3D Imaging – Egyptian Artifacts, Aardvarks, Airplanes and Gamers
The most common form of 3D imaging is ultrasound which involves the use of pulsed sound waves. In a pulsed wave system, the transmit signal consists of short bursts of ultrasonic energy in the 20KHz to 20GHz. Some newer technologies are researching the practical applications of frequencies in the tera-hertz range. The higher the frequency, the greater the resolution and density of material that can be imaged. After each transmit burst, the receiver or sensor samples for a return signal within a small window of time calculated to the time it takes for the sound energy to pass through the object. Only a signal received during this window will qualify for additional signal processing.
Depending on the type of equipment, the sensors may be looking for reflected waves, transmitted waves or a combination of both. The most accurate and complete images will be obtained from systems which have an array of sensors positioned around the examined object.
In addition to sound, these basic principles for imaging apply for waves across the entire electromagnetic spectrum. The wave is generating by mechanical, optical, low-energy radio, x-ray or even high-energy ionizing particles and radioactive isotopes. Microwaves have been used for both animals and humans, especially for detecting cancers.
3D images can also be obtained using magnetic resonance imaging (MRI) in which powerful magnets are used to align the magnetization of atomic nuclei and a radio frequency (RF) alters the alignment. By using different combination of magnetic and RF gradients, the rotational speed of the nuclei is measured and used to construct an image. MRI works best on tissue which is comprised mostly of water. The protons, e.g., the “H” in “H2O” provide the nuclei necessary for the magnetic field interactions.
Another process used primarily in medicine is “Computer Tomography (CT)” or “Computed Axial Tomography (CAT)” scan. X-rays are used to create an image of a very narrow slice of the object, and computer algorithms build the slices into a 3D image.
These procedures aren’t limited to humans. The Chicago Zoological Society’s (CZS) Brookfield Zoo is the first North American zoo with on-site digital radiology and CT equipment in its state-of-the-art animal hospital. The new technology allows the Society’s veterinarians to enhance two-dimensional CT (CAT) scans, MRIs, and ultrasounds with 3D models that will enable them to better treat zoo animals.
For example, using a 3-D scan of 17-year-old aardvark, it was revealed that a hole from a missing tooth was draining into a sinus cavity. The diagnosis would have been impossible without the new imaging technology, and left untreated would have been fatal to the aardvark.
While medicine has been the predominate use of this technology, it has also been applied to many other areas due to its non-destructive properties. Using a variety of signal types, it’s possible to see inside of objects as well as obtain data outside the visible spectrum. In archeology CT imaging showed the contents of Egyptian artifacts and sarcophagi, as well as to help identify their composition without requiring samples.
Anyone that has travelled recently has most likely undergone a “full body scan” at the TSA checkpoint. This equipment uses a millimeter wave scanner to see objects which are hidden under clothes, and even just under the skin. Screening and detection have become a focus technology where privacy is balanced against invasiveness. Rapiscan uses low energy backscatter x-ray.
The scanning technology has also moved into the manufacturing and technology fields, especially for automation and robotics. New applications are allowing machines to acquire a greater range of depth perception. Boeing is one of the most recent companies to take this on a large scan. Using a portable cart with a rotating scanner, they have created a very detailed image of their new 747 plant in Everett, WA. With this level of accuracy they have a detailed representation of where every wall, beam, fixture and piece of machinery is located. As the planes are built, they can create additional scans to monitor progress and check for defects. They can also use this image to communicate with the robots and other mobile machines on the assembly line.
Processing power, low cost lasers and sensors have made this technology readily available outside of the medical and manufacturing applications. It’s probably most well know through the X-Box “Kinect” wireless control and gaming interface. The design uses a low power infrared laser (similar to television remote controllers) and an inexpensive monochrome CMOS sensor. The unit is also robust enough to be able to capture the gamers movements in almost any ambient light condition. The software is what enables this application by automatically calibrating the hardware based on the room configuration and furniture, and with the how the gamer is reacting to what is on-screen.
From your living room, to the zoo, to the hospital and airports, to building airplanes and eventually to outer-space for enabling automated space-craft docking, 3D imaging technology continues to view and shape our lives.