Laser focus2 May 2018
David Callaghan explores how advances in laser diode technology are making devices more portable and patient-friendly, compensating for the shortcomings of photoacoustic imaging, and being cost-effective and less bulky. He speaks to Dr Andreas Kohl of Quantel Laser and Dr Manojit Pramanik, assistant professor at Nanyang Technological University, about groundbreaking industry projects and research that will push the technology to its limits.
One of the most significant breakthroughs in the scanning of patients for serious medical conditions came in the past few years with the development of photoacoustic imaging (PAI). It can deliver far more detailed pictures than was previously possible, and presents doctors with the opportunity to detect skin and thyroid cancer, cardiovascular disease and arthritis early.
With its pulsed laser light, PAI technology is a big improvement on optical imaging and conventional ultrasound. However, there are some drawbacks with PAI, such as the size and bulkiness of the apparatus, as well as the cost. On the other hand, new developments in laser diode technology are helping to overcome these issues. Devices that combine lasers with ultrasound receptors are on their way.
Dr Andreas Kohl, head of operations diode lasers at Quantel Laser, says the company has been working on developing this technology for ten years, and there are some major challenges to overcome.
“The key point is to have a pointof- care device [that] is affordable for a medical doctor – a general practitioner – and not just for hospitals, [which] needs to be compact,” he says.
It was necessary to develop short pulses of less than 100 nanoseconds, he explains. “In order to get the high power, we have to drive these diodes at [a] very high current. The diodes were capable of doing this, but the electronics were not, [so] we had to integrate the diodes with the driver board. This was the technical challenge.
“We have made a lot of improvements to these devices, making them smaller and smaller, and developing them in terms of peak power,” Kohl adds.
“There is a very steep rise in performance and the device is now hardly bigger than the standard ultrasound device. We also had to make the device really efficient or it will heat up. This is something we have solved, which will make the doctors happy.”
There are still several development stages for the new device to pass before it can become available for medical practitioners to use. It is currently at the pre-clinical stage and will be tested by volunteers in a university setting afterwards.
“It will take four to five years to have it completely validated and on the market,” he states. “The major manufacturers will then have a PAI device that is finally portable. It will be like an X-ray device you can put in the car.” The new device will have distinct advantages over the traditional ultrasound machine, Kohl emphasises. “The classic ultrasound sometimes lacks contrast, whereas the laser diode has a distinct wavelength, which can highlight haemoglobin, for example. You can change the setting with different wavelengths in the same device. We already have up to four settings,” he says.
In the future, Kohl predicts that the devices will become even smaller, yet increase pulse energy.
Leading European projects
Quantel Laser is part of two European initiatives that aim to produce a complete scanning package with a multiwavelength laser diode and ultrasound probe.
One of the projects, FULLPHASE, is being developed by Quantel with industrial partners and universities, which have set a goal of producing a scanner that will detect skin cancer or arthritis.
Quantel has said that existing forms of scan, such as MRI, X-ray, and CT, as well as nuclear imaging, including positron emission tomography and the gamma camera, cannot be described as non-complex, low cost, point-ofcare applications. In a press release that announced the company’s participation in the project, Quantel said, “Functional imaging, the extraction of any information regarding physical or chemical processes in tissue, and their alteration through disease, is a key element for accurate and timely diagnosis, and for monitoring therapeutic success.”
Cvent, the other initiative that targets the identification of plaque build-up in the carotid arteries, has received funding from the EU’s Horizon 2020 research programme.
The partners in the consortium want to produce a laser scanner that will identify the composition and structure, as well as the size, shape and mechanical properties, of the plaque. A build-up of plaque can lead to complications that may result in having a stroke, making early detection and treatment vital. Western lifestyles that are characterised by a lack of exercise and obesity contribute to this problem. “Improved diagnosis and risk assessment of plaques after initial detection will lead to a significant reduction in cardiovascular diseases risk, related disability and mortality. Subsequently, by stratifying patients into higher and lower-risk groups, this will lead to a reduction in overtreatment, better allocation of healthcare cost and contribute to the sustainability of the healthcare system in Europe,” said a statement from the consortium.
Once the new devices are fully developed, they will provide images before, during and after heart surgery.
Using laser diodes to detect brain tumours
Research is also being carried out on using pulsed laser diode technology to detect brain tumours.
Dr Manojit Pramanik, assistant professor at Nanyang Technological University in Singapore, has shown how laser diodes can be used to scan an animal’s brain. This could eventually provide a breakthrough in detecting brain tumours in humans.
On describing how the technology is being used with small animals, the professor says, “We are using a pulsed laser diode, based [on a] compact photoacoustic tomography (PAT) imaging system, for small-animal brain cortical vasculature imaging. We can image rat and mice brains with this technology.”
Pramanik explains what the researchers have discovered, stating, “We were able to come up with a very compact desktop PAT imaging system, [which is] cheaper by a factor of five compared with [what existed previously, that is] capable for fast imaging capabilities.
“We could image the cortical vasculature of animals in less than five seconds of imaging time. We could also monitor the wash-in and wash-out of dye or nano particles from the brain vasculature, once they were injected through a tail vein. We are also able to image tumours and monitor nanoparticles uptake in the tumour non-invasively,” he says, adding that the technology has developed to improve its effectiveness. “Traditional PAT imaging systems use bulky, expensive Nd:YAG pump lasers that require optical tables to house the laser, which is nonportable,” Pramanik explains.
“With the use of a pulsed laser diode, the imaging system becomes compact, very cheap and portable. We can build a desktop PAT imaging system that can be housed anywhere and be used for animal imaging. It can be used not only for brain imaging, but also for tumour imaging in other places. Moreover, the high repetition rate of these pulsed laser diodes help to improve imaging speed by more than ten times,” he points out.
Pramanik emphasises that there are important implications for patient care from the research findings. “Although the current imaging system is mainly limited to small animal imaging, in the future this will help the clinical translation of the technology.
“At the moment, researchers can use such portable imaging systems in the lab or a research place to do multiple cuttingedge [pieces of] research. For example, tumour growth monitoring, drug delivery efficacy monitoring and imaging angiogenesis. Hopefully, these basic research outcomes will also impact patient care in the long run,” he states.
New laser diodes are clearly offering a major step forward in medical imaging technology, with added benefits for patients who will be able to have serious conditions detected in next to no time. Health professionals will therefore be able to provide an improved level of care, with easy-to-use portable devices.
What are laser diode scanning devices?
Pulsed laser diode technology is making it possible to manufacture portable – and even handheld – PAI devices that can scan patients. Existing scanners use diodepump solid-state lasers that tend to be bulky, difficult to move around and need to be kept cooled. This breakthrough allows the devices to be shared between care centres, in addition to the patient’s home. These new devices are also cheaper than the bulkier predecessors, thus reducing the burden on healthcare budgets.
Major advances in the effectiveness of laser diodes have made them suitable for incorporation into PAI apparatus, which benefit from a more user-friendly laser source.
The devices can be used to detect various health problems, including arthritis and coronary conditions. However, preclinical tests need to be carried out before the devices can be approved and manufactured commercially, which could be years away.