Patent Application
20120016271
1. Field of the Invention
The present invention is concerned with protection against high intensity focused ultrasound (HIFU) reflection and far field heating.
2. Description of the Prior Art
Magnetic resonance guided high intensity focused ultrasound (MRg HIFU) is a hybrid technology that offers efficient and safe thermal ablation of targeted tumors or other pathological tissues, while preserving the healthy surrounding structures. Theoretically, MRgHIFU has no limitation as to the size of the lesion that can be treated. The primary challenge is to avoid near and far field heating that occur due to the continued passage of HIFU through tissue after the region of interest has been irradiated. Particularly at the patient body location at which the radiation exits the patient's body, reflection and heating can occur due to the tissue/air interface at that location. This location is typically approximately opposite the entry point of HIFU into the patient's body, with the region of interest being between the entry location and the exit location.
It is an object of the present invention to reduce reflection and far field heating that occur in a HIFU procedure.
This object is achieved in accordance with the present invention by a method that includes applying multi-layer ultrasonic coupling gel to the patient at the exit location of HIFU with which a region of interest in the patient has been irradiated. The multi-layer ultrasonic coupling gel is composed of a minimum of two layers. A first layer, which is located directly adjacent to the patient's skin, is composed of commercial ultrasonic coupling gel in untreated form, i.e., homogeneous, with substantially no gas bubbles therein. A second layer, that is directly adjacent the side of the bubble-containing gel layer facing away from the patient, is composed of commercially available ultrasonic coupling gel that has been whipped or beaten in order to introduce air bubbles therein, so that the air bubbles are randomly dispersed and suspended within the gel ultrasonic coupling
The multi-layer gel can be applied topically, with a layer of the foamed gel being applied directly to the patient's skin, followed by application of a layer of the non-foamed gel on top of the foamed gel.
The invention also encompasses a pre-formed gel product, such as a sheet, that is composed of a layer of foamed aquasonic gel and a directly adjacent layer of non-foamed aquasonic gel. The sheet can be rectangular and can then be cut to any desired shape in order to conform to the contours of particular body regions, or can be pre-formed in multiple different shapes.
The foamed aquasonic gel in the layer 3 can be produced by any suitable manner, such as by using beaters to whip or beat an amount of commercially available aquasonic gel.
The bubbles are distributed substantially uniformly in the layer 3.
An example of a commercially available aquasonic gel that is suitable for use as the layer 2, and to produce the layer 3, is Aquasonic® 100.
In a HIFU procedure, a HIFU source 5 is operated to produce a HIFU beam 6 that is focused to a HIFU focus. The HIFU source 5 is positioned and oriented, such as by using magnetic resonance guidance, so that the HIFU focus substantially coincides with a region of interest 7 within tissue of the patient, that is to be treated with HIFU. The HIFU beam 6 is thus radiated into the tissue in a propagation direction. After the region of interest 7 in the propagation direction, HIFU will continue to propagate through the tissue, as radiation 8, which will not necessarily remain as precisely focused as preceding the region of interest 7. Therefore, this radiation 8 is generally described as scatter radiation in
As a result of the radiation 8 exiting the patient at the tissue/air (skin/air) interface, reflection and localized heating of the tissue occur, which can be uncomfortable for the patient and, if severe, could cause injury. By placing the gel composition 1 on the patient's skin so as to substantially cover the exit region, such reflections are significantly reduced by the foamed layer 3 being directly adjacent to the patient's skin, followed by absorption in the non-foamed layer 4. The relevant mechanism appears to be that, when the HIFU beam encounters the foamed layer 3, it proceeds therethrough with substantially no deflection or absorption occurring, and the beam then encounters the non-foamed layer. In the foamed layer 3, the remaining HIFU beam (beam energy) substantially vanishes, presumably due to multiple reflections produced by the bubbles in the foam. The lattice of bubbles is presumed to randomly split the HIFU beam by sequential reflections/deflections, so as to distribute the remaining energy of the HIFU beam in the gel in the layer 3, as well as in the gel of the subsequent layer 2.
Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art.
