JPH04352971A - In vivo temperature measuring method - Google Patents

Abstract

PURPOSE:To obtain a two-dimensional temperature distribution data in vivo with high accuracy and under low intrusion by combining a probe method with an EPI method of using a superhigh speed MRI device, in an in vivo temperature measuring method useful for heating control or the like in a hyperthermistor (heating treatment). CONSTITUTION:In a tested person P placed in a magnet 20 of a superhigh speed MRI device, probes 30a to 30b are pierced in several parts, for instance, in a belly and also mounting an applicator 21 for heating. On the other hand, an RF probe 24 for receiving an MR signal from the tested person P is connected to a data collecting computer through respective preamplifiers 25a, 25b with a temperature measuring device 26 to which the above-mentioned probe is connected. A T1 value before heating the living body and T1, T2 value images are collected to sort a region in vivo based on these images. Next, the living body is heated to obtain increase amounts of the T1 value in each region and a temperature data by heating, and by utilizing a proportional relation of both the increase amounts, a temperature of a region from the T1 value of a region, not pierced with the probe, is calculated.

Description

[Detailed description of the invention]

0001 [Purpose of the invention]

0002

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring temperature inside a living body, which is useful for controlling heating in hyperthermia.

0003

2. Description of the Related Art One method of cancer treatment is the combination of radiation irradiation and hyperthermia (warming treatment). In the case of hyperthermia, it is necessary to easily heat superficial and localized tumors to some extent.
Microwave heating is used.

Microwaves (very short waves) have a frequency of 30
Electromagnetic waves from 0MHz to 30GHz, and even UHF
(frequency 300MHz to 3GHz) and SHF (frequency 3
GHz to 30 GHz), but the UHF band is mainly used for microwave heating.

FIG. 5 is a configuration diagram of a microwave heating system (from Tasaka et al., "Radiology System Special Volume 3 ``Hyperthermia'', p. 63 (Nakayama Shoten, 1987)). An instruction is given to the temperature control circuit 2 through the panel 1, and the microwave oscillator 3 oscillates microwaves.The oscillated microwaves are subjected to necessary frequency and phase tuning and matching in the tuning and matching circuit 4. , is radiated from the applicator 5.

[0006] The microwave efficiently enters the living body 6 through a bolus 7 such as a water bag that is in close contact with the living body 6 and also has a cooling function, and warms the tumor 8 while being converted into heat. At this time, the temperature of the tumor 8 and its surrounding tissue is sensed by a suitable temperature sensor 9 such as a thermocouple or thermistor, and measured by a temperature monitor 10. When the measured temperature exceeds the set temperature of the tumor 8, the temperature monitor 10 performs feedback control of the microwave oscillation output via the temperature control circuit 2. Furthermore, the temperature detected by the temperature sensor 9 is stored in the data recording section 1.
1 as appropriate.

[0007] In hyperthermia, the tumor site to be treated must be heated to a certain temperature, for example, 42° C. or higher, while the temperature of the normal site must be kept below a certain limit. Therefore, it is fundamentally important to measure the temperature of tumor sites and normal sites inside the living body and to control the heating process. Conventionally, there have been four methods for measuring the temperature inside a living body:

1. Probe method: Several thin probes with a diameter of 1 mm or less equipped with temperature sensors such as a thermistor, thermocouple, or optical sensor are inserted into or near the affected area. It is the most accurate (error ±0.1°C).

2. Implantation method: A temperature sensor is implanted near the tumor site and left in place until the treatment is completed. At this time, the skin is sutured and signals are transmitted to the outside using a telemeter system.

3. Non-invasive method: Energy is sent from outside the body and utilizes the fact that the properties of the living body as an energy propagation medium change with temperature. Ultrasonic devices, X-ray CT devices, MRI devices, etc. are used. It has the major advantage of being non-invasive and has excellent spatial resolution.

4. Monitoring method: Measure the deep body temperature using a core thermometer, etc. This method is also performed non-invasively.

0012

[Problems to be Solved by the Invention] Incidentally, the most basic performance of a temperature measurement system is the resolution (accuracy) and spatial resolution of temperature measurement values. In hyperthermia, the temperature resolution is 0.1 to 1℃, and the spatial resolution is 0.5 to 2℃.
It is often considered within a range of about cm.

However, each of the above-mentioned four temperature measurement methods has the following disadvantages. First, the "probe method" has a high resolution of temperature measurement values and a very fine spatial resolution (about 1 mm), but it is extremely invasive, so it is not possible to insert multiple probes. For this reason, the distance between each probe becomes wide, and there is a drawback that two-dimensional temperature distribution cannot be measured continuously.

The "implantation method" has the same accuracy as the probe method, but it is similar to the probe method in that it cannot continuously measure two-dimensional temperature distribution because the temperature sensor cannot be moved. There are drawbacks.

[0015] In the "non-invasive method", it is difficult to calibrate the parameter (T1 value in MRI) used for temperature measurement with the actual temperature of the tissue, making it difficult to improve accuracy. Furthermore, when using MRI, the pulse sequence of the gradient field echo method ('Magnetic Resonance') is generally used as shown in Fig.
ce Imaging'p96“Measuremen
to of temperature distribution
tion ”David D. Stark, M.D.
．． et al, The C. V. Mosby Co
mpany, 1988), the data collection time Ts
MR signals are received to obtain T1 and T2 values, but this pulse sequence requires several minutes of imaging time, so
There is a drawback that the temperature distribution immediately after heating cannot be accurately measured due to the heat dissipation effect due to blood flow and the like. In FIG. 6, Gs,
Ge and Gr are a slice direction gradient magnetic field, a phase encoding gradient magnetic field, and a readout gradient magnetic field, respectively, TR is a repetition time, and Tg is a time difference from data collection to the next non-selected 90° pulse.

[0016] The "monitoring method" uses a core thermometer, so
The drawback is that it is unclear which part of the body is being measured, just because it measures the core temperature.

The present invention has been made in view of the above circumstances, and is useful for controlling the heating process in hyperthermia.
The purpose of this invention is to provide a method for measuring temperature inside a living body that has excellent temperature and spatial resolution and is less invasive. [Structure of the invention]

[0018]

[Means for Solving the Problems] In order to solve the above problems, the present invention provides (1) a step of inserting a probe equipped with a temperature sensor into a living body and collecting temperature data before heating the living body; and (2) the T1 value and T1,
(3) collecting a T2 value image; and (3) the T1, T
(4) heating the living body, and immediately after heating, T1 pulse sequence using the EPI method; a step of collecting a value image and temperature data from the temperature sensor to obtain an increment in the T1 value of each region due to heating and an increment in the temperature data; (5) a step of determining the T1 value of each region due to the heating; The present invention provides a method for measuring temperature inside a living body, which includes a step of calculating the temperature of a region from the T1 value of the region into which a probe has not been inserted, using the proportional relationship between the increment of the temperature data and the increment of the temperature data.

[0019]

[Operation] The method of measuring temperature inside a living body according to the present invention is the EPI (echo planar imaging) method, which uses a highly accurate probe method and an ultra-high-speed MRI device that is non-invasive and has a short imaging time (several tens of milliseconds). It is a combination of temperature measurement data using a probe method and EPI data before and after biological warming.
Collect T1 value image data using the method. Temperature measurement data using the probe method cannot obtain a large number of measurement points, but on the other hand, T1 values can be obtained from all regions of T1 value image data. Therefore, by using the proportional relationship between the increment in T1 value due to heating and the increment in temperature data, we calculated the proportionality constant between the two in the region where the probe is located, and calculated this as the T1 value in the region without the probe. Apply. In this way, two-dimensional temperature distribution data within the body can be obtained while calibrating temperature measurement data obtained by MRI using highly accurate probe-based temperature measurement data.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 to 4.

FIG. 1 is a block diagram of a temperature measurement system that implements the method of the present invention. That is, the subject P, who has had probes inserted into several places on his body, is exposed to the magnet 20 of the ultra-high-speed MRI device.
lie within. Furthermore, the subject P is made to wear an applicator 21 having a built-in microwave antenna for heating. The applicator 21 is connected to a microwave oscillator 23 via an amplifier 22 and is supplied with microwave power.

On the other hand, the RF probe 24 that receives the MR signal from the subject P is connected to a computer for data collection via a preamplifier 25a, and the probe inserted into the subject P is also probed. Needle type temperature measuring device 26 and preamplifier 25
It is also connected to a computer for data collection via b. Note that the RF probe for transmission is not shown here.

FIG. 2 is a sectional view of the abdomen of the subject P. Five probes 30a to 30e are inserted into the abdomen of this subject P, and temperature sensors 31a to 31 such as thermistors, thermocouples, and optical sensors are attached to the tips of the probes 30a to 30e in the abdomen.
e is attached. Among these, temperature sensor 31e is located in tumor tissue X, and other temperature sensors 31a to 31d are located in normal tissues A to D, respectively. Note that the probes 30a to 3
A PVA (polyvinyl acetate) gel marker 32 is applied to the body surface where Oe has been inserted so that the insertion point can be clearly identified.

[0024] Therefore, according to this temperature measurement system,
First, before heating the subject P with microwaves, the temperature of each tissue (region) is measured using the temperature sensors 31a to 31e. That is, the temperatures detected by the temperature sensors 31a to 31e are measured by the probe type temperature measuring device 26 through the probes 30a to 30e, and sent to the data collection computer via the preamplifier 25b.

On the other hand, an ultrahigh-speed MRI apparatus uses the EPI method to obtain one frame's worth of T1 and T2 value images in a short period of several tens of milliseconds. The EPI method generates multiple echoes at high frequency, as shown in the pulse sequence of FIG. 3, and collects data in Fourier space for each echo. This EPI method collects the data that makes up the entire image using one or several free induction decays (FIDs) in one excitation of less than 1 second.
Collect from among. Since the EPI method requires ultra-high-speed switching and sampling of gradient magnetic fields, which places a severe load on the system, ultra-high-speed MR equipped with special hardware is required.
This is done in the I device.

From the two images in which the delay time Td between the pulse sequences of the EPI method was changed, the ``selective irradiation process'' of the RF pulse was determined.
If the correction is taken into account, an accurate T1 value image without errors caused by body motion artifacts can be obtained (P. Mansfield).
d et al. “Measurement of
T1 by echo-planarimaging
and the construction of
computer-generated images
"Phys. Med. Biol., 1986,
Vol. 31, No. 2, pp113-124).

In this case, the MR signal collected by the RF probe 24 is sent to the data collection computer via the preamplifier 25a, where it is detected and the T1 value and T2 value are determined. If an image is reconstructed based on the T1 value and T2 value, an image as shown in FIG. 2 can be obtained, so it can be seen where the temperature sensors 31a to 31e are located and to which region they belong.

Now, when the temperature data measured by the temperature sensor and the T1 and T2 values of the entire image area are obtained before heating the subject P, the next step is to oscillate microwaves from the microwave oscillator 23. let This microwave enters the subject P from the applicator 21 via the amplifier 22, and the inside of the subject P's body is heated.

In this embodiment, as soon as this heating is performed, the temperature sensors 31a to 31e start measuring the temperature, and
T1 values are also collected using the EPI method in the same manner as before heating. In this way, the temperatures t1 and t2 before and after heating at the point where the temperature sensor was inserted are obtained for normal tissues A to D and tumor tissue X, respectively, and the T1 values before and after heating at these points, T1 (t1) and T1 (t2) can also be seen.

By the way, it is known that the time constant T1 value of the spin-lattice relaxation process is influenced by temperature;
As shown in FIG. 4, there is a proportional relationship between the increment of T1 value and the increment of temperature in each region as shown by regression lines a, b, and c (regression lines in different regions). 'Magnetic Resonance I
maging'p97 “Measure-ment
of temperature distribution
on ”David D. Stark, M.D.
et al, The C. V. Mosby Com
Pany, 1988). That is,

[0031]

[Math 1]

[0032]

Therefore, in this example, at this point, for each tissue A to D and X, the values on both sides of equation (1),
and the proportionality constant α(=(t2 −t1)/{T
1 (t2)-T1 (t1)}).

[0034] Then, for each tissue A to D and

[0035]

[Outside 1]

[0036] Then, the temperature at that point is

[0037]

[Outside 2]

[°C] is calculated using the following equation (2).

[0039]

[Math 2]

In this embodiment, the parameter T1 value, which reflects the temperature of each region, is calibrated using temperature measurement data using a highly accurate probe method, and accurate temperature can be obtained from this T1 value. . Thus, α is different for each organization.
applied at many locations within the same organization.

[0041]

[Outer 3]

Find these

[0043]

[Outside 4]

[0044] is expressed by the corresponding brightness to form a two-dimensional image. At this time, the temperatures of the same tissue (determined from T1 and T2 values determined by ultra-high-speed MRI and anatomical findings) are calibrated all at once. In this way, according to this embodiment, a continuous two-dimensional temperature distribution can be measured accurately and in a short time, although the invasiveness is extremely low.

Furthermore, according to the method of this embodiment, all T1 of one frame of MR image used for creating the temperature distribution
Since the value can be collected in tens of milliseconds, this T1 value is not affected by heat dissipation due to blood flow and is an accurate value immediately after heating. Furthermore, it is possible to measure temperature without errors caused by body movement artifacts.

[0046]

[Effects of the Invention] As explained above, according to the present invention,
A two-dimensional continuous temperature distribution inside the body can be obtained accurately and in a short time in a minimally invasive manner without artifacts caused by body movements or the effects of heat radiation. Therefore, in hyperthermia, appropriate heating control can be performed based on this temperature distribution data.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a temperature measurement system that implements a method according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of the abdomen of a subject whose temperature is measured by the temperature measurement system.

FIG. 3: EP performed by a method according to an embodiment of the present invention
The figure which shows the pulse sequence of I method.

FIG. 4 is a graph showing the relationship between the increment in T1 value and the increment in temperature in each region of the living body.

FIG. 5 is a configuration diagram of a microwave heating system.

FIG. 6 is a diagram showing a pulse sequence used in a conventional temperature measurement method using MRI.

[Explanation of symbols] 20 Ultra-high-speed MRI device magnet 21 Applicator 22 Microwave oscillation device 24 RF probe 26 Probe type temperature measuring device

Claims (1)

[Claims] Claim 1: (1) a step of inserting a probe equipped with a temperature sensor into the inside of a living body and collecting temperature data before heating the living body; and (2) a pulse sequence of the EPI method in an ultra-high-speed MRI device. T1 value before biological warming and T1
, T2 value images; (3) the T1 value image;
, the step of dividing the internal regions of the living body based on the T2 value image and associating these regions with the position of the probe, and (4) heating the living body, and immediately after this heating, applying a pulse sequence of the EPI method. T1 value image and temperature data from the temperature sensor
(5) determining the increment in the T1 value and the increment in the temperature data of each region due to the heating; A method for measuring temperature inside a living body, which includes the step of calculating the temperature of an area from the T1 value of the area where a probe is not inserted, using a proportional relationship.