Dose Efficiency of Quarter-Millimeter Photon-Counting Computed Tomography: First-in-Human Results

Purpose The aim of this study was to assess the clinical feasibility, image quality, and radiation dose implications of 0.25-mm imaging mode in a cohort of humans, achieved by dividing the photon-counting detector (PCD) size in half compared with standard-resolution photon-counting computed tomography (CT) (0.5 mm). Methods In this technical feasibility study, a whole-body prototype PCD-CT scanner was studied in the 0.25 mm detector mode (measured at isocenter). A high-resolution PCD-CT protocol was first tested in phantom and canine studies in terms of image noise and spatial resolution. Then, 8 human subjects (mean age, 58 ± 8 years; 2 men) underwent axial PCD 0.25-mm scans of the brain, the thorax, and at the level of the upper left kidney. Filtered backprojection reconstruction was performed with a sharp kernel (B70) for standard-resolution and high-resolution data at 0.5-mm isotropic image voxel. High-resolution data, in addition, were reconstructed with an ultrasharp kernel (U70) at 0.25-mm isotropic voxels. Results Image reconstructions from the PCD 0.25-mm detector system led to an improvement in resolution from 9 to 18 line pairs/cm in a line pair phantom. Modulation transfer function improved from 9.5 to 15.8 line pairs/cm at 10% modulation transfer function. When fully exploiting this improvement, image noise increased by 75% compared with dose-matched 0.5-mm slice PCD standard-resolution acquisition. However, when comparing with standard-resolution data at same in-plane resolution and slice thickness, the PCD 0.25-mm detector mode showed 19% less image noise in phantom, animal, and human scans. Conclusion High-resolution photon-counting CT in humans showed improved image quality in terms of spatial resolution and image noise compared with standard-resolution photon-counting. Received for publication November 13, 2017; and accepted for publication, after revision, January 10, 2018. Conflicts of interest and sources of funding: This study was supported by the NIH Intramural Research Program and a collaborative research agreement with Siemens Healthcare GmbH (Forchheim, Germany). Data inclusion and analysis was performed by the authors who are not employees of or consultants for Siemens. Supplemental digital contents are available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal's Web site (https://ift.tt/2kq7jVD). Correspondence to: Amir Pourmorteza, PhD, Department of Radiology and Imaging Sciences, Winship Cancer Institute of Emory University, 1701 Uppergate Drive, Suite 5018A, Atlanta, GA 30322. E-mail: amir.pourmorteza@emory.edu. Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.

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