• Journal of Biomedical Engineering Research
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• v.29 no.5
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• pp.364-370
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• 2008

Recent development in large area flat-panel x-ray detector technology enables clinical application of digital tomosyntesis. Unlike conventional motion tomography using x-ray films, flat-panel x-ray detectors provide projection images in digital formats so that tomographic images can be synthesized in a more flexible way. For the digital tomosynthesis, precise movements of the x-ray source and the x-ray detector with respect to a fulcrum point are necessary. In this study, we apply the digital tomosynthesis technique to the flat-panel detector based micro-CT in which the flat-panel detector and the x-ray source rotate together on a circular arc. The experimental results suggest that flat-panel detector based 3D CTs can be used for digital tomosynthesis in the clinical environment.

• Journal of Biomedical Engineering Research
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• v.30 no.6
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• pp.476-481
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• 2009

The most troublesome artifacts in micro computed tomography (micro-CT) are ring artifacts. The ring artifacts are caused by non-uniform sensitivity and defective pixels of the x-ray detector. These ring artifacts seriously degrade the quality of CT images. In flat-panel detector based micro-CT systems, the ring artifacts are hardly removed by conventional correction methods of digital radiography, because very small difference of detector pixel signals may make severe ring artifacts. This paper presents a novel method to remove ring artifacts in flat-panel detector based micro-CT systems. First, the bad lines of a sinogram which are caused by defective pixels of the detector are identified, and then, they are corrected using a cubic spline interpolation technique. Finally, a ring artifacts free image is reconstructed from the corrected projections. We applied the method to various kinds of objects and found that the image qualities were much improved.

• The Korean Journal of Nuclear Medicine Technology
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• v.17 no.2
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• pp.15-24
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• 2013

Purpose: With the demand of SPECT/CT increasing, the interest in complex diagnostic information of CT is rising along with the expansion of various studies on potential performance value. But the study on reduction of exposure dose generated by CT is not being conducted enough. Therefore, in this study, the goal is to identify how much dose reduction exists when performing the extremity bone SPECT/CT using the flat-panel CT. Materials and Methods: The extremity bone SPECT/CT was performed with two equipments -BrightView XCT (Philips Healthcare, Cleveland, USA) and Brilliance 16 CT (Philips Healthcare, Cleveland, USA)-to identify the exposed dose and image quality resulted by changing scan parameter (mAs) applying for both equipment respectively. The noise value of image and spatial resolution were measured with AAPM CT phantom. Tube voltage (kVp) was fixed to 120 kVp, tube current (mAs) calculated at different mA (20, 30, 40, 50, 60, 70, 80) was applied to both equipments respectively. DLP (dose length product) were calculated at the same distance at respective mAs. Also, we acquired images and % contrast with NEMA IEC body phantom to confirm the effect on image. The output of statistics was analyzed by SPSS ver.18. Results: Regarding AAPM phantom, the noise decreased as the tube current (mAs) increased and flat-panel had less noise than Helical CT. This difference increased at lower dose exposure. As to the evaluation of spatial resolution, we can differentiate the space up to 0.75 mm with both equipments. With scan parameter (mA) growing, the value of DLP increased up to 54-216 mGy cm at flat-panel CT and up to 177-709 mGy cm at Helical CT. Regarding NEMA IEC body phantom, same sphere with varied parameter (mA) shows that similar results. Conclusion: There is no significant differences of image quality in both flat-panel and Helical CT when the scan parameter (mA) is changed respectively. Moreover, we can identify the reduction of exposure dose and confirm %contrast analysis value with maintaining image quality. Therefore, at the extremity bone SPECT/CT requiring high spital resolution without the wide ROI, the flat-panel CT is considered to be more useful and it expected to result in the similar image quality with lower exposure dose compared to Helical CT. Additionally, through this study, we expect to help the reduction of the unnecessary exposure dose.

• Journal of Biomedical Engineering Research
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• v.28 no.1
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• pp.95-101
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• 2007

Recently, small-animal imaging technology has been rapidly developed for longitudinal screening of laboratory animals such as mice and rats. One of newly developed imaging modalities for small animals is an x-ray micro-CT (computed tomography). We have developed two types of x-ray micro-CT systems for small animal imaging. Both systems use flat-panel x-ray detectors and micro-focus x-ray sources to obtain high spatial resolution of $10{\mu}m$. In spite of the relatively large field-of-view (FOV) of flat-panel detectors, the spatial resolution in the whole-body imaging of rats should be sacrificed down to the order of $100{\mu}m$ due to the limited number of x-ray detector pixels. Though the spatial resolution of cone-beam CTs can be improved by moving an object toward an x-ray source, the FOV should be reduced and the object size is also limited. To overcome the limitation of the object size and resolution, we introduce zoom-in micro-tomography for high-resolution imaging of a local region-of-interest (ROI) inside a large object. For zoom-in imaging, we use two kinds of projection data in combination, one from a full FOV scan of the whole object and the other from a limited FOV scan of the ROI. Both of our micro-CT systems have zoom-in micro-tomography capability. One of both is a micro-CT system with a fixed gantry mounted with an x-ray source and a detector. An imaged object is laid on a rotating table between a source and a detector. The other micro-CT system has a rotating gantry with a fixed object table, which makes whole scans without rotating an object. In this paper, we report the results of in vivo small animal study using the developed micro-CTs.

• Journal of Biomedical Engineering Research
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• v.25 no.2
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• pp.97-102
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• 2004

We developed an x-ray cone-beam micro computed tomography (micro-CT) system for small-animal imaging. The micro-CT system consists of a 2-D flat-panel x-ray detector with a field-of-view (FOV) of 120${\times}$120 mm2, a micro-focus x-ray source, a scan controller and a parallel image reconstruction system. Imaging performances of the micro-CT system have been evaluated in terms of contrast and spatial resolution. The minimum resolvable contrast has been found to be less than 36 CT numbers at the dose of 95 mGy and the spatial resolution about 14 lp/mm. As small animal imaging results, we present high resolution 3-D images of rat organs including a femur, a heart and vessels. We expected that the developed micro-CT system can be greatly used in biomedical studies using small animals.

• Progress in Medical Physics
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• v.19 no.4
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• pp.209-218
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• 2008

According to improved radiation therapy technology such as IMRT and proton therapy, the accuracy of patient alignment system is more emphasized and IGRT is dominated research field in radiation oncology. We proposed to study the feasibility of cone-beam CT system using simple x-ray imaging systems for image guided proton therapy at National Cancer Center. 180 projection views ($2,304{\times}3,200$, 14 bit with 127 ${\mu}m$ pixel pitch) for the geometrical calibration phantom and humanoid phantoms (skull, abdomen) were acquired with $2^{\circ}$ step angle using x-ray imaging system of proton therapy gantry room ($360^{\circ}$ for 1 rotation). The geometrical calibration was performed for misalignments between the x-ray source and the flat-panel detector, such as distances and slanted angle using available algorithm. With the geometrically calibrated projection view, Feldkamp cone-beam algorithm using Ram-Lak filter was implemented for CBCT reconstruction images for skull and abdomen phantom. The distance from x-ray source to the gantry isocenter, the distance from the flat panel to the isocenter were calculated as 1,517.5 mm, 591.12 mm and the rotated angle of flat panel detector around x-ray beam axis was considered as $0.25^{\circ}$. It was observed that the blurring artifacts, originated from the rotation of the detector, in the reconstructed toomographs were significantly reduced after the geometrical calibration. The demonstrated CBCT images for the skull and abdomen phantoms are very promising. We performed the geometrical calibration of the large gantry rotation system with simple x-ray imaging devices for CBCT reconstruction. The CBCT system for proton therapy will be used as a main patient alignment system for image guided proton therapy.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.3 s.168
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• pp.7-14
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• 2005

본 논고에서는 microfocus X 선 발생장치와 평판형 영상센서를 이용한 micro-CT 시스템의 개발과 그 응용에 대해 소개하였다. 개발과 관련하여서는 영상센서 및 시스템의 동작원리뿐만 아니라 성능평가 결과에 대해서도 간단히 언급하였는데, 이와 같은 성능평가는 추후 개선된 혹은 새로운 설계 및 제작을 위해서는 필수적으로 수반되어야 할 부분이다. 개발된 micro-CT 시스템의 응용분야 소개와 관련하여서는 몇 가지 획득 영상을 토대로 바이오 영상과 산업용 영상에 관하여 언급하였다. 바이오 영상분야에서는 현재 세계적으로 유수 의료기기업체에서 이미 제작하여 판매하고 있으며, 대부분 X선 영상증배관 혹은 CCD(charge-coupled device)를 X 선 영상획득 센서로 사용한 반면, 본 논고에서 소개한 시스템은 평판형 영상센서를 사용했다는 점에서 차별성이 있다. Micro-CT 시스템의 산업용 영상분야로의 적용은 이제 시작 단계이며, 기존 라미노그라피 시스템을 대체하거나 혹은 새로운 응용으로 자리매김할 것으로 기대된다.

• Imaging Science in Dentistry
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• v.37 no.4
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• pp.205-209
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• 2007

Purpose: To determine the physical properties of a newly developed cone beam computed tomography (CBCT). Materials and Methods: We measured and compared the imaging properties for the indirect-type flat panel detector (FPD) of a new CBCT and the single detector array (SDA) of conventional helical CT (CHCT). Results: First, the modulation transfer function (MTF) of the CBCT were superior to those of the CHCT. Second, the noise power spectrum (NPS) of the CBCT were worse than those of the CHCT. Third, detective quantum efficiency (DQE) of the indirect-type CBCT were worse than those of the CHCT at lower spatial frequencies, but were better at higher spatial frequencies. Although the comparison of contrast-to-noise ratio (CNR) was estimated in the limited range of tube current, CNR of CBCT were worse than those of CHCT. Conclusion: This study shows that the indirect-type FPD system may be useful as a CBCT detector because of high resolution.

• Progress in Medical Physics
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• v.19 no.2
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• pp.102-112
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• 2008

We developed a high-resolution micro-CT system based on rotational gantry and flat-panel detector for live mouse imaging. This system is composed primarily of an x-ray source with micro-focal spot size, a CMOS (complementary metal oxide semiconductor) flat panel detector coupled with Csl (TI) (thallium-doped cesium iodide) scintillator, a linearly moving couch, a rotational gantry coupled with positioning encoder, and a parallel processing system for image data. This system was designed to be of the gantry-rotation type which has several advantages in obtaining CT images of live mice, namely, the relative ease of minimizing the motion artifact of the mice and the capability of administering respiratory anesthesia during scanning. We evaluated the spatial resolution, image contrast, and uniformity of the CT system using CT phantoms. As the results, the spatial resolution of the system was approximately the 11.3 cycles/mm at 10% of the MTF curve, and the radiation dose to the mice was 81.5 mGy. The minimal resolving contrast was found to be less than 46 CT numbers on low-contrast phantom imaging test. We found that the image non-uniformity was approximately 70 CT numbers at a voxel size of ${\sim}55{\times}55{\times}X100\;{\mu}^3$. We present the image test results of the skull and lung, and body of the live mice.

• Journal of radiological science and technology
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• v.45 no.2
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• pp.127-134
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• 2022

In order to overcome the image quality limitations of the conventional C-arm, a flat panel detector (FPD) is used to enhance spatial resolution, detective quantum efficiency, frame rate, and dynamic range. Three-dimensional (3D) visualized information can be obtained from C-arm computed tomography (CT) equipped with an FPD, which can reduce patient discomfort and provide various medical information to health care providers by conducting procedures in the interventional procedure room without moving the patient to the CT scan room. Unlike a conventional C-arm device, a C-arm CT requires different basic safety and essential performance evaluation criteria; therefore, in this study, basic safety and essential performance evaluation criteria to protect patients, medical staff, and radiologists were derived based on International Electrotechnical Commission (IEC) standards, the Ministry of Food and Drug Safety (MFDS) standards in Korea, and the rules on the installation and operation of special medical equipment in Korea. As a result of the study, six basic safety evaluation criteria related to electrical and mechanical radiation safety (leakage current, collision protection, emergency stopping device, overheating, recovery management, and ingress of water or particulate matter into medical electrical (ME) equipment and ME systems: footswitches) and 14 essential performance evaluation criteria (accuracy of tube voltage, accuracy of tube current, accuracy of loading time, accuracy of current time product, reproducibility of radiation output, linearity and consistency in radiography, half layer value in X-ray equipment, focal size and collimator, relationship between X-ray field and image reception area, consistency of light irradiation versus X-ray irradiation, performance of the mechanical device, focal spot to skin distance accuracy, image quality evaluation, and technical characteristic of cone-beam computed tomography) were selected for a total of 20 criteria.