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Dohyeon Kim*, Hee-Joung Kim*,†

This research at IWORID 2019 focuses on enhancing reconstruction of the interior region of interest (ROI) images. It addresses the high radiation risks associated with CT scans by proposing a novel field modulation acquisition technique. The study aims to improve imaging precision for conditions like chronic sinusitis and dental implant planning, which necessitate precise focus on specific areas. By implementing a proprietary acquisition model and reconstruction algorithm, the project seeks to reduce patient exposure while preserving detailed anatomical information within the ROI. The assessment involves evaluating image quality metrics such as contrast-to-noise ratio, figure of merit, and structural similarity index. The proposed method demonstrates potential to optimize image accuracy and dose efficiency in medical imaging.

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Dohyeon Kim*, Hee-Joung Kim*,†

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  1. The 21st International Workshop on Radiation Imaging Detectors 07-12 July 2019 in Kolympari, Greece IWORID2019 Image accuracy improvement of interior region of interest (ROI) reconstruction using field modulation CT acquisition • Dohyeon Kim*, Hee-Joung Kim*,† • Department of Radiation Convergence Engineering, College of Health Science, Yonsei University, Wonju, Korea*, • Department of Radiological Science, College of Health Science, Yonsei University, Wonju, Korea†, (Yonsei University) (Medical Physics & Imaging Lab.)

  2. Introduction IWORID2019 • High risk of radiation dose : • CT requires high x-ray dose as multiple projection images are to be obtained and processed. • Most of high effective dose is related with CT applications in various medical x-rays. < Australian Radiation Protection and Nuclear Safety Agency (ARPANSA), Typical values of effective dose for various medical x-rays>

  3. Introduction IWORID2019 • Motivation of ROI imaging : • In case of the chronic sinusitis or dental implant, we often focus on sinus and teeth area. • CT imaging is needed for chronic sinusitis surgery or septum diagnosis. < Sinus CT image > • CT imaging is needed for planning dental implant surgery.

  4. Introduction IWORID2019 • Previous work for ROI imaging : < ROI imaging study > < Study of external information restoration > • Do not perform sampling to maintain the quality of ROI internal information. • The x-ray dose to the patient can be reduced by ROI imaging technique. • Existing studies can not restore anatomical informationoutside the ROI. • To solve this problem, we present field modulation CT acquisition.

  5. Materials & Methods IWORID2019 • Schematic diagram of acquisition model : • ROI imaging acquisition : • Field modulation acquisition (D. Kim et al, RPC, 2019): Total number of projections : S = n + m Configuration of ROI imaging projections : (S-n)×Truncated projections + n×Nontruncated projections Configuration of ROI imaging projections : S×Truncated projections • D. Kim et al, Radiation Physics and Chemistry, 2019 • D. Kim et al, Journal of Applied Clinical Medical Physics, 2018

  6. Materials & Methods IWORID2019 • Information of actual acquisition parameter (GERI TVX-IL1500H) : Image acquisition set-up table <Nontruncated projection acquisition (full scan mode)> <Truncated projection acquisition (ROI scan mode)> ROI setting < RSD Anthropomorphic Head Phantom > < RaySafe dosimeter>

  7. Materials & Methods IWORID2019 • Information of actual acquisition parameter (GERI TVX-IL1500H) : Image acquisition set-up table <Nontruncated projection acquisition (full scan mode)> <Truncated projection acquisition (ROI scan mode)> (a) (b) (c) Obtained sinogram in actual CT system: Full scan sinogram (720 non-truncated) ROI scan sinogram (720 truncated) Field modulation scan sinogram (72 non-truncated + 648 truncated)

  8. Materials & Methods IWORID2019 • Flowchart of proposed image restoration method : • Case of projections : • 288 Truncated + 72 Nontruncated • SNT: 72 Nontruncated sinogram • 360 nontruncated sinogram made by forward projection in POCS reconstructed image. • Final restored sinogram : SNT < Flowchart of the image restoration method based on POCS algorithm > • D. Kim et al, Radiation Physics and Chemistry, 2019

  9. Materials & Methods IWORID2019 • POCS reconstruction algorithm : TV minimization Lower-total variation images • Flowchart of POCS reconstruction algorithm: Total-variation minimization processing Sinogram (real acquisition data) Simultaneous Algebraic Reconstruction Technique (SART) Real object Tomographic image Difference Back projection Projection data Ratio Iteration Sinogram Virtual object Projection Update Sinogram Projection data • Sidky and Pan et al, Physics in Medicine & Biology, 2008

  10. Materials & Methods IWORID2019 • Scout view reconstruction method : 6 views <Flowchart of scout view reconstruction method> • Scout view does not have a large number of projection data (less than 5-6 views) • Scout view may be an image taken at another scan time • Kriti Sen Sharma et al., Phys. Med. Biol, 2013

  11. Materials & Methods IWORID2019 • Quantitative evaluation : Image quality and dose evaluation Bright-band reduction evaluation Contrast to noise ratio (CNR) and Figure of merit (FOM) The structural similarity (SSIM) index SSIM (x,y) = [ l(x,y) ]⋅[ c(x,y) ]⋅[ s(x,y) ] ROI (obj) ROI (obj) ROI (bkg) ROI (bkg) • where μx, μy, σx,σy, and σxy are the local means, standard deviations, and cross-covariance for images x, y. • If α = β = γ = 1 (the default), and C3 = C2/2 (default selection of C3). Measured absorbed dose

  12. Materials & Methods IWORID2019 • Dose area product (DAP) value calculation : 15.24 cm 10.16cm < Full view scan dosimetry> 720 FULL : 7.78 ×309.6768 c= 2409.285 · 720 ROI : 7.78 ×42.9768 = 334.359 · 20.32 cm 4.23 cm 648 ROI + 72 FULL : 0.1 FULL + 0.9 ROI= 541.851 ·c 714 ROI + 6 FULL : 0.008 FULL + 0.991 ROI= 351.650 ·c DAP value = × c= ·

  13. Results & Discussions IWORID2019 • Reconstructed images : Interior view (with SSIM values) (a) (c) (b) (e) (d) Ref 0.84 0.91 0.23 0.79 (f) (h) (g) (j) (i) Ref 0.82 0.94 0.34 0.73 Sinus Images (a - e), Dental images (f – j) : (a),(f) Reference image (2409 ·), (b),(g) ROI scan image (334 ·), (c),(h) ROI scan image w/ extrapolation (334 ·), (d),(i) Scout view reconstruction image (6 views) (334 ·), (e),(j) Field modulation scan (6 views) (351 ·)

  14. Results & Discussions IWORID2019 • Reconstructed images : Global view (Upper row : sinus, Lower row : dental) ROI scan Proposed method (6 views) Reference ROI scan w/ extrapolation Scout view reconstruction (6 views) Proposed method (72 views) ROI scan Proposed method (6 views) Reference ROI scan w/ extrapolation Scout view reconstruction (6 views) Proposed method (72 views)

  15. Results & Discussions IWORID2019 • Results of FOM and CNR values (interior view) • Field modulation images (using 72 views) showed the best performance in terms of CNR value. • Field modulation images (using 6 views) showed the best performance in terms of FOM compared to other conventional ROI techniques.

  16. Conclusion IWORID2019 • We proposed a new ROI-based acquisition method to improve the image quality while reducing the dose. • Proposed field modulation acquisition method was applied to actual CT prototype imaging system. • We also proposed image restoration and image processing method for field modulation tomographic imaging. • In terms of FOM value evaluation, the proposed method shows superior performance compared to conventional ROI methods.

  17. MedicalPhysics&ImagingLaboratory Thanks for your attention Presenter’s e-mail address : kimdoo202@yonsei.ac.kr

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