Vision has long been a key tool for doctors to help diagnose and treat patients. Ultrasound imaging, MRI scanning and x-ray photography are part of nearly everyone’s experience of hospitals and medical treatment. Now, advances in imaging technology are allowing doctors to get a clearer view of how the human body works, and to provide greater precision in operations.
A recent innovation has been the development of MEMS (micro electromechanical systems) devices to help focus medical images, providing greater resolution and detail. A MEMS device from Boston Micromachines is even allowing doctors to see beneath the skin of patients, without a cut being made.
This is possible because even though tissue is opaque, it can still transmit light for a very short distance. The imaging technique, called multi-photon microscopy, focuses light at a point under the surface of the sample. When the beam reaches a certain intensity, the tissue starts to emit photons at a different frequency, which provide the basis of the image. However, because the light has to travel back through the tissue, its path is distorted, leaving a blurry image. MEMS mirrors are now correcting these distortions using hundreds of tiny mirrors, to provide clearer images, making it a more effective tool. It means that doctors can see further beneath the surface of the tissue, because the device is capable of correcting the aberrations caused by a greater amount of tissue the light has passed through.
The correction happens in two stages. Firstly, a wavefront sensor detects the amount of distortion occurring, and where it’s happening. This then tilts hundreds of panels that make up the mirror surface to tweak the image back into focus. It may sound like an involved process, but it actually happens in real time. ‘All the end user sees is a cleaner, crisper image,’ says Paul Bierden, president of Boston Micromachines. It would be possible to make similar alterations using image processing software, but this would take longer, and would not give such a realistic picture. The technique should provide a greater understanding of the processes occurring within cells, as they happen, which would be particularly useful when investigating neural signalling processes and neural disorders. ‘The breadth of research going into this is pretty wide,’ says Bierden.
In-vivo images of olfactory bulb wihtin mouse neural tissue using DM in multi-photon microscopy, made by Dr Jerome Mertz, Boston University
It’s currently being used by Dr Jerome Mertz at Boston University’s Biomedical Biomicroscopy Lab, who believes it may also prove useful in skin cancer research. ‘Being able to see deeper into tissue will help the development of realtime histology techniques,’ he says. ‘And because you can monitor tissue health in situ, this technique will hopefully help in the screening and diagnosis of skin cancer.’ When doctors need to see deeper into the body, they use endoscopes, which provide the necessary information for procedures such as keyhole surgery. In the past, endoscopes were expensive and had to be reused on many patients. This required a lengthy sterilisation procedure each time it was used, which was expensive and damaged the delicate instruments.
Vision specialist Cypress has now developed, with Micro-Imaging Solutions, an endoscope that is cheap enough to throw away after each use. The new endoscopes use CMOS sensors rather than CCD chips. CMOS sensors allow control mechanisms for features such as exposure and gain stage, which affect the quality of the image, to be placed onboard the chip rather than on a separate circuit board, simplifying the design of the device and reducing the size and cost.
‘It allows us to put more dedicated circuitry next to the imager,’ says Bram Wolfs, a member of the design team. This also means that doctors can get a better view, more quickly, which is obviously important in the operating theatre where time is everything.
Because the interface between the imaging sensor and the control has been simplified, the number of pixels required for a particular model of endoscope can be altered with little effect to the whole design. This means that a large family of models with different resolutions can be produced fairly easily, each tailored to a different type of surgical task.
Another property of CMOS sensors is now allowing them to play a greater role in cancer radiotherapy, where a beam of radiation is carefully directed on a tumour to kill it. To make sure this doesn’t hit healthy tissue, a device is placed between the radioactive source and the patient that blocks radiation to every other part of the body. This shape-shifting device involves about 100 different fingers that move to outline the shape of the tumour, allowing radiation to pass through the centre while blocking the rest of the body.
The vision system needs to ensure that the fingers have indeed formed the correct shape. CCD cameras are too sensitive to radiation, so CID (charge injection device) cameras were used in the past. These tube cameras are very low resolution, so now 5T (five transistor) CMOS cameras are being used, which have a higher resolution and are immune to radiation. ‘A CCD camera wouldn’t last five minutes,’ says Mark Williamson, director of Firstsight Vision. ‘Now, we can start addressing the highresolution demands of old CID cameras.’ Williamson says that another big application for vision systems in medicine is ophthalmology, both in the diagnosis of diseases like glaucoma, and in laser surgery, where the cameras can carefully control the laser beam, and provide feedback if the eye moves. He says the main demands on these systems are high resolution and high frame rate, to control the laser in real time.
Reliable and precise systems are needed in the manufacture of medical drugs and devices, as well as the hospital ward, to prevent dangerous faults occurring. Firstsight Vision’s systems have also been used by manufacturers of medical sensors for blood sugar level and cardiac output, to automate quality control.
These sensors are consumables, so the manufacturing volumes are high. If a fault developed in the production line it could be fatal for users. They are generally made by overlaying different patterns of materials on top of one another, but if these layers are not correctly aligned it could result in a false reading that could fail to alert a user if he was in danger. ‘Because of the volume and miniature sizes, automated inspection is important,’ says Williamson.
The systems must adhere to the stringent 21 CRF Party 11 regulations imposed by the FDA, which stipulate strict conditions on the running of production lines in the healthcare sector to ensure that quality control is kept and that every change made to the manufacturing procedure is traceable. ‘The vision system must have certain features that enable an auditable trail of use,’ he says.
The sterile conditions of the hospital ward and pharmaceutical laboratory are a far cry from the rugged conditions of the factory floor, and the vastly different requirements have opened up some innovative applications of machine vision equipment. These applications are just a tiny proportion of the huge amount of research being performed to ensure that doctors have every possible piece of information to make the correct diagnosis.
