Imaging tests include ultrasound, MRI, CT, and PET-CT, which are the four most common and major tests. 1. Which test has the highest accuracy rate and why some patients may need more than one test? These tests are complementary and each is good at different things. The main principle of ultrasound is to probe the body with ultrasound, and color ultrasound can also provide information on hemodynamics. Ultrasound is the most accurate for tumors of the breast, thyroid, liver and pancreas, especially microscopic cancers of the thyroid. CT, which uses X-rays to “photograph” every cross-section of the body, has the unique advantage of detecting high density bony tissue and hemorrhage, and calcified lesions of tumors. Low-dose spiral CT is an effective means of screening for lung cancer, and CT is also used to detect deep tumors in the larynx, pharynx, abdomen, and pelvis. Magnetic resonance imaging (MRI for short) occurs when the body is placed in a strong magnetic field and hydrogen protons are excited in the body by radiofrequency pulses. The imaging modalities of MRI are more diverse, the imaging principles are more complex, and the information obtained is richer. MRI has a higher resolution of soft tissues and can clearly show the cranial brain, spinal cord, heart, large blood vessels and muscle tissue. In the case of tumors such as liver cancer, pancreas, and nasopharyngeal skull base, definitely MRI is the most advantageous. Positron emission computed tomography (PET-CT for short) can examine systemic and metastatic solid tumors; PET examination can detect metabolic abnormal cells and CT examination can detect morphological abnormal tissues. For diseases that cannot be characterized by CT or MRI, then PET-CT may be required. 2. Why is it sometimes necessary to do multiple imaging examinations? Imaging tests have different imaging principles and complementary functions. For example, a patient with a suspected malignant enlarged lymph node in the neck may have a primary focus from the base of the skull, larynx, esophagus or thyroid. Without knowing the origin of the primary focus, it is also difficult for the physician to determine which test is best to use, so he or she will choose a test that is appropriate for most cases, such as ultrasound or CT, to screen with a high probability. After the primary focus is found, depending on the results, a more refined or more targeted test may be done. So from the initial diagnosis to the final determination of the treatment plan, it may take more than one imaging examination to look at it in a comprehensive manner, that’s why. 3.How accurate are imaging tests? Imaging modalities have an accuracy rate of over 90% if used for the right disease and site.