||A FPGA-based wearable ultrasound device for monitoring obstructive sleep apnea syndrome
||Department of BioMedical Engineering
Obstructive sleep apnea
Obstructive sleep apnea (OSA), a breathing disorder characterized by repetitive collapse of the pharyngeal airway during sleep, can cause intermittent hypoxemia and frequent arousal. Many studies have demonstrated that the deformation of tongue base plays an important role in OSA. Currently, several medical imaging modalities have been used to record the airway changes, such as cine MRI and ultrafast CT. However, most of them are difficult to be used widely in clinical diagnosis for continuous recording the deformation of tongue in real-time, particularly during sleeping. In order to overcome these problems, a wearable ultrasonic device was developed for real-time monitor of the dynamic change of the tongue base in this study.
The device includes a custom-designed 3-MHz ultrasonic array transducer, an ultrasound pulser/receiver, high speed analog-to-digital converter, and a FPGA board. The ultrasound pulse repetition frequency and pulse center frequency are controlled by the programmable FPGA board. Since this device exhibits non-invasive, real time imaging, portable, and non-ionizing radiation, it can be used to detect the airway situation during natural sleeping with various postures. This new information will help physicians to diagnose the symptoms.
The anthropometric measurement was carried out for verifying the system performance. Results demonstrated that the dynamic variation of tongue base can be clearly distinguished by using this wearable system. It has the potential to be incorporated into polysomnography and to provide information about retroglossal airway behavior during natural sleep. Furthermore, it is very important in devising, applying and determining the effectiveness of tailor-made treatment modalities.
Chapter 1 Introduction 1
1.1 Background 1
1.2 Literature Reviews 3
1.3 Motivations and Purpose 9
Chapter 2 Basic Theory 10
2.1 Ultrasound 10
2.1.1 Fundamental of Acoustic Propagation 10
2.1.2 Reflection, Refraction and Attenuation 11
2.1.3 Ultrasonic Transducer 14
2.2 Gray-Scale Ultrasonic Imaging 16
2.2.1 A (Amplitude)-Mode Imaging 17
2.2.2 B (Brightness)-Mode Imaging 18
2.3 Excitation Pulse of Ultrasonic Imaging 20
2.3.1 Unipolar Pulse 20
2.3.2 Bipolar Pulse 22
Chapter 3 Materials and Methods 23
3.1 System Overview 23
3.1.1 Custom-Designed Ultrasonic Transducer 24
3.1.2 Wearable Ultrasound Device 27
3.1.3 Coordinate Rotation Digital Computer Algorithm 29
3.2 Ultrasound Circuits Design 30
3.2.1 High-Voltage Ultrasound Transmitter 31
3.2.2 Ultrasound Receiver 33
3.2.3 High-Voltage Analog Switching 37
3.2.4 High-Voltage DC to DC Converter 38
3.3 Experimental Setup 40
3.3.1 Patients 41
3.3.2 Polysomnography 41
Chapter 4 Results and Discussion 43
4.1 System Verification 43
4.1.1 Hardware Results 43
4.1.2 Compared with Commercial System 46
4.2 Experimental Results 48
4.2.1 Ultrasonography Images 48
4.2.2 Ultrasonography Measurements 51
4.3 Discussion 55
Chapter 5 Conclusion and Future Work 56
5.1 Conclusion 56
5.2 Future Work 57
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