Intra-operative optical monitoring of bowel tissue viability based on photoplethysmography and laser doppler flowmetry

Determination of bowel viability in patients undergoing bowel resection is essential in gastrointestinal surgery. One of the most common operations in gastrointestinal surgery is bowel resection for patients who have different kinds of bowel cancer or any other occlusion in which anastomosis has to be carried out following the removal of an unhealthy segment of the bowel. Monitoring blood flow in abdominal surgery especially intraoperatively would be a valuable tool for prevention of a postoperative anastomosis complication (e.g. anastomotic leak, which is the main complication after colorectal resection). The development of a continuous method for monitoring perfusion of bowel tissue would assist in early detection of inadequate blood supply which then help to reduce the occurrence of an anastomosis complication. Although various monitoring techniques have been proposed to assess intestinal viability intraoperatively, none of these techniques have proved to be reliable enough to replace visual observation. Therefore, to date there is no widely accepted and readily available intraoperative technique to reliably assess the viability of bowel tissue. The aim of this study was to combine the established techniques, laser Doppler flowmetry (LDF) and Photoplethysmography (PPG), into one probe intended for assessment of perfusion in abdominal tissue during bowel resection intraoperatively. In PPG, changes in transmission of light through tissue due to pulsation of small arteries can be monitored whereas in LDF microcirculatory blood cell velocity and flux can be studied. Such a probe could alert the surgeon immediately of any compromise in blood flow so further investigation and, if necessary, therapeutic steps can be applied immediately to prevent severe consequences. Therefore, custom reflectance PPG along with LDF sensor was designed and built in the form of a probe to investigate the changes in blood volume, blood flow and arterial oxygen saturation in patients undergoing bowel resection. The instrumentation was designed successfully and the data was saved for the further analysis. Twenty-four patients undergoing bowel resection were recruited for monitoring of perfusion and blood flowintraoperatively; twenty had undergone laparoscopy and the remainder had a laparotomy operation. Eight different measurements were performed during each trial. The results revealed that the probe could be an indicator of evaluating perfusion and blood flow changes at different stages of the surgery. The results also suggest that laser Doppler is more sensitive to artefact compared to PPG. Differences in amplitude of PPG between different measurements reveal that the sensor does detect changes in blood volume and flow confirming that it has the ability to verify that pulsatile flow is being preferentially preserved at the last step of the resection procedure (at the edges of the anastomosis sites after anastomosis is been constructed

Kolmiulotteinen lämpötilamittaus protoniresonanssin avulla

Proton resonance frequency (PRF), by which it precesses in the magnetic field, alters due to change in temperature, which can be detected with magnetic resonance imaging (MRI). MRI scanner uses protons’ nuclear magnetic resonance phenomenon. The target is first excited with a radio frequency pulse, then its relaxation to initial stage is observed. Parts with different temperatures can be mapped according to the characteristics of the signal they emit during relaxation. PRF thermometry is recognized as the best method to study in vivo temperature distribution with MRI scanner. PRF thermometry is favored due to a good large scale linearity and tissue independence. When tissue containing water is heated, the hydrogen bonds between water molecules are soften as a result of increased Brownian motion. When hydrogen bonds are weaker, the magnetic shielding from electron cloud around proton is stronger. Now that the magnetic shielding is stronger, the local magnetic field of that proton is weakened. Lower magnetic field leads to lower proton nuclear magnetic resonance. Change in nuclear magnetic resonance can be detected with phase difference mapping as a phase shift in phase images with MRI scanner. Noninvasiveness is universally justified in clinical medicine. Diseases and tumors in living tissues can be noninvasively treated with hyper- or hypothermia. Abnormal situations can be detected by observing the temperature changes in the body. MRI scanner can be used to examine tissue temperatures during temperature treatments. Temperature mapping can also be used to monitor unwanted tissue heating related to MRI examinations. The purpose of this thesis is to produce volumetric thermometry data with proton resonance, and to optimize the imaging parameters in order to achieve the best signal-to-noise ratio for magnetic resonance thermometry.Protonin resonanssitaajuus (PRF), jolla se prekessoi magneettikentässä, muuttuu lämpötilan muutoksen johdosta, joka voidaan nähdä magneettikuvauslaitteen avulla. Magneettikuvauslaite käyttää hyväkseen protonien ydinmagneettista ilmiötä. Kohdetta viritetään ensin radiotaajuuspulssilla, jonka jälkeen seurataan sen palautumista alkutilaan. Eri lämpöiset alueet kohteessa voidaan kartoittaa niiden lähettämän eri taajuisen signaalin avulla palautumisen aikana. PRF muutos on tunnustettu parhaaksi menetelmäksi seurattaessa elävien kudosten sisäisiä lämpötilaeroja magneettikuvauslaitteen avulla. Etuna PRF menetelmässä toisiin magneettikuvauksen avulla tehtäviin lämpömittausmenetelmiin on sen hyvä lineaarisuus laajalla mittausalueella, ja riippumattomuus kudostyypistä. Kun vettä sisältävä kudos lämpenee, siinä olevien vesimolekyylien väliset vetysidokset heikkenevät lisääntyvän lämpöliikkeen vuoksi. Kun vetysidokset heikkenevät, kasvaa veden protonien ympärillä olevien elektronipilvien magneettinen suojaus. Kun magneettinen suojaus kasvaa, kokee protoni magneettikuvauslaitteen magneettikentän paikallisesti heikompana. Kun paikallisesti koettu magneettikenttä on heikompi, on myös protonin resonanssitaajuus pienempi. Tämä havaitaan magneettikuvauslaitteen vaihekuvissa vaihe-erona. Vaihemuutoskartan avulla voidaan kartoittaa kohteen lämpötilaeroja. Minimaalinen kajoamattomuus on yleisesti perusteltua lääketieteellisissä hoidoissa. Kehon lämpötilamuutosten avulla saadaan tietoa kehon anomaalisista tiloista. Elävissä kudoksissa olevia tauteja ja kasvaimia voidaan hoitaa kajoamattomasti lämpö- ja kylmäterapialla. Magneettikuvauslaitteella voidaan seurata kudosten lämpötilaa hoitojen aikana, sekä kartoittaa kehon poikkeavia lämpötilaeroja. Vaihekartoituksen avulla voidaan seurata myös magneettikuvaukseen liittyvää kudosten lämpenemistä. Tämän työn tavoitteena on muodostaa lämpötilatietoa kuvaava tilavuuskartta protonin resonanssitaajuuteen perustuvalla menetelmällä, ja optimoida kuvausparametrejä parhaan signaalikohinasuhteen saavuttamiseksi lämpötilamittauksen osalta

Towards application of thermal infrared imaging in medical diagnosis: protocols and investigations

This thesis ‘Thermal Infrared Imaging: Advancement for Clinical Applications’ documents a series of clinical and laboratory investigations into: development and application of protocols for objective acquisition and processing of clinical TIRI image data, characterisation of human tissue emissivity within clinically-relevant regimes, and use of thermal infrared imaging to determine the depth of subcutaneous heat sources. This work was supported by the Australian Defence Science & Technology Organisation, Western Australian Department of Health, and Flir Systems

UNDERSTANDING ANATOMICAL PERFUSION AND STRATEGIES TO OPTIMIZE VASCULARITY IN FREE TISSUE TRANSFER FOR AUTOLOGOUS BREAST RECONSTRUCTION USING THE DEEP INFERIOR EPIGASTRIC ARTERY PERFORATOR (DIEP) FLAP

Breast cancer is the commonest cancer that affects women in the United Kingdom (UK). Autologous free tissue transfer using abdominal tissue remains an excellent option for breast reconstruction following mastectomy, given greater availability of tissue and lower donor site morbidity associated with muscle-sparing approaches (perforator-based). This research evaluated microvascular anatomy of Deep Inferior Epigastric Artery Perforator (DIEP) flaps, the role of linking vessels on dynamic perfusion in bilateral breast reconstruction and strategies to augment flap vascularity. For the ex-vivo anatomical studies, three and four-dimensional computed tomographic angiography (CTA) were used to evaluate patterns of the microvascular blood supply of individual perforators and corresponding perfusion patterns in the hemi-abdomen. This was combined with an in-vivo clinical study of women undergoing bilateral DIEP breast reconstruction following mastectomy, where both preoperative CTA and intra-operative Laser-Assisted Indocyanine Green Fluorescence Angiography (LA-ICGFA) were used to evaluate perforator anatomy and dynamic perfusion zones of individual perforators. Finally, an experimental in-vivo animal model was used to investigate strategies of pretreatment of perforator flaps with negative pressure wound therapy to augment vascularity of perforator flaps prior to flap harvest. The vascular territories of individual perforator within hemi-DIEP flaps demonstrated variable patterns with unique patterns of perfusion. Concepts including early capture of large calibre direct linking vessels to adjacent perforators or the superficial inferior epigastric artery (SIEA) territories, mostly found in the supra-scarpa’s and subdermal layers of the flap, played a key role in defining overall perfusion area and dynamic perfusion patterns not previously described. In conclusion, this work reported the characterization of the microvasculature within abdominal based perforator flaps to better understand the variation in dynamic perfusion. It also explored the potential role of non-invasive negative pressure treatment to augment flap perfusion that may be translated into the clinical setting.Royal College of Surgeons of England Blond Research Fellowship Restoration of Appearance and Function Trust (RAFT) U

The development of biomedical instrumentation using backscattered laser light

This thesis is concerned with the measurement of blood flow and oxygen saturation in the microcirculation using the techniques of laser Doppler flowmetry and pulse oximetry. An investigation of the responses of Doppler flowmeters using different signal processing bandwidths and laser sources revealed two major findings. Firstly, that careful choice of processing bandwidth is required in order to sample the whole range of possible Doppler frequencies present in the backscattered light. Secondly, that the choice of laser source is important in governing the output stability of a flowmeter. Another investigation focused on the evaluation of a dual channel laser Doppler flowmeter using both in vitro and in vivo models. It was demonstrated that the instrument permitted a useful method of obtaining flow information by comparing simultaneous responses at experimental and control sites. The choice of laser wavelength was investigated in a study to determine whether blood flow measurements are obtained from different depths within the skin tissue. The results indicate that some depth discrimination is obtainable using instruments operating at different wavelengths, however it is difficult to demonstrate the effect in vivo. In a separate study it was shown that pressure applied to the skin surface greatly affects the underlying blood flow. It is recommended that care has to be taken when positioning Doppler probes on the skin. A reflection pulse oximeter was developed using laser light backscattered from the skin. The instrument was evaluated in vitro and in vivo by comparing desaturation responses with a commercial transmission pulse oximeter. The reflection oximeter was demonstrated to reliably follow trends in oxygen saturation but several problems prevented instrument calibration. Finally, a device combining laser Doppler flowmetry with reflection pulse oximetry was developed and used in vivo to follow trends in blood flow and oxygen saturation from the same tissue sample

The computation of blood flow waveforms from digital X-ray angiographic data

This thesis investigates a novel technique for the quantitative measurement of pulsatile blood flow waveforms and mean blood flow rates using digital X-ray angiographic data. Blood flow waveforms were determined following an intra-arterial injection of contrast material. Instantaneous blood velocities were estimated by generating a 'parametric image' from dynamic X-ray angiographic images in which the image grey-level represented contrast material concentration as a function of time and true distance in three dimensions along a vessel segment. Adjacent concentration-distance profiles in the parametric image of iodine concentration versus distance and time were shifted along the vessel axis until a match occurred. A match was defined as the point where the mean sum of the squares of the differences between the two profiles was a minimum. The distance translated per frame interval gave the instantaneous contrast material bolus velocity. The technique initially was validated using synthetic data from a computer simulation of angiographic data which included the effect of pulsatile blood flow and X-ray quantum noise. The data were generated for a range of vessels from 2 mm to 6 mm in diameter. Different injection techniques and their effects on the accuracy of blood flow measurements were studied. Validation of the technique was performed using an experimental phantom of blood circulation, consisting of a pump, flexible plastic tubing, the tubular probe of an electromagnetic flowmeter and a solenoid to simulate a pulsatile flow waveform which included reverse flow. The technique was validated for both two- and three-dimensional representations of the blood vessel, for various flow rates and calibre sizes. The effects of various physical factors were studied, including the distance between injection and imaging sites and the length of artery analysed. Finally, this method was applied to clinical data from femoral arteries and arteries in the head and neck

The Developing of a Smart Elbow Prosthesis for Loosening Detection

Total Elbow Arthroplasty (TEA) is an effective surgical procedure for restoring elbow joint function and improve a patient's quality of life by relieving pain suffered from various musculoskeletal disorders. Despite new designs for prostheses and improved surgical procedures, TEA still suffers today from mid to-long-term complications such as aseptic loosening, infection, dislocation, and pre-prosthetic fractures. With aseptic loosening followed by infection being the most persistent reason for TEA revision, investigating methods for early diagnosis of implant loosening and differentiating between the infection and aseptic loosening is necessary to address this problem. This thesis aims to develop a novel diagnostic tool that can be embedded into the prosthetic and provide a quantitative measurement for early signs of the implant loosening without any usage of radiographs or any contact with the implant. In this study, three types of sensor configurations along with detection algorithms were developed, designed, and tested along with a functional prototype to detect the migration of the elbow prosthesis (Aseptic loosening). The detection system was validated under realistic conditions through experiments with a custom-designed mechanical testing rig. Finally, for infection detection, a biocompatible chemical sensor (Hydrogel) was synthesised and was linked with the aseptic loosening detection system to investigate the early signs of infection. Among the three sensor configurations, the single sensor configuration detected the implant migration at a resolution of 0.3 mm with a detection error of less than 3 %. The configuration was able to detect angular motion up to 3 degrees with a detection error of 5 %. The quad sensor configuration, an arrangement of four closely packed sensors, enhanced the overall detection performance by increasing system resolution to 0.15 mm in multiple axes along with increasing the signal to noise ratio, reducing root mean square error, and compensating the tilt effect of the single sensor. While the dual sensor configuration, two sensors arranged in-line but 42 mm apart, downgraded the detection performance by introducing a detection error of 30 %. The detection system showed negligible effect on the biomaterial used in TEA and was able to differentiate between different migrations types (Linear, Angular, Static and Dynamic). The difference in three fixation scenarios (grossly loose, partially loose, and fully fixed) was identified evidently by the detection system with the grossly loose fixation showed a displacement of 0.187 ± 0.061 mm on the x-axis and 0.387 ± 0.059 mm on the y-axis. The chemical sensor (Hydrogel) was able to detect the change in its surrounding pH level (highlighting the potential to detect infection) and by the amalgamation with the detection system, pH change was detected without the use of an imaging technique. Further improvement in the synthesis of the hydrogel and the optimisation of the detection system has also been suggested. The quad sensor system implies that it has the potential to be used to continually or intermittently monitor implant behaviour without hospital visitation or x-ray exposure. This could be applied more widely to other major joints such as the hips and knees, giving in-situ biomechanical insight into joint replacement behaviour over time

An evaluation of a checklist in Musculoskeletal (MSK) radiographic image interpretation when using Artificial Intelligence (AI)

Background: AI is being used increasingly in image interpretation tasks. There are challenges for its optimal use in reporting environments. Human reliance on technology and bias can cause decision errors. Trust issues exist amongst radiologists and radiographers in both over-reliance (automation bias) and reluctance in AI use for decision support. A checklist, used with the AI to mitigate against such biases, may optimise the use of AI technologies and promote good decision hygiene. Method: A checklist, to be used in image interpretation with AI assistance, was developed. Participants interpreted 20 examinations with AI assistance and then re- interpreted the 20 examinations with AI and a checklist. The MSK images were presented to radiographers as patient examinations to replicate the image interpretation task in clinical practice. Image diagnosis and confidence levels on the diagnosis provided were collected following each interpretation. The participant perception of the use of the checklist was investigated via a questionnaire.Results: Data collection and analysis are underway and will be completed at the European Congress of Radiology in Vienna, March 2023. The impact of the use of a checklist in image interpretation with AI will be evaluated. Changes in accuracy and confidence will be investigated and results will be presented. Participant feedback will be analysed to determine perceptions and impact of the checklist also. Conclusion: A novel checklist has been developed to aid the interpretation of images when using AI. The checklist has been tested for its use in assisting radiographers in MSK image interpretation when using AI.<br/

The development of an anti-scarring burn dressing

Introduction: Scarring has a significant impact on the function and quality of life in burn patients. This thesis describes selected stages of the development of an anti-scarring burn dressing and an objective scar assessment panel. Methods: This thesis is divided into two sections. Section 1 covers the development of an objective scar measurement tool based panel and score via a systematic review and subsequent reliability testing and validation of selected devices. Section 2 covers different aspects of dressing formulation. The cytotoxicity effects of decorin were investigated in dermal fibroblast cultures to provide guidance to safe and effective decorin dosing. Manufacturing, sterilisation and clinical use exposes decorin to elevated temperatures and the effects of this on the structure of decorin and bio-activity of decorin is investigated with circular dichroism and in-vitro cell cultures respectively. Lastly, a skin contact study in healthy volunteers was performed to establish the safety of two gellan formulations (sheet and fluid gel). Results: Objective scar measurement tools were found to be more reliable than subjective scar scores and an objective scar score was created consisting of high frequency ultrasound and pliability measures. Decorin had no measurable cytotoxicity on dermal fibroblasts even at high concentrations. Conformational change in decorin structure was seen at relatively low temperatures however results suggest that heating may enhance its bio-activity. Both gellan formulations were found to be safe for use on intact skin. Conclusion: The new objective scar scale can be used to accurately measure the effects of antiscarring treatments. Decorin and gellan are safe to be used in patients but the dressings may need to be protected against high temperatures