• Journal of the Korean Institute of Telematics and Electronics
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• v.19 no.6
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• pp.33-40
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• 1982

Although ultrasonic CT is one of the useful techniques for tissue characterization, the reconstructed images, such as the velocity distribution and attenuation constant distribution, are degraded by reflection and refraction of ultrasonic beam. This paper studied the degradation effects on attenuation images using agar gel phantoms which were developed to evaluate ultrasonic CT. We found that the reconstructed attenuation constants at the center of the phantoms were less than the actual values by 0.6 dB/cm when phantom velocity differs by 25 m/s from surrounding saline. We also studied a correction method for refraction and phase cancellation effects, where the correction was made using the maximum value in the received subdata, as obtained by sub-arraying microprobes located at each sampling point. Using this method, we could obtain an improvement in the reconstructed image by the correction on the attenuation effect.

• The Journal of the Acoustical Society of Korea
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• v.28 no.7
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• pp.661-667
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• 2009

Trabecular-bone-mimicking phantoms consisting of parallel-nylon-wire arrays were used to investigate correlations of phase velocity and attenuation coefficient with structural properties in trabecular bone. Trabecular separation (Tb.Sp) of the 7 trabecular-bone-mimicking phantoms ranged from 300 to $900\;{\mu}m$ and volume fraction (VF) from 1.6% to 8.7%. Phase velocity and attenuation coefficient of the phantoms were measured by using a through-transmission method in water, with a matched pair of broadband unfocused transducers with a diameter of 12.7 mm and a center frequency of 1 MHz. Phase velocity and attenuation coefficient at 1 MHz decreased almost linearly with increasing Tb. Sp and increased almost linearly with increasing VF. The simple and multiple linear regression models with phase velocity and attenuation coefficient as independent vanables and Tb.Sp and VF as dependent variables demonstrated that the coefficients of determination for the prediction of VF were higher than those for the prediction of Tb.Sp. The results obtained in the trabecular-bone-mimicking phantoms consisting of parallel-nylon-wire arrays were consistent with those in human trabecular bone suggesting that the structural properties can be estimated from the measurements of phase velocity and attenuation coefficient in trabecular bone.

• The Journal of the Acoustical Society of Korea
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• v.39 no.1
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• pp.16-23
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• 2020

In High-Intensity Focused Ultrasound (HIFU) treatment, effective localization of HIFU focus is important for developing a safe treatment plan. While Magnetic Resonance Imaging guided HIFU (MRIgHIFU) can visualize the ultrasound path during the treatment for localizing HIFU focus, it is challenging in ultrasound imaging guided HIFU (USIgHIFU). In the present study, a real-time ultrasound beam visualization technique capable of localizing HIFU focus is presented for USIgHIFU. In the proposed method, a short pulse, with the same center frequency of an imaging ultrasound transducer below the regulated acoustic intensity (i.e., Ispta < 720 mW/㎠), was transmitted through a HIFU transducer whereupon backscattered signals were received by the imaging transducer. To visualize the HIFU beam path, the backscattered signals underwent dynamic receive focusing and subsequent echo processing. From in vitro experiments with bovine serum albumin gel phantoms, the HIFU beam path was clearly depicted with low acoustic intensity (i.e., Ispta of 94.8 mW/㎠) and the HIFU focus was successfully localized before any damages were produced. This result indicates that the proposed ultrasound beam path visualization method can be used for localizing the HIFU focus in real time while minimizing unwanted tissue damage in USIgHIFU treatment.

• The Journal of the Acoustical Society of Korea
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• v.29 no.8
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• pp.504-508
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• 2010

In conventional diagnostic ultrasound strain imaging, when displaying strain image on a monitor, human visual characteristics are utilized such that hard regions are displayed as dark and soft regions are displayed as bright. Thus, hard regions representing tumor or cancer are displayed as dark, decreasing the contrast inside the lesion. Because the lesion area is stiff and thus displayed as dark, a method of inverting the image brightness and thereby increasing the contrast in the lesion for better diagnostic purposes is proposed wherein a postcompression signal is extended in the time domain by a factor corresponding to the reciprocal of the amount of the applied compression using a technique termed globally uniform stretching. Experiments were carried out to verify the proposed method on an ultrasound elasticity phantom with radio-frequency data acquired from a diagnostic ultrasound clinical scanner. It is found that the new method improves the contrast-to-noise ratio by a factor of up to about 1.8 compared to a conventional strain imaging method that employs a reversed gray color map without globally uniform stretching.

• Journal of radiological science and technology
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• v.32 no.3
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• pp.277-283
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• 2009

It is important to get clinical ultrasonic images of good quality for accurate diagnosis. In this study, it observed the change of ultrasonic images against setting frequency, dynamic range(DR) and type of probes on ultrasonic scanner. In the experiment it evaluated image of LCS (Low Contrast Sensitivity) targets(-15, -6, -3, +3, +6, +15 dB) of a standard ultrasonic test phantoms(539,551, ATS, USA) similar to solid and cystic lesions. Its imaged from convex (C3-7IM) and linear probe (L5-12IM) on SA-9900 (Medison Ltd, Korea) scanner. The images obtained altering the setting parameters which are frequency(gen, pen, res, harmonic) mode and DR($40{\sim}100\;dB$). The quality of images evaluated compare with the nominal LCS value of target and measured LCS value. The results show that there was no significant changing of quality images altering DR 40, 60, 80, 100 dB against frequency in Convex probe but the image being the highest in LCS target at DR 60 dB, harmonic of frequency mode in the -15 dB target close to cystic lesion. In Linear probe, DR 40 dB, harmonic mode at -15 dB LCS target close to nominal value. It discussed necessity of evaluation about ROC(Receiver Operating Characteristic) from the psychological viewpoint and limit of evaluation from quantified images.

• Journal of radiological science and technology
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• v.37 no.2
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• pp.117-124
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• 2014

This study has investigated the effects of the defects in the probe elements influence Doppler images in the medical ultrasonic scanners. This work was implemented that the quality of Doppler images depended on the extent and location of the probe element defected. The probe performance was rated in terms of the number of piezoelectric elements lost and this was studied in the experiment by electrical disconnection to the elements. The results showed that Doppler velocity became rapidly reduced as the defected elements encountered with the element group activated at the Doppler mode, not as the flow velocity. The effect of the probe defect is decreased when the defects occurred at the element group activated for Doppler mode, as was increased the number of the elements. It was observed that the higher the flow velocity of Doppler flow phantom is, the wider the spectrum of Doppler is. And the Doppler velocity soared up and the dispersion of image brightness is increased when the defected elements got out of the elements activated at Doppler mode. The result showed that TADVP(time-average-Doppler-velocity-profile) is decreased with the increase of the probe element defect, especilly in the region of high frequency. It is expected that the research of various defects of probe elements are needed, and this study can be practical tools for probe based ultrasonic QA in the future.

• Journal of the Korean Society of Radiology
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• v.15 no.6
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• pp.899-909
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• 2021

In Musculoskeletal ultrasound examination, a linear transducer (12-5 MHz) with a contact surface length of 6 cm, which is commonly distributed in medical institutions, does not contact with bent fingers and wrist depressions only by using a conventional liquid ultrasound gel, which causes image loss. In order to solve this image loss, the use of commercially available Water gel pad is increasing. However, it is a disposable medical product. Repeated use is prohibited and expensive. In this study, in order to reduce the economic burden caused by the use of the commercialized Water gel Pad, we searched for water-soluble food thickener powder that can be easily purchased around our lives and manufactured Gel pads. Among them, kappa-Carrageenan Gel Pad, iota-Carrageenan Gel Pad, and Agar-Agar Gel Pad satisfied the evaluation criteria without artifacts in image evaluation using the N-365 Multipurpose Phantom. Also, the price to purchase the food thickener powder was about 38 times cheaper than the existing commercialized Water gel pad. As a result, if you use the food thickener powder such as kappa-Carrageenan, iota-Carrageenan and Agar-Agar to make solidified elastic Gel pad without a cover instead of the commercially available expensive disposable Water gel pad, the convenience and usefulness of use are improved. It is judged that the manufactured Gel pads can contribute well to the role of efficient ultrasound propagation medium.

• The Journal of the Acoustical Society of Korea
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• v.27 no.2
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• pp.57-65
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• 2008

Setting parameters of Ultrasonic scanners influence the quality of ultrasonic images. In order to obtain optimized images sonographers need to understand the effects of the setting parameters on ultrasonic images. The present study considered typical four parameters including TGC (Time Gain Control), Gain, Frequency, DR (Dynamic Range). LCS (low contrast sensitivity) was chosen to quantitatively compare the quality of the images. In the present experiment LCS targets of a standard ultrasonic test phantom (539, ATS, USA) were imaged using a clinical ultrasonic scanner (SA-9000 PRIME, Medison, Korea). Altering the settings in the parameters of the ultrasonic scanner, 6 LCS target images (+15 dB, +6 dB, +3 dB, -3 dB, -6 dB, -15 dB) to each setting were obtained, and their LCS values were calculated. The results show that the mean pixel value (LCS) is the highest at the max setting in TGC, mid to max in gain and pen mode in frequency and 40-66 dB in DR. Among all images, the image being the highest in LCS was obtained at the setting of DR 40 dB. It is expected that the results will be of use in setting the parameters when ultrasonically examining masses often clinically found In either solid lesions (similar to +15, +6, +3 dB targets) or cystic lesions (similar to -15, -6, -3 dB targets).

• Progress in Medical Physics
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• v.23 no.1
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• pp.42-47
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• 2012

In this paper, Acousto-Optical tomography is modeled by a linear integral equation and an inverse problem involving a diffusion equation in n-spatial dimensions. We make two-step mathematical model. First, we solve a linear integral equation. Assuming the optical energy fluence rate has been recovered from the previous equation, the absorption coefficient ${\mu}$ is then reconstructed by solving an inverse problem. Numerical experiments are presented for the case n=2. The traditional gradient descent method is used for the numerical simulations. The result of the gradient descent method produces the blurring effect. To get rid of the blurring effect, we suggest the total variation regularization for the minimization problem.

• The Journal of the Acoustical Society of Korea
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• v.30 no.5
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• pp.239-248
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• 2011

In order to improve the quality of strain images in medical ultrasound imaging, displacements need to be accurately estimated. In this paper, in order to apply one-dimensional displacement estimation methods to two-dimensional motion estimation, the axial and lateral displacements are separately estimated. In order to estimate lateral displacements, one-dimensional signals aligned in the lateral direction are converted to analytic signals, which are then crosscorrelated. Strain images are produced by first compensating two-dimensional displacements for lateral motion with lateral motion displacement estimates obtained from the proposed lateral displacement estimation algorithm and then estimating axial displacements. Both phantom and human data experiments show that the proposed method provides better signal-to-noise ratio and contrast-to-noise ratio characteristics than a conventional strain imaging method that utilizes axial displacement estimates only.