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High-Resolution Chest Computed Tomography Imaging of the Lungs

Impact of 1024 Matrix Reconstruction and Photon-Counting Detector Computed Tomography

Bartlett, David J., MD*; Koo, Chi Wan, MD*; Bartholmai, Brian J., MD*; Rajendran, Kishore, PhD*; Weaver, Jayse M., BA*; Halaweish, Ahmed F., PhD; Leng, Shuai, PhD*; McCollough, Cynthia H., PhD*; Fletcher, Joel G., MD*

doi: 10.1097/RLI.0000000000000524
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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.

From the *Department of Radiology, Mayo Clinic, Rochester, MN; and

Siemens Healthineers, Malvern, PA.

Received for publication June 28, 2018; and accepted for publication, after revision, August 31, 2018.

Conflicts of interest and sources of funding: Drs McCollough and Fletcher receive grant support to Mayo Clinic from Siemens Healthineers. Dr Ahmed Halaweish is an employee of Siemens Healthineers. For the remaining authors, none were declared. Research reported in this article was supported by the National Institutes of Health under award number BRP 016966 and C06 RR018898. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institute of Health.

Correspondence to: Joel G. Fletcher, MD, Department of Radiology, Mayo Clinic, 200 First St SW, Rochester, MN 55905. E-mail: fletcher.joel@mayo.edu.

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