Lung cancer is the second most common cancer among men and women the world over. It is second only to prostate cancer in men and breast cancer in women. Moreover, it is considered the leading cause of cancer-related deaths among both genders in the United States, as the number of people who die each year of lung cancer is more than the number of people who die of breast and prostate cancers combined . The number of patients suffering from lung cancer has recently increased significantly all over the world, increasing the motivation for developing accurate and fast diagnostic tools to detect lung cancer earlier in order to increase the patient's survival rate. Lung nodules are the first indication to start diagnosing lung cancer. Lung nodules can be benign (normal subjects) or malignant (cancerous subjects). Figure 9.1 shows some samples of benign and malignant lung nodules.