Determination of maximum noise level in an ECG channel under SURE Wavelet filtering for HRV extraction

Abstract Heart Rate Variability (HRV) is the measure of variation between R-R interbeats, it has been demonstrated to be a good representation of physiological features, especially to the alterations in the Autonomic Nervous System (ANS). Considering the values that compose a HRV distribution are extracted from electrocardiography (ECG), many of the electrical disturbances that affect ECG-based diagnosis can also interfere with the results of the HRV analysis. This paper uses a 30-minute portion of a healthy patient (no arrhythmias detected or annotated) from the MIT-BIH ECG database to analyze the effectiveness of the SURE Wavelet denoising method for extracting the HRV from a progressively noisier ECG channel. Results show that the minimum SNR for reliable HRV extraction under these conditions is approximately 5dB and outlines the exponential behavior of HRV extraction for escalating noise levels in the ECG signal.

A compact-sized surface EMG sensor for myoelectric hand prosthesis

Myoelectric prosthesis requires a sensor that can reliably capture surface electromyography (sEMG) signal from amputees for its controlled operation. The main problems with the presently available EMG devices are their extremely high cost, large response time, noise susceptibility, less amplitude sensitivity, and larger size. This paper proposes a compact and affordable EMG sensor for the prosthetic application. The sensor consists of an electrode interface, signal conditioning unit, and power supply unit all encased in a single package. The performance of dry electrodes employed in the skin interface was compared with the conventional Ag/AgCl electrodes, and the results were found satisfactory. The envelope detection technique in the sensor based on the tuned RC parameters enables the generation of smooth, faster, and repeatable EMG envelope irrespective of signal strength and subject variability. The output performance of the developed sensor was compared with commercial EMG sensor regarding signal-to-noise ratio, sensitivity, and response time. To perform this, EMG data with both devices were recorded for 10 subjects (3 amputees and 7 healthy subjects). The results showed 1.4 times greater SNR values and 45% higher sensitivity of the developed sensor than the commercial EMG sensor. Also, the proposed sensor was 57% faster than the commercial sensor in producing the output response. The sEMG sensor was further tested on amputees to control the operation of a self-designed 3D printed prosthetic hand. With proportional control scheme, the myoelectric hand setup was able to provide quicker and delicate grasping of objects as per the strength of the EMG signal.

Effect of ME Collimator Characteristic, Energy Window Width, and Reconstruction Algorithm Selection on Imaging Performance of Yttrium-90: Simulation Study / 대한핵의학회잡지

PURPOSE: The treatment efficiency of ⁹⁰Y and providing reliable estimates of activity are evaluated by SPECT imaging of bremsstrahlung radiation released during beta therapy. In this technique, the resulting spectrum from ⁹⁰Y is very complex and continuous, which creates difficulties on the imaging protocol. Moreover, collimator geometry has an impressive effect on the spatial resolution, system sensitivity, image contrast, and the signal-to-noise ratio (SNR), which should be optimized.METHODS: We evaluated the effect of energy window width, reconstruction algorithms, and different geometries of a medium-energy (ME) parallel-hole collimator on the image contrast and SNR of ⁹⁰Y SPECT images. The Siemens E.Cam gamma camera equipped with a ME collimator and a digital Jaszczak phantom were simulated by SIMIND Monte Carlo program to generate the ⁹⁰Y bremsstrahlung SPECT images.RESULTS: Our results showed that optimal image quality can be acquired by the reconstruction algorithm of OS-EM in the energy window width of 60 to 400 keV for ⁹⁰Y bremsstrahlung SPECT imaging. Furthermore, the optimal values of the hole diameter and hole length of a ME collimator were obtained 0.235 and 4.4 cm, respectively.CONCLUSIONS: The acquired optimal ME collimator and energy window along with using a suitable reconstruction algorithm lead to improved contrast and SNR of ⁹⁰Y bremsstrahlung images of hot spheres of the digital Jaszczak phantom. This can improve the accuracy and precision of the ⁹⁰Y activity distribution estimation after radioembolization in targeted radionuclide therapy.

An automatic gain control circuit to improve ECG acquisition

Abstract Introduction Long-term electrocardiogram (ECG) recordings are widely employed to assist the diagnosis of cardiac and sleep disorders. However, variability of ECG amplitude during the recordings hampers the detection of QRS complexes by algorithms. This work presents a simple electronic circuit to automatically normalize the ECG amplitude, improving its sampling by analog to digital converters (ADCs). Methods The proposed circuit consists of an analog divider that normalizes the ECG amplitude using its absolute peak value as reference. The reference value is obtained by means of a full-wave rectifier and a peak voltage detector. The circuit and tasks of its different stages are described. Results Example of the circuit performance for a bradycardia ECG signal (40bpm) is presented; the signal has its amplitude suddenly halved, and later, restored. The signal is automatically normalized after 5 heart beats for the amplitude drop. For the amplitude increase, the signal is promptly normalized. Conclusion The proposed circuit adjusts the ECG amplitude to the input voltage range of ADC, avoiding signal to noise ratio degradation of the sampled waveform in order to allow a better performance of processing algorithms.

Detection of SNR and geometric accuracy of MRI system based on ACR standards / 医疗卫生装备

Objective To detect the SNR and geometric accuracy of MRI based on American College of Radiology (ACR)standards.Methods The SNR and geometric accuracy of Siemens Skyra 3.0T,Siemens Trio 3.0T and GE Excite HD 1.5T MRI were measured with ACR phantom,and the detection results were calculated according to the standards.Results The SNR values of Siemens Skyra 3.0T,Siemens Trio 3.0T and GE Excite HD 1.5T MRI were 589.98,438.50 and 277.12 respectively.Siemens Skyra 3.0T MRI had the values of geometric accuracy being-1.93％ at X direction,-3.20％ at Y direction and 0.68％ at Z direction,Siemens Trio 3.0T MRI had the value of geometric accuracy being-0.87％ at X direction,-2.33％ at Y direction and 1.49％ at Z direction,GE Excite HD 1.5T MRI had the values of geometric accuracy being 0.20％ at X direction,-1.53％ at Y direction and 1.69％ at Z direction.Conclusion The detection of the SNR and geometric accuracy of MRI can effectively guarantee the image quality.

Detection of SNR and geometric accuracy of MRI system based on ACR standards / 医疗卫生装备

Objective To detect the SNR and geometric accuracy of MRI based on American College of Radiology (ACR)standards.Methods The SNR and geometric accuracy of Siemens Skyra 3.0T,Siemens Trio 3.0T and GE Excite HD 1.5T MRI were measured with ACR phantom,and the detection results were calculated according to the standards.Results The SNR values of Siemens Skyra 3.0T,Siemens Trio 3.0T and GE Excite HD 1.5T MRI were 589.98,438.50 and 277.12 respectively.Siemens Skyra 3.0T MRI had the values of geometric accuracy being-1.93％ at X direction,-3.20％ at Y direction and 0.68％ at Z direction,Siemens Trio 3.0T MRI had the value of geometric accuracy being-0.87％ at X direction,-2.33％ at Y direction and 1.49％ at Z direction,GE Excite HD 1.5T MRI had the values of geometric accuracy being 0.20％ at X direction,-1.53％ at Y direction and 1.69％ at Z direction.Conclusion The detection of the SNR and geometric accuracy of MRI can effectively guarantee the image quality.

"The modulating effect of 5-HT1B and D1DR receptors in neurons within ""SNr/GPi-VL-SMA"" pathway on exercise induced fatigue" / 中国康复医学杂志

Objective:To observe the changes of 5-HT1B and D1DR expression in nucleus of SNr/GPi-VL-SMA pathway in pre and post-exhaustive exercise,and investigate the central mechanism of SNr/GPi-VL-SMA pathway modulating the occurrence and development of exercise-induced fatigue.Method:Twenty-four male Wistar rats were randomly divided into control group (CG),immediately after exhaustion group (EG),and 90min after recovery group (RG),each consists of 8 rats.The expression level of 5-HT1B and D1DR receptors in each group were observed with the immunohistochemistry technique.Result:Compared with CG,the positive cell area/scanning area value (R value) and the average optical density value (AOD value) of 5-HT1B receptor in SNr and GPi of the EG and RG rats both decreased significantly (P ＜ 0.05),while the R value and AOD value of D1DR both increased significantly(P＜ 0.05).The R value and AOD value of 5-HT1B receptor in VL of EG and RG rats increased significantly(P＜0.05,P＜0.01).In SMA,the R value and AOD value of 5-HT1B receptor of EG and RG rats increased significantly (P＜ 0.05),while,the R value and AOD value of D1DR receptor decreased significantly (P ＜ 0.05).Conclusion:Changes of 5-HT1B receptor and D1DR receptor expression in the nuclei of ‘SNr/GPi-VL-SMA'pathway caused the changes of the neurotransmitters release,thus affecting the excitability of the electrical activity of neurons,this might be one of the important ways for ‘SNr/GPi-VL-SMA'pathway modulating the exercise-induced fatigue and exercise performance.

Accelerated Resting-State Functional Magnetic Resonance Imaging Using Multiband Echo-Planar Imaging with Controlled Aliasing

PURPOSE: To report the use of multiband accelerated echo-planar imaging (EPI) for resting-state functional MRI (rs-fMRI) to achieve rapid high temporal resolution at 3T compared to conventional EPI. MATERIALS AND METHODS: rs-fMRI data were acquired from 20 healthy right-handed volunteers by using three methods: conventional single-band gradient-echo EPI acquisition (Data 1), multiband gradient-echo EPI acquisition with 240 volumes (Data 2) and 480 volumes (Data 3). Temporal signal-to-noise ratio (tSNR) maps were obtained by dividing the mean of the time course of each voxel by its temporal standard deviation. The resting-state sensorimotor network (SMN) and default mode network (DMN) were estimated using independent component analysis (ICA) and a seed-based method. One-way analysis of variance (ANOVA) was performed between the tSNR map, SMN, and DMN from the three data sets for between-group analysis. P < 0.05 with a family-wise error (FWE) correction for multiple comparisons was considered statistically significant. RESULTS: One-way ANOVA and post-hoc two-sample t-tests showed that the tSNR was higher in Data 1 than Data 2 and 3 in white matter structures such as the striatum and medial and superior longitudinal fasciculus. One-way ANOVA revealed no differences in SMN or DMN across the three data sets. CONCLUSION: Within the adapted metrics estimated under specific imaging conditions employed in this study, multiband accelerated EPI, which substantially reduced scan times, provides the same quality image of functional connectivity as rs-fMRI by using conventional EPI at 3T. Under employed imaging conditions, this technique shows strong potential for clinical acceptance and translation of rs-fMRI protocols with potential advantages in spatial and/or temporal resolution. However, further study is warranted to evaluate whether the current findings can be generalized in diverse settings.

MEG and EEG dipole clusters from extended cortical sources

Data from magnetoencephalography (MEG) and electroencephalography (EEG) suffer from a rather limited signal-to-noise-ratio (SNR) due to cortical background activities and other artifacts. In order to study the effect of the SNR on the size and distribution of dipole clusters reconstructed from interictal epileptic spikes, we performed simulations using realistically shaped volume conductor models and extended cortical sources with different sensor configurations. Head models and cortical surfaces were derived from an averaged magnetic resonance image dataset (Montreal Neurological Institute). Extended sources were simulated by spherical patches with Gaussian current distributions on the folded cortical surface. Different patch sizes were used to investigate cancellation effects from opposing walls of sulcal foldings and to estimate corresponding changes in MEG and EEG sensitivity distributions. Finally, white noise was added to the simulated fields and equivalent current dipole reconstructions were performed to determine size and shape of the resulting dipole clusters. Neuronal currents are oriented perpendicular to the local cortical surface and show cancellation effects of source components on opposing sulcal walls. Since these mostly tangential aspects from large cortical patches cancel out, large extended sources exhibit more radial components in the head geometry. This effect has a larger impact on MEG data as compared to EEG, because in a spherical head model radial currents do not yield any magnetic field. Confidence volumes of single reconstructed dipoles from simulated data at different SNRs show a good correlation with the extension of clusters from repeated dipole reconstructions. Size and shape of dipole clusters reconstructed from extended cortical sources do not only depend on spike and timepoint selection, but also strongly on the SNR of the measured interictal MEG or EEG data. In a linear approximation the size of the clusters is proportional to the inverse SNR.

Signal-to-noise Ratio Loss in the People with Normal Audiograms / 听力学及言语疾病杂志

Objective To explore the signal-to-noise ratio loss (SNR loss) of the people with normal pure-tone audiograms .Methods A group of 10 patients were recruited into the study ,who complained they could not hear speech clearly in the real world environment but had normal pure-tone audiograms ,immittance and word rec-ognition score (WRS) results .The Mandarin hearing in noise test (M-HINT ) was administered to them and the results were compared to the normal ranges published in the journal .Results All of them had SNR loss when noise (speech spectrum) came from front of them ,but 9 patients had SNR loss when noise came from 90 degree left or 90 degree right of them .Conclusion The current study showed the patients had speech hearing loss in the noisy envi-ronment ,regardless of whether they had normal audiograms ,immittance and WRS results .So we should pay atten-tion to such patients and adopt some special tests (eg M-HINT) .It is better for us to communicate and counsel with them .

Clinical Experience with 3.0 T MR for Cardiac Imaging in Patients: Comparison to 1.5 T using Individually Optimized Imaging Protocols

PURPOSE: To report our clinical experience with cardiac 3.0 T MRI in patients compared with 1.5 T using individually optimized imaging protocols. MATERIALS AND METHODS: We retrospectively reviewed 30 consecutive patients and 20 consecutive patients who underwent 1.5 T and 3 T cardiac MRI within 10 months. A comparison study was performed by measuring the signal-to-noise ratio (SNR), the contrast-to-noise ratio (CNR) and the image quality (by grading each sequence on a 5-point scale, regarding the presence of artifacts). RESULTS: In morphologic and viability studies, the use of 3.0 T provided increase of the baseline SNRs and CNRs, respectively (T1: SNR 29%, p < 0.001, CNR 37%, p < 0.001; T2-SPAIR: SNR 13%, p = 0.068, CNR 18%, p = 0.059; viability imaging: SNR 45%, p = 0.017, CNR 37%, p = 0.135) without significant impairment of the image quality (T1: 3.8 +/- 0.9 vs. 3.9 +/- 0.7, p = 0.438; T2-SPAIR: 3.8 +/- 0.9 vs. 3.9 +/- 0.5, p = 0.744; viability imaging: 4.5 +/- 0.8 vs. 4.7 +/- 0.6, p = 0.254). Although the image qualities of 3.0 T functional cine images were slightly lower than those of 1.5 T images (3.6 +/- 0.7 vs. 4.2 +/- 0.6, p < 0.001), the mean SNR and CNR at 3.0 T were significantly improved (SNR 143% increase, CNR 108% increase, p < 0.001). With our imaging protocol for 3.0 T perfusion imaging, there was an insignificant decrease in the SNR (11% decrease, p = 0.172) and CNR (7% decrease, p = 0.638). However, the overall image quality was significantly improved (4.6 +/- 0.5 vs. 4.0 +/- 0.8, p = 0.006). CONCLUSION: With our experience, 3.0 T MRI was shown to be feasible for the routine assessment of cardiac imaging.

SNR and ADC Changes at Increasing b Values among Patients with Lumbar Vertebral Compression Fracture on 1.5T MR Diffusion Weighted Images / 의학물리

To examine among patients with vertebral compression fracture the extent to which signal-to-noise ratio (SNR) and Apparent Diffusion Coefficient (ADC) values at the lumbar vertebral compression fracture site vary on diffusion-weighted MR images according to varying b values on the 1.5T MR device. Diffusion-weighted MR images of 30 patients with compression fracture due to chronic osteoporosis who underwent vertebral MRI from Jan. 2008 to Nov. 2009 were respectively obtained using a 1.5-T MR scanner with the b values increased from 400, 600, 800, 1,000 to 1,200 s/mm2. For diffusion-weighted MR images with different b values, the signal-to-noise ratio (SNR) was assessed at three sites: the site of compression fracture of the lumbar vertebral body at L1 to L5, and both the upper and lower discs of the said fracture site, while for ADC map images with different b values, the SNR and ADC were respectively assessed at those three sites. As a quantitative analysis, diffusion-weighted MR images and ADC map images with b value of 400 s/mm2 (the base b values) were respectively compared with the corresponding images with each different b value. As far as qualitative analysis is concerned, for both diffusion-weighted MR and ADC map images with b value of 400 s/mm2, the extent to which signal intensity values obtained at the site of compression fracture of the lumbar vertebral body at L1 to L5 vary according to the increasing b values were examined. The quantitative analysis found that for both diffusion-weighted MR and ADC map images, as the b values increased, the SNR were relatively lowered at all the three sites, compared to the base b value. Also, it was found that as the b values increased, ADC values were relatively lowered at all the three sites on ADC map images. On the other hand, the qualitative analysis found that as the b values increased to more than 400 s/mm2, the signal intensity gradually decreased at all the sites, while at the levels of more than 1,000 s/mm2, severe image noises appeared at all of the three sites. In addition, higher signal intensity was found at the site of compression fracture of the lumbar vertebral body than at the discs. Findings showed that with the b value being increased, both the signal-to-noise ratio (SNR) and Apparent Diffusion Coefficient (ADC) values gradually decreased at all the sites of the lumbar vertebral compression fracture and both the upper and lower discs of the fracture site, suggesting that there is a possibility of a wider range of applications to assessment of various vertebral pathologies by utilizing multi b values in the diffusion-weighted MRI examination.

Assessment of Osteoporosis Based on Changes in SNR and ADC Values on MR Diffusion Weighted Images / 의학물리

This study tested how S/N (Signal to Noise Ratio) ratios and ADC (apparent diffusion coefficient) values vary with different T-scores in a group of patients with osteoporosis. Based on DEXA (Dual Energy X-ray Absorptiometry) T-scores for L1?L4 for two groups of subjects consisting of 30 healthy people without osteoporosis and 30 patients who came for treatment of waist (lumbar or low back) pain and were suspected to have osteoporosis as judged from the simple X-ray findings, this study classified every spine into two groups of osteoporosis and osteopenia. Signal intensity measurements were made in the four regions of L1 to L4 on diffusion-weighted MR images obtained using 1.5T MR scanner, while ADC measurements were obtained from ADC map images. As an approach for quantitative analysis, the comparison of the variances in S/N ratios and ADC values for varying T-scores in the selected regions of interest was carried out based on averaged T-scores, S/N ratios, and ADC values. Also, the variances in S/N ratios and ADC values for each of the groups of osteoporosis and osteopenia, which were classified into by T-scores, were compared. For qualitative analysis, a careful naked eye examination of signal intensity differences in the area of L4 was made on T1-weighted sagittal images for each of the healthy (normal), osteopenia, and osteoporosis groups. In the qualitative analysis, it was found that for both the osteopenia group and the osteoporosis group, as T-scores deceased, the S/N ratios on diffusion-weighted MR images also decreased, with the greatest decrease in the S/N ratio found in the osteoporosis group. Additionally, among the three groups, the lowest S/N ratio was found in the osteoporosis group. With respect to ADC map, it was found that for both the osteopenia group and the osteoporosis group, as T-scores deceased, the ADC values on diffusion-weighted MR images also decreased, with the greatest decrease in the ADC values found in the osteoporosis group. Additionally, among the three groups, the lowest ADC value was found in the osteoporosis group. On the other hand, in the qualitative analysis, the osteoporosis group showed the highest signal intensity. Additionally, among the three groups, the lowest signal intensity was found in the healthy (normal) group. It was found that as osteoporosis progressed, S/N ratio and ADC decreased, whereas signal intensity increased on T1-weighted images. Also, in diagnosing osteoporosis, MRI tests turned out to be (more) effective.

The Effect of Coating Material of Copper-wire RF Coil on the Signal-to-Noise Ratio in MR Images

PURPOSE: To investigate the effect of coating material in RF coil, which is one of main parts in MRI machine, on the Q-factor and SNR(signal-to-noise ratio) in MR images. MATERIALS AND METHODS: RF coils with inner diameter of 1.7 mm were made by using copper wires coated with polyester, polyurethane, polyimide, polyamideimide, and polyester-imide, and by using copper wires in which coating materials had been removed. Q-factors of the RF coils were measured by network analyzer, and SNR values in the spin-echo MR images obtained by 600 MHz (14.1 T, Bruker DMX600) micro-imaging system for the coated and uncoated cases. RESULTS: The measured SNRs were almost same for the RF coils with coat-removed copper wires, however SNRs and Q-factors were different for the coated cases depending on the coating material. They were maximized in the polyurethane-coated case in which the SNR was >30% greater than polyester-coated case. CONCLUSION: We made solenoid-type RF coils which were easily used for MR micro-imaging in Bruker MRI probe. There was a significant coating-material dependence in the measured Q values and SNRs for the home-made RF coils. The study demonstrated that the choice of coating material of RF coil may be a critical factor in the MRI sensitivity based on SNR value.

Characteristics of a new cone beam computed tomography / 대한구강악안면방사선학회지

PURPOSE: To determine the physical properties of a newly developed cone beam computed tomography (CBCT). MATERIALS AND METHODS: We measured and compared the imaging properties for the indirect-type flat panel detector (FPD) of a new CBCT and the single detector array (SDA) of conventional helical CT (CHCT). RESULTS: First, the modulation transfer function (MTF) of the CBCT were superior to those of the CHCT. Second, the noise power spectrum (NPS) of the CBCT were worse than those of the CHCT. Third, detective quantum efficiency (DQE) of the indirect-type CBCT were worse than those of the CHCT at lower spatial frequencies, but were better at higher spatial frequencies. Although the comparison of contrast-to-noise ratio (CNR) was estimated in the limited range of tube current, CNR of CBCT were worse than those of CHCT. CONCLUSION: This study shows that the indirect-type FPD system may be useful as a CBCT detector because of high resolution.

Development of Solenoid RF Coil for Animal Imaging in 3T High Magnetic Field MRI

PURPOSE: The purpose of the present study was to develop and optimize solenoid coil for animal- model in 3 T MRI system and investigate and compare with the birdcage coil concerning the image quality with the various parameters such as SNR and Q-factor. MATERIALS AND METHODS: Solenoid coil for animal-model was made on the acryl structure (diameter 4 cm, length 10 cm) 3 times-winding cooper tape of width 2 cm , thickness 0.05 cm and length 10 cm with 2 cm interval between winded tapes. Capacitors from 2 pF to 100 pF were used, and the solenoid coil was designed for receiver only coil. RESULTS: SNR of the developed solenoid was 985 in CuSO4 0.7 g/L and 995 in rat experiment. Q-factor was 84-89 in unloaded condition and 203-206 in loaded condition. CONCLUSION: The resolution of the image obtained from solenoid was relatively higher than that of the conventional birdcage coil. In addition, the homogeneity of RF field by coil simulation was significantly excellent. The present study demonstrated that the solenoid coil could be useful to obtain small animal images with better contrast, resolution, visibility than images from birdcage.

The Influence of Different Channel Adaptive Directional Microphone Setups on the Spoken Language Understandability / 听力学及言语疾病杂志

Objective To compare the effects of speech recognition scores in young normal hearing adults using single-channel adaptive microphone and multi-channel microphone paradigm.Methods 30 normal hearing young adults,15 females and 15 males with a total of 60 ears were fitted binaurally with Diva 9(single-channel adaptive directional microphone mode)and Inteo 9(multi-channel adaptive directional microphone mode).The speech recognition scores were compared as a function of different signal to noise ratios in a diffuse environment.Results The SNR of L50 of single-channel adaptive directional microphone mode was 0.63 dB and that of multi-channel adaptive directional microphone mode was-4.63 dB.There was significant difference between the two microphone setups.Conclusion Multi-channel adaptive directional microphone mode can improve the speech recognition score in noise.

Comparison of Performances of Three Kinds of Direct Current Power Source in the Application of Electrical Impedance Tomography(EIT) / 医疗卫生装备

Objective To provide the hardware system of EIT with an excellent direct current(DC) power source. Methods The spectrums of the outputs of DC power source and the driving source were analyzed by means of Spectrum Analyzer- E4408B when EIT system was respectively powered by battery, linear power source and switching power source. Based on the numbers and power levels of the spurs of the three power sources and the numbers and power levels of the interferences within the driving source, the influence of the three power sources on the error of measuring was estimated. Meanwhile the EIT system did data acquisition, the overall signal-to-noise-ratio(SNR) of the three power sources at the 18 frequencies were calculated and the influence of the three power sources on the error of measuring was judged. Results With respect to the numbers and power levels of the interferences within the driving source when EIT was powered respectively by the three power sources, the battery output 6 interferences, the highest power of which achieved -78.25 dBm; the linear power source output 6 interferences, the highest power of which achieved -67.11 dBm; the switching power source output 15 interferences, the highest power of which achieved -35.83 dBm. The overall SNRs of the battery at the 18 driving frequencies were higher than that of the linear power source, and the overall SNRs of the linear power source were higher than that of the switching power source. Conclusion The power mode of battery is the best for the hardware of EIT among the three power sources.

Development of TEM Head-size Resonator for 3T MRI Head Coil

PURPOSE: To apply a distributed circuit theory, to develop a head-size transverse electromagnetic(TEM) resonator coil for a home-built 3T whole-body MRI system and to report an efficiency of the coil. MATERIALS AND METHODS: The dimension of TEM resonator with 16 cavity element, the diameter of copper rod was 0.63cm and its length was 13.75cm. As raw materials, the purity of copper rod was 98% and the dielectric constant of teflon was 2.08. RESULTS: The TEM head-size resonator with 16cavity elements exhibiting 9-mode resonances was robust to the surrounding influences owing to the self-shielding structure. The isolation of quadrature with a human brain was 364 and the ratio of Q(unloaded/Q(loaded) was 2.9. CONCLUSION: It was successfully demonstrated that the TEM head-size resonator with high Q factor can provide high quality MR images at 3T MRI system. Also, the TEM resonator coil has an advantage for a fine tune with length adjustment of each cavity elements. Thus, it is expected that the TEM resonator at 3T, even higher field could be used in the clinical and research studies in near future.

Comparison of Speech Perception Performance of BTE Hearing Aids With Different Directional Microphones / 听力学及言语疾病杂志

Objective To compare the speech perception performance of BTE hearing aids with different directional microphones. Methods 20 adults with sensorineural hearing loss participated in the research. Two digital hearing aids were programmed for adaptive directional, fixed directional, and omni-directional microphone patterns. The multi-talker noise was presented in three conditions: 180?,?90?, and 360?. Each subject was tested in nine listening conditions (three microphone patterns and three noise presentations) by using modified Hearing In Noise Test. SNR was obtained in each testing condition. Results Under each noise presentation, the sequence of microphone patterns that obtained SNR from low to high was: adaptive directional, fixed directional, and omni-directional. Conclusion Adaptive directional microphone worked best when the noise source was changing or the noise was coming not only from behind but also from other directions; fixed directional microphone could be employed when the noise came from the rear; omni-directional microphone was suitable for hearing in quiet.