerebrovascular health (CVR and tau) in SCD patients were attenuated compared to normal controls. These findings show that CVR represents a promising tool to assess disease state, stroke risk, and therapeutic efficacy of treatments in SCD and merits further investigation.

وصف الملف: electronic resource

العلاقة: https://www.frontiersin.org/articles/10.3389/fphys.2022.886807/fullTest; https://doaj.org/toc/1664-042XTest

الوصول الحر: https://doaj.org/article/bb7c254fe64c4caba2516b42041575b1Test

المؤلفون: Ece Su Sayin, Olivia Sobczyk, Julien Poublanc, David J. Mikulis, Joseph A. Fisher, Kevin H. M. Kuo, James Duffin

المصدر: Frontiers in Physiology, Vol 13 (2022)

مصطلحات موضوعية: sickle cell disease, cerebrovascular reactivity (CVR), hypercapnic stimulus, magnetic resonance imaging, cerebrovascular resistance, Physiology, QP1-981

الوصف: In patients with sickle cell disease (SCD) the delivery of oxygen to the brain is compromised by anemia, abnormal rheology, and steno-occlusive vascular disease. Meeting demands for oxygen delivery requires compensatory features of brain perfusion. The cerebral vasculature’s regulatory function and reserves can be assessed by observing the flow response to a vasoactive stimulus. In a traditional approach we measured voxel-wise change in Blood Oxygen-Level Dependent (BOLD) MRI signal as a surrogate of cerebral blood flow (CBF) in response to a linear progressive ramping of end-tidal partial pressure of carbon dioxide (PETCO2). Cerebrovascular reactivity (CVR) was defined as ΔBOLD/ΔPETCO2. We used a computer model to fit a virtual sigmoid resistance curve to the progressive CBF response to the stimulus, enabling the calculation of resistance parameters: amplitude, midpoint, range response, resistance sensitivity and vasodilatory reserve. The quality of the resistance sigmoid fit was expressed as the r2 of the fit. We tested 35 patients with SCD, as well as 24 healthy subjects to provide an indication of the normal ranges of the resistance parameters. We found that gray matter CVR and resistance amplitude, range, reserve, and sensitivity are reduced in patients with SCD compared to healthy controls, while resistance midpoint was increased. This study is the first to document resistance measures in adult patients with SCD. It is also the first to score these vascular resistance measures in comparison to the normal range. We anticipate these data will complement the current understanding of the cerebral vascular pathophysiology of SCD, identify paths for therapeutic interventions, and provide biomarkers for monitoring the progress of the disease.

وصف الملف: electronic resource

العلاقة: https://www.frontiersin.org/articles/10.3389/fphys.2022.847969/fullTest; https://doaj.org/toc/1664-042XTest

الوصول الحر: https://doaj.org/article/461cb4c9f69f425dacff27abf7daba42Test

المؤلفون: Olivia Sobczyk, Jorn Fierstra, Lakshmikumar Venkatraghavan, Julien Poublanc, James Duffin, Joseph A. Fisher, David J. Mikulis

المصدر: Frontiers in Physiology, Vol 12 (2021)

مصطلحات موضوعية: carbon dioxide, cerebral blood flow, vascular responses, cerebrovascular reactivity, cerebrovascular reactivity to carbon dioxide, Physiology, QP1-981

الوصف: An increase in arterial PCO2 is the most common stressor used to increase cerebral blood flow for assessing cerebral vascular reactivity (CVR). That CO2 is readily obtained, inexpensive, easy to administer, and safe to inhale belies the difficulties in extracting scientifically and clinically relevant information from the resulting flow responses. Over the past two decades, we have studied more than 2,000 individuals, most with cervical and cerebral vascular pathology using CO2 as the vasoactive agent and blood oxygen-level-dependent magnetic resonance imaging signal as the flow surrogate. The ability to deliver different forms of precise hypercapnic stimuli enabled systematic exploration of the blood flow-related signal changes. We learned the effect on CVR of particular aspects of the stimulus such as the arterial partial pressure of oxygen, the baseline PCO2, and the magnitude, rate, and pattern of its change. Similarly, we learned to interpret aspects of the flow response such as its magnitude, and the speed and direction of change. Finally, we were able to test whether the response falls into a normal range. Here, we present a review of our accumulated insight as 16 “lessons learned.” We hope many of these insights are sufficiently general to apply to a range of types of CO2-based vasoactive stimuli and perfusion metrics used for CVR.

وصف الملف: electronic resource

العلاقة: https://www.frontiersin.org/articles/10.3389/fphys.2021.665049/fullTest; https://doaj.org/toc/1664-042XTest

الوصول الحر: https://doaj.org/article/c4e850a578194c928da2be1cee80e9dfTest

المؤلفون: Julien Poublanc, Reema Shafi, Olivia Sobczyk, Kevin Sam, Daniel M. Mandell, Lakshmikumar Venkatraghavan, James Duffin, Joseph A. Fisher, David J. Mikulis

المصدر: Frontiers in Physiology, Vol 12 (2021)

مصطلحات موضوعية: cerebrovascular reactivity, BOLD, CO2, speed of response, blood arrival time, healthy subjects, Physiology, QP1-981

الوصف: Cerebrovascular reactivity (CVR) is defined as the change in cerebral blood flow induced by a change in a vasoactive stimulus. CVR using BOLD MRI in combination with changes in end-tidal CO2 is a very useful method for assessing vascular performance. In recent years, this technique has benefited from an advanced gas delivery method where end-tidal CO2 can be targeted, measured very precisely, and validated against arterial blood gas sampling (Ito et al., 2008). This has enabled more precise comparison of an individual patient against a normative atlas of healthy subjects. However, expected control ranges for CVR metrics have not been reported in the literature. In this work, we calculate and report the range of control values for the magnitude (mCVR), the steady state amplitude (ssCVR), and the speed (TAU) of the BOLD response to a standard step stimulus, as well as the time delay (TD) as observed in a cohort of 45 healthy controls. These CVR metrics maps were corrected for partial volume averaging for brain tissue types using a linear regression method to enable more accurate quantitation of CVR metrics. In brief, this method uses adjacent voxel CVR metrics in combination with their tissue composition to write the corresponding set of linear equations for estimating CVR metrics of gray matter (GM), white matter (WM), and cerebrospinal fluid (CSF). After partial volume correction, mCVR and ssCVR increase as expected in gray matter, respectively, by 25 and 19%, and decrease as expected in white matter by 33 and 13%. In contrast, TAU and TD decrease in gray matter by 33 and 13%. TAU increase in white matter by 24%, but TD surprisingly decreased by 9%. This correction enables more accurate voxel-wise tissue composition providing greater precision when reporting gray and white matter CVR values.

وصف الملف: electronic resource

العلاقة: https://www.frontiersin.org/articles/10.3389/fphys.2021.639360/fullTest; https://doaj.org/toc/1664-042XTest

الوصول الحر: https://doaj.org/article/269635b053af44ee9aacd979b4139742Test