All-optical ultrasound – rejuvenating an imaging workhorse gas you up


Though ultrasound is one of the most common medical imaging tools, conventional devices tend to be bulky and cannot typically be used at the same time as some other imaging technologies. This is why a hybrid combination of optics and ultrasound, coupled to inexpensive fibre-based probes for intravascular imaging, promises to open up new possibilities for medical imaging.

In terms of imaging, optical techniques ensure satisfactory contrast levels, while ultrasound provides high resolution. Optical technologies can also be manipulated to generate low frequency ultrasound which yields greater penetration into tissue, or high frequency ultrasound to obtain higher resolution images, albeit at a shallower depth. In practical terms, such a combination also gives flexibility to physicians in how they use imaging technology to diagnose and treat medical problems. electricity grid uk For example, to provide intravascular imaging and detection of conditions like plaque, ultrasound can provide details of morphology while the optical imaging highlights its composition.

In technical terms, traditional ultrasound image formation covers a narrow frequency band (usually half the central frequency), while signal generation in optical ultrasound is broadband (covering sub-MHz to several hundred MHz frequencies). In addition, the tomographic principles used by optical ultrasound generally entail data collection over wide angles. electricity wikipedia simple english This improves image quality and resolution, while minimizing image artifacts.

Efforts to develop broadband all-optical ultrasound transducers date to over a decade. One prototype was developed and tested for high-resolution ultrasound imaging in 2007 at the University of Michigan, Ann Arbor. It consisted of a two-dimensional gold nanostructure on a glass substrate, followed by polydimethylsiloxane plus gold layers. The system achieved a signal-to-noise ratio of a pulse-echo signal of over 10dB in the far field of the transducer, where the centre frequency was 40MHz with −6dB bandwidth of 57MHz. In a paper published in the August 2008 issue of ‘IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control’, the developers of the system concluded that preliminary imaging results “strongly suggest that all-optical ultrasound transducers can be used to build high-frequency arrays for real-time high-resolution ultrasound imaging.”

Other areas of innovation include micro-ultrasound, which harnesses ultrasound at microscopic levels and provides 3- to 4-fold improvements in resolution compared to conventional ultrasound. electricity distribution map One of the first applications of micro-ultrasound is to allow better targeting of biopsies – for example, in the treatment of prostate cancer by urologists.

In the late 2000s, ultrasound-modulated optical tomography (UOT) showed considerable promise in imaging of biological soft tissues, with promising application in several areas, including cancer detection. UOT detects ultrasonically modulated light to localize and image subjects. The key limitation of UOT, however, is weak modulated signal strength.

Considerable attention has also been given to photoacoustic tomography, which converts absorbed light energy into an acoustic signal. 9gag tv The technique provides compositional information on body tissue in real time without requiring any contrast agents. It also allows much higher depth penetration than conventional optical techniques. Photoacoustic tomography has been used for mapping the deposition of lipids within arterial walls.

However, photoacoustic tomography systems have proved difficult to translate into clinical applications due to their high cost, as well as a relatively large footprint which requires a dedicated optical table to house the laser. On a technical level, moreover, a low pulse repetition rate (in the dozens of hertz) prevents photoacoustic tomography from being used in high frame rate imaging, which are required for clinical applications such as cardiac related problems, where the rate of blood flow is high, or in other similarly fast-moving settings.

There are nevertheless several efforts to cope with the challenges facing photoacoustic tomography. The first is enhancing signal-to-noise ratio and the depth of penetration of optical absorbers. static electricity bill nye Researchers at Purdue University in the US, who are at the forefront of investigations into the technique, believe that new optical manipulation techniques to maximize photon density might provide a way forward. They have recently announced development of a motorized photoacoustic holder, which allows manoeuvring the aim of the device and fine-tuning the depth to where light is focused. This, they believe, could significantly improve light penetration as well as the signal-to-noise ratio.

Other efforts seek to cope with fast-moving and dynamic settings. In Singapore’s Nanyang Technological University, for example, researchers have demonstrated up to 7,000 Hz photoacoustic imaging in B-mode, using a pulsed laser diode as an excitation source and a clinical ultrasound imaging system to capture and display the photoacoustic images.

Such a modality exhibits wide bandwidth and satisfactorily addresses one of the major shortcomings of previous efforts at clinical application – namely, prolonged acquisition times (ranging from minutes to hours). Unlike conventional ultrasound imagers which use electronic transducer arrays to transmit sound waves into tissue and receive the reflections for reconstruction as images by a computer, all-optical ultrasound imagers are also immune to electromagnetic interference. mp electricity bill payment As a result, an all-optical ultrasound system can be safely used alongside a magnetic resonance imaging (MRI) scanner, allowing physicians to obtain a more comprehensive picture of tissues around an area of interest, such as a tumour or blood vessel. Immunity from electromagnetic interference and MRI compatibility also means that all-optical ultrasound can be used during brain or fetal surgery, or for guiding epidural needles.

The absence of electronic components gives yet another advantage, too. Components of conventional ultrasound devices are difficult to miniaturize for internal use. gas jobs pittsburgh This is due to two factors: a drop in sensitivity after a reduction in the area of the active piezoelectric transducer, and the impact on size of the transducer due to the casing of the piezoelectric element and electrical insulation.

Unlike the above limitations for conventional ultrasound devices, the miniaturization of optical detectors (e.g. via interferometric resonators) does not impact on active detection area. In other words, there is no loss of sensitivity. Finally, optical components are not only easily miniaturized but also significantly less expensive to manufacture, compared to compacting electronic ultrasound systems.

The world’s first all-optical ultrasound system capable of video-rate, real-time imaging of biological tissue has been demonstrated by a research team from University College London (UCL) and Queen Mary University of London (QMUL). It was used to capture the dynamics of a pulsating ex-vivo carotid artery within the beating heart of a pig, and revealed key anatomical structures required to safely perform a transseptal crossing, namely left and right atrial walls, the right atrial appendage and the limbus fossae ovalis.

The researchers believe the new technology will allow ultrasound to be integrated into a wide range of minimally invasive devices in different clinical contexts, and provide ultrasound imaging of new and previously-inaccessible regions of the body. Above all, its real-time imaging capabilities allows differentiation between tissues at significant depths, helping to guide surgeons in some of the highest risk moments of procedures. This will reduce the chances of complications occurring in cases such as cardiac ablation.

The developers based their design on a nano-composite optical ultrasound generator coupled to a fibre-optic acoustic receiver with extremely high sensitivity. In turn, harnessing eccentric illumination provided an acoustic source with optimal directivity. This was then scanned with a fast galvo mirror which provided video-rate image acquisition (compared to a time-frame of several hours in previous experiments). It also increased image quality in both 2D and 3D, and made it possible to acquire the images in different modes.

The scanning mirrors in the new system are flexible. They allow for seamless toggling between 2D and 3D imaging as well as a dynamically adjustable trade-off between image resolution and penetration depth. Unlike conventional ultrasound systems, these are achieved without requiring a swap of imaging probe. In a minimally invasive interventional setting, in particular, such probe swapping extends procedure times and introduces risks to the patient.

The technology has been designed upfront by the researchers for use in a clinical setting, with sufficient sensitivity to image moving tissue inside the body at centimetre-scale depth and fit into existing workflow. bp gas prices akron ohio The researchers are currently working on developing a flexible imaging probe for free-hand operation, as well as miniaturized versions for endoscopic applications.