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. 2019 Apr;54(4):204-211.
doi: 10.1097/RLI.0000000000000535.

Reduction of Metal Artifacts and Improvement in Dose Efficiency Using Photon-Counting Detector Computed Tomography and Tin Filtration

Wei Zhou, David J Bartlett, Felix E Diehn, Katrina N Glazebrook, Amy L Kotsenas, Rickey E Carter  1 , Joel G Fletcher, Cynthia H McCollough, Shuai Leng
Affiliations

Reduction of Metal Artifacts and Improvement in Dose Efficiency Using Photon-Counting Detector Computed Tomography and Tin Filtration

Wei Zhou et al. Invest Radiol. 2019 Apr.

Abstract

Objectives: The aim of this study was to investigate the impact on metal artifacts and dose efficiency of using a tin filter in combination with high-energy threshold (TH) images of a photon-counting detector (PCD) computed tomography (CT) system.

Materials and methods: A 3D-printed spine with pedicle screws was scanned on a PCD-CT system with and without tin filtration. Image noise and severity of artifacts were measured for low-energy threshold (TL) and TH images. In a prospective, institutional review board-approved, Health Insurance Portability and Accountability Act-compliant study, 20 patients having a clinical energy-integrating detector (EID) CT were scanned on a PCD-CT system using tin filtration. Images were reviewed by 3 radiologists to evaluate visualization of anatomic structures, diagnostic confidence, and image preference. Artifact severity and image noise were measured. Wilcoxon signed rank was used to test differences between PCD-CT TH and EID-CT images.

Results: Phantom TH images with tin filtration reduced metal artifacts and had comparable noise (32 HU) to TL images (29 HU) acquired without tin filtration. Visualization scores for the cortex, trabeculae, and implant-trabecular interface from PCD-CT TH images (4.4 ± 0.9, 4.4 ± 1.0, and 4.4 ± 1.0) were significantly higher (P < 0.0001) than EID-CT images (3.3 ± 1.3, 3.3 ± 1.2, and 3.3 ± 1.6). A strong preference was shown for PCD-CT TH images due to improved diagnostic confidence and decreased artifact severity. Noise in PCD-CT TH images (93 ± 41 HU) was significantly lower than that in EID-CT images (133 ± 92 HU, P < 0.05).

Conclusions: Threshold high images acquired with tin filtration on PCD-CT demonstrated a substantial decrease in metal artifacts and an increase in dose efficiency compared with EID-CT.

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Conflict of interest statement

Notification of Conflicts of Interest: Drs. McCollough and Fletcher receive industry funding from Siemens Healthcare. For the remaining authors none were declared.

Figures

Figure 1.
Figure 1.
Representative images of a 3D-printed vertebrae containing metallic pedicle screws acquired without (A,B) and with (C,D) use of a 0.4 mm tin filter. (A,C) = Low-energy threshold images that use the full energy spectrum. (B,D) High-energy threshold images that use only higher-energy photons. W/L = 400/40 HU
Figure 2.
Figure 2.
(A) Absolute values of the CT number difference between artifact-free and artifact-contaminated regions of interest. (B) Image noise in uniform regions of interest without metal artifacts. Data are provided for the low-energy threshold [25–140 keV] (TL) and high-energy threshold [75–140 keV] (TH) images, both without (dark grey) and with (light grey) use of the tin filter.
Figure 3.
Figure 3.
59-year-old female with posterior rod and screw fixation of L2-L5 and a posterolateral bone graft demonstrating improved visualization of critical anatomic structures of the spine with threshold high (TH) Sn140 kV PCD-CT. EID-CT 120 kV (A-B) and TH Sn 140 kV PCD-CT (C-D) axial images from the same patient. The TH Sn 140 kV PCD-CT images (C-D) have reduced metal artifact compared with the EID-CT images (A-B) showing improved visualization of the central canal, neural foramina, and nerve roots which are the overall most improved critical anatomic structures in this study. The metal artifact reduction is predominantly evident with the soft tissue algorithm (A) vs. (C) than with the bone algorithm (B) vs. (D). In this particular example, the readers mean evaluation scores for central canal, neural foramina, and nerve roots for TH Sn 140 kV PCD-CT (C-D) were 3.7, 4.0, and 4.0 vs. 0.3, 3.0, and 2.3 for EID-CT (A-B), respectively. A, C: W/L = 400/40 HU. B, D: W/L = 1500/450 HU.
Figure 4.
Figure 4.
69 -year-old male with left tibiotalar arthrodesis with lateral plate and screw fixation showing improved metal artifact reduction of the ankle with threshold high (TH) Sn140 kV PCD-CT. EID-CT 120 kV (A-B) and TH Sn 140 kV PCD-CT (C-D) are shown. The TH Sn 140 kV PCD-CT images (C-D) have reduced metal artifact compared to the EID-CT images (A-B) demonstrating improved visualization of the implant trabecular interface, cortex, trabecula, and soft tissue in the distal tibia near the tibiofibular joint. In this particular example, the readers mean evaluation scores for implant trabecular interface, cortex, and trabecula for TH Sn 140 kV PCD-CT (C-D) were 4.0, 4.3 and 4.0 vs. 2.7, 3.0, and 2.3 for EID-CT (A-B), respectively. A, C: soft tissue algorithm kernel; W/L = 400/40 HU. B, D: bone algorithm kernel; W/L = 1500/450 HU.
Figure 5.
Figure 5.
Summary of the preference and diagnostic confidence rating for the comparison of photon-counting-detector (PCD) CT high-energy threshold images and conventional energy integrating detector (EID) images.
Figure 6.
Figure 6.
Quantitative comparison of the severity of metal artifacts between photon-counting-detector (PCD)-CT high-energy threshold images (TH) and energy-integrating-detector (EID)-CT images. (A) Distribution of the absolute values of the differences in mean CT numbers between region of interests in the artifact-containing region and fat adjacent to but outside of the artifact-containing region. (B) Distribution of the size of the metal artifacts across patients for each imaging protocol.
Figure 7.
Figure 7.
Comparison of noise (standard deviation of CT numbers in a uniform region of interest in fat) between photon-counting-detector (PCD)-CT high-energy threshold images (TH) and energy-integrating-detector (EID)-CT images.
See this image and copyright information in PMC

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