High-intensity focused ultrasound for heating a target zone larger than the electronic focusing zone
Inventors
Partanen, Ari Ilkka Mikael • Dreher, Matthew Robert • Yarmolenko, Pavel Sergeyevich • Wood, Bradford Johns • Carvajal Gallardo, Elma Natalia
Assignees
Profound Medical Inc • National Institutes of Health NIH • US Department of Health and Human Services
Publication Number
US-11116405-B2
Publication Date
2021-09-14
Expiration Date
2033-04-09
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Abstract
The invention provides for a medical instrument (200) comprising a magnetic resonance imaging system (202) and a high-intensity focused ultrasound system (204) with an electronically controllable and a mechanically controllable focus. Execution of instructions by a processor (244) controlling the instrument cause the processor to: receive (100) a target zone (240, 264) descriptive of a zone within the subject; divide (102) the target zone into multiple sub-zones (416, 418, 420, 422, 424, 426, 428, 430, 432, 434); determine (104) a sequence (272) for moving the transducer position to each of the multiple sub-zones; determine (106) a selected sub-zone selected from the multiple sub-zones using the sequence; repeatedly control (108) the mechanical positioning system to move the transducer to the transducer position of the selected sub-zone; repeatedly acquire (110) the magnetic resonance thermometry data; repeatedly determine (112) a temperature property map (274); repeatedly heat (114) the regions independently to the target temperature by controlling the electronically controlled focus with a temperature feedback algorithm (286); and repeatedly change (116) the selected sub-zone using the sequence.
Core Innovation
The invention provides a medical instrument comprising a magnetic resonance imaging (MRI) system and a high-intensity focused ultrasound (HIFU) system with both electronically controllable and mechanically controllable focusing of ultrasound energy. The instrument includes a processor executing instructions to receive a target zone within a subject that is larger than the electronic focusing zone, then divide this target zone into multiple sub-zones, each linked to a transducer position. The processor determines a sequence to move the transducer mechanically to each sub-zone and selects sub-zones to heat by electronic focus within the focusing zone.
The invention addresses the limitation of the small size of the target volume that MR-HIFU can effectively heat due to constraints of electronic steering range (typically around 8 mm) and the slower, artifact-prone mechanical movement of the transducer. It solves the problem of how to apply MR-HIFU treatment to larger regions, of arbitrary shape and heterogeneity, by combining electronic steering for fine control within sub-zones and mechanical repositioning of the transducer for gross control between sub-zones. The processor uses magnetic resonance thermometry data to monitor temperature in each sub-zone, employing a temperature feedback control algorithm to independently heat regions within sub-zones to a target temperature and to select the sequence of heating sub-zones.
Claims Coverage
The patent includes two independent claims focusing on a medical instrument and a computer program product, presenting six main inventive features related to integration of MR imaging, HIFU focusing controls, and temperature feedback algorithms.
Combination of electronic and mechanical focus control for large target zones
The medical instrument includes an ultrasound transducer with electronically-controlled focus adjustable within a focusing zone, and a mechanical positioning system to move the transducer such that the focusing zone can cover large target zones divided into sub-zones.
Sub-zone division and sequenced transducer positioning
The processor divides a target zone larger than the focusing zone into multiple sub-zones, each with associated transducer positions, and determines a sequence for mechanically moving the transducer to each sub-zone to facilitate heating.
Temperature monitoring and feedback control using magnetic resonance thermometry
Repeated acquisition of MR thermometry data produces a temperature property map for each voxel, enabling a temperature feedback algorithm to independently control heating of regions within sub-zones to maintain target temperature over time.
Dynamic sub-zone selection based on temperature properties
The processor uses temperature properties of sub-zones, such as average temperature, to select the next sub-zone to heat, modifying the heating sequence in real time using algorithms like a decision tree.
Calibration and correction of system parameters before and during heating
Before heating, the system acquires calibration MR thermometry data at each transducer position, performs test ultrasound exposures, determines electronic focus corrections, and calculates temperature rise rates to improve accuracy and compensate for mechanical offsets.
Integration of fluid cooling system and correction for spin phase drift
The medical instrument includes a fluid cooling system maintaining fluid temperature, with repeated acquisition of MR data to measure spin phase changes in the fluid and correct temperature property maps to account for magnetic field and temperature drifts.
The claims collectively cover a medical instrument and associated software product that integrate MR thermometry with a dual electronic-mechanical control HIFU system, enabling precise, conformal heating of large target zones through subdivision into sub-zones, sequenced mechanical transducer movement, and voxel-wise thermal feedback control.
Stated Advantages
Enables effective heating of large areas of tissue to a specific temperature, overcoming limitations of electronic steering range.
Provides tight temperature control in the mild hyperthermia range (40-45 °C), which is critical for enhancing anticancer therapies without inducing tissue necrosis.
Allows real-time adaptation of heating by dynamically adjusting sub-zone heating sequences and electronic focus based on MR thermometry feedback.
Minimizes mechanical movement of the transducer, improving temperature stability and reducing artifacts during MR thermometry.
Achieves conformal, homogeneous temperature distribution in arbitrarily shaped target volumes of tissue.
Documented Applications
MR-guided pain palliation.
MR-guided radiation sensitization.
MR-guided chemotherapeutic delivery (local drug delivery).
MR-guided drug activation.
MR-guided gene delivery and gene expression.
Inducing physiological and cellular changes under MR guidance to provide clinical benefits.
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