Nick Byrne

A systematic review of image segmentation methodology, used in the additive manufacture of patient-specific 3D printed models of the cardiovascular system.

Background Shortcomings in existing methods of image segmentation preclude the widespread adoption of patient-specific 3D printing as a routine decision-making tool in the care of those with congenital heart disease. We sought to determine the range of cardiovascular segmentation methods and how long each of these methods takes. Methods A systematic review of literature was undertaken. Medical imaging modality, segmentation methods, segmentation time, segmentation descriptive quality (SDQ) and segmentation software were recorded. Results Totally 136 studies met the inclusion criteria (1 clinical trial; 80 journal articles; 55 conference, technical and case reports). The most frequently used image segmentation methods were brightness thresholding, region growing and manual editing, as supported by the most popular piece of proprietary software: Mimics (Materialise NV, Leuven, Belgium, 1992–2015). The use of bespoke software developed by individual authors was not uncommon. SDQ indicated that reporting of image segmentation methods was generally poor with only one in three accounts providing sufficient detail for their procedure to be reproduced. Conclusions and implication of key findings Predominantly anecdotal and case reporting precluded rigorous assessment of risk of bias and strength of evidence. This review finds a reliance on manual and semi-automated segmentation methods which demand a high level of expertise and a significant time commitment on the part of the operator. In light of the findings, we have made recommendations regarding reporting of 3D printing studies. We anticipate that these findings will encourage the development of advanced image segmentation methods.

Three-dimensional printed models for surgical planning of complex congenital heart defects: an international multicentre study

OBJECTIVES To evaluate the impact of 3D printed models (3D models) on surgical planning in complex congenital heart disease (CHD). METHODS A prospective case-crossover study involving 10 international centres and 40 patients with complex CHD (median age 3 years, range 1 month-34 years) was conducted. Magnetic resonance imaging and computed tomography were used to acquire and segment the 3D cardiovascular anatomy. Models were fabricated by fused deposition modelling of polyurethane filament, and dimensions were compared with medical images. Decisions after the evaluation of routine clinical images were compared with those after inspection of the 3D model and intraoperative findings. Subjective satisfaction questionnaire was provided. RESULTS 3D models accurately replicate anatomy with a mean bias of -0.27 ± 0.73 mm. Ninety-six percent of the surgeons agree or strongly agree that 3D models provided better understanding of CHD morphology and improved surgical planning. 3D models changed the surgical decision in 19 of the 40 cases. Consideration of a 3D model refined the planned biventricular repair, achieving an improved surgical correction in 8 cases. In 4 cases initially considered for conservative management or univentricular palliation, inspection of the 3D model enabled successful biventricular repair. CONCLUSIONS 3D models are accurate replicas of the cardiovascular anatomy and improve the understanding of complex CHD. 3D models did not change the surgical decision in most of the cases (21 of 40 cases, 52.5% cases). However, in 19 of the 40 selected complex cases, 3D model helped redefining the surgical approach.

Three-dimensional printing in robot-assisted radical prostatectomy - an Idea, Development, Exploration, Assessment, Long-term follow-up (IDEAL) Phase 2a study

The surgical management of prostate cancer has been shown to be determined by the anatomical location of the tumour and its associated intricate relationship to the neurovascular bundle and the prostatic capsule. Studies have shown an improvement in decision making about preservation or resection of neurovascular bundles during robotic assisted prostatectomy (RARP) [1,2] during which the surgeon lacks the tactile feedback of conventional open surgery. This article is protected by copyright. All rights reserved.

3D Printed Models in Patients with Coronary Artery Fistulae: Anatomical Assessment and Interventional Planning

AIMS Coronary artery fistulae represent one of the most challenging anatomical defects to define accurately. We aimed to investigate the additional benefit conferred by volume rendering of tomographic images and 3D printing for diagnosis and interventional planning. METHODS AND RESULTS Four cases of coronary fistulae were considered for transcatheter closure. Multidetector computed tomography (three cases) or cardiac magnetic resonance (one case) images were acquired and segmented using Mimics software. Each case was reviewed after incremental consideration of diagnostic resources: two cardiologists reported source and volume-rendered images; device closure was discussed by the interventional cardiology team. All diagnoses and planned management were reviewed after inspection of a 3D model. Using source images alone, both cardiologists correctly described the course and drainage in two out of four cases. Aided by volume rendering, this improved to three out of four cases. Inspection of the 3D printed model prompted the planned interventional approach and device sizing to be altered in two out of four cases. In one out of four cases, the intervention was abandoned after inspection of the 3D printed model. CONCLUSIONS Diagnosis and management of patients with coronary artery fistulae rely on detailed image analyses. 3D models add value when determining the feasibility of, and the approach to intervention in these cases.

A novel 3D-printed hybrid simulation model for robotic-assisted kidney transplantation (RAKT)

Robotic-assisted kidney transplantation (RAKT) offers key benefits for patients that have been demonstrated in several studies. A barrier to the wider uptake of RAKT is surgical skill acquisition. This is exacerbated by the challenges of modern surgery with reduced surgical training time, patient safety concerns and financial pressures. Simulation is a well-established method of developing surgical skill in a safe and controlled environment away from the patient. We have developed a 3D printed simulation model for the key step of the kidney transplant operation which is the vascular anastomosis. The model is anatomically accurate, based on the CT scans of patients and it incorporates deceased donor vascular tissue. Crucially, it was developed to be used in the robotic operating theatre with the operating robot to enhance its fidelity. It is portable and relatively inexpensive when compared with other forms of simulation such as virtual reality or animal lab training. It thus has the potential of being more accessible as a training tool for the safe acquisition of RAKT specific skills. We demonstrate this model here.

Evaluation of a modified Cheatham-Platinum stent for the treatment of aortic coarctation by finite element modelling:

Objectives Stent implantation for the treatment of aortic coarctation has become a standard approach for the management of older children and adults. Criteria for optimal stent design and construction remain undefined. This study used computational modelling to compare the performance of two generations of the Cheatham-Platinum stent (NuMED, Hopkinton, NY, USA) deployed in aortic coarctation using finite element analysis. Design Three-dimensional models of both stents, reverse engineered from microCT scans, were implanted in the aortic model of one representative patient. They were virtually expanded in the vessel with a 16 mm balloon and a pressure of 2 atm. Results The conventional stent foreshortened to 96.5% of its initial length, whereas the new stent to 99.2% of its initial length. Diameters in 15 slices across the conventional stent were 11.6–15 mm (median 14.2 mm) and slightly higher across the new stent: 10.7–15.3 mm (median 14.5 mm) (p= 0.021). Apposition to the vessel wall was similar: conventional stent 31.1% and new stent 28.6% of total stent area. Conclusions The new design Cheatham-Platinum stent showed similar deployment results compared to the conventional design. The new stent design showed slightly higher expansion, using the same delivery balloon. Patient-specific computational models can be used for virtual implantation of new aortic stents and promise to inform subsequent in vivo trials.

Classification of abdominal vascular anomalies and use of 3D printing to support complex renal transplantation in children

Abstract Background Transplantation is the treatment of choice for paediatric renal recipients. However, there are increased challenges in small ( Methods We describe our management in five paediatric renal recipients with vascular anomalies (median age 7 years [IQR 4·5–13·0], median weight 18 kg [IQR 14·5–29·0]). We assessed the utility of 3D printing as a planning tool in four children with complex abnormalities (one retrospective case, three prospective cases) for whom implantation was uncertain as judged by conventional imaging. Surgically relevant donor and recipient anatomy was segmented from MRI or CT data (Mimics Medical v18.0, Materialise, Leuven, Belgium). The segmentation geometry derived from the extracted anatomical data was then exported in STL file format and physically fabricated with multimaterial, polyjet 3D printing technology (Objet500 Connex1, Objet-Stratasys). We assessed the value of models using questionnaires and geometric validation studies. Findings Four (80%) of five children survived after one death from sepsis (with a functioning graft). At the latest median follow-up of 19 months (IQR 10·5–83·0) renal allograft survival was 100% (death censored) with a median estimated glomerular filtration rate of 55 mL/min per 1·73 m 2 (IQR 45–66). We have previously classified these vascular anomolies on the basis of aortic and IVC patency (I=aorta patent, II=infrarenal segment occluded, III=suprarenal segment occluded, IV=all aorta occluded) and similarly for IVC patency (A–D). By independent questionnaire, all prospective 3D printed models were considered useful for preoperative planning, and thereby facilitated transplantation. In our retrospective proof of concept, Bland–Altman analysis found that the mean difference in vascular diameter between the printed model and segmentation geometry was −0·1 mm (95% CI −0·7 to 0·5), which was insignificant when compared with the measurement uncertainty (±0·4 mm) and the limits of surgical precision. All models showed geometrical consistency with preprinting designs and intraoperative anatomical correlation within surgical acceptance for crucial decision making. Interpretation Vascular anomalies do not necessarily preclude transplantation, and a classification system could guide management. Our feasibility study of patient-specific 3D printing suggests that cases classified as sufficiently complex can benefit from this technology. Patient-specific models provide the surgical team with the full, 3D, accessible, haptic, and spatial appreciation of anatomy that is crucial in surgical decision making and planning. This technology can inform the selection of suitable anastamosis sites in the presence of anomalies and the best surgical approach for implantation of an adult-sized kidney into a small child. Funding None.

Morphological three-dimensional analysis of papillary muscles in borderline left ventricles

OBJECTIVE Mitral valve anatomy has a significant impact on potential surgical options for patients with hypoplastic or borderline left ventricle. Papillary muscle morphology is a major component regarding this aspect. The purpose of this study was to use cardiac magnetic resonance to describe the differences in papillary muscle anatomy between normal, borderline, and hypoplastic left ventricles. METHODS We carried out a retrospective, observational cardiac magnetic resonance study of children (median age 5.36 years) with normal (n=30), borderline (n=22), or hypoplastic (n=13) left ventricles. Borderline and hypoplastic cases had undergone an initial hybrid procedure. Morphological features of the papillary muscles, location, and arrangement were analysed and compared across groups. RESULTS All normal ventricles had two papillary muscles with narrow pedicles; however, 18% of borderline and 46% of hypoplastic cases had a single papillary muscle, usually the inferomedial type. In addition, in borderline or hypoplastic ventricles, the supporting pedicle occasionally displayed a wide insertion along the ventricular wall. The length ratio of the superolateral support was significantly different between groups (normal: 0.46±0.08; borderline: 0.39±0.07; hypoplastic: 0.36±0.1; p=0.009). No significant difference, however, was found when analysing the inferomedial type (0.42±0.09; 0.38±0.07; 0.39±0.22, p=0.39). The angle subtended between supports was also similar among groups (113°±17°; 111°±51° and 114°±57°; p=0.99). A total of eight children with borderline left ventricle underwent biventricular repair. There were no significant differentiating features for papillary muscle morphology in this subgroup. CONCLUSIONS The superolateral support can be shorter or absent in borderline or hypoplastic left ventricle cases. The papillary muscle pedicles in these patients often show a broad insertion. These changes have important implications on surgical options and should be described routinely.

Steps towards automated image segmentation as part of a 3D printing pipeline in congenital heart disease

Background The combination of 3D printing with CMR images has the potential to allow full, tactile appreciation of the complex of structures that make up a congenital heart abnormality. However, the use of 3D printing is mostly limited to larger teaching hospitals and research centres. Others working in this area have suggested that the technical and medical expertise necessitated by manual image segmentation procedures preclude the translation of this technology into mainstream care. In particular, the laborious nature of existing methods demand an unrealistic amount of the clinician’s time to achieve a full segmentation of the relevant structures.

Automatic scar segmentation in dual inversion recovery images is more consistent with manual outlining than in conventional inversion recovery images

Background The dual inversion recovery (dual IR) pulse sequence has recently been shown to improve blood suppression and infarct delineation in late gadolinium enhancement (LGE) images of myocardial infarction. This resulted in significantly lower inter-observer variability in manual outlining of scar and higher expert confidence in scar detection and transmurality when compared with conventional inversion recovery (IR) images. Computer algorithms have been shown to improve the accuracy of scar segmentation within IR images. We sought to develop and optimise a set of computer algorithms to quantify scar in both IR and dual IR images. Methods