Functional MRI of brain activation induced by scanner acoustic noise

A method is introduced by which brain activation caused by the acoustic noise associated with echo planar imaging (EPI) is mapped. Two types of time series were compared. The first time series, considered the “task,” involved applying only EPI gradients for 20 s without the application of RF pulses, then, without pause, starting image collection. The second, considered the “control,” involved typical sequential image acquisition without the prior gradient pulses. Subtraction of the first 5 s of the two time series revealed signal enhancement mainly in the primary auditory cortex. The technique was validated using a motor cortex task that mimicked the hypothesized scanner noise induced activation.     

Increment of brain temporal perfusion during auditory stimulation

A study on the dynamic exploration of the auditory pathway is presented, in which technetium-99m hexamethylpropylene amine oxime single-photon emission computed tomography (SPET) was used in volunteers with normal hearing. Changes in ^99mTc-HMPAO distribution were calculated using a region of interest/whole-brain count ratio. The results showed a temporal perfusion increment of 17% (right) and 19% (left) during tonal supraliminar stimulation, which was significantly different from the control ROI. Sensitivity tests for the method were requested before any clinical application. Offprint requests to: Y. Le Scao     

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.     

Time-course of the auditory BOLD response to scanner noise.

It is a concern for auditory fMRI studies that acoustic noise generated by the scanner produces an auditory response that can confound stimulus-induced activation. To establish how to minimize this problem, the present study mapped the time-course of the auditory response to a burst of acoustic scanner noise by employing a single-event method. Recorded bursts of scanner noise were interspersed with clustered-volume acquisitions at a range of stimulus-to-imaging delays to map the response with a temporal resolution of 1 sec. There were strong responses (1.5% signal change) to scanner noise in primary and secondary auditory cortex. In both cortical areas, the mean response rose to a peak by 4-5 sec after stimulus onset and decayed after a further 5-8 sec. The time course indicates that noise contamination in auditory fMRI can be substantially reduced by using a 9-12-sec repetition time, thus maximizing the dynamic range available for displaying the response to acoustical stimuli of interest.     

A silent event-related functional MRI technique for brain activation studies without interference of scanner acoustic noise.

A new data acquisition method for silent, event-related functional MRI in which scanner acoustic noise does not interfere with brain activation is introduced and evaluated in an auditory tonotopic mapping experiment. This method takes into account the hemodynamic-response characteristics of the brain during activation, associated with both task performance and scanner noise. A data acquisition scheme was designed to collect task-induced brain activation signals without interference of scanner noise on stimulus delivery or on the measured response. The advantages of the technique were demonstrated in a tonotopic mapping experiment of human auditory cortex. Tonotopic maps obtained by the technique in normal subjects showed distinct spatial shifts of the activation foci in the lateral part of Heschl's gyrus with changing stimulus frequency, whereas no systematic shift was shown in a conventional event-related experiment using the same stimulation paradigm. Signal change in the activation foci with the new technique was 54% larger than with the conventional technique, suggesting an increased dynamic range of the signal change associated with task-induced brain activation under silent conditions.     

Influence of acoustic masking noise in fMRI of the auditory cortex during phonetic discrimination

The application of functional magnetic resonance imaging (fMRI) to study activation of auditory cortex suffers from one significant confounding factor, namely, that of the acoustic noise generated by the gradient system, which is an integral part of the imaging process. Earlier work has shown that it is indeed possible to distinguish cortical activation resulting from presentation of auditory stimuli despite the presence of background noise from the gradient system. The influence of acoustic noise from the gradient system of the MRI scanner on the blood oxygen level-dependent (BOLD) response during functional activation of the auditory cortex has been investigated in six healthy subjects with no hearing difficulties. Experiments were performed using gradient-echo echoplanar imaging (EPI) and a verbal, auditory discrimination paradigm, presented in a block-wise manner, in which carefully aligned consonant-vowel syllables were presented at a rate of 1 Hz. For each volunteer the experiment was repeated three times with all parameters fixed, except slice number, which was 4, 16, or 64. The positioning of the central four slices in each experiment was common. Thus, the fraction of TR during which the stimulus is on but no imaging is being performed, varies from almost zero, in the case of 64 slices, to over 8 seconds, in the case of four slices. Only the central four slices were of interest; additional slices simply generated acoustic noise and were discarded. During the four-slice experiment, all subjects showed a robust BOLD response in the superior temporal gyrus covering the primary and secondary auditory cortex. The spatial extent and the z-scores of the activated regions decreased with longer duration of gradient noise from the scanner. For a phonetic discrimination task, the results indicate that presentation of the stimulus during periods free from scanner noise leads to a more pronounced BOLD response.     

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.     

Effects of subthreshold electrical stimulation with white noise,pink noise,and chaotic signals on postural control during quiet standing

BackgroundThe stochastic resonance (SR) phenomenon has been used to improve postural control through the application of imperceptible noise to the somatosensory system. White noise signals have been applied in numerous SR studies on postural control. However, because the SR effect depends on the noise structure, the stimulation effects of signals with different structures, such as pink noise and chaotic signals, on postural control, must be determined to achieve better clinical applications of SR technology.Research questionDuring quiet standing, how is postural control affected by subthreshold electrical stimulation to the knee joints when signals with different structures (white noise, pink noise, and chaotic signals) are used?MethodsSixteen healthy young adults stood quietly for 40 s with their eyes closed. To evaluate postural sway, we calculated the mean velocity, root mean square (CoP_RMS), and range (CoP_Range) values for the center of pressure (CoP) in the anteroposterior direction. The standing task was conducted under subthreshold electrical stimulation with white noise, pink noise, and chaotic signals based on the Lorenz system, in addition to the no-stimulation condition. The four stimulation conditions were randomized within each set and repeated seven times.ResultsSignificant effects of stimulation were observed in the CoP_RMS and CoP_Range values. The CoP_RMS value under the pink noise signal was significantly lower than that under the no-stimulation condition. The CoP_Range value also tended to decrease under the pink noise signal compared with the no-stimulation condition; however, the differences were not statistically significant. No significant changes were found with the white noise and chaotic signals compared with the no-stimulation condition.SignificanceWe demonstrated that the pink noise signal was more effective in reducing postural sway than the white noise and chaotic signals based on the Lorenz system during quiet standing.     

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.     

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.     

Increment of brain temporal perfusion during auditory stimulation. Preliminary study with technetium-99m HMPAO SPET.

A study on the dynamic exploration of the auditory pathway is presented, in which technetium-99m hexamethylpropylene amine oxime single-photon emission computed tomography (SPET) was used in volunteers with normal hearing. Changes in 99mTc-HMPAO distribution were calculated using a region of interest/whole-brain count ratio. The results showed a temporal perfusion increment of 17% (right) and 19% (left) during tonal supraliminar stimulation, which was significantly different from the control ROI. Sensitivity tests for the method were requested before any clinical application.     

Interrelation of visual and auditory analyzer functions during extreme stimulation]

By psychophysiological methods the effect of intensive photostimulation on the functional state of the optic analyzer and the influence of extreme optic stimulus on the hearing function were studied. An impulse acoustic stimulus contributed to the recovery of peripheral light sensitivity, left unchanged the central light sensitivity, improved acuity of color distinction, expanded the field of vision of red and green colors and reduced electric sensitivity and critical frequency of disappearance of light flashes. After an exposure to a superbright flash a decrease of absolute thresholds of hearing, electric sensitivity and critical frequency of fusion of electric stimulation of the acoustic analyzer was detected. These data give evidence that sensitivity of one analyzer can be increased by means of short-term intensive stimulation of the other.     

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.     

Acoustic noise characteristics of a 4 Telsa MRI scanner

PURPOSE: To quantify the acoustic noise characteristics of a 4 Tesla MRI scanner, and determine the effects of structural acoustics and gradient pulse excitations on the sound field so that feasible noise control measures can be developed. MATERIALS AND METHODS: Acoustic noise emissions were measured in the ear and mouth locations of a typical adult. The sound pressure measurements were acquired simultaneously with the electrical current signals of the gradient pulses. Two forms of gradient waveforms (impulsive and operating pulses) were studied. RESULTS: The sound pressure levels (SPLs) emitted by the MRI scanner operating in echo-planar imaging (EPI) mode were in the range of 120-130 decibels. Three types of sound pressure responses were observed in the EPI sequences: 1) harmonic, 2) nonharmonic, and 3) broadband. The frequency-encoding gradient pulses were the most dominant and produced generally odd-number harmonics and nonharmonics. The phase-encoding gradient pulses generated mostly even-number harmonics, and the slice-selection gradient pulses produced primarily a broadband spectrum. CONCLUSION: The operating condition acoustic spectrum can be predicted from the magnet-structural acoustic transfer functions, which are independent of imaging sequences. This finding is encouraging because it shows that it is possible to treat such noises with an active noise control application.     

Influence of a rhythmic auditory stimulation on asymptomatic gait

The direct effects of a rhythmic auditory stimulation (RAS) on the gait of asymptomatic subjects are not clear. Previous studies only showed modifications in the gastrocnemius activity, inconsistent effects on temporal parameters, and no modification of spatial parameters. Furthermore, the influence of RAS on kinematics and kinetics has only been reported in pathological gait. The objective of this study was to perform a full comparison of gait characteristics in asymptomatic subjects at preferred and reduced walking speed between without and with RAS conditions. Spatiotemporal parameters, kinematics, kinetics and EMG signals datasets were collected for each condition. RAS conditions were obtained by asking subjects to walk on metronomic beats. 17 asymptomatic subjects were included in the study (12M/5W, 37.4 ± 15.7 years, 74.0 ± 14.8 kg, 1.77 ± 0.09 m). Comparisons between without and with RAS conditions were then performed using the Statistical Parametric Mapping method. For all combined subjects, the effect of RAS was limited whatever the walking speed. Meanwhile, global effects were observed for kinematics, kinetics and EMG at both spontaneous and reduced walking speed, which can only be explained by covariances (i.e., no effect on individual time-series). The use of RAS to impose a specific cadence matching the desired walking speed (e.g., to collect normative data) appears thus possible, as none parameters were modified individually. However, RAS should be used with caution taking into account covariances (i.e., muscle synergy or joint coordination patterns). This study has to be extended to a larger number of subjects to confirm these observations.     

经颅直流电刺激对运动脑功能网络特征影响的研究

目的 为研究飞行学员飞行训练应激源指标间的关系,建立飞行学员飞行训练应激结构模型。方法 采用访谈和文献分析法初筛飞行学员飞行训练应激源指标,应用SHEL模型进行维度分析,建立5个维度共18项应激源指标体系。采用专家评分法评价飞行学员飞行训练应激源,用决策试验和评价实验室(DEMATEL)和解释结构模型(ISM)法对应激结构建模。结果 计算得到各应激源指标的影响度、被影响度、中心度和原因度,建立递阶层次解释结构模型。天气情况、已发生的不安全事件等是飞行学员应激的深层次原因;心理压力状态、飞行训练难度和进度等因素受其他应激源影响大;其中心理压力、飞行训练难度和进度,以及与教员的关系对飞行学员应激的影响最为关键。结论 应用DEMATEL-ISM法成功建立飞行学员飞行训练应激源多级递阶结构模型,模型分析表明航校应加强安全管控,教员应对学员适时施加积极影响。     

Clinical usefulness of artronix brain scanner multiplanar coronal and sagittal brain images

Summary The Artronix 1100 head scanner is a promising unit which allows reconstitution of the images in coronal and sagittal planes from the axial slice. The clinical usefulness of coronal and sagittal images thus obtained is illustrated and discussed.     

In situ active control of noise in a 4 T MRI scanner

Purpose:

To evaluate the effectiveness of the proposed active noise control (ANC) system for the reduction of the acoustic noise emission generated by a 4 T MRI scanner during operation and to assess the feasibility of developing an ANC device that can be deployed in situ.

Materials and Methods:

Three typical scanning sequences, EPI (echo planar imaging), GEMS (gradient echo multislice), and MDEFT (modified driven equilibrium Fourier transform), were used for evaluating the performance of the ANC system, which was composed of a magnetic compatible headset and a multiple reference feedforward filtered‐x least mean square controller.

Results:

The greatest reduction, about 55 dB, was achieved at the harmonic at a frequency of 1.3 kHz in the GEMS case. Approximately 21 dB and 30 dBA overall reduction was achieved for GEMS noise across the entire audible frequency range. For the MDEFT sequence, the control system achieved 14 dB and 14 dBA overall reduction in the audible frequency range, while 13 dB and 14 dBA reduction was obtained for the EPI case.

Conclusion:

The result is highly encouraging because it shows great potential for treating magnetic resonance imaging noise with an ANC application during real‐time scanning. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

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