scholarly journals Simulations of the effect of diffusion on asymmetric spin echo based quantitative BOLD: An investigation of the origin of deoxygenated blood volume overestimation

2019 ◽  
Author(s):  
Alan J Stone ◽  
Naomi C Holland ◽  
Avery J L Berman ◽  
Nicholas P Blockley
Keyword(s):  
Blood Volume ◽  
Spin Echo ◽  
Oxygen Extraction Fraction ◽  
Parameter Estimates ◽  
Analysis Model ◽  
Extraction Fraction ◽  
Echo Time ◽  
Asymmetric Spin Echo ◽  
The Impact ◽  
The Relationship

AbstractQuantitative BOLD (qBOLD) is a technique for mapping oxygen extraction fraction (OEF) and deoxygenated blood volume (DBV) in the human brain. Recent measurements using an asymmetric spin echo (ASE) based qBOLD approach produced estimates of DBV which were systematically higher than measurements from other techniques. In this study, we investigate two hypotheses for the origin of this DBV overestimation using simulations and consider the implications for experimental measurements. Investigations were performed by combining Monte Carlo simulations of extravascular signal with an analytical model of the intravascular signal.Hypothesis 1DBV overestimation is due to the presence of intravascular signal which is not accounted for in the analysis model. Intravascular signal was found to have a weak effect on qBOLD parameter estimates.Hypothesis 2DBV overestimation is due to the effects of diffusion which are not accounted for in the analysis model. The effect of diffusion on the extravascular signal was found to result in a vessel radius dependent variation in qBOLD parameter estimates. In particular, DBV overestimation peaks for vessels with radii from 20 to 30 μm and is OEF dependent. This results in the systematic underestimation of OEF.ImplicationsThe impact on experimental qBOLD measurements was investigated by simulating a more physiologically realistic distribution of vessel sizes with a small number of discrete radii. Overestimation of DBV consistent with previous experiments was observed, which was also found to be OEF dependent. This results in the progressive underestimation of the measured OEF. Furthermore, the relationship between the measured OEF and the true OEF was found to be dependent on echo time and spin echo displacement time.The results of this study demonstrate the limitations of current ASE based qBOLD measurements and provide a foundation for the optimisation of future acquisition approaches.

The Validation Process for Tier-III Variables and Fitness of the Model

2013 ◽  
pp. 238-254
Keyword(s):  
Latent Variables ◽  
Structural Equation ◽  
Theoretical Models ◽  
Parameter Estimates ◽  
Analysis Model ◽  
Validation Process ◽  
Structural Equation Analysis ◽  
Equation Analysis ◽  
Proposed Model ◽  
The Relationship

The validation of the model is dependent on the strength of the relationships established through variables, and Tier-III influencers are designed to ensure the validation process at a macro level. Tier-III influencers of the model help us understand the relations between variables matching (fitting) the data (Tier-I and II) and the way they influence the appropriateness of the model. Tier-III influencers characterize theoretical testing of the model and are mostly based on theory-driven search for the important antecedents of one or more focal variables. Tier-III influencers help us understand the relationship among the variables governing the outcome of the proposed model. It is agreed that the process of testing or validating theoretical models with survey data is addressed by first determining the adequacy of the measures of the unobserved variables in the model and then determining the reasonableness or adequacy of the hypothesized model. Measurements of Tier-III use conceptual definitions of the unobserved or latent variables, along with observed variables or items that measure these unobserved or latent variables. This chapter discusses model-to-data fit and parameter estimates by utilizing structural equation analysis. Model adequacy is determined by using hypotheses and model-to-data fit and parameter estimates from structural models.

scholarly journals Improving qBOLD based measures of oxygen extraction fraction using hyperoxia-BOLD derived measures of blood volume

2020 ◽  
Author(s):  
Alan J Stone ◽  
Nicholas P Blockley
Keyword(s):  
White Matter ◽  
Blood Volume ◽  
Oxygen Extraction Fraction ◽  
Oxygen Extraction ◽  
Transverse Relaxation Rate ◽  
Imaging Data ◽  
Bold Imaging ◽  
Extraction Fraction ◽  
Scan Time ◽  
Cortical Grey Matter

AbstractStreamlined-qBOLD (sqBOLD) is a recently proposed refinement of the quantitative BOLD (qBOLD) technique capable of producing non-invasive and quantitative maps of oxygen extraction fraction (OEF) in a clinically feasible scan time. However, sqBOLD measurements of OEF have been reported as being systematically lower than expected in healthy brain. Since the qBOLD framework infers OEF from the ratio of the reversible transverse relaxation rate (R2’) and deoxygenated blood volume (DBV), this underestimation of OEF has been largely attributed to an overestimation of DBV made using this technique.This study proposes a novel method, hyperoxia-constrained qBOLD (hqBOLD), to improve sqBOLD estimates of OEF. This method circumvents difficulties associated with inferring DBV from the qBOLD model by replacing it with a separate measurement of blood volume derived from hyperoxia-BOLD contrast. In a group of ten healthy volunteers, hqBOLD produced measurements of OEF in cortical grey matter (OEFhqBOLD = 44.7 ± 11.9 %) that were in better agreement with global oximetry measures (OEFTRUST = 40.4 ± 7.7 %), compared to sqBOLD derived measures (OEFsqBOLD = 13.1 ± 4.0 %).However, in the same group hqBOLD measures of OEF were found to be outside the physiological range in white matter regions (> 100%). By deriving maps of simulated R2’ from TRUST and hyperoxia-BOLD imaging data, the hqBOLD overestimation of OEF in white matter was hypothesised to originate from additional sources of magnetic susceptibility beyond deoxyhaemoglobin that are present in white matter.

Abstract WP227: Magnetic Resonance Measurement Of Static Global And Regional Cerebral Autoregulation

Stroke ◽  
2013 ◽  
Vol 44 (suppl_1) ◽  
Author(s):  
Souvik Sen ◽  
Hongyu An ◽  
Jonathan Oakes ◽  
Prema Menezes ◽  
Weili Lin ◽  
...  
Keyword(s):  
Magnetic Resonance ◽  
Cerebral Autoregulation ◽  
Spin Echo ◽  
Oxygen Extraction Fraction ◽  
Oxygen Extraction ◽  
Medical Systems ◽  
Planar Imaging ◽  
Extraction Fraction ◽  
Before And After ◽  
Significant Change

Background: Reliable methods used to test static cerebral autoregulation are time-consuming and/or invasive. Objectives: To evaluate if noninvasive magnetic resonance measured oxygen extraction fraction (OEF), cerebral blood flow (CBF), and oxygen metabolic index (OMI=CBF×OEF) can consistently detect expected physiological changes in humans under normal and 10-15% lowered mean arterial pressure (MAP). Methods: Static cerebral autoregulation was determined by measuring changes in CBF using a pseudo continuous arterial spin labeling (pCASL) approach and Oxygen Extraction Fraction (OEF) using MRI T2‘-weighted asymmetric spin echo echo-planar imaging (EPI) sequences, in response to 10-15% reductions in MAP in stroke-free controls induced by using IV Nicardipine. Images were acquired in 3T MR scanner (Trio, Siemens Medical Systems Inc). Autoregulation was measured globally and regionally in the anterior (ACA), the middle (MCA) and the posterior cerebral artery (PCA) territories of the brain manually defined using autopsy based model. Autoregulatory Index (AI) was computed (AI = %CBF change/% MAP change) supplemented by CBF associated OEF changes. Baseline regional CBF and OEF, AI, CBF and OEF changes to 10-15% lowering of MAP Results: Nineteen normal volunteers (mean age 30, 95% male, 50% white, 40% black, 10% others) were consented to the protocol approved by the institutional review board. MAP lowering was successfully achieved in all subjects (Mean ± standard deviation of MAP lowering of 12.5 ± 5.6 mm Hg). At a global level this resulted in no significant change between pre-MAP lowering CBF (56.0 ± 8.5 ml/100g/min) and post-MAP lowering CBF (55.9± 8.8 ml/100g/min). This translated to a AI of 0 ± 1.2. The CBF results corroborated with no significant change in OEF and OMI. Baseline regional CBF was higher in the MCA territory (66.1 ± 7.6 ml/100g/min) compared with the ACA territory (52.8 ± 8.6ml/100g/min, p<0.001). The AIs were consistent (ANOVA p=0.15) at regional levels across ACA (-1.5 ± 3.1), MCA(-0.3± 2.1) and PCA (-0.1 ± 1.4) territories. Conclusions: Global and regional static cerebral autoregulation can be measured using MR measurement of CBF, OEF and OMI, before and after 10-15% reductions in MAP in healthy volunteers.

scholarly journals Functional oxygen extraction fraction (OEF) imaging with turbo gradient spin echo QUIXOTIC (Turbo QUIXOTIC)

2017 ◽  
Vol 79 (5) ◽  
pp. 2713-2723 ◽  
Author(s):  
Jeffrey N. Stout ◽  
Elfar Adalsteinsson ◽  
Bruce R. Rosen ◽  
Divya S. Bolar
Keyword(s):  
Spin Echo ◽  
Oxygen Extraction Fraction ◽  
Oxygen Extraction ◽  
Extraction Fraction
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