Honors & Awards

  • Moses and Sylvia Greenfield Paper Award, AAPM (Apr 2018)
  • NIH F-31 Ruth L. Kirschstein Predoctoral Individual National Research Service, National Institute of Health (NIH) - NIBIB (Jan 2016 - Dec 2017)
  • National Scholarship for Science and Engineering, Korea Student Aid Foundation (Mar 2006 - Jan 2010)
  • Federal Work-Study Assistantship Recipient, School of Engineering, Stanford (Mar 2011 - Jun 2011)

Professional Education

  • Bachelor of Science, Korea Advanced Institute Of Science and Technology (2010)
  • Doctor of Philosophy, Stanford University, Mechanical Engineering & Radiology (2019)
  • Master of Science, Stanford University, Mechanical Engineering (2012)
  • Bachelor of Science, Korea Advanced Institute of Science and Technology (KAIST), Mechanical Engineering (2010)

Stanford Advisors

All Publications

  • Transdermal vaccination via 3D-printed microneedles induces potent humoral and cellular immunity. Proceedings of the National Academy of Sciences of the United States of America Caudill, C., Perry, J. L., Iliadis, K., Tessema, A. T., Lee, B. J., Mecham, B. S., Tian, S., DeSimone, J. M. 2021; 118 (39)


    Vaccination is an essential public health measure for infectious disease prevention. The exposure of the immune system to vaccine formulations with the appropriate kinetics is critical for inducing protective immunity. In this work, faceted microneedle arrays were designed and fabricated utilizing a three-dimensional (3D)-printing technique called continuous liquid interface production (CLIP). The faceted microneedle design resulted in increased surface area as compared with the smooth square pyramidal design, ultimately leading to enhanced surface coating of model vaccine components (ovalbumin and CpG). Utilizing fluorescent tags and live-animal imaging, we evaluated in vivo cargo retention and bioavailability in mice as a function of route of delivery. Compared with subcutaneous bolus injection of the soluble components, microneedle transdermal delivery not only resulted in enhanced cargo retention in the skin but also improved immune cell activation in the draining lymph nodes. Furthermore, the microneedle vaccine induced a potent humoral immune response, with higher total IgG (Immunoglobulin G) and a more balanced IgG1/IgG2a repertoire and achieved dose sparing. Furthermore, it elicited T cell responses as characterized by functional cytotoxic CD8+ T cells and CD4+ T cells secreting Th1 (T helper type 1)-cytokines. Taken together, CLIP 3D-printed microneedles coated with vaccine components provide a useful platform for a noninvasive, self-applicable vaccination.

    View details for DOI 10.1073/pnas.2102595118

    View details for PubMedID 34551974

  • Publisher Correction: A mountable toilet system for personalized health monitoring via the analysis of excreta. Nature biomedical engineering Park, S. M., Won, D. D., Lee, B. J., Escobedo, D. n., Esteva, A. n., Aalipour, A. n., Ge, T. J., Kim, J. H., Suh, S. n., Choi, E. H., Lozano, A. X., Yao, C. n., Bodapati, S. n., Achterberg, F. B., Kim, J. n., Park, H. n., Choi, Y. n., Kim, W. J., Yu, J. H., Bhatt, A. M., Lee, J. K., Spitler, R. n., Wang, S. X., Gambhir, S. S. 2020


    An amendment to this paper has been published and can be accessed via a link at the top of the paper.

    View details for DOI 10.1038/s41551-020-0562-5

    View details for PubMedID 32382068

  • A mountable toilet system for personalized health monitoring via the analysis of excreta. Nature biomedical engineering Park, S. M., Won, D. D., Lee, B. J., Escobedo, D. n., Esteva, A. n., Aalipour, A. n., Ge, T. J., Kim, J. H., Suh, S. n., Choi, E. H., Lozano, A. X., Yao, C. n., Bodapati, S. n., Achterberg, F. B., Kim, J. n., Park, H. n., Choi, Y. n., Kim, W. J., Yu, J. H., Bhatt, A. M., Lee, J. K., Spitler, R. n., Wang, S. X., Gambhir, S. S. 2020


    Technologies for the longitudinal monitoring of a person's health are poorly integrated with clinical workflows, and have rarely produced actionable biometric data for healthcare providers. Here, we describe easily deployable hardware and software for the long-term analysis of a user's excreta through data collection and models of human health. The 'smart' toilet, which is self-contained and operates autonomously by leveraging pressure and motion sensors, analyses the user's urine using a standard-of-care colorimetric assay that traces red-green-blue values from images of urinalysis strips, calculates the flow rate and volume of urine using computer vision as a uroflowmeter, and classifies stool according to the Bristol stool form scale using deep learning, with performance that is comparable to the performance of trained medical personnel. Each user of the toilet is identified through their fingerprint and the distinctive features of their anoderm, and the data are securely stored and analysed in an encrypted cloud server. The toilet may find uses in the screening, diagnosis and longitudinal monitoring of specific patient populations.

    View details for DOI 10.1038/s41551-020-0534-9

    View details for PubMedID 32251391

  • Performance evaluation of RF coils integrated with an RF-penetrable PET insert for simultaneous PET/MRI MAGNETIC RESONANCE IN MEDICINE Lee, B. J., Watkins, R. D., Lee, K., Chang, C., Levin, C. S. 2019; 81 (2): 1434–46

    View details for DOI 10.1002/mrm.27444

    View details for Web of Science ID 000462086300057

  • Characterization of TOF-PET detectors for a second generation radiofrequency-penetrable PET insert for simultaneous PET/MRI Dong, Q., Lee, B. J., Chang, C., Sacco, I., Watkins, R. D., Fischer, P., Anaya, E., Levin, C. S., IEEE IEEE. 2019
  • MR Performance in the Presence of a Radio Frequency-Penetrable Positron Emission Tomography (PET) Insert for Simultaneous PET/MRI IEEE TRANSACTIONS ON MEDICAL IMAGING Lee, B. J., Grant, A. M., Chang, C., Watkins, R. D., Glover, G. H., Levin, C. S. 2018; 37 (9): 2060–69


    Despite the great promise of integrated positron emission tomography (PET)/magnetic resonance (MR) imaging to add molecular information to anatomical and functional MR, its potential impact in medicine is diminished by a very high cost, limiting its dissemination. An RF-penetrable PET ring that can be inserted into any existing MR system has been developed to address this issue. Employing optical signal transmission along with battery power enables the PET ring insert to electrically float with respect to the MR system. Then, inter-modular gaps of the PET ring allow the RF transmit field from the standard built-in body coil to penetrate into the PET fields-of-view (FOV) with some attenuation that can be compensated for. MR performance, including RF noise, magnetic susceptibility, RF penetrability through and $B_{1}$ uniformity within the PET insert, and MR image quality, were analyzed with and without the PET ring present. The simulated and experimentally measured RF field attenuation factors with the PET ring present were -2.7 and -3.2 dB, respectively. The magnetic susceptibility effect (0.063 ppm) and noise emitted from the PET ring in the MR receive channel were insignificant. $B_{1}$ homogeneity of a spherical agar phantom within the PET ring FOV dropped by 8.4% and MR image SNR was reduced by 3.5 and 4.3 dB with the PET present for gradient-recalled echo and fast-spin echo, respectively. This paper demonstrates, for the first time, an RF-penetrable PET insert comprising a full ring of operating detectors that achieves simultaneous PET/MR using the standard built-in body coil as the RF transmitter.

    View details for DOI 10.1109/TMI.2018.2815620

    View details for Web of Science ID 000443877100010

    View details for PubMedID 29993864

  • Performance Study of a Radio-Frequency Field-Penetrable PET Insert for Simultaneous PET/MRI IEEE TRANSACTIONS ON RADIATION AND PLASMA MEDICAL SCIENCES Chang, C., Lee, B. J., Grant, A. M., Groll, A. N., Levin, C. S. 2018; 2 (5): 422–31
  • Performance study of a radio-frequency field-penetrable PET insert for simultaneous PET/MRI. IEEE transactions on radiation and plasma medical sciences Chang, C. M., Lee, B. J., Grant, A. M., Groll, A. N., Levin, C. S. 2018; 2 (5): 422–31


    Hybrid positron emission tomography (PET)/magnetic resonance imaging (MRI) has risen to the cutting edge of medical imaging technology as it allows simultaneous acquisition of structural, functional and molecular information of the patient. A PET insert that can be installed into existing MR systems can in principle reduce the cost barriers for an existing MR site to achieve simultaneous PET/MRI compared to procuring an integrated PET+MRI system. The PET insert systems developed so far for PET/MRI require the RF transmitter coil to reside inside the PET ring as those PET inserts block the RF fields from the MRI system. Here we report for the first time on the performance of a full-ring brain-sized "RF-penetrable" PET insert we have recently completed. This insert allows the RF fields generated by the built-in body coil to penetrate the PET ring. The PET insert comprises a ring of 16 detector modules employing electro-optical coupled signal transmission and a multiplexing framework based on compressed sensing. Energy resolution, coincidence timing resolution (CTR), photopeak position, and coincidence count rate were acquired outside and inside a 3-Tesla MRI system under simultaneous acquisition to evaluate the impact of MRI on the PET performance. Coincidence count rate performance was evaluated by acquiring a cylinder source with high initial activity decaying over time. Tomographic imaging of two phantoms, a custom 6.5-cm diameter resolution phantom with hot rods of four different sizes (2.8 mm, 3.2 mm, 4.2 mm, and 5.2 mm diameter) and a 3D Hoffman brain phantom, were performed to evaluate the imaging capability of the PET insert. The energy resolution at 511 keV and CTR acquired by the PET insert were 16.2±0.1% and 5.3±0.1 ns FWHM, respectively, and remained stable during MRI operation except when the EPI sequence was applied. The PET system starts to show saturation in coincidence count rate at 2.76 million photon counts per second. Most of the 2.8-mm diameter hot rods and main features of the 3D Hoffman brain phantom were resolved by the PET insert, demonstrating its high spatial resolution and capability to image a complex tracer distribution mimicking that seen in the human brain.

    View details for PubMedID 30911706

  • Low eddy current RF shielding enclosure designs for 3T MR applications. Magnetic resonance in medicine Lee, B. J., Watkins, R. D., Chang, C., Levin, C. S. 2017


    Magnetic resonance-compatible medical devices operate within the MR environment while benefitting from the superior anatomic information of MRI. Avoiding electromagnetic interference between such instrumentation and the MR system is crucial. In this work, various shielding configurations for positron emission tomography (PET) detectors were studied and analyzed regarding radiofrequency (RF) shielding effectiveness and gradient-induced eddy current performances. However, the results of this work apply to shielding considerations for any MR-compatible devices.Six shielding enclosure configurations with various thicknesses, patterns, and materials were designed: solid and segmented copper, phosphor bronze mesh (PBM), and carbon fiber composite (CFC). A series of tests was performed on RF shielding effectiveness and the gradient-induced eddy current.For the shielding effectiveness, the solid copper with various thickness and PBM configurations yield significantly better shielding effectiveness (>15 dB) compared with CFC and segmented configurations. For the gradient-induced eddy current performance, the solid copper shielding configurations with different thicknesses showed significantly worse results, up to a factor of 3.89 dB, compared with the segmented copper, PBM, and the CFC configurations.We evaluated the RF shielding effectiveness and the gradient-induced eddy current artifacts of several shielding designs, and only the PBM showed positive outcomes for both aspects. Magn Reson Med, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

    View details for DOI 10.1002/mrm.26766

    View details for PubMedID 28585334

  • Simultaneous PET/MR imaging with a radio frequency-penetrable PET insert. Medical physics Grant, A. M., Lee, B. J., Chang, C., Levin, C. S. 2017; 44 (1): 112-120


    A brain sized radio frequency (RF)-penetrable PET insert has been designed for simultaneous operation with MRI systems. This system takes advantage of electro-optical coupling and battery power to electrically float the PET insert relative to the MRI ground, permitting RF signals to be transmitted through small gaps between the modules that form the PET ring. This design facilitates the use of the built-in body coil for RF transmission and thus could be inserted into any existing MR site wishing to achieve simultaneous PET/MR imaging. The PET detectors employ nonmagnetic silicon photomultipliers in conjunction with a compressed sensing signal multiplexing scheme, and optical fibers to transmit analog PET detector signals out of the MRI room for decoding, processing, and image reconstruction.The PET insert was first constructed and tested in a laboratory benchtop setting, where tomographic images of a custom resolution phantom were successfully acquired. The PET insert was then placed within a 3T body MRI system, and tomographic resolution/contrast phantom images were acquired both with only the B0 field present, and under continuous pulsing from different MR imaging sequences.The resulting PET images have comparable contrast-to-noise ratios (CNR) under all MR pulsing conditions: The maximum percent CNR relative difference for each rod type among all four PET images acquired in the MRI system has a mean of 14.0 ± 7.7%. MR images were successfully acquired through the RF-penetrable PET shielding using only the built-in MR body coil, suggesting that simultaneous imaging is possible without significant mutual interference.These results show promise for this technology as an alternative to costly integrated PET/MR scanners; a PET insert that is compatible with any existing clinical MRI system could greatly increase the availability, accessibility, and dissemination of PET/MR.

    View details for DOI 10.1002/mp.12031

    View details for PubMedID 28102949

    View details for PubMedCentralID PMC5372382

  • Successful demonstration of simultaneous PET/MR Imaging with a RF-penetrable PET insert. EJNMMI physics Lee, B., Grant, A., Chang, C., Glover, G., Levin, C. 2015; 2: A17-?

    View details for DOI 10.1186/2197-7364-2-S1-A17

    View details for PubMedID 26956272

    View details for PubMedCentralID PMC4798708

  • Technical Note: Characterization of custom 3D printed multimodality imaging phantoms. Medical physics Bieniosek, M. F., Lee, B. J., Levin, C. S. 2015; 42 (10): 5913-?


    Imaging phantoms are important tools for researchers and technicians, but they can be costly and difficult to customize. Three dimensional (3D) printing is a widely available rapid prototyping technique that enables the fabrication of objects with 3D computer generated geometries. It is ideal for quickly producing customized, low cost, multimodal, reusable imaging phantoms. This work validates the use of 3D printed phantoms by comparing CT and PET scans of a 3D printed phantom and a commercial "Micro Deluxe" phantom. This report also presents results from a customized 3D printed PET/MRI phantom, and a customized high resolution imaging phantom with sub-mm features.CT and PET scans of a 3D printed phantom and a commercial Micro Deluxe (Data Spectrum Corporation, USA) phantom with 1.2, 1.6, 2.4, 3.2, 4.0, and 4.8 mm diameter hot rods were acquired. The measured PET and CT rod sizes, activities, and attenuation coefficients were compared. A PET/MRI scan of a custom 3D printed phantom with hot and cold rods was performed, with photon attenuation and normalization measurements performed with a separate 3D printed normalization phantom. X-ray transmission scans of a customized two level high resolution 3D printed phantom with sub-mm features were also performed.Results show very good agreement between commercial and 3D printed micro deluxe phantoms with less than 3% difference in CT measured rod diameter, less than 5% difference in PET measured rod diameter, and a maximum of 6.2% difference in average rod activity from a 10 min, 333 kBq/ml (9 μCi/ml) Siemens Inveon (Siemens Healthcare, Germany) PET scan. In all cases, these differences were within the measurement uncertainties of our setups. PET/MRI scans successfully identified 3D printed hot and cold rods on PET and MRI modalities. X-ray projection images of a 3D printed high resolution phantom identified features as small as 350 μm wide.This work shows that 3D printed phantoms can be functionally equivalent to commercially available phantoms. They are a viable option for quickly distributing and fabricating low cost, customized phantoms.

    View details for DOI 10.1118/1.4930803

    View details for PubMedID 26429265

    View details for PubMedCentralID PMC4575317

  • Performance characterization of compressed sensing positron emission tomography detectors and data acquisition system. Physics in medicine and biology Chang, C., Grant, A. M., Lee, B. J., Kim, E., Hong, K., Levin, C. S. 2015; 60 (16): 6407-6421


    In the field of information theory, compressed sensing (CS) had been developed to recover signals at a lower sampling rate than suggested by the Nyquist-Shannon theorem, provided the signals have a sparse representation with respect to some base. CS has recently emerged as a method to multiplex PET detector readouts thanks to the sparse nature of 511 keV photon interactions in a typical PET study. We have shown in our previous numerical studies that, at the same multiplexing ratio, CS achieves higher signal-to-noise ratio (SNR) compared to Anger and cross-strip multiplexing. In addition, unlike Anger logic, multiplexing by CS preserves the capability to resolve multi-hit events, in which multiple pixels are triggered within the resolving time of the detector. In this work, we characterized the time, energy and intrinsic spatial resolution of two CS detectors and a data acquisition system we have developed for a PET insert system for simultaneous PET/MRI. The CS detector comprises a [Formula: see text] mosaic of [Formula: see text] arrays of [Formula: see text] mm(3) lutetium-yttrium orthosilicate crystals coupled one-to-one to eight [Formula: see text] silicon photomultiplier arrays. The total number of 128 pixels is multiplexed down to 16 readout channels by CS. The energy, coincidence time and intrinsic spatial resolution achieved by two CS detectors were [Formula: see text]% FWHM at 511 keV, 4.5 ns FWHM and 2.3 mm FWHM, respectively. A series of experiments were conducted to measure the sources of time jitter that limit the time resolution of the current system, which provides guidance for potential system design improvements. These findings demonstrate the feasibility of compressed sensing as a promising multiplexing method for PET detectors.

    View details for DOI 10.1088/0031-9155/60/16/6407

    View details for PubMedID 26237671

  • Prototype positron emission tomography insert with electro-optical signal transmission for simultaneous operation with MRI PHYSICS IN MEDICINE AND BIOLOGY Olcott, P., Kim, E., Hong, K., Lee, B. J., Grant, A. M., Chang, C., Glover, G., Levin, C. S. 2015; 60 (9): 3459-3478


    The simultaneous acquisition of PET and MRI data shows promise to provide powerful capabilities to study disease processes in human subjects, guide the development of novel treatments, and monitor therapy response and disease progression. A brain-size PET detector ring insert for an MRI system is being developed that, if successful, can be inserted into any existing MRI system to enable simultaneous PET and MRI images of the brain to be acquired without mutual interference. The PET insert uses electro-optical coupling to relay all the signals from the PET detectors out of the MRI system using analog modulated lasers coupled to fiber optics. Because the fibers use light instead of electrical signals, the PET detector can be electrically decoupled from the MRI making it partially transmissive to the RF field of the MRI. The SiPM devices and low power lasers were powered using non-magnetic MRI compatible batteries. Also, the number of laser-fiber channels in the system was reduced using techniques adapted from the field of compressed sensing. Using the fact that incoming PET data is sparse in time and space, electronic circuits implementing constant weight codes uniquely encode the detector signals in order to reduce the number of electro-optical readout channels by 8-fold. Two out of a total of sixteen electro-optical detector modules have been built and tested with the entire RF-shielded detector gantry for the PET ring insert. The two detectors have been tested outside and inside of a 3T MRI system to study mutual interference effects and simultaneous performance with MRI. Preliminary results show that the PET insert is feasible for high resolution simultaneous PET/MRI imaging for applications in the brain.

    View details for DOI 10.1088/0031-9155/60/9/3459

    View details for Web of Science ID 000354104700007

    View details for PubMedID 25856511

  • Mode-Matching of Wineglass Mode Disk Resonator Gyroscope in (100) Single Crystal Silicon JOURNAL OF MICROELECTROMECHANICAL SYSTEMS Ahn, C. H., Ng, E. J., Hong, V. A., Yang, Y., Lee, B. J., Flader, I., Kenny, T. W. 2015; 24 (2): 343-350
  • RF-Penetrable PET insert for simultaneous PET/MR imaging. EJNMMI physics Lee, B. J., Grant, A. M., Chang, C., Levin, C. S. 2014; 1: A5-?

    View details for DOI 10.1186/2197-7364-1-S1-A5

    View details for PubMedID 26501638

    View details for PubMedCentralID PMC4545802

  • RESONANT PRESSURE SENSOR WITH ON-CHIP TEMPERATURE AND STRAIN SENSORS FOR ERROR CORRECTION 26th IEEE International Conference on Micro Electro Mechanical Systems (MEMS) Chiang, C., Graham, A. B., Lee, B. J., Ahn, C. H., Ng, E. J., O'Brien, G. J., Kenny, T. W. IEEE. 2013: 45–48
  • Characterization of PET Data Acquisition System with Compressed Sensing Detectors 60th IEEE Nuclear Science Symposium (NSS) / Medical Imaging Conference (MIC) / 20th International Workshop on Room-Temperature Semiconductor X-ray and Gamma-ray Detectors Chang, C., Olcott, P. D., Hong, K. J., Grant, A. M., Lee, B. J., Kim, E., Levin, C. S. IEEE. 2013
  • Studies of Electromagnetic Interference of PET Detector Insert for Simultaneous PET/MRI 60th IEEE Nuclear Science Symposium (NSS) / Medical Imaging Conference (MIC) / 20th International Workshop on Room-Temperature Semiconductor X-ray and Gamma-ray Detectors Lee, B. J., Olcott, P. D., Hong, K. J., Grant, A. M., Chang, C., Levin, C. S. IEEE. 2013
  • 3D Printing for Cost-Effective, Customized, Reusable Multi-Modality Imaging Phantoms 60th IEEE Nuclear Science Symposium (NSS) / Medical Imaging Conference (MIC) / 20th International Workshop on Room-Temperature Semiconductor X-ray and Gamma-ray Detectors Bieniosek, M. F., Lee, B. J., Levin, C. S. IEEE. 2013