Cerebral perfusion metrics calculated directly from a hypoxia-induced step change in deoxyhemoglobin.

Resting cerebral perfusion metrics can be calculated from the MRI ΔR* signal during the first passage of an intravascular bolus of a Gadolinium-based contrast agent (GBCA), or more recently, a transient hypoxia-induced change in the concentration of deoxyhemoglobin ([dOHb]). Conventional analysis follows a proxy process that includes deconvolution of an arterial input function (AIF) in a tracer kinetic model. We hypothesized that the step reduction in magnetic susceptibility accompanying a step decrease in [dOHb] that occurs when a single breath of oxygen terminates a brief episode of lung hypoxia permits direct calculation of relative perfusion metrics.

Variability of Resting Carbon Dioxide Tension in Patients with Intracranial Steno-occlusive Disease.

 Controlling the partial pressure of carbon dioxide (PaCO ) is an important consideration in patients with intracranial steno-occlusive disease to avoid reductions in critical perfusion from vasoconstriction due to hypocapnia, or reductions in blood flow due to steal physiology during hypercapnia. However, the normal range for resting PCO in this patient population is not known. Therefore, we investigated the variability in resting end-tidal PCO (P CO ) in patients with intracranial steno-occlusive disease and the impact of revascularization on resting P CO in these patients.

Transient deoxyhemoglobin formation as a contrast for perfusion MRI studies in patients with brain tumors: a feasibility study.

Transient hypoxia-induced deoxyhemoglobin (dOHb) has recently been shown to represent a comparable contrast to gadolinium-based contrast agents for generating resting perfusion measures in healthy subjects. Here, we investigate the feasibility of translating this non-invasive approach to patients with brain tumors. A computer-controlled gas blender was used to induce transient precise isocapnic lung hypoxia and thereby transient arterial dOHb during echo-planar-imaging acquisition in a cohort of patients with different types of brain tumors (n = 9).

Assessing Perfusion in Steno-Occlusive Cerebrovascular Disease Using Transient Hypoxia-Induced Deoxyhemoglobin as a Dynamic Susceptibility Contrast Agent.

Background And Purpose: Resting brain tissue perfusion in cerebral steno-occlusive vascular disease can be assessed by MR imaging using gadolinium-based susceptibility contrast agents. Recently, transient hypoxia-induced deoxyhemoglobin has been investigated as a noninvasive MR imaging contrast agent. Here we present a comparison of resting perfusion metrics using transient hypoxia-induced deoxyhemoglobin and gadolinium-based contrast agents in patients with known cerebrovascular steno-occlusive disease.

The Choroid Plexus as an Alternative Locus for the Identification of the Arterial Input Function for Calculating Cerebral Perfusion Metrics Using MRI.

Background And Purpose: MR imaging-based cerebral perfusion metrics can be obtained by tracing the passage of a bolus of contrast through the microvasculature of the brain parenchyma. Thus, the temporal signal pattern of the contrast agent is typically measured over a large artery such as the MCA to generate the arterial input function. The largest intracranial arteries in the brain may not always be suitable for selecting the arterial input function due to skull base susceptibility artifacts or reduced size from steno-occlusive disease.

Assessment of Cerebrovascular Reactivity Using CO-BOLD MRI: A 15-Year, Single Center Experience.

Background: Cerebrovascular reactivity (CVR) is a measure of the change in cerebral blood flow (CBF) in response to a vasoactive challenge. It is a useful indicator of the brain's vascular health.

Purpose: To evaluate the factors that influence successful and unsuccessful CVR examinations using precise arterial and end-tidal partial pressure of CO control during blood oxygen level-dependent (BOLD) MRI.

Determining the effects of elevated partial pressure of oxygen on hypercapnia-induced cerebrovascular reactivity.

Evaluation of cerebrovascular reactivity (CVR) to hypo- and hypercapnia is a valuable test for the assessment of vasodilatory reserve. While hypercapnia-induced CVR testing is usually performed at normoxia, mild hyperoxia may increase tolerability of hypercapnia by reducing the ventilatory distress. However, the effects of mild hyperoxia on CVR was unknown.

Convolutional Neural Networks to Assess Steno-Occlusive Disease Using Cerebrovascular Reactivity.

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.

DSC MRI in the human brain using deoxyhemoglobin and gadolinium-Simulations and validations at 3T.

Introduction: Dynamic 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.

Transfer function analysis assesses resting cerebral perfusion metrics using hypoxia-induced deoxyhemoglobin as a contrast agent.

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.

Brain Stress Test for Assessing Risk for Hemodynamic Stroke.

Background: In patients with intracranial steno-occlusive disease (SOD), the risk of hemodynamic stroke depends on the poststenotic vasodilatory reserve. Cerebrovascular reactivity (CVR) is a test for vasodilatory reserve. We tested for vasodilatory reserve by using PCO as the stressor, and Blood Oxygen Level Dependent (BOLD) MRI as a surrogate of blood flow.

Investigations of hypoxia-induced deoxyhemoglobin as a contrast agent for cerebral perfusion imaging.

The assessment of resting perfusion measures (mean transit time, cerebral blood flow, and cerebral blood volume) with magnetic resonance imaging currently requires the presence of a susceptibility contrast agent such as gadolinium. Here, we present an initial comparison between perfusion measures obtained using hypoxia-induced deoxyhemoglobin and gadolinium in healthy study participants. We hypothesize that resting cerebral perfusion measures obtained using precise changes of deoxyhemoglobin concentration will generate images comparable to those obtained using a clinical standard, gadolinium.

Assessment of cerebrovascular function in patients with sickle cell disease using transfer function analysis.

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.

Sickle cell cerebrovascular reactivity to a CO stimulus: Too little, too slow.

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.

Assessing Cerebrovascular Resistance in Patients With Sickle Cell Disease.

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.

Does breathing pattern affect cerebrovascular reactivity?

New Findings: What is the central question of this study? Is cerebrovascular reactivity affected by isocapnic changes in breathing pattern? What is the main finding and its importance? Cerebrovascular reactivity does not change with isocapnic variations in tidal volume and frequency.

Abstract: Deviations of arterial carbon dioxide tension from resting values affect cerebral blood vessel tone and thereby cerebral blood flow. Arterial carbon dioxide tension also affects central respiratory chemoreceptors, adjusting respiratory drive.

Cerebrovascular reactivity changes in acute concussion: a controlled cohort study.

Background: Evidence suggests that cerebrovascular reactivity (CVR) increases within the first week after the incidence of concussion, indicating a disruption of normal autoregulation. We sought to extend these findings by investigating the effects of acute concussion on the speed of CVR response and by visualizing global and regional impairments in individual patients with acute concussion.

Methods: Twelve patients aged 18-40 years who experienced concussion less than a week before this prospective study were included.

Perfusion MRI using endogenous deoxyhemoglobin as a contrast agent: Preliminary data.

Purpose: To demonstrate the feasibility of mapping cerebral perfusion metrics with BOLD MRI during modulation of pulmonary venous oxygen saturation.

Methods: A gas blender with a sequential gas delivery breathing circuit was used to implement rapid isocapnic changes in the partial pressure of oxygen of the arterial blood. Partial pressure of oxygen was initially lowered to a baseline of 40 mmHg.

Measuring Cerebrovascular Reactivity: Sixteen Avoidable Pitfalls.

An increase in arterial PCO is the most common stressor used to increase cerebral blood flow for assessing cerebral vascular reactivity (CVR). That CO 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 CO as the vasoactive agent and blood oxygen-level-dependent magnetic resonance imaging signal as the flow surrogate.

Normal BOLD Response to a Step CO Stimulus After Correction for Partial Volume Averaging.

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 CO 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 CO can be targeted, measured very precisely, and validated against arterial blood gas sampling (Ito et al.

The Effect of CO on Resting-State Functional Connectivity: Isocapnia vs. Poikilocapnia.

The normal variability in breath size and frequency results in breath-to-breath variability of end-tidal PCO (PCO), the measured variable, and arterial partial pressure of carbon dioxide (PaCO), the independent variable affecting cerebral blood flow (CBF). This study examines the effect of variability in PaCO on the pattern of resting-state functional MRI (rs-fMRI) connectivity. A region of interest (ROI)-to-ROI and Seed-to-Voxel first-level bivariate correlation, hemodynamic response function (hrf)-weighted analysis for measuring rs-fMRI connectivity was performed during two resting-state conditions: (a) normal breathing associated with breath-to-breath variation in PaCO (poikilocapnia), and (b) normal breathing with breath-to-breath variability of PCO dampened using sequential rebreathing (isocapnia).

The Reproducibility of Cerebrovascular Reactivity Across MRI Scanners.

Cerebrovascular reactivity (CVR) is defined as the ratio of the cerebral blood flow (CBF) response to an increase in a vasoactive stimulus. We used changes in blood oxygenation level-dependent (BOLD) MRI as surrogates for changes of CBF, and standardized quantitative changes in arterial partial pressure of carbon dioxide as the stimulus. Despite uniform stimulus and test conditions, differences in voxel-wise BOLD changes between testing sites may remain, attributable to physiologic and machine variability.

The value of a shorter-delay arterial spin labeling protocol for detecting cerebrovascular impairment.

Background: The aim of this study was to determine the relationship between blood oxygen level dependent (BOLD) cerebrovascular reactivity (CVR) and cerebral blood flow (CBF) obtained from arterial spin labeling (ASL) using different post labeling delays (PLD).

Methods: Forty-two patients with steno-occlusive diseases and impaired CVR were divided into two groups, one scanned with a 1.5-second (1.

Accelerated ethanol elimination via the lungs.

Ethanol poisoning is endemic the world over. Morbidity and mortality depend on blood ethanol levels which in turn depend on the balance between its rates of absorption and clearance. Clearance of ethanol is mostly at a constant rate via enzymatic metabolism.

A Promising Subject-Level Classification Model for Acute Concussion Based on Cerebrovascular Reactivity Metrics.

Concussion imaging research has primarily focused on neuronal disruption with lesser emphasis directed toward vascular dysfunction. However, blood flow metrics may be more sensitive than measures of neuronal integrity. Vascular dysfunction can be assessed by measuring cerebrovascular reactivity (CVR)-the change in cerebral blood flow per unit change in vasodilatory stimulus.