Herke Jan Noordmans

Automated electrocorticographic electrode localization on individually rendered brain surfaces

Brain surface electrocorticographic (ECoG) recordings can investigate human brain electrophysiology at the cortical surface with exceptionally high signal to noise ratio and spatio-temporal resolution. To be able to use the high spatial resolution of ECoG for accurate brain function mapping and neurophysiology studies, the exact location of the ECoG electrodes on the brain surface should be known. Several issues complicate robust localization: surgical photographs of the electrode array made after implantation are often incomplete because the grids may be moved underneath the skull, beyond the exposed area. Computed tomography (CT) scans made after implantation will clearly localize electrodes, but the effects of surgical intervention may cause the exposed brain to move away from the skull and assume an unpredictable shape (the so-called brain shift). First, we present a method based on a preoperative magnetic resonance imaging (MRI) coregistered with a post-implantation CT scan to localize the electrodes and that automatically corrects for the brain shift by projecting the electrodes to the surface of the cortex. The calculated electrode positions are visualized on the individual subjects brain surface rendering. Second, the method was validated by comparison with surgical photographs, finding a median difference between photographic and calculated electrode centers-of-mass of only 2.6mm, across 6 subjects. Third, to illustrate its utility we demonstrate how functional MRI and ECoG findings in the same subject may be directly compared in a simple motor movement experiment even when electrodes are not visible in the craniotomy.

The effect of zirconia and titanium implant abutments on light reflection of the supporting soft tissues

OBJECTIVES To determine the difference in light reflection of oral mucosa covering titanium (Ti) or zirconia (ZrO(2)) abutments as it relates to the thickness of the covering mucosa. MATERIAL AND METHODS Fifteen anterior implants (Astra Osseo speed(®)) in 11 patients were fitted with a Ti or a ZrO(2) abutment (cross-over, within-subject comparison). Hyper-spectral images were taken with a camera fitted on a surgical microscope. High-resolution images with 70 nm interval between 440 and 720 nm were obtained within 30 s (1392 × 1024 pixels). Black- and white-point reference was used for spatial and spectral normalization as well as correction for motion during exposure. Reflection spectra were extracted from the image on a line mid-buccal of the implant, starting 1 mm above the soft tissue continuing up to 3 mm apically. RESULTS Median soft tissue height is 2.3 mm (min: 1.2 mm and max: 3.1 mm). The buccal mucosa rapidly increases in the thickness, when moving apically. At 2.2 mm, thickness is 3 mm. No perceivable difference between the Ti and ZrO(2) abutment can be observed when the thickness of the mucosa is 2±0.1 mm (95% confidence interval) or more. CONCLUSION It is expected that the difference in light reflection of soft tissue covering Ti or ZrO(2) abutments is no longer noticeable for the human eye when the mucosa thickness exceeds 2 mm. Haemoglobin peaks in the reflection spectrum can be observed and make hyper-spectral imaging a practical and useful tool for measuring soft tissue health.

Use of a multi-spectral camera in the characterization of skin wounds

Skin breakdown is a prevalent and costly medical condition worldwide, with the etiologic and healing processes being complex and multifactorial. Quantitative assessment of wound healing is challenging due to the subjective measurement of wound size and related characteristics. We propose that in vivo spectral reflectance measurements can serve as valuable clinical monitoring tool/device in the study of wound healing. We have designed a multi spectral camera able to acquire 18 wavelength sensitive images in a single snapshot. A lenslets array in front of a digital camera is combined with narrowband filters (bandwidth 10 nm) ranging from 460 to 886 nm. Images taken with the spectroscopic camera are composed of 18 identical sub-images, each carrying different spectral information, that can be used in the assessment of skin chromophores. A clinical trial based on a repeated measures design was conducted at the National Rehabilitation Hospital on 15 individuals to assess whether Poly Carboxy Methyl Glucose Sulfate (PCMGS, CACIPLIQ20), a bio-engineered component of the extracellular matrix of the skin, is effective at promoting healing of a variety of wounds. Multi spectral images collected at different wavelengths combined with optical skin models were used to quantify skin oxygen saturation and its relation to the traditional measures of wound healing.

The use of near-infrared light for safe and effective visualization of subsurface blood vessels to facilitate blood withdrawal in children

Obtaining access to blood vessels can be difficult, especially in children. Visualization of subsurface blood vessels might be a solution. Ultrasound and visible light have been used to this purpose, but have some drawbacks. Near-infrared light might be a better option since subsurface blood vessels can be visualized in high contrast due to less absorption and scattering in tissue as compared to visible light. Our findings with a multispectral imaging system support this theory. A device, the VascuLuminator, was developed, based on transillumination of the puncture site with near-infrared light. The VascuLuminator was designed to meet the requirements of compact and safe use. A phantom study showed that the maximum depth of visibility (5.5mm for a 3.6mm blood vessel) is sufficient to visualize blood vessels in typical locations for peripheral venous and arterial access. A quantitative comparison of the VascuLuminator and to two other vessel imaging devices, using reflection of near-infrared light instead of transillumination, was conducted. The VascuLuminator is able to decrease failure at first attempt in blood withdrawal in pediatric patients from 10/80 (13%) to 1/45 (2%; P=.05).

Auditory feedback during frameless image-guided surgery in a phantom model and initial clinical experience

In this study the authors measured the effect of auditory feedback during image-guided surgery (IGS) in a phantom model and in a clinical setting. In the phantom setup, advanced IGS with complementary auditory feedback was compared with results obtained with 2 routine forms of IGS, either with an on-screen image display or with image injection via a microscope. The effect was measured by means of volumetric resection assessments. The authors also present their first clinical data concerning the effects of complementary auditory feedback on instrument handling during image-guided neurosurgery. When using image-injection through the microscope for navigation, however, resection quality was significantly worse. In the clinical portion of the study, the authors performed resections of cerebral mass lesions in 6 patients with the aid of auditory feedback. Instrument tip speeds were slightly (although significantly) influenced by this feedback during resection. Overall, the participating neurosurgeons reported that the auditory feedback helped in decision-making during resection without negatively influencing instrument use. Postoperative volumetric imaging studies revealed resection rates of > or = 95% when IGS with auditory feedback was used. There was only a minor amount of brain shift, and postoperative resection volumes corresponded well with the preoperative intentions of the neurosurgeon. Although the results of phantom surgery with auditory feedback revealed no significant effect on resection quality or extent, auditory cues may help prevent damage to eloquent brain structures.

In vitro comparison of renal stone laser treatment using fragmentation and popcorn technique

To study the effectiveness of two laser techniques clinically used to fragment renal stones: fragmenting technique (FT) and popcorn technique (PT).

Feasibility of multi-spectral imaging system to provide enhanced demarcation for skin tumor resection

Invading tumors like basal cell carcinoma have usually no distinct demarcation for the human eye. Therefore, during resection, an additional rim around the tumor is removed. However, extending sprouts can be missed since most lesions are not uniform. To improve the visualization of the tumor demarcation, we developed a multi-spectral imaging system especially adapted for dermatological applications based on tunable liquid crystal spectral tunable filter technology and LED illumination. Enhanced visualization of skin tumor demarcation was achieved using three strategies. The first strategy is based on creating false color images by combining narrow band spectral filtered images by placing them into the red, green and blue image components of a color image at three specific wavelengths. These specific wavelengths were determined using a trial on error tool to achieve the highest contrast between malignant and healthy tissue. The second strategy is to make ratio images of narrow band spectral filtered images at specific wavelengths. A trail on error tool was created which enables the user to try multiple wavelengths to obtain optimal contrast. This method could be applied in realtime. For the third strategy, on pixel spectral segmentation is applied by selecting the pixel spectra in the center of a tumor, surrounding tissue and healthy tissue far away from the tumor. The correlation between these specific spectra and all image pixels is calculated using a fast algorithm. The degree is correlation is graded by color coding and presented in a false color images showing a detailed demarcation of suspicious regions in the tissue. Although this strategy is expected to provide a higher specificity, it takes more time to calculate than the first strategy.

Validation of exposure visualization and audible distance emission for navigated temporal bone drilling in phantoms.

Background A neuronavigation interface with extended function as compared with current systems was developed to aid during temporal bone surgery. The interface, named EVADE, updates the prior anatomical image and visualizes the bone drilling process virtually in real-time without need for intra-operative imaging. Furthermore, EVADE continuously calculates the distance from the drill tip to segmented temporal bone critical structures (e.g. the sigmoid sinus and facial nerve) and produces audiovisual warnings if the surgeon drills in too close vicinity. The aim of this study was to evaluate the accuracy and surgical utility of EVADE in physical phantoms. Methodology/Principal Findings We performed 228 measurements assessing the position accuracy of tracking a navigated drill in the operating theatre. A mean target registration error of 1.33±0.61 mm with a maximum error of 3.04 mm was found. Five neurosurgeons each drilled two temporal bone phantoms, once using EVADE, and once using a standard neuronavigation interface. While using standard neuronavigation the surgeons damaged three modeled temporal bone critical structures. No structure was hit by surgeons utilizing EVADE. Surgeons felt better orientated and thought they had improved tumor exposure with EVADE. Furthermore, we compared the distances between surface meshes of the virtual drill cavities created by EVADE to actual drill cavities: average maximum errors of 2.54±0.49 mm and −2.70±0.48 mm were found. Conclusions/Significance These results demonstrate that EVADE gives accurate feedback which reduces risks of harming modeled critical structures compared to a standard neuronavigation interface during temporal bone phantom drilling.

Compact multi-spectral imaging system for dermatology and neurosurgery

A compact multi-spectral imaging system is presented as diagnostic tool in dermatology and neurosurgery. Using an electronically tunable filter, a sensitive high resolution digital camera, 140 spectral images from 400 nm up to 720 nm are acquired in 40 s. Advanced image processing algorithms are used to enable interactive acquisition, viewing, image registration and image analysis. Experiments in the department of dermatology and neurosurgery show that multispectral imaging reveals much more detail than conventional medical photography or a surgical microscope, as images can be reprocessed to enhance the view on e.g. tumor boundaries. Using a hardware-based interactive registration algorithm, multi-spectral images can be aligned to correct for motion occurred during image acquisition or to compare acquisitions from different moments in time. The system shows to be a powerful diagnostics tool for medical imaging in the visual and near IR range.

Physically realistic visualization of embedded volume structures for medical image data

When a volume structure is embedded in another volume structure, it is difficult to see the inner structure without destroying the view on the outer structure. We present a solution by letting the volume structures scatter light with a different wavelengths. The outer volume structure only absorbs light scattered by the structure itself and does not absorb the light scattered by the inner structure, by which the inner structure is visible without destroying the view on the outer structure. Examples are shown of vascular imaging, functional MRI, and CT imaging.