IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control ,
vol. 56, no. 10,
October
2009
2207
ULA-OP: An Advanced Open Platform for Ultrasound Research Piero Tortoli, Senior Member, IEEE, Luca Bassi, Enrico Boni, Alessandro Dallai, Francesco Guidi, Member, IEEE, and Stefano Ricci, Member, IEEE Abstract—The experimental test of novel ultrasound (US) investigation methods can be made difficult by the lack of flexibility of commercial US machines. In the best options, these only provide beamformed radiofrequency or demodulated echo-signals for acquisition by an external PC. More flexibility is achieved in high-level research platforms, but these are typically characterized by high cost and large size. This paper presents a powerful but portable US system, specifically developed for research purposes. The system design has been based on high-level commercial integrated circuits to obtain the maximum flexibility and wide data access with minimum of electronics. Preliminary applications involving nonstandard imaging transmit/receive strategies and simultaneous B-mode and multigate spectral Doppler mode are discussed.
I. Introduction
T
he experimental test of novel ultrasound (US) investigation methods may require the transmission (TX) of custom excitation waveforms or pulse sequences, the acquisition of data from different points of the receiver (RX) section, and/or the real-time echo-signal elaboration according to specific algorithms [1]. Most commercial US machines are not flexible enough to fulfill all these tasks. Some machines partially compensate for this problem by making available add-on research interfaces that permit access to radio-frequency (RF) or demodulated in-phase/ quadrature (I/Q) echo data. This feature is implemented, for example, in the Sonoline Antares (Siemens Corporation, New York, NY) that, through the Axius direct ultrasound research interface, enables users to acquire raw RF data from selected regions in the image plane [2]. The Philips/ATL (Phillips, Seattle, WA) HDI scanners provide RF analog and digital data, while the General Electric Logiq 700 (General Electric Medical Systems, Waukesha, WI) provides I/Q data via a custom board added to the system backplane. Many other examples of successful extraction of beamformed echo data from commercial US machines have been reported, and some recent work has been dedicated to the search for optimal acquisition architectures [3]. However, only a few US machines complete with RF front end have been specifically developed for research purposes. A research platform capable of transmitting arbitrary waveforms, storing RF or I/Q data and processing the US echoes in a programmable way, was recently Manuscript received March 30, 2009; accepted June 15, 2009. The authors are with the Microelectronics Systems Design Laboratory, Università degli Studi di Firenze, Italy (e-mail:
[email protected]). Digital Object Identifier 10.1109/TUFFC.2009.1303 0885–3010/$25.00
introduced [4]. The system uses high-performance digital signal processor (DSP) and field programmable gate array (FPGA) in a single board connected to a PC, to control 2 single-element probes working in the range of 2 to 16 MHz. A similar approach was recently used to implement an imaging system based on a mechanical sector scan probe, preliminarily tested in the evaluation of coded transmission for high-frequency (27 MHz) imaging [5]. A few US commercial platforms capable of directly controlling multi-element probes have been introduced. The ES500 machine from Ultrasonix Corporation (Ultrasonix Medical Corporation, Vancouver, BC, Canada) allows access to raw RF data as well as user software control over many system functions [6]. It is based on specialized boards connected to a PC, in which a software development kit allows the researcher to build his own applications. Another commercial machine designed for US research is the OPEN system (Lecoeur Electronique Corporation, Chuelles, France), based on a modular architecture that includes programmable transmitters and beamforming. A large memory buffer can be added to allow saving the raw data sampled from each channel. High-level research platforms have also been developed. One of these is the RASMUS system [7], which allows arbitrary transmission strategies to be tested and any processing method to be applied on multichannel data acquired from the elements of a transducer array. Such high power and flexibility are obtained through 4 distinct modules implemented with several boards, including dedicated TX-RX boards and single board computers. Although this system is fully programmable and suitable to the development and refinement of virtually any new US technique, its flexibility requires cumbersome and expensive electronics that hamper the duplicability and prevents the direct use in a clinical environment. Similar considerations apply to the system developed at the University of Toledo [8], which was mainly intended for the test of novel imaging methods based on the transmission of limited diffraction beams. In this paper, we present a novel ultrasound advanced open platform (ULA-OP), which was completely developed in our university laboratory. All electronics necessary to control simultaneously up to 64 elements of a 192-element array probe was integrated in 2 boards, which can be connected to any commercial PC through USB 2.0. ULA-OP was designed to allow the test of new US methods including original beamforming strategies, real-time image processing, pulsed Doppler, and vector Doppler techniques. The paper is organized as follows. Section II describes the system architecture, providing details of TX (includ-
© 2009 IEEE
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control ,
2208
vol. 56, no. 10,
October
2009
TABLE I. ULA-OP Main Features. General features
Transmitter
Receiver
Beamformer Processing modules Storage capabilities
Software tools
Fig. 1. ULA-OP overview.
ing arbitrary waveform generators) and RX (including the beamformer and DSP) blocks. Software programs devoted to configure the system, to control its actions during realtime operations, and to predict the US field associated with a given configuration are also described. Section III reports examples of limited diffraction beams obtained by transmitting nonstandard waveforms. A new duplex modality, coupling B-mode and multigate spectral Doppler mode [9] to extract detailed morphological and hemodynamic information simultaneously, is also illustrated. Finally, our conclusions are given in Section IV. II. System Description A. System Overview The ULA-OP consists of a metal rack of dimensions 34 × 23 × 14 cm, connected to a PC where a dedicated software runs (see Fig. 1). The backplane in the rack integrates the probe connector and routes the signals among the power unit and 2 main boards: an analog board (AB) and a digital board (DB). The AB includes the RF frontend while the DB hosts the devices in charge of numerical signal processing. The modularity of ULA-OP allows the addition of further boards for possible extension of the system capabilities. Main current features of ULA-OP are summarized in Table I. Fig. 2 illustrates the system architecture. The operation sequence during a scanning session is supervised by the system manager, which coordinates the TX and RX sections. In a typical pulse repetition interval (PRI), after the system manager has issued a PRI start, the TX section generates 64 independent arbitrary waveforms
Open platform 64 independent TX/RX channels Size: 34 × 23 × 14 cm; Weight: 5 kg Power consumption
