Laser lithotripsy destroys urinary stones by ablating them into fine particles and dust. However, the nature of the resulting dust is not well understood, nor how this differs for different stone types. To investigate this, canine stones of different types were ablated in vitro using a Ho:YAG laser and the resulting particles analysed to calculate a characteristic particle size distribution for each stone type. Differences in these size distributions may require the resulting stone dust to be managed differently in vivo.
Stone retropulsion is an inevitable side effect of laser lithotripsy. It is generally considered undesirable but can also be beneficial in techniques such as “popdusting”. It is often described by a single parameter such as a distance moved, which might not correlate with the degree to which retropulsion interferes with clinical use. We report on a novel method of measuring retropulsion in vitro using high-speed video photography to describe the stone trajectory across multiple parameters, and present results from a range of laser systems. Describing the nature of this movement may help explain how some types of retropulsion are considered clinically disruptive and others are not.
Holmium:YAG laser has been the lithotrite of choice for around 30 years in kidney stone surgery. Lasers have evolved over the years to offer higher power, increased pulse frequencies and longer pulse durations. The drivers for change have been to improve stone ablation and to minimise retropulsion. We report on a new prototype Holmium laser that fires multiple “micro-pulses” in “pulse packets” and discuss the stone phantom ablation rate results utilizing a bench model. The prototype laser demonstrated impressive stone ablation rates in our bench testing across a range of power settings. We will discuss the details of these results supporting that pulse-modulation with packets of micro-pulses are a promising technological development. (Disclaimers: Bench Test results may not necessarily be indicative of clinical performance. The testing was performed by or on behalf of BSC.
Stone retropulsion during laser lithotripsy results from various physical phenomena such as recoil momentum, bubble dynamics, and subsequent jet formation. Considerable stone retropulsion has been observed whereby the optical energy is converted into both mechanical and thermal energy as a distinctive bubble generation and collapse. It is hypothesized that by reducing the peak power and lengthening the pulse duration, we can reduce this conversion of optical energy into mechanical energy. This should maximize the thermal effects on the stone leading to enhanced ablation efficiency as well as less stone “chasing”. We are reporting on a new prototype Holmium laser with low pulse power and long temporal pulse durations in an attempt to minimize stone retropulsion.
Holmium:YAG laser is commonly used as an efficient technology for lithotripsy, breaking urinary stones into small particles (dust) and larger residual fragments (RF). One of the ultimate goals is to create fine dust for real-time aspiration, eliminating the need for mechanical retrieval of RFs. A recent study of stone dust definition suggests a maximum particle size of 250-µm to allow complete aspiration through the working channel of a flexible ureteroscope.
We have evaluated the particle size generation of a concept Holmium:YAG laser utilizing a pulse width modulation technique. This technology delivers numerous low-energy micro-pulses per pulse with long temporal pulse duration to potentially enable finer dust particles, better ablation rate, and reduced retropulsion. Overall, the concept device generates a high percentage of fine dust compared with prior results found in literature.
(Disclaimers: Bench Test results may not necessarily be indicative of clinical performance. The testing was performed by or on behalf of BSC. Data on file. Concept device or technology. Not available for sale. This device is not yet available for sale in the United States).
Ureteroscopy is a conventional procedure used for localization and removal of kidney stones. Laser is commonly used to fragment the stones until they are small enough to be removed. Often, the surgical team faces tremendous challenge to successfully perform this task, mainly due to poor image quality, presence of floating debris and occlusions in the endoscopy video. Automated localization and segmentation can help to perform stone fragmentation efficiently. However, the automatic segmentation of kidney stones is a complex and challenging procedure due to stone heterogeneity in terms of shape, size, texture, color and position. In addition, dynamic background, motion blur, local deformations, occlusions, varying illumination conditions and visual clutter from the stone debris make the segmentation task even more challenging. In this paper, we present a novel illumination invariant optical flow based segmentation technique. We introduce a multi-frame based dense optical flow estimation in a primal-dual optimization framework embedded with a robust data-term based on normalized correlation transform descriptors. The proposed technique leverages the motion fields between multiple frames reducing the effect of blur, deformations, occlusions and debris; and the proposed descriptor makes the method robust to illumination changes and dynamic background. Both qualitative and quantitative evaluations show the efficacy of the proposed method on ureteroscopy data. Our algorithm shows an improvement of 5-8% over all evaluation metrics as compared to the previous method. Our multi-frame strategy outperforms classically used two-frame model.
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