Medical Photonics: Using Lasers to Peer into Our Bodies

Photo by Dave Sebele on Unsplash

A Brief Overview on Light

We can think of light as massless “particles, known as photons. These photons travel (propagate) at the speed of light, which is roughly 300,000,000 meters per second in air. Particles has been quoted because quantum mechanics states that light behaves as both particle and wave until openly observed, known as the particle-wave duality theorem of light.

A diagram of the electromagnetic spectrum of light, ranging from radio waves on the left, to X-rays on the right.
A diagram of the electromagnetic spectrum of light, ranging from radio waves on the left, to X-rays on the right.
A image describing the EM spectrum of light. Different states of energy dictate a different position and color on the spectrum, making some lights visible, and others invisible.
Infrared cameras detect infrared radiation precisely enough to showcase the vein patterns on a person’s hand.
Infrared cameras detect infrared radiation precisely enough to showcase the vein patterns on a person’s hand.
Infrared cameras detect infrared radiation precisely enough to showcase the vein patterns on this person’s hand. Blood is warm, and registers as relatively hotter than its surroundings, giving it a distinct color.

Medical Imaging

Current medical imaging devices are bulky, expensive, and most importantly, they use rays that fall in the ionizing sector of the EM spectrum (X-rays, Gamma rays). Ionizing radiation is known to cause harm to your DNA with prolonged use, increasing your risk of diseases such as cancer.

The Process

The most widely known method of constructing medical images with light is known as Diffuse Optical Tomography (DOT).

The tissue penetration of different wavelengths of light. We see a correlation between higher wavelength of light and higher
The tissue penetration of different wavelengths of light. We see a correlation between higher wavelength of light and higher
The tissue penetration of different wavelengths of light. We see a correlation between higher wavelength of light and higher tissue penetration. This is why CT scans use high wavelength radiation — for high penetration.
A nanoscale image constructed from photonic imaging techniques.
A nanoscale image constructed from photonic imaging techniques.
A nanoscale image constructed from photonic imaging techniques. In this image, we see a tumor leaching away oxygen from its surroundings (shown in blue). DOT will be very useful in the field of cancer monitoring and diagnosis.

Challenges

Even with breakthroughs in the field of DOT imaging, researcher face two main challenges, which are penetration and cost.

Penetration:

When light is used in the safe wavelength of the EM spectrum, photons can only penetrate tissue up to a certain extent until sensors cannot detect the transmitted light. To overcome these challenges, researchers are using reflectance-based sensors that are adjacent to the photon source for more accurate readings.

Cost:

To use DOT imaging, or other optical imaging techniques in hospitals would require us to drastically reduce the cost of these systems. DOT setups cost in the range of hundreds of thousands of dollars, and although this is much cheaper than many CT and MRI systems, DOT requires unimaginable amounts of laser calibration, which makes it less feasible as of now.

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