Mark C. K. Hamilton

Bio: Mark C. K. Hamilton is an academic researcher from National Institute for Health Research. The author has contributed to research in topics: Aerobic exercise & Stairstep interpolation. The author has an hindex of 6, co-authored 7 publications receiving 96 citations. Previous affiliations of Mark C. K. Hamilton include University Hospitals Bristol NHS Foundation Trust & Bristol Royal Infirmary.

Transcatheter and endovascular stent graft management of coarctation-related pseudoaneurysms

Abstract: Objective Surgical correction of congenital aortic coarctation can lead to a number of important problems including late pseudoaneurysm formation. Redo surgery has a significant risk. Endovascular stent graft repair is increasingly used but there are limited data regarding this indication. We describe the experience of two UK congenital referral centres. Design Retrospective analysis of patients treated with endovascular aortic stent grafting for late pseudoaneurysms. Setting Two UK congenital heart centres, Bristol Heart Institute and Leeds General Infirmary. Patients 17 patients were treated 2006–2012. This represents all patients treated with this technique. Main outcome measures Procedural and postprocedure success and complications. Results The average time from index repair to endovascular repair of pseudoaneurysm was 24.6 years. The majority (70.6%) had patch aortoplasty as the original surgical procedure and 41.2% were not under follow-up or discharged. Stent grafting procedural success rate was 100%. Median hospital stay postprocedure was 3 days. There was no procedural mortality or immediate complication. There were four minor early and three minor late complications. Imaging follow-up was available for an average of 31.6 months (range 6–65 months). All patients have demonstrated positive remodelling of the pseudoaneurysm with no incidence of continued expansion or stent graft failure up to 5 years following implant. Conclusions Endovascular stent graft treatment of pseudoaneurysms show promising results in a population who have a high risk of surgical re-intervention. Complication rates appear to be low and recovery is quick. Longer-term data remain essential to scrutinise stent graft performance in this situation.

Integrated Segmentation and Interpolation of Sparse Data

Abstract: We address the two inherently related problems of segmentation and interpolation of 3D and 4D sparse data and propose a new method to integrate these stages in a level set framework. The interpolation process uses segmentation information rather than pixel intensities for increased robustness and accuracy. The method supports any spatial configurations of sets of 2D slices having arbitrary positions and orientations. We achieve this by introducing a new level set scheme based on the interpolation of the level set function by radial basis functions. The proposed method is validated quantitatively and/or subjectively on artificial data and MRI and CT scans and is compared against the traditional sequential approach, which interpolates the images first, using a state-of-the-art image interpolation method, and then segments the interpolated volume in 3D or 4D. In our experiments, the proposed framework yielded similar segmentation results to the sequential approach but provided a more robust and accurate interpolation. In particular, the interpolation was more satisfactory in cases of large gaps, due to the method taking into account the global shape of the object, and it recovered better topologies at the extremities of the shapes where the objects disappear from the image slices. As a result, the complete integrated framework provided more satisfactory shape reconstructions than the sequential approach.

Role of cardiac MRI and CT in Fontan circulation

Abstract: A Fontan circulation is a series of palliative surgical procedures, which result in the diversion of the systemic venous return into pulmonary arterial circulation without passing through a ventricle. It is one of the available surgical strategies for patients with cardiac defects that preclude a successful bi-ventricular repair, which encompass a range of complex anatomy. This surgical repair has gone through a series of modifications since the concept was introduced in 1971. Echocardiography remains a vital tool in assessing patients with Fontan circulations but its limitations are well recognised. Cross-sectional imaging modalities such as cardiac MRI and CT are essential components in the systematic clinical evaluation of these patients. The purpose of this review is to understand the information that can be obtained with each cross-sectional modality as well as highlight the challenges that each modality faces.

Adaptations of aortic and pulmonary artery flow parameters measured by phase-contrast magnetic resonance angiography during supine aerobic exercise.

Abstract: Increased oxygen uptake and utilisation during exercise depend on adequate adaptations of systemic and pulmonary vasculature. Recent advances in magnetic resonance imaging techniques allow for direct quantification of aortic and pulmonary blood flow using phase-contrast magnetic resonance angiography (PCMRA). This pilot study tested quantification of aortic and pulmonary haemodynamic adaptations to moderate aerobic supine leg exercise using PCMRA. Nine adult healthy volunteers underwent pulse gated free breathing PCMRA while performing heart rate targeted aerobic lower limb exercise. Flow was assessed in mid ascending and mid descending thoracic aorta (AO) and main pulmonary artery (MPA) during exercise at 180 % of individual resting heart rate. Flow sequence analysis was performed by experienced operators using commercial offline software (Argus, Siemens Medical Systems). Exercise related increase in HR (rest: 69 ± 10 b min−1, exercise: 120 ± 13 b min−1) resulted in cardiac output increase (from 6.5 ± 1.4 to 12.5 ± 1.8 L min−1). At exercise, ascending aorta systolic peak velocity increased from 89 ± 14 to 122 ± 34 cm s−1 (p = 0.016), descending thoracic aorta systolic peak velocity increased from 104 ± 14 to 144 ± 33 cm s−1 (p = 0.004), MPA systolic peak velocity from 86 ± 18 to 140 ± 48 cm s−1 (p = 0.007), ascending aorta systolic peak flow rate from 415 ± 83 to 550 ± 135 mL s−1 (p = 0.002), descending thoracic aorta systolic peak flow rate from 264 ± 70 to 351 ± 82 mL s−1 (p = 0.004) and MPA systolic peak flow rate from 410 ± 80 to 577 ± 180 mL s−1 (p = 0.006). Quantitative blood flow and velocity analysis during exercise using PCMRA is feasible and detected a steep exercise flow and velocity increase in the aorta and MPA. Exercise PCMRA can serve as a research and clinical tool to help quantify exercise blood flow adaptations in health and disease and investigate patho-physiological mechanisms in cardio-pulmonary disease.

High-pitch computed tomography pulmonary angiography with iterative reconstruction at 80 kVp and 20 mL contrast agent volume

Abstract: To evaluate the image quality, radiation dose and diagnostic accuracy of 80kVp, high-pitch CT pulmonary angiography (CTPA) with iterative reconstruction using 20 ml of contrast agent. One hundred patients with suspected pulmonary embolism (PE) were randomly divided into two groups (n = 50 each; group A, 100 kVp, 1.2 pitch, 60 ml of contrast medium and filtered back projection algorithm; group B, 80 kVp, 2.2 pitch, 20 ml of contrast medium and sinogram affirmed iterative reconstruction). Image quality, diagnostic accuracy and radiation dose were evaluated and compared. Mean CT numbers of pulmonary arteries in group B were higher than those in group A (all P 0.05). Compared with group A, radiation dose of group B was reduced by 50.3 % (P < 0.001). High-pitch CTPA at 80 kVp can obtain sufficient image quality in normal-weight individuals with 20 ml of contrast agent and half the radiation dose of a conventional CTPA protocol. • CTPA is feasible at 80 kVp using only 20 ml of contrast agent. • High-pitch CTPA at 80 kVp has an effective dose under 1 mSv. • This CTPA protocol can obtain sufficient image quality in normal-weight individuals.

Effect of Noise-Optimized Monoenergetic Postprocessing on Diagnostic Accuracy for Detecting Incidental Pulmonary Embolism in Portal-Venous Phase Dual-Energy Computed Tomography.

Abstract: Objectives The aim of this study was to evaluate the diagnostic accuracy of virtual monoenergetic images (MEI+) at low kiloelectronvolt levels for the detection of incidental pulmonary embolism (PE) in oncological follow-up portal-venous phase dual-energy (DE-CTpv) staging. Materials and methods Twenty-six patients with incidental PE in DE-CTpv staging, which was confirmed by computed tomography pulmonary angiography (CTPA), were included in this study. In addition, 26 matched control patients who were negative for PE in both DE-CTpv and CTPA were included. All examinations were performed on a third-generation DE-CT system in single-energy (CTPA) and dual-energy mode (DE-CTpv). Subsequently, 2 series of MEI+ data sets were reconstructed at 40 and 55 keV from the DE-CTpv data and compared with CTPA and the linearly blended CTpv images. Diagnostic accuracy and diagnostic confidence were calculated and compared for MEI+ reconstructions and for CTpv images regarding the detection of PE with CTPA as standard of reference. Results In 3 patients, PE was only detectable in CTPA and in the 40-kV and 55-kV MEI+ reconstructions but not in CTpv images. Diagnostic accuracy increased significantly for both MEI+ series (40 keV; area under the curve [AUC], 0.928; 95% confidence interval [CI], 0.879-0.978; 55 keV; AUC, 0.960; 95% CI, 0.922-0.998) as compared with CTpv (AUC, 0.814; 95% CI, 0.741-0.887; P ≤ 0.004). Diagnostic confidence was rated highest in CTPA (median, 5; range, 3-5) followed by 55-keV MEI+ and 40-keV MEI+ (median, 5; range, 2-5 and median, 5; range, 2-5, respectively) and was lowest for CTpv (median, 4; range, 1-5), with significant differences to CTPA and MEI+ reconstructions (P ≤ 0.001). Conclusions Monoenergetic image reconstructions from DE-CT data sets at low kiloelectronvolt levels improve diagnostic accuracy for the detection of incidental PE in oncological follow-up DE-CTpv staging, with the highest subjective diagnostic confidence in MEI+ at 55 keV.

Methodology for image-based reconstruction of ventricular geometry for patient-specific modeling of cardiac electrophysiology.

Abstract: Patient-specific modeling of ventricular electrophysiology requires an interpolated reconstruction of the 3-dimensional (3D) geometry of the patient ventricles from the low-resolution (Lo-res) clinical images. The goal of this study was to implement a processing pipeline for obtaining the interpolated reconstruction, and thoroughly evaluate the efficacy of this pipeline in comparison with alternative methods. The pipeline implemented here involves contouring the epi- and endocardial boundaries in Lo-res images, interpolating the contours using the variational implicit functions method, and merging the interpolation results to obtain the ventricular reconstruction. Five alternative interpolation methods, namely linear, cubic spline, spherical harmonics, cylindrical harmonics, and shape-based interpolation were implemented for comparison. In the thorough evaluation of the processing pipeline, Hi-res magnetic resonance (MR), computed tomography (CT), and diffusion tensor (DT) MR images from numerous hearts were used. Reconstructions obtained from the Hi-res images were compared with the reconstructions computed by each of the interpolation methods from a sparse sample of the Hi-res contours, which mimicked Lo-res clinical images. Qualitative and quantitative comparison of these ventricular geometry reconstructions showed that the variational implicit functions approach performed better than others. Additionally, the outcomes of electrophysiological simulations (sinus rhythm activation maps and pseudo-ECGs) conducted using models based on the various reconstructions were compared. These electrophysiological simulations demonstrated that our implementation of the variational implicit functions-based method had the best accuracy.