A novel bone suppression method that improves lung nodule detection : Suppressing dedicated bone shadows in radiographs while preserving the remaining signal.
OBJECTIVE
Suppressing thoracic bone shadows in chest radiographs has been previously reported to improve the detection rates for solid lung nodules, however at the cost of increased false detection rates. These bone suppression methods are based on an artificial neural network that was trained using dual-energy subtraction images in order to mimic their appearance.


METHODS
Here, a novel approach is followed where all bone shadows crossing the lung field are suppressed sequentially leaving the intercostal space unaffected. Given a contour delineating a bone, its image region is spatially transferred to separate normal image gradient components from tangential component. Smoothing the normal partial gradient along the contour results in a reconstruction of the image representing the bone shadow only, because all other overlaid signals tend to cancel out each other in this representation.


RESULTS
The method works even with highly contrasted overlaid objects such as a pacemaker. The approach was validated in a reader study with two experienced chest radiologists, and these images helped improving both the sensitivity and the specificity of the readers for the detection and localization of solid lung nodules. The AUC improved significantly from 0.596 to 0.655 on a basis of 146 images from patients and normals with a total of 123 confirmed lung nodules.


CONCLUSIONS
Subtracting all reconstructed bone shadows from the original image results in a soft image where lung nodules are no longer obscured by bone shadows. Both the sensitivity and the specificity of experienced radiologists increased.
Digital Imaging, Philips Research, Hamburg, Germany. jens.von.berg@philips.com.
Jens
J
von Berg
Digital Imaging, Philips Research, Hamburg, Germany.
Stewart
S
Young
Digital Imaging, Philips Research, Hamburg, Germany.
Heike
H
Carolus
Clinical Science, Diagnostix X-Ray, Philips Healthcare, Hamburg, Germany.
Robin
R
Wolz
Digital Imaging, Philips Research, Hamburg, Germany.
Axel
A
Saalbach
Department of Radiology, Hospital de la Santa Creu i Sant Pau, Carrer de Sant Quintí, 89, Barcelona, Spain.
Alberto
A
Hidalgo
Department of Radiology, Hospital de la Santa Creu i Sant Pau, Carrer de Sant Quintí, 89, Barcelona, Spain.
Ana
A
Giménez
Department of Radiology, Hospital de la Santa Creu i Sant Pau, Carrer de Sant Quintí, 89, Barcelona, Spain.
Tomás
T
Franquet
D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging*; D012372:ROC Curve; D011857:Radiographic Image Interpretation, Computer-Assisted; D013902:Radiography, Thoracic / Q000379:methods*; D012272:Ribs / Q000000981:diagnostic imaging*; D003074:Solitary Pulmonary Nodule / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed / Q000379:methods*
Bone suppression; Lung nodule; Radiography; Thorax