Overcoming acoustic field and skull non-uniformities
Various approaches for heating a target region substantially uniformly include identifying one or more locations of one or more hot spots in the target region and/or surrounding regions of the target region during an ultrasound sonication process; computing a temporal variation to an output parameter of at least one of the transducer elements based at least in part on the identified location(s) of the hot spot(s); and operating the at least one transducer element to achieve the temporal variation of the output parameter so as to minimize the hot spot(s).
1. A method of heating a target region using an ultrasound transducer comprising a plurality of transducer elements for generating a focal zone at the target region, the method comprising:
(a) dividing the ultrasound transducer into a plurality of sub-regions, each sub-region comprising a plurality of transducer elements;
(b) operating the sub-regions in accordance with an activation and deactivation pattern in which at least one of the sub-regions is activated;
(c) identifying a first location of at least one hot spot, different from the focal zone, in at least one of the target region or a region surrounding the target region during an ultrasound sonication process, the hot spot having an energy density above a predefined acceptable level;
(d) selecting a second location of the at least one hot spot, the second location being different from the first location and, compared to the first location, being low-heat sensitive and/or high-thermal-energy tolerant;
(e) based at least in part on the identified first and second locations of the at least one hot spot, altering the activation and deactivation pattern of the sub-regions such that the at least one hot spot is generated at the second location to thereby reduce the energy density of the first location to the predefined acceptable level while maintaining the focal zone at the target region, wherein following the alteration of the activation and deactivation pattern, at least one of the sub-regions is activated; and
(f) operating the sub-regions of the transducer elements in accordance with the altered activation and deactivation pattern.
2. The method of claim 1 , wherein the activation and deactivation pattern creates a substantially uniform temperature distribution in the target region.
3. The method of claim 1 , further comprising acquiring imaging data of the target region and the surrounding region and, based thereon, determining a temperature distribution in the target region and the surrounding region, at least one of the first or second location of the at least one hot spot being identified based on the temperature distribution.
4. The method of claim 1 , further comprising acquiring imaging data of at least one of the target region or the surrounding region and, based thereon, determining an acoustic field distribution therein, at least one of the first or second location of the at least one hot spot being identified based on the acoustic field distribution.
5. The method of claim 1 , further comprising acquiring imaging data of the surrounding region and, based thereon, generating a predicted temperature distribution in the target region and the surrounding region using a prediction model, at least one of the first or second location of the at least one hot spot being identified based on the predicted temperature distribution.
6. The method of claim 5 , wherein the imaging data is ARFI data.
7. The method of claim 1 , wherein at least one of the first or second location of the at least one hot spot is identified based at least in part on a prediction model.
8. The method of claim 1 , further comprising the step of identifying additional hot spots, the activation and deactivation pattern distributing the hot spots among different locations so the hot spots do not persist at any single location for an amount of time that will cause a clinically adverse effect on non-target tissue.
9. A system for heating a target region, the system comprising an ultrasound transducer comprising a plurality of transducer elements for generating a focal zone at the target region, and
a controller configured to:
(a) divide the ultrasound transducer into a plurality of sub-regions, each sub-region comprising a plurality of transducer elements;
(b) operate the sub-regions in accordance with an activation and deactivation pattern in which at least one of the sub-regions is activated;
(c) identify a first location of at least one hot spot, different from the focal zone, in at least one of the target region or a region surrounding the target region during an ultrasound sonication process, the hot spot having an energy density above a predefined acceptable level;
(d) select a second location of the at least one hot spot, the second location being different from the first location and, compared to the first location, being low-heat sensitive and/or high-thermal-energy tolerant;
(e) based at least in part on the identified first and second locations of the at least one hot spot, altering the activation and deactivation pattern of the sub-regions such that the at least one hot spot is generated at the second location to thereby reduce the energy density of the first location to the predefined acceptable level while maintaining the focal zone at the target region, wherein following the alteration of the activation and deactivation pattern, at least one of the sub-regions is activated; and
(f) operate the sub-regions of the transducer elements in accordance with the altered activation and deactivation pattern.
10. The system of claim 9 , wherein the activation and deactivation pattern creates a substantially uniform temperature distribution in the target region.
11. The system of claim 9 , further comprising an imager, coupled to the controller, for acquiring imaging data of the target region and the surrounding region, wherein the controller is further configured to determine a temperature distribution in the target region and the surrounding region based on the imaging data and identify at least one of the first or second location of the at least one hot spot based on the temperature distribution.
12. The system of claim 9 , further comprising an imager, coupled to the controller, for acquiring imaging data of at least one of the target region or the surrounding region, wherein the controller is further configured to determine an acoustic field distribution therein based on the imaging data, at least one of the first or second location of the at least one hot spot being identified based on the acoustic field distribution.
13. The system of claim 12 , wherein the imager is an ARFI device.
14. The system of claim 9 , further comprising an imager, coupled to the controller, for acquiring imaging data of the surrounding region, wherein the controller is further configured to generate a predicted temperature distribution in the target region and the surrounding region based on the imaging data and a physical model and identify at least one of the first or second location of the at least one hot spot based on the predicted temperature distribution.
15. The system of claim 9 , wherein the controller is further configured to identify at least one of the first or second location of the at least one hot spot based at least in part on a prediction model.