title: Pulmonary nodule detection with digital projection radiography: an ex-vivo study on increased latitude post-processing.
abstract: To evaluate increased image latitude post-processing of digital projection radiograms for the detection of pulmonary nodules. 20 porcine lungs were inflated inside a chest phantom, prepared with 280 solid nodules of 4-8 mm in diameter and examined with direct radiography (3.0x2.5 k detector, 125 kVp, 4 mAs). Nodule position and size were documented by CT controls and dissection. Four intact lungs served as negative controls. Image post-processing included standard tone scales and increased latitude with detail contrast enhancement (log-factors 1.0, 1.5 and 2.0). 1280 sub-images (512x512 pixel) were centred on nodules or controls, behind the diaphragm and over free parenchyma, randomized and presented to six readers. Confidence in the decision was recorded with a scale of 0-100%. Sensitivity and specificity for nodules behind the diaphragm were 0.87/0.97 at standard tone scale and 0.92/0.92 with increased latitude (log factor 2.0). The fraction of "not diagnostic" readings was reduced (from 208/1920 to 52/1920). As an indicator of increased detection confidence, the median of the ratings behind the diaphragm approached 100 and 0, respectively, and the inter-quartile width decreased (controls: p<0.001, nodules: p=0.239) at higher image latitude. Above the diaphragm, accuracy and detection confidence remained unchanged. Here, the sensitivity for nodules was 0.94 with a specificity from 0.96 to 0.97 (all p>0.05). Increased latitude post-processing has minimal effects on the overall accuracy, but improves the detection confidence for sub-centimeter nodules in the posterior recesses of the lung.
authors.affiliation: Department of Diagnostic Radiology, University Hospital Schleswig-Holstein Campus Kiel, Arnold-Heller-Str. 9, Kiel, Germany. juergen.biederer@rad.uni-kiel.de
authors.forename: Juergen
authors.initials: J
authors.lastname: Biederer
authors.forename: Tobias
authors.initials: T
authors.lastname: Gottwald
authors.forename: Hendrik
authors.initials: H
authors.lastname: Bolte
authors.forename: Christian
authors.initials: C
authors.lastname: Riedel
authors.forename: Sandra
authors.initials: S
authors.lastname: Freitag
authors.forename: Richard
authors.initials: R
authors.lastname: Van Metter
authors.forename: Martin
authors.initials: M
authors.lastname: Heller
mesh_terms: D000818:Animals; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008168:Lung / Q000000981:diagnostic imaging*; D015588:Observer Variation; D019047:Phantoms, Imaging; D011856:Radiographic Image Enhancement / Q000379:methods; D012680:Sensitivity and Specificity; D003074:Solitary Pulmonary Nodule / Q000175:diagnosis* / Q000000981:diagnostic imaging*; D013552:Swine