Dental cone-beam CT reconstruction from limited-angle view data based on compressed-sensing (CS) theory for fast, low-dose X-ray imaging

Je, Uikyu,Cho, Hyosung,Lee, Minsik,Oh, Jieun,Park, Yeonok,Hong, Daeki,Park, Cheulkyu,Cho, Heemoon,Choi, Sungil,Koo, Yangseo Korean Physical Society 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.64 No.12

Recently, reducing radiation doses has become an issue of critical importance in the broader radiological community. As a possible technical approach, especially, in dental cone-beam computed tomography (CBCT), reconstruction from limited-angle view data (< 360A degrees) would enable fast scanning with reduced doses to the patient. In this study, we investigated and implemented an efficient reconstruction algorithm based on compressed-sensing (CS) theory for the scan geometry and performed systematic simulation works to investigate the image characteristics. We also performed experimental works by applying the algorithm to a commercially-available dental CBCT system to demonstrate its effectiveness for image reconstruction in incomplete data problems. We successfully reconstructed CBCT images with incomplete projections acquired at selected scan angles of 120, 150, 180, and 200A degrees with a fixed angle step of 1.2A degrees and evaluated the reconstruction quality quantitatively. Both simulation and experimental demonstrations of the CS-based reconstruction from limited-angle view data show that the algorithm can be applied directly to current dental CBCT systems for reducing the imaging doses and further improving the image quality.

Feasibility study for image reconstruction in circular digital tomosynthesis (CDTS) from limited-scan angle data based on compressed-sensing theory

Park, Yeonok,Je, Uikyu,Cho, Hyosung,Hong, Daeki,Park, Chulkyu,Cho, Heemoon,Choi, Sungil,Woo, Taeho Elsevier 2015 Nuclear instruments & methods in physics research. Vol.777 No.-

<P><B>Abstract</B></P> <P>In this work, we performed a feasibility study for image reconstruction in a circular digital tomosynthesis (CDTS) from limited-scan angle data based on compressed-sensing (CS) theory. Here, the X-ray source moves along an arc within a limited-scan angle (≤ 180°) on a circular path set perpendicularly to the axial direction during the image acquisition. This geometry, compared to full-angle (360°) scan geometry, allows imaging system to be designed more compactly and gives better tomographic quality than conventional linear digital tomosynthesis (DTS). We implemented an efficient CS-based reconstruction algorithm for the proposed geometry and performed systematic simulations to investigate the image characteristics. We successfully reconstructed CDTS images with incomplete projections acquired at several selected limited-scan angles of 45°, 90°, 135°, and 180° for a given tomographic angle of 80° and evaluated the reconstruction quality. Our simulation results indicate that the proposed method can provide superior tomographic quality for axial view and even for the other views (<I>i.e.</I>, sagittal and coronal), as in computed tomography, to conventional DTS.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Image reconstruction is done in circular digital tomosynthesis (CDTS). </LI> <LI> The designed geometry allows imaging system to be the better image. </LI> <LI> An efficient compressed-sensing (CS)-based reconstruction algorithm is performed. </LI> <LI> Proposed method can provide superior tomographic quality for the axial view. </LI> </UL> </P>

Compressed-sensing (CS)-based Digital Breast Tomosynthesis (DBT) Reconstruction for Low-dose, Accurate 3D Breast X-ray Imaging

박연옥,조효성,Uikyu Je,홍대기,이민식,박철규,조희문,최성일,구양서 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.65 No.4

In practical applications of three-dimensional (3D) tomographic techniques, such as digital breasttomosynthesis (DBT), computed tomography (CT), etc., there are often challenges for accurateimage reconstruction from incomplete data. In DBT, in particular, the limited-angle and few-viewprojection data are theoretically insufficient for exact reconstruction; thus, the use of commonfiltered-backprojection (FBP) algorithms leads to severe image artifacts, such as the loss of theaverage image value and edge sharpening. One possible approach to alleviate these artifacts mayemploy iterative statistical methods because they potentially yield reconstructed images that are inbetter accordance with the measured projection data. In this work, as another promising approach,we investigated potential applications to low-dose, accurate DBT imaging with a state-of-the-artreconstruction scheme based on compressed-sensing (CS) theory. We implemented an efficientCS-based DBT algorithm and performed systematic simulation works to investigate the imagingcharacteristics. We successfully obtained DBT images of substantially very high accuracy by usingthe algorithm and expect it to be applicable to developing the next-generation 3D breast X-rayimaging system.

Adaptive Panoramic Tomography with a Circular Rotational Movement for the Formation of Multifocal Image Layers

김동수,조효성,박연옥,Uikyu Je,홍대기,최성일,Yangseo Koo 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.3

Panoramic radiography with which only structures within a certain image layer are in focus and others out of focus on the panoramic image has become a popular imaging technique especially in dentistry. However, the major drawback to the technique is a mismatch between the structures to be focused and the predefined image layer mainly due to the various shapes and sizes of dental arches and/or to malpositioning of the patient. These result in image quality typically inferior to that obtained using intraoral radiographic techniques. In this paper, to overcome these difficulties,we suggest a new panoramic reconstruction algorithm, the so-called adaptive panoramic tomography (APT), capable of reconstructing multifocal image layers with no additional exposure. In order to verify the effectiveness of the proposed algorithm, we performed systematic simulation studies with a circular rotational movement and investigated the image performance.

A New Voxelization Strategy in Compressed-Sensing (CS)-Based Iterative CT Reconstruction for Reducing Computational Cost: Simulation and Experimental Studies

Kim, Guna,Park, Soyoung,Je, Uikyu,Cho, Hyosung,Park, Chulkyu,Kim, Kyuseok,Lim, Hyunwoo,Lee, Dongyeon,Lee, Hunwoo,Park, Yeonok,Woo, Taeho Springer-Verlag 2018 Journal of medical and biological engineering Vol.38 No.1

<P>In recent computed tomography (CT) reconstruction, iterative methods have been often used owing to the potential to provide three-dimensional (3D) images of superior reconstruction quality to common filtered-back-projection (FBP)-based methods. However, these methods require enormous computational cost in the iterative process, which has still been an obstacle to put them to practical use. In this work, to overcome these difficulties, we propose a new cone-beam CT reconstruction with a dual-resolution voxelization strategy for a small region-of-interest (ROI) reconstruction in which the voxels outside the target ROI are binned by, for example, 2 x 2 x 2, 4 x 4 x 4, 8 x 8 x 8, etc., while the other voxels remain unbinned. We considered a compressed-sensing (CS)based algorithm with a dual regularization strategy, rather than common FBP-based methods, for more accurate CT reconstruction. We implemented the proposed CS-based algorithm and performed a systematic simulation and experiment. Our results indicate that the proposed method seems to be effective for reducing computational cost considerably in iterative CT reconstruction, keeping the reconstruction quality inside the target ROI not much degraded.</P>

Application of Digital Tomosynthesis (DTS) of Optimal Deblurring Filters for Dental X-ray Imaging

오지은,조효성,김동수,최성일,Uikyu Je 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.7

Digital tomosynthesis (DTS) is a limited-angle tomographic technique that provides some of the tomographic benefits of computed tomography (CT) but at reduced dose and cost. Thus, the potential for application of DTS to dental X-ray imaging seems promising. As a continuation of our dental radiography R&D, we developed an effective DTS reconstruction algorithm and implemented it in conjunction with a commercial dental CT system for potential use in dental implant placement. The reconstruction algorithm employed a backprojection filtering (BPF) method based upon optimal deblurring filters to suppress effectively both the blur artifacts originating from the out-focus planes and the high-frequency noise. To verify the usefulness of the reconstruction algorithm, we performed systematic simulation works and evaluated the image characteristics. We also performed experimental works in which DTS images of enhanced anatomical resolution were successfully obtained by using the algorithm and were promising to our ongoing applications to dental X-ray imaging. In this paper, our approach to the development of the DTS reconstruction algorithm and the results are described in detail.

Compressed-sensing (CS)-based Micro-DTS Reconstruction for Applications of Fast, Low-dose X-ray Imaging

오지은,조효성,홍대기,이민기,박연옥,Uikyu Je,김효정,이선하,최성일,Yangseo Koo,조희문 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.7

In this paper, we introduce limited-angle tomography in which the object being imaged is rotated around the center of an inclined X-ray beam, the so-called <i>micro-DTS</i> (digital tomosynthesis), with a few-view image reconstruction based on the compressed-sensing (CS) theory for applications of fast, low-dose X-ray imaging. We implemented an effective CS-based reconstruction algorithm for micro-DTS and performed systematic simulation works. The assessment of the image characteristics was performed by using several figures of merit such as the root-mean-square error (RMSE), the contrast-to-noise ratio (CNR), and the universal image-quality index (UQI) to compare the reconstructed images to the simulated phantoms. According to our results, compared to the FBP-based method, the CS-based reconstruction method substantially enhanced image accuracy against image artifacts from few-view and limited-angle projections. In the simulation, 41 projections were used for the half-tomographic angles of 30˚, 45˚, and 60˚, giving UQI values of 0.92 ∼ 0.97, which seems promising for potential applications of fast, low-dose X-ray imaging.

Investigation of image characteristics in phase-contrast X-Ray imaging (PCXI)) using a conventional X-Ray grid

Lim, Hyunwoo,Lee, Hunwoo,Cho, Hyosung,Seo, Changwoo,Je, Uikyu,Park, Chulkyu,Kim, Kyuseok,Kim, Guna,Park, Soyoung,Lee, Dongyeon,Kang, Seokyoon,Lee, Minsik 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol. No.

<P>Phase-contrast x-ray imaging (PCXI) is an emerging technology which allows for imaging of smaller features in the examined sample than conventional attenuation-based x-ray imaging with lower x-ray dose. In this work, we investigated a relatively simple approach to PCXI using a conventional x-ray grid, which has potential to open the way to further widespread use of the technique into many application fields. We performed a simulation using a useful PCXI software developed in our previous study to investigate the image characteristics. We also performed a preliminary experiment for PCXI using a table-top setup which consists of a focused-linear xray grid having a 200-lines/in strip density, a microfocus x-ray tube having a 55-mu m focal spot, and a CMOS-type flat-panel detector having a 49-mu m pixel resolution. We successfully extracted absorption, dark-field, and phase-contrast x-ray images of much enhanced visibility at a time from the raw image of the sample by Fourier analysis. Further, we made a composite image by combining the absorption image with the colored dark-field image and compared its image characteristic to that of the absorption image alone.</P>

Industrial x-ray inspection system with improved image characterization using blind deblurring based on compressed-sensing scheme

Kim, Kyuseok,Park, Soyoung,Kim, Guna,Cho, Hyosung,Je, Uikyu,Park, Chulkyu,Lim, Hyunwoo,Lee, Hunwoo,Lee, Dongyeon,Park, Yeonok,Woo, Taeho Taylor Francis 2017 Instrumentation science & technology Vol.45 No.3

디지털 단층합성 X-선 영상의 화질개선을 위한 TV-압축센싱 기반 영상복원기법 연구

제의규,김규석,조효성,김건아,박소영,임현우,박철규,박연옥,Je, Uikyu,Kim, Kyuseok,Cho, Hyosung,Kim, Guna,Park, Soyoung,Lim, Hyunwoo,Park, Chulkyu,Park, Yeonok Korean Society of Medical Physics 2016 의학물리 Vol.27 No.1

본 연구에서는 디지털 단층합성 엑스선 영상의 화질특성을 개선하기 위해 TV-압축센싱 기반 영상복원 기법을 제안한다. 제안된 영상복원 기법의 유효성을 검증하기 위해 우선 관련 영상복원 알고리즘을 구현하였으며, 이를 이용하여 관련 시뮬레이션 및 실험을 함께 수행하였다. 실험을 위해 일반 x-선관($90kV_p$, 6 mAs), CMOS형 평판형 검출기($198{\mu}m$ 픽셀크기)로 구성된 실험장치를 구성하였으며, 제한된 각도 $60^{\circ}$도에서 $2^{\circ}$ 간격으로 총 51장의 투상영상을 획득하고 제안된 알고리즘으로 영상복원을 수행한 후 필터링 역투사법(FBP)을 사용하여 디지털 단층합성 영상을 구현하였다. 본 연구에서 수행된 결과에 의하면, 제안된 영상복원 기법은 일반 엑스선 영상 및 디지털 단층합성 영상의 흐린 영상화질을 선명하게 개선하고 또한 디지털 단층합성 영상의 깊이 분해능을 향상시키는 이점이 있음을 확인함으로써 기존 디지털 단층합성 영상의 화질을 크게 개선할 수 있을 것으로 전망된다. In this work, we considered a compressed-sensing (CS)-based image deblurring scheme with a total-variation (TV) regularization penalty for improving image characteristics in digital tomosynthesis (DTS). We implemented the proposed image deblurring algorithm and performed a systematic simulation to demonstrate its viability. We also performed an experiment by using a table-top setup which consists of an x-ray tube operated at $90kV_p$, 6 mAs and a CMOS-type flat-panel detector having a $198-{\mu}m$ pixel resolution. In the both simulation and experiment, 51 projection images were taken with a tomographic angle range of ${\theta}=60^{\circ}$ and an angle step of ${\Delta}{\theta}=1.2^{\circ}$ and then deblurred by using the proposed deblurring algorithm before performing the common filtered-backprojection (FBP)-based DTS reconstruction. According to our results, the image sharpness of the recovered x-ray images and the reconstructed DTS images were significantly improved and the cross-plane spatial resolution in DTS was also improved by a factor of about 1.4. Thus the proposed deblurring scheme appears to be effective for the blurring problems in both conventional radiography and DTS and is applicable to improve the present image characteristics.