Blood vessel detection in medical procedures using laser Doppler flowmetry

The needle procedures such as coronary angioplasty and coronary artery bypass graft installation are the most common surgical interventions performed in medical practice, and the accuracy of the catheter needle placement defines the success of the whole operation. Due to anatomical variations in patients, finding and puncturing the correct blood vessel is a challenging step, and the needle guidance might significantly simplify the process. Therefore, the primary aim of this work was to develop a novel blood vessel detection system based on laser Doppler flowmetry (LDF) technology that will improve the quality of medical needle procedures. In this work, LDF measurement setup was designed, assembled and evaluated. The setup includes custom laser-detector system, two invasive measurements probes, two experimental phantoms and data acquisition software. The optical properties of human tissue and blood were examined in order to define the required laser characteristics and relevant tissue-mimicking materials. The data processing was based on the power spectrum analysis, from which the perfusion parameter was extracted. The measurement range of the system was assessed in respect to the various criteria such as penetration angle, depth and site. The applicability of LDF in the needle procedures was evaluated. The experimental results demonstrated that the blood vessel can be successfully detected in the wide angles range and at different penetration sites. The differentiation between low and high blood flow speeds is also possible. Moreover, the potential of the measurements in tissue was demonstrated. However, certain limitations need to be addressed. It was discovered, that the distinction between the arteria and the vein is challenging, and the penetration depth inside the tissue is restricted. Nevertheless, the proposed technology can be implemented in the needle procedures and a number of other medical applications, such as laparoscopic surgeries and biopsies

Sensorisation of a novel biologically inspired flexible needle

Percutaneous interventions are commonly performed during minimally invasive brain surgery, where a straight rigid instrument is inserted through a small incision to access a deep lesion in the brain. Puncturing a vessel during this procedure can be a life-threatening complication. Embedding a forward-looking sensor in a rigid needle has been proposed to tackle this problem; however, using a rigid needle, the procedure needs to be interrupted if a vessel is detected. Steerable needle technology could be used to avoid obstacles, such as blood vessels, due to its ability to follow curvilinear paths, but research to date was lacking in this respect. This thesis aims to investigate the deployment of forward-looking sensors for vessel detection in a steerable needle. The needle itself is based on a bioinspired programmable bevel-tip needle (PBN), a multi-segment design featuring four hollow working channels. In this thesis, laser Doppler flowmetry (LDF) is initially characterised to ensure that the sensor fulfils the minimum requirements for it to be used in conjunction with the needle. Subsequently, vessel reconstruction algorithms are proposed. To determine the axial and off-axis position of the vessel with respect to the probe, successive measurements of the LDF sensor are used. Ideally, full knowledge of the vessel orientation is required to execute an avoidance strategy. Using two LDF probes and a novel signal processing method described in this thesis, the predicted possible vessel orientations can be reduced to four, a setup which is explored here to demonstrate viable obstacle detection with only partial sensor information. Relative measurements from four LDF sensors are also explored to classify possible vessel orientations in full and without ambiguity, but under the assumption that the vessel is perpendicular to the needle insertion axis. Experimental results on a synthetic grey matter phantom are presented, which confirm these findings. To release the perpendicularity assumption, the thesis concludes with the description of a machine learning technique based on a Long Short-term memory network, which enables a vessel's spatial position, cross-sectional diameter and full pose to be predicted with sub-millimetre accuracy. Simulated and in-vitro examinations of vessel detection with this approach are used to demonstrate effective predictive ability. Collectively, these results demonstrate that the proposed steerable needle sensorisation is viable and could lead to improved safety during robotic assisted needle steering interventions.Open Acces

A long short-term memory network for vessel reconstruction based on laser doppler flowmetry via a steerable needle

Hemorrhage is one risk of percutaneous intervention in the brain that can be life-threatening. Steerable needles can avoid blood vessels thanks to their ability to follow curvilinear paths, although knowledge of vessel pose is required. To achieve this, we present the deployment of laser Doppler flowmetry (LDF) sensors as an in-situ vessel detection method for steerable needles. Since the perfusion value from an LDF system does not provide positional information directly, we propose the use of a machine learning technique based on a Long Short-term Memory (LSTM) network to perform vessel reconstruction online. Firstly, the LSTM is used to predict the diameter and position of an approaching vessel based on successive measurements of a single LDF probe. Secondly, a "no-go" area is predicted based on the measurement from four LDF probes embedded within a steerable needle, which accounts for the full vessel pose. The network was trained using simulation data and tested on experimental data, with 75 % diameter prediction accuracy and 0.27 mm positional Root Mean Square (RMS) Error for the single probe network, and 77 % vessel volume overlap for the 4-probe setup

Intraoperative detection of blood vessels with an imaging needle during neurosurgery in humans

Intracranial hemorrhage can be a devastating complication associated with needle biopsies of the brain. Hemorrhage can occur to vessels located adjacent to the biopsy needle as tissue is aspirated into the needle and removed. No intraoperative technology exists to reliably identify blood vessels that are at risk of damage. To address this problem, we developed an “imaging needle” that can visualize nearby blood vessels in real time. The imaging needle contains a miniaturized optical coherence tomography probe that allows differentiation of blood flow and tissue. In 11 patients, we were able to intraoperatively detect blood vessels (diameter, \u3e500 μm) with a sensitivity of 91.2% and a specificity of 97.7%. This is the first reported use of an optical coherence tomography needle probe in human brain in vivo. These results suggest that imaging needles may serve as a valuable tool in a range of neurosurgical needle interventions

Historical reviews of the assessment of human cardiovascular function: interrogation and understanding of the control of skin blood flow.

Several techniques exist for the determination of skin blood flow that have historically been used in the investigation of thermoregulatory control of skin blood flow, and more recently, in clinical assessments or as an index of global vascular function. Skin blood flow measurement techniques differ in their methodology and their strengths and limitations. To examine the historical development of techniques for assessing skin blood flow by describing the origin, basic principles, and important aspects of each procedure and to provide recommendations for best practise. Venous occlusion plethysmography was one of the earliest techniques to intermittently index a limb's skin blood flow under conditions in which local muscle blood flow does not change. The introduction of laser Doppler flowmetry provided a method that continuously records an index of skin blood flow (red cell flux) (albeit from a relatively small skin area) that requires normalisation due to high site-to-site variability. The subsequent development of laser Doppler and laser speckle imaging techniques allows the mapping of skin blood flow from larger surface areas and the visualisation of capillary filling from the dermal plexus in two dimensions. The use of iontophoresis or intradermal microdialysis in conjunction with laser Doppler methods allows for the local delivery of pharmacological agents to interrogate the local and neural control of skin blood flow. The recent development of optical coherence tomography promises further advances in assessment of the skin circulation via three-dimensional imaging of the skin microvasculature for quantification of vessel diameter and vessel recruitment

OPTICAL COHERENCE TOMOGRAPHY FOR NEUROSURGEY AND CANCER RESEARCH

Optical Coherence Tomography (OCT) provides non-labeling, real-time and high resolution images, which has the potential to transform the paradigm of surgical guidance and preclinical animal studies. The design and development of OCT devices for neurosurgery guidance and novel imaging algorithms for monitoring anti-cancer therapy have been pursued in this work. A forward-imaging needle-type OCT probe was developed which can fit into minimally invasive tools (I.D. ~ 1mm), detect the at-risk blood vessels, and identify tissue micro-landmarks. This promising guidance tool improves the safety and the accuracy of needle-based procedures, which are currently performed without imaging feedback. Despite the great imaging capability, OCT is limited by the shallow imaging depth (1-2 mm). In order to address this issue, the first MRI compatible OCT system has been developed. The multi-scale and multi-contrast MRI/OCT imaging combination significantly improves the accuracy of intra-operative MRI by two orders (from 1mm to 0.01 mm). In contrast to imaging systems, a thin (0.125 mm), low-cost (1/10 cost of OCT system) and simple fiber sensor technology called coherence gated Doppler (CGD) was developed which can be integrated with many surgical tools and aid in the avoidance of intracranial hemorrhage. Furthermore, intra-vital OCT is a powerful tool to study the mechanism of anti-cancer therapy. Photo-immunotherapy (PIT) is a low-side-effect cancer therapy based on an armed antibody conjugate that induces highly selective cancer cell necrosis after exposure to near infrared light both in vitro and in vivo. With novel algorithms that remove the bulk motion and track the vessel lumen automatically, OCT reveals dramatic hemodynamic changes during PIT and helps to elucidate the mechanisms behind the PIT treatment. The transformative guidance tools and the novel image processing algorithms pave a new avenue to better clinical outcomes and preclinical animal studies

Effects of anaesthesia on haemodynamics and metabolism in horses

Complications related to the musculo-skeletal system (fractures and post-anaesthetic myopathy; PAM) after anaesthesia are more common in the horse than in other species. PAM has been shown to be related to hypotension during anaesthesia, which results in hypoperfusion of the muscle and probably hypoxia or ischaemia. In the present study peripheral perfusion in relation to central circulation was investigated during anaesthesia and in response to pharmacological provocations and during different modes of ventilation. The muscle metabolic response to anaesthesia was also evaluated. The effect of severe illness (colic) on metabolic parameters was studied before, during and after anaesthesia. Peripheral perfusion was assessed using laser Doppler flowmetry (LDF), and central circulation by conventional techniques. Muscle metabolism was studied with microdialysis, analysis of muscle biopsy specimens and biochemical markers in venous blood samples. Peripheral perfusion was more closely related to cardiac output than to arterial blood pressure. Compared to spontaneous breathing, intermittent positive-pressure ventilation negatively affected both central and peripheral perfusion. Central circulation was better preserved but respiration was more depressed during propofol-ketamine anaesthesia than during isoflurane anaesthesia. In clinically healthy horses both inhalation anaesthesia and propofol-ketamine anaesthesia were associated with an anaerobic metabolic response characterised by increased lactate in plasma, muscle and dialysate and in some cases by decreased muscle phosphagen stores. No muscle metabolic differences were detected between the dependent and non-dependent muscles (muscle biopsy and microdialysis) during lateral recumbency. Many colic horses entered anaesthesia with profoundly affected metabolism and activation of both the carbohydrate and lipid metabolic pathways due to increased sympathetic output resulting from pain and insufficient circulation. The content of ATP in these horses was low at start of anaesthesia but anaesthesia did not further deteriorate the metabolic stress. Horses that died or were euthanised at an early stage had the highest concentrations of lactate in plasma, muscle and dialysate before and during anaesthesia. During the first week after anaesthesia the metabolism and electrolyte balance were affected in both healthy and colic horses, but to a greater extent in colic horses

Primary Aging: Thermoregulatory Sweating & Skin Blood Flow

Heat related morbidities and mortalities are disproportionately high in the aged population(=60 yr). Aging without overt illness is associated with the attenuation of heat dissipationmechanisms including cutaneous vasodilation and eccrine sweating responses. These agerelateddecrements in thermoregulatory function are well represented in literature discussingheat dissipation, yet despite attempts to investigate a potential signaling mechanismbetween sweating and skin blood flow (SkBF), a functional link has not beendemonstrated. Recent evidence supports a role of nitric oxide (NO), a potent signalingmolecule in cutaneous vasodilation, as additionally signaling the eccrine sweatingresponse. The aim of this study was to investigate the putative role of NO in eccrine sweatgland signaling in young and primary aged individuals. Prior to experimentation, pilotstudies were conducted to develop experimental drug dilutions to achieve a successful flowmatching protocol. In two subjects, three intradermal microdialysis (MD) probes wereinserted into the left ventral forearm and perfused with 1) Lactated Ringer’s solution, 2)Epoprostenol sodium (EPO) + NG-Nitro-L-arginine (L-NNA), and 3) Sodium Nitroprusside(SNP) + L-NNA. Regional sweating rates (RSR) over each MD membrane were measuredusing ventilated capsules with a laser Doppler probe housed in each capsule formeasurement of red cell flux (laser Doppler flux, LDF) and divided by mean arterial bloodpressure (Cutaneous vascular conductance (CVC) = LDF/MAP) as an index ofSkBF. Subjects completed a whole body heating protocol to a 1°C rise in sublingualtemperature. Maximal CVC values were obtained pharmacologically at the end of eachprotocols using 25 mM SNP. During whole body heating in the second pilot, the L-NNA/EPOsite displayed lower levels of CVC than the control site, implying the EPO had becomeinactive. A buffer solution was created to maintain EPO stability at physiological pH. Thenext steps are to complete pilot tests with EPO in buffer to ensure it remains active and toachieve a successful flow matching protocol before beginning the sweating study

The development and testing of an artificial anal sphincter

The physiological mechanisms for achieving fecal continence and the results of the surgical methods to correct incontinence are reviewed. The devices hitherto designed to attempt to achieve continence artificially are discussed and an analysis of 4130 reported complications of a successful device for the control of urinary incontinence (the AMS 800) are presented. Based on these reviews, the need to design and evaluate a prosthetic anal sphincter is identified and such a device is presented in this thesis.The effect of circumferential occlusive pressure on the blood flow of porcine colon was assessed by a Laser Doppler flow meter. It was demonstrated that distal blood flow is reduced by 50% at 52 mmHg. The occlusion pressure required to achieve continence to semi-solids was shown to be reduced by the introduction of angulation both in a theoretical model and experimentally, using a specifically designed fecal substitute.The Neosphincter was, therefore, designed to simulate the normal physiology of the anorectum by closing and angulating the bowel without causing crenation and ischaemia.The design parameters of the device were evaluated in an in-vitro model and its placement assessed in a series of acute animal experiments in a porcine model. The effects of the prosthesis set at an operating occlusion pressure of 33-45 mmHg were then evaluated in survival animal experiments by implantation in Yucatan minipigs for up to 20 weeks. The device produced fecal continence in 85% of the activation times without causing ischaemic injury. Mechanical complications associated with the control pump were encountered and design faults were identified. A new pump was designed by the author.The effect of Neosphincter function on blood flow distribution in the human colon was studied during colectomy using a prototype Laser Doppler flow scanner. Blood flow remained greater than 50% at 60 mmHg occlusion pressure.d flow remained greater than 50% at 60 mmHg occlusion pressure. The data presented show that the Neosphincter achieves continence in the mini-pig model and further suggest that continence would be achieved in the human without producing intestinal ischaemia. Ethical approval has been obtained to proceed to trials in human patients

Free Flap Monitoring. Using Tissue Oxygen Measurement and Positron Emission Tomography

Aims:This study was carried out to evaluate the feasibility of two different methods to determine free flap perfusion in cancer patients undergoing major reconstructive surgery. The hypotheses was that low perfusion in the flap is associated with flap complications. Patients and methods: Between August 2002 and June 2008 at the Department of Otorhinolaryngology – Head and Neck Surgery, Department of Surgery, and at the PET Centre, Turku, 30 consecutive patients with 32 free flaps were included in this study. The perfusion of the free microvascular flaps was assessed with positron emission tomography (PET) and radioactive water ([15O] H2O) in 40 radiowater injections in 33 PET studies. Furthermore, 24 free flaps were monitored with a continuous tissue oxygen measurement using flexible polarographic catheters for an average of three postoperative days. Results: Of the 17 patients operated on for head and neck (HN) cancer and reconstructed with 18 free flaps, three re-operations were carried out due to poor tissue oxygenation as indicated by ptiO2 monitoring results and three other patients were reoperated on for postoperative hematomas in the operated area. Blood perfusion assessed with PET (BFPET) was above 2.0 mL / min / 100 g in all flaps and a low flap-to-muscle BFPET ratio appeared to correlate with poor survival of the flap. Survival in this group of HN cancer patients was 9.0 months (median, range 2.4-34.2) after a median follow-up of 11.9 months (range 1.0-61.0 months). Seven HN patients of this group are alive without any sign of recurrence and one patient has died of other causes. All of the 13 breast reconstruction patients included in the study are alive and free of disease at a median follow-up time of 27.4 months (range 13.9-35.7 months). Re-explorations were carried out in three patients due data provided by ptiO2 monitoring and one re-exploration was avoided on the basis of adequate blood perfusion assessed with PET. Two patients had donorsite morbidity and 3 patients had partial flap necrosis or fat necrosis. There were no total flap losses. Conclusions: PtiO2 monitoring is a feasible method of free flap monitoring when flap temperature is monitored and maintained close to the core temperature. When other monitoring methods give controversial results or are unavailable, [15O] H2O PET technique is feasible in the evaluation of the perfusion of the newly reconstructed free flaps.Siirretty Doriast