9. Measurement Device for Movement of the Larynx using Magneto-Impedance Sensor

 

K.Tanida, Y.Ikeda, Y.Sato, M.Akutagawa, Y.Kinouchi, T.Ichikawa, S.Hongama

Graduate School of Advanced Technology and Science The Univ. of Tokushima

Institute of Technology and Science The Univ. of Tokushima

Institute of Health Biosciences The Univ. of Tokushima

 

Introduction

The objective of this study is to develop a screening device for the swallowing difficulty using Magneto-Impedance (MI) sensor. videofluorography (VF) is effective to the diagnosis of swallowing difficulty. This diagnosis method is not effective to every patient. Because it has radiation exposure hazard, and is costly and takes long time for the diagnosis [1]. Consequently, an easy screening method has been widely used. The Repetitive Saliva Swallowing Test (RSST) is one of effective screening methods of the swallowing difficulty.

In this study, we developed the screening device to automate the RSST using a MI sensor. The screening device consists of a MI sensor and a magnet. A magnet is attached on the larynx. The movement of magnet, which is the movement of the larynx according to swallowing, is detected with MI sensor as a change in the magnetic field.

In this study, we measure the movement of the larynx for healthy subjects and senior adult. The screening device can measure the movement of the larynx and count the number of swallowing when the subject was healthy people. However, the subject is the senior adult and patient of the swallowing difficulty, it seems to be hard to obtain enough result. In this time, we developed the screening device composed of two MI sensor to this problem.

Materials and Methods

The Repetitive Saliva Swallowing Test (RSST) is safe and simply screening method of the swallowing difficulty. It is performed by counting the frequency of swallowing over a 30 seconds. When the count of swallowing is less than 3 times/30 seconds, the subject is suggested to be further investigated for functional dysphagia by RSST [2].

We developed the screening device to automate the RSST. The screening device consists of a MI sensor and a magnet as shown in figure 1. Figure 2 shows the layout of the screening device on a patient [3]. A magnet is attached on the larynx, and a MI sensor is attached on breastbone. The movement of magnet, which is the movement of the larynx according to swallowing, is detected with MI sensor as a change in the magnetic field. The output signal from MI sensor shows the movement of the larynx with swallowing.

The output signal is analyzed to count the number of swallowing using a threshold and differential value-based algorithm. Figure 3 shows the swallowing count algorithm.  is the minimum voltage in the output signal and  is the mean voltage.  is threshold voltage defined as (1).

  c(1)

If the output signal goes up to the  with differential value maintains a positive value after the signal was under the , the algorithm increase one count of swallowing. The count will not be increased when the other output signal pattern.

We measured the larynx movement by this method for healthy subjects and senior adult subjects. The screening device measured the larynx movement, when subject is healthy people (figure 4). However, we were hard to obtain enough result, when subject is senior adults (figure 5). Because a MI sensor moved by body movement of senior adult, when swallowing. A MI sensor detects terrestrial magnetism besides the larynx movement by this cause.

Consequently, we developed the screening device, composed of two MI sensor, to cancel body movement by senior adult (figure 6). A first MI sensor is attached on the breastbone, and second MI sensor is attached on the shoulder. A first MI sensor detects the larynx movement and body movement, and second MI sensor detects body movement only. We obtain accurate result by difference between first MI sensors output signal and second MI sensors one.

MI sensor : MI-CB-1DS

High sensitivity AC magnetic filed detection type

Sensitivity : 40mV/mG

Frequency band restriction : 0.3`5Hz

Aichi Micro Intelligent Corporation

 

Magnet : Nd-Fe-B

Maximum energy product : 50MGOe
 
 

 

 

 

 


                                                                                                 

 

 

 

 

 

 

 

 

 

    Figure 1 : The MI sensor and a magnet

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


                      Figure 2 : The layout of the screening device

 

 

 

 

 

 

 

 

 

 

                       Figure 3 : The swallowing count algorithm

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


           Figure 4 : Swallowing three times (healthy subject, male, 22 years old)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

           Figure 5 : Swallowing eight times (senior adult, male, 77 years old)

 

 

First MI sensors output signal   = Larynx movement + Body movementc(2)

Second MI sensors output signal = Body movementc(3)

Final output signal            = (2) – (3) = Larynx movementc(4)
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


            Figure 6 : The layout of screening device (composed of two MI sensor)

Results

Figure 4 shows the output signal from MI sensor when healthy subject swallowing three times. We can obtain the count of swallowing by the threshold and differential value-based algorithm as shown in this figure. Figure 5 shows the output signal from MI sensor when senior adult subject swallowing. We can not obtain the count of swallowing by the algorithm, and the naked eye too. Figure 7 shows a result using the screening device, composed of two MI sensor, when healthy subject moved the body by intention at the swallowing. We were confirmed to obtain a result similar figure 4 by using the two MI sensor, as shown in figure 7.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

@@  Figure 7 : Swallowing three times (when the subject moved the body by intention)

Conclusions

We developed the screening device for automate the RSST. The screening device is simply composed of MI sensor and a magnet, and sense the movement of the larynx as the change of magnetic field. We could measure the larynx movement by the screening device, when subject is healthy people. However, the screening device seems to be hard to obtain enough result, when subject is senior adult, because its body moves when swallowing. In this time, we developed the screening device to be able to cancel body movement that composed of two MI sensor. For the future, we will try the demonstration for senior adult by the screening device using two MI sensor.

References

1 Hongama S, Ichikawa T, DDS, PhD, Dr. Eng, Nagao K, DDS, PhD, and Murata M, DDS : MI-sensor Navigated Measuring System for Repetitive Saliva Swallowing Test (RSST).

2 Oguchi K, Saitoh E, Mizuno M, et al : The Repetitive Saliva Swallowing Test (RSST) as a Screening Test of Functional Dysphagia (1) Normal Values of RSST. (In Japanese, English abstract). Jpn J Rehabil Med 2000; 37:375-82.

3 K. Tanida, Y. Ikeda, Y. Sato, M. Akutagawa, Y. Kinouchi, T. Ichikawa, T. Yamamoto, Y. Ishida :

Development of the Screening Device for Dysphagia using Magneto-Impedance Sensor, Journal of the Japanese society for the 6th International Conference on Magnetic Applications in Dentistry, Japan, JSMAD March 1-March 20, 2007.