Sub-aperture control in high intensity focused ultrasound

Abstract

Sub-aperture control is provided for high intensity focused ultrasound. Test transmissions are made sequentially from different sub-apertures. The tissue response at the focal regions is determined and used to select sub-apertures. For example, one or more sub-apertures are not used where temperature does not rise above certain threshold or tissue displacement is weak, such as associated with intervening bone or attenuating tissue. Other factors may be used instead or in addition to tissue response at the focal region. Relative proximity of the sub-apertures to a lesion, angular distribution of the sub-apertures, shape or size of the sub-aperture focal regions as compared to the tissue to be treated, or combinations thereof may be used. Once selected, the relative weight for each sub-aperture may be adjusted based on measured tissue response for each sub-aperture, such as to provide more equal treatment contribution from different sub-apertures.

1 . A method for sub-aperture control for high intensity focused ultrasound, the method comprising:
 identifying a target;   selecting at least a first sub-aperture from a plurality of sub-apertures, the selecting being a function of a match of a region shape of a focus region provided by the at least first sub-aperture to the target; and   applying high intensity focused ultrasound to the target with the at least first sub-aperture and not another of the sub-apertures.   
     
     
         2 . The method of  claim 1  wherein identifying the target comprises identifying a location of the target and a shape of the target. 
     
     
         3 . The method of  claim 1  wherein selecting comprises:
 detecting the region shape; and 
 selecting the first sub-aperture and at least a second sub-aperture such that the focus region provided by the at least first and second sub-apertures covers the desired target shape. 
 
     
     
         4 . The method of  claim 1  wherein selecting is a function of a proximity of the first sub-aperture to the target, the sub-apertures part of a substantially continuous array around the target on an exterior of a patient. 
     
     
         5 . The method of  claim 1  wherein selecting is a function of angular distribution of the at least first sub-aperture to the target. 
     
     
         6 . The method of  claim 1  wherein selecting comprises:
 transmitting sequentially from the sub-apertures; 
 measuring a spatial distribution of effect of the transmitting adjacent the target; and 
 selecting the at least the first sub-aperture as a function of the spatial distribution relative to the target. 
 
     
     
         7 . The method of  claim 1  further comprising:
 adjusting a power of the first sub-aperture relative to a second sub-aperture. 
 
     
     
         8 . The method of  claim 7  wherein adjusting comprises:
 transmitting simultaneously from the at least first sub-apertures; 
 measuring the region shape; and 
 altering the region shape by the adjusting of the power, the altering more closely matching the region shape to the lesion. 
 
     
     
         9 . The method of  claim 8  wherein measuring the region shape comprises performing acoustic radiation force measurement in response to the transmitting. 
     
     
         10 . The method of  claim 8  wherein measuring the region shape comprises detecting temperature or strain change in response to the transmitting. 
     
     
         11 . A system for sub-aperture control for high intensity focused ultrasound, the system comprising:
 a phased array of elements, the array comprising a plurality of phased sub-arrays;   a sub-aperture circuit for activating and deactivating the sub-arrays as sub-apertures of the phased array; and   a processor operable to control the sub-aperture circuit to select some of the sub-apertures and not select others of the sub-apertures, the selection being as a function of a measured distribution, at a target to be treated, due to transmissions from the sub-apertures.   
     
     
         12 . The system of  claim 11  wherein the measured distribution is a measurement, at the target, of temperature or strain change determined sequentially from each of the sub-apertures. 
     
     
         13 . The system of  claim 11  wherein the measured distribution is a measurement, at the target, of tissue displacement determined sequentially from each of the sub-apertures. 
     
     
         14 . The system of  claim 11  wherein the processor is configured to weight a power of a first selected sub-aperture relative to a power of a second selected sub-aperture as a function of another measured distribution, at the target, due to transmission simultaneously from the first and second selected sub-apertures. 
     
     
         15 . The system of  claim 11  wherein the processor is configured to control the sub-aperture circuit to select and not select as a function of a proximity of each of the sub-apertures to the target, an angle distribution of the sub-apertures to the target, and a shape of a focal region by the combination of the selected sub-apertures. 
     
     
         16 . The system of  claim 11  wherein the measured distribution is of focal regions of the sub-apertures. 
     
     
         17 . The system of  claim 11  wherein the processor is configured to simultaneously use at least two different subapertures to each treat at least two different targets. 
     
     
         18 . A non-transitory computer readable storage medium having stored therein data representing instructions executable by a programmed processor for sub-aperture control for high intensity focused ultrasound, the storage medium comprising instructions for:
 selecting a first set of sub-apertures as a subset from a second set of sub-apertures, the selecting being as a function of a spatial proximity of the sub-apertures to a lesion, as a function of an angular distribution of the sub-apertures in the first set to the lesion, or combinations thereof; and   using the first set of the sub-apertures for the high intensity focused ultrasound.   
     
     
         19 . The computer readable storage medium of  claim 18  further comprising instructions for selecting the first set of sub-apertures also as a function of a shape of a focal region from combination of the sub-apertures of the first set relative to a shape of the lesion. 
     
     
         20 . The computer readable storage medium of  claim 18  further comprising instructions for tuning a relative power of the sub-apertures of the first set as a function of a focal distribution. 
     
     
         21 . The computer readable storage medium of  claim 18  further comprising instructions for:
 transmitting sequentially from the sub-apertures; 
 receiving a temperature or displacement measurement of focal regions for the respective sub-apertures; and 
 selecting as a function of the measurement.