Medical imaging has seen many significant technological advances since the X-ray was discovered in 1885. Not only has the X-ray been modified and applied to cross-sectional imaging, but we’ve developed technology that uses alternative forms of energy, such as ultrasound, nuclear imaging, and magnetic resonance imaging.
These imaging modalities are widely used for a variety of applications, but several new techniques have been developed that use, for example, bioluminescence, photoacoustics, and near-infrared. Currently, these devices are limited in scope, but their ever-expanding use shows much promise for what the future may hold.
Bioluminescence utilizes visible light produced by molecules. This method has been used in the laboratory setting for molecular imaging to gain insight into biological processes, and one of its primary advantages is that it allows imaging without the use of X-rays. It works well when studying small transparent cells, but has limitations when imaging deep structures in the human body. Researchers have successfully attached bioluminescent molecules to gold nanoparticles that are designed to bind to calcium rich surfaces, which can create high-resolution images of micro-bone fractures[1]. However, presently this technique requires concurrent imaging with CT or MRI to view the binding agents.
Photoacoustic imaging is another method of imaging that relies upon the photoacoustic effect: light from a laser impulse heats tissue, causing the tissue to expand and release acoustic waves that can be detected by ultrasound[2]. The advantage of this method is the combination of the high contrast resolution of optical imaging and the high spatial resolution of ultrasound. One of the medical applications of this method is imaging melanoma to aid in differentiating tumors from normal surrounding tissue[3]. This technique is suitable for imaging the skin since photoacoustic imaging relies upon light penetration—which also happens to be one of its limitations. Photoacoustics can also be applied with flow cytometry to aid in detecting malignant melanoma cells in the blood circulation with greater sensitivity than currently available assays.
Near-infrared vein imaging is another technique that uses unconventional methodology for imaging, but unlike other technologies, it is market ready[4]. This method uses near-infrared light to create a projected map of veins on the skin. It was developed to aid in phlebotomy and has also been applied to treating varicose veins and venous telangiectasias[5]. As with ultrasound, this device can create a real-time map of anatomy for live diagnosis and treatment.
While bioluminescence, photoacoustics, and near-infrared imaging share the common limitation of depth of penetration, they can still be used in the clinical setting, for example intraoperative applications are being explored to mitigate this restriction. In breast cancer resection, for example, photoacoustic imaging has been used to assess adequate surgical margins[6].
While we spend most of our time as radiologists in the world of traditional imaging techniques, it is always interesting to peer around the corner and catch a glimpse of the world to come. We marvel at the new, less invasive, more effective tools of the future, but more importantly, as is always the goal, these tools will allow us to take better care of our patients.
[1] Surender, Esther M., et al. “Two-Photon Luminescent Bone Imaging Using Europium Nanoagents.” Chem 1.3 (2016): 438-455.
[2] https://www.recendt.at/528_ENG_HTML.php
[3] Mehrmohammadi, Mohammad, et al. “Photoacoustic imaging for cancer detection and staging.” Current molecular imaging 2.1 (2013): 89-105.
[4] One such device is VeinViewer by Christie Medical
[5] Miyake, Roberto Kasuo, et al. “Vein imaging: a new method of near-infrared imaging, where a processed image is projected onto the skin for the enhancement of vein treatment.” Dermatologic surgery 32.8 (2006): 1031-1038.
[6] Xi, Lei, et al. “Evaluation of breast tumor margins in vivo with intraoperative photoacoustic imaging.” Optics express 20.8 (2012): 8726-8731.
