2023年2月25日土曜日
2023年2月9日木曜日
#VitalStream Caretaker Experimental type has been used for fMRI study
Using Physiological MRI
to Estimate Dynamic
Cerebral Autoregulation
Metrics
Functional MRI Feasibility Study
Negar Hawezi
30/04/2015
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Contents
1.1 Background ............................................................................................. 15
1.2 Physiological aspects of Cerebral Autoregulation........................................... 18
2.1 Introduction............................................................................................. 47
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2.2 Methods .................................................................................................. 49
2.3 Results.................................................................................................... 51
2.4 Methods to quantify CA metrics .................................................................. 54
2.4.1 Magnetic resonance imaging (MRI) studies............................................. 54
2.4.2 Trans-cranial Doppler ultrasound studies (TCD) ...................................... 58
2.5 Cerebral autoregulation indices .................................................................. 60
2.6 Discussion ............................................................................................... 64
2.6.1 Non invasive physiological method to measure CA .................................. 64
2.6.2 Consistency of CA metrics .................................................................... 65
2.6.3 Regional heterogeneity ........................................................................ 66
2.6.4 Interventions to fluctuate blood pressure ............................................... 69
2.6.5 Limitations ......................................................................................... 72
2.7 Conclusions and future directions ............................................................... 74
3 Obtaining beat-to-beat Arterial Blood Pressure Measurements using Non invasive
methods ............................................................................................................ 75
3.1 Background ............................................................................................. 75
3.2 Plethysmographic arterial blood pressure recording devices ........................... 78
3.2.1 MR compatible arterial blood pressure monitoring device (NIBPMRI/Caretaker; Biopac®) ............................................................................... 78
3.2.2 Non invasive Continuous Arterial Blood Pressure Monitoring Device from
(Finometer ®)............................................................................................... 79
3.2.3 Technical issues .................................................................................. 82
3.3 Monitoring beat-to-beat arterial blood pressure measures ............................. 83
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3.3.1 Methods and materials......................................................................... 83
4.5.1 Thigh –cuff release............................................................................ 125
4.5.2 Inspiratory breath-hold method iBH .................................................... 128
4.5.3 Statistical analysis............................................................................... 131
4.6 Discussion ............................................................................................. 133
4.7 Limitations............................................................................................. 137
Table of Figures
Figure 1 Classic cerebral autoregulation curve [32]........................................................................................22
Figure 2 Circle of Willis (CoW), Time of Flight Angiography (ToF)...................................................................25
Figure 3 Chart of search results (PRISMA statement) .......................................................................53
Figure 4Methods to simulate dynamic cerebral auto regulation....................................................................57
Figure 5 Summary of non invasive BP fluctuation methods ...........................................................................77
Figure 6 Caretaker finger cuff, port and graphical user interface GUI.............................................................81
Figure 7 Finometer finger cuff and device......................................................................................................81
Figure 8:Schematic representation of cued deep breathing test (CDB) and observed BP response. ...............87
Figure 9: Blood pressure (BP) response curve to thigh-cuff release (TCR) method .........................................91
Figure 10 Mean arterial blood pressure (MAP) from Caretaker device ..........................................................97
Figure 11 :Sequential representation (from left to right) of iBH protocol instruction slides.........................111
Figure 12: Watershed areas segmentation...................................................................................................115
Figure 13: Thigh-cuff release test (TCR) in the scanner.................................................................................119
Figure 14: Breath-hold test (modeling different variables) ..........................................................................120
Figure 15 Reactivity analysis of brain, for iBH challenge (23 years, male subject) ........................................130
Figure 16 Bland-Altman plots.......................................................................................................................132
Figure 17 Graphical representation of the relationship between CBF and PaCO2 [131]. ..............................136
Figure 18: 4D PC MRI data analysis from GT-flow ........................................................................................145
Figure 19: Average flow velocity ..................................................................................................................148
Figure 20 Flow curve through three different arteries .................................................................................149
Figure 21: Peak systolic and end diastolic velocities ....................................................................................150
Figure 22 Mean arterial blood pressure (MAP) during BH and iBH protocols...............................................155
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Table of Tables
Table 1 Summary of the autoregulation indices used to estimate dCA .........................................................63
Table2 Summary of the volunteers who participated in each protocol. TCR, Thigh-cuff release, iBH, deepinspiratory breath-hold test. BH, non-inspiratory breath-hold test. CDB, cued deep-breathing. BOLD,
Blood oxygen level dependent MRI, 4D PC, Time resolved Phase-contrast MR angiography..................86
Table 3: Mean arterial blood pressure measures (MAP) at the baseline from the three devices (Omron-HEM,
Caretaker, and Finometer) .....................................................................................................................92
Table 4 MAP measures from the Caretaker and Finometer devices at different time points after cuffdeflation .....................92
Table 12 Flow velocity for two subjects at averaged 20 phases of cardiac cycle time points. At baseline, at
33% inspiratory breath-hold (iBH), and at 33% non-inspiratory breath-hold (BH)................................151
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Abstract
Cerebral autoregulation is the homeostatic mechanism that maintains sufficient cerebral
circulation despite changes in the perfusion pressure. Dynamic CA refers to the changes
that occur in CBF within the first few seconds after an acute MAP change. Assessment of
the CA impairment plays important role in the prognosis of many cerebrovascular diseases
such as stroke, sub-arachnoid haemorrhage, as well as traumatic brain injury and
neurodegenerative disorders.
This thesis investigates the feasibility of using physiological MRI to estimate dynamic
cerebral autoregulation (dCA) metrics. In particular, this thesis has an emphasis on
measuring beat-to-beat arterial blood pressure inside the scanner to provide better
understanding of the physiological aspects of dCA. Further, continuous blood pressure (BP)
measures in response to different non invasive BP fluctuating methods are acquired to
evaluate the reliability of these methods to induce response changes.
Blood Oxygen Level Dependent (BOLD) fMRI method was used to estimate the expected
variations of tissue oxygenation during induced dCA changes in healthy volunteers. The
non invasive arterial blood pressure measurements were acquired using MR compatible
arterial blood pressure monitoring device (NIBP-MRI/Caretaker; Biopac®). Further,
sudden release of inflated thigh-cuffs (TCR) and inspiratory breath-hold (iBH) methods
were used in the scanner to induce dynamic autoregulatory changes. These two methods
were investigated in a pilot study, to evaluate the reliability prior to the MR study by
comparing BP measurements obtained outside the scanner using non invasive methods.
This pilot study included monitoring BP changes in response to four types of non invasive
BP fluctuating methods.
The reliability of NIBP/MRI Caretaker device was examined by
comparing the BP response changes with the simultaneously acquired BP data from
Finometer plethysmographic device. The cerebral autoregulation metrics were estimated
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by calculating the rate of regulation (RoR) following dynamic BP fluctuating events. Rate
of regulation defines the rate at which the BOLD signal changes depending on MAP changes
at a particular time. Further, the tissue specific regulation parameters were obtained for
grey matter (GM), white matter (WM) and water shed areas (WS). The effect of iBH
method on cerebral blood flow (CBF) and velocity (CBFV) was explored in a preliminary
study by quantitative measures using time resolved 4D PC MRI angiography in two
subjects.
The mean arterial blood pressure (MAP) changes in response to TCR and iBH method were
comparable. The fMRI data demonstrated BOLD signal amplitude change in response to
the induced fast MAP changes. The GM and WS areas showed similar rates of regulation,
and these were nominally higher than WM RoR in both TCR and iBH methods. Further, the
4D PC MRI data suggested 29% CBF-increase in response to 33% iBH in four minutes
acquisition time.
The acquired non invasive arterial BP measures concurrent with the BOLD signal amplitude
response, allowed deriving the rate of regulation as a metric of dCA. It is not known
whether this information is clinically relevant to gauge the haemodynamic risk association
to cerebrovascular disease. However, BOLD signal change and CBF changes after iBH are
confounded by the extent to which the CO2 gradually accumulate in response to iBH and
causes an overshoot in the CBF response-change.
In conclusion, the presented study indicates the feasibility of using physiological MRI to
measure dCA in response to non-invasively induced MAP changes. Estimation of the dCA
metrics could be improved by using advanced data fitting methods as well as controlling
for physiological parameters such as PECO2.
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Declaration
I hereby declare that this thesis is my own work and effort
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