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Determining the position andorientation of in-body medicalinstruments using reactivemagnetic field mapping

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  1. Tez No: 759486
  2. Yazar: VEDAT CAVLU
  3. Danışmanlar: Belirtilmemiş.
  4. Tez Türü: Doktora
  5. Konular: Elektrik ve Elektronik Mühendisliği, Electrical and Electronics Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 2021
  8. Dil: İngilizce
  9. Üniversite: University of London - University College London
  10. Enstitü: Yurtdışı Enstitü
  11. Ana Bilim Dalı: Belirtilmemiş.
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 194

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Özet (Çeviri)

There has been a huge demand for localizing in-body medical instruments (IBMI), such as wireless capsule endoscope (WCE) and nasogastric tube (NGT). Some studies have been conducted to solve this issue over the last three decades. In these studies, they either used a permanent magnet (PM), a static current source (SCS), radio frequency (RF) fields or integration of two of these. The PM is a stable and reliable magnetic field source. However, due to the size restriction of the NGT and the WCE, only a small PM can be used. Subsequently, the small size issue causes low power delivery at the larger tracking distance. Also, the PM field is very susceptible to ambient noise, and the PM-based localization is not possible in applications requiring robotic actuation. Even though an SCS can be used to replace the permanent magnet, and thus the current level can be varied in relation to the distance for optimized power delivery, it requires a relatively high power to generate a higher strength magnetic field. Consequently, a more powerful and larger battery is needed to feed the circuit.Radio frequency field sources require high frequencies to achieve sufficient precision, but these frequencies undergo high attenuation in the body. Therefore, the low-frequency RF field is preferred 1 . In the near-field 2 , plane wave assumption of the far-field fails for localization methods since the waves in this region are spherical. Hence, the wave-front has to be formulated by both the range and the direction of arrival (DOA). The DOA requires the phase difference of neighbouring sensors to be calculated. However, if 1The studies generally focus on low-frequency RF localization techniques because it can deliver higher power to the larger distances with relatively low applied power to the source, and it has negligible attenuation to the tissues. 2The space around the RF transmitters is generally separated into the near-field and far-field regions. The near-field space is usually defined as from the transmitter to up to one wavelength distance, and beyond this space is called the far-field region. Abstract 4 the operating wavelength is much larger than the distance between the source and the receiver, it is not feasible to compute the phase difference between the neighbouring sensors. Thus, there are numerous algorithms in the literature to overcome these issues, such as MUSIC or ESPRIT which are either complicated or computationally expensive. In RF-based localization, generally the time of arrival (TA), the time difference of arrival (TDA), the angle of arrival (AOA) and the received signal strength (RSS) are widely used for localization. However, the TA and TDA require accurate knowledge of field speed and good time synchronization. It is not possible to accurately know while travelling through the body tissues due to complexity of the tissues. The AOA is also impractical for intra-body applications owing to multiple reflections signal from the tissues, commonly known as the multipath effect. The RSS precision is dependent on good knowledge of power loss in complex body tissues. Also, the RSS method requires accurate knowledge of the transmitted signal strength. However, the power of transmitted frequencies may vary due to the capacitive effect of human tissue on Resonant frequency of source, hence RSS-based techniques prove difficult in practice. Therefore, a novel method of mapping the magnetic field vector in the nearfield region is proposed. This magnetic field mapping (MFM) uses single-axis coils placed orthogonally with respect to a sensor plane (SP). These single-axis sensors pick up only the orthogonal component of the magnetic field, which varies as a function of the orientation of the source and distance to the source. Thus, using this information, the field strength captured by each sensor is mapped to its corresponding position on the SP as pixels. Next, these field strengths with known positions are used to detect the location and orientation of the field source relative to the SP. MATLAB and CST Microwave simulation were conducted, and many laboratory experiments were performed, and we show that the novel technique not only overcomes the issues faced in the methods mentioned above but also accomplishes an accurate source positioning with a precision of better than ± 0.5 cm in 3-D and orientation with a maximum error of ±5 ◦ .

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