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Exploiting magnetic resonance angiography imaging improves model estimation of BOLD signal.

Hu Z, Liu C, Shi P, Liu H - PLoS ONE (2012)

Bottom Line: The change of BOLD signal relies heavily upon the resting blood volume fraction ([Formula: see text]) associated with regional vasculature.We thereby argue that introducing physically realistic [Formula: see text] in the assimilation process may provide more reliable estimation of physiological information, which contributes to a better understanding of the underlying hemodynamic processes.Such an effort is valuable and should be well appreciated.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Modern Optical Instrumentation, Zhejiang University, Hangzhou, China.

ABSTRACT
The change of BOLD signal relies heavily upon the resting blood volume fraction ([Formula: see text]) associated with regional vasculature. However, existing hemodynamic data assimilation studies pretermit such concern. They simply assign the value in a physiologically plausible range to get over ill-conditioning of the assimilation problem and fail to explore actual [Formula: see text]. Such performance might lead to unreliable model estimation. In this work, we present the first exploration of the influence of [Formula: see text] on fMRI data assimilation, where actual [Formula: see text] within a given cortical area was calibrated by an MR angiography experiment and then was augmented into the assimilation scheme. We have investigated the impact of [Formula: see text] on single-region data assimilation and multi-region data assimilation (dynamic cause modeling, DCM) in a classical flashing checkerboard experiment. Results show that the employment of an assumed [Formula: see text] in fMRI data assimilation is only suitable for fMRI signal reconstruction and activation detection grounded on this signal, and not suitable for estimation of unobserved states and effective connectivity study. We thereby argue that introducing physically realistic [Formula: see text] in the assimilation process may provide more reliable estimation of physiological information, which contributes to a better understanding of the underlying hemodynamic processes. Such an effort is valuable and should be well appreciated.

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Related in: MedlinePlus

Estimated BOLD signal (Left), and reconstructed physiological states (Right) from the greatest activated locus in primary visual cortex (V).For comparative purpose, model estimation was also performed with a typical assumed . Real  value is .
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pone-0031612-g004: Estimated BOLD signal (Left), and reconstructed physiological states (Right) from the greatest activated locus in primary visual cortex (V).For comparative purpose, model estimation was also performed with a typical assumed . Real value is .

Mentions: Figure 4 shows reconstructed BOLD response (left) and underlying physiological states (right) in the greatest activation locus of primary visual cortex (Figure 3) with actual , given as solid line. As a comparison, we also evaluated the estimated BOLD response and physiological states with assumed value, which was widely employed in previous studies [3]–[8], [10]–[16], [18], given as dash line in Figure 4. We found that two different values produced very similar BOLD estimates (Figure 4, left), only tiny discrepancy in post stimulus undershoot stage could be found. Nevertheless, a significant distinction was observed in reconstructed physiological states between two values (Figure 4, right). Though the experimental stimulus induced a puny change in the blood flow , the blood venous volume and the veins dHb content , the approach used assumed deduced a substantial change during task due to magnifying effect of large blood content. This implied that the presence of large veins in an activated area contributed excess signal in this area. The change of BOLD signal in this area mainly derived from the large-vessel signal, not from the multiple physiological states, namely, not from the experimental related neuronal activity. Since statistical inference essentially is grounded on the amplitude of BOLD response, this area may surely be considered active in statistic analysis of the BOLD signal change, though it is absent at the response efficacy elicited by neuronal activity. This explains why the employment of assumed in detection process still could generate very similar activation map with those obtained from classic linear model [10], [11]. The same difference also can be found in estimated model parameters (Table 1). Specially, neuronal efficacy is with actual derived from MRA image, while is with assumed value. Assumed, underestimated substantially overestimates the neuronal efficacy parameter, . Since parameter reflects the efficacy with which neuronal activity causes an increase in signal, we argue that the estimated efficiency parameter in each voxel might be a good index to sign actual activation level.


Exploiting magnetic resonance angiography imaging improves model estimation of BOLD signal.

Hu Z, Liu C, Shi P, Liu H - PLoS ONE (2012)

Estimated BOLD signal (Left), and reconstructed physiological states (Right) from the greatest activated locus in primary visual cortex (V).For comparative purpose, model estimation was also performed with a typical assumed . Real  value is .
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3285158&req=5

pone-0031612-g004: Estimated BOLD signal (Left), and reconstructed physiological states (Right) from the greatest activated locus in primary visual cortex (V).For comparative purpose, model estimation was also performed with a typical assumed . Real value is .
Mentions: Figure 4 shows reconstructed BOLD response (left) and underlying physiological states (right) in the greatest activation locus of primary visual cortex (Figure 3) with actual , given as solid line. As a comparison, we also evaluated the estimated BOLD response and physiological states with assumed value, which was widely employed in previous studies [3]–[8], [10]–[16], [18], given as dash line in Figure 4. We found that two different values produced very similar BOLD estimates (Figure 4, left), only tiny discrepancy in post stimulus undershoot stage could be found. Nevertheless, a significant distinction was observed in reconstructed physiological states between two values (Figure 4, right). Though the experimental stimulus induced a puny change in the blood flow , the blood venous volume and the veins dHb content , the approach used assumed deduced a substantial change during task due to magnifying effect of large blood content. This implied that the presence of large veins in an activated area contributed excess signal in this area. The change of BOLD signal in this area mainly derived from the large-vessel signal, not from the multiple physiological states, namely, not from the experimental related neuronal activity. Since statistical inference essentially is grounded on the amplitude of BOLD response, this area may surely be considered active in statistic analysis of the BOLD signal change, though it is absent at the response efficacy elicited by neuronal activity. This explains why the employment of assumed in detection process still could generate very similar activation map with those obtained from classic linear model [10], [11]. The same difference also can be found in estimated model parameters (Table 1). Specially, neuronal efficacy is with actual derived from MRA image, while is with assumed value. Assumed, underestimated substantially overestimates the neuronal efficacy parameter, . Since parameter reflects the efficacy with which neuronal activity causes an increase in signal, we argue that the estimated efficiency parameter in each voxel might be a good index to sign actual activation level.

Bottom Line: The change of BOLD signal relies heavily upon the resting blood volume fraction ([Formula: see text]) associated with regional vasculature.We thereby argue that introducing physically realistic [Formula: see text] in the assimilation process may provide more reliable estimation of physiological information, which contributes to a better understanding of the underlying hemodynamic processes.Such an effort is valuable and should be well appreciated.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Modern Optical Instrumentation, Zhejiang University, Hangzhou, China.

ABSTRACT
The change of BOLD signal relies heavily upon the resting blood volume fraction ([Formula: see text]) associated with regional vasculature. However, existing hemodynamic data assimilation studies pretermit such concern. They simply assign the value in a physiologically plausible range to get over ill-conditioning of the assimilation problem and fail to explore actual [Formula: see text]. Such performance might lead to unreliable model estimation. In this work, we present the first exploration of the influence of [Formula: see text] on fMRI data assimilation, where actual [Formula: see text] within a given cortical area was calibrated by an MR angiography experiment and then was augmented into the assimilation scheme. We have investigated the impact of [Formula: see text] on single-region data assimilation and multi-region data assimilation (dynamic cause modeling, DCM) in a classical flashing checkerboard experiment. Results show that the employment of an assumed [Formula: see text] in fMRI data assimilation is only suitable for fMRI signal reconstruction and activation detection grounded on this signal, and not suitable for estimation of unobserved states and effective connectivity study. We thereby argue that introducing physically realistic [Formula: see text] in the assimilation process may provide more reliable estimation of physiological information, which contributes to a better understanding of the underlying hemodynamic processes. Such an effort is valuable and should be well appreciated.

Show MeSH
Related in: MedlinePlus