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Monitoring Blood Coagulation with Acoustic Methods

Blood coagulation time is an important value for medical diagnostics of hemostasis. It is also necessary to control this system during operations and after mechanical heart valve replacement. So there is a great demand on new, fast, inexpensive and easy performable measuring methods as it can be expected from surface acoustic wave (SAW) devices.

Motivation:

The Measurement of the activity of the coagulation system is very important for example

  • for observation needs (alone in Germany 500,000 people are living with a heart valve replacement, whose coagulation system has medicamentous to be treated),
  • before during and after surgery or
  • for routine measurement of blood parameters.

 

So there is a great demand for new sensing devices concerning:

  • the development of new measurement principles,
  • their potential for miniaturisation (small sample volumes) and concerning
  • their cost effectiveness.

Investigations:

STEP 1: Experiments with thickness shear mode resonators

TSM thickness shear mode resonator (TSM)

As a first step we did start our investigations with this device because its suitability for measuring the coagulation process is well known from literature. The following three charts show a short summary of the obtained
results.

loaded_TSM


sketch of blood loaded TSM
The acoustic waves of thickness shear mode resonators are propagating through the whole device between the two electrodes.

 

 

impedance vs. frequency
Depending on the kind of oscillation the TSM has different resonant frequencies. They appear as minimum in the diagram. Loading the resonator with a fluid damps its oscillations and decreases its resonance frequencies (red chart). The change of the resonant frequency depends on the viscosity and density of the fluid. In the next chart we will have a closer look at the with arrows marked resonance.

 

 V86a_TSM3_alleRes_Pfeil_klein

 

 

V252_TSM3_alleRes_klein


impedance vs. frequency
The charts in this diagram are showing the changing impedance course of the TSM caused by coagulating blood. For this measurement the sensor was loaded with a drop of blood. During the coagulation process the viscosity of the sample is increasing. This leads to a further damping and decrease of the resonant frequency. In the next chart the change of this resonance frequency is shown vs. time.

 


resonant frequency vs. time
Shortly said, blood coagulation is the cascade-like activation of certain enzymes. At its end it comes to the formation of fibrin, which is responsible for the increase of the blood viscosity. This change of viscosity can be monitored with acoustic bulk waves. For this sample a change in resonant frequency of almost 1 kHz was measured.

 V435b_TSM3_Quick_dfRes_klein

 

STEP 2: Experiments with SH-SAW resonator filters:

Higher frequencies are promising a higher sensitivity to the change in viscosity. The resonance frequency of a tickness shear mode resonator is restricted by its thickness. For that reason we went on with our investigations to surface acoustic wave devices. Their frequency range is widely adjustable by the shape of the interdigital transducer.

SAW

commercial SAW resonator filter
To our knowledge nothing is reported to the suitability of such devices for monitoring blood coagulation. So, in a second step, we took commercial resonator filters for our further investigations. This devices had a resonant frequency of 170 MHz. Their suitability for monitoring blood coagulation could be proofed.

STEP 3: Design & construction of a SH-SAW based coagulation sensor:

As a third step we designed new shear horizontal polarized surface acoustic wave (SH-SAW) based coagulation sensors. They are realized as one port resonators with a resonant frequency of 170 MHz and 340 MHz.

 

 

 

sketch

 

sketch of the coagulation sensor

setup

experimental setup

 

Summary:

  • The characterisation of the coagulation process with a thickness shear mode resonator was done.
  • The possibility of detecting the coagulation process with surface acoustic waves could be proved.
  • A SH-SAW coagulation sensor was designed, constructed & successful tested.

Outlook:

  • The sensitivity of the coagulation sensor can be increased by the improvement of the sensor design & experimental setup.
  • We are facing the question: Are further blood parameters like blood sugar level, hematocrit valueor single coagulation factors detectable with SAW as well?
  • detection of more than one parameter in one measurement
  • adaption of surface acoustic wave sensors to further biological applications

Publications:

 

  • G. Guhr, S. Gehrisch, R. Kunze, G. Martin, H. Schmidt, G. Siegert, and M. Weihnacht: "Monitoring blood coagulation with QCM and SH-SAW sensors", 2005 IEEE Ultrasonics Symposium Proc. p. 58-61
  • G. Guhr, S. Gehrisch, R. Kunze, G. Martin, H. Schmidt, G. Siegert, and M. Weihnacht: "Thrombelastography using acoustic sensors", 2006 IEEE International Ultrasonics Symposium Proc.

Contact:

Glen Guhr
IFW Dresden e.V.
'Magnetic and acoustic resonances' (Dept. 15)
Surface Dynamics Group
P.O.Box 270116
D-01171 Dresden, Germany
phone: ++49/351/4659 304
fax: ++49/351/4659 313
e-mail: g.guhr + @ifw-dresden.de (Sorry, but we try to prevent automatic SPAM)
Contact


 

Glen Guhr
IFW Dresden e.V.
'Magnetic and acoustic resonances' (Dept. 15)
Surface Dynamics Group
P.O.Box 270116
D-01171 Dresden, Germany
phone: ++49/351/4659 304
fax: ++49/351/4659 313
e-mail: g.guhr + @ifw-dresden.de

(Sorry, but we try to prevent automatic SPAM)