APPARATUS AND METHOD FOR ULTRASOUND MONITORING OF ABLATION BY A COMBINATION OF THE BREAKING DOWN OF AIR BUBBLES AND IMAGING SEQUENCES FIELD OF THE INVENTION
The invention relates to the field of ultrasound monitoring of ablation, and particularly to the apparatus and method for ultrasound monitoring of ablation by means of a combination of the breaking down of air bubbles and imaging sequences.
BACKGROUND OF THE INVENTION
Chemotherapy and radiation therapy are ineffective against primary and secondary hepatic tumors. Therefore, tumor removal through resection surgery is now the dominant first treatment option. However, in some cases, patients are not considered to be suitable candidates for this type of surgery for various reasons.
Recently, minimally invasive ablation methods, such as: laser ablation, radio frequency ablation (RFA), or non-invasive micro-wave ablation and high-intensity focused ultrasound ablation have been introduced into clinics. The goal for the ablations is to cause immediate cell death by heating while minimizing the damage to the surrounding healthy tissue. Experimental results show that the lesion size depends on the ablation power and time and varies greatly between different individuals and different tissue type.
During the ablation process, a lot of air bubbles are generated due to fast heating when temperatures reach boiling at around 80 °C to 120 °C. These generated air bubbles are strong reflectors that will produce strong echoes in regular ultrasound images, which can be used by the operator to assess the heated region. However, since the features of the ultrasound images do not change too much during the ablation process, the sensitivity of ablation monitoring by ultrasound imaging is affected. SUMMARY OF THE INVENTION
In order to increase the sensitivity of ablation monitoring by ultrasound imaging, various kinds of approaches to estimate the acoustic parameters from the ultrasonic RF data or elasticity imaging during the ablation were proposed with limited success in clinical applications due to several reasons. Air bubbles (with a diameter around ten to a few hundred micrometers) generated by thermally injured tissue will affect the accuracy of the estimators of this parameter.
Therefore, the inventors considered that in order to obtain clearer ultrasound images, the generated air bubbles must be broken down to improve the sensitivity of ablation monitoring by ultrasound imaging. Hereby, breaking down air-bubbles means that to vanish the air-bubbles or to break down the air-bubbles into smaller ones.
Specifically, according to one aspect of the present invention, it provides an apparatus for the monitoring of ablation comprising:
an ultrasound transducer for performing the B-scan imaging for a region that is being treated for ablation, and the ultrasound transducer also being configured for the breaking down of air bubbles by ultrasound in the region of ablation; and
a controller that is configured to control the ultrasound transducer to break down the air bubbles within a predetermined period during the ablation and to enable the ultrasound transducer to perform the B-scan imaging for the region of ablation after the predetermined period.
The quality of the ultrasound images is greatly improved, because the generated air bubbles are broken down during the ablation, which prevents the creation of hyperechogenicity on ultrasound images. Moreover, since no extra hardware is needed, the apparatus for the monitoring of ablation is cost-effective.
In accordance with an embodiment of the present invention, to better control the ablation process, it is preferable that the controller is configured to control the ultrasound transducer to repeatedly perform the B-scan imaging and the breaking down of the air bubbles so as to continually obtain clearer ultrasound images during the whole ablation process According to another aspect of the present invention, it provides an apparatus for ablation monitoring comprising:
an ultrasound transducer for performing B-scan imaging for a region that is being treated for ablation; and
an additional ultrasound transducer configured for breaking down air bubbles by transmitting ultrasound in the region of ablation.
In accordance with an embodiment of the present invention, the apparatus for the monitoring of ablation further comprises a controller that is configured to control the additional ultrasound transducer (320) to break down the air bubbles within a predetermined period during the ablation.
In accordance with a further embodiment of the present invention, the controller is configured to control the additional ultrasound transducer to repeatedly perform the breaking down of the air bubbles so as to continually obtain clearer ultrasound images during the whole ablation process.
According to another aspect of the present invention, it provides a method for the monitoring of ablation, comprising:
a) breaking down air bubbles generated in a region that is being treated by ultrasound in a predetermined period during the ablation; and
b) performing B-scan imaging for the region of ablation after the predetermined period.
In accordance with an embodiment of the present invention, the method for ablation monitoring further comprises: repeating the steps a) and b) so as to continually obtain clearer ultrasound images.
Other objects and advantages of the present invention will become more apparent and will be easily understood with reference to the description made in combination with the accompanying drawings.
DESCRIPTION OF THE DRAWINGS
The present invention will be described and explained hereinafter in more detail in combination with embodiments and with reference to the drawings, wherein:
Fig. 1 is a simplified schematic diagram of the apparatus for the monitoring of ablation in accordance with an embodiment of the present invention;
Fig. 2a is a graph that shows a relationship between the temperature and the time in which the ablation is being performed by one kind of ablation device like Valleylab;
Fig. 2b is a timing chart that shows the operation of one kind of ablation device, like Valleylab;
Fig. 3 is a simplified schematic diagram of the apparatus for the monitoring of ablation in accordance with another embodiment of the present invention; and
Fig. 4 is a flowchart of the method for ablation monitoring in accordance with an embodiment of the present invention.
The same reference signs in the figures indicate a similar or corresponding feature and/or functionality.
DETAILED DESCRIPTION
The embodiment of the present invention will be described hereinafter in more detail with reference to the drawings.
Fig. 1 is a simplified schematic diagram of the apparatus 10 for ablation monitoring in accordance with an embodiment of the present invention, which in the illustrated embodiment includes an ultrasound transducer 110 and a controller 120. The ultrasound transducer 110 is not only used for performing B-scan imaging for a region being treated for ablation, but is also configured to break down generated air bubbles by transmitting ultrasound in the region of ablation.
Furthermore, the controller 120 is configured to control the ultrasound transducer 110 to break down the air bubbles within a predetermined period during the ablation and to enable the ultrasound transducer 110 to perform the B-scan imaging for the region of ablation after the predetermined period.
In one embodiment, when an ablation device is powered on and starts to perform the ablation, the controller 120 controls the ultrasound transducer 110 to operate in a first operating mode in which the B-scan imaging is performed for the region of ablation. Then, for example, after the temperature is above 80 °C, or after about 60 seconds has elapsed, the controller 120 controls the ultrasound transducer 110 to operate in a second operating mode in which the air bubbles are broken down by ultrasound from the ultrasound transducer 110 within a predetermined period such as 200 to 400 microseconds. At the end of the second operating mode, the ultrasound transducer 110 switches back to the first operating mode under the control of the controller 120. Ordinarily, the conventional processor and display are utilized to collect and process ultrasonic RF data for the region of ablation and to display the ultrasound images, when the ultrasound transducer 110 operates in the first operating mode.
However, it should be understood that the present invention is not limited to this embodiment. For example, after an ablation device is powered on and starts to perform the ablation, the ultrasound transducer 110 may maintain in turn-off state until it operates in the second operating mode under the control of the controller 120. Fig. 2a is a graph showing a relationship between the temperature and the time in the ablation performed by one kind of ablation device like Valleylab.
As can be seen from Fig. 2a, the temperature increases over time during the ablation performed by this kind of ablation device. For this kind of ablation device, if impedance increases to 10 ohms above the baseline value, power is automatically switched off for e.g. 15 seconds and then switched on again to pause the heating to avoid the temperature being too high during the ablation process (see Fig. 2b). In this case, it is preferable that the predetermined period within which the air bubbles are broken down is arranged in the pause period of the ablation.
According to an embodiment of the present invention, to better control the ablation process, it is preferable that the controller is configured to control the ultrasound transducer 110 to repeatedly perform the B-scan imaging and the breaking down of the air bubbles so as to continually obtain clearer ultrasound images.
Fig. 3 is a simplified schematic diagram of the apparatus 30 for ablation monitoring in accordance with another embodiment of the present invention, which in the illustrated embodiment includes an ultrasound transducer 310 and an additional ultrasound transducer 320. In particular, the ultrasound transducer 310 is used to perform B-scan imaging for a region being treated for ablation, and the additional ultrasound transducer 320 is configured to break down generated air bubbles by transmitting ultrasound in the region of ablation
According to the present invention, the apparatus 30 may further comprise a controller that is configured to control the additional ultrasound transducer 320 to break down the generated air bubbles within a predetermined period during the ablation. For example, after the temperature is above 80 °C, or after about 60 seconds have elapsed since the start of the ablation, the controller controls the additional ultrasound transducer 320 to break down the air bubbles within a predetermined period, such as 200 to 400 microseconds.
In order to better control the ablation process, it is preferable that the controller is configured to control the ultrasound transducer 320 to repeatedly perform the breaking down of the air bubbles so as to continually obtain clearer ultrasound images. embodiment in accordance with the present invention, the above-mentioned ultrasound transducers 110, 320 may be configured to transmit dynamically focused ultrasound within the predetermined period, so as to break down the air bubbles in the whole region of ablation in a scan manner. Alternatively, the above-mentioned ultrasound transducers 110, 320 may be configured to transmit ultrasound at a high Mechanical Index (MI) within the predetermined period so as to break down the air bubbles in the whole region of ablation without using dynamically focused ultrasound. Moreover, normally, the MI is selected to be bigger than 0.5 but less than the safety value of 1.9.
Fig. 4 is a flowchart of the method 40 for the monitoring of RFA in accordance with an embodiment of the present invention.
As can be seen from Fig. 4, air bubbles generated in a region that is being treated are broken down by ultrasound in a predetermined period during the ablation in step 410. For example, the predetermined period may be selected to be 200 to 400 microseconds. Then, B-scan imaging for the region of ablation after the predetermined period is performed in step 420.
As mentioned above, for one kind of ablation device, like Valleylab, there is a pause period in the ablation. In this case, it is preferable that the predetermined period within which the air bubbles are broken down is arranged in this pause period. In accordance with an embodiment of the present invention, the steps 410 and 420 may be repeatedly performed so as to continually obtain clearer ultrasound images. This will help to better control the ablation process.
It should be noted that the above-mentioned embodiments illustrate rather than limit the invention and that those skilled in the art would be able to design alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word "comprising" does not exclude the presence of elements or steps not listed in a claim or in the description. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The usage of the words first and second, et cetera, does not indicate any ordering. These words are to be interpreted as names.