The George R. Harrison Spectroscopy Laboratory in the School of Science at MIT has been awarded a Bioengineering Research Partnership grant to develop and implement spectroscopic techniques for imaging and diagnosing dysplasia -the precursor to cancer – in the uterine cervix and the oral cavity.
Cervical and oral cancer account for approximately 11,000 deaths in the United States each year. Detection of the precancerous state of human tissue is crucial for ease of treatment and greatly improved survival, but it is often invisible and difficult to diagnose. The new techniques are said to provide a method for visualisation and accurate diagnosis based on spectroscopic detection and imaging.
Clinical screening for cervical and oral precancer are multibillion-dollar industries which currently rely on visual detection of suspicious areas followed by invasive biopsy and microscopic examination. Given that visually identified suspicious areas do not always correspond to clinically significant lesions; spectroscopic imaging and diagnosis could prevent unnecessary invasive biopsies and potential delays in diagnosis.
Michael S. Feld, professor of physics and director of the Spectroscopy Lab, says the laboratory has developed a portable instrument that delivers weak pulses of laser light and ordinary white light from a thin optical fibre probe onto the patient’s tissue through an endoscope. This device analyses tissue over a region around 1 millimetre in diameter and has shown promising results in clinical studies. It accurately identified invisible precancerous changes in the colon, bladder and oesophagus, as well as the cervix and oral cavity.
The second device, which has not yet been tested on patients, can image precancerous features over areas of tissue up to a few centimetres in diameter.
Feld predicted that in a couple of years, these devices will lead to a new class of endoscopes and other diagnostic instruments that will allow physicians to obtain high-resolution images. These easy-to-read images will map out normal, precancerous and cancerous tissue the way a contour map highlights elevations in different colours.
The optical fibre probe instrument employs a method called trimodal spectroscopy, in which three diagnostic techniques – light-scattering spectroscopy (LSS), diffuse reflectance spectroscopy (DRS) and intrinsic fluorescence spectroscopy (IFS) – are combined.
IFS provides chemical information about the tissue, LSS provides information about the cell nuclei near the tissue surface and DRS provides structural information about the underlying tissue. The information provided by the three techniques is complementary and leads to a combined diagnosis, though the imaging technique is based on LSS alone.
The LSS optical technique has long been used to study the size and shape of small spheres such as water droplets. For cancer detection, the method is applied to the cell’s spheroid nucleus. Physics theory predicts that scattered light undergoes small but significant colour variations when bouncing back from spheres of a certain size and refractive index.
Light is delivered through the probe onto the patient’s tissue. The probe collects the light that bounces back and analyses its colours. The colour content is then used to extract diagnostic information.
‘By analysing the intensity variations in this back-scattered component from colour to colour, the nuclear size and density can be mapped,’ Feld said. Closely packed cells with larger-than-normal nuclei packed tightly with genetic material are markers of precancerous change.
‘The images created with this new technique are different from ordinary microscopic images in that they provide hard and fast information about cellular features,’ he said. ‘We believe this is an important step that will lead to new optical tools for both [making] early cancer diagnoses and developing a better understanding of how changes in the genetic material inside the cell’s nucleus make the tissue more vulnerable to cancer.’