The term non-invasive in medicine has two meanings:

• A medical procedure which does not penetrate or break 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 (physical examination and inspection), such as pulse-taking, the auscultation of heart sounds and lung sounds (using the stethoscope), temperature examination (using thermometers), respiratory examination, peripheral vascular examination, oral examination, abdominal examination, external percussion and palpation, blood pressure measurement (using the sphygmomanometer), change in body volumes (using plethysmograph), audiometry, eye examination 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
• Magnetic resonance spectroscopy
• 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
• Optical coherence tomography
• Bioluminescence imaging
• Dermatoscopy
• Gene expression imaging
• Etc.

A recent advance is the substitution of invasive medical tests, such as colonoscopy by computer-based 3D reconstructions, such as virtual colonoscopy.

Diagnostic signals

• Electrocardiography (EKG)
• Electroencephalography (EEG)
• Electromyography (EMG)
• Electrical impedance tomography (EIT)
• Electroneuronography (ENoG)
• Electroretinography (ERG)
• Electronystagmography (ENG)
• Magnetoencephalography (MEG)
• Evoked potentials, such as the visual evoked potentials (VEP) and the brain evoked response audiometry (BERA) tests
• Body impedanciometry
• Impedance phlebography
• Nuclear magnetic resonance spectroscopy
• Percutaneous light spectroscopy (such as in pulse oximetry and capnography)
• Breath tests, such as the urea breath test
• Intelligent biomedical clothing
• Non-invasive biomedical sensors
• Endoluminal capsule monitoring
• 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 within 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.
• Biofeedback
• Photodynamic therapy
• Therapeutic ultrasound
• Extracorporeal thermal ablation
• Extracorporeal magnetic innervation
• Photo-infrared pulsed bio-modulation
• Transcranial magnetic stimulation

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.

References

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4. Golder W. Magnetic resonance spectroscopy in clinical oncology. Onkologie. 2004 Jun;27(3):304-9. Review. PMID 15249722
5. Cherry SR. In vivo molecular and genomic imaging: new challenges for imaging physics. Phys Med Biol. 2004 Feb 7;49(3):R13-48. Review. PMID 15012005
6. Lymberis A, Olsson S. Intelligent biomedical clothing for personal health and disease management: state of the art and future vision. Telemed J E Health. 2003 Winter;9(4):379-86. Review. PMID 14980096
7. Soling A, Rainov NG. Bioluminescence imaging in vivo - application to cancer research. Expert Opin Biol Ther. 2003 Oct;3(7):1163-72. Review. Biol Ther. 2003 Dec;3(8):1315. PMID 14519079
8. Rohrscheib M, Robinson R, Eaton RP. Non-invasive glucose sensors and improved informatics--the future of diabetes management. Diabetes Obes Metab. 2003 Sep;5(5):280-4. Review. PMID 12940864
9. Jacobs AH, Winkeler A, Dittmar C, Hilker R, Heiss WD. Prospects of molecular imaging in neurology. J Cell Biochem Suppl. 2002;39:98-109. Review. PMID 12552609
10. Malhi GS, Valenzuela M, Wen W, Sachdev P. Magnetic resonance spectroscopy and its applications in psychiatry. Aust N Z J Psychiatry. 2002 Feb;36(1):31-43. Review. PMID 11929436
11. Jacobs A, Heiss WD. Towards non-invasive imaging of HSV-1 vector-mediated gene expression by positron emission tomography. Vet Microbiol. 2002 Apr 22;86(1-2):27-36. Review. PMID 11888687
12. Leman JA, Morton CA. Photodynamic therapy: applications in dermatology. Expert Opin Biol Ther. 2002 Jan;2(1):45-53. Review. PMID 11772339
13. Richter JE. Ambulatory esophageal pH monitoring. Am J Med. 1997 Nov 24;103(5A):130S-134S. Review. PMID 9422638
14. Yokoyama T, Fujita O, Nishiguchi J, Nozaki K, Nose H, Inoue M, Ozawa H, Kumon H. Extracorporeal magnetic innervation treatment for urinary incontinence. Int J Urol. 2004 Aug;11(8):602-6. PMID 15285749

See also

• Medical imaging
• Biomedical engineeering
• Minimally invasive
• Medical tests