Ebook Intracranial pressure amp; neuromonitoring XVI: Part 2
➤ Gửi thông báo lỗi ⚠️ Báo cáo tài liệu vi phạmNội dung chi tiết: Ebook Intracranial pressure amp; neuromonitoring XVI: Part 2
Ebook Intracranial pressure amp; neuromonitoring XVI: Part 2
Increasing the Contrast-to-Noise Ratio of MRI Signals for Regional Assessment of Dynamic Cerebral AutoregulationJosé L. Jara, Nazia p. Saeed, Ronney B Ebook Intracranial pressure amp; neuromonitoring XVI: Part 2B. Panerai, and Thompson G. RobinsonAbstract Objective: To devise an appropriate measure of the quality of a magnetic resonance imaging (MRI) signal for the assessment of dynamic cerebral autoregulation, and propose simple strategies to improve its quality.Materials and methods: Magnetic resonance i Ebook Intracranial pressure amp; neuromonitoring XVI: Part 2mages of 11 healthy subjects were scanned during a transient decrease in arterial blood pressure (BP). Mean signals were extracted from non-overlappinEbook Intracranial pressure amp; neuromonitoring XVI: Part 2
g brain regions for each image. An ad-hoc contiast-to-noise ratio (CNR) was used to evaluate the quality of these regional signals. Global mean signalIncreasing the Contrast-to-Noise Ratio of MRI Signals for Regional Assessment of Dynamic Cerebral AutoregulationJosé L. Jara, Nazia p. Saeed, Ronney B Ebook Intracranial pressure amp; neuromonitoring XVI: Part 2onent signals.Results: Significant improvements in CNR values of global mean signals were obtained, whilst maintaining significant correlation with the original ones. A Hampel filter with a small moving window and a low rejection threshold combined with a selection of the 50% component signals seems Ebook Intracranial pressure amp; neuromonitoring XVI: Part 2 a recommendable option.Conclusions: This work has demonstrated the possibility of improving the quality of MRI signals acquired during transient dropEbook Intracranial pressure amp; neuromonitoring XVI: Part 2
s in BP. This approach needs validation at a voxel level, which could help to consolidate MRI as a technological alternative to the standard techniqueIncreasing the Contrast-to-Noise Ratio of MRI Signals for Regional Assessment of Dynamic Cerebral AutoregulationJosé L. Jara, Nazia p. Saeed, Ronney B Ebook Intracranial pressure amp; neuromonitoring XVI: Part 2ilee-mail: joseluis.jara<7 usach.clN.p. SaeedAgeing and Stroke Medicine. Department of CardiovascularSciences. University of Leicester. Leicester. UKR.B. Panerai • T.G. RobinsonAgeing and Stroke Medicine. Department of CardiovascularSciences. University of Leicester. Leicester. UKN1HR Biomedical Res Ebook Intracranial pressure amp; neuromonitoring XVI: Part 2earch Unit for Cardiovascular Sciences, University of Leicester. Leicester. UKKeywords Dynamic cerebral autoregulation • Magnetic resonance imaging ■Ebook Intracranial pressure amp; neuromonitoring XVI: Part 2
Contrast-to-noise ratio • Hampel filterIntroductionUsing magnetic resonance imaging (MRI) as an alternative to the standard transcranial Doppler (TCD)Increasing the Contrast-to-Noise Ratio of MRI Signals for Regional Assessment of Dynamic Cerebral AutoregulationJosé L. Jara, Nazia p. Saeed, Ronney B Ebook Intracranial pressure amp; neuromonitoring XVI: Part 2TCD and the MR I signal was established for healthy subjects in Saeed et al. 111 A mean map of dCA efficiency tor a group of healthy subjects was presented in Horstleld et al. (2). More recently, the use of hemispheric TCD signals and hemispheric MRI signals to discriminate between healthy and acute Ebook Intracranial pressure amp; neuromonitoring XVI: Part 2 ischaemic stroke populations was investigated in Panerai et al. [3]. However, as repotted in the most recent study, many time courses were excluded fEbook Intracranial pressure amp; neuromonitoring XVI: Part 2
rom the analysis, mostly from stroke patients, by a panel of four of the authors who visually inspected (he signals on a computer screen, because theyIncreasing the Contrast-to-Noise Ratio of MRI Signals for Regional Assessment of Dynamic Cerebral AutoregulationJosé L. Jara, Nazia p. Saeed, Ronney B Ebook Intracranial pressure amp; neuromonitoring XVI: Part 2 method of evaluating dCA efficiency proposed in Horsfield el al. (21 resembles (he functional MRI paradigm (fMRI) of cognitive neuroimaging Studies. Both approaches seek variations in the blood-oxygen-level-dependent (BOLD) contrast as a surrogate of changes in cerebral blood flow. Although in fMRI Ebook Intracranial pressure amp; neuromonitoring XVI: Part 2, the goal is to identify an increase in the BOLD signal in response to neuronal activity, the MRI-based dCA evaluation is aimed at detecting a drop iEbook Intracranial pressure amp; neuromonitoring XVI: Part 2
n the BOLD signal in response to a slump in BP produced by (he sudden release of inflated bilateral thigh cuffs (THCs). In both cases, the change in BIncreasing the Contrast-to-Noise Ratio of MRI Signals for Regional Assessment of Dynamic Cerebral AutoregulationJosé L. Jara, Nazia p. Saeed, Ronney B Ebook Intracranial pressure amp; neuromonitoring XVI: Part 2iưl Pressure & Neummonitoring XVI. Acta Neurochirurgica Supplement. \w. 126.153https://doi.org/IO, ta>7WS-3-3l9-657W-l_32.£> Springer International Publishing AG 2018154J.L. Jara Cl al.The signal of an individual voxel in an MRI image can be atlected by BOLD fluctuations due loghost images, blood fl Ebook Intracranial pressure amp; neuromonitoring XVI: Part 2ow artefacts in the vicinity of huge vessels and. in particular, by spontaneous neuronal activity |4.51. Similar to the hemispheric MRI signals of PanEbook Intracranial pressure amp; neuromonitoring XVI: Part 2
erai et al. [3]. regional indicators for the efficiency of cerebral autoregulation could be obtained from a dCA efficiency map by averaging the valuesIncreasing the Contrast-to-Noise Ratio of MRI Signals for Regional Assessment of Dynamic Cerebral AutoregulationJosé L. Jara, Nazia p. Saeed, Ronney B Ebook Intracranial pressure amp; neuromonitoring XVI: Part 2in the ROI could yield less noisy regional signals or more accurate regional measures olEbook Intracranial pressure amp; neuromonitoring XVI: Part 2
eous fluctuations should be limited, whereas the variation introduced by the TIIC deflation should be much larger and clear. Second, simple strategiesIncreasing the Contrast-to-Noise Ratio of MRI Signals for Regional Assessment of Dynamic Cerebral AutoregulationJosé L. Jara, Nazia p. Saeed, Ronney B Ebook Intracranial pressure amp; neuromonitoring XVI: Part 2ethodsSubjectsand DataMRI Signal QualityContrast to noise ratio (CNR) has been found to be more suitable for fMRI than more traditional measures of signal quality |6. 7|. as higher CNR values yield to belter identification ol the actual stimulus-related fluctuations and it encapsulates all relevant Ebook Intracranial pressure amp; neuromonitoring XVI: Part 2quality factors into a single and intuitive parameter [8]. There are different definitions and methods of estimating CNR. but all of them conceptualisEbook Intracranial pressure amp; neuromonitoring XVI: Part 2
e this parameter as the ratio between the amplitude of BOLD fluctuations produced by the stimulus and lhe variability of the noise over time [7. 8]. TIncreasing the Contrast-to-Noise Ratio of MRI Signals for Regional Assessment of Dynamic Cerebral AutoregulationJosé L. Jara, Nazia p. Saeed, Ronney B Ebook Intracranial pressure amp; neuromonitoring XVI: Part 2before lhe deflation of the THCs, and the response samples r, correspond to the 10 values between the 3 s and 12 s after the TI1C deflation, in which the reaction to the stimulus is expected. The variability of the noise in the signal is the standard deviation of the baseline residuals: = sd(/>, - m Ebook Intracranial pressure amp; neuromonitoring XVI: Part 2ean(b,)), and the amplitude of the response to the stimulus is determined as the difference between the baseline value and the minimum signal value inEbook Intracranial pressure amp; neuromonitoring XVI: Part 2
the response segment: A = mcan(fti) - min(fy). Thus, the clearer the response to the stimulus with regard to the observed noise, the higher the CNR vIncreasing the Contrast-to-Noise Ratio of MRI Signals for Regional Assessment of Dynamic Cerebral AutoregulationJosé L. Jara, Nazia p. Saeed, Ronney B Ebook Intracranial pressure amp; neuromonitoring XVI: Part 2PI sequences were used to scan the brains of 11 healthy subjects at a rate of 1 Hz. During the initial 3 min, the subjects lay supine in die scanner with tilled THCs. Then, a transient decrease in BP was provoked by the sudden deflation of the TIICs. The series continued until 240 s images were acqu Ebook Intracranial pressure amp; neuromonitoring XVI: Part 2ired. After the first run was completed, the THCs were re-inflated and the procedure was repealed twice more during a single session. 'Die protocol isEbook Intracranial pressure amp; neuromonitoring XVI: Part 2
detailed in Saeed et al.. Horsfield et al. and Panerai el al. 11-31 and the 33 images considered in this study are the same as those used in HorsfielIncreasing the Contrast-to-Noise Ratio of MRI Signals for Regional Assessment of Dynamic Cerebral AutoregulationJosé L. Jara, Nazia p. Saeed, Ronney B Ebook Intracranial pressure amp; neuromonitoring XVI: Part 2ts gave written informed consent.As it would be impossible to hand inspect for improve ments in the quality of the signal of all voxels in a real situation. a more manageable simplification was used: the global mean signal of an image is the result of averaging regional mean signals that result from Ebook Intracranial pressure amp; neuromonitoring XVI: Part 2 the applications of 32 masks of non-overlapping brain regions. In this way. a global mean signal can he compared before and after manipulating its 32Ebook Intracranial pressure amp; neuromonitoring XVI: Part 2
component signals, which can also he examined Io determine the effect on them of any proposed mclhixi.Outlier FilteringThe estimation of CNR involvesIncreasing the Contrast-to-Noise Ratio of MRI Signals for Regional Assessment of Dynamic Cerebral AutoregulationJosé L. Jara, Nazia p. Saeed, Ronney B Ebook Intracranial pressure amp; neuromonitoring XVI: Part 2ave been reported in the signals under study 12, 3|. Thus, outliers must be dealt with to obtain reliable CNR values.Filtering and denoising methods lor fMRI have been intensely studied. Out of many options |4. 9|, the Hampel filler was selected for this study as it is much simpler to compute, it do Ebook Intracranial pressure amp; neuromonitoring XVI: Part 2es not require knowledge of the process model, it replaces only outliers, preserving all other infor (nation in the signal, and it is olten extremelyEbook Intracranial pressure amp; neuromonitoring XVI: Part 2
elfeclive in practice 110|. This filter has two parameters: k. the half-size of a moving window (5_*....5<....sj to assess the “outli-erness” of the cGọi ngay
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