May 20, 2008 A broncoscope guided by means of electromagnetic navigation has managed to achieve the biopsy of 75% of pulmonary nodules greater than 2 cm, according to Doctor Luis Seijo, specialist in Pneumology at the University Hospital of Navarra. This is the Spanish hospital with the most experience in the use of this novel device which enables access to pulmonary lesions without recourse to surgery or transthoracic puncture, conventional techniques that increase risk for the patient.
The basics of navigator-guided broncoscopy is in accessing the interior of the bronchial “tree” of the patient and to the affected nodule(s). It is guided by a system which shows the position of the instrument used to carry out the biopsy in real time. In the case of the lung, the system is equipped with an electromagnetic probe, which acts as the guide. On reaching the nodule in question, the probe is substituted by a biopsy pincers or cytological needle, instruments that enable a sample of the lesion to be obtained. The procedure also facilitates sampling adenopathies or mediastinic ganglia that are of interest for analysis. At the University Hospital of Navarra this procedure, which can be carried out on a day-patient basis, is undertaken with the patient under sedation.
To initiate the broncoscopy it is necessary to plan the operation with the data previously obtained from a conventional thorax CAT scan. This information is transferred to a computer software programme which recreates the patients bronchial tree in a virtual manner.
With this graphical information the pneumologist can plan the operation in detail. “The planning is a key stage in carrying out the procedure successfully. The specialist marks reference points on the computer images which will subsequently enable him or her to navigate in real time to the nodule”, according to Doctor Seijo.
The virtual references marked include the lesion which is the target of the biopsy. It is important to mark identifiable points which, during the operation, will enable a triangulation of the position of the probe within the bronchial tree. Prior to initiating the endoscopic procedure, the specialist refers to this computer planning data from a hard disc inserted into a computer in the operating theatre.
During the broncoscopy
The navigation team creates an electromagnetic field which encompasses the patient’s thorax and enables placing the probe in three-dimensional space within the bronchial tree of the patient. The technique makes it possible to know the position and orientation of the probe at all times, as well as the direction of the lesion to be diagnosed from the probe and the distance separating the two. “The concept is similar to that of a GPS”, said Doctor Seijo.
Once the broncoscope is introduced orally or nasally, the same reference points marked in the virtual planning have now to be marked in real time. With the electromagnetic probe, the same points marked in the virtual planning of the bronchial tree of the patient are fixed. The computer detects if there exist divergences between the virtual and real reference points or not. A divergence of less than 4 mm is ideal.
In this way the system makes ongoing calculations, fixing the position of the probe within the patient’s thorax and, thereby, within the virtual recreation generated from the prior scan. “This is how we manage to navigate to the lesion on which we wish to carry out a biopsy. Normally 5 or 6 reference points are marked although, given the complexity of the bronchial tree, with its multitude of bifurcations, intermediate reference points are marked that act as “radio beacons” during the navigation to the nodule in question”, stated the pneumologist.
The electromagnetic probe travels through the interior of the bronchial ramifications of the patient, inserted within an extendable working tube. Once the target is reached, this tube can be fixed and the probe substituted by the instrument required to take the tissue sample (the biopsy) of the lesion.
The risks involved with this diagnostic procedure are much less than those of transthoracic puncturing and, of course, than those of a thoracotomy (open surgery of the thorax). As an illustration of this reduced risk, the incidence of pneumothorax caused by the conventional transthoracic technique is 20% while, using navigation-guided broncoscopy, this figure drops to 6%.
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