The term non-invasive in Medicine has two meanings:
Physicians have been using for centuries, of course, many simple non-invasive methods based on physical parameters in order to assess body function in health and disease, such as pulse-taking, the auscultation of heart sounds and lung sounds (using the stethoscope), body temperature measurement (using thermometers), external percussion and palpation, vascular pressure measurement (using the sphygmomanometer), change in body volumes (using the plethysmograph) and many others.
However, since the discovery of the first modern non-invasive techniques based on physical methods, electrocardiography and x-rays, at the end of the 19th century, medical technology has advanced more and more towards non-invasive methods for diagnosis and therapy, such as:
Diagnostic images
A recent advance is the substitution of invasive medical tests, such as colonoscopy by computer-based 3D reconstructions, such as virtual colonoscopy.
Diagnostic signals
Electrocardiographic tracing
Therapy
In some cases, non-invasive methods will not work for the intended purpose, so medical technology has developed minimally-invasive methods, such as hypodermic injection (using the syringe), endoscopy, percutaneous surgery, laparoscopic surgery, coronary catheterization, angioplasty, stereotactic surgery and many others.
The benefits for the patient are self-evident.