Step 1: A bedridden patient with sudden pleuritic chest pain (pain worsened by breathing) is a classic presentation of pulmonary embolism (PE), which also causes sudden dyspnea, tachypnea, cough, and hemoptysis.
Step 2: The gold standard for diagnosing PE has traditionally been pulmonary angiography, but it is invasive and now used less often.
Step 3: CT pulmonary angiography (CT scan) has become the preferred modality because it is non-invasive, widely available, and accurately demonstrates the embolus, so option 4 is the best answer.
Step 4: A chest X-ray and USG are non-specific, and a ventilation-perfusion scan is reserved for patients who cannot undergo CT, so they are less helpful first choices.