Systems and methods for reducing thermal skull-induced aberrations during transcranial ultrasound therapeutic procedures
Various example embodiments of the present disclosure provide systems and methods for the dynamic correction and reduction of thermal variations in skull-induced aberrations during a focused ultrasound therapy procedure. Unlike conventional approaches involving static corrections for skull-induced aberrations, various example embodiments of the present disclosure employ ultrasound detection and a skull thickness estimate from volumetric image data to intermittently and dynamically determine corrections for skull-induced aberrations, such that aberration correction reduction is updated intraoperatively and maintained despite local thermally-induced changes in the speed of sound of the local skull region due to intraoperative intracranial heating. Furthermore, in some example embodiments, a measure dependent on the speed of sound with the skull is intraoperatively determined and compared to a previously determined value of the measure to determine a change in the skull temperature, based on a pre-determined relationship between changes in the measure and changes in skull temperature.
1. A method of intraoperatively reducing skull-induced aberrations during an intracranial focused ultrasound therapy procedure, the method comprising:
after initiating delivery of focused ultrasound to an intracranial target within the cranial cavity of a subject using an array of ultrasound transducers:
a) employing an ultrasound transducer of the array to transmit a non-therapeutic ultrasound pulse and receive a reflected ultrasound pulse associated with the reflection from skull surfaces within a local skull region adjacent to the ultrasound transducer, thereby obtaining a receive signal;
b) determining a correction for correcting a therapeutic transmit signal delivered to the ultrasound transducer during subsequent focused ultrasound therapy, wherein the correction is suitable for reducing skull-induced aberrations associated with the local skull region, wherein the correction is determined by processing the receive signal and employing a skull thickness estimate associated with the local skull region, and wherein the skull thickness estimate is obtained based on previously measured volumetric image data associated with the subject;
c) during the subsequent delivery of focused ultrasound to the subject, applying the correction to the therapeutic transmit signal provided to the ultrasound transducer, such that skull-induced phase aberrations are reduced; and
and
d) while a temperature of the local skull region increases due to intracranial heating caused by the delivery of the focused ultrasound, repeating steps a) to c) one or more times to intermittently and intraoperatively recalculate the correction and apply the correction during subsequent delivery of focused ultrasound to dynamically correct for thermally-induced aberrations associated with local changes in the speed of sound in the skull due to spatially nonuniform increases in skull temperature.
2. The method according to claim 1 wherein steps a)-d) are performed to determine respective corrections for at least a subset of ultrasound transducers of the array.
3. The method according to claim 2 further comprising:
processing the receive signal to determine that one or more measures associated with the receive signal satisfy exclusion criteria, and
excluding the ultrasound transducer from use during subsequent delivery of focused ultrasound therapy by the array.
4. The method according to claim 3 wherein assessment of the exclusion criteria dependent on a signal-to-noise ratio of the receive signal.
5. The method according to claim 3 wherein assessment of the exclusion criteria is based on a presence of one or more spikes in a frequency spectrum of the receive signal.
6. The method according to claim 3 wherein the exclusion criteria is based on a comparison of the receive signal with one or more receive signals obtained from one or more neighbouring ultrasound transducers.
7. The method according to claim 3 wherein the exclusion criteria is based on a comparison of the receive signal with one or more receive signals obtained by scanning the ultrasound transducer.
8. The method according to claim 3 wherein the exclusion criteria is based on a measured incidence angle of the ultrasound transducer.
9. The method according to claim 1 further comprising:
generating an additional correction for an additional ultrasound transducer based on respective corrections determined for one or more ultrasound transducers that are adjacent to the additional ultrasound transducer.
10. The method according to claim 1 wherein steps a)-d) a) e) are performed for all of the ultrasound transducers of the array.
11. The method according to claim 1 wherein when performing step b), the receive signal is processed in the frequency domain to identify resonant frequencies associated with the local skull region, and wherein a difference in resonant frequencies and the skull thickness estimate are employed when calculating the correction.
12. The method according to claim 1 wherein when performing step b), the receive signal is processed in the time domain using the pulse-echo method to determine a time delay associated with propagation through the local skull region, and wherein the time delay and the skull thickness estimate are employed when calculating the correction.
13. The method according to claim 1 wherein when performing step b), an incidence angle associated with the ultrasound transducer, relative an external skull surface corresponding to the local skull region, is employed when calculating the correction.
14. The method according to claim 13 wherein the incidence angle is determined by performing registration between a reference frame associated with the volumetric image data and an intraoperative reference frame.
15. The method according to claim 13 wherein the array of ultrasound transducers is supported by a patient-specific headset, wherein an incidence angle associated with a given ultrasound transducer of the array relative to the external skull surface is pre-configured based on an orientation of the given ultrasound transducer relative to the patient-specific headset.
16. The method according to claim 13 wherein the incidence angle associated with the ultrasound transducer is intraoperatively varied to maximize the receive signal for achieving normal incidence.
17. The method according to claim 16 wherein the incidence angle is varied by steering of the non-therapeutic ultrasound pulse.
18. The method according to claim 17 wherein the ultrasound transducer is a phased array ultrasound transducer and wherein the incidence angle is varied by electronic beam steering.
19. The method according to claim 17 wherein the ultrasound transducer is a single-element ultrasound transducer and wherein the incidence angle is varied mechanically.
20. The method according to claim 1 wherein the non-therapeutic ultrasound pulse is focused within the local skull region.
21. The method according to claim 1 wherein a center frequency of the non-therapeutic ultrasound pulse lies within the range of 400-600 KHz.
22. An intracranial focused ultrasound therapy system comprising:
an array of ultrasound transducers;
transducer driving circuitry operatively coupled to the array of ultrasound transducers; and
control and processing circuitry operatively coupled to the transducer driving circuitry, the control and processing circuitry comprising at least one processor and associated memory, the memory storing instructions executable by the at least one processor for performing operations comprising:
after initiating delivery of focused ultrasound to an intracranial target within the cranial cavity of a subject using the array of ultrasound transducers during a focused ultrasound therapy procedure:
a) employing an ultrasound transducer of the array to transmit a non-therapeutic ultrasound pulse and receive a reflected ultrasound pulse associated with the reflection from skull surfaces within a local skull region adjacent to the ultrasound transducer, thereby obtaining a receive signal;
b) determining a correction for correcting a therapeutic transmit signal delivered to the ultrasound transducer during subsequent focused ultrasound therapy, wherein the correction is suitable for reducing skull-induced aberrations associated with the local skull region, wherein the correction is determined by processing the receive signal and employing a skull thickness estimate associated with the local skull region, and wherein the skull thickness estimate is obtained based on previously measured volumetric image data associated with the subject; and
c) controlling the transducer driving circuitry such that the correction is applied to the transmit transducer provided to the ultrasound transducer when focused ultrasound therapy is subsequently delivered to the subject during the intracranial focused ultrasound therapy procedure; and
d) while a temperature of the local skull region increases due to intracranial heating caused by the delivery of the focused ultrasound, repeating steps a)-c) one or more times to intermittently and intraoperatively recalculate the correction apply the correction during subsequent delivery of focused ultrasound to dynamically correct for thermally-induced aberrations associated with local changes in the speed of sound in the skull due to spatially nonuniform increases in skull temperature.