Design Con 2015

Flexible medical sensors aid diagnoses

-September 20, 2013

Modern day MEMS and integrated circuit advances are now making it possible to integrate a tiny, flexible sensor at the tip of a catheter or guidewire.

There exists a generic platform for the fabrication and assembly of partially flexible sensors at the tip and around minimally invasive medical devices such as catheters and guidewires. This is called the Flex-to-Rigid (F2R) platform. (See reference [1])

 

This technology can enhance the accuracy of coronary artery angiography via X-ray and other guidewire procedures. The major limitation of the present process of angiograms is that it is trying to estimate a three-dimensional stenosis (restriction in the artery) using two dimensional projections. With MEMS technology we can now combine pressure and flow sensing capabilities in a guidewire using simultaneous measurement technology to get a better view of the arterial restriction size and shape.

 

Examples of different IC-based sensors that can be made from this flexible technology are as follows:

 
  • The transducing IC function of a forward looking medical imager needs to be located at the tip of the instrument. In this case, a circular or a ring-shaped transducer is needed (Fig. 1(a)).
 
  • The difference in diameter between guidewires and catheters plays an important role when a sensing functionality has to be implemented around the instrument. In the case of a catheter, it is possible to use tiny rigid silicon tiles connected with flexible interconnects [Fig. 1(b)].
 
  • A 360o thermal flow sensor can be positioned around a guidewire and it requires a fully flexible sensor foil, and at the same time a pressure sensor can be placed inside of it [Fig. 1(c)].
   

 

 

Fig. 1: Shown here is a representation of three different types of sensors at the tip of smart medical instruments. (a) Ring-shaped forward looking chips at the tip of a 2 mm diameter catheter and a 360 μm diameter guidewire. (b) A tiled sensor device mounted around and at the tip of a 2 mm diameter catheter. (c) A flexible sensor bent around a 360 μm diameter guidewire and connected to a 50 μm thick silicon sensor chip which is placed inside the medical instrument. (Image courtesy of reference [1])

     

Here is an example of what this technology is capable. Figure 2 shows a 2 mm diameter silicon IC containing capacitive micromachined ultrasound transducers (CMUTs)

 

 

Figure 2: Forward looking demonstrator to be mounted at the tip of a 2 mm diameter catheter. The device remains attached to the supporting wafer by small polyimide tabs. (Image courtesy of reference [1])

   

The diameter of a catheter is large enough so that we can fold an array of thin rigid flexibly interconnected silicon islands around the instrument. The catheter-based device is segmented in 50 μm thin, 1.7 mm long and 800 μm wide silicon tiles and a 2 mm diameter 400 μm thick circular chip, containing ultrasound transducers and interconnected by polyimide-based flexible interconnects. See Figure 3.

   

 

Figure 3: This figure shows the forward and side looking demonstrator which will be included at the tip of a 2 mm diameter catheter. The entire “tiled” device is attached in a silicon frame using polyimide tabs. (Image courtesy of reference [1])

 

The circular chip is first glued on the tip of the catheter (Fig. 4(a)). Next, the silicon tiles are folded and glued around the circumference of the catheter. Fig. 4(b) shows the forward and 360o viewing angle ultrasound transducer mounted on a 2 mm diameter catheter tip.

 

 

Figure 4: (a) The forward and side looking demonstrator mounting process is shown here. (b) Finally, the device gets mounted at the tip of a 2 mm diameter catheter. (Image courtesy of reference [1])

 

This fascinating technology of flexible MEMS will revolutionize the medical diagnostic process and aid in the proper treatment of diseases and other medical conditions with less invasive technology sizes and higher resolution device technology. I can’t wait to see what is coming next.

And speaking of what is coming next in creative engineering for sensor technology, EDN and TI has put a Sensing Design Challenge together to stimulate the creative brains of our designer/readers. Here is a link to that Challenge.

References

 

1 Flex-to-Rigid (F2R): A Generic Platform for the Fabrication and Assembly of Flexible Sensors for Minimally Invasive Instruments, Benjamin Mimoun, Vincent Henneken, Arjen van der Horst and Ronald Dekker

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