Non-invasive (medical)

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.

For centuries, physicians have employed 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:

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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)
• Photoplethysmograph(PPG)
• 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
• CPAP (Continuous Positive Airway Pressure) used to treat sleep apnea
• VPAP
• BIPAP
• Biphasic Cuirass Ventilation (BCV, eg. Hayek RTX)
• Photodynamic therapy
• Therapeutic ultrasound
• Extracorporeal thermal ablation
• Extracorporeal magnetic innervation [1]
• Photo-infrared pulsed bio-modulation [2]
• 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.

See also

• Medical imaging
• Biomedical engineering
• Minimally invasive
• Medical tests

References

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• Kim PE, Singh M. Functional magnetic resonance imaging for brain mapping in neurosurgery. Neurosurg Focus. 2003 Jul 15;15(1):E1. Review. PMID 15355003
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• Golder W. Magnetic resonance spectroscopy in clinical oncology. Onkologie. 2004 Jun;27(3):304-9. Review. PMID 15249722
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• 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
• 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
• 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
• Leman JA, Morton CA. Photodynamic therapy: applications in dermatology. Expert Opin Biol Ther. 2002 Jan;2(1):45-53. Review. PMID 11772339
• Richter JE. Ambulatory esophageal pH monitoring. Am J Med. 1997 Nov 24;103(5A):130S-134S. Review. PMID 9422638
• 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