Nadine Barrie Smith

Overview of Therapeutic Ultrasound Applications and Safety Considerations

Applications of ultrasound in medicine for therapeutic purposes have been accepted and beneficial uses of ultrasonic biological effects for many years. Low‐power ultrasound of about 1 MHz has been widely applied since the 1950s for physical therapy in conditions such as tendinitis and bursitis. In the 1980s, high‐pressure‐amplitude shock waves came into use for mechanically resolving kidney stones, and “lithotripsy” rapidly replaced surgery as the most frequent treatment choice. The use of ultrasonic energy for therapy continues to expand, and approved applications now include uterine fibroid ablation, cataract removal (phacoemulsification), surgical tissue cutting and hemostasis, transdermal drug delivery, and bone fracture healing, among others. Undesirable bioeffects can occur, including burns from thermal‐based therapies and severe hemorrhage from mechanical‐based therapies (eg, lithotripsy). In all of these therapeutic applications of ultrasound bioeffects, standardization, ultrasound dosimetry, benefits assurance, and side‐effect risk minimization must be carefully considered to ensure an optimal benefit to risk ratio for the patient. Therapeutic ultrasound typically has well‐defined benefits and risks and therefore presents a manageable safety problem to the clinician. However, safety information can be scattered, confusing, or subject to commercial conflicts of interest. Of paramount importance for managing this problem is the communication of practical safety information by authoritative groups, such as the American Institute of Ultrasound in Medicine, to the medical ultrasound community. In this overview, the Bioeffects Committee of the American Institute of Ultrasound in Medicine outlines the wide range of therapeutic ultrasound methods, which are in clinical use or under study, and provides general guidance for ensuring therapeutic ultrasound safety.

Targeting V600EB-Raf and Akt3 Using Nanoliposomal-Small Interfering RNA Inhibits Cutaneous Melanocytic Lesion Development

Most events promoting early melanoma development are yet to be identified, but deregulation of the B-Raf and Akt3 signaling cascades is an important regulator of this process. Approximately 90% of normal moles and approximately 60% of early invasive cutaneous melanomas contain a T1799A B-Raf mutation ((V600E)B-Raf), leading to 10 times higher enzyme activity and constitutive activation of the mitogen-activated protein kinase pathway. Furthermore, approximately 70% of melanomas have elevated Akt3 signaling due to increased gene copy number and PTEN loss. Therefore, targeting (V600E)B-Raf and Akt3 signaling is necessary to prevent or treat cutaneous melanocytic lesions. Agents specifically targeting these proteins are needed, having fewer side effects than those inhibiting both normal and mutant B-Raf protein or targeting all three Akt isoforms. In this study, a unique nanoliposomal-ultrasound-mediated approach has been developed for delivering small interfering RNA (siRNA) specifically targeting (V600E)B-Raf and Akt3 into melanocytic tumors present in skin to retard melanoma development. Novel cationic nanoliposomes stably encapsulate siRNA targeting (V600E)B-Raf or Akt3, providing protection from degradation and facilitating entry into melanoma cells to decrease expression of these proteins. Low-frequency ultrasound using a lightweight four-cymbal transducer array enables penetration of nanoliposomal-siRNA complex throughout the epidermal and dermal layers of laboratory-generated or animal skin. Nanoliposomal-mediated siRNA targeting of (V600E)B-Raf and Akt3 led to a cooperatively acting approximately 65% decrease in early or invasive cutaneous melanoma compared with inhibition of each singly with negligible associated systemic toxicity. Thus, cationic nanoliposomes loaded with siRNA targeting (V600E)B-Raf and Akt3 provide an effective approach for targeted inhibition of early or invasive cutaneous melanomas.

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.

Gradient scaling phenomenon in microsize flexoelectric piezoelectric composites

The flexoelectric-type piezoelectric composites offer an alternative avenue for the development of piezoelectric ceramics, and since the flexoelectric response is diminished rather than enhanced in lead containing compositions, one of the merits of such composites is that those of highest sensitivity will be lead-free. The composites are fabricated by using certain nonpiezoelectric components with a texture symmetry which breaks up applied uniform fields, leading to the field gradients in the active flexoelectric components of the composites. Since these induced field gradients increase as the composite dimensions decrease, it is logical to expect that the piezoelectric performance of such composites would be enhanced with their reduced sizes. In this letter, we report the experimental studies that confirm such a gradient scaling phenomenon in two flexoelectric piezoelectric composites. The fabrication and measurement of the composites are discussed.

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/cm/sup 2/. 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.

Short ultrasound exposure times for noninvasive insulin delivery in rats using the lightweight cymbal array

The purpose of this study is to demonstrate the feasibility of using short ultrasound exposure times to noninvasively deliver insulin with a lightweight (<22 g), low-profile (37/spl times/37/spl times/7 mm/sup 3/) cymbal array (f=20 kHz). Using hyperglycemic rats, previous experiments using the array demonstrated that blood glucose would decrease approximately 250 mg/dl from 60 and 20 minutes of pulsed ultrasound exposure for transdermal insulin delivery. Using a similar intensity (I/sub sptp/=100 mW/cm/sup 2/, 20% duty cycle), the goal was to determine if the same effect can be achieved with only 5 minutes of ultrasound exposure. For these experiments, 20 Sprague Dawley rats were anesthetized and shaved, and a 1-mm watertight standoff reservoir that held the insulin or saline was placed between the rats abdomen and the ultrasound array. At the beginning of the experiment and every 30 minutes, 0.3 ml of blood was collected from the jugular vein to determine the blood glucose level (milligrams per deciliter) for a total of 90 minutes. For comparison purposes 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 without any ultrasound. The second control group had saline in the reservoir with ultrasound operating at I/sub sptp/=100 mW/cm/sup 2/ for 60 minutes. For the noncontrol experiments, the third group used insulin with ultrasound exposure for 10 minutes. The last group used insulin with ultrasound operating with a 5-minute exposure to examine the effects of using short ultrasound exposure times on delivery. For the 10- and 5-minute ultrasound exposure groups, the glucose level was found to decrease from the baseline to -174.6/spl plusmn/67.2 and -200.4/spl plusmn/43.4 mg/dl measured after 1 hour, respectively. These results indicated that ultrasound exposure times do not need to be long to deliver a clinically significant insulin dose to reduce a high blood glucose level.

Quantitative analysis of peristaltic and segmental motion in vivo in the rat small intestine using dynamic MRI.

Conventional methods of quantifying segmental and peristaltic motion in animal models are highly invasive; involving, for example, the external isolation of segments of the gastrointestinal (GI) tract either from dead or anesthetized animals. The present study was undertaken to determine the utility of MRI to quantitatively analyze these motions in the jejunum region of anesthetized rats (N = 6) noninvasively. Dynamic images of the GI tract after oral gavage with a Gd contrast agent were acquired at a rate of six frames per second, followed by image segmentation based on a combination of three‐dimensional live wire (3D LW) and directional dynamic gradient vector flow snakes (DDGVFS). Quantitative analysis of the variation in diameter at a fixed constricting location showed clear indications of both segmental and peristaltic motions. Quantitative analysis of the frequency response gave results in good agreement with those acquired in previous studies using invasive measurement techniques. Principal component analysis (PCA) of the segmented data using active shape models resulted in three major modes. The individual modes revealed unique spatial patterns for peristaltic and segmental motility. Magn Reson Med, 2009.

In vivo determination of human breast fat composition by 1H magnetic resonance spectroscopy at 7 T

The role of diet and fat consumption in the pathogenesis of breast cancer is an important subject. We report a method for noninvasive determination of lipid composition in human breast by proton magnetic resonance spectroscopy (MRS) at 7 T. Two respiratory‐triggered TE‐averaged stimulated echo acquisition mode (STEAM) acquisitions were performed on the adipose tissue of 10 healthy volunteers where the second acquisition had all gradients inverted. This acquisition protocol allows the suppression of modulation sidebands that complicate spectral analysis at the short TEavg = 24.5 ms. The entire acquisition takes ∼10 min. Ten lipid peaks were typically resolved. T1 and T2 were also measured and used to correct the peak intensities. The calculated average lipid composition for saturated was 28.7 ± 8.4%, monounsaturated, 48.5 ± 7.9%, and polyunsaturated, 22.7 ± 3.1%, in close agreement with reported values from subcutaneous adipose measurements. Intrasubject variability was 2.0, 1.6, and 3.6% for the saturated, monounsaturated, and polyunsaturated fractions, respectively. In conclusion, we have shown that a chemical analysis of lipids in breast tissue can be determined quite simply, quickly, and noninvasively by proton MRS at 7 T. Magn Reson Med, 2011.

Noninvasive Ultrasonic Glucose Sensing with Large Pigs (∼200 Pounds) Using a Lightweight Cymbal Transducer Array and Biosensors

Background: To prevent complications in diabetes, the proper management of blood glucose levels is essential. Since conventional glucose meters require pricking fingers or other areas of the skin, a noninvasive method for monitoring blood glucose levels is desired. Using a lightweight cymbal transducer array, this study was conducted to noninvasively determine the glucose levels of pigs having a similar size to humans. Method: In vivo experiments using eight pigs (∼200 pounds) were performed in five groups. A cymbal array with four biosensors was attached to the axillary area of the pig. The array was operated at 20 kHz at special peak-temporal peak intensity (Isptp) equal to 50 or 100 mW/cm2 for 5, 10, or 20 minutes. After the ultrasound exposure, glucose concentrations of the interstitial fluid were determined using biosensors. For comparison, glucose levels of blood samples collected from the ear vein were measured by a commercial glucose meter. Result: In comparison, glucose levels determined by a cymbal array and biosensor system were close to those measured by a glucose meter. After a 20-minute ultrasound exposure at Isptp = 100 mW/cm2, the average glucose level determined by the ultrasound system was 175 ± 7 mg/dl, which is close to 166 ± 5 mg/dl measured by the glucose meter. Conclusion: Results indicate the feasibility of using a cymbal array for noninvasive glucose sensing on pigs having a similar size to humans. Further studies on the ultrasound conditions, such as frequency, intensity, and exposure time, will be continued for effective glucose sensing.

Rectangular cymbal arrays for improved ultrasonic transdermal insulin delivery

Circular cymbal ultrasound arrays have been shown to be effective in delivering therapeutic levels of insulin in rats, rabbits, and pigs. To improve delivery efficiency, a rectangular cymbal design was desired in order to achieve a broader spatial intensity field without increasing the size of the device or the spatial-peak temporal-peak intensity (I(SPTP)). With a similar intensity (50 mWcm(2)), the goal was to determine if the 3x1 rectangular cymbal array could perform significantly better than the 3x3 circular array for glucose reduction in hyperglycemic rabbits. Rabbit experiments were performed using three groups: nonsonicated control (n=3), ultrasound exposure using a circular cymbal array (n=3), and ultrasound exposure using a rectangular cymbal array (n=3). Rabbits were anesthetized and a water tight reservoir that held the insulin was fastened on the rabbits thigh. At the beginning of the experiment and every 15 min for 90 min, the blood glucose level was determined. For comparison between individual rabbits, the absolute level is normalized by subtracting out the baseline in order to arrive at the change in glucose level. For the control group, the normalized glucose level increased (more hyperglycemic) to +80.0+/-28.8 mgdl (mean+/-SEM). Using the circular array, the glucose level decreased to -146.7+/-17.8 mgdl at 90 min. However, using the rectangular cymbal array, the glucose decreased faster and to a level of -200.8+/-5.9 mgdl after 90 min. These results indicated the feasibility of the rectangular cymbal array as an improved device for drug delivery.