Publications by authors named "Kisung Lee"

24 Publications

  • Page 1 of 1

A comparative experimental study of distributed storage engines for big spatial data processing using GeoSpark.

J Supercomput 2021 Jul 1:1-24. Epub 2021 Jul 1.

Department of Industrial Engineering, Seoul National University of Science and Technology, Seoul, Republic of Korea.

With increasing numbers of GPS-equipped mobile devices, we are witnessing a deluge of spatial information that needs to be effectively and efficiently managed. Even though there are several distributed spatial data processing systems such as GeoSpark (Apache Sedona), the effects of underlying storage engines have not been well studied for spatial data processing. In this paper, we evaluate the performance of various distributed storage engines for processing large-scale spatial data using GeoSpark, a state-of-the-art distributed spatial data processing system running on top of Apache Spark. For our performance evaluation, we choose three distributed storage engines having different characteristics: (1) HDFS, (2) MongoDB, and (3) Amazon S3. To conduct our experimental study on a real cloud computing environment, we utilize Amazon EMR instances (up to 6 instances) for distributed spatial data processing. For the evaluation of big spatial data processing, we generate data sets considering four kinds of various data distributions and various data sizes up to one billion point records (38.5GB raw size). Through the extensive experiments, we measure the processing time of storage engines with the following variations: (1) sharding strategies in MongoDB, (2) caching effects, (3) data distributions, (4) data set sizes, (5) the number of running executors and storage nodes, and (6) the selectivity of queries. The major points observed from the experiments are summarized as follows. (1) The overall performance of MongoDB-based GeoSpark is degraded compared to HDFS- and S3-based GeoSpark in our experimental settings. (2) The performance of MongoDB-based GeoSpark is relatively improved in large-scale data sets compared to the others. (3) HDFS- and S3-based GeoSpark are more scalable to running executors and storage nodes compared to MongoDB-based GeoSpark. (4) The sharding strategy based on the spatial proximity significantly improves the performance of MongoDB-based GeoSpark. (5) S3- and HDFS-based GeoSpark show similar performances in all the environmental settings. (6) Caching in distributed environments improves the overall performance of spatial data processing. These results can be usefully utilized in decision-making of choosing the most adequate storage engine for big spatial data processing in a target distributed environment.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1007/s11227-021-03946-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8246422PMC
July 2021

Shielding effect of radiation dose reduction fiber during the use of C-arm fluoroscopy: a phantom study.

J Radiat Res 2020 Sep;61(5):705-711

Department of Orthopaedic Surgery, Seoul National University Bundang Hospital, Gyeonggi, Korea.

This study evaluated the shielding effect of a newly developed dose-reduction fiber (DRF) made from barium sulfate, in terms of radiation doses delivered to patients' radiosensitive organs and operator during C-arm fluoroscopy and its impact on the quality of images. A C-arm fluoroscopy unit was placed beside a whole-body phantom. Radiophotoluminescent glass dosimeters were attached to the back and front of the whole-body phantom at 20 cm intervals. Radiation doses were measured without DRF and with it applied to the back (position 1), front (position 2) or both sides (position 3) of the phantom. To investigate the impact of DRF on the quality of fluoroscopic images, step-wedge and modulation transfer function phantoms were used. The absorbed radiation doses to the back of the phantom significantly decreased by 25.3-88.8% after applying DRF to positions 1 and 3. The absorbed radiation doses to the front of the phantom significantly decreased by 55.3-93.6% after applying DRF to positions 2 and 3. The contrast resolution values for each adjacent step area fell in the range 0.0119-0.0209, 0.0128-0.0271, 0.0135-0.0339 and 0.0152-0.0339 without and with DRF applied to positions 1, 2 and 3, respectively. The investigated DRF effectively reduces absorbed radiation doses to patients and operators without decreasing the quality of C-arm fluoroscopic images. Therefore, routine clinical use of the DRF is recommended during the use of C-arm fluoroscopy.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1093/jrr/rraa060DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7482166PMC
September 2020

Apparatus to Measure Subnanometer Fluctuation of Giant Unilamellar Vesicle Membranes.

J Phys Chem A 2020 Jun 26;124(22):4512-4516. Epub 2020 May 26.

Center for Soft and Living Matter, Institute for Basic Science, Ulsan 44919, South Korea.

The design, calibration, and performance of an apparatus are described to study the nanometer-scale thermal or driven fluctuations of free-standing vesicle membranes using a design resembling the position detection system of optical tweezers except for the laser power lower by orders of magnitude to avoid trapping. Over four decades of frequency, 1-10,000 Hz, it reports membrane fluctuation amplitudes 0.01-100 nm by measuring scattering of a laser beam as it passes membranes (∼1 μm cross-section) suspended in the aqueous medium. The low-power laser beam, <100 μW, is sharply focused on the edge of a giant unilamellar vesicle, and fluctuations of position are measured using a position-sensitive photodetector. The central result of this approach is the capability to reach small fluctuations otherwise inaccessible using other techniques. The typical obtained data are fit to the standard Helfrich mechanical model. The applications and limitations of the device are discussed, as well as other potential uses to which the apparatus may be applied by rational extension of the approach presented.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.jpca.0c02619DOI Listing
June 2020

Wavelength discrimination (WLD) TOF-PET detector with DOI information.

Phys Med Biol 2020 02 28;65(5):055003. Epub 2020 Feb 28.

Department of Bio-Convergence, Korea University, Seoul, Republic of Korea. Equal contribution.

Depth-of-interaction (DOI) encoding can contribute to improving spatial resolution uniformity and sensitivity in positron-emission-tomography (PET) scanners. In addition, time-of-flight (TOF) PET scanners with DOI encoding have received considerable interest because of their potential for improving the spatial resolution, sensitivity, and image quality of the overall system. In this study, a new DOI detector configuration utilizing scintillators' emission wavelength is proposed, and experimental results on the energy, timing, and DOI performance of the detector are provided. The DOI information from the proposed phoswich-type detector can be acquired at the detector level without complex signal processing by utilizing a single optical filter with customized optical properties. For this, we used either a short pass filter (SPF) or a long pass filter (LPF) that allows light photons of a specific wavelength to pass. The two-layered phoswich detector was configured with two scintillators with different photon-emission spectra. In this study, we used Ce:GAGG (3 mm  ×  3 mm  ×  10 mm) and LYSO:Ce (3 mm  ×  3 mm  ×  10 mm) as the top and bottom layer scintillators, respectively. A digital silicon photomultiplier (dSiPM) was used as the photosensor and for data acquisition. The phoswich detector was placed in the center of two dSiPM pixels, where one of the dSiPM pixels was covered with the optical filter, and the light guide was placed on the other pixel. The detector was tested for energy, timing, and DOI encoding performance. When an SPF was used, the energy resolutions of 16.2% and 11.8% were achieved for the Ce:GAGG (top layer) and LYSO:Ce (bottom layer) respectively without correcting for saturation effect. With a small (3 mm  ×  3 mm  ×  5 mm) LYSO crystal as the reference detector, CRTs (coincidence-resolving times) of 338 ps and 244 ps were recorded for the top and bottom layers respectively. The detector configuration also provides an excellent DOI-separation figure-of-merit (FoM) value of 1.9. In the case of LPF, the energy resolutions of 12.0% and 12.9% were achieved for the Ce:GAGG (top layer) and LYSO:Ce (bottom layer), respectively. CRTs (coincidence resolving times) of 314 ps and 263 ps were recorded for the top and bottom layers, respectively. The DOI-separation FoM value of 1.5 was achieved in this setup. Results show that the proposed method can provide excellent discrete DOI positioning accuracy without compromising the timing performance of the detector.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1088/1361-6560/ab6579DOI Listing
February 2020

A hybrid and scalable error correction algorithm for indel and substitution errors of long reads.

BMC Genomics 2019 Dec 20;20(Suppl 11):948. Epub 2019 Dec 20.

School of Electrical Engineering and Computer Science, Center for Computation and Technology, Louisiana State University, Baton Rouge, Baton Rouge, LA, USA.

Background: Long-read sequencing has shown the promises to overcome the short length limitations of second-generation sequencing by providing more complete assembly. However, the computation of the long sequencing reads is challenged by their higher error rates (e.g., 13% vs. 1%) and higher cost ($0.3 vs. $0.03 per Mbp) compared to the short reads.

Methods: In this paper, we present a new hybrid error correction tool, called ParLECH (Parallel Long-read Error Correction using Hybrid methodology). The error correction algorithm of ParLECH is distributed in nature and efficiently utilizes the k-mer coverage information of high throughput Illumina short-read sequences to rectify the PacBio long-read sequences.ParLECH first constructs a de Bruijn graph from the short reads, and then replaces the indel error regions of the long reads with their corresponding widest path (or maximum min-coverage path) in the short read-based de Bruijn graph. ParLECH then utilizes the k-mer coverage information of the short reads to divide each long read into a sequence of low and high coverage regions, followed by a majority voting to rectify each substituted error base.

Results: ParLECH outperforms latest state-of-the-art hybrid error correction methods on real PacBio datasets. Our experimental evaluation results demonstrate that ParLECH can correct large-scale real-world datasets in an accurate and scalable manner. ParLECH can correct the indel errors of human genome PacBio long reads (312 GB) with Illumina short reads (452 GB) in less than 29 h using 128 compute nodes. ParLECH can align more than 92% bases of an E. coli PacBio dataset with the reference genome, proving its accuracy.

Conclusion: ParLECH can scale to over terabytes of sequencing data using hundreds of computing nodes. The proposed hybrid error correction methodology is novel and rectifies both indel and substitution errors present in the original long reads or newly introduced by the short reads.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1186/s12864-019-6286-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6923905PMC
December 2019

Strategies to improve the photocatalytic activity of TiO: 3D nanostructuring and heterostructuring with graphitic carbon nanomaterials.

Nanoscale 2019 Apr;11(15):7025-7040

Department of Materials Science and Engineering, KAIST Institute for the Nanocentury, Advanced Battery Center, KAIST, Daejeon 34141, Republic of Korea.

TiO2-based photocatalysis has been considered to be one of the most promising avenues for environmental remediation including water purification. However, several technical issues such as the limited surface area of bulk TiO2, the large band gap of TiO2, and rapid charge recombination still limit the practical application of TiO2 photocatalysts. Therefore, here we focus on two structural design strategies: (i) monolithic three-dimensional (3D) nanostructuring, and (ii) heterostructuring with graphitic carbon nanomaterials. A monolithic 3D nanostructure enables maximal surface area in a given volume and efficient reuse of the photocatalyst without recollection. Heterostructuring with carbon nanomaterials helps achieve maximal utilization of the solar spectrum and charge separation and provides efficient TiO2 photocatalysts. In this review, recent progress on TiO2 photocatalysts toward the abovementioned strategies will be summarized. Further discussion and direction will provide insights into the rational design of highly efficient TiO2 photocatalysts, and help develop advanced photocatalyst models.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c9nr01260eDOI Listing
April 2019

Dextran adsorption onto red blood cells revisited: single cell quantification by laser tweezers combined with microfluidics.

Biomed Opt Express 2018 Jun 22;9(6):2755-2764. Epub 2018 May 22.

Experimental Physics, Saarland University, Saarbrücken, D-66041, Germany.

The aggregation of red blood cells (RBC) is of importance for hemorheology, while its mechanism remains debatable. The key question is the role of the adsorption of macromolecules on RBC membranes, which may act as "bridges" between cells. It is especially important that dextran is considered to induce "bridge"-less aggregation due to the depletion forces. We revisit the dextran-RBC interaction on the single cell level using the laser tweezers combined with microfluidic technology and fluorescence microscopy. An immediate sorption of ~10 molecules of 70 kDa dextran per cell was observed. During the incubation of RBC with dextran, a gradual tenfold increase of adsorption was found, accompanied by a moderate change in the RBC deformability. The obtained data demonstrate that dextran sorption and incubation-induced changes of the membrane properties must be considered when studying RBC aggregation .
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1364/BOE.9.002755DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6154185PMC
June 2018

Effect of metallic tools on scattered radiation dose during the use of C-arm fluoroscopy in orthopaedic surgery.

J Radiat Res 2019 Jan;60(1):1-6

Department of Orthopaedic Surgery, Seoul National University Bundang Hospital, 82 Gumi-ro 173 Beon-gil, Bundang-Gu, Sungnam, Gyeonggi, Korea.

This study investigated the effect of metallic tools on the scattered radiation dose delivered to surgeons' radiosensitive organs while simulating hip surgery using C-arm fluoroscopy. Two phantoms, a pelvis and a Rando phantom, were used to simulate a patient and a surgeon in this study. Photoluminescence dosimeters were inserted into the Rando phantom in the positions of the eye, thyroid and gonad. A drill was positioned above the hip of the pelvis phantom or beside the pelvis phantom of the same height. For each drill location, the scattered radiation dose was measured when the angle to the operator phantom was 45°; this was repeated when the angle was 90°. The scattered radiation doses to the eye, thyroid and gonad when the drill was placed beside the pelvis phantom with 90° angulation to the operator phantom were significantly lower than the reference values and those when the drill was placed beside the pelvis phantom at a 45° angulation to the operator phantom. The scattered radiation doses to the eye and thyroid when the drill was placed above the hip were significantly lower than the references values. Of the four different scenarios, the scattered radiation doses to the eye, thyroid and gonad were lowest when the drill was placed beside the pelvis phantom with 90° angulation. This study showed that the scattered radiation doses to radiosensitive organs were affected by the location and angle of the metallic tools in relation to the operator. Therefore, orthopedic surgeons should consider the effect of metallic tools on the scattered radiation dose during intraoperative use of C-arm fluoroscopy.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1093/jrr/rry073DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6373686PMC
January 2019

An iterative sinogram gap-filling method with object- and scanner-dedicated discrete cosine transform (DCT)-domain filters for high resolution PET scanners.

Jpn J Radiol 2018 Jan 30;36(1):59-67. Epub 2017 Oct 30.

Department of Electronics and Electrical Engineering, Dankook University, 152, Jukjeon-ro, Suji-gu, Yongin-Si, Gyeonggi-do, 16890, South Korea.

Purpose: We aimed to develop a gap-filling algorithm, in particular the filter mask design method of the algorithm, which optimizes the filter to the imaging object by an adaptive and iterative process, rather than by manual means.

Methods: Two numerical phantoms (Shepp-Logan and Jaszczak) were used for sinogram generation. The algorithm works iteratively, not only on the gap-filling iteration but also on the mask generation, to identify the object-dedicated low frequency area in the DCT-domain that is to be preserved. We redefine the low frequency preserving region of the filter mask at every gap-filling iteration, and the region verges on the property of the original image in the DCT domain.

Results: The previous DCT2 mask for each phantom case had been manually well optimized, and the results show little difference from the reference image and sinogram. We observed little or no difference between the results of the manually optimized DCT2 algorithm and those of the proposed algorithm.

Conclusions: The proposed algorithm works well for various types of scanning object and shows results that compare to those of the manually optimized DCT2 algorithm without perfect or full information of the imaging object.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1007/s11604-017-0697-9DOI Listing
January 2018

Assessment of the "cross-bridge"-induced interaction of red blood cells by optical trapping combined with microfluidics.

J Biomed Opt 2017 09;22(9):91516

Lomonosov Moscow State University, Faculty of Physics, Moscow, RussiadLomonosov Moscow State University, International Laser Center, Moscow, Russia.

Red blood cell (RBC) aggregation is an intrinsic property of the blood that has a direct effect on the blood viscosity and circulation. Nevertheless, the mechanism behind the RBC aggregation has not been confirmed and is still under investigation with two major hypotheses, known as “depletion layer” and “cross-bridging.” We aim to ultimately understand the mechanism of the RBC aggregation and clarify both models. To measure the cell interaction in vitro in different suspensions (including plasma, isotonic solution of fibrinogen, isotonic solution of fibrinogen with albumin, and phosphate buffer saline) while moving the aggregate from one solution to another, an approach combining optical trapping and microfluidics has been applied. The study reveals evidence that RBC aggregation in plasma is at least partly due to the cross-bridging mechanism. The cell interaction strength measured in the final solution was found to be significantly changed depending on the initial solution where the aggregate was formed.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1117/1.JBO.22.9.091516DOI Listing
September 2017

Effect of shear-induced platelet activation on red blood cell aggregation.

Clin Hemorheol Microcirc 2017 ;66(2):97-104

School of Mechanical Engineering, Korea University, Seoul, Korea.

Mechanical shear stress is one of the important factors for platelet activation. Although shear stress has been frequently utilized in many applications of diagnostic bio-equipment, there has been little consideration as to whether shear stress induces platelet activation and consequently alters hemorheological characteristics. Therefore, we investigated the effect of shear-induced platelet activation on red blood cell (RBC) aggregation. The hypothesis of the present research is as follows: Platelets activated by high shear stress secrete substances, which can affect hemorheological characteristics to promote RBC aggregation. In our study, an increase in RBC aggregation indices (critical shear stress (CSS) and aggregation index (AI)) by shear-induced platelet activation was observed. Significantly, an increase of 19% in CSS was observed. However, deformability remained unchanged. These phenomena could be a result of the increased cellular adhesion force on RBC membranes due to secreted substances from activated platelets. Therefore, since high shear application results in the unexpected effect on RBC aggregation, conditions for shear application in diagnostic bio-equipment are to be carefully determined.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3233/CH-16191DOI Listing
December 2017

Simulation study of a novel target oriented SPECT design using a variable pinhole collimator.

Med Phys 2017 Feb;44(2):470-478

Research Institute of Global Health Tech., College of Health Science, Korea University, Seoul, 02841, Republic of Korea.

Purpose: In the past decade, demands for organ specific (target oriented) single-photon emission computed tomography (SPECT) is increasing, and several groups have conducted studies on developing clinical dedicated SPECT with pinhole collimator to improve the spatial resolution. However, acceptance angle of the collimator cannot be adjusted to fit the different ROIs of target objects because the shape of pinhole could not be changed, and the magnifying factor cannot be maximized as the collimator-to-detector distance is fixed. Furthermore, those dedicated pinhole SPECTs are typically made for a single purpose and therefore possess a drawback in that it cannot be utilized for any other purpose. In this study, we propose a novel SPECT system using variable pinhole collimator (VP SPECT) whose parameters are flexible.

Methods: The proposed variable pinhole collimator is modeled on conventional pinhole by piling several tungsten layers of different apertures. Depending on the combination of the holes in each layer, a variety of hole diameters and acceptance angles of the pinhole can be made. In addition, VP SPECT system allows attaching the collimator to the object as close as possible to maximize the sensitivity and adjust the distance of the pinhole from the scintillation detector to optimize the system resolution for each rotation angle, automatically. For quantitative measurement, we compared the sensitivity and spatial resolution of VP SPECT with those of conventional pinhole SPECT. To determine the possibility of the clinical and preclinical use of proposed system, a digital mouse whole-body (MOBY) phantom is used for simulating the live mouse model.

Results: The result of simulation using ultra-micro hot spot phantom shows that the sensitivity of the proposed VP SPECT system is about 297% of that of the conventional system. While hot rods of diameter 0.6 mm can be distinguished in the image with the proposed VP SPECT system, 1.2-mm hot rods are barely discernible in the conventional pinhole SPECT image. According to the result of MOBY phantom simulation, heart walls separated by 3 mm were not distinguished in conventional pinhole SPECT images, but were clearly discerned in VP SPECT images.

Conclusions: In this study, we designed a novel pinhole collimator for SPECT and presented preliminary results of target oriented imaging with a simulation study. Currently, we are pursuing strategies to realize the proposed system, with the goal to apply the technology into a high-sensitivity and high-resolution preclinical SPECT. Should VP SPECT be applied to the clinical setting, we anticipate a high-sensitivity, high-resolution system for applications such as heart dedicated SPECT or related fields.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/mp.12075DOI Listing
February 2017

Performances of a protector against scattered radiation during intraoperative use of a C-arm fluoroscope.

J Radiol Prot 2016 Sep 12;36(3):629-640. Epub 2016 Aug 12.

Department of Orthopaedic Surgery, Seoul National University Bundang Hospital, 300 Gumi-Dong, Bundang-Gu, Seongnam, Gyeonggi 13620, Korea.

The scattered radiation protector for mobile x-ray systems, Creative Valuable Protector-2, has been recently developed. However, there have been no studies investigating the effects of this device. We aim to investigate the effects of the scattered radiation protector on the equivalent doses from scattered radiation delivered to radiosensitive organs while simulating spine surgery using a C-arm fluoroscope. Chest and rando phantoms were used to simulate a patient and a surgeon in this study. The equivalent dose from scattered radiation to radiosensitive organs was measured in four different situations according to the use of the scattered radiation protector and the C-arm configuration. To compare the quality of the images with and without the scattered radiation protector, an acryl step phantom with five steps was used, and the contrast resolution of each step was calculated. The equivalent dose from the scattered radiation to the surgeon's eye, thyroid, and gonad decreased significantly by using the scattered radiation protector for both the Posteroanterior (PA) (p  <  0.001) and Anteroposterior (AP) (p  <  0.001) C-arm configurations. The installation of the scattered radiation protector also reduced the direct radiation dose to the chest phantom. A scattered map showed that scattered radiation doses decreased by approximately 50% for the PA configuration and 75% for the AP configuration by using the scattered radiation protector. Before and after installation of the scattered radiation protector, the contrast resolution of each adjacent step area was 0.025-0.404 and 0.216-0.421. The scattered radiation protector was effective in reducing not only the equivalent dose from scattered radiation to the surgeon's radiosensitive organs, but also the direct radiation dose to the patient. This was all achieved without decreasing the quality of the C-arm fluoroscopic images.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1088/0952-4746/36/3/629DOI Listing
September 2016

Optical tweezers study of red blood cell aggregation and disaggregation in plasma and protein solutions.

J Biomed Opt 2016 Mar;21(3):35001

Lomonosov Moscow State University, Faculty of Physics, Chair of Quantum Electronics, Leninkie Gory 1/62, Moscow 119991, Russia.

Kinetics of optical tweezers (OT)-induced spontaneous aggregation and disaggregation of red blood cells (RBCs) were studied at the level of cell doublets to assess RBC interaction mechanics. Measurements were performed under in vitro conditions in plasma and fibrinogen and fibrinogen + albumin solutions. The RBC spontaneous aggregation kinetics was found to exhibit different behavior depending on the cell environment. In contrast, the RBC disaggregation kinetics was similar in all solutions qualitatively and quantitatively, demonstrating a significant contribution of the studied proteins to the process. The impact of the study on assessing RBC interaction mechanics and the protein contribution to the reversible RBC aggregation process is discussed.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1117/1.JBO.21.3.035001DOI Listing
March 2016

Types and arrangement of thyroid shields to reduce exposure of surgeons to ionizing radiation during intraoperative use of C-arm fluoroscopy.

Spine (Phila Pa 1976) 2013 Nov;38(24):2108-12

*Department of Orthopaedic Surgery, Seoul National University Bundang Hospital, Kyungki, Korea †Department of Radiologic Science, College of Health Science, Korea University, Seoul, Korea; and ‡Biomedical Research Institute, Seoul National University Bundang Hospital, Kyungki, Korea.

Study Design: Measurement of radiation dose from C-arm fluoroscopy during a simulated intraoperative use in spine surgery.

Objective: To assess how the radiation dose is affected by changes in the types of thyroid shields used and by the arrangements or ways in which they are worn during the intraoperative use of C-arm fluoroscopy.

Summary Of Background Data: Although the danger to the thyroid from exposure to radiation is well known, there are no guidelines for the proper use of thyroid shields.

Methods: Two photoluminescence dosimeters were used to measure the dose of scattered radiation arriving at the location of the thyroid in a whole-body phantom in the position of the surgeon. On an operating table beside this setup was an anthropomorphic chest phantom representing a patient for which treatment with C-arm fluoroscopy was simulated. Radiation doses were measured using 3 different arrangements of the thyroid shield: worn tightly, worn loosely, and worn loosely with a bismuth masking reagent. The same tests were performed using 2 kinds of thyroid shield: lead and lead-equivalent.

Results: For the lead-shield group, radiation doses were measured in 3 arrangements; worn tightly, worn loosely, and worn loosely with a bismuth masking reagent, for which the results were 1.91 ± 0.13, 2.35 ± 0.22, and 1.86 ± 0.13 μSv/min, respectively. Wearing the shield tight against the throat and wearing it loose with a bismuth masking reagent led to lower radiation exposure levels than by simply wearing the shield loosely (P ≤ 0.001). For the lead-equivalent shield group, doses were measured for the same 3 arrangements, for which the results were 1.79 ± 0.12, 1.82 ± 0.11, and 1.74 ± 0.12 μSv/min. Lower scattered radiation doses were delivered to the thyroid in the lead-equivalent thyroid shield group compared with the lead thyroid shield group (P ≤ 0.001). The unshielded thyroid group received a radiation dose of 16.32 ± 0.48 μSv/min.

Conclusion: The use of some form of thyroid shield is essential during the use of C-arm fluoroscopy. It was found that the best way to reduce scattered radiation exposure to the thyroid was wearing the thyroid shield tightly or wearing it loosely in combination with a bismuth masking reagent.

Level Of Evidence: 2.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1097/BRS.0b013e3182a8270dDOI Listing
November 2013

Feasibility study of a plasma display-like radiation detector for X-ray imaging.

J Xray Sci Technol 2012 ;20(3):269-76

Department of Electronics and Electrical Engineering, Dankook University, Gyeonggi-do, Korea.

In this study we have investigated a 2-dimensional gas type detector based on plasma display technology as a candidate for the flat-panel radiation detector. By using the Garfield code, the dependence of X-ray absorption and multiplication on gas composition, cell gap and electric field were examined. Considering the simulation results, three prototype detectors were designed and fabricated. The performance of these detectors was evaluated by measuring the collected charge density, dark current density and sensitivity. The collected charge had the highest value at a condition when Xe 100% and 2.8 mm gap was 108.8 nC/cm² at 1000 V. The dark current of the same detector was varied from 0.0095 to 0.10 nA/cm² and about a fourth of the dark current density of a-Se based detector was at the bias range of 100-1000 V. The sensitivity of Xe 100% and 2.8 mm detector was 0.20 nC/mR·cm² at 0.36 V/um. It is about a tenth lower than that of a-Se based detector at 10 V/um.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3233/XST-2012-0335DOI Listing
January 2013

Measurements of surgeons' exposure to ionizing radiation dose during intraoperative use of C-arm fluoroscopy.

Spine (Phila Pa 1976) 2012 Jun;37(14):1240-4

Department of Radiologic Science, College of Health Science, Korea University, Seoul, Republic of Korea.

Study Design: Measurement of radiation dose from C-arm fluoroscopy during a simulated intraoperative use in spine surgery. OBJECTIVE.: To investigate scatter radiation doses to specific organs of surgeons during intraoperative use of C-arm fluoroscopy in spine surgery and to provide practical intraoperative guidelines.

Summary Of Background Data: There have been studies that reported the radiation dose of C-arm fluoroscopy in various procedures. However, radiation doses to surgeons' specific organs during spine surgery have not been sufficiently examined, and the practical intraoperative radioprotective guidelines have not been suggested.

Methods: Scatter radiation dose (air kerma rate) was measured during the use of a C-arm on an anthropomorphic chest phantom on an operating table. Then, a whole body anthropomorphic phantom was located besides the chest phantom to simulate a surgeon, and scatter radiation doses to specific organs (eye, thyroid, breast, and gonads) and direct radiation dose to the surgeon's hand were measured using 4 C-arm configurations (standard, inverted, translateral, and tube translateral). The effects of rotating the surgeon's head away from the patient and of a thyroid shield were also evaluated.

Results: Scatter radiation doses decreased as distance from the patient increased during C-arm fluoroscopy use. The standard and translateral C-arm configurations caused lower scatter doses to sensitive organs than inverted and tube translateral configurations. Scatter doses were highest for breast and lowest for gonads. The use of a thyroid shield and rotating the surgeon's head away from the patient reduced scatter radiation dose to the surgeon's thyroid and eyes. The direct radiation dose was at least 20 times greater than scatter doses to sensitive organs.

Conclusion: The following factors could reduce radiation exposure during intraoperative use of C-arm; (1) distance from the patient, (2) C-arm configuration, (3) radioprotective equipments, (4) rotating the surgeons' eyes away from the patient, and (5) avoiding direct exposure of surgeons' hands.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1097/BRS.0b013e31824589d5DOI Listing
June 2012

Dose area product measurement for diagnostic reference levels and analysis of patient dose in dental radiography.

Radiat Prot Dosimetry 2012 Jul 5;150(4):523-31. Epub 2011 Dec 5.

Department of Radiological Science, College of Health Science, Korea University, Seoul, Korea.

In this study, diagnostic reference levels (DRLs) were suggested and patient doses were analysed through the dose-area product value in dental radiography. In intraoral radiography, at three sites, i.e. molar, premolar and incisor on the maxilla and acquired third quartile values: 55.5, 46 and 36.5 mGy cm(2), respectively, were measured. In panoramic, cephalometric and cone beam computed tomography, the values were 120.3, 146 and 3203 mGy cm(2) (16 × 18 cm), respectively. It has been shown that, in intraoral radiography, the patient dose changes proportionally to the value of mA s, but the change in extraoral radiography in response to mA s could not be confirmed. The authors could confirm, however, the difference in dose according to the manufacturer in all dental radiography examinations, except for panoramic radiography. Depending on the size of hospital, there were some differences in patient dose in intraoral radiography, but no difference in patient dose in extraoral radiography.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1093/rpd/ncr439DOI Listing
July 2012

The perspectives of users and developers in designing and developing O-arm imaging system.

J Xray Sci Technol 2011 ;19(2):199-204

Department of Orthopedic Surgery, Seoul National University Bundang Hospital, 300 Gumi-Dong, Bundang-Gu,Sungnam, Kyungki, Korea.

A questionnaire survey was performed to investigate the different knowledge of radiation exposure, awareness and expectation for O-arm imaging system between the users (orthopaedic surgeons) and the developers (engineers). A total of 93 orthopaedic surgeons and 19 engineers participated and answered the questionnaire consisting of 18 items designed for this study. The items were focused on knowlege, awareness, and expectation. Orthopaedic surgeons had higher scores for items of knowledge domains regarding radiation exposure than the engineers while the engineers were more sensitive to radiation hazards and adopted higher levels of radiation protection than orthopaedic surgeons in the awareness domain. Most engineers and orthopaedic surgeons answered that the requirements of diagnostic and intraoperative imaging systems differ. Image resolution, a low radiation exposure, and the time required for image acquisition was the top three requirements of O-arm selected by engineers. On the other hand, the top three requirements according to orthopaedic surgeons were; image resolution, expediency, and spatial occupancy. User requirements need to be reflected in developing O-arm along with basic requirements such as image resolution and low radiation exposure.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3233/XST-2011-0286DOI Listing
September 2011

Comparison of operator radiation exposure between C-arm and O-arm fluoroscopy for orthopaedic surgery.

Radiat Prot Dosimetry 2012 Mar 26;148(4):431-8. Epub 2011 Apr 26.

Department of Orthopedic Surgery, Seoul National University Bundang Hospital, Sungnam, Korea.

The O-arm system has recently been introduced and has the capability of combined two-dimensional (2-D) fluoroscopy imaging and three-dimensional computed tomography imaging. In this study, an orthopaedic surgical procedure using C-arm and O-arm systems in their 2-D fluoroscopy modes was simulated and the radiation doses to susceptible organs to which operators can be exposed were investigated. The experiments were performed in four configurations of the location of the X-ray source and detector. Shielding effects on the thyroid surface and the direct exposure delivered to the surgeon's hands were also compared. The results obtained show that the O-arm delivered higher doses to the sensitive organs of the operator in all configurations. The thyroid shield cut-off 89 % of the dose in the posteroanterior configuration of both imaging systems. Thus, the operators need to pay more attention to managing radiation exposure, especially when using the O-arm system.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1093/rpd/ncr149DOI Listing
March 2012

Impact on Image Noise of Incorporating Detector Blurring into Image Reconstruction for a Small Animal PET Scanner.

IEEE Trans Nucl Sci 2009 Oct;56(5):2769-2776

We study the noise characteristics of an image reconstruction algorithm that incorporates a model of the non-stationary detector blurring (DB) for a mouse-imaging positron emission tomography (PET) scanner. The algorithm uses ordered subsets expectation maximization (OSEM) image reconstruction, which is used to suppress statistical noise. Including the non-stationary detector blurring in the reconstruction process (OSEM(DB)) has been shown to increase contrast in images reconstructed from measured data acquired on the fully-3D MiCES PET scanner developed at the University of Washington. As an extension, this study uses simulation studies with a fully-3D acquisition mode and our proposed FORE+OSEM(DB) reconstruction process to evaluate the volumetric contrast versus noise trade-offs of this approach. Multiple realizations were simulated to estimate the true noise properties of the algorithm. The results show that incorporation of detector blurring (FORE+OSEM(DB)) into the reconstruction process improves the contrast/noise trade-offs compared to FORE+OSEM in a radially dependent manner. Adding post reconstruction 3D Gaussian smoothing to FORE+OSEM and FORE+OSEM(DB) reduces the contrast versus noise advantages of FORE+OSEM(DB).
View Article and Find Full Text PDF

Download full-text PDF

Source
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2805005PMC
http://dx.doi.org/10.1109/tns.2009.2021610DOI Listing
October 2009

Detector Light Response Modeling for a Thick Continuous Slab Detector.

J Nucl Sci Technol 2008 ;45(7):634-638

Department of Radiology, University of Washington, Seattle, WA, 98195, U.S.A.

We investigate a method to improve the position decoding for thick crystal versions (i.e., ≥8 mm) of the continuous miniature crystal element (cMiCE) PET detector by more accurately modeling the detector light response function (LRF). The LRF for continuous detectors varies with the depth of interaction (DOI) of the detected photon. This variation in LRF can result in a positioning error for two-dimensional positioning algorithms. We explore a method to improve positioning performance by deriving two lookup tables, corresponding to the front and back regions of the crystal. The DETECT2000 simulation package was used to investigate the light response characteristics for a 48.8 mm by 48.8 mm by 10 (8) mm slab of LSO coupled to a 64-channel, flat-panel PMT. The data are then combined to produce the two-dimensional light collection histograms. Light collection histograms that have markedly non-Gaussian distributions are characterized as a combination of two Gaussian functions, where each Gaussian function corresponds to a DOI region of the crystal. The results indicate that modest gains in positioning accuracy are achieved near the central region of the crystal. However, significant improvements in spatial resolution and positioning bias are achieved for the corner section of the detector.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3327/jnst.45.634DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2709864PMC
January 2008

Development of a single detector ring micro crystal element scanner: QuickPET II.

Mol Imaging 2005 Apr-Jun;4(2):117-27

University of Washington, Seattle, WA 98195-6004, USA.

This article describes a single ring version of the micro crystal element scanner (MiCES) and investigation of its spatial resolution imaging characteristics for mouse positron emission tomography (PET) imaging. This single ring version of the MiCES system, referred to as QuickPET II, consists of 18 MiCE detector modules mounted as a single ring in a vertical gantry. The system has a 5.76-cm transverse field of view and a 1.98-cm axial field of view. In addition to the scanner and data acquisition system, we have developed an iterative reconstruction that includes a model of the system's detector response function. Evaluation images of line sources and mice have been acquired. Using filtered backprojection, the resolution for a reconstructed line source has been measured at 1.2 mm full width at half maximum. F-18-2-fluoro-2-deoxyglucose mouse PET images are provided. The result shows that QuickPET II has the imaging characteristics to support high-resolution, static mouse PET studies using 18-F labeled compounds.
View Article and Find Full Text PDF

Download full-text PDF

Source
October 2005

Pragmatic fully 3D image reconstruction for the MiCES mouse imaging PET scanner.

Phys Med Biol 2004 Oct;49(19):4563-78

Department of Radiology, University of Washington, Seattle, WA 98195, USA.

We present a pragmatic approach to image reconstruction for data from the micro crystal elements system (MiCES) fully 3D mouse imaging positron emission tomography (PET) scanner under construction at the University of Washington. Our approach is modelled on fully 3D image reconstruction used in clinical PET scanners, which is based on Fourier rebinning (FORE) followed by 2D iterative image reconstruction using ordered-subsets expectation-maximization (OSEM). The use of iterative methods allows modelling of physical effects (e.g., statistical noise, detector blurring, attenuation, etc), while FORE accelerates the reconstruction process by reducing the fully 3D data to a stacked set of independent 2D sinograms. Previous investigations have indicated that non-stationary detector point-spread response effects, which are typically ignored for clinical imaging, significantly impact image quality for the MiCES scanner geometry. To model the effect of non-stationary detector blurring (DB) in the FORE+OSEM(DB) algorithm, we have added a factorized system matrix to the ASPIRE reconstruction library. Initial results indicate that the proposed approach produces an improvement in resolution without an undue increase in noise and without a significant increase in the computational burden. The impact on task performance, however, remains to be evaluated.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1088/0031-9155/49/19/008DOI Listing
October 2004
-->