Which of the following services is not covered under Medicare Part B?

Medicare Part B covers a variety of medically necessary services and items, including outpatient care, preventive services, and certain types of durable medical equipment. Anesthesiologist services, which include the administration of anesthesia during surgical procedures, are indeed covered under Medicare Part B, as they are considered essential to the surgical procedure and are billed for separately by the anesthesiologist.

In contrast, Medicare Part B focuses on outpatient services, preventive health services, and durable medical equipment like wheelchairs or oxygen tanks. It also covers specific preventive screenings, such as mammograms for women starting at age 50. Given that anesthesiology services are clearly applicable under the ecosystem of surgical care, they do not fall into a category deemed "not covered" by Medicare Part B. Thus, the choice indicating that anesthesiologist's services are not covered under this part of Medicare is accurate in concluding that they indeed are covered.