IMPLEMENTATION OF A PORTABLE ULTRASOUND
DENSITOMETRY BASED ON FPGA
Jian-Xing Wu, Tain-Song Chen, Pei-Jarn Chen
1
Institute of Biomedical Engineering, National Cheng Kung University
Abstract—This work was major in utilizing the
power electronics technology to build a high-voltage
ultrasonic pulser (300 ~ 500 volts ) with high power
factor(>0.9). Then the high-speed AD converters and
the ultrasonic receiver were integrated with FPGA
technology. Finally the transmitted or the echo
ultrasound signal was designed to transfer to a
notebook (NB) with USB port through the designed
platform between the FPGA and the LabVIEW. In
addition, the speed of sound (SOS) and the
broadband ultrasound attenuation (BUA) could be
measured on the LabVIEW environment. AS a result,
the ultrasonic densitometry can estimate the
characteristic of bone tissue based on transmitted or
the echo signal with the portable system based on
proposed FPGA technique.
Index Terms—Power electronics、FPGA、LabVIEW
Ⅰ. INTRODUCTION
The population who suffers from osteoporosis in
Taiwan rises year by year. To develop an easy to use
Ultrasound densitometry is a quite important subject.
Recently, some researchers reported that the acoustic
speed and attenuation of ultrasound waves on bone
tissue may convey more information of bone quality,
such as, microstructure, elasticity, density etc., to
predict the bone fracture. Therefore, the ultrasound
densitometry has become an alternative way for
osteoporosis assessment with no X-ray exposure
concerns and low cost. Therefore, how to develop a
novel technique to obtain above ultrasonic
parameters has become an important issue on
ultrasound densitometry development.
The measurement of ultrasonic parameters
including broadband ultrasound attenuation (BUA,
dB/MHz), speed of sound (SOS, m/s) has been
applied for bone densitometry. It is a bone density
measurement technology called Quantitative
Ultrasound (QUS) which in and without risking
subjects to radiation. QUS is a measure of
mechanical wave that can be influenced by the
microstructure as well as the density of bone. QUS
seems therefore to offer an alternative to
conventional absorptiometry, in providing structure
information in additional on density . Recently QUS
has been developed for fast, accessible and less
expensive use, as well as QUS of the tibia, patella
and multiple other sites. Theoretic QUS
development of the ultrasound interacting with bone
will be discussed in following paragraph.
Presently, to measure the bones density,
ultrasound densitometry is used. But this systems
feature is limited with the Pulser/Receiver, which
can not provide high-voltage ultrasonic pulse to
penetrate twice the thickness of the bone. Meaning,
not enough penetration is produced. In this study, we
won’t design the pulse frequency for the different
body parts, only for the feet’s heel. Two systems will
be used, first is the power electronics technology to
provide the high-voltage ultrasonic pulse and second
is the FPGA hardware language. By combining these
two systems we were able to implement a high
voltage portable ultrasound densitometry model. The
FPGA will create the different pulse frequencies in
the bone by using a high-speed AD transform and
then links this to the USB translator. Therefore, we
were able to design and implement a portable
ultrasound densitometry system.
Ⅱ. METHODS
The development system is portable, low-cost,
and is able to gain a high accuracy output. FPGA
does the integration for the following: Control
System, Ultrasound densitometry (Fig 1. shows the
block diagram for the development system):
Fig 1. Block Diagram
A. Power supply
A power supply system controlled by the L6562 IC
is the source of high-voltage ultrasonic pulse. This is
used to improve the power factor rating by
compensating the lag or lead of the phase angle of
the current with respect to the output voltage (Fig 2.)
s, and can acquire a high power factor rated power
supply. By using the L6562 a high power factor rate
(90%) will be acquired this can improve the output
effects because we were able to avoid distortion
problems in the power output like the crossover and
total harmonic. The power supplies voltage is
adjustable ranging from 300 to 500 volts since there
are different measurements conditions present in the
system. In addition, the system was made automatic;
it will turn on and off by itself to prevent harm from
happening to the user and the system.
Fig 2. voltage and current phase
B. Pulser
Pulser's structure includes two parts, one part is
PRF Generator and the other is Pulser Generator, the
front end is PRF Generator that designed by using
FPGA to control ultrasound pulse frequency signals.
(Fig 3.) Back end is Pulser Generator. Back end is
Pulser Generator. There two integrated these two
parts into a pulser. We use FPGA to replace the
traditional PRF Generator that using oscillator, by
improving the noise of the signal from hardware
circuitry. The cost and hardware circuit volume of
FPGA PRF Generator both are decreased.
Moreover, the PRF Generator become precise for
frequency and provides with lots kind of frequency.
Fig 4. Receiver signal
D. A/D Converter
The A/D converter of the system uses TLC5540 IC,
and it’s the maximum conversion rate is 40MHz. By
using the FPGA we can control the sampling rate
and the operating frequency of A/D converter. Not
only can it produce a high-speed sampling rate for
the ultrasound, but also economize the development
costs. Since we have a digitized form of the signal
we can now connect it to the USB of the notebook
computer, this can show the real-time waveform (Fig
5.) and be able to analyze the signal.
Fig 5. LabVIEW 端存取訊號
Fig 3. Pulser signal
C. Receiver
The receiver amplifies the weak signals received
(mv) and also attenuates the noise in the receiving
probe (Fig 4.). At the end of the receiver an
Analog-to- Digital converter is added so that a
digitized output is produced. Two IC’s were used for
the amplification, namely AD797 for the first level
amplification and AD811 for the second level; this
can amplify the signals from 8 up to 88 times. The
advantage of using this IC’s is that, AD797 can
produce low noise and distortion, and AD811 is a
high performance Op Amp. The bandwidth of the
receiver starts from 8Hz to 20Hz. The signal
received was increased from a small output voltage
to a positive output voltage of 1~10 volts.
E. FPGA System
In ultrasonic densitometry, the core controller
used is FPGA (Fig 6.), to produce various pulse
frequencies for different conditions. FPGA will
replace the
analog circuit elements but will retain the
high-voltage electronic part in the Hardware, this
will minimize the pulse systems size by a third of its
original size, resulting to less noise in the signal and
development costs. FPGA controls how the A/D
converter works and then connects the USB system
to convey data to the HMI for analysis. Since the
input current of 110volts is not enough to run the
whole system we needed to add an inductor that
provides 500 volts direct current. Having a high
voltage system, we need to attenuate the voltage
inputs necessary for the FPGA to run. An automatic
turn off device is designed to avoid harm from users
and to the system. For the future works the plan is to
first use an LCDM for displaying the ultrasound
signal in real time, second, by replacing VHDL and
using NIOS II as the design circuit we can reduce
the complexity of system, lastly, we hope to create a
stand alone embedded ultrasonic densitometry
system.
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Fig 6. FPGA block diagram
Ⅲ.CONCLUSIONS
In this study, the instrument structure has been
accomplished (Fig 7& 8 ), for Pulser/Receiver test, a
simple and low cost Pulser/Receiver (500V). for
simple Ultrasound densitometry system based on
FPGA.
Can show the real-time waveform and be able to
analyze the signal by LabVIEW. The error less than
10%. The results are consistent to the manufacture’s
specifications and accuracy.
Fig 7. Ultrasonic densitometry
Fig 8. LabVIEW system
Ⅳ. REFERENCES
[1] G. T. Clement, and Kullervo Hynynen, “ A
computer-controlled ultrasound pulser-receiver
system for transskull fluid detection using a shear
wave transmission technique tai chun tang ,” IEEE,
vol. 54, no. 9, 2007
[2] K. Wear, “ Measurements of phase velocity and
group velocity in human calcaneus,” Ultrasound in
Med. & Biol., vol. 26, no. 4, pp.641-646, 2000.
[3] J. Toyras, M. T. Nieminen, H. Kroger, and J. S.
Jurvelin, “Bone mineral density, ultrasound velocity,
and broadband attenuation predict mechanical
predict mechanical properties of trabecular bone
differently,” Bone, vol. 31, pp. 503-507, 2002.
[4]C. Christiansen, “Osteoporosis: diagnosis and
management today and tomorrow,” Bone, vol. 17, pp.
513-516, 1995.
[5] J. A. Evans and M. B. Tavakoli, “Ultrasonic
attenuation and velocity in bone,” Phys. Med. Biol,
vol. 35, pp. 1387-1396, 1990.
[6] L. Serpe and J. Y. Rho, “The nonlinear transition
period of broadband ultrasound attenuation as bone
density veries,”J. Biomechanics, vol. 29, pp.
963-966, 1996.
[7] G. Brandenburger, L. Avioii, C. C. III, R. Heaney,
R. Poss, G. Pratt, and R. Recker, “In-vivo
measurement of osteoporostic bone fragility with
apparent velocity of ultrasound,” IEEE Ultrasonic
Symposium, pp. 1023-1027, 1989.
[8] J. A. Zagzebski, P. J. Rossman, C. M. Richard, B.
Mazess, and E. L. Madsen,“Ultrasound transmission
measurements through the os calcis,” Calcif Tissue
Int., vol. 1991, pp. 107-111, 1991.
[9] M. J. Grimm , and J. L. Williams,“Assessment of
bone quantity and 'quality' by ultrasound attenuation
and velocity in the heel,” Clinical Biomechanics, vol.
12, pp. 281-285, 1997.
[10] D. Hans, T. Fuerst, and F.Duboeul,“
Quantitative ultrasound bone meanurement,”
Eur.Radiol., vol. 7, pp. 43-50, 1997