Alan A. Winder

Power Doppler Assessment of Vascular Changes During Fracture Treatment With Low-Intensity Ultrasound

Objective. To study the use of power Doppler sonography for assessing changes in vascularity during treatment of fracture sites with low‐intensity ultrasound. Methods. In 6 dogs (3 pairs), subcutaneous dissection of the midshaft of the ulna allowed symmetrical osteotomies to be made with a reciprocation saw. Three dogs were treated and 3 were used as controls. The fracture site was subjected to 1.5‐MHz low‐intensity ultrasound (30 mW/cm2) for 20 minutes daily from a therapeutic ultrasonic device. Gray scale sonography was performed to evaluate the fracture site. Power Doppler sonography was used to assess flow patterns at the fracture site and surrounding soft tissue. A sonographic contrast agent was administered intravenously. The dose was 0.2 mL/kg. Results. Power Doppler sonography showed an increase in flow around the fracture site in the treated dogs compared with that in control dogs. Color pixel values on day 7 were 3‐fold higher in treated legs than control legs and on day 11 were 33% higher in treated legs than control legs. Enhancement after contrast agent administration was consistently higher in treated legs than control legs. Conclusions. Power Doppler sonography showed increased vascularity around the fracture sites in treated dogs with and without contrast agent administration.

25 MHz ultrasonic transducers with lead- free piezoceramic, 1-3 PZT fiber-epoxy composite, and PVDF polymer active elements

This paper presents the fabrication and characterization of single-element ultrasonic transducers whose active elements are made of lead-free piezoceramic, 1-3 PZT/polymer composite and PVDF film. The lead free piezoelectric KNNLT- LS(K0.44Na0.52Li0.04)(Nb0.84Ta0.10S0.06b)O3 powders and ceramics were prepared under controlled humidity and oxygen flow rate during sintering. Due to its moderate longitudinal piezoelectric charge coefficient (175 pC/N) and kt of 0.50, the KNN-LT-LS composition may be a good candidate for high frequency transducer applications. PZT fibers with 25 mum diameter formed by the viscose suspension spinning process were incorporated into epoxy to fabricate 1-3 composites with the averaged kt = 0.64 and d33 = 400 pC/N. Using KNN-LS-LT ceramic, 1-3 PZT fiber composite, and PVDF film, 3 different unfocused single element transducers with center frequencies of 25 MHz were fabricated. The acoustic characterization of the transducers demonstrated that wideband and low insertion loss could be obtained employing KNN-LS-LT ceramic. The -6 dB bandwidth and insertion loss were 70% and -21 dB, respectively. In comparison, the insertion loss of the ceramic transducer was much smaller than those made with 1-3 composite and PVDF film. This was attributed to closer electrical impedance match to 50 Omega and higher thickness coupling coefficient of the ceramic transducer.

Broad band single crystal transducer for contrast agent harmonic imaging

A broadband single element transducer was constructed from single crystal PMN-PT and tested to determine the feasibility of using this material for simultaneous sub-harmonic and second harmonic imaging. The transducer consisted of a 1-3 PMN-PT/epoxy composite with two quarter wave matching layers and a backing. The transducer face was spherically curved to yield a 53 mm focal point. The transducers impulse response had a center frequency of 5.2 MHz and -6 dB bandwidth over 130%. The transmit response for tone burst excitation indicated a shift in center frequency to 6.5 MHz and a 6 dB bandwidth of 100%. Receive sensitivity was high at the lower end of the band and decreased with increasing frequency; this behavior was probably due to electrical impedance mismatch. Contrast agent testing using Sonazoid/spl reg/ showed that the second harmonic could be easily detected. The sub-harmonic was not detected due to the center frequency shift under tone burst excitation. Simultaneous sub, and second harmonic testing could probably be accomplished with a lower center frequency and better electrical impedance matching.

Indirect MR arthrography of the knee: effects of low-intensity ultrasound on the diffusion rate of intravenously administered Gd-DTPA in healthy volunteers.

Weishaupt D, Schweitzer ME, Rawool NM, et al. Indirect MR arthrography of the knee: Effects of low-intensity ultrasound on the diffusion rate of intravenously administered Gd-DTPA in healthy volunteers. Invest Radiol 2001;36:493–499. rationale and objectives. To evaluate whether application of low-intensity ultrasound may increase the diffusion rate of intravenously administered gadopentetate dimeglumine (Gd-DTPA) and increase the amount of joint fluid on indirect magnetic resonance (MR) arthrography. methods.Conventional MR imaging, indirect MR arthrography, and power Doppler ultrasonography were performed before and after application of therapeutic, pulsed low-intensity ultrasound in 12 asymptomatic knees of 12 volunteers. Intra-articular diffusion of intravenously administered Gd-DTPA as measured by signal intensity differences of the intra-articular joint fluid before and after ultrasound treatment was assessed. In addition, the amount of joint fluid was rated, and differences in synovial blood flow as evidenced by power Doppler ultrasonography were noted. results.All volunteers tolerated well the application of therapeutic low-intensity ultrasound. A significant increase in intra-articular diffusion of intravenously administered Gd-DTPA was noted in all knees, and an increase in joint fluid was noted in 8 of 12 knees (66.6%). Detection of power Doppler flow signal in the synovium of the suprapatellar recess was possible in one instance at posttreatment exam. conclusions.Use of pulsed, therapeutic low-intensity ultrasound may increase the diffusion rate of intravenously administered Gd-DTPA and may induce joint effusion.

Design and acoustic characterization of a multi-frequency harmonic array for nonlinear contrast imaging

Two novel ultrasound multi-frequency harmonic transducer arrays (MFHAs) for contrast enhanced second harmonic (HI) and subharmonic (SHI) imaging have been designed. Each consisted of 3 multi-element piezo-composite sub-arrays (A, B & C) mounted in an arch with a common mechanical focus of 5 cm. The sub-arrays were constructed so the center frequencies were 4f/sub A/=2f/sub B/=f/sub C/ (2.5/5.0/10.0 MHz and 1.75/3.5/7.0 MHz). This enabled SHI by transmitting on sub-array C receiving on B and, similarly, from B to A as well as HI by transmitting on A receiving on B and, likewise, from B to C. Transmit and receive pressure levels of the arrays were measured. Following contrast administration, in vitro HI and SHI S/N ratios of up to 40 dB were obtained. In conclusion, the special design of the MFHA produced S/N ratios for HI and SHI comparable to that of regular B-mode and better than commercially available HI systems.

Synthetic Structural Imaging (SSI): A new ultrasound method for tracking breast cancer morphology

A new signal interrogation concept, based on Synthetic Structural Imaging (SSI) physics, has been developed to guide therapies. The SSI method was previously successful in radar and sonar imaging; here it is demonstrated for acoustic scattering from penetrable biological targets. Operating at ultrasonic frequencies of several hundred kilohertz, SSI trades the higher resolution of typical B-mode ultrasound imaging for a significantly stronger correlation to target shape and volume, which are among the primary tissue classifiers. Tissue phantom models were fabricated with embedded spheroidal inclusions ranging from 2.41 mm through 6.3 mm in diameter. The phantom medium was 10 wt% porcine gelatin and the inclusions were 28 wt% porcine gelatin. The inclusion dimensions were measured with calipers. The phantom was interrogated with two impulse-excited Panametrics transducers: a model V301 with a peak frequency of 0.50 MHz and a −6 dB bandwidth of 81%, and a model V314 with a peak frequency of 0.99 MHz and a −6 dB bandwidth of 77%. The backscattered RF data were digitized, recorded, and digitally bandpass-filtered. The experimental profile functions were computed. Volumes were estimated by integrating the experimental profile functions. SSI-determined volume ratios were demonstrated to be within 7% to 18% of caliper-determined volume ratios.

4F-1 Optimization of Single Crystal Composite Arrays for Harmonic Imaging

The design concept for a single-active layer ultrasound transducer array for simultaneous sub- and second-harmonic imaging of contrast agents was tested for feasibility. Using PMN-PT single crystal in a 1-3 composite, multiple matching layers and a back plate, a design for imaging at 2, 4 and 8 MHz was implemented in a series of transducers. The effects of array pitch and piezocomposite thickness were examined. Transmit and receive sensitivities show the pitch and piezoelectric thickness can vary effects across the passband by more than 10 dB for different transducer parameters. Maximum transmit sensitivities of 230 dB re 1 uPa/V at 1 mm were achieved for the arrays. Contrast agent testing using Definityreg showed the second harmonic could be detected. The sub-harmonic was not detected, and could be due to a low peak pressure from the unfocused array sub- aperture.