LEDs and Medicine: Diffuse Optical Tomography Uses LEDs to Scan Brain

A look at current DOT testing

A look at current DOT testing

According to a report in BioOptics World, scientists at the Washington School of Medicine in St. Louis, Missouri have developed a new way to study the brain, diffuse optical tomography (DOT), a new non-invasive technique that relies on LEDs rather than magnets or radiation. While still experimental, it offers promise for a new non-invasive test for the human brain.

While it looks primitive now, DOT scans use LED light to measure brain activity. For a DOT scan, a subject wears a cap composed of many light sources and sensors connected to cables. A DOT cap covers two-thirds of the head and involves shining LED lights directly into the head. DOT images show brain processes taking place in multiple regions and brain networks, like those involved in language processing and self-reflection (daydreaming). It also avoids radiation exposure and bulky magnets required by positron emission tomography (PET) and magnetic resonance imaging (MRI) respectively.

DOT works best for patients with electronic implants that can be problematic with MRI testing such as pacemakers, cochlear implants, and deep brain stimulators (used to treat Parkinson’s disease). The magnetic fields in MRI may disrupt either the function or safety of implanted electrical devices while DOT doesn’t impact these types of devices.

How does DOT work? According to author Joseph Culver, Ph.D., associate professor of radiology, DOT can detect the movement of highly oxygenated blood flows to the parts of the brain that are working harder when the neuronal activity of a region in the brain increases. He told BioOptics World that, “It’s roughly akin to spotting the rush of blood to someone’s cheeks when they blush.”  According to the magazine, DOT works by detecting light transmitted through the head and capturing the dynamic changes in the colors of the brain tissue.

DOT has a lot of potential benefits for medicine concerning the brain.  Since DOT technology does not use radiation, doctors could monitor progress of patients using multiple scans performed over time without worry. It could be useful for patients recovering from brain injuries, patients with developmental disorders such as autism, and patients with neurodegenerative disorders such as Parkinson’s.

Currently, a full-scale DOT unit takes up an area slightly larger than a phone booth, but Culver and his team have built versions of the scanner mounted on wheeled carts. The DOT device is designed to be portable, so it could be used at a patient’s bedside in the hospital or at home, in a doctor’s office, or even in the operating room in the future.

For more details about DOT, visit:

BioOptics World, DIFFUSE OPTICAL TOMOGRAPHY ABLE TO SCAN THE BRAIN WITHOUT RADIATION, MAGNETS, http://www.bioopticsworld.com/articles/2014/05/diffuse-optical-tomography-able-to-scan-the-brain-without-radiation-magnets.html

Nature, Mapping distributed brain function and networks with diffuse optical tomography, http://www.nature.com/nphoton/journal/v8/n6/full/nphoton.2014.107.html (registration required)



General Lighting Brightens Up with LEDs

Clearlysapphire.com continues to follow the growth of LED lighting as well as sapphire and alternative substrates. This week, we’ll focus on a new report from Yole Developpement, a research firm that covers LEDs and the semiconductor industry.  Yole recently reported that the packaged LED market will grow from $13.9 billion in 2013 to $16 billion by 2018, driven mainly by general lighting and completed by display applications.  The report, Status of the LED Industry, details how LED-based general lighting has surpassed all other applications, representing nearly 39 percent of total revenue of packaged LEDs In 2012.

2013 packaged LED revenue by application.  The total market size is nearly $13B. (Source: Status of the LED Industry report, Yole Developpement, September 2013)

2013 packaged LED revenue by application. The total market size is nearly $13B. (Source: Status of the LED Industry report, Yole Developpement, September 2013)

Costs need to continue to drop to keep LED-based lighting’s momentum in the general lighting market according to the report’s author, Pars Mukish, market and technology analyst, LED for Yole Developpement.  He commented, “Cost represents the main barrier LEDs must overcome to fully compete with incumbent technologies.  Since 2010, the price of packaged LEDs have sharply decreased, which has had the consequence of decreasing the price of LED-based lighting products.”

Mukish notes that in order to maintain growth, the industry needs to continue reducing pricing.  He pointed out that while LED still has some potential for cost reduction, widespread adoption will require manufacturers to reduce costs on all components of the system such as drivers, heat sink, and PCB.

Yole also updates their reporting on the use of alternative substrates in the LED market.  This situation hasn’t changed since we last covered alternatives in these posts:  Clearlysapphire.com, Alternative Substrates – Dimming the Hype, http://blog.clearlysapphire.com/?p=496 and Clearlysapphire.com, Alternative Substrates for LEDs, http://blog.clearlysapphire.com/?p=293.

According to Yole, companies working on alternatives such as silicon and GaN still face major obstacles.  Mukish says the benefit of GaN-on-silicon LEDs depends on decreasing manufacturing cost by using cheaper 8 inch silicon substrates that can leverage fully depreciated and highly automated CMOS fabs. However, he maintains that GaN-on-silicon LEDs still suffer from low manufacturing yields and full compatibility with CMOS fab still needs to be achieved.  He added that GaN-on-GaN LEDs benefit from a lower defect density in the epitaxial layers, allowing the device to be driven at higher current levels and to use a lower number of LED devices per system.   However, he said that GaN-on-GaN LEDs suffer from low GaN substrate availability and high costs.

For Further Reading

iMicronews, Sample, State of LED Industry, SLI report,  http://www.i-micronews.com/upload/Rapports/SLI%20Sample.pdf

Compound Semiconductor, Yole: Inexpensive LED Solutions Pushing Adoption In General Lighting, http://www.compoundsemiconductor.net/csc/detail-news/id/19736834/name/Yole:-Inexpensive-LED-solutions-pushing-adoption-in-general-lighting.html

Novus Light Today, Yole Releases Status of LED Industry Report, http://www.novuslight.com/yole-releases-status-of-led-industry-report_N1675.html


Sapphire – Quality Matters, Part 2: Transmission Quality

Recently, Novus Light Today published an article by Dr. Jonathan Levine, Director of Technical Business Development at Rubicon Technology, about sapphire quality.  His article shares a thorough review of the measures of sapphire quality for optical-grade applications.  Last week, we looked at the first two metrics, chemical analysis and X-ray rocking curves.  This week, we’ll look at transmission quality.

Levine writes that the quality of a sapphire is determined by how closely the grown crystal matches the ideal structure with respect to the arrangement of atoms within the lattice, dislocations, defects, and stress.  Root causes for these problems often originate from insufficient purity of the starting material and the growth process itself.

Sapphire exhibits excellent transmission in the ultraviolet (UV) to the mid-infrared (IR) range (~200 – 5000 nm).   According to Levine, conditions within the sapphire growth furnace can induce subtle interactions between the molten sapphire and the growth environment.  These interactions can produce bubbles, dislocations and other stresses that could impact optical performance.   Levine says that carefully controlling the growth environment produces sapphire that maintains excellent transmission at 200 nm through the mid-IR wavelengths.  He illustrates the impact of furnace interactions by comparing Rubicon’s ES-2 sapphire with another commercial sapphire maker’s crystal produced using a different growth method in the figure below.  From the image in the post, you can see a sharp absorption peak at 200 nm for sapphire produced by the commercial maker that is absent in sapphire grown by Rubicon.

Optical transmission of sapphire depicting a sharp absorption peak at 200 nm for sapphire produced by a commercial producer that is absent in sapphire grown by Rubicon.  Inset: Optical transmission for Rubicon sapphire from the visible to mid-IR range approaching 90% due to the high quality of the material.

Optical transmission of sapphire depicting a sharp absorption peak at 200 nm for sapphire produced by a commercial producer that is absent in sapphire grown by Rubicon. Inset: Optical transmission for Rubicon sapphire from the visible to mid-IR range approaching 90% due to the high quality of the material.

For Further Reading

Novus Light Today, Optical-Grade Sapphire, Where Quality Matters, http://www.novuslight.com/optical-grade-sapphire-where-quality-matters_N1596.html#sthash.giGipxT1.dpuf

New Applications for Sapphire: Medical (Part 2 of 3)

rod of asclepiusNew industries are finding man-made sapphire a desirable material. The field of medicine is looking at sapphire for its optical transmission range, durability and chemical inertness for bio-compatibility.

Sapphire’s optical properties and durability offer advantages for specific medical laser applications in dermatology, ophthalmology and dentistry. Sapphire is widely used in surgical systems for its laser transmission, high resistance to heat and non-thrombogenic properties (meaning it doesn’t promote clotting).  It is used as a laser window for endoscope lenses, laser hair removal systems and blood cell counters.  In addition, sapphire products are used for surgical tools, implants, braces.  Sapphire microscalpels are transparent blades that make it easier to visualize and illuminate capillary vessels, nerves, cutting zones and cutting depth compared with traditional metal alternatives.

One area that has potential for sapphire is in artificial joint replacements.  Many joint replacements include metal, ceramic, metal-polymer and ceramic polymer endoprosthesis. This is an area that may develop friction and wear over time causing the joint to fail.  Endoprostheses made of metal and ceramics may interact with the body and also degrade from friction over time.  For example, metal-on-metal artificial hips have a lifetime of 15 to 30 years, but have been known to fail earlier.  Sapphire is attractive for endoprostheses for its bio-compatibility since it is chemically inert and won’t react with the body as well as its low friction coefficient, hardness and durability

For Further Reading

The New York Times, The High Cost of Failing Artificial Hips, http://www.nytimes.com/2011/12/28/business/the-high-cost-of-failing-artificial-hips.html?pagewanted=all

IMS Research/Rubicon Technology, White Paper: Opportunities for Sapphire, Jamie Fox, http://rubicontechnology.com/resources/papers,

Sapphire: Material, Manufacturing, Applications, by E. R. Dobrovinskaya, Leonid A. Lytvynov, V. V. Pishchik. Springer Sciences Business Media, ISBN: 978-1441946737.