Metal Artifact Reduction and Dose Efficiency Improvement on Photon Counting Detector CT using an Additional Tin Filter

Transcription

1 Metal Artifact Reduction and Dose Efficiency Improvement on Photon Counting Detector CT using an Additional Tin Filter Wei Zhou, Dilbar Abdurakhimova, Kishore Rajendran, Cynthia McCollough, Shuai Leng Dept. of Radiology, Mayo Clinic, Rochester, MN

2 Disclosures This work was supported by a Bioengineering Research Partnership grant R01 EB16966 from the National Institutes of Health (NIH). CHM: Others: Research Grant Siemens Nothing to disclose

3 Introduction The prevalence of metal implants leads to more frequent presentation of metal artifacts in routine CT practice General metal artifact reduction approaches: Projection based metal artifact reduction Dual energy CT virtual monochromatic imaging (high energy) Image courtesy: Michael Bruesewitz, Mayo Clinic 3

4 Introduction PCD CT System Overview Based on a 2 nd generation DSDE CT EID: Energy Integrating Detector PCD: Photon Counting Detector 1. Kappler et al, "A research prototype system for quantum counting clinical CT". in SPIE Medical Imaging Yu et al., "Evaluation of conventional imaging performance in a research whole body CT system with a photon counting detector array." PMB (2016).

5 Introduction PCD CT System Overview PCD counts individual pulses that exceed a threshold Threshold low (TL): 20 50keV Threshold high (TH): 50 90keV TL [25, 140] kev TH [75, 140] kev 2 threshold images (TL, TH) 2 bin images (Bin1, 2) Bin1 Bin2 5

6 Introduction PCD CT System Overview TL TH TH has higher effective energy than TL Less metal artifacts in TH TH has less photons than TL More noisy in TH Bin1 Bin2 6

7 PCD CT System Additional Tin Filtration 60.5 E eff = % of photons kev 42.2 E eff = % of photons kev With additional 0.4 mm tin filtration on PCD CT: the photon beam will be pre hardened the percentage of photons will increase for TH images 7

8 Purpose To investigate the impact of additional spectral filtration on metal artifacts, image noise and radiation dose on a PCD CT system. To determine the optimal energy threshold (TH) configuration. 8

9 Methods Phantoms 3D printed spine model with pedicle screws, embedded in a 30 cm water tank 9

10 Methods Imaging Techniques on PCD CT No Additional Tin 140 kv TL = 25 kev TH = 70, 75, 80 kev 144 mas Match clinical CTDIvol mgy Data completion scan Recon with D30, 1.0/1.0 mm 0.4 mm Tin 140 kv TL = 25 kev TH = 70, 75, 80 kev 458 mas Match clinical CTDIvol mgy Data completion scan Recon with D30, 1.0/1.0 mm 10

11 Methods Analysis Artifact Quantification Define 5 artifacts region and 1 background in water region Calculate absolute CT # difference between artifacts and background regions Repeat for 5 slices Noise Average background from 5 consecutive slices 11

12 Results Tin Effects on Image Quality [25 140) kev w/o with Tin [75 140) kev w/o Tin [75 140) kev with Tin W/L = 400/40 HU 12

13 Results Tin Effects on Image Quality Less metal artifact contamination with additional Tin filtration 13

14 Results Tin Effects on Image Quality Image noise reduced from 43.8 HU to 32.3 HU for the [75, 140) kev images using a 0.4 mm Tin filter Increased percentage of photons with Tin in TH 14

15 Purpose To investigate the impact of additional spectral filtration on metal artifacts, image noise and radiation dose on a PCD CT system. To determine the optimal energy threshold (TH) configuration. 15

16 Results Optimal TH with Tin [70 140) kev [75 140) kev [80 140) kev 16

17 Results Optimal TH with Tin 37.0 HU 30.0 HU 32.3 HU 17

18 Conclusion The additional Tin filtration on the PCD CT system substantially reduced metal artifacts and increased dose efficiency [25 140] kev w/o Tin [75 140] kev w/o Tin [75 140] kev with Tin Reduce artifacts Reduce noise 18

19 Conclusion Our results suggested TH = 75 kev was the optimal threshold for the 140 kv protocol on PCD CT to balance between metal artifacts and image noise. Future study could combine tin filtration with iterative reconstruction and VMI to further reduce artifacts. 19

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21 CT Clinical Innovation Center

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