PhotoAcoustic imaging is an imaging modality that uses laser light and ultrasound detectors to image tissues. Photo = Light. Acoustic = Sound. The imaging uses the photoacoustic effect principle. The photoacoustic effect is not new in terms of discovery as it was reported by none other than Alexander Graham Bell (yes! Rings a bell doesn’t it?) as early as 1880. But, the unavailability of proper detectors and instruments at his time was an obstacle to expanding research in this field.
Ultrasound is good for more than monitoring fetuses and identifying heart defects. According to engineers in Canada, it can help tell what people are thinking as well. Their research suggests that ultrasound-based devices could lead to a new kind of brain-computer interface.
Brain-computer interface technology allows users to control devices with brain activity alone. Researchers have focused primarily on clinical applications for people with severe disabilities who would otherwise have difficulty interacting with the outside world.
A commonly used, and relatively inexpensive, imaging technology depends on acoustic or ultrasonic waves sent into the body where they are both refracted and reflected (this is an example of medical remote sensing that does not draw upon EM radiation). The result is a sonogram or echogram which to the layman appears fuzzy and limited in definition but is informative to the physician and trained technicians. A transducer that both generates acoustic waves and receives their reflections (echos) can be placed directly near the specific organ being investigated. The acoustic signal that passes through the body is between 1 and 10 MHz (3.5 to 7.0 MHz most frequently used). A brief summary of Ultrasonic imaging is found at the HowStuffWorks site. Once there additional information can be sought by clicking on “Lots More Information” and then on “Basic Concepts of Ultrasound” that gets you to “Diagnostic Ultrasound” by Beverly Stern of Yale University (putting on a direct link on this page fails to work). Both the text and the references on the HowStuffWorks site touch upon Doppler sonography and 3-D sonography.