Coherent and consistent relational transfer learning with auto-encoders

Human defined concepts are inherently transferable, but it is not clear under what conditions they can be modelled effectively by non-symbolic artificial learners. This paper argues that for a transferable concept to be learned, the system of relations that define it must be coherent across domains and properties. That is, they should be consistent with respect to relational constraints, and this consistency must extend beyond the representations encountered in the source domain. Further, where relations are modelled by differentiable functions, their gradients must conform – the functions must at times move together to preserve consistency. We propose a Partial Relation Transfer (PRT) task which exposes how well relation-decoders model these properties, and exemplify this with ordinality prediction transfer task, including a new data set for the transfer domain. We evaluate this on existing relation-decoder models, as well as a novel model designed around the principles of consistency and gradient conformity. Results show that consistency across broad regions of input space indicates good transfer performance, and that good gradient conformity facilitates consistency

Geometric semi-automatic analysis of radiographs of Colles’ fractures

Fractures of the wrist are common in Emergency Departments, where some patients are treated with a procedure called Manipulation under Anaesthesia. In some cases, this procedure is unsuccessful and patients need to revisit the hospital where they undergo surgery to treat the fracture. This work describes a geometric semi-automatic image analysis algorithm to analyse and compare the x-rays of healthy controls and patients with dorsally displaced wrist fractures (Colles’ fractures) who were treated with Manipulation under Anaesthesia. A series of 161 posterior-anterior radiographs from healthy controls and patients with Colles’ fractures were acquired and analysed. The patients’ group was further subdivided according to the outcome of the procedure (successful/unsuccessful) and pre- or post-intervention creating five groups in total (healthy, pre-successful, pre-unsuccessful, post-successful, post-unsuccessful). The semi-automatic analysis consisted of manual location of three landmarks (finger, lunate and radial styloid) and automatic processing to generate 32 geometric and texture measurements, which may be related to conditions such as osteoporosis and swelling of the wrist. Statistical differences were found between patients and controls, as well as between pre- and post-intervention, but not between the procedures. The most distinct measurements were those of texture. Although the study includes a relatively low number of cases and measurements, the statistical differences are encouraging

RF-Energized Intracoronary Guidewire to Enhance Bipolar Ablation of the Interventricular Septum: In-silico Feasibility Study

"This is an Accepted Manuscript of an article published by Taylor & Francis in International Journal of Hyperthermiaon [date of publication], available online: https://doi.org/10.1080/02656736.2018.1425487"[EN] Purpose: Although bipolar radiofrequency (RF) ablation (RFA) is broadly used to eliminate ventricular tachycardias in the interventricular septum wall, it can fail to create transmural lesions in thick ventricular walls. To solve this problem, we explored whether an RF-energised guidewire inserted into the ventricular wall would enhance bipolar RFA in the creation of transmural lesions through the ventricular wall.Methods: We built three-dimensional computational models including two irrigated electrodes placed on opposing sides of the interventricular septum and a metal guidewire inserted into the septum. Computer simulations were conducted to compare the temperature distributions obtained with two ablation modes: bipolar mode (RF power delivered between both irrigated electrode) and time-division multiplexing (TDM) technique, which consists of activating the bipolar mode for 90% of the time and applying RF power between the guidewire and both irrigated electrodes during the remaining time.Results: The TDM technique was the most suitable in terms of creating wider lesions through the entire ventricular wall, avoiding the hour-glass shape of thermal lesions associated with the bipolar mode. This was especially apparent in the case of thick walls (15mm). Furthermore, the TDM technique was able to create transmural lesions even when the guidewire was displaced from the midplane of the wall.Conclusions: An RF-energised guidewire could enhance bipolar RFA by allowing transmural lesions to be made through thick ventricular walls. However, the safety of this new approach must be assessed in future pre-clinical studies, especially in terms of the risk of stenosis and its clinical impact.This work was supported by the Spanish Ministerio de Economia, Industria y Competitividad under "Plan Estatal de Investigacion, Desarrollo e Innovacion Orientada a los Retos de la Sociedad" Grant "TEC2014-52383-C3 (TEC2014-52383-C3-1-R)". A. Gonzalez-Suarez has a "Juan de la Cierva-formacion" Postdoctoral Grant (FJCI-2015-27202) supported by the Spanish Ministerio de Economia, Industria y Competitividad, Secretaria de Estado de Investigacion, Desarrollo e Innovacion.Pérez, JJ.; González Suárez, A.; D Avila, A.; Berjano, E. (2018). RF-Energized Intracoronary Guidewire to Enhance Bipolar Ablation of the Interventricular Septum: In-silico Feasibility Study. International Journal of Hyperthermia. 34(8):1202-1212. https://doi.org/10.1080/02656736.2018.1425487S12021212348Baszko, A., Telec, W., Kałmucki, P., Iwachów, P., Kochman, K., Szymański, R., … Siminiak, T. (2016). Bipolar irrigated radiofrequency ablation of resistant ventricular tachycardia with a septal intramural origin: the initial experience and a description of the method. Clinical Case Reports, 4(10), 957-961. doi:10.1002/ccr3.648Gizurarson, S., Spears, D., Sivagangabalan, G., Farid, T., Ha, A. C. T., Masse, S., … Nanthakumar, K. (2014). Bipolar ablation for deep intra-myocardial circuits: human ex vivo development and in vivo experience. Europace, 16(11), 1684-1688. doi:10.1093/europace/euu001Koruth, J. S., Dukkipati, S., Miller, M. A., Neuzil, P., d’ Avila, A., & Reddy, V. Y. (2012). Bipolar irrigated radiofrequency ablation: A therapeutic option for refractory intramural atrial and ventricular tachycardia circuits. Heart Rhythm, 9(12), 1932-1941. doi:10.1016/j.hrthm.2012.08.001Baldinger, S. H., Kumar, S., Barbhaiya, C. R., Mahida, S., Epstein, L. M., Michaud, G. F., … Stevenson, W. G. (2015). Epicardial Radiofrequency Ablation Failure During Ablation Procedures for Ventricular Arrhythmias. Circulation: Arrhythmia and Electrophysiology, 8(6), 1422-1432. doi:10.1161/circep.115.003202Santangeli, P., Shaw, G. C., & Marchlinski, F. E. (2017). Radiofrequency Wire Facilitated Interventricular Septal Access for Catheter Ablation of Ventricular Tachycardia in a Patient With Aortic and Mitral Mechanical Valves. Circulation: Arrhythmia and Electrophysiology, 10(1). doi:10.1161/circep.116.004771Berjano, E. J., Hornero, F., Atienza, F., & Montero, A. (2003). Long electrodes for radio frequency ablation: comparative study of surface versus intramural application. Medical Engineering & Physics, 25(10), 869-877. doi:10.1016/s1350-4533(03)00125-5McLELLAN, A. J. A., ELLIMS, A. H., PRABHU, S., VOSKOBOINIK, A., ILES, L. M., HARE, J. L., … KISTLER, P. M. (2016). Diffuse Ventricular Fibrosis on Cardiac Magnetic Resonance Imaging Associates With Ventricular Tachycardia in Patients With Hypertrophic Cardiomyopathy. Journal of Cardiovascular Electrophysiology, 27(5), 571-580. doi:10.1111/jce.12948Berjano, E. J. (2006). Theoretical modeling for radiofrequency ablation: state-of-the-art and challenges for the future. BioMedical Engineering OnLine, 5(1). doi:10.1186/1475-925x-5-24Pérez, J. J., González-Suárez, A., & Berjano, E. (2017). Numerical analysis of thermal impact of intramyocardial capillary blood flow during radiofrequency cardiac ablation. International Journal of Hyperthermia, 34(3), 243-249. doi:10.1080/02656736.2017.1336258Labonte, S. (1994). Numerical model for radio-frequency ablation of the endocardium and its experimental validation. IEEE Transactions on Biomedical Engineering, 41(2), 108-115. doi:10.1109/10.284921Doss, J. D. (1982). Calculation of electric fields in conductive media. Medical Physics, 9(4), 566-573. doi:10.1118/1.595107PÉREZ, J. J., D’AVILA, A., ARYANA, A., & BERJANO, E. (2015). Electrical and Thermal Effects of Esophageal Temperature Probes on Radiofrequency Catheter Ablation of Atrial Fibrillation: Results from a Computational Modeling Study. Journal of Cardiovascular Electrophysiology, 26(5), 556-564. doi:10.1111/jce.12630Jo, B., & Aksan, A. (2010). Prediction of the extent of thermal damage in the cornea during conductive keratoplasty. Journal of Thermal Biology, 35(4), 167-174. doi:10.1016/j.jtherbio.2010.02.004Gonzalez-Suarez, A., & Berjano, E. (2016). Comparative Analysis of Different Methods of Modeling the Thermal Effect of Circulating Blood Flow During RF Cardiac Ablation. IEEE Transactions on Biomedical Engineering, 63(2), 250-259. doi:10.1109/tbme.2015.2451178WINTERFIELD, J. R., JENSEN, J., GILBERT, T., MARCHLINSKI, F., NATALE, A., PACKER, D., … WILBER, D. J. (2015). Lesion Size and Safety Comparison Between the Novel Flex Tip on the FlexAbility Ablation Catheter and the Solid Tips on the ThermoCool and ThermoCool SF Ablation Catheters. Journal of Cardiovascular Electrophysiology, 27(1), 102-109. doi:10.1111/jce.12835PÉREZ, J. J., D’AVILA, A., ARYANA, A., TRUJILLO, M., & BERJANO, E. (2016). Can Fat Deposition After Myocardial Infarction Alter the Performance of RF Catheter Ablation of Scar-Related Ventricular Tachycardia?: Results from a Computer Modeling Study. Journal of Cardiovascular Electrophysiology, 27(8), 947-952. doi:10.1111/jce.13006Haines, D. E. (2011). Letter by Haines Regarding Article, «Direct Measurement of the Lethal Isotherm for Radiofrequency Ablation of Myocardial Tissue». Circulation: Arrhythmia and Electrophysiology, 4(5). doi:10.1161/circep.111.965459González-Suárez, A., Trujillo, M., Koruth, J., d’ Avila, A., & Berjano, E. (2014). Radiofrequency cardiac ablation with catheters placed on opposing sides of the ventricular wall: Computer modelling comparing bipolar and unipolar modes. International Journal of Hyperthermia, 30(6), 372-384. doi:10.3109/02656736.2014.949878Gianni, C., Mohanty, S., Trivedi, C., Di Biase, L., Al-Ahmad, A., Natale, A., & David Burkhardt, J. (2017). Alternative Approaches for Ablation of Resistant Ventricular Tachycardia. Cardiac Electrophysiology Clinics, 9(1), 93-98. doi:10.1016/j.ccep.2016.10.006Boll, D. T., Lewin, J. S., Duerk, J. L., & Merkle, E. M. (2003). Do Surgical Clips Interfere with Radiofrequency Thermal Ablation? American Journal of Roentgenology, 180(6), 1557-1560. doi:10.2214/ajr.180.6.1801557Eung Je Woo, Tungjitkusolmun, S., Hong Cao, Jang-Zem Tsai, Webster, J. G., Vorperian, V. R., & Will, J. A. (2000). A new catheter design using needle electrode for subendocardial RF ablation of ventricular muscles: finite element analysis and in vitro experiments. IEEE Transactions on Biomedical Engineering, 47(1), 23-31. doi:10.1109/10.817616BLOUIN, L. T., & MARCUS, F. I. (1989). The Effect of Electrode Design on the Efficiency of Delivery of Radiofrequency Energy to Cardiac Tissue In Vitro. Pacing and Clinical Electrophysiology, 12(1), 136-143. doi:10.1111/j.1540-8159.1989.tb02640.xTao, W., Jian-ping, G., Xu, H., Wen-sheng, L., Liang, C., Guo-ping, C., … Jin-hua, S. (2013). The effects of endovenous radiofrequency ablation on coagulation and the vein wall in an experimental canine model. Vascular, 21(4), 215-219. doi:10.1177/1708538113478762Badham, G. E., Strong, S. M., & Whiteley, M. S. (2014). An in vitro study to optimise treatment of varicose veins with radiofrequency-induced thermo therapy. Phlebology: The Journal of Venous Disease, 30(1), 17-23. doi:10.1177/0268355514552005Kreidieh, B., Rodríguez-Mañero, M., A. Schurmann, P., Ibarra-Cortez, S. H., Dave, A. S., & Valderrábano, M. (2016). Retrograde Coronary Venous Ethanol Infusion for Ablation of Refractory Ventricular Tachycardia. Circulation: Arrhythmia and Electrophysiology, 9(7). doi:10.1161/circep.116.00435

Accountability in AI: From principles to industry-specific accreditation

Recent AI-related scandals have shed a spotlight on accountability in AI, with increasing public interest and concern. This paper draws on literature from public policy and governance to make two contributions. First, we propose an AI accountability ecosystem as a useful lens on the system, with different stakeholders requiring and contributing to specific accountability mechanisms. We argue that the present ecosystem is unbalanced, with a need for improved transparency via AI explainability and adequate documentation and process formalisation to support internal audit, leading up eventually to external accreditation processes. Second, we use a case study in the gambling sector to illustrate in a subset of the overall ecosystem the need for industry-specific accountability principles and processes. We define and evaluate critically the implementation of key accountability principles in the gambling industry, namely addressing algorithmic bias and model explainability, before concluding and discussing directions for future work based on our findings

Graph-based Neural Modules to Inspect Attention-based Architectures: A Position Paper

Encoder-decoder architectures are prominent building blocks of state-of-the-art solutions for tasks across multiple fields where deep learning (DL) or foundation models play a key role. Although there is a growing community working on the provision of interpretation for DL models as well as considerable work in the neuro-symbolic community seeking to integrate symbolic representations and DL, many open questions remain around the need for better tools for visualization of the inner workings of DL architectures. In particular, encoder-decoder models offer an exciting opportunity for visualization and editing by humans of the knowledge implicitly represented in model weights. In this work, we explore ways to create an abstraction for segments of the network as a two-way graph-based representation. Changes to this graph structure should be reflected directly in the underlying tensor representations. Such two-way graph representation enables new neuro-symbolic systems by leveraging the pattern recognition capabilities of the encoder-decoder along with symbolic reasoning carried out on the graphs. The approach is expected to produce new ways of interacting with DL models but also to improve performance as a result of the combination of learning and reasoning capabilities

A Genome-Wide Screening and SNPs-to-Genes Approach to Identify Novel Genetic Risk Factors Associated with Frontotemporal Dementia

Frontotemporal dementia (FTD) is the second most prevalent form of early onset dementia after Alzheimer’s disease (AD). We performed a case-control association study in an Italian FTD cohort (n = 530) followed by the novel SNPs-to-genes approach and functional annotation analysis. We identified two novel potential loci for FTD. Suggestive SNPs reached p-values ~10-7 and OR > 2.5 (2p16.3) and 1.5 (17q25.3). Suggestive alleles at 17q25.3 identified a disease-associated haplotype causing decreased expression of -cis genes such as RFNG and AATK involved in neuronal genesis and differentiation, and axon outgrowth, respectively. We replicated this locus through the SNPs-to-genes approach. Our functional annotation analysis indicated significant enrichment for functions of the brain (neuronal genesis, differentiation and maturation), the synapse (neurotransmission and synapse plasticity), and elements of the immune system, the latter supporting our recent international FTD-GWAS. This is the largest genome-wide study in Italian FTD to date. Although our results are not conclusive, we set the basis for future replication studies and identification of susceptible molecular mechanisms involved in FTD pathogenesis

Radiofrequency cardiac ablation with catheters placed on opposing sides of the ventricular wall: Computer modelling comparing bipolar and unipolar modes

Purpose: The aim of this study was to compare the efficacy of bipolar (BM) vs. unipolar (UM) mode of radiofrequency ablation (RFA) in terms of creating transmural lesions across the interventricular septum (IVS) and ventricular free wall (VFW). Materials and methods: We built computational models to study the temperature distributions and lesion dimensions created by BM and UM on IVS and VFW during RFA. Two different UM types were considered: sequential (SeUM) and simultaneous (SiUM). The effect of ventricular wall thickness, catheter misalignment, epicardial fat, and presence of air in the epicardial space were also studied. Results: Regarding IVS ablation, BM created transmural and symmetrical lesions for wall thicknesses up to 15 mm. SeUM and SiUM were not able to create transmural lesions with IVS thicknesses >= 12.5 and 15 mm, respectively. Lesions were asymmetrical only with SeUM. For VFW ablation, BM also created transmural lesions for wall thicknesses up to 15 mm. However, with SeUM and SiUM transmurality was obtained for VFW thicknesses <= 7.5 and 12.5 mm, respectively. With the three modes, VFW lesions were always asymmetrical. In the scenario with air or a fat tissue layer on the epicardial side, only SiUM was capable of creating transmural lesions. Overall, BM was superior to UM in IVS and VFW ablation when the catheters were not aligned. Conclusions: Our findings suggest that BM is more effective than UM in achieving transmurality across both ventricular sites, except in the situation of the epicardial catheter tip surrounded by air or placed over a fat tissue layer.This work received financial support from the Spanish 'Plan Nacional de I+D+I del Ministerio de Ciencia e Innovacion' (TEC2011-27133-C02-01), and from the Universitat Politecnica de Valencia (PAID-06-11 Ref. 1988). A. Gonzalez-Suarez is the recipient of a Grant VaLi+D (ACIF/2011/194) from the Generalitat Valenciana, Spain. The authors alone are responsible for the content and writing of the paper.González Suárez, A.; Trujillo Guillen, M.; Koruth, J.; D'avila, A.; Berjano, E. (2014). Radiofrequency cardiac ablation with catheters placed on opposing sides of the ventricular wall: Computer modelling comparing bipolar and unipolar modes. International Journal of Hyperthermia. 30(6):372-384. https://doi.org/10.3109/02656736.2014.949878S372384306SIVAGANGABALAN, G., BARRY, M. A., HUANG, K., LU, J., POULIOPOULOS, J., THOMAS, S. P., … KOVOOR, P. (2010). Bipolar Ablation of the Interventricular Septum is More Efficient at Creating a Transmural Line than Sequential Unipolar Ablation. Pacing and Clinical Electrophysiology, 33(1), 16-26. doi:10.1111/j.1540-8159.2009.02602.xNagashima, K., Watanabe, I., Okumura, Y., Ohkubo, K., Kofune, M., Ohya, T., … Hirayama, A. (2011). Lesion Formation by Ventricular Septal Ablation With Irrigated Electrodes. Circulation Journal, 75(3), 565-570. doi:10.1253/circj.cj-10-0870D’ Avila, A., Houghtaling, C., Gutierrez, P., Vragovic, O., Ruskin, J. N., Josephson, M. E., & Reddy, V. Y. (2004). Catheter Ablation of Ventricular Epicardial Tissue. Circulation, 109(19), 2363-2369. doi:10.1161/01.cir.0000128039.87485.0bDukkipati, S. R., d’ Avila, A., Soejima, K., Bala, R., Inada, K., Singh, S., … Reddy, V. Y. (2011). Long-Term Outcomes of Combined Epicardial and Endocardial Ablation of Monomorphic Ventricular Tachycardia Related to Hypertrophic Cardiomyopathy. Circulation: Arrhythmia and Electrophysiology, 4(2), 185-194. doi:10.1161/circep.110.957290Sosa, E., Scanavacca, M., d’ Avila, A., Oliveira, F., & Ramires, J. A. F. (2000). Nonsurgical transthoracic epicardial catheter ablation to treat recurrent ventricular tachycardia occurring late after myocardial infarction. Journal of the American College of Cardiology, 35(6), 1442-1449. doi:10.1016/s0735-1097(00)00606-9Nagashima, K., Watanabe, I., Okumura, Y., Sonoda, K., Kofune, M., Mano, H., … Hirayama, A. (2012). Epicardial Ablation With Irrigated Electrodes. Circulation Journal, 76(2), 322-327. doi:10.1253/circj.cj-11-0984Berjano, E. J. (2006). BioMedical Engineering OnLine, 5(1), 24. doi:10.1186/1475-925x-5-24Abraham, J. P., & Sparrow, E. M. (2007). A thermal-ablation bioheat model including liquid-to-vapor phase change, pressure- and necrosis-dependent perfusion, and moisture-dependent properties. International Journal of Heat and Mass Transfer, 50(13-14), 2537-2544. doi:10.1016/j.ijheatmasstransfer.2006.11.045Jo, B., & Aksan, A. (2010). Prediction of the extent of thermal damage in the cornea during conductive keratoplasty. Journal of Thermal Biology, 35(4), 167-174. doi:10.1016/j.jtherbio.2010.02.004HAINES, D. E., & WATSON, D. D. (1989). Tissue Heating During Radiofrequency Catheter Ablation: A Thermodynamic Model and Observations in Isolated Perfused and Superfused Canine Right Ventricular Free Wall. Pacing and Clinical Electrophysiology, 12(6), 962-976. doi:10.1111/j.1540-8159.1989.tb05034.xZhao, G., Zhang, H.-F., Guo, X.-J., Luo, D.-W., & Gao, D.-Y. (2007). Effect of blood flow and metabolism on multidimensional heat transfer during cryosurgery. Medical Engineering & Physics, 29(2), 205-215. doi:10.1016/j.medengphy.2006.03.005Chang, I. A., & Nguyen, U. D. (2004). BioMedical Engineering OnLine, 3(1), 27. doi:10.1186/1475-925x-3-27Whitney, J., Carswell, W., & Rylander, N. (2013). Arrhenius parameter determination as a function of heating method and cellular microenvironment based on spatial cell viability analysis. International Journal of Hyperthermia, 29(4), 281-295. doi:10.3109/02656736.2013.802375Pearce, J. A. (2013). Comparative analysis of mathematical models of cell death and thermal damage processes. International Journal of Hyperthermia, 29(4), 262-280. doi:10.3109/02656736.2013.786140Doss, J. D. (1982). Calculation of electric fields in conductive media. Medical Physics, 9(4), 566-573. doi:10.1118/1.595107Watanabe, I., Nuo, M., Okumura, Y., Ohkubo, K., Ashino, S., Kofune, M., … Hirayama, A. (2010). Temperature-Controlled Cooled-Tip Radiofrequency Ablation in Left Ventricular Myocardium. International Heart Journal, 51(3), 193-198. doi:10.1536/ihj.51.193Yokoyama, K., Nakagawa, H., Wittkampf, F. H. M., Pitha, J. V., Lazzara, R., & Jackman, W. M. (2006). Comparison of Electrode Cooling Between Internal and Open Irrigation in Radiofrequency Ablation Lesion Depth and Incidence of Thrombus and Steam Pop. Circulation, 113(1), 11-19. doi:10.1161/circulationaha.105.540062Kumar, P., Mounsey, J. P., Gehi, A. K., Schwartz, J. D., & Chung, E. H. (2013). Use of a closed loop irrigated catheter in epicardial ablation of ventricular tachycardia. Journal of Interventional Cardiac Electrophysiology, 38(1), 35-42. doi:10.1007/s10840-013-9799-1Schutt, D., Berjano, E. J., & Haemmerich, D. (2009). Effect of electrode thermal conductivity in cardiac radiofrequency catheter ablation: A computational modeling study. International Journal of Hyperthermia, 25(2), 99-107. doi:10.1080/02656730802563051Gopalakrishnan, J. (2002). A Mathematical Model for Irrigated Epicardial Radiofrequency Ablation. Annals of Biomedical Engineering, 30(7), 884-893. doi:10.1114/1.1507845Suárez, A. G., Hornero, F., & Berjano, E. J. (2010). Mathematical Modeling of Epicardial RF Ablation of Atrial Tissue with Overlying Epicardial Fat. The Open Biomedical Engineering Journal, 4(1), 47-55. doi:10.2174/1874120701004020047Haemmerich, D., Chachati, L., Wright, A. S., Mahvi, D. M., Lee, F. T., & Webster, J. G. (2003). Hepatic radiofrequency ablation with internally cooled probes: effect of coolant temperature on lesion size. IEEE Transactions on Biomedical Engineering, 50(4), 493-500. doi:10.1109/tbme.2003.809488Koruth, J. S., Dukkipati, S., Miller, M. A., Neuzil, P., d’ Avila, A., & Reddy, V. Y. (2012). Bipolar irrigated radiofrequency ablation: A therapeutic option for refractory intramural atrial and ventricular tachycardia circuits. Heart Rhythm, 9(12), 1932-1941. doi:10.1016/j.hrthm.2012.08.001González-Suárez, A., Trujillo, M., Burdío, F., Andaluz, A., & Berjano, E. (2012). Feasibility study of an internally cooled bipolar applicator for RF coagulation of hepatic tissue: Experimental and computational study. International Journal of Hyperthermia, 28(7), 663-673. doi:10.3109/02656736.2012.716900Agah, R., Gandjbakhche, A. H., Motamedi, M., Nossal, R., & Bonner, R. F. (1996). Dynamics of temperature dependent optical properties of tissue: dependence on thermally induced alteration. IEEE Transactions on Biomedical Engineering, 43(8), 839-846. doi:10.1109/10.508546Haines, D. E. (2011). Letter by Haines Regarding Article, «Direct Measurement of the Lethal Isotherm for Radiofrequency Ablation of Myocardial Tissue». Circulation: Arrhythmia and Electrophysiology, 4(5). doi:10.1161/circep.111.965459Wood, M., Goldberg, S., Lau, M., Goel, A., Alexander, D., Han, F., & Feinstein, S. (2011). Direct Measurement of the Lethal Isotherm for Radiofrequency Ablation of Myocardial Tissue. Circulation: Arrhythmia and Electrophysiology, 4(3), 373-378. doi:10.1161/circep.110.961169Jain, M. K., & Wolf, P. D. (2000). A Three-Dimensional Finite Element Model of Radiofrequency Ablation with Blood Flow and its Experimental Validation. Annals of Biomedical Engineering, 28(9), 1075-1084. doi:10.1114/1.131021

Predicting recovery following stroke: Deep learning, multimodal data and feature selection using explainable AI

Machine learning offers great potential for automated prediction of post-stroke symptoms and their response to rehabilitation. Major challenges for this endeavour include the very high dimensionality of neuroimaging data, the relatively small size of the datasets available for learning and interpreting the predictive features, as well as, how to effectively combine neuroimaging and tabular data (e.g. demographic information and clinical characteristics). This paper evaluates several solutions based on two strategies. The first is to use 2D images that summarise MRI scans. The second is to select key features that improve classification accuracy. Additionally, we introduce the novel approach of training a convolutional neural network (CNN) on images that combine regions-of-interests (ROIs) extracted from MRIs, with symbolic representations of tabular data. We evaluate a series of CNN architectures (both 2D and a 3D) that are trained on different representations of MRI and tabular data, to predict whether a composite measure of post-stroke spoken picture description ability is in the aphasic or non-aphasic range. MRI and tabular data were acquired from 758 English speaking stroke survivors who participated in the PLORAS study. Each participant was assigned to one of five different groups that were matched for initial severity of symptoms, recovery time, left lesion size and the months or years post-stroke that spoken description scores were collected. Training and validation were carried out on the first four groups. The fifth (lock-box/test set) group was used to test how well model accuracy generalises to new (unseen) data. The classification accuracy for a baseline logistic regression was 0.678 based on lesion size alone, rising to 0.757 and 0.813 when initial symptom severity and recovery time were successively added. The highest classification accuracy (0.854), area under the curve (0.899) and F1 score (0.901) were observed when 8 regions of interest were extracted from each MRI scan and combined with lesion size, initial severity and recovery time in a 2D Residual Neural Network (ResNet). This was also the best model when data were limited to the 286 participants with moderate or severe initial aphasia (with area under curve = 0.865), a group that would be considered more difficult to classify. Our findings demonstrate how imaging and tabular data can be combined to achieve high post-stroke classification accuracy, even when the dataset is small in machine learning terms. We conclude by proposing how the current models could be improved to achieve even higher levels of accuracy using images from hospital scanners