BLADDER TEMPERATURE MEASUREMENT FOR HIGH INTENSITY FOCUSED ULTRASOUND

Abstract

The invention provides for a medical instrument (100) comprising: a high intensity focused ultrasound system (122) for sonicating a target region (139) within a subject (118); a light source (158) for exciting a temperature sensitive fluorescent dye, wherein the light source is configured for coupling to an optical fiber cable (148) of a urinary catheter (140); a light source (160) for measuring fluorescence (190) emitted by the temperature sensitive fluorescent dye, wherein the light source is configured for coupling to the optical fiber cable; a memory (178) for storing machine executable instructions (180); and a processor (174) for controlling the medical instrument. Execution of the machine executable instructions cause the processor to: receive (200) a sonication plan (188) descriptive of a sonication of the target region; measure (202) the fluorescence using the light sensor; calculate (204) a bladder temperature (192) using the fluorescence; and generate (206) sonication commands (194) using the sonication plan and the bladder temperature, wherein the sonication commands are adapted for controlling the high intensity focused ultrasound system to sonicate the target region.

Claims

1. A medical instrument comprising: a high intensity focused ultrasound system for sonicating a target region within a subject; a light source for exciting a temperature sensitive fluorescent dye, wherein the light source is configured for coupling to an optical fiber cable of a urinary catheter; a light sensor for measuring fluorescence emitted by the temperature sensitive fluorescent dye, wherein the light sensor is configured for coupling to the optical fiber cable; a fluorescent dye reservoir; and a pump system configured for connecting to the urinary catheter, wherein the pump system is further connected to the fluorescent dye reservoir, wherein the pump system is configured for pumping from the fluorescent dye reservoir to the distal end of the urinary catheter; a memory for storing machine executable instructions; and a processor for controlling the medical instrument; wherein execution of the machine executable instructions cause the processor to: receive a sonication plan descriptive of a sonication of the target region; measure the fluorescence using the light sensor; calculate a bladder temperature using the fluorescence; and generate sonication commands using the sonication plan and the bladder temperature, wherein the sonication commands are adapted for controlling the high intensity focused ultrasound system to sonicate the target region.

2. The medical instrument of claim 1, wherein the medical instrument comprises the urinary catheter, wherein the optical fiber cable extends from a distal end of the urinary catheter along a length of the urinary catheter, wherein the optical fiber cable is connected to the light source, wherein the optical fiber cable is further connected to the light sensor, and wherein the light source is configured to illuminate the distal end of the urinary catheter using the optical fiber cable.

3. The medical instrument of claim 1, wherein execution of the machine executable instructions further cause the processor to control the pump system to pump contents of the fluorescent dye reservoir to the distal end of the urinary catheter if the fluorescence has a magnitude below a predetermined threshold.

4. The medical instrument of claim 3, wherein the fluorescent dye reservoir contains the temperature sensitive fluorescent dye and a scattering material.

5. The medical instrument of claim 3, wherein the scattering material comprises any one of the following: titanium dioxide particles, ultrasound contrast medium, lipide droplets, milk droplets, soya droplets, intralipid droplets, latex particles, and combinations thereof.

6. The medical instrument of claim 1, wherein the fluorescent dye is any one of the following: fluroescein, fluorescein I, fluorescein sodium. Indocyanine green, Photofrin, and 5-aminolevulinic acid.

7. The medical instrument of claim 1, wherein the sonication commands are further calculated by using the bladder temperature as a starting temperature for the sonication.

8. The medical instrument of claim 7, wherein the sonication plan comprises a specified thermal dose, and wherein the sonication commands are calculated to deliver the specified thermal dose to the target region using the starting temperature.

9. The medical instrument of claim 1, wherein execution of the machine executable instructions further causes the processor to control the high intensity focused ultrasound system using the sonication commands.

10. The medical instrument of claim 1, wherein execution of the machine executable instructions further cause the processor to: repeatedly calculate the bladder temperature during controlling of the high intensity focused ultrasound system, and repeatedly correct the sonication commands using the bladder temperature during controlling of the high intensity focused ultrasound system.

11. The medical instrument of claim 1, wherein the sonication commands specify multiple sonications, wherein the measurement of the bladder temperature and the generation of the sonication commands is repeated at least once for each of the multiple sonications.

12. The medical instrument of claim 1, wherein the high intensity focused ultrasound system has an adjustable focus, wherein the medical instrument further comprises a medical imaging system, wherein execution of the machine executable instructions further cause the processor to acquire a medical image from an imaging zone, wherein the imaging zone comprises the target region, wherein the sonication commands are adapted for controlling the location of the adjustable focus.

13. A computer program product comprising machine executable instructions stored on a non-transitory computer readable and executable by a processor to control a medical instrument, wherein the medical instrument comprises: a high intensity focused ultrasound system for sonicating a target region within a subject; a light source for exciting a temperature sensitive fluorescent dye, wherein the light source is configured for coupling to an optical fiber cable of a urinary catheter; a light sensor for measuring fluorescence emitted by the temperature sensitive fluorescent dye, wherein the light sensor is configured for coupling to the optical fiber cable; a fluorescent dye reservoir; and a pump system configured for connecting to the urinary catheter, wherein the pump system is further connected to the fluorescent dye reservoir, wherein the pump system is configured for pumping from the fluorescent dye reservoir to the distal end of the urinary catheter; wherein execution of the machine executable instructions cause the processor to: receive a sonication plan descriptive of a sonication of the target region; measure fluorescence using the light sensor; calculate a bladder temperature using the fluorescence; and generate sonication commands using the sonication plan and the bladder temperature, wherein the sonication commands are adapted for controlling the high intensity focused ultrasound system to sonicate the target region.

14. A method of operating medical instrument, wherein the medical instrument comprises: a high intensity focused ultrasound system for sonicating a target region within a subject; a light source for exciting a temperature sensitive fluorescent dye, wherein the light source is configured for coupling to an optical fiber cable of a urinary catheter; a light sensor for measuring fluorescence emitted by the temperature sensitive fluorescent dye, wherein the light sensor is configured for coupling to the optical fiber cable; a fluorescent dye reservoir; and a pump system connected to the urinary catheter, wherein the pump system is further connected to the fluorescent dye reservoir, wherein the pump system is configured for pumping from the fluorescent dye reservoir to the distal end of the urinary catheter; wherein the method comprises: receiving a sonication plan descriptive of a sonication of the target region; measuring the fluorescence using the light sensor; calculating a bladder temperature using the fluorescence; and generating sonication commands using the sonication plan and the bladder temperature, wherein the sonication commands are adapted for controlling the high intensity focused ultrasound system to sonicate the target region.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0075] In the following preferred embodiments of the invention will be described, by way of example only, and with reference to the drawings in which:

[0076] FIG. 1 illustrates and example of a medical instrument;

[0077] FIG. 2 shows a flow chart which illustrates a method of using the medical instrument of FIG. 1;

[0078] FIG. 3 illustrates an example of a urinary catheter;

[0079] FIG. 4 shows a cross sectional view of the urinary catheter of FIGS. 3 and 5;

[0080] FIG. 5 illustrates a further example of a urinary catheter;

[0081] FIG. 6 illustrates a further example of a urinary catheter;

[0082] FIG. 7 shows a cross sectional view of the urinary catheter of FIG. 6;

[0083] FIG. 8 illustrates a further example of a urinary catheter; and

[0084] FIG. 9 shows a cross sectional view of the urinary catheter of FIG. 8;

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0085] 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.

[0086] FIG. 1 shows an example of a medical instrument 100. The medical instrument 100 comprises a magnetic resonance imaging system 102. The magnetic resonance imaging system comprises a magnet 104. The magnet 104 is a cylindrical type superconducting magnet with a bore 106 through the center of it. The magnet has a liquid helium cooled cryostat with superconducting coils. It is also possible to use permanent or resistive magnets. 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 106 of the cylindrical magnet there is an imaging zone 108 where the magnetic field is strong and uniform enough to perform magnetic resonance imaging.

[0087] Within the bore 106 of the magnet there is also a set of magnetic field gradient coils 110 which are used for acquisition of magnetic resonance data to spatially encode magnetic spins within the imaging zone 108 of the magnet 104. The magnetic field gradient coils are connected to a magnetic field gradient coil power supply 112. The magnetic field gradient coils 110 are intended to be representative. Typically magnetic field gradient coils contain three separate sets of coils for spatially encoding in three orthogonal spatial directions. A magnetic field gradient power supply 112 supplies current to the magnetic field gradient coils 110. The current supplied to the magnetic field coils is controlled as a function of time and may be ramped or pulsed.

[0088] Adjacent to the imaging zone 108 is a radio-frequency coil 114 for manipulating the orientations of magnetic spins within the imaging zone 108 and for receiving radio transmissions from spins also within the imaging zone. The radio-frequency coil may contain multiple coil elements. The radio-frequency coil may also be referred to as a channel or an antenna. The radio-frequency coil 114 is connected to a radio frequency transceiver 116. The radio-frequency coil 114 and radio frequency transceiver 116 may be replaced by separate transmit and receive coils and a separate transmitter and receiver. It is understood that the radio-frequency coil 114 and the radio-frequency transceiver 116 are representative. The radio-frequency coil 114 is intended to also represent a dedicated transmit antenna and a dedicated receive antenna. Likewise the transceiver 116 may also represent a separate transmitter and receivers.

[0089] A subject 118 is shown as reposing on a subject support 120 and is located partially within the imaging zone 108. The example shown in FIG. 1 comprises a high-intensity focused ultrasound system 122. The high-intensity focused ultrasound system comprises a fluid-filled chamber 124. Within the fluid-filled chamber 124 is an ultrasound transducer 126. Although it is not shown in this figure the ultrasound transducer 126 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 138 electronically by controlling the phase and/or amplitude of alternating electrical current supplied to each of the ultrasound transducer elements. A target region 139 is also marked on FIG. 1. The sonication point 138 can be steered to sonicate the target region 139.

[0090] The ultrasound transducer 126 is connected to a mechanism 128 which allows the ultrasound transducer 126 to be repositioned mechanically. The mechanism 128 is connected to a mechanical actuator 130 which is adapted for actuating the mechanism 128. The mechanical actuator 130 also represents a power supply for supplying electrical power to the ultrasound transducer 126. 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 130 is located outside of the bore 106 of the magnet 104.

[0091] The ultrasound transducer 126 generates ultrasound which is shown as following the path 132. The ultrasound 132 goes through the fluid-filled chamber 128 and through an ultrasound window 134. In this embodiment the ultrasound then passes through a gel pad 136. The gel pad 136 is not necessarily present in all embodiments but in this embodiment there is a recess in the subject support 120 for receiving a gel pad 136. The gel pad 136 helps couple ultrasonic power between the transducer 126 and the subject 118. After passing through the gel pad 136 the ultrasound 132 passes through the subject 118 and is focused to a sonication point 138. The sonication point 138 may be moved through a combination of mechanically positioning the ultrasonic transducer 126 and electronically steering the position of the sonication point 138.

[0092] The medical instrument 100 is further shown as containing an optical unit 150 and a pump unit 152. A catheter 140 is shown as being connected to the optical unit 150 and the pump unit 152. The catheter 140 is a urinary catheter. The catheter 140 has a distal end 144 which is inserted into the bladder 142 of the subject 118. The bladder 142 is adjacent to the target region 139.

[0093] In this example the catheter 140 has a balloon 146 that is inflated and keeps the distal end 144 from leaving the bladder 142. The pump unit 152 is able to pump fluid either in or out of the bladder 142. It has two reservoirs, a waste reservoir 154 for receiving fluid that is pumped out of the bladder 142 and a fluorescent dye reservoir 156 for fluid that is pumped into the bladder 142.

[0094] In some examples, the catheter 140 only has a main tube. In this case material is both pumped into and out of the bladder 142 by the main tube. In other examples there may be a main tube for removing fluid from the bladder 142 and an auxiliary tube for pumping fluid into the bladder 142. Running along the length of the catheter 140 is also an optical fiber cable 148. It is shown as being connected or coupled to the optical unit 150. The optical unit 150 comprises a light source 158 and a spectrometer 160. Another type of light sensor such as a monochromater may be used in different examples. In some examples there is a separate optical fiber for the light source 158 and the spectrometer 160. In other examples the light source and the spectrometer share a single fiber optic.

[0095] The magnetic field gradient coil power supply 112, the high-intensity focused ultrasound system 122, the transceiver 116, the optical unit 150 and the pump unit 152 are shown as being connected to a hardware interface 172 of a computer system 170. The computer system 170 also comprises a processor 174. The processor 174 may actually represent more than one processor and may also represent processors distributed amongst one or more computers. The processor 174 is in communication with the hardware interface 172, a user interface 176, and a memory 178. The hardware interface 172 is an interface which enables the processor 174 to send and receive data and/or commands to the rest of the medical instrument 100 and to control it. The memory 178 may be any combination of volatile or non-volatile memory which the processor 174 has access to.

[0096] The memory 178 is shown as containing a set of machine-executable instructions 180 which the processor 174 can use for performing calculations and/or controlling the magnetic resonance imaging system 100.

[0097] In this example the high-intensity focused ultrasound system 122 is shown as being integrated with a magnetic resonance imaging system 102. This however is optional. The magnetic resonance imaging system 102 may not be present or may be replaced with another medical imaging system such as a diagnostic ultrasound imaging system or a radio logic imaging system such as a computer tomography imaging system. In this example the high-intensity focused ultrasound system 122 has an adjustable focus 138. The magnetic resonance imaging system is used for guiding the location of the focus 138.

[0098] The computer memory 178 is shown as optionally containing a pulse sequence 182. The pulse sequence 182 is a timing diagram or a set of commands which may be used for controlling the magnetic resonance imaging system 102 for acquiring magnetic resonance data. The computer memory 178 is further shown as containing magnetic resonance data 184 that has been acquired by controlling the magnetic resonance imaging system 102 with the pulse sequence 182. The storage 178 is further shown as containing a magnetic resonance image 186 that has been reconstructed from the magnetic resonance data 184. The computer storage 178 is further shown as containing a sonication plan 188 which is a specification of a target region which is to be targeted by the focus 138.

[0099] The memory 178 is further shown as containing a fluorescence spectrum 190 that is measured with the spectrometer 160. The computer memory 178 is further shown as containing a bladder temperature 192 that was calculated from the fluorescence spectrum 190. The computer memory 178 is further shown as containing sonication commands 194. The sonication commands are commands used by the processor 174 to control the high-intensity focused ultrasound system to sonicate the target region 139. The sonication commands 194 for instance may be constructed using the bladder temperature 192 as a body core or base temperature and the sonication plan 188. The magnetic resonance image 186 may be optionally used in creating the sonication commands 194 also. The magnetic resonance image 186 may be used for identifying the location of specific anatomic landmarks and may be used for registering the sonication plan 188 to the subject 118.

[0100] FIG. 2 shows a flowchart of a method which illustrates how to operate the medical instrument 100 of FIG. 1. First in step 200 the sonication plan 188 is received. The sonication plan is descriptive of the sonication of the target region 139. Next in step 204 the fluorescence spectrum 190 is measured using the spectrometer 160. Then in step 204 the bladder temperature 192 is calculated using the fluorescence spectrum 190. Finally in step 206 the sonication commands are generated or calculated by using the sonication plan 188 and the bladder temperature 192.

[0101] FIG. 3 shows a side view of a urinary catheter 140. The catheter has an opening 300 near the distal end 144. Also near the distal end 144 can be seen an optical element 302 that is connected to the optical fiber cable 148. In this example there is only a single optical element 302. The light from the light source may be emitted here as well as light being received that is routed to the spectrometer. The catheter 140 has a length direction 304. The fiber optic 148 runs parallel to the length of the catheter 304 for at least a portion of the catheter.

[0102] FIG. 4 shows a cross-sectional view of the catheter 140 away from the distal end 144. It can be seen that the catheter has a main tube 400 and a catheter wall 402. The optical fiber cable 148 is in this example embedded within the catheter wall 402.

[0103] FIG. 5 shows a further example of a catheter 140. The catheter in FIG. 5 is similar to the catheter shown in FIG. 3 except in this case at the distal end 144 there are two optical elements 302 and 302. One of the optical elements may be for emitting light and the other may be receiving light for the spectrometer. In this case the optical fiber cable 148 may contain two individual fiber optics, one going to optical element 302 and the other going to optical element 302. The optical elements 302 and 302 may be lenses which may be used to couple the fiber optics more efficiently to the bladder. In the example shown in FIG. 5 the cross-sectional view of the catheter 140 will be equivalent to the cross-sectional view shown in FIG. 4.

[0104] FIG. 6 shows a further example of a catheter 140. The catheter 140 is similar to the catheter shown in FIG. 3 except this catheter has a balloon 600 which may be inflated and may be used to prevent the catheter from leaving the bladder. Urinary catheters with such a balloon may be known as a so-called Foley catheter.

[0105] FIG. 7 shows a cross-sectional view of a portion of the catheter 140 along the length 304. The catheter can be seen as having two tubes. There is a main tube 400, an inflation tube 700 which is used to provide a saline solution to inflate the balloon 600 and the fiber optic cable 148. All three of these are embedded within the wall 402 of the catheter 140.

[0106] FIG. 8 illustrates a further example of the catheter 140. The catheter shown in FIG. 8 is similar to the catheter shown in FIG. 6 except this catheter also has an outlet 800. At the outlet 800 fluid may be pumped into the bladder. Fluid may then be pumped out or removed through the inlet 300. This for example may be used for efficiently adding the temperature-sensitive fluorescent dye and/or scattering material to fluid within the bladder. It may also be used to efficiently mix the temperature-sensitive fluorescent dye within the bladder. For example fluid could be pumped in at a constant or periodic rate through the outlet 800. Fluid may also be removed at the same rate through the inlet 300. This may serve to efficiently mix fluid within the bladder.

[0107] FIG. 9 shows a cross-sectional view of the catheter 140 of FIG. 8. It can be seen that within the wall 402 of the catheter there is a main tube 400 which is connected to the outlet 300. The inflation tube 700 which is connected to the balloon 600 is still present. There is also an auxiliary tube 900 which is connected to the outlet 800. Also shown is the fiber optic cable 148.

[0108] The body core temperature can change during the MR-HIFU ablation of uterine fibroid caused by blankets on the patient or air conditioner of the MR scanner. Having a better baseline temperature would lead to a better thermal dose control. Bladder temperature is a good predictor of the core temperature and is near the uterus. By co-injecting Fluorescein and scatter media into bladder long term temperature changes can be detected measuring the frequency shift of the fluorescence in the urine. By fitting the fluorescence spectrum average temperature and temperature variations could be determined without the use of multiple temperature sensors which could interact with the ultrasound field.

[0109] As mentioned above, before the start of a MR-HIFU ablation therapy of uterine fibroids the core body temperature is often times determined by ear thermometer. This gives a good estimation of the baseline temperature within and near the uterus at the start of the MR-HIFU therapy. The total treatment time can last for several hours. During the therapy it is not common to perform a second core body temperature measurement. During the procedure the core body temperature can change by applying blankets for comforting the patient, the air conditioner of the MR scanner or physiological changes inside the patient's body. Since the MR is only capable of measuring temperature differences an absolute temperature readout close the target area would improve the thermal dose control.

[0110] The core body temperature could be measured by temperature sensors in the rectum, vagina or bladder during the procedure. The the bladder may be better in measuring core body temperature compared to rectal and skin measurements and is nearest to the target area. Since we would like to have baseline temperature we can use the inertia of the urine to measure long term average temperature which is not strongly affected by nearby heating during therapy.

[0111] Secondly, when temperature sensors are used their position need to be known avoiding them to be positioned within the beam path of the HIFU transducer. Since the ultrasound absorption coefficient of a liquid is very low it is not expected that the ultrasonic field traveling through the bladder will induce a temperature within the bladder.

[0112] Examples may comprise a bladder catheter with optical fibre or optical cable embedded. A lens may be mounted at the end of the fibre to illuminate the full volume of the bladder with, for example, 480 nm light. By co-injecting Fluorescein or another temperature dependent fluorescent dye and a scatter medium in the urine, via the catheter, a temperature depended emission spectrum can be observed. The scatter medium can be added to create a more homogenous readout fluorescence through the whole volume of the bladder. Fluorescein is FDA approved and shows a temperature depended: absorption spectrum, relative emitted fluorescence signal and a positive peak shift by increasing temperature when dissolved in water. Especially the peak shift can be used as an absolute temperature readout.

[0113] In one example, a standard or modified bladder catheter can be used as well as two optical fibres (excitation and emission) attached within the lumen of the catheter. Via de catheter the Fluorescein as well as scatter media can be injected. A spectrometer can analyze the emission spectrum. Prior injection the emission spectrum can be recorded to remove any background light.

[0114] 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.

[0115] 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

[0116] 100 medical instrument [0117] 102 magnetic resonance imaging system [0118] 104 magnet [0119] 106 bore of magnet [0120] 108 imaging zone [0121] 110 magnetic field gradient coils [0122] 112 magnetic field gradient coils power supply [0123] 114 radio-frequency coil [0124] 116 transceiver [0125] 118 subject [0126] 120 subject support [0127] 122 high intensity focused ultrasound system [0128] 124 fluid filled chamber [0129] 126 ultrasound transducer [0130] 128 mechanism [0131] 130 mechanical actuator/power supply [0132] 132 path of ultrasound [0133] 134 ultrasound window [0134] 136 gel pad [0135] 138 sonication point [0136] 139 target region [0137] 140 catheter [0138] 142 bladder [0139] 144 distal end [0140] 146 balloon [0141] 148 optical fiber cable [0142] 150 optical unit [0143] 152 pump unit [0144] 154 waste reservoir [0145] 156 fluorescent dye reservoir [0146] 158 light source [0147] 160 light sensor or spectrometer [0148] 170 computer [0149] 172 hardware interface [0150] 174 processor [0151] 176 user interface [0152] 178 memory [0153] 180 machine executable instructions [0154] 182 pulse sequence [0155] 184 magnetic resonance data [0156] 186 magnetic resonance image [0157] 188 sonication plan [0158] 190 fluorescence spectrum [0159] 192 bladder temperature [0160] 194 sonication commands [0161] 200 receive a sonication plan descriptive of the sonication of the target region [0162] 202 measure the fluorescence spectrum using the spectrometer [0163] 204 calculate a bladder temperature using the fluorescence spectrum [0164] 206 generate sonication commands using the sonication plan and the bladder temperature [0165] 300 opening [0166] 302 optical element [0167] 304 length of catheter [0168] 400 main tube [0169] 402 wall of catheter [0170] 600 balloon [0171] 700 inflation tube [0172] 800 outlet [0173] 900 auxiliary tube