Michael Friebe

Magnetic Resonance-Guided Angioplasty With Delivery of Contrast-Media Doped Solutions to the Vessel Wall : An Experimental Study in Swine

Objectives:To assess the feasibility of magnetic resonance (MR)-guided delivery of a solution containing contrast-medium and immediate online monitoring of its distribution to the vessel wall during MR-guided angioplasty in peripheral arteries. Materials and Methods:In 3 pigs, the feasibility of MR-guided atraumatic delivery of a solution containing contrast-medium and tissue dye (0.05 mmol/mL Gd-DTPA, 3% Evans blue dye) into the vessel wall of the iliac arteries was tested using a permeable balloon catheter (8 mm). Catheter placement was monitored using a steady-state free precession real-time imaging sequence. Additionally, in 5 pigs, surgically created bilateral stenoses in the external iliac artery were dilatated with the porous balloon. In these animals, contrast-enhanced MR angiography was performed before and after the interventions to assess the degree of the stenosis. In all animals, the vessel wall was delineated before and after dilatation using a T1-weighted gradient echo (GE) sequence. Results:In the 3 animals without stenosis, contrast medium was successfully applied to the vessel wall. On the GE images, the normalized signal intensity of the vessel wall was 0.95 ± 0.015 arbitrary units (a. u.) prior and 2.15 ± 0.105 a. u. after the intervention (P < 0.01). In the animals with stenosis, MR angiography performed before and after the intervention demonstrated successful dilatation of 9 of the 10 stenoses. Before the intervention, 7 stenoses were severe (76%–99%) and 3 moderate (50%–75%), and after the intervention, 4 stenoses were completely removed and 5 mild (<50%). Also in these 5 animals, the solution was visible in the vessel wall of the arteries on the T1-weighted GE MR images (normalized signal intensity prior the intervention 1.33 ± 0.16 a. u. and 2.97 ± 0.23 after angioplasty; P < 0.05). Histology demonstrated the distribution of the Evans blue dye within the vessel wall in all animals. Conclusions:MR-guided delivery of a contrast-medium containing solution and immediate online assessment of its distribution to the vessel wall during angioplasty in peripheral arteries is feasible.

Combination of intra-operative freehand SPECT imaging with MR images for guidance and navigation

Nowadays for clinical applications such as sentinel lymph node biopsy in breast or prostate cancer, only pre-operative image data is used for navigation, i.e. CT, SPECT/CT or PET/CT. Freehand SPECT and freehand PET provide intra-operative functional imaging techniques that can be complemented with pre- and intra-operative MR imaging to allow for better planning, navigation and guidance. In this paper we propose a method to enable navigation based on pre- or intra-operatively acquired MR images. A fully MR compatible phantom and a dedicated MR compatible optical tracking target with MR markers is built for this study. PET/MR, SPECT/CT and freehand SPECT scans of the phantom are performed. Registration is done using point based registration of the known marker and target geometries and a ground truth is obtained from a SPECT/CT and an MR image that are directly registered. The RMS errors was 0.31mm for the ground truth and 3.29mm when using segmentation of the MR markers and their spatial relationship with the optical tracking spheres of the dedicated target. Thus, the freehand SPECT can be registered easily by this approach without the need of any additional CT scans and therefore without any additional radiation dose for the patient. This enables intra-operative fusion of the pre- or intra-operatively acquired MR data, which could provide valuable additional information for intra-operative applications such as guidance based on accurate anatomy or verifying exact tumor location in combination with detailed morphological patient data.

Advanced inside-out tracking approach for real-time combination of MRI and US images in the radio-frequency shielded room using combination markers

For the real-time fusion of different modalities, a variety of tracking methods are available including the optical, electromagnetic (EM) and image-based tracking. But as a drawback optical tracking suffers from line of sight issues and EM tracking requires the manual referencing for the fusion procedure and is not usable in Magnetic Resonance Imaging (MRI) environment. To avoid these issues, we propose a real-time setup containing a camera capable of inside-Out tracking using combined circular markers attached to Ultrasound (US) probe and a suitable platform for automatic overlay of MRI and US image using markers. This new approach could help clinicians carry out successful surgical procedures by requiring least system interaction and solving line of sight issues. As a proof-of-concept, we show our first result by mimicking common liver tumor intervention using framed marker fusion technique in a candle gel phantom. We evaluated the tracking error distances using the combination of special markers with Inside-Out approach and conventional optical tracking. The results achieved show comparable performance to the standard Outside-In tracking and manual reference approach, while easing the interventional procedure in terms of hardware and line of sight requirements.

3D segmentation of thyroid ultrasound images using active contours

Abstract In this paper, we propose a method to segment the thyroid from a set of 2D ultrasound images. We extended an active contour model in 2D to generate a 3D segmented thyroid volume. First, a preprocessing step is carried out to suppress the noise present in US data. Second, an active contour is used to segment the thyroid in each of the 2D images. Finally, all the segmented thyroid images are passed to a 3D reconstruction algorithm to obtain a 3D model of the thyroid. We obtained an average segmentation accuracy of 86.7% in six datasets with a total of 703 images.

Inside-Out access strategy using new trans-vascular catheter approach

Abstract Image guided minimal invasive treatment can have large benefits for patient recovery and is lowering hospitalisation costs. But an access path, minimizing patient’s risk, is needed to reach the target structure inside of the body. Beside the use of natural orifices like oral, vaginal or anal cavities, a percutaneous puncture is common to enter the body. Also an interstitial path can be selected but if the pathological structure is situated in the deep, a long accesses path is required. Thereby the risk of additional damage and affecting organ functionality is increased. A possible option to come closer to the target structure with less organ damage is by using the vascular system. Entering the vessel from an uncritical point, the vasculature can be used as “highway” to the target structures. For the treatment of these nearby structures, the vessel has to be punctured and occluded afterwards by a save procedure. We propose an Inside-Out access strategy using a new trans-vascular catheter approach.

Novel clinical device tracking and tissue event characterization using proximally placed audio signal acquisition and processing

We propose a new and complementary approach to image guidance for monitoring medical interventional devices (MID) with human tissue interaction and surgery augmentation by acquiring acoustic emission data from the proximal end of the MID outside the patient to extract dynamical characteristics of the interaction between the distal tip and the tissue touched or penetrated by the MID. We conducted phantom based experiments (n = 955) to show dynamic tool/tissue interaction during tissue needle passage (a) and vessel perforation caused by guide wire artery perforation (b). We use time-varying auto-regressive (TV-AR) modelling to characterize the dynamic changes and time-varying maximal energy pole (TV-MEP) to compute subsequent analysis of MID/tissue interaction characterization patterns. Qualitative and quantitative analysis showed that the TV-AR spectrum and the TV-MEP indicated the time instants of the needle path through different phantom objects (a) and clearly showed a perforation versus other generated artefacts (b). We demonstrated that audio signals acquired from the proximal part of an MID could provide valuable additional information to surgeons during minimally invasive procedures.

In-room ultrasound fusion combined with fully compatible 3D-printed holding arm – rethinking interventional MRI

There is no real need to discuss the potential advantages – mainly the excellent soft tissue contrast, nonionizing radiation, flow, and molecular information – of magnetic resonance imaging (MRI) as an intraoperative diagnosis and therapy system particularly for neurological applications and oncological therapies. Difficult patient access in conventional horizontal-field superconductive magnets, very high investment and operational expenses, and the need for special nonferromagnetic therapy tools have however prevented the widespread use of MRI as imaging and guidance tool for therapy purposes. The interventional use of MRI systems follows for the last 20+ years the strategy to use standard diagnostic systems and add more or less complicated and expensive components (eg, MRI-compatible robotic systems, specially shielded in-room monitors, dedicated tools and devices made from low-susceptibility materials, etc) to overcome the difficulties in the therapy process. We are proposing to rethink that approach using an in-room portable ultrasound (US) system that can be safely operated till 1 m away from the opening of a 3T imaging system. The live US images can be tracked using an optical inside–out approach adding a camera to the US probe in combination with optical reference markers to allow direct fusion with the MRI images inside the MRI suite. This leads to a comfortable US-guided intervention and excellent patient access directly on the MRI patient bed. This was combined with an entirely mechanical MRI-compatible 7 degrees of freedom holding arm concept, which shows that this test environment is a different way to create a cost-efficient and effective setup that combines the advantages of MRI and US by largely avoiding the drawbacks of current interventional MRI concepts.

Proximally placed signal acquisition sensoric for robotic tissue tool interactions

Abstract Robotic surgeries are still limited with respect to the surgeon’s natural senses. The tactile sense is exceptional important in conventional clinical procedures. To identify critical structures inside the tissue, palpation is a commonly used technique in conventional open surgeries. The underlying organ or pathological structures conditions (healthy, abnormally hard or soft) can for example be localized and assessed through this process. Palpation needs a tactile sense; however, that is commonly not available or limited in robotic surgeries. The palpation need was already addressed by several research groups that integrated complex sensor-feedback-systems into prototype surgical instruments for robotic systems. We propose a new technique to acquire data of the tissue tool interaction of the surgical instruments. The structure borne transmission path is used to measure acoustic emission (AE) at the outpatient (proximal) end of the instruments with the help of different sensors attached to the surface of the surgical tool. Initial tests were performed using a microphone in combination with a stethoscope. This setup showed promising results and a more integrated prototype was subsequently designed. A piezoelectric charge accelerometer was used as vibration sensor and compared to a MEMS microphone. A signal acquisition system was developed to acquire signals from both sensors in parallel. The sensors were then attached onto the shaft of a daVinci Prograsp Forceps instrument. According to the surgery observation, a series of simulated experiments was conducted. The tip of the grasper was swiped manually over a human subject’s dorsal and palmar hand side, lateral side of neck and over the carotid artery. Additionally, contact with soft tissue and other instruments were evaluated since these are events of interest during surgery. Advanced signal processing techniques allowed the identification and characterization of significant events such as palpation dynamics, contact and pulsation. Signals acquired by the MEMS microphone showed the most promising results. This approach will now be used to build a prototype for further evaluation in a clinical setup. The paper presents the first results that show that this novel technique can provide valuable information about the tool-tissue interaction in robotic surgery that typically can only be obtained through advanced distal sensor systems or actual human touch.

Conceptual design of a personalized radiation therapy patch for skin cancer

Abstract Radiation therapy is a valuable option for treatment of skin cancer. In order to deliver the radiation dose to the superficial skin tumor, an X-ray source, electron beam radiation therapy or a radioisotope is applied. The effectiveness of these procedures is well established in the literature. Findings of some recent studies have indicated that beta particles can be of particular interest in suppressing skin tumor growth. Betaemitting radioisotopes are favorable because of the short penetration depth of their emitted particles. Beta radiation can induce significant damage in superficial skin tumor, and at the same time, result in enhanced protection of the underlying healthy tissues. In this study, we propose the design of a patch that can be used in beta radiation therapy of skin cancer patients. For that, we describe the components of this radioactive patch, as well as a proposal for the subsequent clinical application procedure. A scaffold was used as a substrate for embedding the desired beta-emitting radioisotope, and two layers of hydrogel to provide protection and shielding for the radioactively labelled scaffold. The proposed design could provide a universal platform for all beta-emitting radioisotopes. Depending on the depth of the tumor spread, a suitable beta emitter for that specific tumor can be selected and used. This is of particular and critical importance in cases where the tumor is located directly on top of the bone and for which the depth of penetration of radiation should be limited to only the tumor volume. The proposed design has the mechanical flexibility to adapt to curved body regions so as to allow the use in anatomically challenging areas of the body.

Flexible interventional imaging system based on miniaturized X-ray tubes (FlexScan)

Abstract In orthopedic hand surgeries C-arms are the standard imaging modalities for procedure and tool guidance. However, the currently used systems have a large footprint and high weight, which can lead to workspace restrictions and difficult positioning of the device at the desired imaging position. The aim of this paper is to present a prototype of a new, flexible, lightweight and small footprint X-ray system, which is capable to create 2D projection images from different orientations. The new design includes a miniaturized Xray tube covered in a custom-made case mounted on a flexible holding arm attached to the standard OR table rail. With that, fast positioning and fixation for the subsequent image acquisition is achieved. A flat panel detector is placed in an adjustable metal sheet construction below the table. For safety aspects an overlay of the X-ray cone beam with an integrated light source visualizes the irradiation area. The acquired images are visualized on a 2-in-1 netbook. A foot pedal initiates the imaging process. A prototype of the free movable miniaturized X-ray system FlexScan was build. Workspace restriction, usability and general imaging needs were simulated and tested. FlexScan has the potential to improve X-ray guided interventions on extremities especially for small private surgery centers. It fulfills the general imaging needs and is capable of producing 2D projection images from different orientations within a small and lightweight setup.