New Ultrasound Imaging Method to Become Available Soon

Undoubtedly, ultrasound technology is one of the most important innovations in the medicine of the last century. It allows doctors to peer inside a pregnant woman's womb, and assess the health of her unborn child. At times, they can even discover a number of congenital defects early on in the pregnancy, and then some experts might be able to fix them even before birth. More than three decades ago, the bases for this new analysis technique were set, and, since then, future parents from around the world were awed by the doctor's practice, after seeing their baby for the first time.

Most of these people are usually amazed when they learn that the rather intricate images they see in front of their eyes are actually entirely generated by sound-waves, and that the faint reflection of these noises is trapped by senors in the medical instrument, and then processed by a computer to yield the image. A number of researchers from the Stanford acoustics group have tried to constantly improve the performance of ultrasound devices for about a decade, and especially that of transducers.

The latter device is the most important part of the ultrasound machine, and has inside it sensors that generate high-frequency sounds, between the 1- and 50-megahertz range. When these sounds hit tissue with lower or higher densities, they reflect back at different intensities themselves, and are again captured by the sensors that created them. At this point, they are converted back to electrical impulses, which are then analyzed by a processor, and turned into optical representations of the womb and the baby.

Microelectromechanical systems (MEMS) have enabled the Stanford researchers to construct a capacitive micro-machined ultrasonic transducer, the first innovation as far as ultrasound transducers go in a very, very long time. Known more commonly as CMUT, or silicon ultrasound, the new device is very different from standard transducers, which often use piezoelectric materials as a base.

“Further work also showed why these capacitive0-transducers have greater bandwidth than piezoelectrics. The difference arises because a piezoelectric transducer is by nature a highly tuned device, like the pendulum of a clock. At its particular resonant frequency, a piezoelectric transducer undergoes high-amplitude oscillations, even with very little forcing, but at other frequencies, it barely moves at all – which is to say that it has very limited bandwidth,” the experts say.

“The transducer is able to emit and detect the many different frequencies that are contained in a short ultrasonic pulse. The shorter the pulse you use to probe the patient’s body, of course, the better the depth solution in the resulting image. And improved resolution is, after all, just what the doctor ordered,” they add.