Users’ guide for the
Field II program,
version 2.70 of May 26, 1999
Jørgen Arendt Jensen
Department of Information Technology, Build. 344,
Technical University of Denmark
DK-2800 Lyngby, Denmark
June 23, 1999
Contents
1 Introduction 2
2 Program organization 3
3 Method of simulation 4
3.1 The spatial impulse response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2 Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.3 Focusing and apodization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.4 Attenuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4 Installation 7
5 Description of Matlab procedures 8
5.1 List of current procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.2 Procedures for Field initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.3 Procedures for transducer definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.4 Procedures for element manipulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
5.5 Procedures for field calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
6 Examples 72
6.1 Phased array imaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
6.2 Linear array imaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
6.2.1 Computer cyst phantom . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
6.3 Flow data generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
1
Chapter 1
Introduction
This is the user guide for the 2.70 version of the Field II program. This version of the program runs
under Matlab, and can simulate ultrasound transducers and the associated images. The focusing and
apodization of the transducers can be controlled dynamically, and it is, thus, possible to simulate all
kinds of ultrasound imaging systems.
This guide is intended as a presentation of the currently available routines. Little background information
and feedback is, therefore, welcomed. The user can consult the Web-site for the program:
http://www.it.dtu.dk/
jaj/field/
where up-to-date references and papers can be found.
2
Chapter 2
Program organization
The program consists of a C program and a number of Matlab m-functions that calls this program. All
calculations are performed by the C program, and all data is kept by the C program.
Three types of m-functions are found. The are used for initializing the program, defining and manipu-
lating transducers, and for performing calculations. The initializing routines are preceeded by field
, the
transducer commands by xdc
, and the calculation routines by calc . Help on use of the routines can be
obtained by typing help
<
routine name
>
. Each of the routines are described in the following section
and then three examples of use are given. The first shows how a phased array image is generated, the
second simulates a flow system, and the last example is for a linear array system. The last example uses
a computer generated phantom. The m-file for this phantom is also given in the example section.
3
Chapter 3
Method of simulation
3.1 The spatial impulse response
The Field program system uses the concept of spatial impulse responses as developed by Tupholme and
Stepanishen in a series of papers [1, 2, 3]. The approach relies on linear systems theory to find the
ultrasound field for both the pulsed and continuous wave case. This is done through the spatial impulse
response. This response gives the emitted ultrasound field at a specific point in space as function of time,
when the transducer is excitated by a Dirac delta function. The field for any kind of excitation can then be
found by just convolving the spatial impulse response with the excitation function. The impulse response
will vary as a function of position relative to the transducer, hence the name spatial impulse response.
The received response from a small oscillating sphere can be found by acoustic reciprocity. The spatial
impulse response equals the received response for a spherical wave emitted by a point. The total received
response in pulse-echo can, thus, be found by convolving the transducer excitation function with the
spatial impulse response of the emitting aperture, with the spatial impulse response of the receiving
aperture, and then taking into account the electro-mechanical transfer function of the transducer to yield
the received voltage trace. An explanation and rigorous proof of this can be found in 4 and 5.
Any excitation can be used, since linear systems theory is used. The result for the continuous wave case
is found by Fourier transforming the spatial impulse response for the given frequency. The approach
taken here can, thus, yield all the diffent commenly found ultrasound fields for linear propagation.
3.2 Simulation
A number of different authors have calculated the spatial impulse response for different transducer ge-
ometries. But in general it is difficult to calculate a solution, and especially if apodization of the trans-
ducer is taken into account. Here the transducer surface does not vibrate as a piston, e.g. the edges
might vibarte less then the center. The simulation program circumvents this problem by dividing the
transducer surface into squares and the sum the response of these squares to yield the response. Thereby
any tranducer geometry and any apodization can be simulated. The approach is described in reference 6.
The time for one simulation is also of major concern. As the squares making up the tranducer apertue
are small, it is appropriate to use a far-field approximation, making simulation simple. Another issue in
keeping the simulation time down is to use a low sampling frequency. Often spatial impulse responses
4
