JPH0244281A - Positron ct apparatus scanning mechanism - Google Patents

Abstract

PURPOSE:To enhance sampling characteristics at the time of gate measurement by providing a mechanism for controlling a scanning speed so that the scanning cycle of a detector ring always becomes non-synchronous to the heartbeat period of an electrocardiogram. CONSTITUTION:In the scanning mechanism of this CT apparatus, a heartbeat cycle Tc is measured at first by an electrocardiograph 1. This heartbeat cycle Tc, a sampling delay time T1, a measuring time T2 and the total measuring time TT are inputted to a microcomputer 2 to calculate the optimum scanning cycle TS. The computer output signal of the scanning cycle TS thus calculated is converted to speed data due to frequency by a motor driver and said speed data is inputted to a pulse motor 3 and transmitted to the drive mechanism of a scanning device to set a wobbling scanning speed and the sampling characteristics at the time of gate measurement are markedly enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a positron CT apparatus, and more particularly to a scanning mechanism suitable for measurement by electrocardiogram-gated cardiac angiography.

[Conventional technology]

A positron CT device (hereinafter abbreviated as a PCT device) is a device that generates a distribution image within a subject of a positron-emitting nuclide administered to a subject from measurement data of positron annihilation gamma rays. FIG. 2 is an overall view of the gamma ray detection section of the PCT device. A plurality of detection rings 4 are arranged in an annular shape surrounding the subject 5. A plurality of four detector rings detect gamma rays emitted from the subject 5 and receive them as information inside the subject. FIG. 3 shows an example of the movement of the detector ring and detector in wobbling scanning. When the center point of the detector ring 4 moves on the orbit 6 (
This is called wobbling), and each detector draws a circle with its center point on the circumference 7. This wobbling allows gamma rays to be detected at far more positions than the number of detectors the device is actually equipped with, increasing the sampling density. In addition, the influence of detector arrangement is reduced, and quantitative performance is improved.

In the conventional scanning mechanism of a PCT apparatus equipped with the above-mentioned quabbling function, the wobbling scanning speed is determined at the time of designing and adjusting the apparatus, and is used as a scanning speed unique to the apparatus.

[Problem to be solved by the invention]

When the PCT device according to the prior art performs measurement using electrocardiogram-gated cardiac imaging (hereinafter referred to as gate measurement), if the heartbeat cycle of the subject 5 matches the scanning cycle, the position of the detector ring 4 at the time of sampling will always be unchanged,
This is the same state as if the ring were always at rest. Furthermore, even if the two periods do not completely match, if they are synchronized with a short period, sampling points will be biased. As described above, the above-mentioned conventional technology has a large influence on the measurement of the heartbeat cycle, and there is a possibility that the sampling density and distribution condition may be significantly reduced. Furthermore, since the data obtained has poor reproducibility, there are also problems in terms of quantitativeness and reliability.

An object of the present invention is to prevent deterioration of sampling characteristics and quantitative performance during gate measurement in a PCT apparatus.

[Failure to solve the problem]

The above object is to increase the scanning speed so that the scanning period of the detector ring is always asynchronous with the electrocardiogram heartbeat period in a positron CT device that is equipped with a mechanism for scanning a detector ring and can change the scanning speed of the detector ring. This is achieved by a positron CT apparatus characterized by being provided with an adjustment mechanism.

[Effect]

By constantly scanning the PCT device using a wobbling scan, for example, at a scanning period that is not synchronized with the heartbeat cycle,
The influence of the heartbeat cycle on the measurement results during gated measurement is eliminated, and the same sampling characteristics and quantitative performance as during normal measurement can be guaranteed during gated measurement.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. 1st
The figure shows an example of a PCT device equipped with a full wobbling function. During gate measurement with a PCT device equipped with a wobbling function, first the heartbeat cycle Tc' is measured using the electrocardiograph 1.
Measure. This Tc and the sampling delay time T1
, the measurement time T2, and the total time T2 are input into the microcomputer 2, etc. to determine the optimal scanning period Ts''. Fig. 5 shows the relationship between the beat period and the measurement time. As shown in Fig. 5. As shown, measurement is performed only during the measurement time T2 during the heartbeat cycle Tc0, and the measurement is started after a delay time T1 from the reference point.The calculation method for T8 is as follows: This will be explained with reference to FIG. 4, which is shown on orbit.

The heartbeat cycle Tck is divided by the sampling time T2, the quotient is Nl, and the remainder is α. However, Nl is a natural number, and α is a positive value smaller than Tz. Next, if the heartbeat cycle Tc is N2
The sum of (Nl −1) times the sampling time T2 and the previously set α is defined as the scanning period Ts.

That is, Ts=N2XTc+(Nl 1)XTz+α −(
1) However, N2 is O or a natural number. T as above
By setting mf, the position of the detector ring 4 at the first moment of the sampling time matches the position of the detector ring 4 at the last moment of the (N*+1) previous sampling time.

That is, in the second cycle, measurement is started from a time point shifted later than the previous cycle by Tz. If the scanning speed is to be slowed and the total time is to be lengthened, Nz should be set sharply, and if the scanning speed is to be slowed down, Nzft may be set to be small. N2 is determined by considering the speed setting range of the scanning device, the total time T〒, etc. Also, when N3 times the scanning period Tg is divisible by the measurement time T2, N3 is.

This is the minimum number of scans required to make the presence time of the detector ring 4 equal at each point on the orbit of the quab ring.

However, Ns is a natural number. Therefore, the total time must be a multiple of N3 times the scanning period, so the actual measurement time 11 is determined as a multiple of N3 times the scanning period TII that is closest to Tt.

The computer output signal with the scanning period Tg obtained as described above is converted into frequency-based speed information using a motor driver or the like, and the information is input to the pulse motor 3 or the like. The rotational speed of the pulse motor 3 is adjusted according to the frequency, and this is transmitted to the drive mechanism of the scanning device, thereby setting the scanning speed of the scanning ring.

If the T'τ time is measured in the above embodiment, mechanically unbiased sampling can be achieved.

〔Effect of the invention〕

According to the present invention, the sampling characteristics during gate measurement are significantly improved, so that better images can be obtained. In addition, reliable data can be obtained in a short period of time when measurement is performed using conventional methods, and quantitative performance is also improved.

[Brief explanation of the drawing]

Fig. 1 is a diagram of an embodiment of the present invention, Fig. 2 is a diagram of a detector section, and Fig. 3 is a diagram of an embodiment of the present invention.
4 is a diagram showing the displacement of the center position of the detection ring due to wobbling, and FIG. 5 is a diagram showing the relationship between heartbeat cycle and measurement time. 1... Electrocardiograph for measuring the heartbeat cycle of the subject, 2
...Microcomputer for calculating optimum scanning period, 3.
...Pulse motor for scanning speed adjustment, 4...Detector ring, 5...Object, 6...Trajectory of the center point of the detector ring, 7...Operation of each detector during wobbling scanning. Fuuta

Claims (1)

[Claims] 1. In a positron CT device equipped with a mechanism for scanning a detector ring and capable of changing the scanning speed of the detector ring, the scanning speed is adjusted so that the scanning period of the detector ring is always asynchronous with the electrocardiogram heartbeat period. A positron CT device characterized by being equipped with a mechanism.