World Congress Thoracic Imaging June 18-21, 2017, Hynes Convention Center, Boston, Massachusetts June 18-21, 2017, Hynes Convention Center, Boston, Massachusetts

Sponsoring Societies:

Fleischner Society Society of Thoracic Radiology European Society of Thoracic Imaging Japanese Society of Thoracic Radiology Korean Society of Thoracic Radiology
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Observer Performance for Detection of Pulmonary Nodules at Unenhanced Chest CT Over a Large Range of Radiation Dose Levels
David Levin, Joel G Fletcher, Anne-Marie Sykes, Rebecca Lindell, Darin White, Ronald Kuzo, Lifeng Yu, Maria Shiung, Adam Bartley, Shuai Leng
Mayo Clinic, Rochester, MN

Purpose: To estimate the ability of varying radiation dose levels to detect indeterminate pulmonary nodules ≥ 5 mm (IPNs) and the need for iterative reconstruction (IR). Materials and Methods: CT projection data from 83 chest CT exams performed at routine dose (120 kV, 70 quality ref mAs [QRM]) were collected. Reference IPNs were identified by two non-reader thoracic radiologists using routine dose CT exams. Using a validated noise insertion tool, six datasets were reconstructed corresponding to 5 dose levels with filtered back projection (FBP) or IR (70 QRM-FBP, 30 QRM-FBP, 10 QRM-IR, 5 QRM-FBP, 5 QRM-IR, 2.5 QRM-IR). Three thoracic radiologists evaluated each patient's data once/session using thin 1 mm and MIP images. Readers circled IPNs, provided confidence (0 - 100), and graded image quality. JAFROC analysis was also performed on a per-IPN basis using JAFROC figure of merit (FOM) and a non-inferiority limit of -0.10.
Results: There were 53 reference IPN's (mean size 9.1 3.7 mm), with mean CTDIvol = 5.3 2.0 mGy (SSDE 6.5 1.8mGy). The JAFROC FOM was non-inferior for all configurations except for 2.5 QRM-IR (e.g., FOM at 70 QRM-FBP = 0.86 (0.81 - 0.91); FOM at 5 QRM-IR=0.81 (0.74 - 0.87); 5 QRM-FBP=0.83 (0.76 - 0.89)]. At 5 QRM, pooled sensitivities and specificities were nearly identical between FBP and IR (FBP: 83% [95% CI:72-91%] & 86% [79-94%], IR: 83% [95% CI: 73-89%] & 86% [77-92%]; respectively). Diagnostic image quality decreased with decreasing dose (p<0.001) and was better with IR at 5 QRM (p<0.05). Conclusions: CT images reconstructed at dose levels down to 5 QRM (SSDE 0.4 mGy) performed non-inferiorly to routine dose images at SSDE 6.5 mGy. IR did not appear to be necessary for detection of IPNs at lower dose levels despite subjective improvement in image quality.

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