A STUDY OF SPINAL NEEDLE VISIBILITY INCONSISTENCY BASED ON ACOUSTIC SCATTERING THEORY AND A-MODE ULTRASONIC SPECTROSCOPY

• Main Author: Susanti, Hesty
• Format: Dissertations
• Language: Indonesia
• Subjects: Teknik (Rekayasa, enjinering dan kegiatan berkaitan)
• Online Access: https://digilib.itb.ac.id/gdl/view/47843
• Institution: Institut Teknologi Bandung

In the medical world, needle insertion can be categorized into minimally invasive interventional procedure that emphasizes on minimizing injury. For ensuring successful procedure, image information as visual feedback is needed. Ultrasonography is chosen as imaging modality because it has no radiation risk, but it has high temporal resolution, relatively small equipment and transducer, and the availability of multiple imaging planes. In ultrasound imaging for needle insertion application, one of the crucial problems is the inconsistency of needle visibility. Optimal consistency of needle visibility has various advantages, including avoiding the risk of insertion errors, speeding up the procedure, while reducing pain and discomfort for patients. The initial experiment of B-mode needle imaging through the development of needle visibility quantification method showed that the visibility of the needle is influenced by several physical parameters including, insertion angle, ultrasonic wave frequency, and needle characteristics. However, no linearity was found in the relationship between needle visibility and the physical parameters. The quantification method and needle visibility map developed in this research can represent the actual needle visibility, so that it can be used to predict needle visibility patterns in the range of angle and frequency of operational insertion. Physically, the needle visibility is influenced by the mechanism of ultrasonic wave propagation through the intermediate medium and the needle until it is reflected back as back propagation received by the transducer. The inconsistency of needle visibility in the B-mode image (brightness modulation) is closely related to the amplitude of the acoustic scattering pressure from the total back propagation of the needle received by the transducer. In this study an evaluation method is developed to understand the fundamental physical phenomena underlying the needle visibility inconsistency in B-mode ultrasound image through modeling and simulation by developing analytical model and numerical simulation, as well as experimental approach. Firstly, the pattern of inconsistency of needle visibility is observed through development of analytical model based on resonance scattering theory and numerical simulation of ultrasonic wave propagation across the needle by varying physical parameters, i.e., frequency, angle of insertion, and needle characteristics. Through this approach, the spectrum of back propagation pressure field from the needle is obtained. Analytical model of ultrasound wave propagation based on resonance scattering theory can represent acoustic scattering patterns on the spinal needles associated with resonant wave modes around critical angles, i.e., ???????? = 17,4°, ???????? = 27,8°, and ???????? = 30,5° in the range of frequency and insertion angle. The frequency, the incident angle of ultrasound beam, as well as the needle characteristic parameters, except the length of the needle simultaneously affect the pattern of amplitude spectrum of the acoustic scattering pressure on spinal needle with non-linear patterns. The combination of all these physical parameters influences the total acoustic scattering pressure which becomes the basis of the inconsistency pattern of spinal needle visibility in the B-mode ultrasound image. Furthermore, through the experiment of A-mode ultrasonic spectroscopy, back scattering signal parameters of 18G, 20G, and 22G spinal needles in homogeneous and anechoic water phantom, are compared to the analytical model as a standard reference. Raw Radio Frequency (RF) signals recorded on each transducer element are processed into signal parameters that become the parameters of B-mode image reconstruction which can represent unique information of the total back propagation of the needle received by the transducer. The characteristics of acoustic scattering of spinal needles with precision insertion angles in the range of 0°–45° (resolution of 5°) and optimal transducer frequency of 1.87 MHz can be represented by the design of the needle visibility evaluator system with the A-mode ultrasonic spectroscopy method. Signal parameters in the frequency domain, i.e., maximum Power Spectral Density (PSD) and Energy Spectral Density (ESD) more represent the acoustic scattering characteristics of the spinal needles with a dominant pattern of increasing visibility around critical angles of 15°–30°, compared to the standard B-mode image reconstruction parameters in the time domain, i.e., envelope detected signal. Therefore, these two parameters can be used in the B-mode image reconstruction to increase needle contrast. From this comparison, it is not expected that they are similar in absolute values because the conditions in the modeling and simulation are assumed to be ideal and different from the condition in the experiment, i.e., the differences in the ultrasound wave source, the acoustic characteristics of medium, and needle positioning. The amplitude spectrum of acoustic scattering pressure and the A-mode acoustic scattering signal parameters confirm that the inconsistency of needle visibility is the simultaneous influence of physical parameters, i.e., ultrasound wave frequencies, insertion angles, and needle characteristics, which are related to the generation of resonant wave modes around the critical angles. The reconstruction of needle images in B-mode ultrasound image from A-mode signals can be improved by extracting signal parameters in the frequency domain, i.e., Power Spectral Density (PSD) and Energy Spectral Density (ESD).