What is the principal imaging study useful in diagnosing sarcoidosis?

Chest X-ray is the principal imaging study useful in diagnosing sarcoidosis because it allows for the assessment of pulmonary involvement, which is common in this condition. Sarcoidosis frequently affects the lungs and can present with characteristic findings such as lymphadenopathy, especially hilar lymph nodes, and interstitial lung patterns. In many cases, the diagnosis of sarcoidosis starts with a chest X-ray, which can reveal these pulmonary changes early in the disease process.

Further imaging, such as a CT scan, may be used to provide more detailed information if needed, but the chest X-ray remains the initial and most important imaging modality for evaluating sarcoidosis. Other imaging techniques like MRI and ultrasound are not typically employed for diagnosing sarcoidosis as they do not provide the pertinent information regarding lung involvement that is crucial for this specific condition.