Transducers Used in the Cardiac Ultrasound Machine.

Topics: Piezoelectricity, Ultrasound, Ferroelectricity Pages: 8 (3604 words) Published: August 16, 2011
Abstract

Ultrasound imaging depends on the ability of piezoelectric crystals to generate sound when excited with alternating current and the reverse effect of charge accumulation or current flow when such crystals are subjected to pressure from sound waves. The first known ultrasound imaging machine was designed by K. T. Dussik in Australia in 1937. However, despite its widespread acceptance today, medical ultrasound did not develop as rapidly as X-ray imaging. Despite the relatively slow start, medical ultrasound imaging is very widely accepted today because there is no ionising radiation involved and hence the procedure is relatively safe. Ultrasound equipment is also cheaper as compared to X-ray imaging, magnetic resonance imaging, MRI and other techniques associated with nuclear medicine. The procedure involves minimal patient discomfort and is very useful for examining the soft tissues or the developing foetus. A dramatic increase in the number of older patients with chronic heart and valve disease has resulted in a prolific demand for the ultrasound cardiac imaging machines which can satisfy the requirements associated with fast and cost effective measurement of cardiac anatomy or function. One of the critical elements in the medical ultrasound imaging system is the ultrasound transducer without which signal processing and visualisation of the soft tissue images is impossible. Although many naturally occurring substances such as quartz exhibit the piezoelectric effect, lead zirconate titanate (PZT) ceramic ferroelectric materials have for many years been used for biomedical applications because of their superior characteristics for soft tissue imaging. Polyvinylidene difluoride (PVDF), transducer material has demonstrated advantages as a high frequency receiver. Single or multilayer transducers made of these elements can be used for ultrasound imaging as single transducers operating in A-mode or a two or three dimensional transducer array for B-mode, C-mode or M-mode ultrasound imaging. This brief essay takes a look at transducers for medical ultrasound.

Introduction

The principle of operation of a cardiac ultrasound imaging device is based on the information that is provided by the varying delay times of echoes that are reflected from various depths of the human body tissue as a result of the ultrasound pulses that are generated by an ultrasound transducer being incident on the body tissue. Delay times of echoes from different depths are different and ultrasound is reflected from the interface of different types of tissues. A Doppler shift in frequency is also generated as a result of moving objects and the attenuation of ultrasound waves depends on the type of tissue that the ultrasound wave is travelling through. The ultrasound transducer which is responsible for the generation and detection of reflected ultrasound is, therefore, an essential component of the ultrasound imaging device. Ultrasound transducers work on the basis of the piezoelectric effect in which an alternating voltage applied to piezoelectric crystal material causes the crystals to become electrically polarised as a result of the applied electric field and hence vibrate with the alternating voltage to produce sound. Such crystals also become electrically polarised when stress is applied to them and hence any sound waves which are incident on them result in charge accumulation on the crystal surface and hence the generation of an alternating voltage. Thus, an ultrasound transducer consists of a suitable piezoelectric material sandwiched between electrodes that are used to provide a fluctuating electric field when the transducer is required to generate ultrasound. When the transducer is required to detect ultrasound, the electrodes may be used to detect any fluctuating voltages produced as a result of the polarisation of the crystals of the piezoelectric material in response to incident sound which generates fluctuating mechanical stresses...

References: 3.Brandt, Einar. “Segmentation Techniques for Echocardiographic Image Sequences”. University of Linkopings. 1998. August 4, 2005. http://www.imv.liu.se/klinfys/einar/publications/pdf_open/Ex1934.pdf
4.Bridal, Lori S et al
5.Diederichs, Rolf. “Ultrasound Transducer Library”. Diederichs, Rolf. March, 1998. August 4, 2005. http://www.ndt.net/wshop/wshop_tr/trans_li.htm
6.Eberhard, Brunner
7.Erikson, Kenneth R et al. “Ultrasound in Medicine – A Review”. IEEE TRANSACTIONS ON SONICS AND ULTRASONICS, VOL. SU-21, NO. 3, JULY 1971. August 4, 2005. http://www.ieee-uffc.org/ultrasonics/teaching/t7430144.pdf
8.Fink, Mathias
11.Goel, Malti. “Electret sensors, filters and MEMS devices: New challenges in materials research”. Current Science. Volume 85. No. 4. August 25, 2004. August 4, 2005. http://www.ias.ac.in/currsci/aug252003/443.pdf
12.Hazas, Mike and Andy Ward
13.Holm, Sverre. “Ultrasim – A Toolbox for Ultrasound Field Simulation”. University of Oslo. 2000. August 6, 2005. http://heim.ifi.uio.no/~sverre/papers/01_Matlab.pdf
14.Krochak, Paul and Stefan Story
17.M. Greenstein, P. Lum, H. Yoshida, M.S. Seyed-Bolorforosh. “A 2.5 MHz 2D Array with Z-Axis Electrically Conductive Backing”. 2004. August 4, 2005. http://www.hpl.hp.com/techreports/96/HPL-96-89.pdf
18.Measurement Specialties Inc
19.Michael Greenstein. “Multilayer Piezoelectric Transducers for Medical Ultrasound Transducers”. Hewlett Packard Laboratories. 2000. August 4, 2005. http://www.hpl.hp.com/techreports/95/HPL-95-79.ps
20.Morgan Electro Ceramics
21.North Dakota State University. “Imaging Systems”. North Dakota State University. 2004. August 4, 2005. http://venus.ece.ndsu.nodak.edu/~schroeder/Imaging%20Systems.doc
22.Nottingham University
23.Petersen R.B. and J. Hutchins. “The iE33 intelligent echocardiography system”. Philips Ultrasound Medical Systems. 2004. August 4, 2005. http://www.medical.philips.com/main/news/assets/docs/medicamundi/mm_vol48_no3/11_Peterson.pdf
24.Picture IQ.com
29.Ronald E McKeighen. “Design Guidelines for Medical Ultrasonic Arrays”. Acoustic Imaging Transducers Inc. 2000. August 4, 2005. http://www.wai.com/AppliedScience/Software/Pzflex/Papers-other/spie-man.pdf
30.Saleh K
31.Schmidt, M. “Ultrasonic Signal Processing Chip For Intraluminal Catheter Based Systems”. Fraunhofer Institute of Microelectronic Circuits and Systems. 2004. August 4, 2005. http://www.imec.be/esscirc/papers-96/143.pdf
32.Shindler, Daniel M
33.Ultran. “Medical Ultrasonic Transducers”. Ultran. 2004. August 4, 2005. http://www.ultrangroup.com/pdfs/ultran_trans_cat.pdf
34.University of Central London
Continue Reading

Please join StudyMode to read the full document

You May Also Find These Documents Helpful

  • Essay on Transducers
  • Transducer Essay
  • Cardiac Essay
  • Essay on Transducers
  • Values Used in Ultrasound Essay
  • Machine Essay
  • Essay about Patient Monitoring Systems and Ultrasound Machines
  • Ultrasound Essay

Become a StudyMode Member

Sign Up - It's Free