Alessandro Ramalli

Università degli Studi di Firenze (University of Florence), Information Engineering, Faculty Member

KU Leuven, Cardiovascular Imaging and Dynamics, Post-Doc

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Alessandro Ramalli was born in Prato, Italy, in 1983. He received the master’s degree in electronics engineering from the University of Florence, Florence, Italy, in 2008; the joint Ph.D. degree in electronics system engineering and in automation, systems and images from the University of Florence and the University of Lyon, Lyon, France, respectively, in 2012. From 2012 to 2017, he was involved in the development of the imaging section of a programmable open ultrasound system by the University of Florence. From 2017 to 2019, he worked as a Post-Doctoral Researcher with the Laboratory of Cardiovascular Imaging and Dynamics, KU Leuven, Leuven, Belgium, granted by the European Commission through a “Marie Skłodowska-Curie Individual Fellowships”. Here, he developed high frame rate imaging techniques for echocardiography. From 2020 to 2022, he worked as a research fellow at the University of Florence, where currently he is an assistant professor. His research interests include medical imaging, echocardiography, beamforming methods, ultrasound simulation, arrays and systems design.

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Roberto Giorgi

University of Siena / Università di Siena

Rohit Nayak

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Amir Manbachi

Johns Hopkins University

Aida Khairuddin

Universiti Teknologi Malaysia - UTM

Bisser Raytchev

Hiroshima University

Mohammad Mehrmohammadi

Wayne State University

Santhosh KV

Manipal Institute of Technology

Tasnuva Faruk

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Ashraf M Anwar

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Peter Backx

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Papers by Alessandro Ramalli

A reconfigurable and programmable FPGA-based system for nonstandard ultrasound methods

by Piero Tortoli and Alessandro Ramalli

IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 2000

The availability of programmable and reconfigurable ultrasound (US) research platforms may have a... more The availability of programmable and reconfigurable ultrasound (US) research platforms may have a considerable impact on the advancement of ultrasound systems technology; indeed, they allow novel transmission strategies or challenging processing methods to be tested and experimentally refined. In this paper, the ULtrasound Advanced Open Platform (ULA-OP), recently developed in our University laboratory, is shown to be a flexible tool that can be easily adapted to a wide range of applications. Five nonstandard working modalities are illustrated. Vector Doppler and quasi-static elastography applications emphasize the real-time potential and versatility of the system. Flow-mediated dilation, pulse compression, and high-frame-rate imaging highlight the flexibility of data access at different points in the reception chain. For each modality, the role played by the onboard programmable devices is discussed. Experimental results are reported, indicating the relative performance of the system for each application.

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Adaptive beamforming for ultrasonic phased array focusing through layered structures

by Kiyanoosh Shapoori, Fedar Seviaryn, and Alessandro Ramalli

2010 IEEE International Ultrasonics Symposium, 2010

ABSTRACT Successful realization of ultrasonic imaging through a multilayered composite barrier is... more ABSTRACT Successful realization of ultrasonic imaging through a multilayered composite barrier is hampered by scattering, attenuation, and multiple reflections of acoustic waves at and inside the barrier. These effects tend to distort the beam pattern produced by conventional phased arrays, defocusing the ultrasonic field transmitted through the barrier and causing image quality degradation and resolution loss. To compensate for the refraction and multiple reflection effects, we developed an adaptive beamforming algorithm for small-aperture linear phased arrays. After assessing the barrier&#39;s local geometry, the method calculates a new timing distribution to refocus the distorted beam at its original location. The procedure is in fact a construction of a matched filter that automatically adapts the transmission pattern of the phased array to the local geometry of the barrier and cancels its distorting effect. In this work, the adaptive beamforming algorithms, in transmission mode, for the barriers in the form of a flat homogeneous layer, a layer with a smooth, randomly curved back surface and a two-layered combination of the above have been developed and experimentally verified on custom-engineered samples with prescribed acoustical properties. The algorithms were implemented on ULA-OP, an ultrasound advanced open-platform (University of Florence), controlling 64 active elements on a 128-elements phased array. Experimental measurements of original, distorted and corrected beam profiles confirm the ability of our algorithms to refocus the beam after passing through a scattering and refractive sample. Different excitation signals and windowing options introduced through ULA-OP were examined and compared.

An Improved Ultrasound System for Biometric Recognition Based on Hand Geometry and Palmprint

by Gabriel Hine and Alessandro Ramalli

Procedia Engineering, 2014

In Vitro and in Vivo tissue harmonic images obtained with parallel transmit beamforming by means of orthogonal frequency division multiplexing [Correspondence]

by Libertario Demi and Alessandro Ramalli

IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, 2015

In classic pulse-echo ultrasound imaging, the data acquisition rate is limited by the speed of so... more In classic pulse-echo ultrasound imaging, the data acquisition rate is limited by the speed of sound. To overcome this, parallel beamforming techniques in transmit (PBT) and in receive (PBR) mode have been proposed. In particular, PBT techniques, based on the transmission of focused beams, are more suitable for harmonic imaging because they are capable of generating stronger harmonics. Recently, orthogonal frequency division multiplexing (OFDM) has been investigated as a means to obtain parallel beamformed tissue harmonic images. To date, only numerical studies and experiments in water have been performed, hence neglecting the effect of frequencydependent absorption. Here we present the first in vitro and in vivo tissue harmonic images obtained with PBT by means of OFDM, and we compare the results with classic B-mode tissue harmonic imaging. The resulting contrast-to-noise ratio, here used as a performance metric, is comparable. A reduction by 2 dB is observed for the case in which three parallel lines are reconstructed. In conclusion, the applicability of this technique to ultrasonography as a means to improve the data acquisition rate is confirmed.

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2D and 3D Palmprint Extraction by an Automated Ultrasound System

by Gabriel Hine and Alessandro Ramalli

Lecture Notes in Electrical Engineering, 2015

Density-Tapered Spiral Arrays for Ultrasound 3-D Imaging

by Alessandro Stuart Savoia, Piero Tortoli, and Alessandro Ramalli

The current high interest in 3-D ultrasound imaging is pushing the development of 2-D probes with... more The current high interest in 3-D ultrasound imaging is pushing the development of 2-D probes with a challenging number of active elements. The most popular approach to limit this number is the sparse array technique, which designs the array layout by means of complex optimization algorithms. These algorithms are typically constrained by a few steering conditions, and, as such, cannot guarantee uniform side-lobe performance at all angles. The performance may be improved by the ungridded extensions of the sparse array technique, but this result is achieved at the expense of a further complication of the optimization process. In this paper, a method to design the layout of large circular arrays with a limited number of elements according to Fermat's spiral seeds and spatial density modulation is proposed and shown to be suitable for application to 3-D ultrasound imaging. This deterministic, aperiodic, and balanced positioning procedure attempts to guarantee uniform performance over a wide range of steering angles. The capabilities of the method are demonstrated by simulating and comparing the performance of spiral and dense arrays. A good trade-off for small vessel imaging is found, e.g., in the 60λ spiral array with 1.0λ elements and Blackman density tapering window. Here, the grating lobe level is −16 dB, the lateral resolution is lower than 6 , λ the depth of field is 120λ and, the average contrast is 10.3 dB, while the sensitivity remains in a 5 dB range for a wide selection of steering angles. The simulation results may represent a reference guide to the design of spiral sparse array probes for different application fields.

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Tissue harmonic images obtained with parallel transmit beamforming by means of orthogonal frequency division multiplexing

by Libertario Demi, Alessandro Ramalli, and Piero Tortoli

2014 IEEE International Ultrasonics Symposium, 2014

In classic pulse echo ultrasound imaging, the data acquisition rate is limited by the speed of so... more In classic pulse echo ultrasound imaging, the data acquisition rate is limited by the speed of sound. To overcome this limitation, parallel beamforming techniques in transmit (PBT) and in receive mode (PBR) have been developed. To perform harmonic imaging, PBT techniques are preferable being capable of generating stronger harmonics thanks to the possibility to use focused beams in transmission. Recently, orthogonal frequency division multiplexing (OFDM) has been explored to perform PBT. To date, only numerical studies and in-vitro experiments in water have been performed, thus neglecting the effect of frequency dependent absorption. In this paper, PBT by means of OFDM tissue harmonic images are presented. A homemade agarose tissue mimicking phantom containing water filled cylindrical cavities was utilized as test object. The ULA-OP ultrasound open platform was used in combination with the linear array probe LA533 (Esaote Italy). Starting from the available transducer bandwidth, sub-bands were allocated to each beam transmitted in parallel. Three orthogonal sub-bands were used, improving the frame rate by a factor three. A classic B-mode tissue harmonic image was then obtained with the same setup for comparison. The contrast to noise ratio (CNR) and average background brightness inside the cavities were evaluated to provide an indirect measure of the influence of interbeam interference.

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Implementation of non standard methods with the Ultrasound Advanced Open Platform (ULA-OP)

IEEE International Ultrasonics Symposium, IUS, 2011

ABSTRACT The Ultrasound Advanced Open Platform (ULA-OP) was recently developed with the specific ... more ABSTRACT The Ultrasound Advanced Open Platform (ULA-OP) was recently developed with the specific goal of enabling the implementation of non standard working modalities, either in real-time or off-line, as made possible by the access to raw echo-data at each point of the receiver chain. Three case studies, demonstrating the fulfillment of initial specifications, are reported here. They consist in the implementation of: 1) a high frame rate (HFR) imaging approach producing images with uniform resolution; 2) an original real-time vector Doppler technique based on two US beams concurrently controlled by the on board DSP; 3) the simultaneous measurement of both the stimulus (wall shear stress increase) and the effect (diameter enlargement) in Flow Mediated Dilation (FMD) studies. In each of the aforementioned applications, the hardware &amp; software resources of ULA-OP are differently exploited, showing that the system is a nice tool to implement non standard US modalities.

Fourier domain and high frame rate based elastography for breast nodules investigation

IEEE International Ultrasonics Symposium, IUS, 2011

ABSTRACT The malignant/benign characterization of breast nodules represents a main concern in cur... more ABSTRACT The malignant/benign characterization of breast nodules represents a main concern in current senology diagnostic practice. Investigation through manual palpation and B-mode imaging plays a major role, but the attainable specificity is still too low. Several studies show that elastography could help reducing false positive cases. In freehand elastography the probe is manually moved to produce an axial compression in the tissue to be investigated. The axial strain tensor is then estimated by calculating the gradient of the produced displacement. A new elastography method, based on a Fourier domain displacement estimator and a high frame-rate averaging technique, has been recently shown to produce robust strain estimates on phantoms compressed with computer control. In this study we extend the test of this method to in-vivo investigation on breast. Results of the investigation of 6 malignant and 10 benign lesions in 11 patients aged between 30 and 84 are reported.

High-frame-rate 2-D vector blood flow imaging in the frequency domain

IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, 2014

Conventional ultrasound Doppler techniques estimate the blood velocity exclusively in the axial d... more Conventional ultrasound Doppler techniques estimate the blood velocity exclusively in the axial direction to produce the sonograms and color flow maps needed for diagnosis of cardiovascular diseases. In this paper, a novel method to produce bi-dimensional maps of 2-D velocity vectors is proposed. The region of interest (ROI) is illuminated by plane waves transmitted at the pulse repetition frequency (PRF) in a fixed direction. For each transmitted plane wave, the backscattered echoes are recombined offline to produce the radio-frequency image of the ROI. The local 2-D phase shifts between consecutive speckle images are efficiently estimated in the frequency domain, to produce vector maps up to 15 kHz PRF. Simulations and in vitro steady-flow experiments with different setup conditions have been conducted to thoroughly evaluate the method's performance. Bias is proved to be lower than 10% in most simulations and lower than 20% in experiments. Further simulations and in vivo experiments have been made to test the approach's feasibility in pulsatile flow conditions. It has been estimated that the computation of the frequency domain algorithm is more than 50 times faster than the computation of the reference 2-D cross-correlation algorithm.

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An enhanced ultrasound technique for 3D palmprint recognition

by Alessandro Ramalli and Francesco Guidi

2013 IEEE International Ultrasonics Symposium (IUS), 2013

ABSTRACT In the present work, and enhanced ultrasound technique for extracting 3D palmprint for b... more ABSTRACT In the present work, and enhanced ultrasound technique for extracting 3D palmprint for biometric recognition purposes is presented. The ULtrasound Advanced Open Platform (ULA-OP) is employed as ultrasound imaging system. A commercial high frequency (12 MHz) linear array is moved in the elevation direction by an automated scanning system based on numeric controlled pantograph, which guarantees stable and repeatable measurements. The 3D data are then acquired and elaborated in MATLAB environment to provide several renderings of the 3D palmprint. The experimental results are compared with those acquired with conventional techniques.

B-MSD Mode for the Simultaneous Detection of Dynamic Morphologic and Hemodynamic Information

by Piero Tortoli, Alessandro Ramalli, and Andrea Cellai

IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control - IEEE T ULTRASON FERROELECTR, 2009

Fundamental and second-harmonic ultrasound field computation of inhomogeneous nonlinear medium with a generalized angular spectrum method

by Alessandro Ramalli and Piero Tortoli

IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 2000

The simulation of nonlinear propagation of ultrasound waves is typically based on the Kuznetsov-Z... more The simulation of nonlinear propagation of ultrasound waves is typically based on the Kuznetsov-Zabolotskaya-Khokhlov equation. A set of simulators has been proposed in the literature but none of them takes into account a possible spatial 3-D variation of the nonlinear parameter in the investigated medium. This paper proposes a generalization of the angular spectrum method (GASM) including the spatial variation of the nonlinear parameter. The proposed method computes the evolution of the fundamental and second-harmonic waves in four dimensions (spatial 3-D and time). For validation purposes, the one-way fields produced by the GASM are first compared with those produced by established reference simulators and with experimental one-way fields in media with a homogeneous nonlinear parameter. The same simulations are repeated for media having an axial variation of the nonlinear parameter. The mean errors estimated in the focal region are less than 4.0% for the fundamental and 5.4% for the second harmonic in all cases. Finally, the fundamental and second-harmonic fields simulated for media having nonlinear parameter variations in the axial, lateral, and elevation directions, which cannot be simulated with other currently available methods, are presented. The new approach is also shown to yield a reduction in computation time by a factor of 13 with respect to the standard nonlinear simulator. depend on the resolution considered in the spatial and temporal dimensions. For each Δz step, the evolution of the fundamental wave P 1 in 3-d (x, y, t) is computed, first in the Fourier domain and then in the temporal domain. It must be noted that the fundamental does not depend on the z sampling. With the temporal evolution of the fundamental, the matrix M(z + Δz) could be computed. Then, to obtain the final evolution of the second-harmonic wave, an integral part, denoted I, must be computed. a classic finite difference method has been chosen to compute this integral. Thanks to the previous computed value at M(z), the new value of the integral can be obtained by

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A reconfigurable and programmable FPGA-based system for nonstandard ultrasound methods

by Alessandro Ramalli, Enrico Boni, and Francesco Guidi

IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 2000

Simulation of ultrasound nonlinear propagation on GPU using a generalized angular spectrum method

by Alessandro Ramalli and Piero Tortoli

EURASIP Journal on Image and Video Processing, 2011

Acoustic simulation has always played an important role in the development of new ultrasound imag... more Acoustic simulation has always played an important role in the development of new ultrasound imaging techniques. In nonlinear ultrasound imaging particularly, the simulators are accurate but time-consuming, because of the high derivative order of the propagation equation and to the classic solution based on finite difference schemes. This article presents a fast 3D + t nonlinear ultrasound simulator, based on a generalized angular spectrum method, particularly fit for the graphics processing unit (GPU). Indeed, the Fourier domain approach decreases the derivative order of the propagation, thus significantly speeding up the simulation time. The simulator was implemented and optimized on a central processing unit (CPU) and a GPU, respectively. The processing times measured on two different graphic cards show that, compared to the CPU, GPU-based implementation is 3.5-13.6 times faster.

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A reconfigurable and programmable FPGA-based system for nonstandard ultrasound methods

by Piero Tortoli and Alessandro Ramalli

IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 2000

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Adaptive beamforming for ultrasonic phased array focusing through layered structures

by Kiyanoosh Shapoori, Fedar Seviaryn, and Alessandro Ramalli

2010 IEEE International Ultrasonics Symposium, 2010