Our Annual Young Investigators Symposium of Medical Physics Research and Development was held on May 29th 2015 at the University of California, Berkeley campus.
Students, postdocs, and residents from the Lawrence Berkeley National Laboratory, Stanford University, UC Berkely, UC Davis, UC Merced, and UC San Francisco participated in this year's symposium.
San Francisco Chapter of the AAPM –
Young Investigators Symposium
May 29, 2015: Noon – 6PM
University of California, Berkeley
Energy Biosciences Building
2151 Berkeley Way, Berkeley, CA 94720
11:30AM REGISTRATION OPEN
NOON-1PM LUNCH / Meet & Greet Friends and Colleagues
12:30PM INTRODUCTION / ANNOUNCEMENTS
12:45-2:30PM PRESENTATIONS (Part I)
Graduate Students & Post-Doctoral Scholars:
1. John Ready, PhD Candidate, Medical Physics, Nuclear Engineering Department, University of California, Berkeley Advisor: Kai Vetter, Title: A New Aperture-Based Imaging System for Prompt-Gamma Range Verification of Proton Beam Therapy
2. Eric Berg, Grad Student, UC Davis Biomedical Engineering, Advisor: Simon Cherry, Title: Detector development for EXPLORER: a high sensitivity, total-body PET scanner
3. Wei Zhang, Postdoc, UC Merced, School of Engineering, Advisor: Changqing Li, Title: CT guided diffuse optical tomography for breast cancer imaging
4. Jose A. Ramos-Mendez, PhD., Postdoctoral Scholar, UCSF Helen Diller Family Comprehensive Cancer Center, Advisor: Bruce Faddegon, Title: “TOPAS: Extending Geant4 for 4D radiation therapy simulations”
5. Paul Keselman, Graduate Student, UC Berkeley and UCSF joint Graduate Program in Bioengineering, Advisor: Steven Conolly, Title: High Contrast MR Saline Angiography: A safer alternative for patients suffering from Chronic Kidney Disease
6. Raiyan T. Zaman , Postdoctoral Fellow, Department of Radiation Oncology, Stanford University Cancer Center, Advisor: Lei Xing, Title: A Novel Scintillating-Balloon-Enabled Dual-Modality Catheter Based Imaging System to Characterize Atherosclerotic Plaque with Superior Sensitivity and Spatial Resolution
7. Mathew Adams, Graduate Student, UC Berkeley and UCSF joint Graduate Program in Bioengineering, Advisor: Chris Diederich, Title: Endoluminal Ultrasound Applicators for MR-guided Thermal Therapy of Pancreatic Tumors: Theoretical and Experimental Investigations
2:30-3PM Refreshment Break (Judges Confer)
3:00-4:30 PRESENTATIONS (Part II)
Graduate Students & Post-Doctoral Scholars (CONT’D):
8. Felipe Godinez, PhD, Chancellor’s Post Doctoral Fellow UC Davis, Department of Biomedical Engineering, Advisor: Ramsey Badawi, Title: High Spatial Resolution PET Imaging with Hybrid DOI Detectors.
9. Elaine Yu, PhD Candidate, UC Berkeley and UCSF joint Graduate Program in Bioengineering, Advisor: Steven Conolly, Title: Next Generation Field-Free Line Magnetic Particle Imaging
10. Mareike Held, PhD Candidate, UC Berkeley and UCSF joint Graduate Program in Bioengineering, Advisor: Olivier Morin, Title: Image quality of on-board imaging systems: can we use kV CBCT, MV CBCT, and/or MV CT images for rapid dose planning in urgent palliative radiotherapy treatment situations?
11. Bo Zheng, PhD Candidate, Bioengineering, UC Berkeley, Advisor: Steven Conolly, Title: System Hardware and Initial in vivo Experiments for Preclinical Magnetic Particle Imaging
12. M.G. Buddika Sumanasena, UC Davis Biomedical Engineering, Advisor: Ramsey Badawi, Title: Modular hybrid DOI detectors for PET
4:30-4:45PM Refreshment Break (Judges Confer)
4:45-5:45PM PRESENTATIONS (Part III)
MEDICAL PHYSICS RESIDENTS:
13. Erika Chin, Ph.D., Medical Physics Resident, Department of Radiation Oncology, Stanford Cancer Center, Advisor: Dr. Benjamin Fahimian, Title: Trajectory Modulated Arc Therapy: Development of Novel Arc Delivery Techniques Integrating Dynamic Table Motion for Extended Volume Treatments
14. David Hoffman, PhD, Medical Physics Resident, UC Davis Radiation Oncology Advisor: Stan Benedict, Title: Comprehensive Evaluation of Two Novel Transmission Detector Systems for Online Quality Assurance of External Beam Radiation Therapy
15. Chris McGuinness, Resident, UCSF Radiation Oncology, Advisor: Igor Barani, Title: A Patient Specific, Three-Component Model for Glioblastoma Growth and Radio-sensitivity
16. Michael Hadsell, Medical Physics Resident, Department of Radiation Oncology, Stanford Cancer Center, Advisor: Karl Bush Title: Tangential modulated arc therapy: A novel technique using megavoltage photons for the treatment of superficial disease
5:45PM JUDGES CONFER
6:00PM ANNOUNCEMENT OF AWARDS
Winners - Graduate Student/Post Doc Category
From left to right: Bo Zheng (1st prize), Paul Keselman (2nd prize) and Matthew Adams (3rd prize)
Winners - Resident Category
From left to right: Michael Hadsell (3rd prize), Erika Chin (1st prize) and Chris Mcguinness (2nd prize)
ALL Presentation Titles and Abstracts
(In Alphabetical Order)
1. Mathew Adams, Graduate Student, UC Berkeley / UCSF Joint Graduate Program in Bioengineering,
Advisor: Chris Diederich,
Title: Endoluminal Ultrasound Applicators for MR-guided Thermal Therapy of Pancreatic Tumors: Theoretical and Experimental Investigations
Abstract: Successful treatment of pancreatic cancer remains a significant challenge. Thermal therapy techniques, including thermal ablation for pain palliation and hyperthermia as an adjunctive therapy to enhance chemotherapy, radiation, or targeted drug delivery appear promising although remain technically limited. The objective of this study is to develop and evaluate an ultrasound applicator, intended for minimally-invasive placement into the stomach or duodenal lumen, for image-guided endoluminal thermal therapy of pancreatic tumors. A finite-element (FEM) 3D acoustic and biothermal model was implemented for theoretical analysis of the approach. Parametric studies over transducer geometries and frequencies revealed that focal, low frequency (1-3 MHz) transducers maximize penetration depth and improve thermal sparing of the luminal wall. 3D patient-specific FEM models of pancreatic tumors were generated and incorporated into modeling studies, and indicated that over 80% of the volume of small tumors (~2 cm diameter) within 35 mm of the duodenum could be safely ablated in less than 30 minutes or maintained at hyperthermic temperatures. Significant volumetric coverage of large head or body tumors (> 4 cm diameter) required sequential applicator repositionings and sonications along the gastric lumen. Prototype applicators containing two 3 MHz planar or lightly curvilinear transducers were fabricated and evaluated in ex vivo porcine carcass heating experiments under MR temperature imaging (MRTI) guidance. The applicator was positioned in the stomach adjacent to the pancreas, and sonications were performed for 10 min at 5 W/cm2 applied intensity. MRTI indicated over 20 ⁰C temperature rise in pancreatic tissue with heating penetration extending 3 cm from the luminal wall. A pilot MR-guided in vivo porcine study was performed and confirmed capability of producing thermal necrosis of pancreatic tissue with an endoluminal applicator positioned in the stomach lumen.
2. Eric Berg, Grad Student, UC Davis Biomedical Engineering,
Advisor: Simon Cherry, UC Davis Biomedical Engineering
Title: Detector development for EXPLORER: a high sensitivity, total-body PET scanner
Abstract: Our group is leading a consortium to build a high sensitivity, total-body PET scanner with a 2 meter axial field-of-view to expand the use of PET in many research areas and non-invasively study elusive physiology. As part of this aim, we are developing advanced detector technologies to accommodate and make full use of the scanner geometry. Specifically, the detectors should be capable of providing both a very precise measure of the 511 keV gamma interaction time in the detector (timing resolution) to be used for time-of-flight image reconstruction and 3D localization of the gamma interaction in the detector. For current clinical PET scanners, 2D localization of the gamma interaction is sufficient and is achieved by using a 2D array of long scintillator crystals; determining the crystal in which the gamma interacted provides two dimensions of the interaction position. This work focuses on using phosphor-coated scintillator crystals to provide the gamma interaction position along the crystal length (3rd dimension) without compromising timing resolution. The phosphor coating provides additional spatial information by altering the detector’s output signal shape according to the gamma interaction position. Here, we apply phosphor coating to the crystals in a detector module used in a state-of-art clinical PET scanner and characterize its performance. Various phosphor-coating configurations are applied to separate quadrants (6 x 6 crystals) for comparison. We found the original detector coincidence timing resolution to be 404 ps, which increased to 442 ps with phosphor coating. Further, we were able to estimate the gamma interaction depth with ~3 mm precision (> 50% improvement from original detector), demonstrating the suitability of this detector for use in the EXPLORER scanner.
3. Erika Chin, Ph.D., Medical Physics Resident, Department of Radiation Oncology, Stanford Cancer Center,
Advisor: Dr. Benjamin Fahimian,
Title: Trajectory Modulated Arc Therapy: Development of Novel Arc Delivery Techniques Integrating Dynamic Table Motion for Extended Volume Treatments.
Abstract: Integration of coordinated robotic table motion with inversely-planned arc delivery has the potential to resolve table-top delivery limitations of large-field treatments such as Total Body Irradiation (TBI), Total Lymphoid Irradiation (TLI), and Cranial-Spinal Irradiation (CSI). We formulate the foundation for Trajectory Modulated Arc Therapy (TMAT), and using Varian Developer Mode capabilities, experimentally investigate its practical implementation for such techniques.Methods A MATLAB algorithm was developed for inverse planning optimization of the table motion, MLC positions, and gantry motion under extended-SSD geometry. To maximize the effective field size, delivery trajectories for TMAT TBI were formed with the table rotated at 270º IEC and dropped vertically to 152.5cm SSD. Preliminary testing of algorithm parameters was done through retrospective planning analysis. Robotic delivery was programmed using custom XML scripting on the TrueBeam Developer Mode platform. Final dose was calculated using the Eclipse AAA algorithm. Initial verification of delivery accuracy was measured using OSLDs on a solid water phantom of varying thickness. Results A comparison of DVH curves demonstrated that dynamic couch motion irradiation was sufficiently approximated by static control points spaced in intervals of less than 2cm. Optimized MLC motion decreased the average lung dose to 68.5% of the prescription dose. The programmed irradiation integrating coordinated table motion was deliverable on a TrueBeam STx linac in 6.7 min. With the couch translating under an open 10cmx20cm field angled at 10°, OSLD measurements along the midline of a solid water phantom at depths of 3, 5, and 9cm were within 3% of the TPS AAA algorithm with an average deviation of 1.2%.Conclusions A treatment planning and delivery system for Trajectory Modulated Arc Therapy of extended volumes has been established and experimentally demonstrated for TBI. Extension to other treatment techniques such as TLI and CSI is readily achievable through the developed platform.
4. Felipe Godinez, PhD, Chancellor’s Post Doctoral Fellow UC Davis, Department of Biomedical Engineering,
Advisor: Ramsey Badawi,
Title: High Spatial Resolution PET Imaging with Hybrid DOI Detectors,
Abstract: Positron Emission Tomography (PET) is a molecular imaging modality capable of imaging trace amounts of radiolabeled molecules targeting biomarkers. Accurate PET studies of small targets require high image spatial resolution, for example, imaging small objects such as inflamed joints in Rheumatoid Arthritis. It has been shown that PET can measure the degree of inflammation in the synovium compartment of joints. PET imaging can also be used in pre-clinical research to study murine models of arthritis. However, imaging arthritic mouse paws poses a significant challenge, since a very high spatial resolution is required to accurately quantify the uptake in the paw joints. Imaging applications like these have set the need for the development of high-resolution detectors. These detectors should have depth of interaction (DOI) encoding capabilities to maintain resolution uniformity across the image. The focus of this work is the development and characterization of high-resolution DOI capable PET detectors and a scanner for mouse paw imaging called PawPET. The two PET detectors presented in this work were composed of arrays with LSO crystals of 0.5 x 0.5 x 8 mm3, coupled to a position sensitive photomultiplier tube on one end and an avalanche photodiode on the opposite end. The performance characterization of the detectors is presented in terms of their spatial, DOI, energy, and timing resolution. The scanner performance is measured in terms of spatial resolution and sensitivity. A description of the scanner gantry design is also given along with descriptions of the fabrication techniques used, such as rapid prototyping using 3D printing technology.
5. Michael Hadsell, Medical Physics Resident, Department of Radiation Oncology, Stanford Cancer Center,
Advisor: Karl Bush
Title: Tangential modulated arc therapy: A novel technique using megavoltage photons for the treatment of superficial disease
Abstract: In recent decades, great leaps forward in the treatment of deep-seated cancers have been made using arcs and static fields of intensity modulated megavoltage photon radiation. However, the treatment of more superficial lesions has made comparatively fewer advances, with breast treatments still relying on opposed tangent photon fields coupled with electron boosts and skin surface sarcomas being treated with superficial radionuclides or unmodulated electron fields and arcs. We propose a new type of treatment that employs a modulated and sliding tangential photon field to provide superior coverage of such superficial target volumes while drastically reducing dose to the underlying sensitive structures often present in these cases. Materials/Methods: Treatment plans were formulated for two representative chest wall cases. The first was a treatment of a sarcoma located on the right posterior chest wall with a concurrent boost to the gross tumor volume and the second was a hypothetical bilateral chest wall treatment of a breast cancer patient. For these cases, asymmetric jaw placements, angular limitations, and non-standard isocenter placements were used to force the optimization algorithm into finding solutions with beamlines that were tangential to the body surface. For the first case, the method proposed here was compared to both a conventional VMAT treatment and a conventional 3D treatment employing laterally opposed tangents and an electron boost, while for the second case, only a comparison to conventional VMAT was made because a standard 3D treatment failed to adequately cover the hypothetical target volume. Results: When compared with the use of conventional VMAT, the tangential arc treatment of the posterior chest wall case reduced the mean dose delivered to the lung by 3.3Gy (from 6.5 to 3.2Gy), while retaining the same level of target coverage for both the primary and boost volumes. When compared with conventional laterally opposed tangents plus and electron boost field, tangential VMAT succeeded in lowering the maximum lung dose from 50.9Gy to 26.4Gy. When applied to the hypothetical bilateral breast case, tangential VMAT achieved reductions in the V5 dose to the total lung by roughly a factor of two (98.6% to 47.7%) while the mean heart dose was lowered from 10.2Gy to 6.8Gy when compared to conventional VMAT treatment while achieving the same level of target coverage and homogeneity. Conclusion: Tangential modulated arc therapy as defined and shown in these and other preliminary studies has outperformed the more conventional modalities of treatment for superficial lesions and target volumes typically used in our clinic, combining the benefits of VMAT and conventional static opposed tangents while eliminating the weaknesses. It is our hope that with the advent of digitally controlled linear accelerators and patient couches, we can continue to explore the benefits of this new technique and extend its availability to a wider variety of patients in need of highly conformal superficial treatment.
6. Mareike Held, PhD Candidate, UCSF Dept of Radiation Oncology
Advisor: Olivier Morin
Title: Image quality of on-board imaging systems: can we use kV CBCT, MV CBCT, and/or MV CT images for rapid dose planning in urgent palliative radiotherapy treatment situations?
Abstract: We have developed a clinical workflow for urgent palliative radiotherapy treatments that integrates patient simulation, planning, quality assurance, and treatment in one treatment session. This has been successfully tested and implemented clinically on a linac with MV CBCT capabilities. To increase the clinical relevance of this approach, image quality and dose calculation accuracies were compared between images of other available on-board imaging systems. Methods: Water and anthropomorphic phantom images were acquired on four different Linac on-board imagers (OBIs), including kV CBCT (Varian TrueBeam and Elekta VersaHD), MV CBCT (Siemens Artiste) and MV CT (Accuray Tomotherapy). Simple treatments of single or opposed beams were planned on the respective kV CT images and copied to all CT images. The dose distribution was calculated using machine-specific image value to density calibrations. Image suitability for dose planning was based on the overall mean dose differences and 3D gamma index with 3%/3mm criteria for a prescription of monitor units (MU) and differences in calculated MUs per plan for dose prescriptions to mid-plane. Image quality (noise, contrast, uniformity) was also evaluated and compared between all machines. Results: Image contrast was sufficient to visualize bony anatomy on all machines. Despite a high noise level and low contrast, MV CT images provided the most accurate treatment plans relative to kV CT-based planning in all studied cases (γ-index >97%). The gamma index for 3%/3 mm criteria was >94% for all other systems. The comparison of treatment plans showed that monitor units calculated based on a prescription to mid-plane were within 5% difference relative to kV CT-based plans for all machines and all studied treatment sites (head, neck, pelvis). Local dose differences of >5% were found near the image edges. Conclusion: Based on this phantom study, kV CBCT, MV CBCT, and MV CT image quality was sufficient for treatment planning in all tested cases. Treatment plans provided acceptable dose calculation accuracies for simple urgently planned palliative treatments. However, dose calculation accuracy was compromised towards the edges of an image. Best dose calculation results were obtained when the treatment isocenter was near the image isocenter for all machines. Feasibility for clinical implementation should be assessed separately and may be complicated by machine specific features. A large field of view, long scan length, and immediate image export to the treatment planning system were essential for a smooth workflow and were not provided on all devices.
7. David Hoffman, PhD, Medical Physics Resident, UC Davis, Radiation Oncology
Advisor: Stan Benedict
Title: Comprehensive evaluation of two novel transmission detector systems for online quality assurance of external beam radiation therapy
Abstract: Purpose: Two new transmission detectors have been evaluated for online quality assurance of external beam radiation therapy. One is a large-area ion chamber mounted on a linac accessory to monitor photon fluence during patient treatment. The ion chamber has gradient in the MLC motion direction, which provides variable response dependent on photon beam position. The second is a 4040 diode array. This device also measures photon fluence before and during patient treatment.Methods: Our institution evaluated the reproducibility of measurements made on volumetric modulated arc therapy (VMAT) treatment plans made with the ion chamber and the diode array. Additionally, the IQM’s effect on photon beam fluence, response to dose, and the accuracy of the integrated barometer, thermometer, and inclinometer were characterized. The evaluated photon beam errors are based on the annual tolerances specified in AAPM Task Group Report 142. Results: The ion chamber measured repeated VMAT treatments with 0.16% (standard deviation) reproducibility. Similarly, the diode array measured repeated VMAT treatments with 0.55% reproducibility. The ion chamber attenuated 6, 10, and 15 MV photon beams by 5.43±0.02%, 4.60±0.02%, and 4.21±0.03% respectively. Photon beam profiles were changed by <1.5% in the non-penumbra regions of the beams. The ion chamber's dose response was linear and the thermometer, barometer, and inclinometer agreed with other calibrated devices. The device detected variations in MU delivered (1%), field position (3mm), single MLC leaf positions (13mm), and photon energy. Conclusion: Both detectors demonstrate substantial utility for online verification and quality assurance of photon external beam radiation therapy. Additional presentations will demonstrate the reproducibility of checksum measurements for 3D conventional and IMRT with varying patient target volume sizes that cover the range of clinically relevant photon treatments.
8. Paul Keselman, Graduate Student, Joint Graduate Group in Bioengineering UC Berkeley / UC San Francisco,
Advisor: Steven Conolly
Title: High Contrast MR Saline Angiography: A safer alternative for patients suffering from Chronic Kidney Disease
Abstract: Coronary Artery Disease (CAD) is the leading cause of death in the United States. Coronary imaging is a clinically indispensable tool for diagnosing CAD, as well as guiding real-time interventional procedures. Currently, the two main procedures for diagnosing CAD are X-Ray and CT angiography, both of which rely on injection of iodinated contrast agents. However, about 25% of patient undergoing these procedures suffer from Chronic Kidney Disease (CKD). For this patient subpopulation iodine is risky, and can lead to complete kidney failure, but MDs have no better option currently. We propose to develop an alternative MR based angiographic method for coronary imaging – one that provides great resolution, contrast and speed, and also has an advantage of using non-ionizing radiation and a safe contrast agent, namely saline. Our innovation relies on a novel electromagnetically shielded catheter and a tailored Multiple Inversion Recovery pulse sequence with a single shot RARE acquisition.
9. Chris McGuinness, Resident, UCSF Radiation Oncology,
Advisor: Jean Pouliot,
Title: A Patient Specific, Three-Component Model for Glioblastoma Growth and Radio-sensitivity,
Abstract: Gliomas are known to be radio-resistant, and almost always recur following treatment. Current radiotherapy treatments assume a homogeneous (one-component) tumor. Gliomas are very heterogeneous, consisting of normoxic, hypoxic, and necrotic tissues, each responding differently to radiation. An enhanced linear-quadratic model which takes into account the different radio-sensitivity of the heterogeneous tumor regions can guide treatment planning to optimize dose distributions and maximize the therapeutic effect. We used a set of differential equations to model the growth of glioma tumors. Our model expands on the one component model developed by (Rockne,2010) by including normoxic, hypoxic, and necrotic components and radiosensitivity values for each component separately. Proliferation and diffusion parameters are extracted by contouring the tumor on two sets of pre-treatment MRI images and modeling it as a volume equivalent sphere. We compared two examples of glioma tumors presented in (Rockne,2010) with our three-component model and find better predictive capabilities using the three component model. The one-component model over-predicts the effects of radiation because radio-resistant hypoxic and necrotic tissue is not accounted for. The three-component model accurately models tumor growth dynamics and radiation response.
10. Jose A. Ramos-Mendez, PhD., Postdoctoral Scholar, UCSF Helen Diller Family Comprehensive Cancer Center
Advisor: Bruce Faddegon, PhD.
Title: “TOPAS: Extending Geant4 for 4D radiation therapy simulations”
Abstract: TOPAS is been developed by a consortium integrated by the University of California San Francisco, the SLAC National Laboratory and the Massachusetts General Hospital. The tool allows to model proton therapy treatment heads; complex patient geometries based on DICOM or XiO images for subsequent scoring of dose, fluence, etc.; save and reuse phase space files, time features to incorporate complex movement, and visualization by means of advanced graphics representation. All these features are controlled by means of a custom-designed TOPAS parameter control system that allows ease of use, reliability, and repeatability without sacrificing flexibility. Further attractive features include: customized variance reduction techniques for phase space creation, dose-volume histogram calculation, contour reading from DICOM-RT format and dose response models for the calculation of NTCP and TCP values among others. We recently concluded a Beta test with academic users that consist of about 300 authorized users, 87 institutions, 21 countries at 5 continents, whereas the TOPAS has been moved to Full Release. TOPAS not only shorts the learning curve of using Monte Carlo simulation tools but also offers reliability for the end-user.
11. John Ready, PhD Candidate, Medical Physics, Nuclear Engineering Department, University of California, Berkeley
Advisor: Kai Vetter, UC Berkeley
Title: A New Aperture-Based Imaging System for Prompt-Gamma Range Verification of Proton Beam Therapy
Abstract: As proton treatment facilities continue to proliferate, accurate and effective range verification is essential to ensuring the efficacy and optimization of the treatment modality. To realize the maximum potential benefits of proton therapy, the precise location of the Bragg peak must be measured. This work presents a new method of prompt-gamma verification of proton beam therapy using a novel aperture-based imaging system. The imaging system consists of a multi-knife-edge slit collimator paired with an array of LSO scintillation detectors, and will provide 2-dimensional imaging capability for verification of proton beam range and Bragg peak dose via prompt-gamma detection. Initial simulations were performed using the TOPAS Geant4-based Monte Carlo package. Iterative reconstruction methods were combined with simulated point response functions to characterize the imaging performance of the system. Experimental characterization was performed using 2.6 MeV gamma-rays from a Th-228 source. Both simulation and experimental results indicate that this collimated system provides imaging capability in the energy range of interest for prompt-gamma dose verification. In the current configuration, with collimator-to-source distance of 13 cm, image reconstruction of point sources resulted in spatial resolution (FWHM) of approximately 4 mm in both x- and y-directions in the imaging plane. The accuracy of positioning the point source peak is less than 1 mm. The multi-slit pattern is designed to increase detection efficiency and provide spatial information in 2-dimensions -- an improvement over a single-slit collimator design.
12. M.G. Buddika Sumanasena, Post-Doctoral Scholar, UC Davis Biomedical Engineering, Advisor: Ramsey Badawi,
Title: Modular hybrid DOI detectors for PET,
Abstract: We developed a compact, modular, depth encoding detector for high resolution positron emission tomography (PET). The detector is a self contained unit and can be easily integrated into new scanner designs with no changes to the detector itself. This facilitates rapid and cost effective development of application specific PET scanners. Such modules may also be rapidly transferred from one scanner gantry to another. It consists of a 3×3 array of Sensl C series 6 mm Silicon Photo-multipliers (SiPM) and the Hamamatsu C12 position sensitive photo-multiplier tube (PSPMT) coupled to either end of a 14×14 element array of unpolished 1.55 mm pitch, 20 mm thick lutetium yttrium orthosilicate (LYSO) scintillation crystals. We have previously developed a similar detector using a RMD, Inc. avalanche photodiode (APD) instead of the SiPM array. APDs require very high bias voltages and are susceptible to interference due to the weaker signal. SiPMs are used in this modular detector to eliminate those disadvantages. The PSPMT provides six position encoding signals in each of the X and Y directions, which were combined by a resistive network to form two position encoding signals in each direction. Signals from the 3×3 array of SiPMs were combined to a single signal using a resistor network. The resulting five analog signals were amplified by five pre-amplifiers. In the SiPM array there is a 1.2mm gap between the active areas of two Adjacent SiPMs due to device packaging. A 1.4mm thick acrylic light guide is sandwiched between the crystal array and SiPM array to improve light collection from crystals coinciding with the dead-area. A thermistor is used to readout the temperature at the SiPM array. The detector provides FWHM DOI resolution of 2.15mm, FWHM energy resolution of 20.5% and FWHM timing resolution of 1.7ns. All crystals can be identified at all depths.
13. Elaine Yu, PhD Candidate, UC Berkeley and UCSF joint Graduate Program in Bioengineering,
Advisor: Steven Conolly
Title: Next Generation Field-Free Line Magnetic Particle Imaging
Abstract: Magnetic particle imaging is a new tracer imaging technique that shows extraordinary promise for biomedical applications. The major improvement required for MPI is spatial resolution, currently ~1 mm. We have built the world’s first laminated iron-core Field-Free Line (FFL) MPI magnet with a 6.3 T/m selection field gradient strength to exceed the linear spatial resolution of our current FFL by 3 fold. Here, we present the design and construction of a full-scale murine FFL MPI imager with 7.5 T/m selection field. The improved resolution of 600 μm will open doors for future biomedical applications.
14. Raiyan T. Zaman , Postdoctoral Fellow, Department of Radiation Oncology, Stanford University Cancer Center
Advisor: Lei Xing,
Title: A Novel Scintillating-Balloon-Enabled Dual-Modality Catheter Based Imaging System to Characterize Atherosclerotic Plaque with Superior Sensitivity and Spatial Resolution
Abstract: Atherosclerosis is a progressive inflammatory condition that underlies coronary artery disease (CAD)—the leading cause of death in the United States. The current clinical paradigm for detecting CAD is an invasive angiography, which only evaluates the luminal encroachment of the disease, without providing information about plaque extent and content. However, noninvasive detection of coronary plaque inflammation remains challenging due to current limitations, including poor spatial and temporal resolution. In this study, we developed a novel catheter-based scintillating-balloon-enabled fiber-optic radionuclide imaging (CRI) system combined with an catheter fluorescence imaging (CFI) system to image 18F-fluorodeoxyglucose (18F-FDG) and fluorescent glucose probes, respectively, with increased sensitivity and spatial resolution, and tested in a murine model. Methods: A novel design implements a flexible fiber-optic catheter (Fig. 1) consisting of both a radio-luminescence and a fluorescence imaging system to detect radionuclide 18F-FDG and the fluorescent analog 6-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)-6-deoxyglucose (6-NBDG), respectively. The catheter system includes 35 mm and 8 mm fixed focal length lenses, which are subsequently connected to a highly sensitive CMOS camera and fiber holder. The distal ferrule of an image bundle is terminated with a wide-angle lens. The novelty of this system is a scintillating balloon with a crystal tip in the front of the wide angle lens to image light from the decay of 18F-FDG emission signal. To identify the optimal scintillating materials for the balloon with respect to highest radioluminescence signal, several scintillating membranes were made from various phosphors and tested with three closed β sources (Tl-204: 0.1 μCi). The highest radioluminescence signal intensity from the sample was identified from the images after the flat-field correction was applied for the specific camera used in the IVIS-200 system (Fig. 2A). A custom-written MATLAB code was implemented to automatically extract the radioluminescence signal from the images (Fig. 2B). The scintillating balloon was fabricated from 1mL of silicone RTV catalyst mixed with 1 mL base and 50 mg/mL calcium fluoride doped with europium (CaF2:Eu). To identify the optimal scintillating materials with respect to resolution, we calculated modulation transfer function (MTF) of yttrium aluminum garnet doped with cerium (YAG:Ce), anthracene, and CaF2:Eu phosphors using a thin line optical phantom (Fig. 3A, 3A-1). Before ex vivo imaging, we established 6-NBDG fluorophore uptake by macrophages, as a potential molecular marker for plaque vulnerability (Figs. 6A-B). FVB Murine macrophage-rich atherosclerotic carotid plaques (n=8) were imaged ex vivo after intravenous delivery of 18F-FDG or 6-NBDG. Confirmatory imaging was also performed by an external optical imaging system (IVIS-200) and autoradiography. Results: Our fiber-optic imaging system successfully visualized both 18F-FDG and 6-NBDG probes in atherosclerotic plaques. Based on the optimal phosphor analysis on the extracted signal, we identified that 100 μm thick scintillator made from CaF2:Eu (254 photon counts) provided the highest radioluminescence signal that was 68% and 20% brighter than YAG:Ce (81.4 photon counts) and anthracene (204 photon counts), respectively (Fig. 2C). Analyses of the different phosphors showed that CaF2:Eu enabled the best resolution of 1.2 μm (Fig 3B). The CRI system detected almost 4-fold higher radioluminescence signal from the ligated left carotid arteries (LCs) compared to the non-ligated right carotid (RCs): 1.63×102±4.01×101 vs. 4.21×101±2.09×100, (photon counts), p=0.006 (Fig. 4D). We found no significant benefit to adding a scintillator crystal to the balloon: 1.65×102±4.07×101 vs. 4.44×101±2.17×100, photon counts, and p=0.005. Similarly, for 6-NBDG with the CFI system, the ligated LCs emitted 4.3-fold brighter fluorescent signals than the control RCs (1.6×102±2.7×101 vs. 3.8×101±5.9 A.U., P = 0.002) (Fig. 7C). The higher uptake of both 18F-FDG and 6-NBDG in ligated LCs were confirmed with an IVIS-200 (Figs. 4E, 7D). Autoradiography further verified the higher uptake of 18F-FDG by the LCs (Fig. 5). Conclusions: This novel fiber-optic imaging system enables high-resolution and sensitive detection of 18F-FDG and 6-NBDG uptake by murine atherosclerotic plaques. In addition, 6-NBDG is a promising novel fluorescent probe for detecting macrophage-rich atherosclerotic plaques.
15. Dr. Wei Zhang, Postdoc, UC Merced, School of Engineering
Advisor: Changqing Li
Title: CT guided diffuse optical tomography for breast cancer imaging
Abstract: Diffuse optical tomography (DOT) has been emerged for two decades as a functional and noninvasive imaging modality to image the absorption chromophore concentration in deep tissues such as breast cancers. However, the applications of DOT have been limited by its low spatial resolution caused by strong optical scattering. The structural guidance provided by computed tomography (CT) enhances the DOT imaging substantially. Here, we report a CT guided DOT imaging system for breast cancer detection. We have built a prototype DOT imaging system. The CT guided DOT algorithms and concepts are validated with numerical simulations and phantom experiments. The imaging setup parameters such as the measurement projections and the effects of signal to noise ratio on the DOT reconstruction have been investigated. Our results indicate that an electron multiplier charge coupled device (EMCCD) with air-cooling is good enough for the transmission mode DOT imaging. We have found that measurements at six projections are sufficient for DOT to reconstruct the optical absorption targets. Finally, our efforts on the integration of the DOT imaging system inside a breast CT scanner will also be reported.
16. Bo Zheng, PhD Candidate, Bioengineering, UC Berkeley,
Advisor: Steven Conolly,
Title: System Hardware and Initial in vivo Experiments for Preclinical Magnetic Particle Imaging
Abstract: Magnetic Particle Imaging is a new tracer-based medical imaging modality that directly images and quantifies superparamagnetic iron oxide nanoparticles. Because of its high image contrast and sensitivity, quantitativeness, tissue penetration, and safety, MPI can be used for applications including angiography, perfusion imaging, and cell therapy tracking. In this work, we present novel hardware to improve MPI sensitivity and demonstrate the first use of MPI for tracking the in vivodynamic response and biodistribution of stem cell implants.
6/5/2015 4:09:02 PM