Small, High Sensitivity, High Frame Rate
Image Sensor for Medical Endoscopes
1/9.25" 0.7 MP IMX446
1/5.36" 2.11 MP IMX447

Small chip size package (CSP)

Flexible endoscopes need finer scopes in order to reduce the burden on patients. This means, by necessity, the installed image sensor must also be smaller, since an area in the scope end needs to be reserved for surgical procedure instruments.
We have developed a small CMOS image sensor that is ideal for an endoscopic system satisfying these requirements.

The IMX446 and IMX447 have a CSP cavity-less structure. This is different to the standard CSP structure which uses resin to bond the glass and chip on four edges, forming a cavity structure. As this resin is not designed with optical properties, it is positioned outside the pixel area to avoid interfering with the sensor’s optical properties. In order to ensure a sufficient bonding strength, the resin area must have a certain width.
Instead, these two Sony image sensors adopt a resin that addresses both the optical properties and bonding strength, enabling the resin layer to be formed over the entire chip area between the glass and chip, eliminating any cavity from the chip structure (cavity-less structure). This successfully reduces the sensor size as there is no need for the peripheral resin area required by a cavity.

High sensitivity

An endoscope needs a lighting device for capturing images inside the human body, a dark environment where external light does not reach. However, the endoscope light may not be powerful enough to illuminate deep inside. Even under this circumstance, it is paramount in medical practices that the image be clear both up close and as far back as possible in order to improve diagnostic accuracy. While a low-sensitivity camera would require more powerful lighting, the opportunity to increase luminosity is limited because of the heat generated at the scope end of the lighting equipment.
Given this challenge, the IMX446 and IMX447 adopt a  cell size of 1.62 µm, relatively larger than conventional endoscope image sensors. This realizes excellent camera sensitivity, giving vital support in physicians’ diagnostic operations by providing clear images even in low-luminosity situations.

Image equivalent to the cell size of 1.1 µm

Image captured using IMX447 (cell size of 1.62 µm)

Wide dynamic range and DOL HDR

Sony’s image sensors for endoscopes offer a wide dynamic range feature. Dynamic range is the luminosity range within which a sensor can render images without overexposure or underexposure.
Inside the human body, there are often depths and shiny surfaces, making it difficult to discern the target under certain lighting conditions. The IMX446 and IMX447 take advantage of the wide dynamic range to capture clear images of bright and dark areas at the same time, facilitating smooth, stress-free visibility.
In addition, the Digital-Overlap High Dynamic Range (DOL HDR) feature has expanded the sensors’ dynamic ranges. With this technology, two images are captured in quick succession with varying exposure: one short for the bright area and one long for the dark area. These images are then synthetized, making the dynamic range wider than usual.
These image sensors will contribute to improving diagnostic accuracy thanks to high-definition images that maintain superior image quality both in bright and dark areas.

High frame rate

Since the endoscope is usually very close to the target, imaging is highly susceptible to the slightest vibration coming from the equipment, internal organs, intestinal interior walls, and so on. The blur caused by this vibration may spoil the clarity of the details, and if the endoscope moves relatively too fast, it may skip over lesions.
Addressing these issues, the IMX446 and IMX447 have achieved a frame rate as high as 120 fps.

Blurring comparison between the videos at different frame rates

The videos above compare moving images of a stomach mockup captured at different frame rates.
In the left movie at 60 fps, the circled area is considerably blurred, which could hinder accurate diagnoses. By contrast, the right movie at 120 fps renders the image clearly with less blurring. Overall, the 120-fps movie is smoother than the blurry 60-fps one, with the target more sharply defined.

Comparing high-frame-rate photography in missing targets

The endoscope may miss an important target image depending on its insertion angles or moving directions and speeds.
The illustration below shows two streams of images capturing a stomach mockup with a model tumor, recorded at different frame rates of 120 and 60 fps and aligned synchronically.

This example shows that the 60-fps one almost failed to capture certain parts, which were caught at 120 fps. High-frame-rate imaging increases the number of images to be obtained within a unit time frame, boosting opportunities to identify tumors and other lesions. Using high-frame-rate image sensors ensures sufficient frames and, therefore, lowers the risk of overlooking important information.

Long-distance transmission (SLVS-EC) and reduced pins

Some endoscopy systems employ cables of 1 m or longer to examine the gastrointestinal system. In order to inspect narrow digestive tracts, the cables need to be fine and flexible.
The IMX446 and IMX447 adopt SLVS-EC as an interface. This reduces the number of signal lines, helping to minimize the cable diameter. Since SLVS-EC adopts the embedded clock method, it reduces the number of lanes, while also simplifying the transmission route design and extending the transmission range. These characteristics make SLVS-EC-enabled products ideal for medical applications. Moreover, the customized SPI communication feature, like the I2C, of the IMX446 and IMX447 allows removal of one power line while maintaining a two-pin arrangement. This facilitates system operation with as few as 5 pins^*1.

The eye pattern of signal (B) is open wide after transmission through the 5 m cable, indicating little signal deterioration.