Safe and accurate placement of spinal screws remains a critical step during open and minimally invasive spinal fusion surgery. We investigated the application of diffuse reflectance spectroscopy (DRS) for real-time instrument guidance during a spinal screw placement procedure. A custom-built screw probe with integrated optical fibers was inserted into a vertebra under image guidance in an ex vivo human setting. We found that fat content derived from the spectra gradually changed as the probe approached the cortical bone boundary. The results indicate that DRS integrated into surgical instruments has the potential to improve the safety and accuracy of spinal screw placement procedures.
Safe and accurate placement of screws remains a critical issue in open and minimally invasive spine surgery. We propose to use diffuse reflectance (DR) spectroscopy as a sensing technology at the tip of a surgical instrument to ensure a safe path of the instrument through the cancellous bone of the vertebrae. This approach could potentially reduce the rate of cortical bone breaches, thereby resulting in fewer neural and vascular injuries during spinal fusion surgery. In our study, DR spectra in the wavelength ranges of 400 to 1600 nm were acquired from cancellous and cortical bone from three human cadavers. First, it was investigated whether these spectra can be used to distinguish between the two bone types based on fat, water, and blood content along with photon scattering. Subsequently, the penetration of the bone by an optical probe was simulated using the Monte-Carlo (MC) method, to study if the changes in fat content along the probe path would still enable distinction between the bone types. Finally, the simulation findings were validated via an experimental insertion of an optical screw probe into the vertebra aided by x-ray image guidance. The DR spectra indicate that the amount of fat, blood, and photon scattering is significantly higher in cancellous bone than in cortical bone (p < 0.01), which allows distinction between the bone types. The MC simulations showed a change in fat content more than 1 mm before the optical probe came in contact with the cortical bone. The experimental insertion of the optical screw probe gave similar results. This study shows that spectral tissue sensing, based on DR spectroscopy at the instrument tip, is a promising technology to identify the transition zone from cancellous to cortical vertebral bone. The technology therefore has the potential to improve the safety and accuracy of spinal screw placement procedures.
There is a strong need to develop clinical instruments that can perform rapid tissue assessment at the tip of smart clinical instruments for a variety of oncological applications. This study presents the first in vivo real-time tissue characterization during 24 liver biopsy procedures using diffuse reflectance (DR) spectroscopy at the tip of a core biopsy needle with integrated optical fibers. DR measurements were performed along each needle path, followed by biopsy of the target lesion using the same needle. Interventional imaging was coregistered with the DR spectra. Pathology results were compared with the DR spectroscopy data at the final measurement position. Bile was the primary discriminator between normal liver tissue and tumor tissue. Relative differences in bile content matched with the tissue diagnosis based on histopathological analysis in all 24 clinical cases. Continuous DR measurements during needle insertion in three patients showed that the method can also be applied for biopsy guidance or tumor recognition during surgery. This study provides an important validation step for DR spectroscopy-based tissue characterization in the liver. Given the feasibility of the outlined approach, it is also conceivable to make integrated fiber-optic tools for other clinical procedures that rely on accurate instrument positioning.
Despite the widespread use of radio frequency (RF) ablation, an effective way to assess thermal tissue damage during and after the procedure is still lacking. We present a method for monitoring RF ablation efficacy based on thermally induced methemoglobin as a marker for full tissue ablation. Diffuse reflectance (DR) spectra were measured from human blood samples during gradual heating of the samples from 37 to 60, 70, and 85°C. Additionally, reflectance spectra were recorded real-time during RF ablation of human liver tissue ex vivo and in vivo. Specific spectral characteristics of methemoglobin were extracted from the spectral slopes using a custom optical ablation ratio. Thermal coagulation of blood caused significant changes in the spectral slopes, which is thought to be caused by the formation of methemoglobin. The time course of these changes was clearly dependent on the heating temperature. RF ablation of liver tissue essentially led to similar spectral alterations. In vivo DR measurements confirmed that the method could be used to assess the degree of thermal damage during RF ablation and long after the tissue cooled.
This contribution describes a novel algorithm for the automated quantification of visceral and subcutaneous
adipose tissue volumes from abdominal CT scans of patients referred for colorectal resection. Visceral and
subcutaneous adipose tissue volumes can accurately be measured with errors of 1.2 and 0.5%, respectively. Also
the reproducibility of CT measurements is good; a disadvantage is the amount of radiation. In this study the
diagnostic CT scans in the work - up of (colorectal) cancer were used. This implied no extra radiation. For
the purpose of segmentation alone, a low dose protocol can be applied. Obesity is a well known risk factor
for complications in and after surgery. Body Mass Index (BMI) is a widely accepted indicator of obesity, but
it is not specific for risk assessment of colorectal surgery. We report on an automated method to quantify
visceral and subcutaneous adipose tissue volumes as a basic step in a clinical research project concerning preoperative
risk assessment. The outcomes are to be correlated with the surgery results. The hypothesis is that
the balance between visceral and subcutaneous adipose tissue together with the presence of calcifications in the
major bloodvessels, is a predictive indicator for post - operatieve complications such as anastomotic leak. We
start with four different computer simulated humanoid abdominal volumes with tissue values in the appropriate
Hounsfield range at different dose levels. With satisfactory numerical results for this test, we have applied the
algorithm on over a 100 patient scans and have compared results with manual segmentations by an expert for a
smaller pilot group. The results are within a 5% difference. Compared to other studies reported in the literature,
reliable values are obtained for visceral and subcutaneous adipose tissue areas.
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