# US 11,442,128 B2 · Method for filtering erroneous pixels in a thermal therapy control system

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- Number: US 11,442,128 B2
- Document ID: US11442128B2
- Status: Granted
- Kind: B2
- Application number: 16/589,784
- Filed: 2019-10-01
- Published: 2021-04-01
- Granted: 2022-09-13
- Earliest claimed: 2019-10-01
- Assignees: Profound Medical Inc.
- Applicants: Profound Medical Inc.
- Inventors: Alexandre Bigot; Benjamin Yat-Chung Leung
- Web page: https://patentgrep.com/patent/US11442128B2

## CPC

- A61B 5/01: Measuring temperature of body parts {; Diagnostic temperature sensing, e.g. for malignant or inflamed tissue} (clinical contact thermometers G01K13/20)
- A61B 5/004: {adapted for image acquisition of a particular organ or body part (A61B5/0082 takes precedence; arrangements for optical scanning A61B5/0062)}
- A61B 5/4381: {Prostate evaluation or disorder diagnosis}
- A61N 7/02: Localised ultrasound hyperthermia
- G01R 33/443: {Assessment of an electric or a magnetic field, e.g. spatial mapping, determination of a B0 drift or dosimetry}
- G01R 33/4804: {Spatially selective measurement of temperature or pH}
- G01R 33/5608: {Data processing and visualization specially adapted for MR, e.g. for feature analysis and pattern recognition on the basis of measured MR data, segmentation of measured MR data, edge contour detection on the basis of measured MR data, for enhancing measured MR data in terms of signal-to-noise ratio by means of noise filtering or apodization, for enhancing measured MR data in terms of resolution by means for deblurring, windowing, zero filling, or generation of gray-scaled images, colour-coded images or images displaying vectors instead of pixels (image data processing or generation, in general G06T)}
- G16H 20/30: relating to physical therapies or activities, e.g. physiotherapy, acupressure or exercising
- G16H 30/40: for processing medical images, e.g. editing
- G16H 50/20: for computer-aided diagnosis, e.g. based on medical expert systems
- A61B 5/015: {By temperature mapping of body part}
- A61B 5/4836: {Diagnosis combined with treatment in closed-loop systems or methods (A61B5/0036 takes precedence)}
- A61B 34/10: Computer-aided planning, simulation or modelling of surgical operations
- A61B 2018/00547: {Prostate}
- A61B 2034/107: {Visualisation of planned trajectories or target regions}
- A61B 2090/374: {NMR or MRI}
- A61B 2576/02: specially adapted for a particular organ or body part
- A61N 5/00: Radiation therapy (ultrasound therapy A61N7/00; devices or apparatus applicable to both therapy and diagnosis A61B6/00)
- A61N 7/022: {intracavitary}
- A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D)
- A61N: ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY (measurement of bioelectric currents A61B; surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body A61B18/00; anaesthetic apparatus in general A61M; incandescent lamps H01K; infrared radiators for heating H05B)
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)
- G16H: HEALTHCARE INFORMATICS, i.e. INFORMATION AND COMMUNICATION TECHNOLOGY [ICT] SPECIALLY ADAPTED FOR THE HANDLING OR PROCESSING OF MEDICAL OR HEALTHCARE DATA

## Abstract

During the delivery of thermal therapy, the measured temperature at each pixel in a cross-sectional temperature slice of a multi-pixel thermal image is compared to a maximum temperature limit. When the measured temperature of a pixel is higher than the maximum temperature limit for a predetermined number of consecutive cross-sectional temperature slices, the pixel is masked if the absolute value of the average difference between the measured temperature at the pixel and the measured temperatures at the pixel's neighbors is greater than a maximum temperature variation. The measured temperature of the masked pixel is ignored in subsequent cross-sectional temperature slices until the delivery of thermal therapy is complete.

## Claims

### Claim 1

A method for controlling thermal therapy, comprising:
using a thermal therapy applicator, delivering a thermal therapy dose to a target volume within a patient's body; and
in a computer:
(i) receiving, at a first point in time, a first cross-sectional slice of temperature data for pixels corresponding to respective spatial locations in the target volume, wherein at least one pixel in the first cross-sectional slice is unmasked and has a respective measured temperature higher than a maximum temperature limit;
(ii) determining whether each pixel in the first cross-sectional slice is masked or unmasked;
(iii) determining whether a respective measured temperature of a first unmasked pixel in the first cross-sectional slice is higher than the maximum temperature limit;
(iv) when the respective measured temperature at the first unmasked pixel in the first cross-sectional slice is higher than the maximum temperature limit, increasing a respective pixel counter associated with the first unmasked pixel in the first cross-sectional slice,
(v) when the respective pixel counter associated with the first unmasked pixel is higher than a persistent threshold count, calculating an average temperature difference between a first measured temperature at the first unmasked pixel in the first cross-sectional slice and measured temperatures at neighboring pixels in the first cross-sectional slice;
(vi) applying a mask to the first unmasked pixel when an absolute value of the average temperature difference is greater than a maximum temperature difference;
(vii) repeating steps (iii)-(vi) for each unmasked pixel remaining in the first cross-sectional slice; and
(viii) determining the respective measured temperature at only the unmasked pixels remaining after step (vii); and
stopping the delivery of the thermal therapy to the target volume when the respective measured temperature at each unmasked pixel has reached a minimum therapeutic temperature.

### Claim 2 (depends on 1)

The method of claim 1, further comprising:
temporarily shutting off power to an ultrasound element on the thermal therapy applicator when the first measured temperature at the first unmasked pixel in the first cross-sectional slice is greater than the maximum temperature limit, the ultrasound element insonifying a spatial location that corresponds to the first unmasked pixel, whereby the spatial location that corresponds to the first unmasked pixel is cooled.

### Claim 3 (depends on 2)

The method of claim 2, further comprising providing power to the ultrasound element when the first measured temperature at the first unmasked pixel is less than or equal to the maximum temperature limit.

### Claim 4 (depends on 2)

The method of claim 2, further comprising resetting the first pixel counter when the first measured temperature at the first unmasked pixel is less than or equal to the maximum temperature.

### Claim 5 (depends on 1)

The method of claim 1, wherein the maximum temperature limit is within a temperature range of about 80° C. to about 100° C.

### Claim 6 (depends on 5)

The method of claim 5, wherein the maximum temperature limit is about 86° C.

### Claim 7 (depends on 1)

The method of claim 1, wherein the persistent threshold count is within a range of 4 to 8.

### Claim 8 (depends on 7)

The method of claim 7, wherein the persistent threshold count is 6.

### Claim 9 (depends on 1)

The method of claim 1, wherein the maximum temperature difference is within a range of 4° C. to about 20° C.

### Claim 10 (depends on 9)

The method of claim 9, wherein the maximum temperature difference is about 12° C.

### Claim 11 (depends on 1)

The method of claim 1, wherein the minimum therapeutic temperature is within a temperature range of about 50° C. to about 70° C.

### Claim 12 (depends on 1)

The method of claim 1, wherein:
the first cross-sectional slice of temperature data comprises an uncorrected temperature at each pixel,
the temperature data comprises magnetic resonance (MR) thermometry data received from an MR imaging (MRI) machine, and
the method further comprises correcting fora drift of a magnetic field of the MRI machine for each uncorrected temperature to determine the respective measured temperature.

### Claim 13 (depends on 1)

The method of claim 1, further comprising:
receiving, at a second point in time, a subsequent cross-sectional slice of temperature data for the pixels corresponding to the respective spatial locations in the target volume;
replacing a respective subsequent measured temperature at each masked pixel in the subsequent cross-sectional slice with a respective substitute calculated temperature, each substitute calculated temperature calculated from the respective subsequent measured temperatures at respective neighboring pixels, in the corresponding subsequent cross-sectional slice, to each masked pixel.

### Claim 14 (depends on 13)

The method of claim 13, wherein:
the average temperature difference is a first average temperature difference;
the neighboring pixels are first neighboring pixels; and
the method further comprises:
(i) determining whether each pixel in the subsequent cross-sectional slice is masked or unmasked;
(ii) determining whether a respective subsequent measured temperature of a first unmasked pixel in the subsequent cross-sectional slice is higher than the maximum temperature limit;
(iii) when the respective subsequent measured temperature at the first unmasked pixel in the subsequent cross-sectional slice is higher than the maximum temperature limit, increasing a respective pixel counter associated with the first unmasked pixel in the subsequent cross-sectional slice;
(iv) when the respective pixel counter associated with the first unmasked pixel in the subsequent cross-sectional slice is higher than the persistent threshold count, calculating a second average temperature difference between the subsequent measured temperature at the first unmasked pixel in the subsequent cross-sectional slice, and the measured temperatures at second neighboring pixels in the subsequent cross-sectional slice, wherein the second neighboring pixels comprise a first masked pixel and the measured temperature at the first masked pixel is a first substitute calculated temperature;
(v) applying a mask to the first unmasked pixel in the subsequent cross-sectional slice when an absolute value of the second average temperature difference is greater than the maximum temperature variation; and
(vi) repeating steps (ii)-(v) for each unmasked pixel remaining in the subsequent cross-sectional slice.

### Claim 15 (depends on 1)

The method of claim 1, further comprising defining at least one reference image and at least one current image, and spatially shifting said reference image relative to said current image so as to correct for a drift with respect to the spatial locations in the target volume.

### Claim 16 (depends on 1)

The method of claim 1, further comprising image-shifting each pixel in the first cross-sectional slice when an accumulated image shift of a first dynamic, with respect to a reference dynamic, is greater than a threshold value, the first dynamic comprising the first cross-sectional slice.

### Claim 17

A system for thermal therapy, comprising:
a thermal therapy applicator, configured to deliver a thermal therapy dose to a target volume within a patient's body; and
a computer having at least a processor, a data store and a data communication interface;
the computer configured and arranged to execute in said processor, machine-readable instructions, and to operate on data obtained over said data communication interface and stored in said data store;
the computer further configured and arranged as above to:
(i) receive, at a first point in time, a first cross-sectional slice of temperature data for pixels corresponding to respective spatial locations in the target volume;
(ii) determine whether each pixel in the first cross-sectional slice is masked or unmasked;
(iii) determine whether a respective measured temperature of a first unmasked pixel in the first cross-sectional slice is higher than a maximum temperature limit;
(iv) when the respective measured temperature at the first unmasked pixel in the first cross-sectional slice is higher than the maximum temperature limit, increasing a respective pixel counter associated with the first unmasked pixel in the first cross-sectional slice,
(v) when the respective pixel counter associated with the first unmasked pixel is higher than a persistent threshold count, calculate an average temperature difference between a first measured temperature at the first unmasked pixel in the first cross-sectional slice and measured temperatures at neighboring pixels in the first cross-sectional slice;
(vi) apply a mask to the first unmasked pixel when an absolute value of the average temperature difference is greater than a maximum temperature difference;
(vii) repeat steps (iii)-(vi) for each unmasked pixel remaining in the first cross-sectional slice; and
(viii) determine the respective measured temperature at only the unmasked pixels remaining after step (vii); and
the computer further configured to stop the delivery of the thermal therapy to the target volume when the respective measured temperature at each unmasked pixel has reached a minimum therapeutic temperature.

### Claim 18 (depends on 17)

The system of claim 17, wherein the thermal therapy applicator comprises an ultrasound thermal therapy apparatus that delivers ultrasonic energy to the target volume and the ultrasound therapy apparatus is controlled by the computer according to said claim 17.