Influence of gradient acoustic noise on fMRI response in the human visual cortex.

A paired-stimuli paradigm combined with fMRI was utilized to study the effect of gradient acoustic noise on fMRI response in the human primary visual cortex (V1) in terms of the auditory-visual cross-modal neural interaction. The gradient noise generated during the fMRI acquisition was used as the primary stimulus, and a single flashing light was used as the secondary stimulus. An interstimulus interval (ISI) separated the two. Six tasks were designed with different ISIs ranging from 50 to 700 ms. Both BOLD signal intensity and the number of activated pixels in V1 were analyzed and examined, and they showed a significant reduction when the gradient noise preceded the flashing light by approximately 300 ms. These results indicate that the gradient acoustic noise generated during fMRI acquisitions does interfere with neural behavior and the BOLD signal in the human visual cortex. This interference is modulated by the delay between the gradient noise and visual stimulation, and it can be studied quantitatively when the stimulation paradigm is designed appropriately. This study provides evidence of the auditory-visual interaction during fMRI studies, and the results should have an impact on fMRI applications.     

Sinusoidal echo-planar imaging with parallel acquisition technique for reduced acoustic noise in auditory fMRI

Purpose:

To extend the parameter restrictions of a silent echo‐planar imaging (sEPI) sequence using sinusoidal readout (RO) gradients, in particular with increased spatial resolution. The sound pressure level (SPL) of the most feasible configurations is compared to conventional EPI having trapezoidal RO gradients.

Materials and Methods:

We enhanced the sEPI sequence by integrating a parallel acquisition technique (PAT) on a 3 T magnetic resonance imaging (MRI) system. The SPL was measured for matrix sizes of 64 × 64 and 128 × 128 pixels, without and with PAT (R = 2). The signal‐to‐noise ratio (SNR) was examined for both sinusoidal and trapezoidal RO gradients.

Results:

Compared to EPI PAT, the SPL could be reduced by up to 11.1 dB and 5.1 dB for matrix sizes of 64 × 64 and 128 × 128 pixels, respectively. The SNR of sinusoidal RO gradients is lower by a factor of 0.96 on average compared to trapezoidal RO gradients.

Conclusion:

The sEPI PAT sequence allows for 1) increased resolution, 2) expanded RO frequency range toward lower frequencies, which is in general beneficial for SPL, or 3) shortened TE, TR, and RO train length. At the same time, it generates lower SPL compared to conventional EPI for a wide range of RO frequencies while having the same imaging parameters. J. Magn. Reson. Imaging 2012;36:581–588. © 2012 Wiley Periodicals, Inc.     

掩蔽声对豚鼠听阈和频率辨别阈的影响

目的：探讨噪声对听觉辨别功能的影响及其作用规律，为特殊作业环境噪声控制提供参考依据。方法：用纯音和重复短声调频诱发的慢反应阈值作为指标，利用平均叠加技术测定清醒豚鼠在安静状态无外加噪声和在７５、８０、８５、９０与９５ｄＢＡ５种强度噪声掩蔽下的听阈和频率辨别阈变化。结果：听阈随掩蔽声强度的增加而递增。暴露强度为７５～８５ｄＢＡ，频率辨别阈（Δｆｒ）变化不明显，当强度增加到９０～９５ｄＢＡ时，Δｆｒ显著增加，与安静状态无外加噪声比较差异十分显著。结论：当环境噪声≤８５ｄＢＡ时，只要将接收信号声调节到阈上１０～１５ｄＢ，就能得到满意的辨别效果；当环境噪声＞９０ｄＢＡ时，即使将接受信号声提高到较高水平，听觉辨别功能仍会出现明显影响，这时应考虑采取隔声减噪措施。     

Event-related fMRI technique for auditory processing with hemodynamics unrelated to acoustic gradient noise.

Acoustic noise from the imaging gradients presents a major difficulty in functional MRI (fMRI) studies of auditory cortical function. For studies involving hearing-impaired pediatric subjects, the auditory stimuli should be presented during completely silent gradient intervals. In addition, the scan time is limited by constraints involving subject motion and subject compliance. A novel event-related method for conducting fMRI studies of auditory function is proposed. Auditory stimuli are presented during completely silent gradient intervals, but using a variable TR. A general nonlinear model (GNLM) is proposed as a postprocessing methodology for the data. The technique increases the flexibility of the experimental design, with minimal loss of sensitivity compared to standard fMRI acquisition techniques, and may therefore be useful for fMRI studies of auditory function in hearing-impaired pediatric subjects.     

Silent fMRI acquisition methods for large acoustic noise during scan.

Functional magnetic resonance imaging (fMRI) is now the method of choice for studying neural correlates of various tasks in normal subjects as well as patients. This method, however, is inevitably coupled with the acoustic noise produced during the image acquisition process. This is a problem not only in auditory experiments but also in other cognitive tasks in general. The problems caused by such noise are modulation of auditory activation, impaired perception of auditory stimuli, and deterioration of task performance possibly due to stress from the abnormal circumstances. While both hardware and software solutions have been reported, several methods are introduced here that focus on software solutions that can be implemented in scanners already installed. Their advantages and disadvantages differ depending on the kinds of tasks involved, i.e. whether block design or event-related design, and they are discussed with a view to better utilization.     

fMRI of the auditory cortex in patients with unilateral carotid artery steno-occlusive disease

PURPOSE: To examine whether an internal carotid artery (ICA) steno-occlusive disease leads to a reduced blood oxygenation level dependent (BOLD)-signal change due to a decreased vasodilatory reserve capacity.MATERIALS AND METHODS: Patients suffering from unilateral ICA stenosis or occlusion were examined using functional magnetic resonance imaging (fMRI) of the auditory cortex with a bilateral stimulation applying a pulsed 1000 Hz sine-tone.RESULTS: Compared to control subjects, who showed symmetric bilateral BOLD-responses within the auditory cortex, the ICA patients revealed either a normal bilateral cortical activation pattern or a reduced cortical activation on the steno-occluded side. This latter decrease of BOLD-signal change might indicate a depressed vasomotor reserve capacity. The observed coincidence between this asymmetric reduction in BOLD-signal and ischemic borderzone lesions on the affected side in this subgroup of patients strongly supports this assumption.CONCLUSION: This study shows that fMRI of the auditory cortex appears to have clinical merit in the workup of cerebrovascular conditions.     

Effects of the acoustic noise of the gradient systems on fMRI: A study on auditory,motor, and visual cortices

MR acoustic, or sound, noise due to gradient pulsing has been one of the problems in MRI, both in patient scanning as well as in many areas of psychiatric and neuroscience research, such as brain fMRI. Especially in brain fMRI, sound noise is one of the serious noise sources that obscures the small signals obtainable from the subtle changes occurring in oxygenation status in the cortex and blood capillaries. Therefore, we have studied the effects of acoustic, or sound, noise arising in fMR imaging of the auditory, motor, and visual cortices. The results show that the effects of acoustic noise on motor and visual responses are opposite. That is, for motor activity, there is an increased total motor activation, whereas for visual stimulation, the corresponding (visual) cortical activity is diminished substantially when the subject is exposed to a loud acoustic sound. Although the current observations are preliminary and require more experimental confirmation, it seems that the observed acoustic-noise effects on brain functions, such as in the motor and visual cortices, are new observations and could have significant consequences in data observation and interpretation in future fMRI studies.     

Hearing thresholds during Gz acceleration with masking noise

BACKGROUND: Future fighter aircraft will include three-dimensional sound signals as part of the human-machine interface. The reduction in cerebral vascular flow associated with maneuvering acceleration (+Gz) may affect a pilot's ability to perceive and interpret such aural cues. We hypothesized that vascular deprivation along the cochlea produced by +Gz would raise hearing thresholds either globally or specifically at 1000 Hz. METHODS: We compared hearing thresholds for pure tones at 250, 1000, 6000 and 10,000 Hz during exposure to +1 Gz vs. +4 Gz. Experiments were conducted with steady noise input to the earphones to mask centrifuge noise. RESULTS: Paradoxically the hearing threshold was slightly yet significantly reduced for 1000 Hz (53 dB at 1 G vs. 47 dB at 4 G) while remaining unchanged at other frequencies. DISCUSSION: Audition did not change at +4 Gz, contradicting our hypothesis. We infer that the change at 1000 Hz is not a central effect, but instead represents a disturbance of middle ear transmission mechanisms. The absence of any general hearing loss at +4 Gz favors the possibility of using complex sounds such as three-dimensional sound in aeronautical human-machine interfaces during acceleration.     

Release from masking in virtual auditory space during sustained positive acceleration

BACKGROUND: The use of a three-dimensional (3-D) auditory display to significantly lower subject detection level while maintaining comprehension under sustained positive G-stress was explored in this study. METHODS: Auditory threshold levels were measured for detecting a band limited pulsed signal in the presence of a broadband diotic masker at both + 1 Gz (rest position) and under sustained +3 Gz. The pulsed signal was presented diotically and was spatialized at one of four static azimuth positions on the horizontal plane. RESULTS: Results showed that auditory thresholds were not significantly affected by sustained +3 Gz stress. Compared with a diotic presentation, subjects reached an average of 6.8 dB lower auditory threshold at +1 Gz and under sustained +3 Gz when the pulsed signal was spatialized at a static position of 90 degrees azimuth on the horizontal plane. CONCLUSION: The implication of these results and suggestions for further research are discussed.     

The MR tomograph as a sound generator: fMRI tool for the investigation of the auditory cortex

An automatic fMRl protocol for the investigation of the human auditory cortex has been developed. For the activation of the auditory system, the scanner noise itself is the source of sound. Rapid switching of 6, gradients allows the generation of tones of defined frequencies and amplitude on a conventional scanner without hardware change. No additional device for sound generation or sound delivety is needed. The proposed technique allows functional MRI of the auditory cortex in a clinical routine session.     

镇静状态下先天性感音神经性耳聋婴幼儿听觉及语言中枢fMRI研究

目的 采用fMRI低频震荡振幅(ALFF)方法评价睡眠状态下先天性极重度感音神经性耳聋婴幼儿的听觉及语言相关脑区脑功能活动.方法 选取先天性极重度感音聋婴幼儿20例,根据大脑发育的关键时期进行分组.I组:0~24个月(包含24月)10例,II组:24~48个月10例;对照组10例.采集SEEPI 血氧水平依赖法全脑fMRI序列,将功能影像原始数据经SPM8软件进行预处理,采用ALFF算法,得到每个体素标准化后的ALFF值(mALFF).利用REST软件中的Statistical Analysis进行聋儿组与对照组、不同年龄聋儿组分别与对照组、2组聋儿之间mALFF值的双样t检验,统计结果用xjview进行显示.结果 聋儿组与对照组比较,左侧BA41、BA22、BA44/45区、缘上回、角回ALFF值减低;0~2岁聋儿组与对照组相比,左侧BA41 、BA22 、BA44/45区、颞上回,右侧BA44/45区ALFF值减低;2~4岁聋儿组与对照组相比,左侧BA22、BA44/45、缘上回、角回、颞中回ALFF值减低;0~2岁与2~4岁聋儿组相比,ALFF值减低的区域包括:左侧BA41、BA45区、颞中回,右侧BA45区;0~2岁、2~4岁聋儿组分别与对照组相比,ALFF值减低的体素总数分别为145、77.结论 睡眠状态下先天性感音聋婴幼儿听觉及语言相关脑区ALFF值较听力正常同龄人减低,且随着耳聋持续时间的延长,听觉及语言相关脑区的ALFF值减低的范围减小.     

fMRI studies of sensitivity and habituation effects within the auditory cortex at 1.5 T and 3 T

PURPOSE: To assess habituation effects in relation to field strength by fMRI at 1.5 vs. 3.0 T within the auditory cortex of healthy subjects. MATERIALS AND METHODS: fMRI experiments were performed on 19 healthy subjects at 1.5 T (N = 12) and 3 T (N = 12). The auditory cortex was stimulated binaurally by digitally generated pulsed (nu = 5 Hz) 800 Hz sine tones with three alternating on and off periods. RESULTS: The mean activation after stimulation (4.4% +/- 1.2% (1.5 T) and 5.3% +/- 2.3% (3 T)) and number of activated pixels (96.7 +/- 49.8 (1.5 T) and 139.9 +/- 101 (3 T)) were higher at 3 T compared to 1.5 T; however, that difference did not reach statistical significance. A characteristic signal decay with repeated stimuli was revealed at both 1.5 and 3 T, and the response to the second and third stimulation blocks was significantly lower compared to the first. The habituation pattern was the same, independently of field strength and age. CONCLUSION: The mean activation and number of pixels were only modestly higher at 3 T, probably due to higher physiologic noise and higher local macroscopic susceptibility gradients within the temporal lobes at 3 T. Our data reveal that measured auditory habituation is independent of field strength, and data obtained at two different field strengths do not differ fundamentally in this context.     

Functional MR of the primary auditory cortex: an analysis of pure tone activation and tone discrimination.

PURPOSETo use functional MR imaging to measure the effect of frequency (pitch), intensity (loudness), and complexity of auditory stimuli on activation in the primary and secondary auditory cortexes.METHODSMultiplanar echo-planar images were acquired in healthy subjects with normal hearing to whom auditory stimuli were presented intermittently. Functional images were processed from the echo-planar images with conventional postprocessing methods. The stimuli included pure tones with a single frequency and intensity, pure tones with the frequency stepped between 1,000, 2,000, 3,000, or 4,000 Hz, and spoken text. The pixels activated by each task in the transverse temporal gyrus (TTG) and the auditory association areas were tabulated.RESULTSThe pure tone task activated the TTG. The 1,000-Hz tone activated significantly more pixels in the TTG than did the 4,000-Hz tone. The 4,000-Hz tone activated pixels primarily in the medial TTG, whereas the 1,000-Hz tone activated more pixels in the lateral TTG. Higher intensity tones activated significantly more pixels than did lower intensity tones at the same frequency. The stepped tones activated more pixels than the pure tones, but the difference was not significant. The text task produced significantly more activation than did the pure tones in the TTG and in the auditory association areas. The more complex tasks (stepped tones and listening to text) tended to activate more pixels in the left hemisphere than in the right, whereas the simpler tasks activated similar numbers of pixels in each hemisphere.CONCLUSIONAuditory stimuli activate the TTG and the association areas. Activation in the primary auditory cortex depends on frequency, intensity, and complexity of the auditory stimulus. Activation of the auditory association areas requires more complex auditory stimuli, such as the stepped tone task or text reading.     

Reducing correlated noise in fMRI data.

The sensitivity of functional MRI (fMRI) in detecting neuronal activation is dependent on the relative levels of signal and noise in the time-series data. The temporal noise level within a single voxel is generally substantially higher than the intrinsic NMR (thermal) noise, and the noise is often correlated between voxels. This work introduces and evaluates a method that allows fMRI sensitivity improvement by reduction of these correlated noise sources. The method allows model-free estimation of the correlated noise from brain regions not activated by the functional paradigm using a short (1-2 min) reference scan. A single regressor representing this noise-source estimate is added to the design matrix used in the data analysis. Results obtained from five volunteers show an average t-score improvement of 11.3% and a 24.2% increase in the size of the activated area.     

Interactions between hemodynamic responses to scanner acoustic noise and auditory stimuli in functional magnetic resonance imaging.

In functional MRI experiments on the central auditory system, activation caused by acoustic scanner noise is a dominating factor that partially masks the hemodynamic response signals to sound stimuli of interest. In this study, the nonlinear interaction between auditory responses to single scans and those to tone stimuli was investigated. By using irregular acquisition repetition times and quasi-random stimulus timings, the brain responses to pure tone stimuli were analyzed, as well as their interaction with scanner noise. The tone frequencies were chosen to match either the fundamental frequency of the scanner noise (730 Hz) or a region with little spectral power (4.70 kHz). The hemodynamic responses could be characterized by amplitudes of 1.3% and a time-to-peak of 4.0-4.5 sec in the absence of scanner noise. Interaction effects due to a single previous scan typically decreased the response magnitudes to 0.9%. The functional shape of the interaction was analyzed and could be described by a highly separable, dominantly symmetric interaction function that fairly agreed with a low-order Volterra expansion of a simple nonlinear model. Interactions were stronger and more complex in shape when the spectral content of the tone stimulus and the scanner noise were more similar.     

Binaural speech discrimination under noise in hearing-impaired listeners

This study was undertaken to assess speech discrimination under binaural listening with background noise in hearing-impaired subjects. Subjects (58 sensori-neural, 23 conductive, and 19 mixed) were administered an indigenous version of W-22 PB words under: Condition I--Quiet--chamber noise below 28 dB with speech at 60 dB; and at a constant signal-to-noise (S/N) ratio of +10 dB with background white noise at 70 dB in Condition II and 80 dB in Condition III. The scores were a) 81 +/- 16%, b) 77 +/- 9%, and c) 79 +/- 13%. Mean scores decreased significantly (p less than 0.001) with noise in all groups while the score was more (p less than 0.001) at the higher noise level only in the sensori-neural group. The decrease in scores with advancing hearing impairment was less in noise than in quiet, probably due to binaural and satisfactory S/N ratio. The scores did not fall below 70% unless the handicap was marked. The need for suitable standards of binaural speech discrimination under noise in aircrew assessment is emphasized.     

宫内期暴露于MR成像听觉噪声的新生儿耳蜗功能测试

目的确定新生儿耳蜗损伤和后继的听力丧失是否与胎儿期暴露于1.5TMR操作噪声有关。材料与方法此项研究经伦理委员会批准,双亲签署知情同意书。收集在     

Functional sex differences in human primary auditory cortex

Background We used PET to study cortical activation during auditory stimulation and found sex differences in the human primary auditory cortex (PAC). Regional cerebral blood flow (rCBF) was measured in 10 male and 10 female volunteers while listening to sounds (music or white noise) and during a baseline (no auditory stimulation). Results and discussion We found a sex difference in activation of the left and right PAC when comparing music to noise. The PAC was more activated by music than by noise in both men and women. But this difference between the two stimuli was significantly higher in men than in women. To investigate whether this difference could be attributed to either music or noise, we compared both stimuli with the baseline and revealed that noise gave a significantly higher activation in the female PAC than in the male PAC. Moreover, the male group showed a deactivation in the right prefrontal cortex when comparing noise to the baseline, which was not present in the female group. Interestingly, the auditory and prefrontal regions are anatomically and functionally linked and the prefrontal cortex is known to be engaged in auditory tasks that involve sustained or selective auditory attention. Thus we hypothesize that differences in attention result in a different deactivation of the right prefrontal cortex, which in turn modulates the activation of the PAC and thus explains the sex differences found in the activation of the PAC. Conclusion Our results suggest that sex is an important factor in auditory brain studies.