The term non-invasive in Medicine has two meanings:

• A medical procedure which does not penetrates or breaks the skin or a body cavity, i.e., it doesn't require an (invasive) incision into the body or the removal of biological tissue.
• An abnormal tissue growth, such as a neoplasm or tumor, that doesn't spread (invades) to the surrounding healthy tissue.

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

• Ultrasonography and echocardiography using ultrasound waves for imaging
• Radiography, fluoroscopy and Computed Tomography, using x-rays
• Magnetic resonance imaging, using external magnetic fields
• Gamma camera and other scintillographical methods, such as Positron Emission Tomography (PET) and Single-Photon Emission Tomography (SPECT), using radioactive tracers in the body
• Infrared imaging of the body
• Diffuse optical tomography
• Elastography
• Posturography
• Etc.

Diagnostic signals

• Electrocardiography (EKG)
• Electroencephalography (EEG)
• Electromyography (EMG)
• Electrical impedance tomography
• Electroneuronography (ENoG)
• Electronystagmography (ENG)
• Body impedanciometry
• Impedance phlebography
• Nuclear magnetic resonance spectroscopy
• Percutaneous light spectroscopy (such as in pulse oximetry and capnography )
• Etc.

Therapy

• Radiation therapy and radiosurgery, procedures that uses external atomic particles (protons, neutrons, photons, alpha particles, etc.) or gamma rays to destroy pathological tissue withing the body
• Lithotripsy, a procedure that uses ultrasound shock waves to break urinary calculus
• Defibrillation, a procedure to block heart fibrillation and start normal rhythm
• Mechanical ventilation, such as the iron lung.
• Transdermal patches, used to deliver drugs applied to the skin.

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.