Mr. Karthik Ranganathan Profile

Karthik Ranganathan

Graduate Student at Univ of Virginia

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Publications (4)

Proceedings Article | 16 March 2006 Paper

The sonic window: second generation results

William Walker, Michael Fuller, Edward Brush, Matthew D. C. Eames, Kevin Owen, Karthik Ranganathan, Travis Blalock, John Hossack

Proceedings Volume 6147, 61470B (2006) https://doi.org/10.1117/12.661507

KEYWORDS: Digital signal processing, Ultrasonography, Transducers, Prototyping, Analog electronics, LCDs, Signal processing, Phased arrays, System integration, Signal to noise ratio

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Medical Ultrasound Imaging is widely used clinically because of its relatively low cost, portability, lack of ionizing radiation, and real-time nature. However, even with these advantages ultrasound has failed to permeate the broad array of clinical applications where its use could be of value. A prime example of this untapped potential is the routine use of ultrasound to guide intravenous access. In this particular application existing systems lack the required portability, low cost, and ease-of-use required for widespread acceptance. Our team has been working for a number of years to develop an extremely low-cost, pocket-sized, and intuitive ultrasound imaging system that we refer to as the "Sonic Window." We have previously described the first generation Sonic Window prototype that was a bench-top device using a 1024 element, fully populated array operating at a center frequency of 3.3 MHz. Through a high degree of custom front-end integration combined with multiplexing down to a 2 channel PC based digitizer this system acquired a full set of RF data over a course of 512 transmit events. While initial results were encouraging, this system exhibited limitations resulting from low SNR, relatively coarse array sampling, and relatively slow data acquisition. We have recently begun assembling a second-generation Sonic Window system. This system uses a 3600 element fully sampled array operating at 5.0 MHz with a 300 micron element pitch. This system extends the integration of the first generation system to include front-end protection, pre-amplification, a programmable bandpass filter, four sample and holds, and four A/D converters for all 3600 channels in a set of custom integrated circuits with a combined area smaller than the 1.8 x 1.8 cm footprint of the transducer array. We present initial results from this front-end and present benchmark results from a software beamformer implemented on the Analog Devices BF-561 DSP. We discuss our immediate plans for further integration and testing. This second prototype represents a major reduction in size and forms the foundation of a fully functional, fully integrated, pocket sized prototype.

Proceedings Article | 28 April 2004 Paper

Synthetic aperture methods for angular scatter imaging

Drake Guenther, Karthik Ranganathan, Michael McAllister, K. Rigby, William Walker

Proceedings Volume 5373, (2004) https://doi.org/10.1117/12.540671

KEYWORDS: Scattering, Spatial resolution, Backscatter, Spatial frequencies, Tissues, Acoustics, Data acquisition, Transducers, Ultrasonography, Multiple scattering

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Angular scatter offers a new source of tissue contrast and an opportunity for tissue characterization in ultrasound imaging. We have previously described the application of the translating apertures algorithm (TAA) to coherently acquire angular scatter data over a range of scattering angles. While this approach works well at the focus, it suffers from poor depth of field (DOF) due to a finite aperture size. Furthermore, application of the TAA with large focused apertures entails a tradeoff between spatial resolution and scattering angle resolution. While large multielement apertures improve spatial resolution, they encompass many permutations of transmit/receive element pairs. This results in the simultaneous interrogation of multiple scattering angles, limiting angular resolution. We propose a synthetic aperture imaging scheme that achieves both high spatial resolution and high angular resolution. In backscatter acquisition mode, we transmit successively from single transducer elements, while receiving on the same element. Other scattering angles are interrogated by successively transmitting and receiving on different single elements chosen with the appropriate spatial separation between them. Thus any given image is formed using only transmit/receive element pairs at a single separation. This synthetic aperture approach minimizes averaging across scattering angles, and yields excellent angular resolution. Likewise, synthetic aperture methods allow us to build large effective apertures to maintain a high spatial resolution. Synthetic dynamic focusing and dynamic apodization are applied to further improve spatial resolution and DOF. We present simulation results and experimental results obtained using a GE Logiq 700MR system modified to obtain synthetic aperture TAA data. Images of wire targets exhibit high DOF and spatial resolution. We also present a novel approach for combining angular scatter data to effectively reduce grating lobes. With this approach we have been able to push the grating lobes below -50 dB in simulation and effectively eliminate their presence in the experimental wire target images.

Proceedings Article | 28 April 2004 Paper

A prototype low-cost handheld ultrasound imaging system

Karthik Ranganathan, Mary Santy, Michael Fuller, Shiwei Zhou, Travis Blalock, John Hossack, William Walker

Proceedings Volume 5373, (2004) https://doi.org/10.1117/12.537724

KEYWORDS: Phased arrays, Ultrasonography, Digital signal processing, Data centers, Transducers, Apodization, Linear filtering, Image quality, Prototyping, Optical simulations

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Proceedings Article | 11 April 2002 Paper

Novel aperture design method in ultrasound imaging

Karthik Ranganathan, William Walker

Proceedings Volume 4687, (2002) https://doi.org/10.1117/12.462159

KEYWORDS: Point spread functions, Ultrasonography, Chemical elements, Apodization, Computer simulations, Transducers, Linear algebra, Imaging systems, Continuous wave operation

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