Chemical exchange saturation transfer MR imaging of articular cartilage glycosaminoglycans at 3 T: Accuracy of B0 Field Inhomogeneity corrections with gradient echo method

Glycosaminoglycan Chemical Exchange Saturation Transfer (gagCEST) is an important molecular MRI methodology developed to assess changes in cartilage GAG concentrations. The correction for B₀ field inhomogeneity is technically crucial in gagCEST imaging. This study evaluates the accuracy of the B₀ estimation determined by the dual gradient echo method and the effect on gagCEST measurements. The results were compared with those from the commonly used z-spectrum method. Eleven knee patients and three healthy volunteers were scanned. Dual gradient echo B₀ maps with different ?TE values (1, 2, 4, 8, and 10 ms) were acquired. The asymmetry of the magnetization transfer ratio at 1 ppm offset referred to the bulk water frequency, MTR_asym(1 ppm), was used to quantify cartilage GAG levels. The B₀ shifts for all knee patients using the z-spectrum and dual gradient echo methods are strongly correlated for all ?TE values used (r = 0.997 to 0.786, corresponding to ?TE = 10 to 1 ms). The corrected MTR_asym(1 ppm) values using the z-spectrum method (1.34% ± 0.74%) highly agree only with those using the dual gradient echo methods with ?TE = 10 ms (1.72% ± 0.80%; r = 0.924) and 8 ms (1.50% ± 0.82%; r = 0.712). The dual gradient echo method with longer ?TE values (more than 8 ms) has an excellent correlation with the z-spectrum method for gagCEST imaging at 3 T.     

The influence of later-arriving sounds on the ability of listeners to judge the lateral position of a source

This study examined the deleterious effects of a later-arriving sound on the processing of interaural differences of time (IDTs) from a preceding sound. A correlational analysis assessed the relative weight given to IDTs of source and echo clicks for echo delays of 1-64 ms when the echo click was attenuated relative to the source click (0-36 dB). Also measured were proportion correct and the proportion of responses predicted from the weights. The IDTs of source and echo clicks were selected independently from Gaussian distributions (mu=0 s, sigma = 100/s). Listeners were instructed to indicate the laterality of the source click. Equal weight was given to the source and echo clicks for echo delays of 64 ms with no echo attenuation. For echo delays of 16-64 ms, attenuating the echo had no substantial effect on source weight or proportion correct until the echo was attenuated by 18-30 dB. At echo delays < or =4 ms, source weights and proportions correct remained high regardless of echo attenuation. The proportions of responses predicted from the weights were lower at echo delays > or =16 ms. Results were discussed in terms of backward recognition masking and binaural sluggishness and compared to measurements of echo disturbance.     

Factors affecting sound exposure from firing an SA80 high-velocity rifle

The effect of distance on the peak sound pressure level and sound exposure level from an SA80 rifle has been investigated. Sound pressure waveforms were measured in two directions from the gun: downrange, from 50 m to 300 m, and to the left-hand side, from 0.3 m to 32 m. Some additional measurements were made to the right of the gun. Measurements made downrange showed three distinct features of the waveform; the shock wave from the supersonic bullet, the reflection from the ground, and the muzzle blast. The time elapsed between the shock wave and the muzzle blast increased with increasing distance: 94 ms for a distance of 50 m, and 507 ms for a distance of 300 m. The highest peak sound level downrange from a single round was between 151 dB(C) and 148 dB(C) at distances from 50 m to 300 m, and varied little if at all with distance. To the left of the gun, the peak sound pressure level of 161 dB(C) at 0.3 m reduced to 128 dB(C) at 32 m. The peak sound pressure level was estimated to be 137 dB(C) at a distance of approximately 20 m to the left-hand side. Hearing protection must therefore be worn by anyone closer than 20 m to a person firing. The peak sound pressure level was estimated to be 135 dB(C) at a distance of approximately 25 m and therefore hearing protection is recommended at distances of up to 25 m. The sound exposure level of 98 dB(A) at 20 m indicated that an observer at this distance could hear about 1440 rounds without hearing protection before the noise exposure reached the upper exposure action value specified in the Control of Noise at Work Regulations 2005. Peak sound pressure levels were on average 2.4 dB higher at the left ear compared with the right ear.     

On the defect pattern evolution in sapphire irradiated by swift ions in a broad fluence range

Sapphire samples, irradiated with swift Kr (245 MeV) ions at room temperature in a broad fluence range, were investigated using a continuous and a pulsed positron beam to study the defect structure created by the passage of the ions in depths of a few micrometers. At small doses, monovacancies were identified as dominant defects and positron trapping centres. These monovacancies are assumed to be highly concentrated inside a cylindrical volume around the ion path with an estimated radius of ∼1.5 nm. For higher doses a second type of trapping centre emerges. This second class of structural imperfection was associated with the overlap of the individual ion tracks leading to the formation of larger vacancy clusters or voids.     

Heart ablation using a planar rectangular high intensity ultrasound transducer and MRI guidance

The aim of this study was to evaluate a flat rectangular (3 × 10 mm²) MRI compatible transducer operating at 5 MHz. The main task was to explore the feasibility of creating deep lesions in heart at a depth of at least 15 mm. The size of thermal necrosis in heart tissue was estimated as a function of power and time using a simulation model. The system was then tested in an excised lamb heart. In this study, we were able to create lesions of 15 mm deep with acoustic power of 6 W for an exposure of approximately 1 min. The contrast to noise ratio (CNR) between lesion and heart tissue was evaluated using fast spin echo (FSE). The CNR value was approximately 22 using T1 W FSE. Maximum CNR was achieved with repetition time (TR) between 300 and 800 ms. Using T2W FSE, the corresponding CNR was approximately 13 for the 14 in vivo experiments. The average lesion depth was 11.93 mm with a standard deviation of 0.62 mm. In vivo irradiation conditions were 6 W for 60 s. The size of the lesion in the other two dimensions was close to 3 × 10 mm² (size of the transducer element).     

Passive acoustic location of bowhead whales in a population census off Point Barrow, Alaska

A sonobuoy array placed in the nearshore lead was used for locating bowhead whale sounds to determine if whales migrated past census stations beyond visual range and were uncounted. Based on a sample of 182 whale sounds (over 48 h) from closest point of approach (CPA) distances out to more than 10 km, 68% originated beyond 2 km (CPA), where only 1% of the 242 whales were sighted. No whales were sighted beyond 3 km during this time, but 53% of the located sounds originated that far and beyond. Thirty-seven other bowhead sounds over 15 h were distributed out to 6 km. Two tracked whales moved at average speeds of 1.5 and 1.8 kn. Maximum location error was 1%-25% in a sector of 120 degrees X 5-10 km, depending upon bearing and range. Most whale sounds were low-frequency moans, trumpeting roars, and repetitive sequences (songs) with peak spectrum source level up to 189 dB re: 1 microPa, 1 m. Lack of correlations between numbers of sounds and sighted whales precluded using bowhead sounds to count individuals or even to extrapolate ratios of unseen to observed whales.     

Rhythmic masking release: contribution of cues for perceptual organization to the cross-spectral fusion of concurrent narrow-band noises

The contribution of temporal asynchrony, spatial separation, and frequency separation to the cross-spectral fusion of temporally contiguous brief narrow-band noise bursts was studied using the Rhythmic Masking Release paradigm (RMR). RMR involves the discrimination of one of two possible rhythms, despite perceptual masking of the rhythm by an irregular sequence of sounds identical to the rhythmic bursts, interleaved among them. The release of the rhythm from masking can be induced by causing the fusion of the irregular interfering sounds with concurrent "flanking" sounds situated in different frequency regions. The accuracy and the rated clarity of the identified rhythm in a 2-AFC procedure were employed to estimate the degree of fusion of the interferring sounds with flanking sounds. The results suggest that while synchrony fully fuses short-duration noise bursts across frequency and across space (i.e., across ears and loudspeakers), an asynchrony of 20-40 ms produces no fusion. Intermediate asynchronies of 10-20 ms produce partial fusion, where the presence of other cues is critical for unambiguous grouping. Though frequency and spatial separation reduced fusion, neither of these manipulations was sufficient to abolish it. For the parameters varied in this study, stimulus onset asynchrony was the dominant cue determining fusion, but there were additive effects of the other cues. Temporal synchrony appears to be critical in determining whether brief sounds with abrupt onsets and offsets are heard as one event or more than one.     

Micromachined high frequency PMN-PT/epoxy 1-3 composite ultrasonic annular array

This paper reports the design, fabrication, and performance of miniature micromachined high frequency PMN-PT/epoxy 1-3 composite ultrasonic annular arrays. The PMN-PT single crystal 1-3 composites were made with micromachining techniques. The area of a single crystal pillar was 9 × 9 μm. The width of the kerf among pillars was ∼5 μm and the kerfs were filled with a polymer. The composite thickness was 25 μm. A six-element annular transducer of equal element area of 0.2 mm² with 16 μm kerf widths between annuli was produced. The aperture size the array transducer is about 1.5 mm in diameter. A novel electrical interconnection strategy for high density array elements was implemented. After the transducer was attached to the electric connection board and packaged, the array transducer was tested in a pulse/echo arrangement, whereby the center frequency, bandwidth, two-way insertion loss (IL), and cross talk between adjacent elements were measured for each annulus. The center frequency was 50 MHz and −6 dB bandwidth was 90%. The average insertion loss was 19.5 dB at 50 MHz and the crosstalk between adjacent elements was about −35 dB. The micromachining techniques described in this paper are promising for the fabrication of other types of high frequency transducers, e.g. 1D and 2D arrays.     

A reduced-scale railway noise barrier's insertion loss and absorption coefficients: comparison of field measurements and predictions

In situ testing determined the insertion loss (IL) and absorption coefficients of a candidate absorptive noise barrier (soundwall) to abate railway noise for residents of Anaheim, CA. A 4000 m barrier is proposed south of the tracks, but residential areas to the north have expressed concerns that barrier reflections will increase their noise exposure. To address these concerns, a 3.66 m high by 14.6 m long demonstration barrier was built in the parking lot of Edison Field, Anaheim, as part of a public open house, thereby allowing for acoustical measurements.Insertion loss (IL) was measured in third-octave bands assuming 1/2-scale construction. The IL for three, scaled railway noise sub-sources (rail/wheel interface, locomotive, and train horn) was measured at six, scaled distances. The highest total, A-weighted IL, after corrections for finite-barrier and point-source speaker effects was 22 dB(A) for rail/wheel noise, 18 dB(A) for locomotive noise, and 20 dB(A) for train horn noise. These results can be compared favourably to IL predictions made using algorithms from the US Federal Rail Administration (FRA) noise assessment guidelines. For the actual barrier installation, shielded residential receivers located south of the project are expected to see their future noise exposures reduced from an unmitigated 78 CNEL to 65 CNEL.Absorption coefficients were measured using time delay spectrometry. At lower frequencies, measured absorption coefficients were notably less than the reverberation room results advertised in the manufacturer's literature, but generally conformed with impedance tube results. At higher frequencies the correspondence between measured absorption coefficients and reverberation room results was much improved. For the actual barrier installation, unshielded residential receivers to the north are expected to experience noise exposure increases of less than 1 dB(A). This factor of increase is consistent with a finding of no impact when assessed using FRA guidelines for allowable increases of noise exposure.     

Investigation of the relationship among three common measures of precedence: fusion, localization dominance, and discrimination suppression

Listeners have a remarkable ability to localize and identify sound sources in reverberant environments. The term "precedence effect" (PE; also known as the "Haas effect," "law of the first wavefront," and "echo suppression") refers to a group of auditory phenomena that is thought to be related to this ability. Traditionally, three measures have been used to quantify the PE: (1) Fusion: at short delays (1-5 ms for clicks) the lead and lag perceptually fuse into one auditory event; (2) Localization dominance: the perceived location of the leading source dominates that of the lagging source; and (3) Discrimination suppression: at short delays, changes in the location or interaural parameters of the lag are difficult to discriminate compared with changes in characteristics of the lead. Little is known about the relation among these aspects of the PE, since they are rarely studied in the same listeners. In the present study, extensive measurements of these phenomena were made for six normal-hearing listeners using 1-ms noise bursts. The results suggest that, for clicks, fusion lasts 1-5 ms; by 5 ms most listeners hear two sounds on a majority of trials. However, localization dominance and discrimination suppression remain potent for delays of 10 ms or longer. Results are consistent with a simple model in which information from the lead and lag interacts perceptually and in which the strength of this interaction decreases with spatiotemporal separation of the lead and lag. At short delays, lead and lag both contribute to spatial perception, but the lead dominates (to the extent that only one position is ever heard). At the longest delays tested, two distinct sounds are perceived (as measured in a fusion task), but they are not always heard at independent spatial locations (as measured in a localization dominance task). These results suggest that directional cues from the lag are not necessarily salient for all conditions in which the lag is subjectively heard as a separate event.     

Performance evaluation of IDW,Kriging and multiquadric interpolation methods in producing noise mapping: A case study at the city of Isparta,Turkey

In order to produce an accurate noise map of a city or a region, it is necessary to make noise measurements at certain locations and these measurements must be modeled with the most suitable mathematical algorithm. A homogeneous and representative distribution of the noise measurement points is the first key factor in the production of sound noise maps. The second key element is the calculation of the noise values of gridding points based on noise measurement points according to the selected mathematical calculation method and the generation of maps according to these gridding points. In this study, a noise map of the Isparta city center and its periphery was produced using inverse distance weighted (IDW), Kriging and multiquadric interpolation methods with different parameters and four grid resolution. Then, the influence of parameter selection for each method was investigated in themself by taking into account grid resolution, namely 10 ∗ 10 m, 50 ∗ 50 m, 100 ∗ 100 m and 200 ∗ 200 m, and the performance of three method with 50 ∗ 50 m grid resolution were compared with each other. In addition, the noise mapping of the city of Isparta were produced by Kriging method with respect to maximum, average and minimum noise data and they were evaluated by considering the national environmental noise thresholds.     

Anthropogenic sound exposure of marine mammals from seaways: Estimates for Lower St. Lawrence Seaway, eastern Canada

The impact of shipping noise on marine life and quality of marine mammal habitats in oceans and coastal environments has become a major concern worldwide. Background noise can also limits detection of marine mammal sounds in passive acoustic monitoring (PAM) systems. Characterisation of this noise over long time periods and estimates of the exposure of the different marine mammal groups are still very fragmentary and limited to only a few locations. This paper presents such observations for a part of a busy seaway of North America, the St. Lawrence Seaway, which cuts through the Gulf of St. Lawrence and crosses several cetaceans and pinnipeds feeding areas. Noise was continuously recorded for a 5-month period in summer 2005 by an AURAL autonomous hydrophone deployed close to the bottom in the 300-m deep seaway. The maximum received noise level in the 20 Hz-0.9 kHz band reached 136 dB re 1 μPa_rms. The median level of 112 dB re 1 μPa_rms was exceeded 50% of the time due to transiting merchant ships. Median spectral level tracks the reference curve for heavy traffic in oceans and 50% of the noise is within a ±6 dB envelope around it. Strong spectral lines were common at low frequencies and in the 400-800 Hz band. M-weighting functions applied for the three groups of cetaceans and pinnipeds indicate wideband median levels varying from 106 to 112 dB-M re 1 μPa_rms surrounded by a ±5 dB two-quartile interval. Higher values are expected for animals frequenting the sound channel at intermediate depths. As expected, the highest M-weighting levels correspond to low-frequency specialists and pinnipeds. Criteria for assessing the behavioural and physiological impacts of long term exposure of marine mammals to such shipping noise levels need to be worked out.     

Signal processing efficiency of Doppler global velocimetry with laser frequency modulation

Novel Doppler global velocimeters using laser frequency modulation can optically measure flow velocity fields and offer promising perspectives, but so far unknown limits, for achieving low measurement uncertainties. One approach, e.g. is based on sinusoidal frequency modulation and a harmonic signal analysis. In order to determine the minimum achievable measurement uncertainty, the known theorem of Cramér and Rao is applied to a derived signal model, initially excluding the harmonic signal analysis. For a typical scattered light power of 1 nW and a desired temporal resolution of 16 ms, the calculated minimum velocity standard deviation amounts to 0.02 and 0.06 m/s for signal dependent (quantum shot) noise and signal independent (thermal and dark current) noise, respectively. It is subsequently investigated, how efficient the harmonic signal analysis extracts the Fisher information content. The ratio of the Cramér-Rao lower bound and the estimated measurement uncertainty, where the signal processing is taken into account, was found to be >75% in terms of standard deviations in the entire measurement range of about . For the challenge of measuring velocity fields in turbomachine flows (requirements: 5 kHz measurement rate, ≤1% statistical error, velocities (50-240) m/s), the presented results indicate a necessary minimum scattered light power of 1.5 nW, which seems feasible.     

Sounds, source levels, and associated behavior of humpback whales, southeast Alaska

Humpback whales in Southeast Alaskan waters produced five categories of sounds: moans, grunts, pulse trains, blowhole-associated sounds, and surface impacts. Frequencies (Hz) of moans and grunts were 20-1900. Major energy in low-frequency pulse trains was in a band of 25-80 Hz with pulse duration of 300-400 ms. Blowhole-associated sounds, recorded as transiting whales encountered one another, were of two types: shrieks, 555-2000 Hz, and trumpetlike horn blasts with fundamental at 414 Hz (median). Pulses and spread spectrum noise were associated with gas bubble formation and explosive bursts, respectively, in connection with spiral feeding maneuvers. Surface impacts resulted from fluke or flipper slaps in sequences of 3-21 sounds. Source levels ranged from 162 (low-frequency pulse trains) to 192 dB (surface impacts), re: 1 microPa, 1 m. Songs, commonly heard on winter breeding grounds, were absent from our recordings. Feeding and perhaps certain other whale activities can be monitored based on sound production.     

Mathematical, statistical and neural models capable of predicting LA,max for the Tehran-Karaj express train

This paper presents mathematical logarithmic, statistical linear regression, and neural models capable of predicting maximum A-weighed noise level (L_A,max) for the Tehran-Karaj express train. The models have been developed upon the basis of the measurements from sampling locations at distances of 25 m, 45 m, and 65 m from the centreline of the track and at a height of 1.5 m. In the next step, the predictive capability of the models have been tested on the data associated with the sampling locations, situated, respectively at distances of 35 and 55 m from the centreline of the track at a height of 1.5 m. The non-parametric tests i.e. two-related samples Wilcoxon, and two-independent samples Kolmogorov-Smirnov, carried out, respectively for training and testing steps, indicate satisfactory results. In the final step the non-parametric k-related samples Friedman test detects no significant differences amongst the absolute testing set error of the models.     

A fuzzy expert system capable of computing LA,max for the Tehran-Karaj commuter train

This paper describes the methodology through which a fuzzy expert system capable of computing maximum A-weighed noise level (L_A,max) for the Tehran-Karaj commuter train is developed, tested, tuned and validated on the basis of the 50 measurements from five locations at distances of 25 m, 35 m, 45 m, 55 m, and 65 m from the centre of the track and at a height of 1.5 m. The expert system is initially developed, tested and tuned through the judgements made on the premise of the samples taken at the distances of 25, 45 and 65 m. The conducted hypothesis test, the non-parametric two-related samples Wilcoxon test, for this stage indicates satisfactory results. Eventually the developed expert system is validated for the measurements related to the distances of 35 and 55 m through carrying out the non-parametric two-independent samples Kolmogorov-Smirnov test.     

A rail noise prediction model for the Tehran-Karaj commuter train

Rail noise prediction models enable consideration of different scenarios for the optimal management of noise prevention and mitigation. This project is aimed at developing an equation that enables computation of L_A,max for the Tehran-Karaj commuter train, a type of Diesel-Electric Locomotive. The form of the proposed model is derived from equations for predicting L_A,max for a single locomotive pass-by, proposed in the manual prepared by Harris Miller Miller & Hanson Inc. for the US Federal Transit Administration, and in the French rail noise prediction model. The algorithm for predicting L_A,max for the Tehran-Karaj commuter train has been developed on the basis of the 50 measurements from 5 locations at distances of 25 m, 35 m, 45 m, 55 m, and 65 m from the centre of the track and at a height of 1.5 m. In the field measurements, the reference distance and the reference vehicle speed have respectively been set equal to 25 m and 80 km per hour. The reference L_A,max, length and the speed correction coefficients have been estimated from the field measurements and have been found to be 86.2 dB(A), 11.3, and 18.4 respectively. The fitness test (Kolmogorov-Smirnov) and regression analysis indicate satisfactory results.     

Widely tunable, high-repetition-rate, dual signal-wave optical parametric oscillator by using two periodically poled crystals

This paper reports on a high-repetition-rate dual signal-wave (DSW) optical parametric oscillator (OPO) operating at the 1.5 μm band with tunable wavelength intervals from 2.5 nm to 69.1 nm. Two periodically poled crystals, a periodically poled lithium niobate (PPLN) with multiple gratings and a single grating MgO-doped PPLN (PPMgOLN), are cascaded in the same OPO cavity to generate dual signal-waves by using quasi-phase-matched (QPM) technique. The pump source was a Q-switched diode-pumped Nd:YVO₄ laser operating at 50 kHz. At an incident pump power of 3 W, an average output power of 169.6 mW at 1489.2 nm and 1558.3 nm has been achieved.     

The study of a Tm:YLF laser pumped by a Raman shifted Erbium fiber laser at 1678 nm

A Tm:YLF laser pumped by a Raman shifted Er-fiber laser at 1.678 μm was studied at two Tm³⁺ ion concentrations equal to 1.5% and 5%. At output powers up to 460 mW the measured lasing efficiency at a wavelength of ~ 1.93 μm was as high as ~ 50%. The lasing performance was compared with that obtained under pumping by a 792-nm laser diode. The temporal structure of the laser pulse was recorded and the beam propagation factor M² was measured for all pumping conditions.     

Wind dependence of ambient noise in shallow water of Bay of Bengal

This work reports on investigations into the wind dependence of ambient noise in the Bay of Bengal. Ambient noise measurements were made in the shallow water of Bay of Bengal using a portable broadband, high frequency data acquisition system together with a sensitive hydrophone suspended from the measuring platform at a depth of 5 m from the surface where the ocean depth was 25 m. Periodic measurements were carried out for one year corresponding to a wind speed range between 2 m/s and 9 m/s during summer, monsoon and winter seasons. The proportionality of the noise level with wind speed for frequencies ranging from 500 Hz to 6 kHz for each season was studied. The analysis reveals that the correlation between the wind speed and the ambient noise spectrum level was higher at lower frequencies. The results of empirical fitting based on analysis were used for noise level prediction and the model predictions compare well with the measured noise level. Further it was observed that the wind generated noise level measured during summer was approximately 8 dB less than that in other seasons. On the other hand the proportionality between the noise level and the wind speed was less during winter.