Negative Effects of Noise on NICU Graduates' Cochlear Functions.

AIM: To evaluate the adverse effects of noise on hearing. Methods: Thirty-two infants that had been admitted to neonatal intensive care unit (NICU) and 25 healthy controls were included in this study. Noise levels were recorded continously during the hospitalization period. Results: All healthy controls passed the hearing screening tests before discharge and on the sixth-month follow up. Hospitalized infants had lower "Distortion Product Auto Acoustic Emission Signal Noise Ratio" (DPOAE SNR) amplitudes (dB) at five frequencies (1001, 1501, 3003, 4004, 6006 Hz in both ears). DPOAE fail rates at 1001 Hz and 1501 Hz were higher than in hospitalized infants (81.8% and 50.0% vs 20.0% and 4.0%). Infants who failed the test at 1001 and 1501 Hz were exposed to noise above the recommended maximum level for longer periods of time. Conclusion: Hearing tests performed at sixth-months of life were adversely affected in NICU graduates.

Fully automated gradient based breast boundary detection for digitized X-ray mammograms.

Accurate segmentation of the breast from digital mammograms is an important pre-processing step for computerized breast cancer detection. In this study, we propose a fully automated segmentation method. Noise on the acquired mammogram is reduced by median filtering; multidirectional scanning is then applied to the resultant image using a moving window 15×1 in size. The border pixels are detected using the intensity value and maximum gradient value of the window. The breast boundary is identified from the detected pixels filtered using an averaging filter. The segmentation accuracy on a dataset of 84 mammograms from the MIAS database is 99%.

Improving image quality of diagnostic ultrasound by using the safe use time model with the dynamic safety factor and the effect of the exposure time on the image quality.

Resolution and penetration are primary criteria for image quality of diagnostic ultrasound. In theory (and usually in practice), the maximum depth of imaging in a tissue increases as power (pressure) is increased. Alternatively, at a particular effective penetration, an increased power may be used to allow a higher ultrasound frequency for higher resolution and tissue contrast. Recently, Karagoz and Kartal proposed a safety parameter for thermal bioeffects of diagnostic ultrasound; that is, SUT (safe use time). The SUT model is constructed to determine how long one piece of tissue can be insonated safely according to a threshold exposure. Also, Karagoz and Kartal suggested that an increase in acoustic intensity beyond the current US Food and Drug Administration (FDA) limit of intensity can be theoretically possible by using SUT model while staying within the safe limit. The present study was motivated particularly by the goals of higher resolution and/or deeper penetration by using SUT model. The results presented here suggest that the safe use of higher exposure levels than currently allowed by the FDA may be possible for obtaining substantial improvements in penetration depth and/or resolution. Also, the study reveals that image quality can be functionally related to exposure time in addition to acoustic energy and frequency.

A new safety parameter for diagnostic ultrasound thermal bioeffects: safe use time.

It is widely accepted that diagnostic ultrasound has the potential to elevate the temperature of tissue being scanned. Because both the maximum value of the temperature rise and the temporal profile of that rise are necessary to estimate the risk correctly, the temperature rise [DeltaT(t)] at an observation point for an exposure condition is presumed to have two components, that is, DeltaT(t)=DeltaT(max)X(t). The amplitude component DeltaT(max) is the maximum value of DeltaT(t), and the exposure time component X(t) represents the time dependency of that DeltaT(t). Ninety-six cases were investigated to obtain the proposed DeltaT(t) model at six frequencies, four source diameters, and four f-numbers. Then, using the relative change in the rate of induction of a thermal effect due to ultrasound exposure that produces DeltaT(t) different from a threshold exposure, the safe use time (SUT) model was constructed. SUT informs the user of the maximum duration of exposure in a region at a particular output level that would be no more hazardous than scanning at the threshold exposure. Using the SUT model, high power ultrasound can be applied for a short time so that the user can improve imaging performance while staying within safe limits.

Evaluation of free radical formation associated with diagnostic ultrasound.

Our objective was to evaluate kidney antioxidant status in rats subjected to an ultrasound examination. Thirty rats were divided into five groups for injection of saline (S) or anesthetic (A), and application of ultrasound using different modes, B mode, pulsed wave Doppler, and continuous wave Doppler, under anesthesia. Ultrasound was performed on days 1, 3, and 5 relative to the initiation of the experiment. Rats were then scarified on day 6. The kidney tissue thiobarbituric acid reactive substance (TBARS) level and superoxide dismutase (SOD) activity were measured. Both TBARS level and SOD activity increased, 21% and 38%, respectively, due to anesthesia (P < 0.04 for both). SOD activity increased further by a factor of 1.2 in response to ultrasound examination (P < 0.05), whereas TBARS level was not affected by Doppler and continuous wave Doppler compared to anesthesia. Increases in the level of TBARS (P < 0.03) and SOD activity (P < 0.01) were greatest when B-mode ultrasound was employed. These substances did not increase further when continuous wave Doppler was employed. The peak-negative acoustic pressure (9.16 vs. 9.74 MPa) and frequency (3.57 vs. 6.95 MHz) for B mode and pulsed wave Doppler were greater than those for continuous wave Doppler (0.22 MPa and 1.96 MHz). The estimated mechanical indexes were 4.87, 3.70, and 0.15 for B mode, pulsed wave Doppler, and continuous wave Doppler, respectively. In conclusion, anesthesia may cause tissue damage as reflected by elevated lipid peroxidation and free radical formation and ultrasound examination may amplify tissue damage through mechanical effects caused by ultrasound absorption.

Evaluation of biological effects induced by diagnostic ultrasound in the rat foetal tissues.

In recent years, there has been growing interest in estimating the degree of heating caused by the diagnostic ultrasound in clinical practice. Both theoretical and experimental methods have been suggested for estimating the heating potential, or thermal hazard, of diagnostic ultrasound. Aim of this study was to evaluate in vivo effects of ultrasound exposure of variable duration (from 10 up to 20 min) with commercially available imaging systems commonly used for diagnostic imaging. Numerical results related to the thermal effect are obtained by simulation program based on B-mode (scanning) and Doppler (non-scanning). To investigate the biological effects of the ultrasound exposure to the brain and liver tissues, the antioxidant enzyme activity and thiobarbituric acid reactive substances (TBARS) of the tissues were evaluated. In liver tissue, as a lipid peroxidation index, TBARS levels very significantly increase in Doppler group compared to control. However, in B-mode, TBARS levels are the same with the control group. Use of B-mode in foetal tissue is more reliable than Doppler mode because temperature rise is very small compared to the Doppler mode. On the other hand, the antioxidant enzyme activities tend to increase in B-mode and Doppler groups compared to the control group as a defensive mechanism. In the brain tissue, lipid peroxidation is increased slightly in B-mode compared to the control group. This situation is related to the molecular structure of the brain tissue because of its high lipid concentration. In brain tissue, the antioxidant enzyme activities and lipid peroxidation were significantly increased, such as liver tissue in Doppler groups. Doppler ultrasound may produce harmful effects in rat foetus liver and brain tissues as a result of the high temperature rises.

Evaluation of nonscanned mode soft-tissue thermal index in the presence of the residual temperature rise.

Previously, the temperature rise (deltaT) caused by diagnostic ultrasound and the AUIM/NEMA-defined thermal indices were examined to evaluate whether these indices were reasonable indicators of potential bioeffects due to ultrasound heating in the absence of a residual temperature rise (RTR). In our study, deltaT induced by diagnostic ultrasound exposures was estimated in the presence of an RTR using the Bioheat Transfer Equation. To evaluate deltaT/TIS in the presence of an RTR, 11 frequencies, eight cooling times, eight insonation times for the second ultrasound examination, and three source powers for a circular aperture (A(aprt)< or = 1 cm2) were investigated. In our comparison of the ratios of deltaT/TIS in the absence and presence of an RTR, a higher deltaT/TIS value was obtained in the examination with the RTR. We showed that the deltaT/TIS value is equal to 2.88 in the presence of an RTR, whereas the deltaT/TIS value without the RTR equals 1.90. In the presence of the RTR, although the TIS does not inform the user of higher ultrasound heating due to TIS values that do not exceed 1.00, deltaT reaches 2.62 degrees C, and the deltaT without the RTR reaches 1.68 degrees C in the case of a TIS value that does not exceed 1.00. These results suggest that, for nonscanned mode situations where soft tissue is insonated, the TIS should not be regarded as a reliable indicator of potential bioeffects due to ultrasound heating in the presence of the RTR. Our study also indicates the necessity for a new indicator that provides the clinical user with accurate in vivo temperature rise feedback (possibly even true deltaT), and includes adding an exposure time component to the Bio-Heat Equation model.

The effects of residual temperature rise on ultrasound heating.

In recent theoretical studies, the temperature rise produced by diagnostic ultrasound was estimated by solving the Bioheat Transfer Equation (BHTE) but ignoring the initial temperature rise. The temperature rise was determined in our study by the BHTE including an initial temperature rise. We discuss how the initial temperature rise occurs during an ultrasound examination, and how the initial temperature rise affects subsequent ultrasound heating. We theoretically show that the temperature rise produced by the ultrasound examination (exposure time of 500 s) in a tissue sample having an initial temperature rise was higher than that in a tissue sample with no initial temperature rise that was exposed to ultrasound (exposure time of 1200 s). The theoretical results for these two cases were 5.64 degrees C and 3.58 degrees C, respectively. In our experimental study, the highest temperature rise was measured in the presence of an initial temperature rise as in the theoretical study under the same exposure conditions. Mean temperature rises for tissue without an initial temperature rise and for tissue with an initial temperature rise were 2.42 +/- 0.13 degrees C and 3.62 +/- 0.17 degrees C, respectively. Both theoretical and experimental studies show that unless the initial temperature rise produced by the first ultrasound examination decreases to 0 degrees C, the next ultrasound examination on the same tissue sample may cause the temperature rise to be higher than expected.