Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “NOISE”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 271 records · Page 15Linked to original sources
PubMed2006

Signal-to-noise ratio, contrast-to-noise ratio and their trade-offs with resolution in axial-shear strain elastography.

In axial-shear strain elastography, the local axial-shear strain resulting from the application of quasi-static axial compression to an inhomogeneous material is imaged. In this paper, we investigated the image quality of the axial-shear strain estimates in terms of the signal-to-noise ratio (SNR(asse)) and contrast-to-noise ratio (CNR(asse)) using simulations and experiments. Specifically, we investigated the influence of the system parameters (beamwidth, transducer element pitch and bandwidth), signal processing parameters (correlation window length and axial window shift) and mechanical parameters (Young's modulus contrast, applied axial strain) on the SNR(asse) and CNR(asse). The results of the study show that the CNR(asse) (SNR(asse)) is maximum for axial-shear strain values in the range of 0.005-0.03. For the inclusion/background modulus contrast range considered in this study (<10), the CNR(asse) (SNR(asse)) is maximum for applied axial compressive strain values in the range of 0.005%-0.03%. This suggests that the RF data acquired during axial elastography can be used to obtain axial-shear strain elastograms, since this range is typically used in axial elastography as well. The CNR(asse) (SNR(asse)) remains almost constant with an increase in the beamwidth while it increases as the pitch increases. As expected, the axial shift had only a weak influence on the CNR(asse) (SNR(asse)) of the axial-shear strain estimates. We observed that the differential estimates of the axial-shear strain involve a trade-off between the CNR(asse) (SNR(asse)) and the spatial resolution only with respect to pitch and not with respect to signal processing parameters. Simulation studies were performed to confirm such an observation. The results demonstrate a trade-off between CNR(asse) and the resolution with respect to pitch.

Acoustics↗
PubMed2005

Brain tumor enhancement in magnetic resonance imaging: comparison of signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) at 1.5 versus 3 tesla.

OBJECTIVE: The objective of this study was to compare the difference in lesion enhancement between 1.5 and 3 T using an extracellular gadolinium chelate in a rat brain glioma model. METHODS: Five rats (CDF Fischer 344) with implanted C6/LacZ brain gliomas were evaluated using matched T1-weighted spin echo techniques and hardware configurations at 1.5 and 3 T. Serial imaging over 10 minutes after gadoteridol (ProHance) administration was performed. Contrast enhancement (CE), signal-to-noise ratios (SNR) for brain and tumor, as well as contrast-to-noise ratios (CNR) were evaluated using region-of-interest (ROI) analysis at both field strengths. All gliomas were also evaluated by histopathology. RESULTS: CE at 3 T increased by 106% to 137% (all P<0.05) with maximum CE occurring at 5 minutes for both 1.5 and 3 T (9.8+/-2.2 vs 21.1+/-3.5; P=0.0004). At 3 T, SNR increased for normal brain by 66% to 76% (P<0.01) and SNR for tumor increased by 70% to 89% (P<0.01). CNR increased by 101% to 137% (P<0.05) depending on the time postcontrast. The highest CNR for both 1.5 T and 3 T occurred 5 minutes after contrast (1.5 T: 9.4+/-1.1 vs 3 T: 20.3+/-2.4; P<0.0004). CONCLUSION: Using a standardized animal model and matched scan techniques, this study shows a significant benefit of 3 T compared with 1.5 T in contrast-enhanced brain tumor magnetic resonance imaging.

Animals↗
PubMed1998

A novel experimental apparatus to study the impact of white noise and 1/f noise on animal populations.

This paper reports on the design and construction of a novel apparatus that allows a set of aquatic microcosms to experience complex temporal environmental fluctuations. Replicate microcosms were maintained in 18 water baths with independent environmental controls. We give results from a preliminary experiment designed to look at the effects of varying temperatures with different variance spectra (i.e. white noise or 1/f noise) on single species population dynamics. Matching time series (with identical elements, differently ordered) of environmental temperatures with different Fourier spectra were created for use as input to the apparatus using a novel spectral mimicry method. The apparatus functioned well during the course of the experiment making this an extremely useful research tool. This apparatus now provides ecologists with a means of studying how environmental variability and directional trends in this variability, are filtered and translated by real populations and micro-ecosystems.

Animals↗
PubMed2004

Thermoelastic-damping noise from sapphire mirrors in a fundamental-noise-limited interferometer.

We report the first high-precision interferometer using large sapphire mirrors, and we present the first direct, broadband measurements of the fundamental thermal noise in these mirrors. Our results agree well with the thermoelastic-damping noise predictions of Braginsky, et al. and Cerdonio et al., which have been used to predict the astrophysical reach of advanced interferometric gravitational wave detectors.

Journal Article↗
PubMed1986

Noise reversion of a dual chamber pacemaker without noise.

Three patients are reported whose DDD pacemakers reverted to the asynchronous mode in the absence of skeletal muscle or electromagnetic (EMI) interference. In all three cases, the basic cardiac rhythm was atrial fibrillation with fast ventricular response due to intrinsic AV conduction. Noise reversion was triggered by the patients' own ventricular activity at cycle lengths shorter than the ventricular refractory period of the pulse generator. In one patient, asynchronous AV sequential pacing during atrial fibrillation was noted shortly after resuscitation from ventricular fibrillation; however, the initiation of the malignant ventricular arrhythmia by the pacemaker remains unproven. The mechanism of noise reversion by rapid cardiac activity and possible solutions to the problem by adequate pacemaker design are discussed.

Aged↗
PubMed2001

Regional improvement of signal-to-noise and contrast-to-noise ratios in dual-screen CR chest imaging--a phantom study.

The improvement of signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) in dual-screen computed radiography (CR) has been investigated for various regions in images of an anthropomorphic chest phantom. With the dual-screen CR technique, two image plates are placed in a cassette and exposed together during imaging. The exposed plates are separately scanned to form a front image and a back image, which are then registered and superimposed to form a composite image with improved SNRs and CNRs. The improvement can be optimized by applying specifically selected weighting factors during superimposition. In this study, dual-screen CR images of an anthropomorphic chest phantom were acquired and formed with four different combinations of standard resolution (ST) and high-resolution (HR) screens: ST-ST, ST-HR, HR-ST, and HR-HR. SNRs and their improvements were measured and compared over twelve representative regions-of-interest (ROIs) in these images. A 19.1%-45.7% increase of the SNR was observed, depending on the ROI and screen combination used. The optimal weighting factors were found to vary by only 4.5%-12.4%. Largest improvement was found in the lung field for all screen combinations. Improvement of CNRs was investigated over two ROIs in the lung field using the rib bones as the contrast objects and a 29.2%-43.9% improvement of the CNR was observed. Among the four screen combinations, ST-ST resulted in the most SNR and CNR improvement, followed in order by HR-ST, HR-HR, and ST-HR. The HR-ST combination yielded the lowest spatial variation of the optimal weighting factors with improved SNRs and CNRs close to those of the ST-ST combination.

Biophysical Phenomena↗
PubMed1997

Improvement of signal-to-noise and contrast-to-noise ratios in dual-screen computed radiography.

A dual-screen computed radiography (CR) technique has been developed to improve and optimize the overall image signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR). With this technique, two CR screens are exposed together and separately scanned to form a front and a back image. These two images are then superimposed to form an image of improved SNR and CNR. A mathematical model has been derived to describe the improvement and optimization of the SNR and CNR. Based on this model, the front and back images should be weighted in proportion to their SNR squared to optimize the SNR of the composite image. Imaging experiments have been conducted to verify the theoretical model under mammographic and chest imaging conditions. The results largely agree with the theoretical predictions. It has also been found that optimization of the SNR results in nearly optimal CNR and vice versa. For mammographic imaging, a 14%-22% improvement in the SNR and a 13%-19% improvement in the CNR have been demonstrated. For chest imaging, a 31%-36% improvement in the SNR and a 28%-30% improvement in the CNR has been demonstrated.

Biophysical Phenomena↗
PubMed1991

[Noise origin and noise-induced complaints after heart valve replacement with mechanical prostheses].

143 patients were investigated in order to determine whether there is a difference in the intensity of the closing click between different mechanical heart valve prostheses. 35 had St. Jude Medical (SJM), 38 Duromedics Edwards (DE), 36 Björk Shiley Monostrut (BSM) and 34 had Carbomedics prostheses implanted. Sound pressure level determined at 1 meter distance was significantly higher for the DE 33.5 +/- 6 dB(A) and BSM 31 +/- 4 dB(A) than for the SJM 24 +/- 4 dB(A) and CM 25 +/- 6 dB(A) prostheses (p = 0.0001). Valves developing higher sound pressures were more frequently audible for the patients (p = 0.0012), caused more sleep disturbances (p = 0.024) and more complaints during daytime (p = 0.07). Significantly more patients carrying such valves wished to have a less noisy valve implanted (0.0047). Symptomatic patients wear louder valves, were younger, had better hearing and were more frequently in sinus rhythm. Valve diameter correlated with the developed sound pressure level. 349 patients answered a questionnaire after valve replacement with DE (256) or BSM (93) prostheses. 5% registered their noise-related complaints as being severe, but more than one third wished to have a less noisy valve implanted. The noise created by the closing click of mechanical prostheses causes significant complaints and this factor should be considered when a mechanical valve is selected.

Adult↗
PubMed1979

Noise-noise effect upon the spreading of the posttraumatic progressive necrosis in the organ of Corti.

Progressive necrosis of the organ of Corti caused by a disturbance of the ionic composition of the Cortilymph resulting from the infiltration of endolymph into the organi of Corti after traumatization of its barrier against the scala media, is greatly intensified by posttraumatic stimulation with noise of physiological intensities. This effect is attributed to oscillation of the cochlear partition, with resultant greater blending of the Cortilymph and the endolymph. Stimulation augments necrosis fourfold towards the base of the cochlea and twofold towards the helicotrema. Posttraumatic stimulation is one of the factors which markedly potentiate the regressive effect of acoustic trauma.

Acoustic Stimulation↗
PubMed2007

Assessing the influence of scanner background noise on auditory processing. I. An fMRI study comparing three experimental designs with varying degrees of scanner noise.

We compared two experimental designs aimed at minimizing the influence of scanner background noise (SBN) on functional MRI (fMRI) of auditory processes with one conventional fMRI design. Ten subjects listened to a series of four one-syllable words and had to decide whether two of the words were identical. This was contrasted with a no-stimulus control condition. All three experimental designs had a duration of approximately 17 min: 1) a behavior interleaved gradients (BIG; Eden et al. [1999] J Magn Reson Imaging 41:13-20) design (repetition time, TR, = 6 s), where stimuli were presented during the SBN-free periods between clustered volume acquisitions (CVA); 2) a sparse temporal sampling technique (STsamp; e.g., Gaab et al., [2003] Neuroimage 19:1417-1426) acquiring only one set of slices following each of the stimulations with a 16-s TR and jittered delay times between stimulus offset and image acquisition; and 3) an event-related design with continuous scanning (ERcont) using the stimulation design of STsamp but with a 2-s TR. The results demonstrated increased signal within Heschl's gyrus for the STsamp and BIG-CVA design in comparison to ERcont as well as differences in the overall functional anatomy among the designs. The possibility to obtain a time course of activation as well as the full recovery of the stimulus- and SBN-induced hemodynamic response function signal and lack of signal suppression from SBN during the STsamp design makes this technique a powerful approach for conducting auditory experiments using fMRI. Practical strengths and limitations of the three auditory acquisition paradigms are discussed.

Acoustic Stimulation↗
PubMed1976

[Experiments on the medicamental treatment of the noise-induced cochlear damage. Part I. The effect of dipyridamol and allopurinol on the RMP of the cochlea (guinea pig) after noise (author's transl)].

Dipyridamol has in addition to a coronardilatating effect an ati-thrombotic one too. Moreover it facilitates the release of O2 from haemoglobin by increase of the concentration of 2,3-diphosphoglycerate in the erythrocytes. Allopurinol causes a potential resynthesis of ATP in the cells by inhibition of the metabolism of uric acid. Both substances therefore seemed to be suitable for a medicamental therapy of the noise-induced cochlear damage. The expected favourable effect of Dipyridamol and Allopurinol on the organ of Corti after sound exposure (RMP-measurement before and after exposure to pure tone 120 dB SPL) however had not been confirmed by experiment on animals (guinea pig).

Allopurinol↗
PubMed2002

Effects of cochlear ablation on noise induced hyperactivity in the hamster dorsal cochlear nucleus: implications for the origin of noise induced tinnitus.

Chronic increases in multiunit spontaneous activity are induced in the dorsal cochlear nucleus (DCN) following exposures to intense sound. This hyperactivity has been implicated as a neurophysiological correlate of noise induced tinnitus. However, it is not known whether this hyperactivity originates centrally, or instead, reflects an increase in the level of spontaneous input from the auditory nerve. In the present study we addressed this issue by testing whether hyperactivity, induced in the DCN by previous exposure to intense sound, persists after ipsilateral cochlear input to the DCN has been removed. To induce hyperactivity, Syrian golden hamsters were exposed under anesthesia to an intense pure tone (122-127 dB SPL at 10 kHz) for 4 h. Additional hamsters, which were anesthetized for 4 h, but not tone exposed, served as controls. Electrophysiological recordings of spontaneous activity were performed on the surface of the left DCN in animals in which the ipsilateral cochlea was either intact or ablated. The degree of cochlear removal was determined by microdissection and histologic evaluation of the cochlea after completion of each recording session. Comparisons between the levels of activity recorded in animals with and without intact cochleas revealed that the induced hyperactivity in the DCN persisted after both partial and complete cochlear ablations. These results indicate that the maintenance of hyperactivity is not dependent on input from the ipsilateral cochlea, implying that hyperactivity originates centrally.

Animals↗