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Use of a MEMS Accelerometer to Monitor Breathing Motion

A Markovic

A Markovic1*, (1) Banner Health, Greeley, CO

SU-E-T-362 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:Breathing motion is routinely monitored for purposes of gating a linear accelerator beam during radiotherapy treatment or for binning CT images during a 4D CT scan. This study proposes the use of a MEMS (micoelectromechanical system) accelerometer placed on a patient's chest to measure the timing and magnitude of regular breathing motion. A small package of electronics (Fig 2.) can be assembled with a battery which can unobtrusively be placed on a patient under their gown precluding the need to expose their skin as required by other camera-based monitoring systems. The accelerometer communicates with a computer running specialized software that displays a breathing pattern viewable by the radiation therapists at the control console.

Methods:A 12-bit ST Microelectronics accelerometer (LIS3DH) of dimensions 3x3x1 mm connected to a 5x6 cm breadboard (Fig. 1) was used to measure breathing motion under simulated treatment conditions for this pilot study. The accelerometer can transfer data at rates ranging from 100 to 1600 Hz via either a USB cable or Bluetooth that relays acceleration data to a computer running a MATLAB program. The high-speed data rate allows data averaging which aids in the reduction of signal noise. The accelerometer provides an acceleration resolution of 9.8x10⁻³ m/sec². We are currently investigating the use of a new low-noise 16-bit accelerometer which will improve signal to noise response.

Results:Fig. 3 shows accelerometer data acquired at a rate of 100Hz during regular breathing while placed on a subject's chest. High speed data rates allow for averaging (20 points, in this case) which reduces noise but does not affect the breathing trace period or amplitude.

Conclusion:This pilot study used an accelerometer placed on a subject's chest to measure breathing motion during radiotherapy treatments. The small size of the electronics package can easily be placed on a patient under their gown.

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