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Physics in Medicine and Biology

Martin Rädler, Guillaume Landry, Simon Rit, Reinhard W Schulte, Katia Parodi, Georgios Dedes
We present a formalism for two dimensional (2D) noise reconstruction in proton computed tomography (pCT). This is necessary for the application of fluence modulated pCT (FMpCT) since it permits image noise prescription and the corresponding proton fuence optimization. We aimed at extending previously published formalisms to account for the impact of multiple Coulomb scattering (MCS) on projection noise, and the use of filtered back projection (FBP) reconstruction along \hl{curved paths} with distance driven binning (DDB)...
October 2, 2018: Physics in Medicine and Biology
Bjorn Stemkens, Eric S Paulson, Rob H N Tijssen
Magnetic Resonance Imaging (MRI) is increasingly being used in the radiotherapy workflow because of its superior soft tissue contrast and high flexibility in contrast. In addition to anatomical and functional imaging, MRI can also be used to characterize the physiologically induced motion of both the tumor and organs-at-risk. Respiratory-correlated 4D-MRI has gained large interest as an alternative to 4D-CT for the characterization of respiratory motion throughout the thorax and abdomen. Over the last 15 years numerous methods have been presented in literature...
October 1, 2018: Physics in Medicine and Biology
Carly Pellow, Christopher N Acconcia, Gang Zheng, David E Goertz
Nanobubbles hold potential for expanding utility of ultrasound contrast-based applications to extravascular targets, but their acoustic response and the effects of the surrounding environment remain relatively unexplored. Here we investigate the dynamics of porphyrin-encapsulated nanobubbles (diameter <0.4 µm; 10^6 mL-1) at clinically relevant frequencies (2.5 MHz and 8 MHz) as a function of pressure (0.2 - 1.0 MPa) in vessel- and tissue-mimicking phantoms to gain an understanding of nanobubble behaviour in intra- and extravascular compartments...
October 1, 2018: Physics in Medicine and Biology
Kyle Lafata, Jing Cai, Chunhao Wang, Julian Hong, Christopher R Kelsey, Fang-Fang Yin
The purpose of this research was to study the sensitivity of Computed Tomography (CT) radiomic features to motion blurring and signal-to-noise ratios (SNR), and investigate its downstream effect regarding the classification of non-small cell lung cancer (NSCLC) histology.
 Methods: Forty-three radiomic features were considered and classified into one of four categories: Morphological, Intensity, Fine Texture, and Coarse Texture. First, a series of simulations were used to study feature-sensitivity to changes in spatial-temporal resolution...
October 1, 2018: Physics in Medicine and Biology
Chemseddine Fatnassi, Habib Zaidi
In 3D gradient echo (GRE) and echo planar imaging (EPI), strong macroscopic field gradients are observed at air/tissue interfaces. The respective field gradients lead to an apparent increase in intravoxel dephasing, and, subsequently, to signal loss or image distortion. We propose an analytical approximation and a consequent method to compute low and high resolution field maps over all field map regimes (small and large echo spacing). A number of approaches which compute field maps from reconstructed phase data rely upon optimized linear least square fit and complex division approaches owing to the simplicity of their implementation...
October 1, 2018: Physics in Medicine and Biology
Hossein Arabi, Habib Zaidi
PET images commonly suffer from the high noise level and poor signal-to-noise ratio (SNR), thus adversely impacting lesion detectability and quantitative accuracy. In this work, a novel hybrid dual-domain PET denoising approach is proposed, which combines the advantages of both spatial and transform domain filtering to preserve image textures while minimizing quantification uncertainty. Spatial domain denoising techniques excel at preserving high-contrast patterns compared to transform domain filters, which perform well in recovering low-contrast details normally smoothed out by spatial domain filters...
October 1, 2018: Physics in Medicine and Biology
Evan McNabb, Raimond Wong, Michael D Noseworthy
Magnetic resonance imaging (MRI) has superior soft tissue contrast and lower interobserver variability compared to computed tomography and advances in equipment and pseudo-CT estimation have allowed for MR-only radiation therapy planning. Dedicated MR sequences have been used to localize paramagnetic structures with positive contrast, and most implanted seeds are gold fiducial markers (GFMs). We used a fast, dual-plane co-RASOR sequence to localize implanted GFMs with positive contrast in phantom and tissue to
 assess their resolution and registration accuracy of registration to CT...
September 27, 2018: Physics in Medicine and Biology
Jack Sauvage, Martin Flesch, Guillaume Ferin, An Nguyen-Dinh, Jonathan Poree, Mickael Tanter, Mathieu Pernot, Thomas Deffieux
4D Ultrafast ultrasound imaging was recently proposed to image and quantify blood flow with high sensitivity in 3D (Provost et al., 2014) as well as anatomical, mechanical or functional information. In 4D Ultrafast imaging, coherent compounding of tilted planes waves emitted by a 2-D matrix array are used to image the medium at high volume rate. 4D ultrafast imaging, however, requires high count electronics (>1000) to drive those probes. Alternatives approaches have been proposed and investigated to efficiently reduce the density of elements such as sparse or under-sampled arrays while maintaining a decent image quality and high volume rate...
September 25, 2018: Physics in Medicine and Biology
Michael Matter, Lena Nenoff, Gabriel Meier, Damien Charles Weber, Antony John Lomax, Francesca Albertini
Patient specific verification (PSV) measurements for pencil beam scanning (PBS) proton therapy are resource-consuming and necessitate substantial beam time outside of clinical hours. As such, efforts to safely reduce the PSV-bottleneck in the clinical work-flow are of great interest. Here, capabilities of current PSV methods to ensure the treatment integrity were investigated and compared to an alternative approach of reconstructing the dose distribution directly from the machine control- or delivery log files with the help of an independent dose calculation (IDC)...
September 20, 2018: Physics in Medicine and Biology
Lokesh Basavarajappa, Arun Kumar Thittai
Rotation Elastogram (RE) is a 2D spatial distribution map of the estimated local rigid-body rotation undergone by a target when subjected to an external compression, which is one of the recent variants in elastographic imaging. A recent study has shown that inclusion-contrast in RE is independent of inclusion-background modulus contrast and thus may be helpful in distinguishing between barely-stiff benign and malignant lesions. However, estimation of quality RE requires not only precise axial displacement estimates but also lateral displacement estimates...
September 17, 2018: Physics in Medicine and Biology
Aaron R Selfridge, Simon R Cherry, Martin S Judenhofer
Preclinical positron emission tomography, combined with magnetic resonance imaging (PET/MRI), is increasingly used as a tool to simultaneously characterize functional processes in vivo. Many emerging preclinical applications, however, are limited by PET detection sensitivity, especially when generating short imaging frames for quantitative studies. One such application is dynamic multifunctional imaging, which probes multiple aspects of a biological process, using relationships between the datasets to quantify interactions...
December 6, 2018: Physics in Medicine and Biology
Daniel Suarez Escudero, Guillaume Goudot, Michael Vion, Mickael Tanter, Mathieu Pernot
Pulsed cavitation ultrasound therapy (PCUT) is an effective non-invasive therapeutic approach in various medical indications that relies on the mechanical effects generated by cavitation bubbles. Even though limited by the poor contrast, conventional ultrasound B-Mode imaging has been widely used for the guidance and monitoring of the therapeutic procedure, allowing the visualization of the cavitation bubble cloud. However, the visualization of the bubble cloud is often limited in deep organs such as the liver and the heart and remains moreover completely subjective for the operator...
December 6, 2018: Physics in Medicine and Biology
Pedro L Esquinas, Cristina Rodríguez-Rodríguez, Tullio V F Esposito, Jeppe Harboe, Marta Bergamo, Anna Celler, Katayoun Saatchi, Vesna Sossi, Urs O Häfeli
Dual-isotope (DI) studies offer a number of advantages in pre-clinical imaging. These include: reducing study times when compared with sequential scans, reducing the number of animals required for any given study, and most importantly, producing images perfectly registered in space and time that provide simultaneous information about two distinct body functions. The ability of single photon emission computed tomography (SPECT) to measure and differentiate energies of the emitted photons makes it well suited for DI imaging...
December 6, 2018: Physics in Medicine and Biology
Yue-Houng Hu, Matthew W Jacobson, Mengying Shi, Marios Myronakis, Adam Wang, Paul Baturin, Pascal Huber, Rony Fueglistaller, Daniel Morf, Josh Star-Lack, Ross I Berbeco
In radiation therapy, improvements in treatment conformality are often limited by movement of target tissue. To better treat the target, tumor tracking strategies involving beam's-eye-view (BEV) have been explored. However, localization surrogates like implanted fiducial markers may sometimes leave the field-of-view (FOV), as defined by the linear accelerator (LINAC) multi-leaf collimator (MLC). Radiation leakage through the MLC has been measured previously at approximately 1%-2%. High sensitivity prototype detectors imagers may improve the ability to visualize objects outside of the MLC FOV during treatment...
December 6, 2018: Physics in Medicine and Biology
Frank M Gagliardi, Rick D Franich, Moshi Geso
This research investigated the dose response and post-irradiation stability of water-equivalent PRESAGE® dosimeters exposed to synchrotron radiation. Water-equivalent PRESAGE® dosimeters were irradiated up to 1000 Gy in a synchrotron x-ray beam with a mean energy of 95.3 keV. The change in optical density was measured using UV/visible spectrophotometry pre- and post-irradiation using a wavelength of 630 nm. Dose response was found to be approximately linear from 0-200 Gy with saturation occurring above 300 Gy...
December 6, 2018: Physics in Medicine and Biology
Travis W Sawyer, Swati Chandra, Photini F S Rice, Jennifer W Koevary, Jennifer K Barton
Ovarian cancer has the lowest survival rate among all gynecologic cancers due to predominantly late diagnosis. Optical coherence tomography (OCT) has been applied successfully to experimentally image the ovaries in vivo; however, a robust method for analysis is still required to provide quantitative diagnostic information. Recently, texture analysis has proved to be a useful tool for tissue characterization; unfortunately, existing work in the scope of OCT ovarian imaging is limited to only analyzing 2D sub-regions of the image data, discarding information encoded in the full image area, as well as in the depth dimension...
December 4, 2018: Physics in Medicine and Biology
Vasant Kearney, Jason W Chan, Samuel Haaf, Martina Descovich, Timothy D Solberg
The goal of this study is to demonstrate the feasibility of a novel fully-convolutional volumetric dose prediction neural network (DoseNet) and test its performance on a cohort of prostate stereotactic body radiotherapy (SBRT) patients. DoseNet is suggested as a superior alternative to U-Net and fully connected distance map-based neural networks for non-coplanar SBRT prostate dose prediction. DoseNet utilizes 3D convolutional downsampling with corresponding 3D deconvolutional upsampling to preserve memory while simultaneously increasing the receptive field of the network...
December 4, 2018: Physics in Medicine and Biology
M Biondi, E Vanzi, G De Otto, S F Carbone, V Nardone, F Banci Buonamici
Texture analysis (TA) applied to CT imaging is an intensely studied topic and many studies suggested TA potential value in imaging characterisation for diagnostic purposes in different fields. However, often authors do not consider the reproducibility and the robustness versus variations in acquisition parameters; in this work, we wanted to explore the robustness of the TA features extracted from CT images. We scanned a commercial phantom (CIRS model 062M) containing plugs with nine different tissue equivalent electron densities using two different CT scanners of the same vendor and changing tube current (100 and 200 mA without modulation) and peak voltage (80 and 140 kVp)...
December 4, 2018: Physics in Medicine and Biology
D Modena, M Baragona, D Bošnački, B J T Breuer, A Elevelt, R T H Maessen, P A J Hilbers, H M M Ten Eikelder
Magnetic resonance-guided high intensity focused ultrasound (MR-HIFU) is a noninvasive thermal technique that enables rapid heating of a specific area in the human body. Its clinical relevance has been proven for the treatments of soft tissue tumors, like uterine fibroids, and for the treatments of solid tumors in bone. In MR-HIFU treatment, MR-thermometry is used to monitor the temperature evolution in soft tissue. However, this technique is currently unavailable for bone tissue. Computer models can play a key role in the accurate prediction and monitoring of temperature...
December 4, 2018: Physics in Medicine and Biology
Seong Tae Kim, Jae-Hyeok Lee, Hakmin Lee, Yong Man Ro
Recently, deep learning technology has achieved various successes in medical image analysis studies including computer-aided diagnosis (CADx). However, current CADx approaches based on deep learning have a limitation in interpreting diagnostic decisions. The limited interpretability is a major challenge for practical use of current deep learning approaches. In this paper, a novel visually interpretable deep network framework is proposed to provide diagnostic decisions with visual interpretation. The proposed method is motivated by the fact that the radiologists characterize breast masses according to the breast imaging reporting and data system (BIRADS)...
December 4, 2018: Physics in Medicine and Biology
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