For this answer, I am assuming that you are asking about recent advances and I am assuming that drugs do not count as technology.  Given those assumptions, I would argue that relatively non-invasive surgical procedures are the most important advance that has had the greatest impact on health care.

In times past, all surgery was done by actually cutting patients open with scalpels.  This resulted in large wounds.  It also resulted in very long recovery times.  Patients had to undergo and recover from the trauma of having large incisions even if the actual treatment was relatively minor.  In addition, there were some kinds of surgery (like laser eye surgery) that were simply not possible.

With newer and less invasive procedures, surgery can be much less traumatic to the patient.  The use of arthroscopic surgery on joints, for example, is very important in relieving pain in many people without subjecting them to very prolonged recovery periods. 

Because these procedures make surgery more widely available and much less traumatic, I would say that they have had the greatest impact of any modern technological advance.