Biomedical subjects

K Kirk Shung

Publications and source records attributed to K Kirk Shung.

29 records · Page 2Linked to original sources

PubMed2004

High-resolution ultrasonic imaging of the posterior segment.

PURPOSE: Conventional ophthalmic ultrasonography is performed using 10-megahertz (MHz) transducers. Our aim was to explore the use of higher frequency ultrasound to provide improved resolution of the posterior pole. DESIGN: Prospective case series. PARTICIPANTS: One normal subject and 5 subjects with pathologies affecting the posterior coats, including nevii, small melanomas, and macular hole. METHODS: We modeled the frequency-dependent attenuation of ultrasound across the eye to develop an understanding of the range of frequencies that might be practically applied for imaging of the posterior pole. We compared images of the posterior coats made at 10, 15, and 20 MHz, and 20-MHz ultrasound images of pathologies with 10-MHz ultrasound and optical coherence tomography (OCT). MAIN OUTCOME MEASURES: Ability to resolve normal and pathologic structures affecting posterior coats of the eye. RESULTS: Modeling showed that frequencies of 20 to 25 MHz might be used for posterior pole imaging. Twenty-megahertz images allowed differentiation of the retina, choroid, and sclera. In addition, at 20 MHz the retina showed banding patterns suggesting an internal structure comparable in many respects to that seen in OCT and histology. Images of ocular pathology provided much improved detail relative to 10-MHz images and deeper penetration than OCT. CONCLUSIONS: Twenty-megahertz ultrasound can be practically employed for imaging of the posterior pole of the eye, providing a 2-fold improvement in resolution relative to conventional 10-MHz instruments. Although not providing the resolution of OCT, ultrasound can be used in the presence of optical opacities and allows evaluation of deeper tissue structures.

Adult↗

PubMed2004

Echogenicity variations from porcine blood I: the "bright collapsing ring" under pulsatile flow.

The temporal and radial variations of the echogenicity from porcine blood were investigated using a linear M12L transducer with a GE LOGIQ 700 Expert system. The "bright collapsing ring" (BRCR) phenomenon, a bright echogenic ring converging from the periphery to the center of the tube wall and eventually collapsing during a pulsatile cycle in cross-sectional B-mode images, was observed from porcine blood in a mock flow loop within a 0.95-cm diameter tube under certain flow conditions. The BRCR phenomenon from porcine blood was stronger as the peak speed was increased from 10 to 25 cm/s, and the mean echogenicity and the "black hole" (BLH) phenomenon, a central echo-poor zone surrounded by a bright hyperechoic zone, became weaker. As stroke rate was increased from 20 to 60 beats/min (bpm), both the BRCR and the BLH phenomena became weaker. These two phenomena were observed at three transmitting frequencies (9, 11 and 13 MHz). As hematocrit was increased from 12 to 45%, the BRCR phenomenon became more apparent. The nonlinear behavior of backscatter as a function of hematocrit reaching a maximum at hematocrit of 10 approximately 20% was observed near the tube wall, but it changed at the center of the tube, indicating the importance of hemodynamics on the ultrasonic backscatter from flowing blood. The combined effects of shear rate and acceleration on red blood cell aggregation are suggested as a possible mechanism for these phenomena.

Animals↗

PubMed2004

Echogenicity variations from porcine blood II: the "bright ring" under oscillatory flow.

Echogenicity variations from porcine blood were observed in a mock flow loop under pulsatile flow in a series of experiments (Paeng et al. 2004). In this paper, oscillatory flow was generated to further investigate the cyclic and radial variation of blood echogenicity and its origin and mechanisms by several parameters, including stroke volume, stroke rate, mean steady flow and transducer angle, using a GE LOGIQ 700 Expert system. The echogenicity at the center of the tube was enhanced during acceleration and lower during deceleration, and the expansion and collapse of the "bright ring" was observed twice per cycle. The "black hole," a central echo-poor zone surrounded by a hyperechoic zone, was barely observable under oscillatory flow, and these patterns differed from those under pulsatile flow. The cyclic and radial variation of echogenicity under oscillatory flow was affected by such hemodynamic parameters as stroke volume, stroke rate and mean steady flow. It was suggested that rouleaux might be aligned at an angle of about 25 degrees relative to the tube axis during the acceleration phase, based on the experimental results reaching a maximum of the echogenicity variation at a transducer angle of 25 degrees. Radial distribution of rouleaux alignments was proposed to be another important factor to blood echogenicity variation, in addition to combined effects of shear rate and flow acceleration on erythrocyte aggregation and blood echogenicity. The weak cyclic variation of echogenicity was also observed from the porcine erythrocyte suspensions under pure oscillatory flow, but not under pulsatile flow. It is postulated that the echogenicity variations from erythrocyte suspensions are from red cell deformation.

Animals↗

PubMed2003

Ultrasound-mediated transdermal transport of insulin in vitro through human skin using novel transducer designs.

Recent studies have shown that ultrasound (US)-mediated transdermal drug delivery offers a promising potential for noninvasive drug administration. The purpose of this study was to improve low-frequency (20 kHz) US methods for enhancing the transport of insulin in vitro across human skin. The feasibility of using US produced by small, lightweight novel transducers was explored for enhancing the transport of insulin across skin. Previous investigators have used US devices such as large, heavy sonicators or commercially obtained transducers for this type of research. The experiments carried out in this study used two low-profile novel US transducer arrays, the stack and standard array, for improved transport of insulin. The stack array generated a spatial peak temporal peak intensity (I(SPTP)) of 15.4 +/- 0.6 mW/cm(2) and the standard array had an I(SPTP) of 173.7 +/- 1.2 mW/cm(2). Spectrophotometeric absorption techniques were used for determining insulin transport in vitro across human skin. Compared with passive transmission (4.1 +/- 0.5 U) over an exposure period of 1 h, the standard array facilitated over a sevenfold increase in the noninvasive transdermal transport of Humulin R insulin (45.9 +/- 12.9 U). Using Humalog insulin with the standard array, there was a fourfold increase in the US-facilitated transmission over that in the control. These promising results indicate that low-frequency US can be used in a practical device for enhanced transport across the stratum corneum.

Administration, Cutaneous↗

PubMed2003

Ultrasound-mediated transdermal in vivo transport of insulin with low-profile cymbal arrays.

The purpose of this study was to demonstrate the feasibility of ultrasound (US)-mediated transdermal delivery of insulin in vivo using rats with a novel, low profile two-by-two US array based on the "cymbal" (due to its unique shape) transducer. As a practical device, the cymbal array (f = 20 kHz) was 37 x 37 x 7 mm in size, and weighed less than 22 g. A total of 20 Sprague-Dawley rats (350 to 450 g) were divided into four groups, two controls and two US exposure, with five rats in each group. The rats were anesthetized and shaved; a water-tight standoff reservoir, which held the insulin or saline, was sealed against the rat's abdomen and the US array. At the beginning of the experiment and every 30 min for 90 min, 0.3 mL of blood was collected from the jugular vein to determine the blood glucose level (mg/dL). For comparison between the rats, the change in the glucose level for each rat was normalized to a baseline (i.e., 0 mg/dL). The first control group used insulin in the reservoir with no US and the second control group had saline in the reservoir with US operating at I(SPTP) = 100 mW/cm(2) for 60 min. For the experiments, the third group employed insulin with US exposure for 60 min (I(SPTP) = 100 mW/cm(2)), whereas the last group used insulin with US operating with a 20-min exposure (I(SPTP) = 100 mW/cm(2)) to examine the effects of time on delivery. For the 60-min US exposure group, the glucose level was found to decrease from the baseline to -267.5 +/- 61.9 mg/dL in 1 h. Moreover, to study the effects of US exposure time on insulin delivery, the 20-min group had essentially the same result as the 60-min exposure at a similar intensity, which indicates that the expose time does not need to be as long for delivery.

Administration, Cutaneous↗

PubMed2003

Cyclic and radial variation of the Doppler power from porcine whole blood.

The Doppler power from porcine blood was observed in a mock flow loop to have cyclic and radial variation during a pulsatile cycle. It was found to decrease with shear rate under steady flow, except near the center of the tube at which other mechanisms such as the effects of radial distribution on the rouleaux might be involved. Under pulsatile flow, the timing of the peak of the Doppler power measured at the center of the tube became closer to the peak systole from 20 to 60 beats/minute (BPM), and the power and velocity peaks coincided at 60 BPM. The overall radial variation of the Doppler power during a whole pulsatile cycle was prominent due to the increase of shear rate from the center to 4.5 mm radial position within a tube of 6.35 mm radius. The cyclic variation of the Doppler power varied with the radial position, being relatively large at the center, reaching a minimum at an intermediate radial position, and increasing again near the wall. The peak of the Doppler power occurred at early systole near the tube wall and lagged the flow closer to the center. The "black hole" phenomenon was observed only over portions of the flow cycle. All these complex variations of the Doppler power across the tube over a cycle are thought to be the result of red cell aggregation, which can be affected by shear rate and acceleration.

Acceleration↗

PubMed2003

Design of efficient, broadband single-element (20-80 MHz) ultrasonic transducers for medical imaging applications.

This paper discusses the design, fabrication, and testing of sensitive broadband lithium niobate (LiNbO3) single-element ultrasonic transducers in the 20-80 MHz frequency range. Transducers of varying dimensions were built for an f# range of 2.0-3.1. The desired focal depths were achieved by either casting an acoustic lens on the transducer face or press-focusing the piezoelectric into a spherical curvature. For designs that required electrical impedance matching, a low impedance transmission line coaxial cable was used. All transducers were tested in a pulse-echo arrangement, whereby the center frequency, bandwidth, insertion loss, and focal depth were measured. Several transducers were fabricated with center frequencies in the 20-80 MHz range with the measured -6 dB bandwidths and two-way insertion loss values ranging from 57 to 74% and 9.6 to 21.3 dB, respectively. Both transducer focusing techniques proved successful in producing highly sensitive, high-frequency, single-element, ultrasonic-imaging transducers. In vivo and in vitro ultrasonic backscatter microscope (UBM) images of human eyes were obtained with the 50 MHz transducers. The high sensitivity of these devices could possibly allow for an increase in depth of penetration, higher image signal-to-noise ratio (SNR), and improved image contrast at high frequencies when compared to previously reported results.

Computer-Aided Design↗

PubMed2002

High-frequency backscatter and attenuation measurements of porcine erythrocyte suspensions between 30-90 MHz.

There are now diagnostic ultrasonic imaging devices that operate at very high frequencies (VHF) of 20 MHz and beyond for clinical applications in ophthalmology, dermatology and vascular surgery. To be able to better interpret these images and to further the development of these devices, knowledge of ultrasonic attenuation and scattering of biologic tissues, such as blood, in the high-frequency range is crucial. VHF attenuation and backscatter experiments were made on porcine red blood cell (RBC) suspensions, for which much data on attenuation and backscatter can be found in the literature in the lower frequency range. Attenuation and backscatter at hematocrits of 6%, 10%, 15%, 20%, 25% and 30% from 30 to 90 MHz were measured using a modified substitution method that allows the utilization of focused transducers. The results show that the attenuation coefficient from all suspensions increased linearly with frequency and the backscatter coefficient for low hematocrit suspensions was found to have a maximum between 10% and 15%. At higher hematocrits, a decrease in the frequency-dependence was observed, possibly indicating that Rayleigh scattering is no longer valid because the wavelength in the VHF range is comparable to the size of a porcine RBC.

Animals↗

PubMed2002

Design, fabrication, and evaluation of high frequency, single-element transducers incorporating different materials.

The performance of high frequency, single-element transducers depends greatly on the mechanical and electrical properties of the piezoelectric materials used. This study compares the design and performance of transducers incorporating different materials. The materials investigated include 1-3 lead zirconate titanate (PZT) fiber composite, lead titanate (PbTiO3) ceramic, poly(vinylidene fluoride) (PVDF) film, and lithium niobate (LiNbO3) single crystal. All transducers were constructed with a 3-mm aperture size and an f-number between 2 and 3. Backing and matching materials were selected based on design goals and fabrication limitations. A simplified coaxial cable tuning method was employed to match the transducer impedance to 50 ohms for the PZT fiber composite and PbTiO3 ceramic transducers. Transducers were tested for two-way loss and -6 dB bandwidth using the pulse/echo response from a flat quartz target. Two-way loss varied from 21 to 46 dB, and bandwidths measured were in the range from 47 to 118%. In vitro ultrasonic backscatter microscope (UBM) images of an excised human eye were obtained for each device and used to compare imaging performance. Both press-focusing and application of a lens proved to be useful beam focusing methods for high frequency. Under equal gain schemes, the LiNbO3 and PbTiO3 transducers provided better image contrast than the other materials.

Equipment Design↗

PubMed2002

A 30-MHz piezo-composite ultrasound array for medical imaging applications.

Ultrasound imaging at frequencies above 20 MHz is capable of achieving improved resolution in clinical applications requiring limited penetration depth. High frequency arrays that allow real-time imaging are desired for these applications but are not yet currently available. In this work, a method for fabricating fine-scale 2-2 composites suitable for 30-MHz linear array transducers was successfully demonstrated. High thickness coupling, low mechanical loss, and moderate electrical loss were achieved. This piezo-composite was incorporated into a 30-MHz array that included acoustic matching, an elevation focusing lens, electrical matching, and an air-filled kerf between elements. Bandwidths near 60%, 15-dB insertion loss, and crosstalk less than -30 dB were measured. Images of both a phantom and an ex vivo human eye were acquired using a synthetic aperture reconstruction method, resulting in measured lateral and axial resolutions of approximately 100 microm.

Artifacts↗

PubMed2002

Transducer design for a portable ultrasound enhanced transdermal drug-delivery system.

For application in a portable transdermal drug-delivery system, novel transducers have been designed to enhance insulin transmission across skin using ultrasound. Previous research has shown transdermal delivery of insulin across skin using commercial sonicators operating at 20 kHz with intensities ranging from 12.5 to 225 mW/cm2. The goal of this research was to design and construct a small, lightweight transducer or array that could operate with a similar frequency and intensity range as a commercial sonicator used in previous transdermal ultrasound insulin experiments, but without the weight and mass of a sonicator probe. To obtain this intensity range, a cymbal transducer design was chosen because of its light, compact structure and low resonance frequency in water. To increase the spatial ultrasound field for drug delivery across skin, two arrays, each comprising of four cymbal transducers, were constructed. The first array, designated the standard array, used four cymbals transducer elements in parallel. A second array (named the stack array) used four cymbal transducers that used stacked piezoelectric discs to drive the titanium flextensional caps. Under similar driving conditions, the standard array produced intensities comparable to those achieved using a commercial sonicator.

Administration, Cutaneous↗