Time filter

Source Type

Ballerup, Denmark

Gudmundson E.,Lund University | Gudmundson E.,Swedish Defence Research Agency | Jakobsson A.,Lund University | Gran F.,GN ReSound
IEEE International Ultrasonics Symposium, IUS | Year: 2012

Spectral Doppler ultrasound imaging typically consists of a spectrogram, showing the velocity distribution of the blood, and a brightness (B-) mode image allowing the operator to navigate. It is desirable to have both high spectral and velocity resolution, so that details in the blood flow can be traced, as well as a high B-mode frame rate to allow for tracking of movements and to adjust the position of the transducer. The blood flow signal is often sampled 1) using alternating transmissions for blood flow estimation and for B-mode imaging, or, 2) by acquiring a full Doppler spectrum and then parts of the B-mode image. The former has the disadvantage that it halves the sampling rate, making it likely that aliasing will occur when imaging fast moving blood or deeply positioned vessels; the latter that gaps appears in the spectrogram, and that if the frame rate of the B-mode images is slow, it will be difficult to track movements. Adaptive methods have been implemented to circumvent such problems, but even so, to get an acceptable frame rate of the B-mode images, the number of transmissions for Doppler estimation will be limited, restricting the spectral resolution. Alternatively, one may use an irregularly spaced emission pattern, but existing work on the topic is limited and generally suffers from poor resolution and spurious velocity components resulting from the irregular sampling pattern. In this paper, we examine the BIAA algorithm, showing that this approach allows for an accurate velocity estimate even from irregularly sampled measurements. Using an irregular emission pattern, with half the emissions used to form the B-mode image, the remaining emissions are found to yield accurate velocity estimates without reducing the maximally measurable velocity and without the spurious velocity components. Moreover, we show that the approach will allow for the same maximal velocity without aliasing as if all emissions would have been used for the velocity estimation. © 2012 IEEE. Source

Hansen K.L.,Section of Ultrasound | Hansen K.L.,Technical University of Denmark | Gran F.,GN ReSound | Gran F.,Technical University of Denmark | And 5 more authors.
Ultrasonics | Year: 2010

Spectrograms in medical ultrasound are usually estimated with Welch's method (WM). WM is dependent on an observation window (OW) of up to 256 emissions per estimate to achieve sufficient spectral resolution and contrast. Two adaptive filterbank methods have been suggested to reduce the OW: Blood spectral Power Capon (BPC) and the Blood Amplitude and Phase EStimation method (BAPES). Ten volunteers were scanned over the carotid artery. From each data set, 28 spectrograms were produced by combining four approaches (WM with a Hanning window (W.HAN), WM with a boxcar window (W.BOX), BPC and BAPES) and seven OWs (128, 64, 32, 16, 8, 4, 2). The full-width-at-half-maximum (FWHM) and the ratio between main and side-lobe levels were calculated at end-diastole for each spectrogram. Furthermore, all 280 spectrograms were randomized and presented to nine radiologists for visual evaluation: useful/not useful. BAPES and BPC compared to WM had better resolution (lower FWHM) for all OW < 128 while only BAPES compared to WM had improved contrast (higher ratio). According to the scores given by the radiologists, BAPES, BPC and W.HAN performed equally well (p > 0.05) at OW 128 and 64, while W.BOX scored less (p < 0.05). At OW 32, BAPES and BPC performed better than WM (p < 0.0001) and BAPES was significantly superior to BPC at OW 16 (p = 0.0002) and 8 (p < 0.0001). BPC at OW 32 performed as well as BPC at OW 128 (p = 0.29) and BAPES at OW 16 as BAPES at OW 128 (p = 0.55). WM at OW 16 and 8 failed as all four methods at OW 4 and 2. The intra-observer variability tested for three radiologist showed on average good agreement (90%, κ = 0.79) and inter-observer variability showed moderate agreement (78%, κ = 0.56). The results indicated that BPC and BAPES had better resolution and BAPES better contrast than WM, and that OW can be reduced to 32 using BPC and 16 using BAPES without reducing the usefulness of the spectrogram. This could potentially increase the temporal resolution of the spectrogram or the frame-rate of the interleaved B-mode images. © 2009 Elsevier B.V. All rights reserved. Source

Croghan N.B.H.,University of Colorado at Boulder | Arehart K.H.,University of Colorado at Boulder | Kates J.M.,GN ReSound
Journal of the Acoustical Society of America | Year: 2012

Dynamic-range compression (DRC) is used in the music industry to maximize loudness. The amount of compression applied to commercial recordings has increased over time due to a motivating perspective that louder music is always preferred. In contrast to this viewpoint, artists and consumers have argued that using large amounts of DRC negatively affects the quality of music. However, little research evidence has supported the claims of either position. The present study investigated how DRC affects the perceived loudness and sound quality of recorded music. Rock and classical music samples were peak-normalized and then processed using different amounts of DRC. Normal-hearing listeners rated the processed and unprocessed samples on overall loudness, dynamic range, pleasantness, and preference, using a scaled paired-comparison procedure in two conditions: un-equalized, in which the loudness of the music samples varied, and loudness-equalized, in which loudness differences were minimized. Results indicated that a small amount of compression was preferred in the un-equalized condition, but the highest levels of compression were generally detrimental to quality, whether loudness was equalized or varied. These findings are contrary to the louder is better mentality in the music industry and suggest that more conservative use of DRC may be preferred for commercial music. © 2012 Acoustical Society of America. Source

Gn Resound and GN RESOUND NORTH AMERICA Corporation | Date: 2000-04-21

audio headset receivers; headphones; microphones; audio receivers, speakers, and transmitters.

Gn Hearing Care Corporation and Gn Resound | Date: 2002-02-19

hearing aids.

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