Abstracts

Ook tijdens TiiM 2019 zullen er posters gepresenteerd worden. Na vooraanmelding is er een selectie gemaakt van 5 abstracts die naast hun posterpresentatie ook een plenaire pitch zullen geven tijdens het programma. Het publiek beslist wie deze pitchwedstrijd wint en wie er met de best pitch award naar huis gaat: een prijs van €100.

Overzicht van alle posters

Multiparametric combined FDG-PET/CT and MR imaging to predict response to chemoradiotherapy in rectal cancer – whole tumor versus sub-volume analysis
Schurink, Niels

Usability and wearability of a patch sensor for continuous monitoring of TAVI-patients – First lessons learned from the TELE-TAVI study
Braem, Carlijn

Inter- and intrafraction displacement of individual axillary lymph nodes
Groot Koerkamp, Maureen

Changes in anaconda endograft limb configuration after endovascular aneurysm repair
Simmering, Jaimy

Effect of electrode position on transcutaneous electromyography of the diaphragm
Leuteren, Ruud van

EEG controlled triage in the ambulance for acute ischemic stroke
Potters, Wouter

Monitoring infant brain perfusion by trans-fontanel echography (MIFFY)
Kortenbout, Jorinde

Clinical implementation of eHealth pediatric asthma care
Kamp, Matienne van der

Modelling sleep state misperception at sleep onset
Hermans, Lieke

Monitoring electrical brain responses around nociceptive detection threshold
Berfelo, Tom

Research into the employability of a 3D printer in making personalized medical aids in a rural area of Sierra Leone
Stelt, Merel van der

Nasal high-flow therapy during treatment of COPD exacerbations: a matter of monitoring and controlling settings?
Elshof, Judith

Clinical feasibility of whole brain radiation therapy without a mask
Dekker, Janita

Towards blood flow dynamics in a stented carotid artery aneurysm model
Hoving, Astrid

Measuring eye deformation between planning and proton beam therapy position
Jaarsma, Myriam

3D Reconstruction of fetoscopic videos for artificial field of view expansion during fetal surgery
Schot, Anouk van der

De 5 abstracts die gepitcht worden

Multiparametric combined FDG-PET/CT and MR imaging to predict response to chemoradiotherapy in rectal cancer – whole tumor versus sub-volume analysis
Schurink, Niels

Introduction: Prediction of response to neoadjuvant treatment is increasingly relevant in rectal cancer, especially given the introduction of organ preserving treatments as potential alternative to surgical resection for patients that show a (near-)complete response to treatment. Biomarkers derived from imaging could play a potential role to predict response. With this study we aim to combine pre-treatment MRI with FDG-PET/CT and assess the individual and combined performance of quantitative image ‘bio-markers’ derived from these modalities to predict response to chemoradiotherapy (CRT).
Methods: A pilot group (n=20) underwent multiparametric MRI (T2W + DWI) and FDG-PET/CT before neoadjuvant treatment + surgery. Images were anatomically co-registered using rigid + non-rigid registration. Whole-tumor volumes were segmented on T2W-MRI and transferred to the other modalities/sequences; each tumor was additionally divided into 7mm3 sub-volumes. The following parameters were calculated per-tumor and sub-volume: T2-texture (uniformity/entropy), T2-signal intensity (SI), ADC (mean/max/min/median/10th&90th percentile), SUV (mean/max/median), CT-HU. Performance to predict poor response (=Mandard TRG3-5) vs. good response (TRG1-2) was calculated using ROC-analysis for [1] each individual parameter (whole-tumor), [2] multiparametric combination of the 5 best-performing parameters (whole-tumor), and [3] the proportion (%) of ‘poor-response’ sub-volumes within the tumor. Sub-volumes were defined as ‘poor response’ when ≥4 (out of 5) parameters within that sub-volume were indicative of TRG3-5, using a cut-off derived from dichotomisation by median split.
Results: Best single predictive parameters were T2-uniformity (AUC0.78), T2-SI (AUC0.70), ADCmax (AUC0.76), SUVmax (AUC0.78) and SUVmean (AUC0.73). Combined multiparametric performance (whole-tumor) was AUC0.91. The proportion of ‘poor-response’ sub-volumes resulted in AUC0.74.
Conclusion: Multiparametric analysis of quantitative MRI and FDG-PET/CT data has potential added value to predict response to neoadjuvant treatment. If there is a potential benefit for performing sub-volume (or voxel-wise) analysis, this needs to be established by further and larger studies; with our current method we have so far not demonstrated a clear added value.

 

Usability and wearability of a patch sensor for continuous monitoring of TAVI-patients – First lessons learned from the TELE-TAVI study
Braem, Carlijn

Introduction: For high surgical risk patients with severe aortic valve stenosis, transcatheter aortic valve replacement (TAVI) is currently standard care. A wearable patch could possibly extend screening, monitoring and follow-up. TELE-TAVI is an observational, prospective, investigator-initiated study to examine the usability and wearability of a wearable patch and phone receiver in TAVI patients.
Methods: The patch (Biosensor, Philips North America, USA) is worn in three time points; 1) screening pre-TAVI, 2) directly post-procedural and 3) at 6 weeks follow-up post-TAVI. The biosensor measures mono-lead ECG, heartrate (HR), respiratory rate (RespR) and tri-axial acceleration up to four consecutive days. Patient experiences are evaluated with a usability (PSSUQ) and custom-made wearability questionnaire. Heart and respiratory rate reliability were compared to a high-end monitoring, using the Philips MP70 monitor (Philips Healthcare, Eindhoven, the Netherlands).
Results: Between June 2018 and February 2019, 24 included patients were included of which 8 completed all measurements. Most patients experienced skin no irritation, itch or hindrance (94%, 89% and 89%, respectively) and users’ system satisfaction was rated as 56% (± 26%). Measurements were 62.5 (± 37.5) hours long of which 93% (± 18%) of the data was usable. Heart rate (HR) had a bias of 2 (± 3.8) and limit of agreement (LOA) between -7.9 (± 8.1) and 12 (± 10.4) beats per minute. Bias of RespR was 0.5 (± 1.8) and LOA between -7.0 (± 1.7) and 8.1 (± 3.2) breaths per minute.
Discussion: Although the wearability of the patch was good, the usability of the system proved more difficult. Data collection reliability is sufficient, but measurement length is only 60% from the expected 96 hours.
Conclusions: Preliminary results of the TELE-TAVI study show the possibilities of the wearable biosensor in screening, monitoring and follow-up of TAVI-patients. However, challenges remain, as the user interface and data collection should be improved.

 

Inter- and intrafraction displacement of individual axillary lymph nodes
Groot Koerkamp, Maureen

Introduction: Displacement of target volumes between or during radiotherapy treatment fractions may lead to decreased target coverage and increased dose to surrounding normal tissue. We evaluated inter- and intrafraction displacements of individual axillary lymph nodes (LN) on MRI in breast cancer patients and healthy volunteers to assess potential impact on future MRI-guided (stereotactic) radiotherapy.
Methods: 3D T1-weighted scans (T1) and coronal-sagittal free breathing cine scans (0.6s/slice) of five breast cancer patients were acquired on a 1.5T MRI scanner. Interfraction motion was simulated by patient repositioning between repeated scan sets. Additionally, sagittal cine scans (0.3s/slice) of seven volunteers were assessed. To quantify interfraction displacement, the T1 scans were rigidly registered. Registration was performed on two different regions: a) sternum+anterior chest wall; b) axillary level I. Subsequently, interfraction displacement was quantified in axillary levels I-IV as the difference in LN center-of-gravity. Intrafraction LN displacement in the cine scans was investigated with deformable registration with an optical flow algorithm. The mean displacement of pixels within one LN was calculated to determine intrafraction displacements. The maximum peak-to-peak difference was determined in left-right, superior-inferior, and anterior-posterior direction.
Results: 12 T1 and 14 cine scans were analyzed. 127 individual LNs were identified in the T1 scans. Average interfraction displacements ranging from 1.4-2.5mm were observed in axillary levels I-IV. LN displacements per level differed between the two registration regions, which showed showed deformation in anatomy, i.e. LNs in different levels could move  with respect to each other. Average maximum (range) intrafraction displacement was 1.6mm (1.2-2.0mm) in left-right, 1.7mm (0.9-2.5mm) in superior-inferior, and 2.0mm (1.1-3.2mm) in anterior-posterior direction.
Conclusions: Inter- and intrafraction displacements of individual LNs were small. With current planning margins (5-7mm) these displacements are not clinically relevant. However, the displacements should be considered for future MRI-guided (stereotactic) radiotherapy with smaller planning margins, e.g. for tumour-positive LNs.

 

Changes in anaconda endograft limb configuration after endovascular aneurysm repair
Simmering, Jaimy

Background: Limb occlusion after endovascular aneurysm repair (EVAR) of abdominal aortic aneurysms (AAA) is observed in up to 6% of the patients. At long term the Anaconda endograft is associated with a relatively high limb occlusion rate. The independent ring-stent configuration of the limbs provides flexibility in angulated anatomy. Yet, shrinkage of the aneurysm may result in changes in the original configuration and infolding of the graft fabric. This so-called “concertina effect” may lead to areas of blood stasis and increased thrombogenicity and thereby contribute to the emergence of limb occlusion. The the aim of this work was to evaluate in detail postoperative change in Anaconda endograft limb configuration.
Methods: This study used postoperative ECG-gated CT scans of 13 AAA patients with an Anaconda endograft. These patients participated in a clinical observational trial (Trialregister.nl identifier NTR4276) and were followed by protocol for 24 months after EVAR. Postoperative changes from discharge to 24 months in limb length and distances between the individual nitinol rings of the limbs were evaluated. The length of the limbs was measured as the length of the center lumen line. For each patient the mean and minimal distances between individual rings were automatically calculated and averaged for each limb after applying a previously validated segmentation algorithm.
Results: At 24 months follow-up the average length of the Anaconda endograft limbs had decreased by 10.2 ± 1.1 mm (p<0.001). The mean distances between rings decreased on average by 0.17 ± 0.24 mm (p=0.001). The minimal distances between rings decreased on average by 0.37 ± 0.38 mm (p<0.001).
Conclusion: The length of the Anaconda limbs significantly decreased 2 years after EVAR as well as the inter-ring distances of the limbs. This observation may be associated with the relatively high emergence of limb occlusions.

 

Effect of electrode position on transcutaneous electromyography of the diaphragm
Leuteren, Ruud van

Introduction: Monitoring electrical activity of the diaphragm with transcutaneous electromyography (dEMG) is feasible in preterm infants. The dEMG signal provides respiratory rate (RR), heart rate (HR), and neural breathing effort. The recommended electrode positioning is the right and left mid-clavicular line at the costo-abdominal margin. However, monitoring in daily clinical practice requires multiple different electrode positions to avoid skin lesions. Aim of the study was to describe the impact of different electrode positions on the derived dEMG parameters compared with the recommended position.
Methods: dEMG was simultaneously recorded for one hour by two pairs of electrodes in spontaneously breathing preterm infants. One pair was placed at the recommended position. The other position was randomly assigned: lateral, medial, superior, inferior to the recommended position or dorsal on the back. Peak and tonic activity, amplitude and variability were derived from the dEMG signal and compared between the two positions.
Results: Thirty infants (gestational age 30.1 ± 3.0 weeks, birth weight 1460 ± 645 grams) were included. HR and RR derived from dEMG did not significantly differ between recommended and alternative positions. Amplitude of the dEMG signal was lower at all different positions. The lateral position recorded the strongest signal (19.7% lower peak activity compared with recommended position). The variability of the signal was comparable for all positions (coefficient of variation 22.5 – 29.6% for peak activity).
Conclusion: This study suggests that different positions of dEMG electrodes can be used to monitor vital signs and detect diaphragmatic activity.  Although dEMG amplitude decreases, monitoring of HR and RR  remain reliable.

Overige abstracts

EEG controlled triage in the ambulance for acute ischemic stroke
Potters, Wouter

Acute ischemic stroke (AIS) is a major cause of mortality and morbidity worldwide, affecting approximately 1 per 1000 people per year[1]. In the Netherlands, 20.000 people are hospitalized with AIS each year, of whom 25-30% die because of the stroke[2,3]. Since the 1990’s, intravenous thrombolysis (IVT) has been standard treatment for AIS[4]. In 2015, there was a breakthrough in treatment of AIS with the publication of 5 large randomized controlled trials showing the effectiveness of endovascular thrombectomy (EVT) in patients with a large vessel occlusion in the anterior circulation (LVO-a)[5]. Since then, EVT has been become standard therapy for this population until 6 hours after stroke onset, and as of recently, for a selected population, up to 24 hours[5-7]. It is important to initiate treatment as soon as possible, as this increases the chance of a good clinical outcome[8]. Because of its complexity, EVT is performed only in selected hospitals. Currently, approximately half of EVT eligible patients are initially admitted to a hospital that does not provide this therapy. After the initial work-up, these patients are transferred to an EVT capable hospital. This delays initiation of treatment by approximately an hour, which decreases the absolute chance of functional independence 3 months after the stroke by 5-8%[8,9]. An advanced triage method that reliably identifies patients with an LVO-a in the ambulance is necessary, so that these patients can be directly transported to an EVT capable stroke center. We hypothesize that dry-electrode EEG can accurately predict the likelihood of the presence or absence of an LVO-a in patients with a suspected AIS when performed in the ambulance by paramedics. If this is indeed true, then dry-electrode EEG could be used for triage for patients with a suspected AIS, in a similar way the electrocardiography (ECG) is currently used for triage in patients with suspected myocardial infarction in the ambulance: by bringing patients with a high likelihood of necessity of endovascular therapy directly to an EVT capable center. We will present the study design of the investigator-initiated, diagnostic ELECTRA-STROKE study that started in September 2018.

 

Monitoring infant brain perfusion by trans-fontanel echography (MIFFY)
Kortenbout, Jorinde

Abstract: Very preterm neonates are born in a critical period of brain development and maturation. The brain is extremely vulnerable in this period and injuries during this phase may lead to long term cognitive, motor and behavioural problems. Adequate brain perfusion is important in prevention of preterm brain injury [1]. Objective continuous monitoring of brain perfusion is not yet possible. High frame rate (HFR) ultrasound (>1000 Hz) enables sensitive vascular imaging and non-invasive elasticity imaging [3]. To permit continuous HFR neonatal brain monitoring a trans-fontanel ultrasound probe (MIFFY probe) will be developed. Volumetric ultrasound data of the premature brain will be acquired in HFR to obtain high resolution grey scale images, perfusion images of the vascular tree and elasticity images. RF data will be collected with a wide opening angle and a broad frequency band through the anterior fontanel every ten minutes, during at least one cardiac cycle. The high frequency probe makes it possible to image and quantify flow in vessels with a size of 100-200 μm. The method is sensitive for slow flow as well and even subtle changes in hemodynamics can be detected. Since the data will be acquired every ten minutes, the infant can act as its own reference, so that an alarm can be given if the perfusion changes significantly. The elasticity images give information about local stiffness of the preterm brain. We are currently developing this technique in stiffness phantoms. The aim is to explore the natural occurring shear waves and this might provide information of changes in tissue stiffness after perfusion deficiencies. The MIFFY probe with high resolution will have the ability to improve diagnostic value, since minor changes in perfusion or elasticity can be measured in a timely manner to provide continuous neuromonitoring in the most critical days of neonatal intensive care.

 

Clinical implementation of eHealth pediatric asthma care
Kamp, Matienne van der

Introduction: Asthma is one of the most common chronic diseases in childhood with a large impact on physical and emotional well-being. One in ten children suffers from asthma, which means that more than 280.000 children in the Netherlands are at risk of a decreased quality of life [1]. Modern eHealth technology allows real-time monitoring of symptoms, enabling caregivers and healthcare providers to timely anticipate to the worsening of asthma control [2,3].
Objective: The goal of MST/Menzis Asthma Monitoring App (MAMA) project is to evaluate the implementation of eHealth technology in the pediatric asthma care.
Methods: 40 Children, between 4 and 18 years old, with moderate to severe asthma will receive eHealth asthma care instead of regular outpatient consultations for the duration of 6 months. The eHealth care consists of 1) online communication within the Puffer-app portal. 2) home-monitoring of symptoms, lung function, medication adherence, inhalation technique, and activity patterns using several wearable devices. The MAMA project will evaluate the implemented eHealth care on several aspects: The quality of care (CSQ-8), the level of self-management (PAM13), the healthcare costs in comparison to historic data (DBC registration), system usability (TAM+, SUS) and improvement of asthma control (based on the monitoring data and the childhood asthma control test (C-ACT)).
Results: Currently, 15 children are enrolled in the MAMA project. Preliminary results are expected in the beginning of March.

 

Modelling sleep state misperception at sleep onset
Hermans, Lieke

Abstract: Insomniacs often overestimate their sleep onset latency (SOL). The underlying mechanisms are unclear. We hypothesize that the length of uninterrupted sleep fragments after sleep onset influences the perception of the SOL because too short sleep fragments are overlooked. We made a model of the minimum length that a sleep fragment should have in order to be perceived as sleep, and we fit the model to subjective data.
Standard in-lab polysomnographic recordings were performed in 20 elderly insomniacs and 21 age-matched controls. Recordings were visually scored according to R&K criteria. In the model sleep onset was defined as the first epoch of the first sleep fragment longer than L minutes, with L varying from 0.5 to 40. We selected the parameter L with the smallest Mean Square Error (MSE) of the difference between modelled SOL and SOL perceived by the subject for each group.
For insomniacs, the lowest MSE was found for a length L of 30 minutes (MSE without model: 7195 vs. L=30: 3927). In the healthy subjects, applying the model only resulted in small improvements of the MSE. The lowest MSE was found for L=10 (MSE without model: 1185 vs. L=10: 969), although the results for all model parameters L below 20 were very similar.
We aimed to investigate the mechanisms underlying sleep onset misperception, by modelling the influence of sleep interruption on subjective SOL. Results indicate that interruptions of sleep fragments after less than 30 minutes can influence sleep onset perception in insomniacs. Additionally, the results suggest that insomniacs are more sensitive to sleep interruptions than healthy subjects. In order to extend our findings to the general population, the analysis should be repeated in different age groups. Additionally, other parameters could be added to the model, for instance the duration of the sleep disruption.

 

Monitoring electrical brain responses around nociceptive detection threshold
Berfelo, Tom

Introduction: There is a lack of objective diagnostics for monitoring key neural mechanisms underlying chronic pain, such as central sensitization and deficient descending inhibition. Recently, we combined psychophysical Multiple Threshold Tracking (MTT) with evoked potentials (EPs) to study neurophysiological activity related to processing of single and double pulse electronociceptive stimuli.  Results from pain-free subjects measured at the Technical Medical Centre (TechMed Centre) of the University of Twente showed that nociceptive detection thresholds (NDTs) habituate during the experiment and that EPs are strongly modulated by subjective stimulus detection, but also by stimulus amplitude and number of pulses. This suggests that the MTT-EP method might be a promising step toward a diagnostic tool for chronic pain patients. A next step is exploration of its replicability in a hospital environment and in chronic pain patients.
Methods: We explored the replicability of the MTT-EP experiment in twenty pain-free (Central Sensitization Inventory (CSI) score 14.6 ± 8.8) subjects at St. Antonius Hospital. Secondly, we measured NDTs and EPs from seven failed back surgery syndrome (FBSS) patients (CSI-score 49.0 ± 15.5).
Results: Preliminary results show that NDTs and EPs present values, habituation and paired-pulse facilitation, which are in line with results from the University of Twente. Again, the EP is modulated by stimulus detection and amplitudes. Strikingly, we found higher NDTs in FBSS patients and the EP appeared modulated by stimulus detection, but not by amplitude.
Conclusions: Since similar phenomena in NDTs and EPs were observed during nociceptive stimulation in pain-free subjects at St. Antonius Hospital, it can be concluded that results of MTT-EP experiment can be replicated. Secondly, the observed  altered behavior of NDTs and EPs in FBSS patients showing signs of central sensitization allows further hypotheses regarding responsiveness to mechanisms underlying chronic pain.

 

Research into the employability of a 3D printer in making personalized medical aids in a rural area of Sierra Leone
Stelt, Merel van der

Background: 3D printing is rarely used in resource-limited settings, especially in the healthcare sector.  We believe that because of it’s low cost and relatively easy technology, 3D printing could be useful for health care purposes, especially in resource-limited settings.
Aim: The aim of this feasibility study is to investigate healthcare related areas in a resource-limited setting in which a 3D printer can be used best. We have examined whether a 3D printer can contribute by making prostheses, braces or splints for patients who have undergone an amputation related to complex wounds or due to conflict, congenital abnormalities or burns.
Methods: During a 3 month period we investigated the benefit of customized 3D printed arm prostheses, splints and braces. In combination with a hand scanner (Einscanner Pro), 3D models can be adapted to the individual patient. With a 3D printer, Ultimaker 2+ (Ultimaker BV, the Netherlands), located at the Masanga Hospital in Sierra Leone, upper and lower arm prostheses and medical aids were designed, manufactured and tested. Questionnaires for testing the patient satisfaction and function ability of the prostheses were used during short-term follow-up.
Results: Four cosmetic prostheses have been made; 2 prostheses of the hand, 1 of the forearm and 1 of the total arm. We followed up on those patients after 3 – 4 weeks to obtain the questionnaire results and to investigate the quality of the prostheses. Also, 4 splints for hands and arms were made to prevent burn scar contractures after skin transplantation. Finally, a brace for a 7-year-old boy with kyphoscoliosis has been made.
Discussion: The first prosthetic results seem to be very positive. Even though the prostheses are “only” cosmetic, they also seem to exhibit some degree of functionality. The boy with kyphoscoliosis has accepted the brace and will be followed-up over the months to come. Long-term follow-up needs to be done to prove the sustainability of the 3D printed brace and prosthetics arms.

 

Nasal high-flow therapy during treatment of COPD exacerbations: a matter of monitoring and controlling settings?
Elshof, Judith

Introduction: Patients with Chronic Obstructive Pulmonary Disease (COPD) often experience exacerbations, i.e. periods of symptom worsening, which negatively affect quality of life. Therefore, strategies to treat and prevent exacerbations are needed. Nasal High-Flow Therapy (nHFT) is a relatively new therapy which supplies heated, humidified, and desirably oxygen-enriched air at high flow rates through a nasal cannula. Preliminary evidence suggests that nHFT in stable COPD patients might be effective. However, no data are present about nHFT in the acute setting of an exacerbation. We therefore designed a study with the aim of investigating the physiological effects of nHFT during a COPD exacerbation, thereby getting evidence for optimal settings of nHFT during an exacerbation.
Methods: Twenty COPD patients admitted with an exacerbation and ready for discharge will be included. At baseline, spontaneous breathing without nHFT will be performed for ten minutes. Afterwards, different flow rates of nHFT varying from 10-60 L/min will be performed in random order for ten minutes each. The following measurements will be carried out during the protocol: non-invasive electromyography of the diaphragm and intercostal muscles to assess neural drive, transdiaphragmatic pressure measurements to assess work of breathing, and respiratory inductance plethysmography to assess tidal volumes. Furthermore, the pressure at the end of the cannula, i.e. pressure inside the patient’s nose, will be determined by measuring the pressure in the nHFT system to non-invasively monitor breathing patterns. The optimal nHFT setting will be defined as the setting during which patients feel comfortable, breathing effort is minimal, and during which an effective breathing pattern is reached.
Conclusion: We have described a study protocol designed to investigate the physiological effects of nHFT in patients during a COPD exacerbation. With this study, we hope to gain further insight into the working mechanisms of nHFT during the acute setting of a COPD exacerbation.

 

Clinical feasibility of whole brain radiation therapy without a mask
Dekker, Janita

Introduction: To ensure a reproducible position of the patient a thermoplastic mask is used during radiotherapy to the brain. However, wearing a mask can be unpleasant or in some cases even intolerable. The aim of the study is to investigate the clinical feasibility of radiation therapy without a thermoplastic mask using optical surface scanning.
Methods: Positioning and motion monitoring was done using optical surface scanning. The system consists of LEDs projecting a rapid and near-visible line pattern onto the object and triangulation is used to make a 3D reconstruction of the surface. Patients were instructed to lie as still as possible, in a comfortable position. If the isocenter motion exceeded the threshold of 3 mm, the radiation beam was interrupted and the patient was repositioned. Clinical feasibility is defined as: more than 70% of the patients can complete the radiation treatment with a limited number of repositioning procedures, which is tested by using a one-tailed binomial test with a significance level of 0.05.
Results: Two out of the 30 patients were not able to lie still and continued the treatment with a mask. For the other patients, 24 repositioning procedures were needed in total. With a probability of success of 93.3% (28 out of 30), we reject the null hypothesis that the probability of success equals 0.7 and conclude that more than 70% of the patients can complete radiation treatment successfully without a thermoplastic mask (p=0.0021, 95% confidence interval for the probability of success is [0.80, 1.0]).
Conclusion: To improve patient friendliness and comfort of whole brain radiation therapy a new method of positioning and stabilizing the patient has been developed, using optical surface imaging. It is observed that patients are able to lie still below the threshold of 3 mm. Hence, it is concluded that irradiation without a mask is a clinically feasible method.

 

Towards blood flow dynamics in a stented carotid artery aneurysm model
Hoving, Astrid

Introduction: Extracranial carotid artery aneurysm (ECAA) is a rare disease for which a favorable treatment strategy is unknown. One of the treatment options is placement of the flow-diverting stent to exclude the aneurysm sac from the blood flow. Simulation and visualization of changes in blood flow dynamics after stent placement gives information on the performance of this treatment option. We present a novel model fabrication and visualization technique that can be used to study the effect of flow-diverting stent placement on blood flow dynamics.
Methods: Based on literature reporting on common ECAA morphologies, a model geometry is designed and 3D printed. Next, a PVA-phantom is fabricated by casting the 3D-printed model (Fig. 1A). Inside this phantom, flow patterns are visualized and analyzed using echoPIV – a high-frame-rate contrast-enhanced ultrasound protocol combined with particle image velocimetry analysis. Numerical simulations are performed in OpenFoam, geometry (with and without virtually placed flow-diverting stent) is represented using the Immersed Boundary Method.
Results: The echoPIV measurements and numerical simulations both show a jet flowing into the aneurysm sac, which splits into a flow stream to the outflow artery and one to the aneurysm, where vortices are visible (Fig. 1B). Simulations in the stented geometry show reduction of about 25% of flow in the aneurysm sac (Fig. 1C).
Discussion: Although this research does not yet involve in vitro flow studies in a stented geometry, numerical results are already showing the effect of a flow-diverting stent on the blood flow dynamics. Similar results are expected when a flow-diverting stent is placed in the phantom.
Conclusion: EchoPIV in a carotid artery aneurysm phantom, fabricated using novel 3D-processing techniques, shows realistic flow patterns, as compared to numerical simulations. This technique can be used to study the effect of flow-diverting stent placement on blood flow patterns, thereby indicating treatment performance.

 

Measuring eye deformation between planning and proton beam therapy position
Jaarsma, Myriam

Introduction: Proton beam irradiation (PBT) is often the therapy of choice for large uveal melanoma (UM). MRI is used for the clinical target volume definition and PBT treatment planning. However, PBT is performed in sitting position and the acquisition of the MRI images are done in supine position. This change in gravity direction potentially changes the shape of the eye and tumour. We used MRI to investigate and quantify the effect of different patient positions on eye shape.
Methods: Seven volunteers and two UM patients were scanned in two positions on a 3T Philips MRI scanner. One set of images was acquired in supine position, while a second set was acquired mimicking the patient sitting for PBT. Additionally, two volunteers were scanned twice in the supine position to assess the reproducibility. After registration and segmentation the distances between both positions was calculated. For the UM patients only the tumour-vitreous border could be accurately compared.
Results: In healthy controls the median difference between the supine and flexed scans was 0.1mm (95th percentile (P): 0.3mm), which is in the order of the reproducibility of the method (95th P: 0.3mm). The slightly larger difference in eye-shapes of subjects 5 was caused by eye-motion artefacts. In the UM patients we found a median UM deformation of the tumour of 0.1 mm (95th P: 0.4mm).
Conclusion: Changes in gravity direction produce no substantial changes in sclera and tumour shape. The results indicate that supinely acquired MR images can be used to accurately plan ocular PBT.

 

3D Reconstruction of fetoscopic videos for artificial field of view expansion during fetal surgery
Schot, Anouk van der

Introduction: The twin-twin transfusion syndrome (TTTS) occurs in identical twins where two twins share a placenta. In 10-20% of the cases, connecting blood vessels in this placenta cause an unbalanced feto-fetal blood transfusion. Untreated, this syndrome is associated with a 90% mortality rate. Fetoscopic laser coagulation of placental vessels is commonly used to treat TTTS, but has the disadvantage of a limited field of view during the procedure. The surgeon has the difficult task to map the placental surface in his mind. Based on this mapping, he determines which and in which order to coagulate the vessels.
Methods: In this research project we aim to replace the ‘map’ that is now created in the mind of the operator. The main objective is to develop and implement an algorithm that combines all video images into a complete real-time textured 3D reconstruction of the placenta. Based on this real-time placenta topography, the operator can make informed choices and thereby reduce the associated risks and complications.
Results: We developed an algorithm, which can automatically create a real-time map of the placenta with only the visual information of the fetoscope. In addition, the current position of the fetoscope can be tracked. The preliminary results in an ex-vivo setting shows that it is possible to create a real-time reconstruction of a dye-injected placenta in an ex-vivo set-up.
Discussion/conclusion: The next step in our pipeline is to enhance the algorithm to make it possible to perform clinical tests. Thereafter, we aim to implement this technique in fetal therapy and investigate the clinical outcomes. The hypothesis is that, with the real-time map of the placenta, surgeons can use smaller diameter instruments during the procedure and hereby reduce the associated risks and complications, like pregnancy loss.