The Value of Inverted Images for Pulmonary Nodule Detection

Chest X-ray (CXR) is the most commonly used initial modality for most lung diseases, including pulmonary nodules. In diseases such as lung cancer, tuberculosis, and fungal infections, detecting a single nodule in the early stages will facilitate treatment. One of the most important obstacles to searching for a single pulmonary nodule on a CXR is peripheral background contrast enhancement, and density differences. The aim of this study was to demonstrate the superiority of inverted gray scale to the standard image of CXR in the detection of a single pulmonary nodule.

The design of the study included the evaluations of two radiologists unaware of each other, and past computed tomography reports. They randomly evaluated standard and inverted gray scale images of posteroanterior CXRs of both nodule-containing and non-nodule-containing patients, totaling 100 in total. Each evaluation was graded from one to three as one stood for nodule negative, two was for doubtful and three was for nodule positive ones.

The percentage of the patients who were correctly identified as having the nodule [sensitivity (inverted 68.15% - standard 57.14%)] and not having [specificity (inverted 87.56% - standard 88.71%)] showed a statistically significant difference in inverted gray scale (negative) image compared to the standard image (P ≤ 0.001).

Inverted chest radiogram is significantly exposing the nodule presence over the white background so that should be highlighted and considered as a part of useful scanning. So that in terms of functional benefit and additionally cost effectiveness, we advice this technique in part of routine CXR evaluation.