Background Inter- and intra patient morphological differences and absence of visual feedback make the placement of pedicle screws technically very demanding. As the spine is surrounded by neurovascular tissue, complications can have severe consequences, including paralysis. Guidance techniques are often very expensive and can overexpose surgeons to radiation, while there is a high variability in reported accuracy rates. Diffuse reflectance spectroscopy (DRS) is a technique that allows for real-time tissue discrimination using an optical fiber which can e.g. be placed in a K-wire. It can detect difference in fat fraction between cortical and cancellous bone. Purpose This master thesis aims at investigating the capability of the DRS equipped K-wire to anticipate cortical breach by measuring a decrease in fat fraction, while being oscillated with a power hammering tool. Mechanical experiments investigate the amount of control over penetration depth during powered hammering insertion of a K-wire. Methods This thesis contains three experiments. Two focus on mechanical properties and one on optical properties. In the mechanical experiments, a 1.6 X 60 mm trocar tip K-wire without integrated optical fibers is used. In the first experiment, the K-wire and its oscillator are attached to a carriage on a horizontal guide rail. A mechanical bone phantom is placed at the end of the rail and is penetrated at varying oscillation frequencies (0 – 50 Hz). To move the carriage towards the bone phantom, masses are attached in discrete steps of 250 grams. Penetration depth is measured as insertion mass increases at constant oscillation frequency. In the second mechanical experiment, the same K-wire and K-wire oscillator are attached to a vertical linear stage. The K-wire penetrates the mechanical bone phantom at an oscillation frequency of 0 Hz or 35 Hz. Feed rates are varied (0.5 – 2.5 mm/s) and force on the bone phantom is continuously measured. For the optical experiment, a 1.6 X 300 mm fiber-optic K-wire is used with fiber distance equalling 1.22 mm. The K-wire with the oscillator are attached to a linear stage, and lowered at constant feed rate (0.5 mm/s) into an optical bone phantom. NIR spectra are acquired with a sampling frequency of 1.6 Hz. The effect of varying oscillation frequency (0 – 50 Hz) on measured fat fractions is quantified. Results The first mechanical experiment showed that for every oscillation frequency, penetration started at the first weight increment (0.1 kg). Without oscillations, phantom penetration initiated at a mass of 1.85 Kg. Regression analysis proved the penetration depth depends on the square root of applied axial force. In the mass range of 0 – 1.6 kg, 45 Hz led to the largest penetration depth (25 mm), with a relatively narrow 95% confidence interval (17 – 33 mm). The second mechanical experiment showed that measured mean force is lower when oscillating the K-wire (1.4 – 5.8 N vs. 9.5 – 12.3 N, p<0.0001). Effect of feed rate on measured mean force is found not significant (p=0.15 for oscillating and p=0.61 for not oscillating). In the optical test, it was found that look ahead distance (LAD) increases with increasing oscillation frequency and amplitude. 50 Hz was the only frequency where the LAD was larger than its oscillation amplitude (1.22 mm and 0.5 mm, respectively). Conclusion Powered hammering of a K-wire requires a lower axial force for penetration and therefore allows for more control over penetration depth. From the tested range, this effect is most significant for oscillations with high frequencies, adequate forces and low amplitudes. It is possible to measure a decrease in fat fraction with a fiber-optic k-wire during penetration. High oscillation frequencies with low amplitudes allow for earliest anticipation. An adequate sized sampling frequency is required to allow for breach anticipation.

In spinal surgery, the misplacement of spinal screws is a common problem that causes (severe) pain, bleedings or even paralysis [1] [2] [3]. In order to improve the navigational support of spine surgeons, this research focuses on the development of an optical sensing diffuse reflectance spectroscopy (DRS) orthopaedic drill that identifies bone tissue boundaries, based on fat fraction. The developed drill concept introduces a stagnant optical fiber-equipped probe into a cannulated orthopaedic drill. To verify the clinical applicability of the developed system, the accuracy of the optical tissue boundary detection has been analysed under different tissue penetration speeds, as well as the axial drilling force increases due to the introduction of a stagnant probe into a cannulated drill. The maximum feed rate at which the drill consistently detects the tissue boundary before breaching it, is 0,5mm/s. The force increase due to the introduction of a stagnant probe is a factor 2,96 on average and varies widely between different feed rates and probe diameters (a factor 1,15–5,75). The established feed rate speed limit of 0,5mm/s is lower than drilling feed rates of up to 5mm/s, observed in the operation room. Increasing the sampling frequency –especially decreasing the inactive period between the measurements– is required. The feed force increase of approximately a factor 3 can be regarded as a challenge for surgeons, who indicated that they preferred feed forces to be kept low.

Atrial Fibrillation (AF) is a common type of arrhythmia, characterized by rapid and irregular contraction of the atria. Irregular contraction of the atria is caused by erroneous electrical activation, originating from the tissue around the Pulmonary Veins (PV) in the Left Atrium (LA). Catheter-based treatment of AF includes ablation of the tissue around the PV. Imaging of ablation catheters and LA-anatomy is of great importance for accurate and successful treatment of AF. In current state of the art LA-ablation procedures, static, pre-procedural acquired 3D models of the LA are used for catheter navigation and monitoring. However, due to the limited accuracy of these static 3D models there is a continuous demand for real-time 3D imaging techniques during catheter based treatment of AF. A possible solution for real time imaging is to use trans-balloon, miniaturized transesophageal echocardiography (TEE) as imaging modality for AF ablation procedures. Trans-balloon, miniaturized TEE can provide real-time 3D ultrasound imaging of the LA. Since trans-balloon, miniaturized TEE is not used in clinical practice yet, it is unknown whether image quality of the miniaturized TEE probe will be sufficient for imaging during AF ablation procedures. Therefore, the image quality of trans-balloon, miniaturized TEE has to be compared to image quality current state of the art TEE probes. In this thesis, image quality of the miniaturized ultrasound probe was compared to current state of the art TEE probes, and the influence of the balloon on image quality was investigated. Image quality was assessed using standardized ultrasound image quality assessment phantoms and software. Image quality was measured using the following image quality parameters: contrast to noise ratio (CNR), spatial resolution and penetration depth of the ultrasound signal. The results have shown that CNR of the miniaturized probe is equal to that of state of the art probes, but that spatial resolution of the miniaturized probe strongly depends on the rotation angle of the ultrasound imaging plane. Rotating the imaging plane of the miniaturized TEE probe negatively impacts spatial resolution, which was not observed for the state of the art TEE probes. The penetration depth of the ultrasound signal was significantly less compared to state of the art TEE probes. The rotation-dependent spatial resolution of the miniaturized probe is undesired, since rotating the imaging plane is common practice in TEE. A review study involving clinical experts is recommended to judge whether image quality of the miniaturized probe with rotated imaging plane is sufficient. Since the anatomical structures of interest during AF are close to the transducer, the limited penetration depth of the miniaturized probe will not be a major limitation. Despite aforementioned limitations, the results suggest that trans-balloon miniaturized TEE can be used for real-time ultrasound imaging during AF ablation procedures. The research in this thesis provides a theoretical framework to measure and compare image quality of ultrasound probes, which is an important first step in the development of a novel, real-time 3D imaging technique for imaging of AF ablation procedures.

Introduction. In spinal surgery, the misplacement of spinal screws is a problem that causes (severe) pain, bleedings or even paralysis [2]. Screw misplacements are common as navigating in the spine is difficult due to the small vertebral dimensions and a lack of anatomical landmarks [3] [4]. In order to improve the navigational support of spine surgeons, this research focuses on the development of an optical sensing diffuse reflectance spectroscopy (DRS) surgical drill that identifies bone tissue boundaries. The developed drill concept introduces a stagnant optical fiber-equipped probe into a cannulated orthopaedic drill. To verify the clinical applicability of the developed system, the accuracy of the optical tissue boundary detection has been analysed under different tissue penetration speeds, as well as the axial drilling force increases due to the introduction of a stagnant probe into a drill. Results. When increasing the drilling feed rate in the optical phantom, the drill overshoot (the difference between the DRS-derived tissue boundary location identification and the actual location of the phantom boundary) shows a larger spread. The maximum feed rate at which no overshoot takes place is 0,5mm/s. Increasing the sampling frequency –especially decreasing the inactive period between the measurements– can improve this. None of the K-wire equipped drills can penetrate the used Sawbones® cortical bone phantom. The axial peak feed forces occurring in the Sawbones® cancellous bone phantom while using a regular 2,7mmØ orthopaedic drill is 38,2N. When using the 2,7mmØ orthopaedic drill with a 1,6mmØ K-wire, a peak of 57,6N is observed. Because the data from drilling in the Sawbones® cancellous bone is not normally distributed, a benchmark experiment on cheese is analysed. On average, the introduction of a K-wire increases the required drilling forces by a 296% (roughly a factor 3). Among the different feed rates and drill types, the force increase of introducing a stagnant K-wire varies between 16% and 575%. Conclusion. To prevent orthopaedic screws from breaching the bone surface (an overshoot of 0mm) in spinal surgery, the established feed rate speed limit of 0,5mm/s is too low. To meet the observed feed rates applied by surgeons of up to 5mm/s, it is of interest to reduce the DRS sampling time – the inactive period between two measurements in particular. The feed force increase of approximately a factor 3 can be regarded as a challenge for surgeons, who indicated that they preferred feed forces to be kept low. Further testing on real (cadaveric) vertebrae can more give information about the DRS drill’s optical performance in pedicles, and whether the identified feed force increase proves to be problematic for clinical applications.