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HEALTH

Diagnostic in the form of light

The use of a laser helps to tell healthy tissue from the ones altered by cancer

When it is necessary to differentiate exactly if a tissue is healthy or has cancer, doctors generally turn to a biopsy. They remove a piece of the suspect material and send it off for a laboratory exam, which will say with a determined degree of confidence, if the sample contains tumor cells or not and what type of cells they are. Shortly, it will be possible for health professionals to count upon another ally to produce their verdict, the so-called fluorescence spectroscopy, a new technique for use with a laser beam in the diagnosis of illnesses, especially tumors.

Experiments carried out by researchers from the Physics Institute of São Carlos of the University of Sao Paulo (IFSC/USP) indicate that the methodology manages to distinguish in a rapid, non-invasive and confidential manner, a normal tissue from another with cancer – at least if the patient was a hamster and the affected organ was a tongue. “In rodents, our degree of correctly asserting the diagnosis of tumors in this organ is 96%, a very good result”, says the physicist Vanderlei Salvador Bagnato, the coordinator of the studies with the new technique who researches at the Optics and Photoptics Research Center (Cepof) of IFSC/USP, which, alongside the Cepof of the State University of Campinas (Unicamp), forms one of the ten Research, Innovation and Diffusion Centers (Cepids) financed by FAPESP.

The tests with the fluorescence equipment, via a fine cannula or lantern that emits a laser beam upon the area to be analyzed and absorbs the light devolved by the biological tissue, were carried out on 72 rodents. Some animals were healthy, others had cancer in various degrees of development and there were those in a terminal phase. The animals were examined every two weeks using the equipment and were followed up for five months. For now, the diagnosis provided by this coverage has managed only to separate the rodents into two major groups: those that have cancer and those that do not.

The method, which still needs to be perfected, is not capable of distinguishing if a tumor is found in the initial, intermediary or advanced phase, nor can it provide information as to the degree of aggression. “Each type of cell lesion has common and different characteristics to other lesion forms”, says the dentist Cristina Kurachi, who carried out the work with the rodents and concluded her doctorate degree in optics at Sao Carlos. “At this moment, we want to understand what there is in common in the optical responses provided by whatever type of tongue tumor.” There are other studies, in their preliminary phase, concerning the use of the laser to identify skin tumors, also in hamsters.

Bagnato’s team has had good experience in the use of fluorescence spectroscopy for diagnostic ends. Some three years ago, the researchers from IFSC invented a device based on this technology capable of pointing out precisely and instantaneously if an orange tree had been compromised with citric canker, the illness caused by the pathogen Xanthomonas axonopodis pv. Citri, which brings tens of millions of R$ losses to the São Paulo citrus industry. The reasoning that led to the use of laser beams, whether it be in vegetal or animal samples, is the same. The tissue molecules in question absorb a part of the light dispersed by the cannula and remit back an altered fraction of the original laser light showered upon them. This luminous response, which is captured and reprocessed by the equipment’s spectroscope, contains information concerning the composition of the examined tissue. In other words, when in contact with the laser, normal tissue and each type of tumor exhibit a specific optical signature. “We’re comparing the spectrums of healthy and altered tissues in order for us to create optical standards that rapidly differentiate normal cells from cancerous cells”, says Cristina.

The scientists themselves are the first to admit that the eventual adoption of diagnostic methods via fluorescence does not have as its objective the substitution of the traditional form of identifying tumors or other illnesses. The technique that makes use of the laser will be yet another tool at the disposition of the health professional. “In the conventional biopsy, subjectivity is present in many stages of the work”, commented professor Bagnato. “We want to create a form of diagnosis capable of giving more objective and rapid responses, which will allow the pathologists to locate even pre-malignant lesions, in their very early phase.”‘

In an experimental character, the gastroenterologist Orlando de Castro e Silva Junior, from USP’s Medical School at Ribeirao Preto, has used, with good results, the equipment developed at São Carlos in order to demarcate, with precision, the extension of liver tumors in ten patients who had suffered surgery for the removal of the cancer. In these cases, no matter how experienced the professionals responsible for the operation are, almost always a point of doubt remains: has all of the tumor been removed during surgery or has a nodule remained in a neighboring area? The advantage of the fluorescence spectroscope is to provide a response in real time to this question during the very surgery itself. “But we still have to test the equipment in a further 40 or 50 cases so that we can be certain that it’s truly efficient in the diagnosis of hepatic tumors”, ponders Silva Junior, who is also experimenting, with his colleagues from São Carlos, the fluorescence technique in work on the selection of donated livers for transplants.

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