Lung Cancer

Perception is the first challenge confronting the radiologist in the task of lung cancer detection. 23 , 202 , 400 Good radiographic technique is essential for the detection of a pulmonary nodule. Woodring’s review ⁶⁵¹ of the pitfalls in the diagnosis of lung cancer reminds us that detection of small pulmonary nodules requires good technique and careful review of the radiograph. The standard chest examination includes a frontal radiograph, taken with the patient facing the detector and the radiograph beam passing posterior to anterior, and a lateral radiograph, which is taken with the patient’s left side against the detector (left lateral). Both images should be taken at maximum inspiration. There is no perfect technique for all cases. The ideal frontal chest radiograph provides good detail of the central structures (e.g., trachea, carina, thoracic spine, intervertebral disk). This permits visualization of the normal vasculature posterior to the heart and thus makes detection of nodules posterior to the heart and posterior to the domes of the diaphragm possible. Adequate penetration of these opaque areas must be done while preserving good visualization of the peripheral vascular markings. This cannot be accomplished with low peak kilovoltage (kVp) techniques. 83 , 505 For example, a posteroanterior (PA) chest radiograph taken at 60 kVp will be too light for adequate evaluation of the mediastinum. With the low-kVp technique, the lungs will be black if the mediastinum and left lower lobe are adequately penetrated. This has led to the development of higher kVp techniques for standard chest radiography. It is generally agreed that the optimal kVp is in the range of 120 to 150 kVp. This is a major limiting feature of portable chest radiography, which makes it inadequate for the exclusion of pulmonary nodules. The only major disadvantage of the high-kVp technique is the reduced visibility of calcium.

Viewing time for the detection of a nodule on a chest radiograph by an experienced radiologist may be surprisingly short, but it requires a trained, systematic visual search. Kundel et al. ³²⁰ demonstrated that obvious cancers are often detected with flash viewing of the image and that subtle cancers may be detected with as short a viewing time as 4 seconds. It was even suggested that prolonged viewing of longer than 10 seconds does not improve the number of true-positive results but increases false-positive results. Detection of less conspicuous nodules is improved by knowledge of the anatomic areas in which lesions are likely to be obscured. Comparisons are vital. For example, the right and left pulmonary arteries should be symmetrically opaque. Asymmetric opacity at the junction of the costal cartilage and the rib must be carefully scrutinized. Nodules in the medial portions of the lung may be obscured by large vessels or the heart and may thus be more easily detected on the lateral than on the PA view ( Fig 20.3, A and B ). Obvious abnormalities that may even be insignificant sometimes capture the viewer’s attention and interfere with the detection of a subtle lung cancer. After detecting an abnormality, observers should make a conscious effort to complete the review of the examination and avoid the phenomenon of satisfaction of search as a cause of missed abnormalities. ⁶⁴⁴ Comparisons with previous examinations also enhance the visual search and may make subtle or minimal opacities more detectable.

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