JPH09269378A - Nuclear medical inspection apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a nuclear medical inspection apparatus which can start an inspection without waiting for the attenuation of radioactivity. SOLUTION: The data acquisition operation of a formal inspection by dosing a radioisotope (RI) is performed by a data acquisition memory 3, and background data is obtained by a data acquisition operation, in every prescribed time, which is repeated a plurality of times just before the data acquisition operation. On the basis of the measured background data, an Ao computing circuit 4 computes background radioactivity Ao at a point of time of t=0 by the method of least squares, a BK computing circuit 5 estimates a background value BK in the formal inspection on the basis of the Ao by using an expression which is derived from the theory of attenuation, and a correction circuit 6 subtracts the BK from the measured data on the formal inspection so as to be corrected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a PET (positron emission computer tomography) apparatus, a SPECT (single photon emission computer tomography) apparatus, a nuclear medicine inspection apparatus such as a gamma camera.

[0002]

2. Description of the Related Art A nuclear medicine examination apparatus detects radiation from an outside of a human when a drug labeled with RI (radioisotope) is administered to a human body and accumulates in a specific organ. To get information. A gamma camera simply shoots a projected image viewed from one direction.
In the T device and the SPECT device, the collected data is subjected to image reconstruction processing by a computer to reconstruct a distribution image at a specific cross section.

In these nuclear medicine examination devices, when the same subject (patient) is administered with RI several times and each is measured, the previously administered RI remains in the body and is measured as background. It Usually, in order to prevent this, the next inspection is performed after waiting for the decay due to the half-life.

For example, PET using O-15 labeled water
In the inspection by the device, the inspection itself (data collection) is completed in about 90 to 180 seconds, but in order to measure the resting state and the loaded state, the inspection is performed 2 to 6 times. At this time, the half-life of O-15 is about 2 minutes, so 1
With the interval of 0 to 15 minutes, it is sufficiently attenuated, and the next inspection can be performed without the influence of the background.

[0005]

However, if the second and subsequent examinations are performed after waiting for the attenuation as in the conventional case, the entire examination time is extended, the patient is restrained for a long time, and the throughput is reduced. It's a problem.

In view of the above, the present invention makes it possible to start the next inspection even when the damping is not sufficient,
It is an object of the present invention to provide a nuclear medicine examination apparatus which does not restrain a patient for a long time and can improve the throughput.

[0007]

In order to achieve the above object, in a nuclear medicine examination apparatus according to the present invention, background data collection is repeated a plurality of times immediately before data collection of the main examination by RI administration. The background value at the time of this inspection is estimated using the method of calculating the background radioactivity at the reference time by the method of least squares from the data of the above and the formula derived from the theory of attenuation from the obtained background radioactivity at the reference time. Means to do
It is characterized in that means for correcting the data by subtracting the estimated background value from the data of the main inspection is provided.

When data is collected just before the main examination performed by administering RI, background data at that time can be collected. This is collected at several sampling points, and the background radioactivity at the reference time is obtained using the least squares method. As a result, it is possible to prevent the statistical error from increasing with one point of data. If the background radioactivity at the reference time is obtained in this way, the background value at the time of the main inspection can be estimated by using the formula derived from the theory of attenuation. Estimated background values can be subtracted from the data collected by this study to correct for background effects. Therefore, the next inspection can be started without waiting for the attenuation.

[0009]

Next, embodiments of the present invention will be described in detail with reference to the drawings. In FIG.
It is assumed that the head of the subject 1 is inserted into the gantry 2 of the PET device and the head is inspected. A large number of radiation detectors are arranged in a ring shape on the gantry 2, and the head is inserted into the ring. When the radiation from the RI in the head is incident on any of the detectors that surround it in a ring shape, an event signal indicating an incident event and a position signal indicating the incident position are output to the data acquisition memory 3. Sent. In the data collection memory 3, the event signal is counted at the address designated by the position signal. The raw data collected in this way is sometimes called a sinogram.

For example, as shown in FIG. 2, if RI is administered at a time point t1 and data is collected from the time point t1, data collection is started from a certain time point (t = 0) immediately before that time point. In the data collection before this main inspection, event signals are integrated within a unit time, and this is repeated n times for each unit time to obtain n pieces of data. At this point in time, the radiation from the RI remaining in the previous inspection is detected, and this becomes the background measurement data of the main inspection performed from t1. If this background measurement data is Abk (t), Abk (1), Abk (2),
.., Abk (n) n pieces of background measurement data are obtained.

Here, in general, the radioactivity A at a certain time t
(T) is attenuated with the passage of time as represented by the following mathematical formula 1.

[Equation 1] Ao is the radioactivity at the reference time (t = 0), and λ is the attenuation constant. With respect to this λ, when the half-life is T ′, there is a relationship of the following mathematical formula 2.

[Equation 2]

Since the above-mentioned formula 1 holds true also for the background radioactivity at issue here, the measured background radioactivity Abk (t) is Ao which minimizes the squared error expressed by the following formula 3. It can be seen that the background radioactivity at t = 0 can be obtained by calculating

(Equation 3) In this equation, n is the sampling number and λ is a known damping constant, so Ao can be obtained by the following equation 4 by the least square method.

(Equation 4) It should be noted that since the data at the time of t = 0 is Ao itself, it seems that the data at t = 0 should be measured and used, but this will include a large statistical error and the accurate Ao. Can't ask. That is, the accurate Ao that is not affected by the statistical error is obtained from the n pieces of data.

This calculation is performed by the Ao calculation circuit 4. That is, the Ao calculation circuit 4 uses the n pieces of background measurement data collected in the data collection memory 3 to perform the above calculation to calculate the background radioactivity Ao at t = 0. The Ao value thus obtained is sent to the BK calculation circuit 5.

The BK calculating circuit 5 collects data (t1 to t2) in the main inspection performed from time t1 to t2.
The integrated value BK of the background count that is likely to be included in the (integrated value of the count up to) is calculated.
That is, the main examination is performed from the time point t1 to the time point t2 when RI is administered, and the integral value of the count during that time is obtained as the main examination data. In the meantime, the integrated value BK of the background count is measured as shown in FIG. That is, the measurement data D in this inspection includes BK.

The integrated value BK of the background count from t1 to t2 is calculated by the following expression 5 based on the above expression 1.

(Equation 5) When the BK value is obtained from the BK calculation circuit 5 by this calculation, it is sent to the correction circuit 6.

In the correction circuit 6, a calculation for subtracting BK from the measurement data D in the main inspection is performed as shown in the following formula 6. Do = D-BK Equation 6 That is, as shown in FIG. 2, the background data BK can be subtracted from the measurement data D to obtain the true data Do that is not affected by the background.

The background BK (also designated by the position signal) is obtained from the individual data (integrated value of the count for each address designated by the position signal) D of the sinogram in this inspection collected by the data collection memory 3. (Obtained for each address) is subtracted to correct the effect, and the corrected data is sent to the image reconstructing device 7 to reconstruct the image using an algorithm such as the back projection method. It This reconstructed image data is recorded in the magnetic disk recording device 8 or the like.

In the above, the correction for subtracting the background is performed on the integrated value, but it may be configured to be subtracted for each event. Further, instead of correcting the raw data (sinogram), it is possible to correct each pixel of the reconstructed image.
In this case, also for BK, the image reconstruction processing is performed to obtain the background integrated value for each pixel, and this is subtracted from the pixel value for each pixel of the image reconstructed from the data D of the main inspection. Although the circuits for performing the respective operations such as the Ao calculation circuit 4, the BK calculation circuit 5, the correction circuit 6 and the like are configured as hardware in the above, they can be configured in software. Further, although the PET apparatus has been described above as an example, it is needless to say that the same can be applied to other nuclear medicine inspection apparatuses such as a SPECT apparatus and a gamma camera.

[0019]

As described above, according to the nuclear medicine inspection apparatus of the present invention, it is possible to perform correction so as to eliminate the influence of the background. Therefore, the next inspection can be started without waiting for the attenuation. This allows
Since the next examination can be started even when the patient is not sufficiently attenuated, the problem of restraining the patient for a long time is solved and the throughput is improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a graph showing the time course of radioactivity.

[Explanation of symbols]

 1 Subject 2 Gantry of PET Device 3 Data Collection Memory 4 Ao Calculation Circuit 5 BK Calculation Circuit 6 Correction Circuit 7 Image Reconstruction Device 8 Magnetic Disk Recording Device

Claims (1)

[Claims] 1. A means for calculating a background radioactivity at a reference time by a least-squares method from data obtained by collecting background data at predetermined intervals repeated a plurality of times immediately before the data collection of this test by RI administration. The method of estimating the background value at the time of this inspection by using the formula derived from the theory of attenuation from the background radioactivity at the reference time and the data correction by subtracting the estimated background value from the data at this inspection A nuclear medicine examination apparatus comprising: means for performing.