Enabling New Medical Interventions through Medical Nanorobotics
26 Jun, 2007 05:17 pm
Nearly 100,000 km of blood vessels inside the human body could provide the best routes for conducting new or improved medical interventions non-invasively. Modern interventional instruments such as catheters are constrained to larger blood vessels and as such, can only access a very small fraction of this blood circulatory network.
A first demonstration with experimental results recently published in the scientific Journal Applied Physics Letters, March 12, 2007, suggests that such new therapeutic interventions may not be that far way. In fact, the experiment conducted by the research team led by Prof. Sylvain Martel of École Polytechnique de Montréal (EPM) in Canada demonstrated for the first time the feasibility of automatically navigate an untethered object in the blood vessels of a living animal. During the experiment, a 1.5 mm ferromagnetic bead was navigated without human intervention at an average speed of 10 cm/s in the carotid artery of a 25 kg living swine placed in a 1.5 T magnetic resonance imaging (MRI) system. From a special custom interface on a computer display, waypoints were plotted on top of an image of the carotid artery obtained with the MRI system. Once the bead was injected in the artery, its presence and location were automatically detected by the MRI system previously updated with specially developed software modules, and corrective actions were immediately performed automatically by the same system to bring the bead to its first waypoint. Determining the position of the bead and performing corrective actions to bring the object along a pre-planned trajectory following successive waypoints were executed 24 times per second by specially control software programs developed by the research team.
To propel the bead in a given direction, a propulsion force is induced in the ferromagnetic bead by varying the surrounding magnetic field or in another term, by applying magnetic gradients. The same three orthogonal coils used for slice selection during MR imaging were also used to track the object being navigated and to create the 3D magnetic gradients necessary to propel the bead at a speed and direction necessary to correct its trajectory within the artery.
This demonstration could be considered as a major technological breakthrough in modern interventional medicine and medical robotics considering that the researchers managed to integrate and synchronize at a sufficient speed, all the components necessary to efficiently navigate an object within the blood vessels. But more importantly, the fact that the experiments were done in the same type of clinical MRI platforms used for human and that an animal model relatively close to the human anatomy was used for the experiments, suggest that the same technique could also be used in human. In fact, the same research team also successfully navigated the same bead in laboratory settings reproducing precisely complex human blood vessels pathways.
Now that a functional platform is in place, the next step which has already begun is the miniaturization of the devices being navigated. To reach a tumor through the smallest capillaries, the overall diameter of each of these micro-devices or micro-carriers is estimated to be in the vicinity of 2 micrometers or approximately 1/40 the thickness of a human hair. Because the overall size of these micro-carriers will be smaller that a red blood cell, agglomeration of larger number of these micro-carriers will be steered between red cells. MRI-based magnetic gradients will be used to influence their paths at blood vessel bifurcations until the tumor being targeted is reached. Various drug release mechanisms are also under investigations as well as other medical applications that may benefit from this technology.
Martel, Sylvain, et al. “Automatic navigation of an untethered device in the artery of a living animal using a conventional clinical magnetic resonance imaging system”, Applied Physics Letters , vol. 90, no. 11, March 12, 2007