Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session J35: Physics of Medical Imaging, Measurement, and Tissue Characterization |
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Sponsoring Units: GMED Chair: Wojciech Zbijewski, Johns Hopkins University Room: 110 |
Tuesday, March 3, 2020 2:30PM - 2:42PM |
J35.00001: Imaging the brain across scales using light, magnetic fields, and models Michèle Desjardins Functional Magnetic Resonance Imaging (fMRI) is a powerful tool to map brain activity non-invasively and is the foundation of tens of thousands of published neuroscience studies. However, fMRI does not measure neurons directly. Instead, in the most common form of fMRI called Blood Oxygen Level Dependent (BOLD), changes in the concentration of paramagnetic deoxyhemoglobin in the blood are detected. Although BOLD is correlated with neural activity, its interpretation in healthy and diseased brain remains limited. |
Tuesday, March 3, 2020 2:42PM - 2:54PM |
J35.00002: Calculation of carbon-ion beam’s range in different media used for radiation therapy Panagiota Galanakou, Theodora Leventouri, Wazir Muhammad Carbon-ion radiotherapy (CIRT) is a new radiation modality with significant physical and biological advantages over photon irradiation. Range assessment is a major challenge and it is considered the key for using the full potential of carbon ion therapies. The purpose of this research is to develop a novel and practical method for monitoring accurately the carbon ion range in different types of tissue during treatment. The proposed method is based on the Doppler Shift Effect of Prompt Gammas (PGs), which give real–time information due to the instantaneous nuclear de-excitation, and thus PG shifted energy can quantify the mean carbon energy with respect to PG spectrum, and then the predicted range can be calibrated. We develop a mathematical model with initial carbon ion energies within the range of 100MeV/u-450 MeV/u for different detection angles of 0°-90°, and different target materials including water, air, and soft tissue. The results of our calculations are verified by Monte Carlo simulations. |
Tuesday, March 3, 2020 2:54PM - 3:06PM |
J35.00003: MRI Mapping of Heat Dissipation from Polydopamine Particles under Infra-Red Irradiation Janusz Hankiewicz, John Stroud, Zbigniew J Celinski, Yuriy Garbovskiy, Aiming Lu, Krzysztof Gorny, David Woodrum, Stefan Jurga, Kosma Szutkowski, Radoslaw Mrowczynski Polydopamine (PDA) is a new nanomaterial with promising properties for photothermal therapies. We investigated heating of phantoms made of agar gel with different concentrations (from 1 to 200 mg/ml) of PDA 100 nm particles. Spectrophotometry measurements show significant absorption in near-infrared range with increases below 300 nm. The laser beam (808 nm, 5W) was guided through a fiberglass guide and dispersed by a diffuser. A 25 ml phantom was placed in styrofoam thermal insulation. The temperature of the phantom after 5 minutes of continuous laser irradiation increased dramatically for concentrations above 100 mg/ml. For concentration of 200 mg/ml, an increase of 41 oC was achieved, about 14 times higher than for the control pure agar gel. Larger phantoms were studied in MRI settings to obtain heat dissipation maps, i.e. relative change of temperature in the phantom volume for different laser irradiation time and power. Temperature maps were obtained by analyzing the phase change due to proton resonance frequency shift (PRF). PRF results were compared to measurements using four miniature MRI compatible temperature sensors. Results allowed us to determine thermal gradients produced by single point heating which may be useful in MRI guided laser ablations of cancers. |
Tuesday, March 3, 2020 3:06PM - 3:18PM |
J35.00004: Multi-Regularization Reconstruction of One-Dimensional T2 Distributions in Magnetic Resonance Relaxometry Chuan Bi, Yvonne M. Ou, Wenshu Qian, You Zhuo, Richard Spencer Measurements of T2 relaxation time distributions in magnetic resonance relaxometry are increasingly used to probe microstructural details of materials or tissues. However, extracting the model from the acquired data is a severely ill-conditioned problem. Tikhonov regularization and related methods are widely used to address this. Methods such as the L-curve and generalized cross-validation (GCV) select a single regularizer to obtain an optimal approximation to the underlying distribution. However, this procedure does not make use of the information content of the non-selected regularized results; given the lack of definitive criteria for regularization parameter selection, this represents a potential loss of substantial information. In contrast, we propose a new reconstruction method, Multi-Reg, incorporating a range of calculated regularized solutions. Multi-Reg is based on a dictionary of noise-corrupted regularized reconstructions of distribution basis functions. We demonstrate that Multi-Reg can out-perform the L-curve or GCV methods in simulation analyses of Gaussian distribution components, and present experimental results on mouse spinal cord and human muscle tissue. |
Tuesday, March 3, 2020 3:18PM - 3:30PM |
J35.00005: Hidden Dangers in MRI: Investigating Heating of Metallic Objects from Switching Gradient Fields John Stroud, Karl Stupic, Tucker Walsh, Tim Read, Zbigniew J Celinski, Janusz Hankiewicz With the number of medical implants increasing every year it is inevitable that some patients with implants will at some time undergo an MRI procedure. Investigating the safety of implants during an MRI scan is vital as with current medical record keeping it can be difficult to track implants, which may put patients in possible danger. It is known in MRI oscillating magnetic fields produced by an MRI scanner have the potential to induce eddy currents in metallic implants in turn these eddy currents can heat surrounding tissue and may potentially cause damage to healthy tissue. However, much of the research evaluating the safety risks that are associated with imaging around metallic implants has focused mainly on the magnetic component of RF radiation present in the MRI scanner, and not much attention has been paid to switching gradient fields in MRI which oscillate at much lower frequencies. We investigate local heating of conductive materials within an MRI scanner producing quantitative data on the position dependence of induced EMF and heating, as well as the interaction between different gradients within the scanner. This work will assist in evaluating any dangers that may be present to patients with a metallic implants. |
Tuesday, March 3, 2020 3:30PM - 3:42PM |
J35.00006: Superparamegnetic particles as MRI temperature contrast agent Janusz Hankiewicz, John Stroud, Stephen Russek, Karen Livesey, Casey Chalifour, Giacomo Parigi, Zbigniew J Celinski, Robert Camley, Dorota Lachowicz, Angelika Kmita, Marta Gajewska, Ela Trynkiewicz, Roma Wirecka, Marek Przybylski A method of MRI temperature contrast developed by our group, which employs temperature dependent local field inhomogeneities due to a presence of micrometer sized magnetic particles and corresponding changes in image intensity (T2* contrast), faces limitations due to particle size. For human applications, large particles cannot be used as they face problems with delivery and secretion. Smaller particles are required. However, spin transverse relaxation process for such particles is no longer governed by a static dephasing regime and T2* temperature dependent inhomogeneity contributions vanish due to averaging by spin motion. We hypothesize that superparamagnetic particles may provide contrast mechanisms only if nuclear relaxation is temperature dependent. To test this hypothesis, we used Mn-Zn ferrite superparamagnetic particles with an average size of 7.8 ± 2.1 nm. Particles with a 2 mM concentration were embeded in agar gel for NMR and MRI measurements at temperature 5 - 50 oC. At 3.0 T, NMR results show that T1 is temperature independent, while observed NMR linewidth drops from 130 Hz to 70 Hz and T2 increases from 1.3 ms to 2.8 ms. Intensity of T2 weighted MR images depends linearly on temperature, providing the contrasting mechanism necessary for temperature determination. |
Tuesday, March 3, 2020 3:42PM - 3:54PM |
J35.00007: Modeling of human body tissue compositions for Monte Carlo algorithm of Proton therapy dose computation with the Single Energy Computed Tomography Calibration Curve Maryam Ghasemi Ghonchehnazi, Grant Evans, Charles Shang
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Tuesday, March 3, 2020 3:54PM - 4:06PM |
J35.00008: Method, Mechanism, and Metrology for Measurement of Multi-Dimensional MTF in Medical Imaging Pengwei Wu, Mahadevappa Mahesh, John Boone, Jeffrey H Siewerdsen The spatial resolution characteristics of CT and cone-beam CT (CBCT) systems is well characterized by the spatial-frequency-dependent modulation transfer function (MTF). Emerging scanner technologies and reconstruction algorithms challenge conventional methods for MTF assessment, including the degree to which the system / image exhibits 3D resolution characteristics that are isotropic (vary in direction), stationary (vary with location), and linear (vary with contrast). We report an angled-edge test tool and oversampling method to measure the MTF in any direction in 3D image data, with extension to a spherical test tool for measurement in all directions. One particular direction (45° relative to the axial plane) is shown to avoid null space effects in cone-beam geometries and provide useful 1D quantitation of the fully 3D resolution characteristics. This method was tested using a mobile C-arm CBCT system and a high-resolution diagnostic CT scanner and shown to reveal underlying sources of non-isotropic resolution characteristics – for example, asymmetric apodization filters, detector binning modes, and focal spot size. The angled-edge or spherical test tools provide a practical means for quantitative characterization of 3D MTF characteristics for medical imaging systems. |
Tuesday, March 3, 2020 4:06PM - 4:18PM |
J35.00009: A novel approach to lead concentration measurements in bone using the L-shell x-ray fluorescence and strontium Kβ/Kα ratio. Mihai Gherase, Josh Jardenil, Sarah Kroeker Lead (Pb) is a well-known toxic element which accumulates in the bone after years or decades of exposure. Long-term Pb exposure is, therefore, assessed by in vivo bone Pb concentration measurements. In vivo bone Pb x-ray fluorescence (XRF) measurements are typically done in tibia bone to minimize the soft tissue (ST) x-ray attenuation. Bone Pb L-shell XRF (LXRF) can use compact XRF systems – a useful feature for potential bone Pb surveys. An optimal grazing-incidence position (OGIP) method was developed in our lab to enhance Pb detection by mitigating the x-ray scatter. The obstacle to in vivo applications is the unknown ST x-ray attenuation. The average ST x-ray linear attenuation coefficient and ultrasound-measured thickness past approach gave inaccurate results. In our method, the measured Kβ/Kα ratio of strontium (an essential trace element in the bone) was used to estimate the ST attenuation of the Pb x-rays. Plaster-of-Paris (poP) bone phantoms made with known Pb and Sr concentrations and polyoxymethylene (POM) ST phantoms of varying thickness were measured. The concordance correlation coefficients between the computed and the known Pb concentrations were in the -0.444 to 0.998 range. |
Tuesday, March 3, 2020 4:18PM - 4:30PM |
J35.00010: Quantifying Macroscopic and Microscopic Radiation Dose Enhancement with Gold Nanoparticles for a Range of Therapeutic Energies Tara Gray, Nema Bassiri, Shaquan David, Devanshi Patel, Neil Kirby, Kathryn Mayer The purpose of this study is to computationally quantify the macroscopic and microscopic radiation dose enhancement effects of different sizes and shapes of gold nanoparticles. A MicroSelectron HDR Ir-192 brachytherapy seed and a Varian 600C gantry head with 6 MV and 18 MV photon energies were modeled using Monte Carlo N-Particle radiation transport software (MCNP 6.2, Los Alamos National Laboratory). The repeating structures capability of MCNP6.2 was utilized to simulate nanoparticles of varying sizes inside a tumor with a diameter of 1 x 1 x 1 cm3. Additionally, a phase space file was created to compute dose deposited from secondary electrons around single nanoparticles of varying shapes (nanocubes, nanoprisms and nanospheres). Macroscopic simulations show an increase in dose enhancement generally with increasing mass percentage of gold and compare well with experimental results. Microscopic simulations show an increased dose enhancement of 20% - 50% due to secondary electrons up to 1 µm from the nanoparticle and is highest for nanoprisms due to a larger surface area to volume ratio. This work indicates the potential for gold nanoparticles to provide significant dose enhancement and more effective tumor cell killing in radiation oncology practice. |
Tuesday, March 3, 2020 4:30PM - 4:42PM |
J35.00011: Dependence of deep learning-based whole organ segmentation on training dataset size in computed tomography (CT) images Daniel Huff, Amy J Weisman, Robert Jeraj A significant drawback of deep learning-based medical image segmentation is its reliance on large amounts of labeled training data. However, little literature has characterized the dependence of model performance on the amount of training data provided. Here, we examine this dependence in the application of abdominal organ segmentation on patient CT images. |
Tuesday, March 3, 2020 4:42PM - 4:54PM |
J35.00012: Monte-Carlo simolation of X-ray energy spectrum for single and dual-energy radiography NASTARAN KHAMOOSHI Single-energy radiography is one of the most everyday nondestructive/noninvasive imagine methods that generate detailed images of tumors, nodules, crackes, defects,and discountuities has inside of human body |
Tuesday, March 3, 2020 4:54PM - 5:06PM |
J35.00013: Complex impedance quantification of cell migration for the physics of cancer Michael J Mimlitz, Andrew J. Walther, Michael Merrick, Catherine Weeder, Joe Bamesberger, Haris Akhter, Honour Djam, Andrew Ekpenyong Cell migration is a crucial step in cancer metastasis, the complex process which accounts for over 90% of cancer-related deaths. There is emerging evidence that radiotherapeutic doses meant to kill cancer cells can promote metastasis by enhancing cell migration. Here we quantify radiation-induced changes in cell migration as part of the physics of cancer: a novel research frontier unraveling the roles of physical properties of cells in cancer. We used a standard laboratory irradiator to irradiate both non-cancer (HCN2 neurons) and cancer cells (T98G glioblastoma) with 2 Gy, 10 Gy and 20 Gy of X-rays. To assess cell migration post-irradiation, we used a commercially available device, ECIS Z-Theta, which non-invasively measures and converts complex cell-substrate electric impedance into series resistance and capacitance in real time. We also used CdSe/ZnS core-shell quantum dots to quantify molecular changes in cells following radiotherapy. Both irradiated cell lines showed significantly (p <0.01) enhanced migration compared to non-irradiated cells, within the first 40 hours following irradiation with 20 Gy. Our results suggest cell migration as a new therapeutic target in anti-metastasis strategies for improved radiotherapy outcomes. |
Tuesday, March 3, 2020 5:06PM - 5:18PM |
J35.00014: Test-retest Reproducibility for Resting State Networks in fMRI Margarita Lopez, Brenda Bedolla-Moctezuma Resting state networks (rsN) are important to assess the neural connectivity in the brain in repose. The assessment of the rsN could help to the diagnosis and treatment of different psychological and psiquiatric disorders, for example different studies have found that the DMN is affected in patients with major depression. The BOLD signal could be affected and change by technical and phyisiological factors as: movement, cardiac function, different potioning of the subject in the scan, the hour of the day, etc. for that reason is important to evaluate the rsN reproducibility between subjects and sessions. In the present study we obtain the rsN for 36 volunteer healthy subjects (18-60 years old) in three different sessions separated by 15 days each one, we acquired two different BOLD rsfMRI sequences (eyes open) with different spatial resolution in a 3T scanner with a 32 head sense channel coil, the FE-EPI sequences have the following parameters TE/TR = 30/ 2000 ms, FA = 75, FOV= 240 mm x 240 mm x 123 mm, matrix 80x 78 x 35, with isometric spatial resolution of 3 mm and other with anisotropic resolution. The Intraclass Correlation Coefficient (ICC) was calculated and we found the ICC between first and second sessions less than the ICC between second and third sessions. |
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