Thomas Wendler

Towards intra-operative 3D nuclear imaging: reconstruction of 3D radioactive distributions using tracked gamma probes

Nuclear medicine imaging modalities assist commonly in surgical guidance given their functional nature. However, when used in the operating room they present limitations. Pre-operative tomographic 3D imaging can only serve as a vague guidance intra-operatively, due to movement, deformation and changes in anatomy since the time of imaging, while standard intra-operative nuclear measurements are limited to 1D or (in some cases) 2D images with no depth information. To resolve this problem we propose the synchronized acquisition of position, orientation and readings of gamma probes intra-operatively to reconstruct a 3D activity volume. In contrast to conventional emission tomography, here, in a first proof-of-concept, the reconstruction succeeds without requiring symmetry in the positions and angles of acquisition, which allows greater flexibility. We present our results in phantom experiments for sentinel node lymph node localization. The results indicate that 3D intra-operative nuclear images can be generated in such a setup up to an accuracy equivalent to conventional SPECT systems. This technology has the potential to advance standard procedures towards intra-operative 3D nuclear imaging and offers a novel approach for robust and precise localization of functional information to facilitate less invasive, image-guided surgery.

First Deployments of Augmented Reality in Operating Rooms

Researchers are developing augmented reality visualization systems to provide accessible and user-friendly interfaces for medical intervention and patient information systems. A related video can be seen here: http://youtu.be/kifj0ZP4Mos. It shows how augmented reality visualization systems can provide accessible and user-friendly interfaces for medical intervention and patient information systems.

EndoTOFPET-US: a novel multimodal tool for endoscopy and positron emission tomography

The EndoTOFPET-US project aims to develop a multimodal detector to foster the development of new biomarkers for prostate and pancreatic tumors. The detector will consist of two main components: an external plate, and a PET extension to an endoscopic ultrasound probe. The external plate is an array of LYSO crystals read out by silicon photomultipliers (SiPM) coupled to an Application Specific Integrated Circuit (ASIC). The internal probe will be an highly integrated and miniaturized detector made of LYSO crystals read out by a fully digital SiPM featuring photosensor elements and digital readout in the same chip. The position and orientation of the two detectors will be tracked with respect to the patient to allow the fusion of the metabolic image from the PET and the anatomic image from the ultrasound probe in the time frame of the medical procedure. The fused information can guide further interventions of the organ, such as biopsy or in vivo confocal microscopy.

First Experiences with Navigated Radio-Guided Surgery Using Freehand SPECT

Background: Sentinel lymph node biopsy (SLNB) in melanoma using one-dimensional gamma probes is a standard of care worldwide. Reports on the performance are claimed by most groups to successfully detect the SLNs during the surgical procedure in almost 100% of the patients. In clinical practice, however, several issues remain which are usually not addressed: the difficulty of intraoperative detection of deeply located nodes, SLN detection in obese patients or in the groin and the impossibility to make a scan of the entire wound after SLN resection to avoid false negative testing for eventually remaining SLNs. Materials and Methods: The concept behind freehand SPECT is to combine a gamma probe as used for conventional radio-guided surgery with a tracking system as used in neurosurgical navigation. From this combination and a proper algorithm framework the 3D reconstruction of radioactivity distributions and displaying these intraoperatively is possible. Conclusion: In summary, the feasibility of freehand SPECT could be shown and provides an image-guided SLNB and a truly minimally invasive and optimized surgical procedure.

Real-time fusion of ultrasound and gamma probe for navigated localization of liver metastases

Liver metastases are an advanced stage of several types of cancer, usually treated with surgery. Intra-operative localization of these lesions is currently facilitated by intra-operative ultrasound (IOUS) and palpation, yielding a high rate of false positives due to benign abnormal regions. In this paper we present the integration of functional nuclear information from a gamma probe with IOUS, to provide a synchronized, real-time visualization that facilitates the detection of active metastases intra-operatively. We evaluate the system in an ex-vivo setup employing a group of physicians and medical technicians and show that the addition of functional imaging improves the accuracy of localizing and identifying malignant and benign lesions significantly. Furthermore we are able to demonstrate that the inclusion of an advanced, augmented visualization provides more reliability and confidence on classifying these lesions in the presented evaluation setup.

Navigated three dimensional beta probe for optimal cancer resection

In minimally invasive tumor resection, the desirable goal is to perform a minimal but complete removal of cancerous cells. In the last decades interventional nuclear medicine probes supported the detection of remaining tumor cells. However, scanning the patient with an intraoperative probe and applying the treatment are not done simultaneously. The main contribution of this work is to extend the one dimensional signal of a beta-probe to a four dimensional signal including the spatial information of the distal end of the probe. We generate a color encoded surface map of the scanned activity and guide any tracked surgical instrument back to the regions with measured activity. For navigation, we implement an augmented reality visualization that superimposes the acquired surface on a visual image of the real anatomy. Alternatively, a simulated beta-probe count rate in the tip of a tracked therapeutic instrument is simulated showing the count number and coding it as an acoustic signal. Preliminary tests were performed showing the feasibility of the new designed system and the viability of such a three dimensional intraoperative molecular imaging modality.

MR in OR: First analysis of AR/VR visualization in 100 intra-operative Freehand SPECT acquisitions

For the past two decades, medical Augmented Reality visualization has been researched and prototype systems have been tested in laboratory setups and limited clinical trials. Up to our knowledge, until now, no commercial system incorporating Augmented Reality visualization has been developed and used routinely within the real-life surgical environment. In this paper, we are reporting on observations and analysis concerning the usage of a commercially developed and clinically approved Freehand SPECT system, which incorporates monitor-based Mixed Reality visualization, during real-life surgeries. The workflow-based analysis we present is focused on an atomic sub-task of sentinel lymph node biopsy. We analyzed the usage of the Augmented and Virtual Reality visualization modes by the surgical team, while leaving the staff completely uninfluenced and unbiased in order to capture the natural interaction with the system. We report on our observations in over 100 Freehand SPECT acquisitions within different phases of 52 surgeries.

Toward (Hybrid) Navigation of a Fluorescence Camera in an Open Surgery Setting

With the introduction of the hybrid tracer indocyanine green (ICG)-99mTc-nanocolloid, a direct relation between preoperative imaging and intraoperative fluorescence guidance was established. However, fluorescence guidance remains limited by its superficial nature. This study evaluated the feasibility of a nuclear medicine–based navigation concept that allowed intraoperative positioning of a fluorescence camera (FC) in the vicinity of preoperatively defined ICG-99mTc-nanocolloid containing sentinel nodes (SNs). Methods: Five patients with penile cancer scheduled for SN biopsy were injected with ICG-99mTc-nanocolloid followed by preoperative SPECT/CT imaging. The navigation device was used to provide a real-time augmented reality overlay of the SPECT/CT images and video output of the FC. This overlay was then used for FC navigation. Results: SPECT/CT identified 13 SNs in 9 groins. FC navigation was successful for all 12 intraoperatively evaluated SNs (average error, 8.8 mm; range, 0–20 mm). Conclusion: This study reveals the potential benefits of FC navigation during open surgery procedures.

FhSPECT-US guided needle biopsy of sentinel lymph nodes in the axilla: is it feasible?

Until now, core needle biopsy of the axillary sentinel lymph nodes in early stage breast cancer patients is not possible, due to the lack of a proper combination of functional and anatomical information. In this work we present the first fully 3D freehand SPECT--ultrasound fusion, combining the advantages of both modalities. By using spatial positioning either with optical or with electromagnetic tracking for the ultrasound probe, and a mini gamma camera as radiation detector for freehand SPECT reconstructions, we investigate the capability of the introduced multi-model imaging system, where we compare both 3D freehand SPECT and 3D ultrasound to ground truth for a realistic breast mimicking phantom and further analyze the effect of tissue deformation by ultrasound. Finally, we also show its application in a real clinical setting.

First Robotic SPECT for Minimally Invasive Sentinel Lymph Node Mapping

In this paper we present the usage of a drop-in gamma probe for intra-operative Single-Photon Emission Computed Tomography (SPECT) imaging in the scope of minimally invasive robot-assisted interventions. The probe is designed to be inserted and reside inside the abdominal cavity during the intervention. It is grasped during the procedure using a robotic laparoscopic gripper enabling full six degrees of freedom handling by the surgeon. We demonstrate the first deployment of the tracked probe for intra-operative in-patient robotic SPECT enabling augmented-reality image guidance. The hybrid mechanical- and image-based in-patient probe tracking is shown to have an accuracy of 0.2 mm. The overall system performance is evaluated and tested with a phantom for gynecological sentinel lymph node interventions and compared to ground-truth data yielding a mean reconstruction accuracy of 0.67 mm.