Preliminary Investigation| Volume 30, ISSUE 4, P739-748, April 2023

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Deep Learning–Based Digitally Reconstructed Tomography of the Chest in the Evaluation of Solitary Pulmonary Nodules: A Feasibility Study


      • Digitally reconstructed tomograms (DRTs) with frontal and lateral radiographic projections (planar radiography, PR) showed higher diagnostic performance than PR alone (area under the receiver operating characteristic curve 0.95–0.98 versus 0.80–0.85; p < 0.02) in the identification of solitary pulmonary nodules (SPNs).
      • SPNs were diagnosed in 11 more patients using DRTs than using PR alone.

      Rationale and Objectives

      Computed tomography (CT) is preferred for evaluating solitary pulmonary nodules (SPNs) but access or availability may be lacking, in addition, overlapping anatomy can hinder detection of SPNs on chest radiographs. We developed and evaluated the clinical feasibility of a deep learning algorithm to generate digitally reconstructed tomography (DRT) images of the chest from digitally reconstructed frontal and lateral radiographs (DRRs) and use them to detect SPNs.


      This single-institution retrospective study included 637 patients with noncontrast helical CT of the chest (mean age 68 years, median age 69 years, standard deviation 11.7 years; 355 women) between 11/2012 and 12/2020, with SPNs measuring 10–30 mm. A deep learning model was trained on 562 patients, validated on 60 patients, and tested on the remaining 15 patients. Diagnostic performance (SPN detection) from planar radiography (DRRs and CT scanograms, PR) alone or with DRT was evaluated by two radiologists in an independent blinded fashion. The quality of the DRT SPN image in terms of nodule size and location, morphology, and opacity was also evaluated, and compared to the ground-truth CT images


      Diagnostic performance was higher from DRT plus PR than from PR alone (area under the receiver operating characteristic curve 0.95–0.98 versus 0.80–0.85; p < 0.05). DRT plus PR enabled diagnosis of SPNs in 11 more patients than PR alone. Interobserver agreement was 0.82 for DRT plus PR and 0.89 for PR alone; and interobserver agreement for size and location, morphology, and opacity of the DRT SPN was 0.94, 0.68, and 0.38, respectively.


      For SPN detection, DRT plus PR showed better diagnostic performance than PR alone. Deep learning can be used to generate DRT images and improve detection of SPNs.

      Key Words


      AUC (Area under the curve), BMI (Body mass index), CI (Confidence interval), COPD (Chronic obstructive pulmonary disease), CT (Computed tomography), CXR (Chest radiograph), DRR (Digitally reconstructed radiograph), DRT (Digitally reconstructed tomogram), LSTM (Long short-term memory), MSE (Mean squared error), PIL (Python image library), PR (Planar radiography), SD (Standard deviation), SPN (Solitary pulmonary nodule)
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