LOCATING ABLATED TISSUES USING ELECTRIC PROPERTIES TOMOGRAPHY

Abstract

The invention provides for a medical system (100, 300, 400, 500) comprising: a memory (110) for storing machine executable instructions (150) and a processor (104) for controlling the medical system. Execution of the machine executable instructions cause the processor to: receive (200) first electric properties tomography data (152) descriptive of a first spatially dependent mapping (166) of an RF electrical property within a region of interest (310) of a subject (318), wherein the RF electrical property is a real valued permittivity or real valued conductivity; receive (202) second electric properties tomography data (154) descriptive of a second spatially dependent mapping (168) of the spatially dependent RF electrical property within the region of interest of the subject; calculate (204) a change (160) in the spatially dependent RF electrical property derived from a difference between the first electric properties tomography data and the second electric properties tomography data; and calculate (206) a spatially dependent ablation map (164) by indicating regions within the region of interest where the change in the spatially dependent RF electrical property is above a predetermined threshold.

Claims

1. A medical system comprising: a memory for storing machine executable instructions, a processor for controlling the medical system, wherein execution of the machine executable instructions cause the processor to: receive first electric properties tomography data descriptive of a first spatially dependent mapping of an RF electrical property within a region of interest of a subject, wherein the RF electrical property is a real valued permittivity or real valued conductivity; receive second electric properties tomography data descriptive of a second spatially dependent mapping of the spatially dependent RF electrical property within the region of interest of the subject; calculate a change in the spatially dependent RF electrical property derived from a difference between the first electric properties tomography data and the second electric properties tomography data; and calculate a spatially dependent ablation map by indicating regions within the region of interest where the change in the spatially dependent RF electrical property is above a predetermined threshold.

2. The medical system of claim 1, wherein the predetermined threshold is any one of the following: 5%, 10%, 20%, and between 5% and 20%.

3. The medical system of claim 1, wherein execution of the machine executable instructions further causes the processor to: receive a first spatially dependent temperature map of the region of interest for the first electric properties tomography data; and receive a second spatially dependent temperature map of the region of interest for the second electric properties tomography data; and wherein the change in the spatially dependent RF electrical property is temperature corrected using a change between the first spatially dependent temperature map and the second spatially dependent temperature map.

4. The medical system of claim 1, wherein the medical system further comprises a magnetic resonance imaging system, wherein the memory further stores EPT pulse sequence commands configured for controlling the magnetic resonance imaging system to acquire the first electric properties tomography data and the second electric properties tomography data according to an electrical properties tomography magnetic resonance imaging protocol, wherein the first electric properties tomography data is received by controlling the magnetic resonance imaging system with the EPT pulse sequence commands, and wherein the second electric properties tomography data is received by controlling the magnetic resonance imaging system with the EPT pulse sequence commands.

5. The medical system of claim 4, wherein the magnetic resonance imaging system has an imaging zone, wherein the medical system further comprises a tissue heating system for heating a target zone within the imaging zone, wherein the tissue heating system is configured for heating within the region of interest between the acquisition of the first electric properties tomography data and the second electric properties tomography data.

6. The medical system of claim 5, wherein the tissue heating system is any one of the following: a high intensity focused ultrasound heating system, radio-frequency heating system, a microwave ablation system, a hyperthermia therapy system, a laser ablation system, and an infrared ablation system.

7. The medical system of claim 5, wherein the tissue heating system is a high intensity focused ultrasound system with a controllable focus for depositing ultrasonic energy within the target zone, wherein the memory further comprises sonication commands for controlling targeting of the controllable focus; wherein the sonication commands are configured for controlling the high intensity focused ultrasound system to sonicate the target zone in discrete sonication periods separated by cooling periods, wherein execution of the machine executable instructions further causes the processor to repeatedly acquire the first electric properties tomography data and the second electric properties tomography data during at least a portion of the cooling periods.

8. The medical system of claim 7, wherein execution of the machine executable instructions further causes the processor to modify the sonication commands using the spatially dependent ablation map after acquisition of the first electric properties tomography data and the second electric properties tomography data.

9. The medical system of claim 4, wherein the memory further stores temperature sensitive pulse sequence commands configured for controlling the magnetic resonance imaging system to acquire first thermal magnetic resonance data and second thermal magnetic resonance data according to a magnetic resonance imaging thermometry protocol, wherein execution of the machine executable instructions further causes the processor to: control the magnetic resonance imaging system to acquire the first thermal magnetic resonance data using the temperature sensitive pulse sequence commands, wherein the first thermal magnetic resonance data is acquired within a predetermined period of when the first electric properties tomography data is acquired, wherein the first spatially dependent temperature map is received by reconstructing the first spatially dependent temperature map from the first thermal magnetic resonance data; and control the magnetic resonance imaging system to acquire the second thermal magnetic resonance data using the temperature sensitive pulse sequence commands, wherein the second thermal magnetic resonance data is acquired within a predetermined period of when the second electric properties tomography data is acquired, wherein the second spatially dependent temperature map is received by reconstructing the second spatially dependent temperature map from the second thermal magnetic resonance data.

10. The medical system of claim 1, wherein the spatially dependent RF electrical property is determined at a frequency between 1 MHz and 3 GHz or between 10 MHz and 500 MHz

11. A method of operating a medical system, wherein the method comprises: receiving first electric properties tomography data descriptive of a first spatially dependent mapping of an RF electrical property within a region of interest of a subject, wherein the RF electrical property is a real valued permittivity or real valued conductivity; receiving second electric properties tomography data descriptive of a second spatially dependent mapping of the spatially dependent RF electrical property within the region of interest; calculating a change in the spatially RF dependent electrical property derived from a difference between the first electric properties tomography data and the second electric properties tomography data; and calculating a spatially dependent ablation map by indicating regions within the region of interest where the change in the spatially dependent RF electrical property is above a predetermined threshold.

12. A computer program product comprising machine executable instructions stored on a non-transitory computer readable medium for execution by a processor controlling a medical instrument, wherein execution of the machine executable instructions cause the processor to: receive first electric properties tomography data descriptive of a first spatially dependent mapping of an RF electrical property within a region of interest of a subject, wherein the RF electrical property is a real valued permittivity or real valued conductivity; receive second electric properties tomography data descriptive of a second spatially dependent mapping of the spatially dependent RF electrical property within the region of interest of the subject; calculate a change in the spatially dependent RF electrical property derived from a difference between the first electric properties tomography data and the second electric properties tomography data; and calculate a spatially dependent ablation map by indicating regions within the region of interest where the change in the spatially dependent RF electrical property is above a predetermined threshold.

13. The computer program product of claim 12, wherein the medical system further comprises a magnetic resonance imaging system, wherein the first electric properties tomography data is received by controlling the magnetic resonance imaging system with EPT pulse sequence commands, wherein the EPT pulse sequence commands configured for controlling the magnetic resonance imaging system to acquire the first electric properties tomography data and the second electric properties tomography data according to an electrical properties tomography magnetic resonance imaging protocol, and wherein the second electric properties tomography is received by controlling the magnetic resonance imaging system with the EPT pulse sequence commands.

14. The computer program product of claim 13, wherein the medical instrument further comprises a high intensity focused ultrasound system with a controllable focus for depositing ultrasonic energy within the target zone, wherein the target zone is within the imaging zone, wherein the high intensity focused ultrasound is configured for heating within the region of interest between the acquisition of the first electric properties tomography data and the second electric properties tomography data, wherein the memory further comprises sonication commands for controlling targeting of the controllable focus, wherein the sonication commands are configured for controlling the high intensity focused ultrasound system to sonicate the target zone in discrete sonication periods separated by cooling periods, wherein execution of the machine executable instructions further causes the processor to repeatedly acquire the first electric properties tomography data and the second electric properties tomography data during at least a portion of the cooling periods.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0059] In the following preferred embodiments of the invention will be described, by way of example only, and with reference to the drawings in which:

[0060] FIG. 1 illustrates an example of a medical system;

[0061] FIG. 2 shows a flow chart which illustrated a method of operating the medical system of FIG. 1;

[0062] FIG. 3 illustrates a further example of a medical system;

[0063] FIG. 4 illustrates a further example of a medical system;

[0064] FIG. 5 illustrates a further example of a medical system; and

[0065] FIG. 6 shows a mapping of the electrical conductivity before and after a HIFU ablation.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0066] Like numbered elements in these figures are either equivalent elements or perform the same function. Elements which have been discussed previously will not necessarily be discussed in later figures if the function is equivalent.

[0067] FIG. 1 illustrates an example of a medical system 100. In this example the medical system 100 comprises a computer 102 which has at least one processor 104. The processor is connected to a hardware interface 106, a user interface, and a memory 110. The optional user interface 106 may be used to connect the computer 102 to other pieces of equipment, hardware or computers for exchanging information or for controlling these other devices. The user interface 108 may enable a user to interact with and/or control the processor 104. The memory 110 may be any sort of memory or combination of memories which are accessible to a processor 104. This may include such things as main memory, cached memory, and also non-volatile memory such as flash RAM, hard drives, or other storage devices. In some examples the memory 110 may be considered to be a non-transitory computer-readable medium.

[0068] The memory 110 is shown as containing machine-executable instructions 150.

[0069] The machine-executable instructions 150 enable the processor 140 to control other pieces of equipment and/or to perform operations on data. The memory 110 is further shown as containing first electric properties tomography data 152 and second electric properties tomography data 154. The first electric properties tomography data is descriptive of a first spatially dependent mapping of an electric property within a region of interest of a subject. The electric property is real valued permittivity and/or real valued conductivity. The second electric properties tomography data is also descriptive of a second spatially dependent mapping of the spatially dependent RF electrical property within the region of interest of the subject.

[0070] The memory 110 is shown as optionally containing a first spatially dependent temperature map 156 and a second spatially dependent temperature map 158. The first spatially dependent temperature map is descriptive of the temperature of the region of interest within a predetermined time period of when the first electric properties tomography data was acquired. The second spatially dependent temperature map 158 is descriptive of the temperature of the region of interest of the second electric properties tomography data 154 also within a predetermined time interval or period. The computer memory 110 is further shown as containing a mapping of a change in the spatially dependent RF electrical property 160 that was calculated using the first electric properties tomography data 152 and the second electric properties tomography data 154.

[0071] The memory 110 is further shown as containing a predetermined threshold 162. The memory 110 is further shown as containing a spatially dependent ablation map 164 which was created by thresholding the mapping of change 160 in the spatially dependent RF electrical property with the predetermined threshold 162.

[0072] The memory 110 is further shown as containing an optional first spatially dependent mapping 166 of an RF electrical property that was calculated from the first electric properties tomography data 152. The memory 110 is further shown as containing a second spatially dependent mapping 168 of the RF electrical property that was calculated from the second electric properties tomography data 154.

[0073] In some instances, the first spatially dependent temperature map 156 and the second spatially dependent temperature map 158 may be used for correcting the mapping 160. In some examples the mapping 160 is calculated directly from the first electric properties tomography data 152 and the second electric properties tomography data 154. In other instances the first electric properties tomography data 152 is first used to calculate the first spatially dependent mapping and the second electric properties tomography data 154 is used to calculate the second spatially dependent mapping. In this case the first spatially dependent mapping and the second spatially dependent mapping are used to calculate the mapping 160 of change in the spatially dependent RF electrical property.

[0074] FIG. 2 shows a flowchart which illustrates a method of operating the medical system 100 illustrated in FIG. 1. First in step 200, the processor 104 receives 200 the first electric properties tomography data 152. Next in step 202, the processor receives the second electric properties tomography data 154. Then in step 204, the processor calculates a change or mapping 160 of change in the spatially dependent RF electrical property. In step 206, the processor 104 calculates a spatially dependent ablation map 164 by indicating regions within the region of interest where the change in the spatially dependent RF electrical property is above the predetermined threshold 162.

[0075] In a modification to the method shown in FIG. 2 the processor may also receive the first spatially dependent temperature map 156 and the second spatially dependent temperature map 158 and then use this data to correct the mapping 160 of change in spatially dependent RF electrical property.

[0076] FIG. 3 shows a further example of a medical system 300. The medical system 300 is similar to that shown in FIG. 1 except that it additionally comprises a magnetic resonance imaging system 302. (note to self: insert standard text here)

[0077] The magnetic resonance imaging system 302 comprises a magnet 304. The magnet 304 is a superconducting cylindrical type magnet with a bore 306 through it. The use of different types of magnets is also possible; for instance it is also possible to use both a split cylindrical magnet and a so called open magnet. A split cylindrical magnet is similar to a standard cylindrical magnet, except that the cryostat has been split into two sections to allow access to the iso-plane of the magnet, such magnets may for instance be used in conjunction with charged particle beam therapy. An open magnet has two magnet sections, one above the other with a space in-between that is large enough to receive a subject: the arrangement of the two sections area similar to that of a Helmholtz coil. Open magnets are popular, because the subject is less confined. Inside the cryostat of the cylindrical magnet there is a collection of superconducting coils. Within the bore 306 of the cylindrical magnet 304 there is an imaging zone 308 where the magnetic field is strong and uniform enough to perform magnetic resonance imaging. A region of interest 309 is shown within the imaging zone 308. A subject 318 is shown as being supported by a subject support 320 such that at least a portion of the subject 318 is within the imaging zone 308 and the region of interest 309.

[0078] Within the bore 306 of the magnet there is also a set of magnetic field gradient coils 310 which is used for acquisition of magnetic resonance data to spatially encode magnetic spins within the imaging zone 308 of the magnet 304. The magnetic field gradient coils 310 connected to a magnetic field gradient coil power supply 312. The magnetic field gradient coils 310 are intended to be representative. Typically magnetic field gradient coils 310 contain three separate sets of coils for spatially encoding in three orthogonal spatial directions. A magnetic field gradient power supply supplies current to the magnetic field gradient coils. The current supplied to the magnetic field gradient coils 310 is controlled as a function of time and may be ramped or pulsed.

[0079] Adjacent to the imaging zone 308 is a radio-frequency coil 314 for manipulating the orientations of magnetic spins within the imaging zone 308 and for receiving radio transmissions from spins also within the imaging zone 308. The radio frequency antenna may contain multiple coil elements. The radio frequency antenna may also be referred to as a channel or antenna. The radio-frequency coil 314 is connected to a radio frequency transceiver 316. The radio-frequency coil 314 and radio frequency transceiver 316 may be replaced by separate transmit and receive coils and a separate transmitter and receiver. It is understood that the radio-frequency coil 314 and the radio frequency transceiver 316 are representative. The radio-frequency coil 314 is intended to also represent a dedicated transmit antenna and a dedicated receive antenna. Likewise the transceiver 316 may also represent a separate transmitter and receivers. The radio-frequency coil 314 may also have multiple receive/transmit elements and the radio frequency transceiver 316 may have multiple receive/transmit channels. For example if a parallel imaging technique such as SENSE is performed, the radio-frequency could 314 will have multiple coil elements.

[0080] The transceiver 316 and the gradient controller 312 are shown as being connected to a hardware interface 106 of a computer system 102.

[0081] The memory 110 is further shown as containing EPT pulse sequence commands 350. The EPT pulse sequence commands 350 are configured for controlling the magnetic resonance imaging system 302 to acquire the first electric properties tomography data 152 and the second electric properties tomography data 154. The EPT pulse sequence commands are configured to acquire the electric properties tomography data 152 and 154 according to an electrical properties tomography magnetic resonance imaging protocol.

[0082] The memory 110 is shown as optionally containing temperature sensitive pulse sequence commands 352 which enable the magnetic resonance imaging system to perform magnetic resonance thermometry. The temperature sensitive pulse sequence commands are configured for acquiring the first 354 thermal magnetic resonance data and second 356 thermal magnetic resonance data according to a magnetic resonance imaging thermometry protocol. The first thermal magnetic resonance data 354 is associated with the first electric properties tomography data 152. The second thermal magnetic resonance data 356 is associated with the second electric properties tomography data 154. The first thermal magnetic resonance data 354 is used to reconstruct the first 156 spatially dependent temperature map. The second thermal magnetic resonance data 356 is used to reconstruct the second 158 spatially dependent temperature map.

[0083] The medical system 300 shown in FIG. 3 may be implemented using a conventional magnetic resonance imaging system. For example the subject 318 could be imaged prior to a thermal ablation procedure and then imaged after the procedure has been finished. In some examples the processor 104 may be further configured to register the first electric properties tomography data 152 to the second electric properties tomography data 154 such that the position of the subject 318 can be corrected for. For example there may be preliminary or scouting images which are acquired to each of the data 152 and 154 which enables them to be accurately registered to each other.

[0084] FIG. 4 shows a further example of a medical system 400. The medical system 400 is similar to that shown in FIG. 3 except there is additionally a tissue heating system 402. The tissue heating system 402 is shown to comprise an applicator 404. Items 402 and 404 are intended to be representative and may not necessarily depict all of the features of the particular embodiment. For example the tissue heating system 402 may become but is not limited to: a high-intensity focused ultrasound heating system, a radio-frequency heating system, a microwave ablation system, a hyperthermia therapy system, a laser ablation system, and an infrared ablation system. The applicator 404 may take different forms in different embodiments. It may be a heat exchanger, an infrared source, a laser source, a probe, a catheter, or even an antenna. The applicator 404 may in some instances be fixed with respect to its position in the magnet 304 or the subject support 320.

[0085] In other examples it may be mounted on or in the subject 318. In the example shown in FIG. 4 the subject 318 is lying in the magnetic resonance imaging system 302 and the thermal ablation can be performed using the tissue heating system 402. The first thermal magnetic resonance data 354 can be acquired before using the tissue heating system 402 and the second thermal magnetic resonance data 356 can be acquired after using the tissue heating system 402. In some instances the thermal magnetic resonance imaging may also be used to provide for the first spatially dependent temperature map 156 and the second spatially dependent temperature map 158 to correct the mapping 160.

[0086] FIG. 5 illustrates a further example of a medical system 500. The medical system 500 is similar to the medical system 400 shown in FIG. 4. In FIG. 5 the tissue heating system is specifically a high-intensity focused ultrasound system 522.

[0087] A subject 318 is shown as reposing on a subject support 320 and is located partially within the imaging zone 308. The embodiment shown in FIG. 3 comprises a high-intensity focused ultrasound system 522. The high-intensity focused ultrasound system comprises a fluid-filled chamber 524. Within the fluid-filled chamber 524 is an ultrasound transducer 526. Although it is not shown in this figure the ultrasound transducer 526 may comprise multiple ultrasound transducer elements each capable of generating an individual beam of ultrasound. This may be used to steer the location of a sonication point 538 (the controllable focus) electronically by controlling the phase and/or amplitude of alternating electrical current supplied to each of the ultrasound transducer elements.

[0088] The ultrasound transducer 526 is connected to a mechanism 528 which allows the ultrasound transducer 526 to be repositioned mechanically. The mechanism 528 is connected to a mechanical actuator 530 which is adapted for actuating the mechanism 528. The mechanical actuator 530 also represents a power supply for supplying electrical power to the ultrasound transducer 526. In some embodiments the power supply may control the phase and/or amplitude of electrical power to individual ultrasound transducer elements. In some embodiments the mechanical actuator/power supply 530 is located outside of the bore 506 of the magnet 504.

[0089] The ultrasound transducer 526 generates ultrasound which is shown as following the path 532. The ultrasound 532 goes through the fluid-filled chamber 528 and through an ultrasound window 534. In this embodiment the ultrasound then passes through a gel pad 536. The gel pad 536 is not necessarily present in all embodiments but in this embodiment there is a recess in the subject support 520 for receiving a gel pad 536. The gel pad 536 helps couple ultrasonic power between the transducer 526 and the subject 518. After passing through the gel pad 536 the ultrasound 532 passes through the subject 518 and is focused to a sonication point 538 within a target volume 406. The sonication point 406 is being focused within a target volume 406. The sonication point 538 may be moved through a combination of mechanically positioning the ultrasonic transducer 426 and electronically steering the position of the sonication point 338 to treat the entire target volume 340.

[0090] The the high-intensity focused ultrasound system 522 are shown as being connected to the hardware interface 106 of computer 102.

[0091] The memory 110 is further shown as containing sonication commands 550. The sonication commands 550 are commands which enable the processor 104 to control the high-intensity focused ultrasound system 522 to move the sonication point 406 or controllable focus to sonicate the target zone or volume 406.

[0092] In many practical applications the target zone 406 will be sonicated by performing a number of sonications which are interrupted by cooling periods. During the cooling periods, magnetic resonance thermometry or acquisition of the first 152 and second 154 electric properties tomography data could be acquired. This may enable direct measurement of ablated tissue within the subject 318 during the sonication process. In some examples the machine-executable instructions 150 may be configured such that the mapping 160 of the change in the spatially dependent RF electrical property is updated repeatedly and used to generate an updated spatially dependent ablation map 164. The spatially dependent ablation map 164 could be used to identify which portions of the target zone have actually been ablated and adjust the sonication commands 550 during the cooling periods. This may enable more accurate ablation of the target zone 406 and/or to perform the ablation more rapidly. Such modifications could be performed automatically by the processor 104 or they could be displayed during the cooling period for adjustment by a human operator. FIG. 6 below provides an example where ablated tissue was detected using

[0093] EPT. In this example, 37-year-old female patient with multiple fibroids was treated with a volumetric 1.5 T MR-HIFU system. EPT was based on a balanced Fast Field Echo (bFFE) sequence (TR/TE=2.4/1.2 ms, voxel=2.5×2.5×2.5 mm.sup.3, flip=30°) acquired prior to and at 1.5 hours after MR-HIFU ablation. It is assumed that after this time, temperature of treated tissue is back to normal body temperature, and thus conductivity is not impacted by direct thermal effects. Conductivity reconstruction was performed using the phase-based approach of EPT and a subsequent bilateral median filter using tissue boundaries delineated from the bFFE magnitude image. The average conductivity was determined by drawing a region of interest around the whole index fibroid.

[0094] FIG. 6 shows an example of a first spatially dependent mapping 166 of an electric property in the form of a conductivity map. FIG. 6 also shows a second spatially dependent mapping 168 of an electric property. The electric property is again conductivity and the region of interest for images 166 and 168 are identical. FIG. 6 shows the average conductivities of the subserosal fibroid before and after sonication that were 1.02 S/m and 1.14 S/m respectively. Similarly the subserosal fibroid showed a 20.9% increase in conductivity from 1.10 S/m before to 1.33 S/m post treatment. The subserosal fibroid is the region labeled 600 and the submucosal fibroid is labeled 602. The images in FIG. 6 clearly demonstrate that a change in an RF electrical property such as the conductivity can be used to identify regions which have been ablated.

[0095] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments.

[0096] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope.

LIST OF REFERENCE NUMERALS

[0097] 100 medical system [0098] 102 computer [0099] 104 processor [0100] 106 hardware interface [0101] 108 user interface [0102] 110 memory [0103] 150 machine executable instructions [0104] 152 first electric properties tomography data [0105] 154 second electric properties tomography data [0106] 156 first spatially dependent temperature map [0107] 158 second spatially dependent temperature map [0108] 160 mapping of change in the spatially dependent RF electrical property [0109] 162 predetermined threshold [0110] 164 spatially dependent ablation map [0111] 166 first spatially dependent mapping of an RF electrical property [0112] 168 second spatially depenent mapping of an electircal property [0113] 200 receive first electric properties tomography data descriptive of a first spatially dependent mapping of an RF electrical property within a region of interest of a subject, wherein the RF electrical property is a real valued permittivity or real valued conductivity [0114] 202 receive second electric properties tomography data descriptive of a second spatially dependent mapping of the spatially dependent RF electrical property within the region of interest of the subject [0115] 204 calculate a change in the spatially dependent RF electrical property derived from a difference between the first spatially dependent mapping and the second spatially dependent mapping [0116] 206 calculate a spatially dependent ablation map by indicating regions within the region of interest where the change in the spatially dependent RF electrical property is above a predetermined threshold [0117] 300 medical system [0118] 302 magnetic resonance imaging system [0119] 304 magnet [0120] 306 bore of magnet [0121] 308 imaging zone [0122] 309 region of interest [0123] 310 magnetic field gradient coils [0124] 312 magnetic field gradient coil power supply [0125] 314 radio-frequency coil [0126] 316 transceiver [0127] 318 subject [0128] 320 subject support [0129] 350 EPT pulse sequence commands [0130] 352 temperature sensitive pulse sequence commands [0131] 354 first thermal magnetic resonance data [0132] 356 second thermal magnetic resonacne data [0133] 400 medical system [0134] 402 tissue heating system [0135] 404 applicator [0136] 406 target zone [0137] 500 medical system [0138] 522 high intensity focused ultrasound system [0139] 524 fluid filled chamber [0140] 526 ultrasound transducer [0141] 528 mechanism [0142] 530 mechanical actuator/power supply [0143] 532 path of ultrasound [0144] 534 ultrasound window [0145] 536 gel pad [0146] 538 controllable focus [0147] 550 sonication commands