Quantitative image reconstruction for total-body PET imaging using the 2-meter long EXPLORER scanner

Figure 10.

Xuezhu Zhang1, Jian Zhou1, Simon R Cherry1,2, Ramsey D Badawi1,2, Jinyi Qi1

1 Department of Biomedical Engineering, University of California, Davis, CA, United States of America; 2 Department of Radiology, University of California, Davis, CA, United States.of America.

DOI: 10.1088/1361-6560/aa5e46

The EXPLORER project aims to build a 2 meter long total-body PET scanner, which will provide extremely high sensitivity for imaging the entire human body. It will possess a range of capabilities currently unavailable to state-of-the-art clinical PET scanners with a limited axial field-of-view. The huge number of lines-of-response (LORs) of the EXPLORER poses a challenge to the data handling and image reconstruction. The objective of this study is to develop a quantitative image reconstruction method for the EXPLORER and compare its performance with current whole-body scanners. Fully 3D image reconstruction was performed using time-of-flight list-mode data with parallel computation. To recover the resolution loss caused by the parallax error between crystal pairs at a large axial ring difference or transaxial radial offset, we applied an image domain resolution model estimated from point source data. To evaluate the image quality, we conducted computer simulations using the SimSET Monte–Carlo toolkit and XCAT 2.0 anthropomorphic phantom to mimic a 20 min whole-body PET scan with an injection of 25 MBq 18F-FDG. We compare the performance of the EXPLORER with a current clinical scanner that has an axial FOV of 22 cm. The comparison results demonstrated superior image quality from the EXPLORER with a 6.9-fold reduction in noise standard deviation comparing with multi-bed imaging using the clinical scanner.

In vitro comparative assessment of decellularized bovine pericardial patches and commercial bioprosthetic heart valves

Figure 4.

Paola Aguiari1,2, Laura Iop1,2, Francesca Favaretto3, Cátia Marisa Lourenco Fidalgo1,2, Filippo Naso1, Gabriella Milan3, Vincenzo Vindigni4, Michel Spina5, Franco Bassetto4, Andrea Bagno6, Roberto Vettor3 and Gino Gerosa1,2

1 Department of Cardiac, Thoracic and Vascular Sciences, University of Padua, via Giustiniani 2, I-35128, Padua, Italy; 2 Venetian Institute of Molecular Medicine, Padua, Italy; 3 Internal Medicine, Clinica Medica 3, Department of Medicine, University of Padua, via Giustiniani 2, I-35128, Padua, Italy; 4 Department of Neuroscience, University of Padua, via Giustiniani 2, Padua, Italy; 5 Department of Biomedical Sciences, University of Padua, viale Giuseppe Colombo 3, Padua, Italy; 6 Department of Industrial Engineering, University of Padua, via Marzolo 9, I-35128, Padua, Italy.


Notwithstanding their wide exploitation, biological prosthetic heart valves are characterized by limited durability (10–15 years). The treatment of biological tissues with chemical crosslinking agents such as glutaraldehyde accounts for the enhanced risk of structural deterioration associated with the early failure of bioprosthetic valves. To overcome the shortcomings of the currently available solutions, adoption of decellularized biological tissues of animal origin has emerged as a promising approach. The present study aims to assess in vitro cardiovascular scaffolds composed of bovine pericardium decellularized with the novel TRITDOC (TRIton-X100 and TauroDeOxyCholic acid) procedure. The effects of the treatment have been assessed by means of histological, biomolecular, cellular, biochemical and biomechanical analyses. The TRITDOC procedure grants the complete decellularization of bovine pericardial scaffolds while preserving the extracellular matrix architecture and the biomechanical properties. With a dedicated ELISA test, the TRITDOC procedure has been proven to ensure the complete removal of the alphaGal antigen, responsible for hyperacute rejection and for long-term deterioration of xenogenic biomaterials. Static seeding of the acellular pericardial patches with human adipose-derived stem cells resulted in an evenly repopulated scaffold without signs of calcification. The in vitro cyto-/immuno-compatibility response of the TRITDOC-bovine pericardium was compared with glutaraldehyde-treated xenogenic pericardium collected from two bioprosthetic devices currently used in clinical practice: PERIMOUNT MAGNA and TRIFECTATM. TRITDOC-bovine pericardium exhibited lower complement activation, lower cytotoxicity and a lower tendency to secrete pro-inflammatory cytokines compared to the tested commercial bioprostheses. Therefore, TRITDOC-decellularized pericardium could be considered as possible candidate material for the production of prosthetic heart valves.

Fractal and gray level co-occurrence matrix texture analysis of senescent and non-senescent deciduous teeth stem cells: A pilot study

Ivan Zaletel,1, Nebojša T. Milošević,2, Vera Todorović,3, Milica Kovačević-Filipović,4, Nela Puškaš,1

1 Institute of Histology and Embryology “Aleksandar Đ. Kostić”, School of Medicine, University of Belgrade, Belgrade, Serbia; 2 Department of Biophysics, School of Medicine, University of Belgrade, Belgrade, Serbia; 3 Department of Histology and Embryology, Faculty of Dentistry, Business Academy University, Novi Sad, Serbia; 4 Department of Pathophysiology, Faculty of Veterinary Medicine, University of Belgrade, Belgrade, Serbia.

DOI: 10.15761/FGNAMB.1000131

All cells in the human organism, including stem cells, have a limited lifespan and cease to divide after a certain number of divisions. The process of cellular senescence refers to incapability to progress through the cell cycle, thus leading the cell to an irreversible growth arrest. One of the most common biomarkers of cell senescence is senescence-associated β-galactosidase (SA-β-Gal/SABG), a lysosomal enzyme detectable at pH = 6.0. However, the proper identification of senescent cells is still insufficient and lacks adequate quantification parameters. In this paper we showed that fractal and gray level co-occurrence matrix (GLCM) texture analysis of cell nuclei are able to discriminate senescent from non-senescent cells. A total of 105 images of DTSCs nuclei from both SA-β-Gal+ and SA-β-Gal cells were used in this study. All of the computed parameters (fractal dimension, angular second moment, inverse difference moment, contrast, entropy and correlation) showed significant statistical difference between the nuclei of senescent and non-senescent stem cells (p < 0.001). Our results show the possible practical value of fractal and GLCM texture analysis as the new markers in the determination and quantification of DTSCs senescence.

Mathematical modeling of dormant cell formation in growing biofilm


Kotaro Chihara1, Shinya Matsumoto2, Yuki Kagawa3, Satoshi Tsuneda1,3
1Department of Life Science and Medical Bioscience, Waseda University, Tokyo, Japan; 2Center for Biofilm Engineering, Montana State University, Bozeman, MT, USA; 3Institute for Nanoscience and Nanotechnology, Waseda University, Tokyo, Japan
Understanding the dynamics of dormant cells in microbial biofilms, in which the bacteria are embedded in extracellular matrix, is important for developing successful antibiotic therapies against pathogenic bacteria. Although some of the molecular mechanisms leading to bacterial persistence have been speculated in planktonic bacterial cell, how dormant cells emerge in the biofilms of pathogenic bacteria such as Pseudomonas aeruginosa remains unclear. The present study proposes four hypotheses of dormant cell formation; stochastic process, nutrient-dependent, oxygen-dependent, and time-dependent processes. These hypotheses were implemented into a three-dimensional individual-based model of biofilm formation. Numerical simulations of the different mechanisms yielded qualitatively different spatiotemporal distributions of dormant cells in the growing biofilm. Based on these simulation results, we discuss what kinds of experimental studies are effective for discriminating dormant cell formation mechanisms in biofilms.

Understanding the dynamics of superparamagnetic particles under the influence of high field gradient arrays


Lester C Barnsley1, Dario Carugo1,2, Miles Aron1, Eleanor Stride1

1 Institute of Biomedical Engineering, Department of Engineering Science, University of Oxford, Old Road Campus Research Building, Oxford, OX3 7DQ, United Kingdom; 2 Faculty of Engineering and the Environment, University of Southampton, University Road, Southampton, SO17 1BJ, United Kingdom

DOI: 10.1088/1361-6560/aa5d46

The aim of this study was to characterize the behaviour of superparamagnetic particles in magnetic drug targeting (MDT) schemes. A 3-dimensional mathematical model was developed, based on the analytical derivation of the trajectory of a magnetized particle suspended inside a fluid channel carrying laminar flow and in the vicinity of an external source of magnetic force. Semi-analytical expressions to quantify the proportion of captured particles, and their relative accumulation (concentration) as a function of distance along the wall of the channel were also derived. These were expressed in terms of a non-dimensional ratio of the relevant physical and physiological parameters corresponding to a given MDT protocol.

The ability of the analytical model to assess magnetic targeting schemes was tested against numerical simulations of particle trajectories. The semi-analytical expressions were found to provide good first-order approximations for the performance of MDT systems in which the magnetic force is relatively constant over a large spatial range.

The numerical model was then used to test the suitability of a range of different designs of permanent magnet assemblies for MDT. The results indicated that magnetic arrays that emit a strong magnetic force that varies rapidly over a confined spatial range are the most suitable for concentrating magnetic particles in a localized region. By comparison, commonly used magnet geometries such as button magnets and linear Halbach arrays result in distributions of accumulated particles that are less efficient for delivery.

The trajectories predicted by the numerical model were verified experimentally by acoustically focusing magnetic microbeads flowing in a glass capillary channel, and optically tracking their path past a high field gradient Halbach array.

Image quality transfer and applications in diffusion MRI

Demonstration of IQT image-resolution enhancement. The figure shows DEC maps ...

Daniel C. Alexandera, Darko Zikicb, Aurobrata Ghosha, Ryutaro Tannoa, Viktor Wottschelc, Jiaying Zhanga, Enrico Kadena, Tim B. Dyrbyd, e, Stamatios N. Sotiropoulosf, g, Hui Zhanga, Antonio Criminisib

a Centre for Medical Image Computing and Dept. Computer Science, UC1EL, Gower Street, London, WC 6BT; b Microsoft Research Cambridge, Cambridge, UK; c Institute of Neurology, UCL, Queen Square, London; d Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital Hvidovre, Hvidovre, Denmark; e Dept. Applied Maths and Computer Science, Technical University of Denmark, Lyngby, Denmark; f FMRIB Centre, University of Oxford, John Radcliffe Hospital, Headington, UK; g Sir Peter Mansfield Imaging Centre, School of Medicine, University of Nottingham, UK

DOI: 10.1016/j.neuroimage.2017.02.089

This paper introduces a new computational imaging technique called image quality transfer (IQT). IQT uses machine learning to transfer the rich information available from one-off experimental medical imaging devices to the abundant but lower-quality data from routine acquisitions. The procedure uses matched pairs to learn mappings from low-quality to corresponding high-quality images. Once learned, these mappings then augment unseen low quality images, for example by enhancing image resolution or information content. Here, we demonstrate IQT using a simple patch-regression implementation and the uniquely rich diffusion MRI data set from the human connectome project (HCP). Results highlight potential benefits of IQT in both brain connectivity mapping and microstructure imaging. In brain connectivity mapping, IQT reveals, from standard data sets, thin connection pathways that tractography normally requires specialised data to reconstruct. In microstructure imaging, IQT shows potential in estimating, from standard “single-shell” data (one non-zero b-value), maps of microstructural parameters that normally require specialised multi-shell data. Further experiments show strong generalisability, highlighting IQT’s benefits even when the training set does not directly represent the application domain. The concept extends naturally to many other imaging modalities and reconstruction problems.

Proton therapy of prostate cancer by anterior-oblique beams: implications of setup and anatomy variations

Figure 1.

M Moteabbed, A Trofimov, G C Sharp, Y Wang, A L Zietman, J A Efstathiou, H-M Lu

Massachusetts General Hospital, Boston, MA 02114, United States of America; Harvard Medical School, Boston, MA 02115, United States of America

DOI: 10.1088/1361-6560/62/5/1644

Proton therapy of prostate by anterior beams could offer an attractive option for treating patients with hip prosthesis and limiting the high-dose exposure to the rectum. We investigated the impact of setup and anatomy variations on the anterior-oblique (AO) proton plan dose, and strategies to manage these effects via range verification and adaptive delivery. Ten patients treated by bilateral (BL) passive-scattering proton therapy (79.2 Gy in 44 fractions) who underwent weekly verification CT scans were selected. Plans with AO beams were additionally created. To isolate the effect of daily variations, initial AO plans did not include range uncertainty margins. The use of fixed planning margins and adaptive range adjustments to manage these effects was investigated. For each case, the planned dose was recalculated on weekly CTs, and accumulated on the simulation CT using deformable registration to approximate the delivered dose. Planned and accumulated doses were compared for each scenario to quantify dose deviations induced by variations. The possibility of estimating the necessary range adjustments before each treatment was explored by simulating the procedure of a diode-based in vivo range verification technique, which would potentially be used clinically. The average planned rectum, penile bulb and femoral heads mean doses were smaller for initial AO compared to BL plans (by 8.3, 16.1 and 25.9 Gy, respectively). After considering interfractional variations in AO plans, the target coverage was substantially reduced. The maximum reduction of V 79.2/D 95/D mean/EUD for AO (without distal margins) (25.3%/10.7/1.6/4.9 Gy, respectively) was considerably larger than BL plans. The loss of coverage was mainly related to changes in water equivalent path length of the prostate after fiducial-based setup, caused by discrepancies in patient anterior surface and bony-anatomy alignment. Target coverage was recovered partially when using fixed planning margins, and fully when applying adaptive range adjustments. The accumulated organs-at-risk dose for AO beams after range adjustment demonstrated full sparing of femoral heads and superior sparing of penile bulb and rectum compared to the conventional BL cases. Our study indicates that using AO beams makes prostate treatment more susceptible to target underdose induced by interfractional variations. Adaptive range verification/adjustment may facilitate the use of anterior beam approaches, and ensure adequate target coverage in every fraction of the treatment.