Transillumination is the technique of sample illumination by transmission of light through the sample. Transillumination is used in a variety of methods of imaging.

Microscopy

In microscopy transillumination refers to the illumination of a sample by transmitted light. In its most basic form it generates a bright field image, and is commonly used with transillumination techniques such as

phase contrast Phase-contrast imaging is a method of imaging that has a range of different applications. It exploits differences in the refractive index of different materials to differentiate between structures under analysis. In conventional light microscopy, ph ...

and

differential interference contrast Differential interference contrast (DIC) microscopy, also known as Nomarski interference contrast (NIC) or Nomarski microscopy, is an optical microscopy technique used to enhance the contrast in unstained, transparent samples. DIC works on the p ...

microscopy.

Medicine

In medicine transillumination generally refers to the transmission of light through tissues of the body. A common example is the transmission of light through fingers, producing a red glow due to red blood cells absorbing other wavelengths of light. Organs analysed include the sinuses, the breasts and the testes. It is widely used by pediatricians to shine light in bodies of infants and observe the amount of scattered light. Since their skeleton is not fully calcified, light can easily penetrate tissues. Common examples of diagnostic applications are:

Hydrocele

Failed obliteration of the processus vaginalis allows serous fluid to collect around the testes via a communicating connection between the tunica vaginalis and the peritoneum. The resulting hydrocele presents as painless enlargement of the scrotum, similar to what may be encountered with testicular neoplasms. A convenient method to differentiate the conditions is to transilluminate the scrotum, as the hydrocele will appear a soft red while a solid tumor will not transmit light. Any uncertainty should be followed up with an ultrasound.Junnila et al. "Testicular Masses." Am Fam Physician. 1998 Feb 15;57(4): 685-692. www.aafp.org/afp/1998/0215/p685.html

Hydranencephaly (water head)

Hydranencephaly is a condition in which the brain's cerebral hemispheres are absent to a great degree and the remaining cranial cavity is filled with cerebrospinal fluid. Transillumination can be used to diagnose hydranencephaly. The device used in this operation is a Chun gun that uses a 150 watt projection bulb as a light source.

Pneumothorax (collapsed lungs)

Bright light penetrates the thin front chest wall and reflects off the back chest wall to indicate the degree of pneumothorax. To treat it, a physician inserts a needle attached to a syringe into the area of collapse to remove the air between lungs and chest wall, causing the lung to reinflate.

Meningocele and Meningomyelocele

There is brilliant transillumination in case of meningocele due to presence of CSF inside the cyst. Meningomyelocele, on the other hand, is partially transilluminant as it contains nerve root fibres along with the CSF.

Dentistry

Bright transilluminated light can highlight

dental caries Tooth decay, also known as cavities or caries, is the breakdown of teeth due to acids produced by bacteria. The cavities may be a number of different colors from yellow to black. Symptoms may include pain and difficulty with eating. Complicat ...

and sign of dental trauma such as enamel infractions.

Other

Light bright enough to penetrate the shell can be used to verify egg yolks are intact, as the yolk is opaque while the albumin is transparent.

References

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