High Frequency Subharmonic Imaging of the Mouse Heart

A nonlinear microbubble imaging system has been developed and evaluated for transmit frequencies in the 10 to 50 MHz range. At high frequencies, both subharmonic and ultraharmonic imaging show good performance in terms of tissue suppression, while second harmonic imaging performs poorly due to nonlinear propagation. These images provide an example of the potential for nonlinear microbubble imaging at a 20 MHz transmit frequency. The contrast agent employed was Definity, which has been previously shown to have substantial nonlinear activity at high frequencies. The upper panel shows a fundamental mode short axis image of a mouse heart and surrounding tissue immediately after the injection of contrast agent. The lower panel is an image in subharmonic mode (10 MHz), where is can be seen that tissue signals have been suppressed leaving a clear picture of agent contained within the left ventricle (LV), and in larger collateral vessels. The spatial scale is 1 mm between large hash marks. See article on page 65.

Images courtesy of David E. Goertz, Emmanuel Cherin, Andrew Needles, Raffi Karshafian, Allison S. Duckett, Peter N. Burns, F. Stuart Foster, University of Toronto, Medical Biophysics, Toronto, Canada. D. E. Goertz is also with Erasmus Medical Centre, Experimental Echocardiography, Rotterdam, The Netherlands. F. S. Foster is also with University of Toronto, Mouse Imaging Centre, Toronto, Canada.

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Acoustic propagation of a coded signal and a short pulse

Those images show the transmitted fields for a conventional short pulse excitation and for a linear FM excitation using the simulation program Field II, written by Prof. J. A. Jensen. The signals are applied to all elements of a 128-element array using a Hanning aperture apodization and a fixed transmit focus of 55 mm. The transducer has a 65% fractional bandwidth and a center frequency of 4 MHz. The pulse excitation (top) is a 3-cycle Hanning-apodized pulse at 4 MHz, and the coded signal (bottom) is a tapered linear FM signal 12 μs long, designed to have the same bandwidth as the pulse excitation. See series of articles beginning on page 176.

Images courtesy of Thanassis Misaridis, National Technical University of Athens, GR, Institute of Accelerating Systems and Applications, Athens, Greece.

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Strain Imaging of the Skin utilizing High Frequency Ultrasound

The front cover shows results of measurements with a high frequency ultrasound based strain imaging system. A stepwise decreased pressure was applied to the skin surface in order to cause suction. Consecutive frames of radio frequency echo signals were acquired after each pressure change utilizing ultrasound in the 20 MHz range. The presented B-mode image is the envelope of the first acquired frame of echo signals. A hypoechoic nevus inside the hyperechoic dermis and the subjacent subcutaneous fat are visible. Furthermore, the segmented skin surface contours, which were segmented in each signal frame, are shown. Axial displacements between echo signals in consecutive frames were estimated applying a phase sensitive correlation approach, and axial strains were calculated as the spatial derivative of estimated displacements. The color coded strain image shows that large elongational strains occur in the subcutaneous fat, whereas compressional strains are given in the nevus.

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Variation of Surface Displacement of a 1-3 Piezelectric Composite Transducer as a Function of Temperature

The images show the variation in the surface displacement of a 1-3 connectivity piezoelectric composite transducer as a function of temperature. In each case the magnitude and phase of the surface displacement of an area of 3 × 3 ceramic pillars being driven at the fundamental thickness mode is shown. At room temperature, the magnitude and phase indicate that the device displacement is uniform and the pillars and the polymer are acting in phase. At elevated temperature, beyond the glass transition temperature of the polymer filler, it is clear that the ceramic pillars and polymer are displacing out of phase.

Images courtesy of Richard L. O'Leary, Agnes C. S. Parr, and Gordon Hayward, Centre for Ultrasonic Engineering, Dept. of Electronic and Electrical Engineering, Glasgow, United Kingdom. See article on page 550.

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UFFC 50th Anniversary Medallion

The UFFC 50th Anniversary Medallion was designed by Paul Doto of IEEE staff to commemorate the celebration of the 50th Anniversary of the Ultrasonics, Ferroelectrics, and Frequency Control Society which took place during the 2004 IEEE International Ultrasonics, Ferroelectrics and Frequency Control 50th Anniversary Joint Conference 24 - 27 August 2004 that was held in the historic city of Montréal, Quebec, Canada, at the Palais des Congrès, Montréal's convention center.

The metallic rendering was prepared by Lapel Pins R Us who were commissioned to make lapel pin mementos for the attendees.

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In-vivo Synthetic Aperture Flow image of the Carotid Artery

The front page shows an in-vivo color flow image of the blood velocity in the carotid artery in the diastolic phase from a 29 years old male. A 64 elements 7 MHz linear array transducer was used in combination with an experimental ultrasound scanner. The whole image is acquired in 24 pulse emissions using a synthetic aperture technique, where spherical ultrasound pulses are emitted from four different places on the aperture. These four emissions are repeated 6 times to yield the 24 emissions, and the B-mode image is beamformed from the first 4 emissions to create a high resolution image. A high resolution image can be created after each emissions after the fourth emission, and these data are used in a cross-correlation estimator to find the velocity along the focused beam directions. The color scale on the right indicates the magnitude of the velocity.

Images courtesy of Svetoslav Ivanov Nikolov and Jørgen Arendt Jensen, Technical University of Denmark, Ørsted•DTU, Lyngby, Denmark. See related article: S. I. Nikolov and J. A. Jensen, "In-vivo synthetic aperture flow imaging in medical ultrasound," IEEE Trans. Ultrason., Ferroelect., Freq. Contr., vol. 50, no. 7, pp. 848-856, Jul. 2003.

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Spatio-Temporal and Spectral Domain Data Obtained by Ultrasonic System with Lateral Scanning

The upper image shows the output waveform of the wide-aperture, line-focused ultrasonic system recorded for a brass foil 0.2 mm thick as a function of time t and lateral position of the receiving transducer x. The amplitude and phase of the spectrum of the recorded data are presented in the left and right lower pictures, respectively, where f is the frequency and fx is the spatial frequency. Because of the strong dispersion of Lamb waves, the experimental waveform is complicated, whereas in the spectrum the symmetric S0, S1, S2 and antisymmetric A0, A1 modes appear as phase jumps at the critical angles of the leaky Lamb waves.

Images courtesy of Roman Gr. Maev, Sergey A. Titov, and Alexey N. Bogatchenkov. R.Gr. Maev and S. A. Titov are with the University of Windsor, Department of Physics, Windsor, Ontario, Canada. A. N. Bogatchenkov is with the Institute of Biochemical Physics of the Russian Academy of Science, Moscow, Russian Federation. See article S. Titov, R. Maev, A. Bogatchenkov, "Wide-aperture, line-focused ultrasonic material characterization system based on lateral scanning," IEEE Trans. Ultrason., Ferroelect., Freq. Contr., vol. 50, no. 8, pp. 1046-1056, Aug. 2003.

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A Traveling-Wave Modified Ring Linear Piezoelectric Microactuator with Enclosed Piezoelectric Elements-The "Scream" Actuator

The front cover image contains an image of "The Scream" by Edvard Munch, the progression of the traveling wave about the circumference of the "Scream" actuator calculated by numerical methods, and a photograph of a newly assembled version of the actuator. Note the close resemblance.

Images courtesy of James R. Friend, Kentaro Nakamura, and Sadayuki Ueha, Tokyo Institute of Technology, Precision and Intelligence Laboratory, Yokohama, Japan. See article on page 1343.

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Acoustomigration Under the Microscope

The cover image is an artistic rendering of the damaging effect of a standing wavefield on a thin aluminum film. Stress induced material transport in SAW devices, so-called acoustomigration, is a prominent failure mechanism, especially in high-power applications. We present the quantitative calculation of the stress in the metal film employing a P-matrix model in combination with the Partial Wave Method. This approach provides the flexibility to determine the stress at any given point in a SAW device.

We used scanning probe microscopy techniques to study acoustomigration of metal structures in-situ, i.e. during the high-power loading of the device. Scanning Acoustic Force Microscopy (SAFM) allows for the simultaneous measurement of the acoustic wavefield and the topography with submicron lateral resolution.

Image courtesy of Thorsten Hesjedal of the Paul Drude Institute for Solid-State Electronics in Berlin, Germany. Special thanks for the artwork goes to Roman Engel-Herbert and Tonia Stengelin. See article on page 1584.

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Local Temporal Coherence Images of Diffuse Ultrasonic Waves Showing Progression of Material Damage

These successive images show the local temporal coherence between a reference diffuse ultrasonic signal and subsequently measured signals after progressive introduction of artificial damage. The measurements were obtained using piezoelectric sensors permanently bonded to an aluminum specimen, and the loss in coherence as a function of time-from-transmit correlates to the amount of damage.

A Compact Schlieren System for Ultrasound Beam Imaging

A new compact Schlieren system (40 cm x 100 cm x 40 cm) for ultrasound beam imaging and tomography based on an optical fiber laser source has been developed at Acoustoelectronics Laboratory (ACULAB), University Roma Tre, Italy. The optical beam is focused by means of 2.54 cm diameter lenses. Images are obtained by mechanically scanning the entire ultrasound field up to 20 cm length, and merging several sub-images. The correct merging of the sub-images, which is impeded by luminance artefacts due to both the spatial Gaussian distribution of the light source and the non-ideal optical components including lenses, screen and camera, is carried out by an adaptive filtering algorithm developed by the contributors. The left figure is an axial scan of a 3 cm ultrasound field (the emitting surface is on the top) of a 10 MHz ultrasonic transducer for ophthalmic applications. The three figures on the right are, starting from the top, the tomographic sections of the beam at 5 mm, 15 mm, and 25 mm, respectively.

Images courtesy of Giosue Caliano, Alessandro Miti, Riccardo Carotenuto, and Massimo Pappalardo, University Roma Tre, Dept. of Electronic Engineering, Roma, Italy.

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Forward-Viewing CMUT Arrays for Medical Imaging

Image shows a 64-element forward-viewing annular array fabricated using the standard CMUT fabrication process. Experiments measured the operating frequency, bandwidth and the transmit/receive efficiency of the array elements. The annular array elements, designed for imaging applications in the 20 MHz range, had a resonance frequency of 13.5 MHz in air. The immersion pulse-echo data collected from a plane reflector showed that the device operates in the 5-26 MHz range with a fractional bandwidth of 135%. The output pressure at the surface of the transducer was measured to be 24 kPa/V. These values translate into a dynamic range of 131.5 dB for 1-V excitation in 1-Hz bandwidth with a commercial low noise receiving circuitry. The forward-viewing annular CMUT array is suitable for mounting on the front surface of a cylindrical catheter probe and can provide Doppler information for measurement of blood flow and guiding information for navigation through blood vessels in intravascular ultrasound imaging.

Image courtesy of Utkan Demirci, Ömer Oralkan, A. Sanli Ergun, Mustafa Karaman, B.T. Khuri-Yakub. U. Demirci is with Harvard Medical School, Center for Engineering in Medicine - BioMEMs Resource Center, Charlestown, MA. Ö. Oralkan, A. S. Ergun and B.T. Khuri-Yakub are with Stanford University, Electrical Engineering, Stanford, CA. M. Karaman is with Isik University, Electrical Engineering, Istanbul, Turkey. See article U. Demirci, A. S. Ergun, Ö. Oralkan, M. Karaman, and B. T. Khuri-Yakub, "Forward-viewing CMUT arrays for medical imaging," IEEE Trans. Ultrason., Ferroelect., Freq. Contr., vol. 51, no. 7, pp. 887-895, Jul. 2004.

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