Innovations in Image Sensors

Frost & Sullivan estimated the global image sensors market to be worth $13 billion in 2017, and predicts that the value will exceed $16 billion by 2020. Read more about the latest advances.

This author was recently asked a question: “Which company sells the most cameras in the world?” The usual suspects—Canon, Nikon, Fujifilm and Sony—were all summarily shot down. More obscure brands were suggested, all of which received the same disdainful rejection. When the white flag was waved, the questioner smugly gave the answer: Samsung, followed by Apple and then Nokia. Before the author could scoff, he got the following explanation: every phone that is manufactured today comes with a camera; by that logic, the company that sells the most phones is the largest camera company in the world. Building on that cheeky logic, the largest segment of sensors should be image sensors—an integral part of cameras. Hundreds of millions of people walk around with image sensors in their pockets. 

Frost & Sullivan estimated the global image sensors market to be worth $13 billion in 2017, and predicts that the value will exceed $16 billion by 2020. Image sensors convert visible light or a visual image into an electronic or digital signal. There are two main types of image sensors: charge-coupled device (CCD) and complementary metal oxide semiconductor (CMOS) sensors.

In a CCD sensor, incident light is captured with the help of photoactive regions. This induces a change in the electrical charge, which is sequentially transmitted to the readout register. The amplified signal is finally sent to a signal converter and is read as a digital output. The design of a CCD sensor is such that the signal is read one row after another. This necessitates a specialized manufacturing process, and increases the sensor’s image processing time and energy consumption. A CMOS sensor, on the other hand, consumes 100 times less power than a CCD sensor. It is composed of picture elements of pixels, each of which has a photodetector and a signal amplifier.

CMOS image sensors are cheaper to make, easy to integrate into devices, and above all are smaller and require less energy. Because of all this, they are fast replacing CCD sensors as the preferred choice in imaging systems. Frost & Sullivan has identified innovations in the sensing platforms and their use in biomedical applications.

Ultra-High-Definition Endoscopy

A clinical research team from Nohon University in Tokyo has designed what’s being dubbed the highest-resolution clinical imaging system by reengineering commercially available imaging systems with clinical tools. The team assembled a camera head that had a single 2.5-inch CMOS sensor (7680 × 4320 pixels) with lenses and a rigid endoscopy probe to create an endoscopy unit that produces images with resolution nearly 4 times higher than what is possible through conventional endoscopy systems. This unit has been used in pilot clinical studies to great results.

High-Resolution Microendoscopy

A team of bioengineers led by Rebecca Richards-Kortum at Houston’s Rice University has fashioned a low-cost microendoscopy device that is capable of cellular and sub-cellular imaging. By incorporating a commercially available CCD-based camera in a flexible optical fiber probe, the device becomes equipped for cellular and tissue imaging to diagnose cancer. This low-cost, low-power unit allows the visualization of the mucosa at 1,000 times magnification and a 4.4-micrometer resolution. The field of view, of the extent to which the probe can image the target sample, is limited to 720 microns, which means that the systems is suited for point imaging rather than macro scanning. Regardless, the high resolution and the low cost have raised the device’s profile for cancer screening, especially in low-resource settings. Pilot studies using the device have firmly established its sensitivity and specificity in diagnosing non-neoplastic or neoplastic colorectal polyps.

On-Chip Imaging System

Since the incident light comes through a long scope in endoscopy procedures, the field of view is limited to the specific imaging site. In order to overcome the limited field of view that endoscopy modalities offer, researchers have designed on-chip imaging systems. In these systems, a cell culture or a tissue sample is placed directly on the CCD or CMOS image sensor. This way, the images are not restricted by any probe; rather, the entire active area of the sensor is available for imaging. Several research groups, including one led by Associate Professor Hatice Altug of the Department of Bioengineering at the Swiss Federal Institute of Technology in Lausanne, have developed prototypes of portable, lens-free systems that employ on-chip imaging.

The Road Ahead

Innovations in image sensors are centered on improving image quality by increasing the pixel density on the sensor, reducing noise, and optimizing the size of the sensor platform. Features such as depth sensing will add considerable value to image sensors as they are used in robotic surgery systems and in navigation and guidance systems for surgery.

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