Eungi Min

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

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 &mgr;Sv/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 &mgr;Sv/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 &mgr;Sv/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

FPGA-based multichannel data acquisition system for prototype in-beam PET

In-beam positron emission tomography (PET) is a clinically proven imaging technique for the online investigation of position emitters induced by hadron irradiation. Because the PET involves the use of many photodetectors, the data acquisition (DAQ) system of the PET system requires many elements and a high processing speed to handle many input signals and complex data sets simultaneously. To create a fast and compact DAQ system for a prototype in-beam PET system, we used an FPGA-based multichannel analysis board and developed a firmware program that was geared to acquire the prototype in-beam PET data. As a result, a flood map of the detector block with 22Na 10μCi sources was acquired, and all pixels were well separated. 18F-FDG (4-mm diameter, 3 mCi), which was located in the center of a PET ring, was explored to acquire preliminary results from the prototype in-beam PET system. We produced an energy histogram with an energy resolution of 26% at 511 keV and a reconstructed point image. The measured maximum count rate on the host PC using the developed DAQ system was 120,000 cps. Although there were many improvements in terms of the count rate, the calculation of the pulse timing and correction methods can still be improved, and we were able to assess the feasibility of the prototype in-beam PET system from the achieved preliminary results.

Development of plasma-display-panel-based x-ray detector (PXD)

The plasma display panel (PDP) is popular in the large area flat panel display market due to its relatively simple cell structure, low cost materials, and uncomplicated manufacturing process. The cell structure of PDP, which consists of electrodes and gas mixture, could be utilized in the manufacture of radiation detectors. In this study, we developed a plasma display panel based x-ray detector (PXD) based on Monte-Carlo simulation. This prototype detector panel has row and column strips, and it can thus be utilized as an imaging detector. To achieve the 2D x-ray image from the developed panel, a PXD dedicated driving and data acquisition circuit has been developed. Now we integrate the individual modules into a system. We hope to further study signal processing to achieve the first x-ray image of PXD.

A peak detection in noisy spectrum using principal component analysis

A spectrum of a radio isotope (RI) contains a single or multiple photo-peaks and radio-activities of all energy levels. These characteristics of each RI source are measured by radiation monitor (RM) systems. However, if the radiation count is extremely low and source to detector distance is too far, we cannot acquire good spectroscopic results for RI identification by RM devices while we still able to measure some counting statistics. Thus, precise peak detection in noisy spectrums is one of the most important tasks in the RM system. In this study, we developed an accurate peak detection method based on wavelet decomposition followed by principal component analysis. We used a discrete wavelet transform (DWT) for reduction of unnecessary high frequency noises in low counts spectrums. To reduce effect of a background radiation, we made a background template using a pre-measured background spectrum and calculated square errors for suppressing a background of low energy levels and maintaining true photo-peaks. Finally, we analyzed pre-processed data and detected photo-peaks using PCA. We measured Cesium 137(Cs-137) and Barium 133(Ba133) with 1 and 10 micro curies collected from the various distance. Each spectrum was collected for a second and total 60 sets were stored for each isotope. Results of our research show that the proposed algorithm achieves high sensitivity and specificity, proving that the algorithm is appropriate for RM systems.

Development of a Multipurpose Gamma-Ray Imaging Detector Module With Enhanced Expandability

A silicon photomultiplier (SiPM) is considered a next generation photo-sensor for low-light applications. In this study, we propose and develop the general concept of a multipurpose submillimeter gamma-ray (MSG) imaging module that is applicable to most gamma-ray imaging devices. The main features of the MSG module are submillimeter intrinsic resolution, geometrically expandable structure, expandable data acquisition system, multi-energy capability and usability in intense magnetic fields. The elements of the gamma-ray detector are pixelated Ce:GAGG (

Development of a DAQ circuit for a plasma-display-panel-based X-ray detector

31\times 31

Simulation study of plasma display panel with GMD structure for x-ray imaging detector

pixels, 0.8 mm pitch), a 1.5-mm acrylic light guide, and one SiPM array (

Development of a prototype SPECT system using a variable pinhole collimator

8 \times 8

Identification of radionuclides for the spectroscopic radiation portal monitor for pedestrian screening under a low signal-to-noise ratio condition

pixels). The readout electronics are composed of a symmetric charge division resistive network, 16 channel preamplifiers, multiplexing amplifiers, and analog-to-digital converter (ADC) circuits. We use a subminiature field-programmable gate array (FPGA) board as a data acquisition system. To make the system more expandable, we apply a 10 GbE-based tree structure using a FPGA-based data acquisition board and switching hub. To verify multipurpose capabilities, the energy spectra and the flood images are obtained using Co-57, Na-22, and Cs-137 isotopes. We measure temperature characteristics of the detector module. A pinhole image is obtained to confirm high resolution property. The maximal data transfer rate that is measured using dummy gamma-ray event packets is 963.143 Mbps. This detector module can be applied to nuclear medicine imaging devices and radiation monitoring systems.

Development of Compact, Cost-effective, FPGA-Based Data Acquisition System for the iPET System

The plasma display panel (PDP) is one of the most widely used display components in flat panel displays. It is popular in the TV market because of its relatively simple cell structure, low-cost materials, and uncomplicated manufacturing process. Recently, several research groups have shown that the cell structure of a PDP, which consists of electrodes and a gas mixture, can be used in the manufacture of radiation detectors. In the previous study, we developed a PDP-based X-ray detector (PXD). This prototype detector panel has row and column strips, and hence, it can be used as an imaging detector. To obtain the 2D X-ray image from the developed panel, a PXD dedicated driving and data acquisition (DAQ) circuit was developed. The proposed DAQ system consists of a multichannel high-voltage switching board, a multichannel DAQ board, and an FPGA-based control board. The prototype system has a compact design that can be easily used for various object imaging experiments. Each of the developed module boards of the DAQ system was tested, and the integrated system was verified as well. We hope to further study the signal processing in the system to obtain a clear image from the detector.