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. 2019 Mar;54(3):129-137.
doi: 10.1097/RLI.0000000000000524.

High-Resolution Chest Computed Tomography Imaging of the Lungs: Impact of 1024 Matrix Reconstruction and Photon-Counting Detector Computed Tomography

David J Bartlett, Chi Wan Koo, Brian J Bartholmai, Kishore Rajendran, Jayse M Weaver, Ahmed F Halaweish  1 , Shuai Leng, Cynthia H McCollough, Joel G Fletcher
Affiliations

High-Resolution Chest Computed Tomography Imaging of the Lungs: Impact of 1024 Matrix Reconstruction and Photon-Counting Detector Computed Tomography

David J Bartlett et al. Invest Radiol. 2019 Mar.

Abstract

Objectives: The aim of this study was to evaluate if a high-resolution photon-counting detector computed tomography (PCD-CT) system with a 1024×1024 matrix reconstruction can improve the visualization of fine structures in the lungs compared with conventional high-resolution CT (HRCT).

Materials and methods: Twenty-two adult patients referred for clinical chest HRCT (mean CTDI vol, 13.58 mGy) underwent additional dose-matched PCD-CT (mean volume CT dose index, 13.37 mGy) after written informed consent. Computed tomography images were reconstructed at a slice thickness of 1.5 mm and an image increment of 1 mm with our routine HRCT reconstruction kernels (B46 and Bv49) at 512 and 1024 matrix sizes for conventional energy-integrating detector (EID) CT scans. For PCD-CT, routine B46 kernel and an additional sharp kernel (Q65, unavailable for EID) images were reconstructed at 1024 matrix size. Two thoracic radiologists compared images from EID and PCD-CT noting the highest level bronchus clearly identified in each lobe of the right lung, and rating bronchial wall conspicuity of third- and fourth-order bronchi. Lung nodules were also compared with the B46/EID/512 images using a 5-point Likert scale. Statistical analysis was performed using a Wilcoxon signed rank test with a P < 0.05 considered significant.

Results: Compared with B46/EID/512, readers detected higher-order bronchi using B46/PCD/1024 and Q65/PCD/1024 images for every lung lobe (P < 0.0015), but in only the right middle lobe for B46/EID/1024 (P = 0.007). Readers were able to better identify bronchial walls of the third- and fourth-order bronchi better using the Q65/PCD/1024 images (mean Likert scores of 1.1 and 1.5), which was significantly higher compared with B46/EID/1024 or B46/PCD/1024 images (mean difference, 0.8; P < 0.0001). The Q65/PCD/1024 images had a mean nodule score of 1 ± 1.3 for reader 1, and -0.1 (0.9) for reader 2, with one reader having improved nodule evaluation scores for both PCD kernels (P < 0.001), and the other reader not identifying any increased advantage over B46/EID/1024 (P = 1.0).

Conclusions: High-resolution lung PCD-CT with 1024 image matrix reconstruction increased radiologists' ability to visualize higher-order bronchi and bronchial walls without compromising nodule evaluation compared with current chest CT, creating an opportunity for radiologists to better evaluate airway pathology.

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Figures

Figure 1.
Figure 1.
Bar plots of the frequency of higher (more peripheral) bronchial order detection for both readers in right upper (a), middle (b), and lower (c) lobes by CT acquisition and image reconstruction method. Higher order bronchi were detected in all right lung lobes for the PCD-CT images with 1024 ×1024 matrices regardless of the kernel used (light grey (B46), patterned (Q65) bars) compared to clinical reference (black bar) (a-c). The addition of the Q65 sharp kernel (patterned bars) increased the detection of 7th and 8th order bronchi compared to all other CT acquisition and image reconstruction methods.
Figure 2
Figure 2
(a-b). (a) Bar plot of mean score for 3rd order bronchial wall evaluation for the B46/EID/1024, B46/PCD/1024, and Q65/PCD/1024 images compared to clinical reference (B46/EID/512) images demonstrating definitely better visualization of the 3rd order bronchial walls for the Q65/PCD/1024 images (mean = 1.1). The Q65/PCD/1024 mean score is also statistically higher than the B46/EID/1024 (mean= 0.5) and B46/PCD/1024 (mean= 0.5) images (p <0.0001).(b) Bar plot demonstrating 3rd order bronchial wall evaluation by individual reader.
Figure 3
Figure 3
(a-b). (a) Bar plot of mean score for 4th order bronchial wall evaluation for the B46/EID/1024, B46/PCD/1024, and Q65/PCD/1024 images compared to clinical reference (B46/EID/512) images demonstrating definitely better visualization of the 4th order bronchial walls for the Q65/PCD/1024 images (mean = 1.5). The Q65/PCD/1024 mean score is also statistically higher than the B46/EID/1024 (mean= 0.5) and B46/PCD/1024 (mean= 0.5) images (p <0.0001). (b) Bar plot demonstrating 4th order bronchial wall evaluation by individual reader.
Figure 4.
Figure 4.
80-year-old female evaluated for hemoptysis. B46/EID/512 (a), B46/EID/1024 (b), B46/PCD/1024 (c), Q65/PCD/1024 (d) images demonstrating improved visualization of the same normal 4th order bronchial wall in the Q65/PCD/1024 (d) image compared to clinical reference (a). The readers mean evaluation scores for 4th order bronchial wall evaluations were 0.5 (b), 0.5 (c), and 1.5 (d), respectively; W/L = 1200/−600 HU.
Figure 5.
Figure 5.
68-year-old male evaluated for dyspnea secondary to pulmonary fibrosis caused by systemic scleroderma. B46/EID/512 clinical reference images (left side; a,c) and Q65/PCD/1024 images (right side; b,d) demonstrating improved visualization of honeycombing and fibrosis (a,b) as well as, traction bronchiectasis (c,d) in the Q65/PCD/1024 images (b,d) compared to the B46/EID/512 clinical reference images (c,d). W/L = 1200/−600 HU.
Figure 6.
Figure 6.
B46/EID/512 (a) and Q65/PCD/1024 (b) images showing an apparent wall around a small area of centrilobular emphysema mimicking a cyst on EID images (a) and no apparent wall around the same area on PCD CT (b), compatible with emphysema. B46/EID/512 (c) and Q65/PCD/1024 (d) images of a different patient demonstrating improved visualization of margins of a 6 mm nodule on PCD CT (d) compared to EID CT (c); W/L = 1200/−600 HU.
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