JPS60215352A - Electrocardiac synchronous nmr imaging method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application Field The present invention relates to an electrocardiogram-gated NMR method in which an image of the heart of a subject such as a human body is constructed by an NMR signal excited in synchronization with the 6 beats of the heart. Concerning imaging methods.

(B) Prior Art Generally, in order to obtain an NMR image of the heart, it is necessary to sample the NMR signal generated by an excitation pulse synchronized with the 6-stroke pulse in order to improve the temporal resolution. In such a conventional electrocardiogram gated NMR imaging method, an image is constructed using the NMR signals obtained in this way as they are.

However, because the human 6 beats fluctuate from moment to moment, the time interval between one excitation pulse and the next always fluctuates, so the intensity of the obtained NMR signal changes with each sampling. There is. That is, normal NMR
In imaging, since excitation pulses are generated at predetermined constant time intervals, it is possible to sample NMR signals due to excitation pulses in a state where the degree of relaxation of magnetization M (a collection of nuclear magnetic moments) is always constant.

However, as mentioned above, when the excitation pulse is generated in synchronization with the 6th beat, the generation cycle of the excitation pulse is not always constant;
Excitation pulses are generated at different times when the degree of relaxation of magnetization M is always different, and the NMR signal intensity takes different values depending on the period of the excitation pulse. If the T+ (longitudinal relaxation time) value is calculated using such a signal, it is obvious that the result will contain a considerable error, and no matter what imaging method is used, the image obtained cannot be said to be accurate. hard.

(c) Purpose The present invention has been made in view of the above, and it is possible to calculate error-free Tl values etc. from NMR signals obtained by excitation pulses at irregular time intervals, thereby making it possible to calculate electrocardiographically gated NM.
The purpose of this invention is to provide a method that can make images in R imaging more accurate.

(d) Structure The present invention is characterized by generating an excitation pulse in synchronization with the test subject's test subject, sampling the NMR signal, and actually measuring and storing the test interval for each sampling. The present invention is configured such that the intensity of sampling data is corrected using a corresponding predetermined interval, and the corrected data is used to image the heart of a subject.

(e) Examples Embodiments of the present invention will be described based on the drawings.

FIG. 1 shows an overall configuration diagram of an electrocardiogram-gated NMR imaging apparatus that generates excitation pulses using an ECG (electrocardiogram) signal as a synchronization signal.

The subject W is placed in a shielded room 1 of the NMR device, and is connected to an ECG device 3 via an ECG cable device 2 that is specially designed to prevent external noise from being introduced into the space of the shielded room 1. Ru. Inside the shield room 1 are static magnetic field coils, gradient magnetic field coils, and RF coils (not shown).
Coils etc. are arranged. RF pulses from the RF coil and control signals for gradient magnetic fields are supplied from a sequencer 5 under the control of a computer system 4. The output timing of the RF pulse from the sequencer 5 and the reading timing of the NMR signal are determined by the computer system 4 using, for example, the generation of an R wave of the ECG signal from the ECG device 3 as a trigger.
A predetermined delay time is determined by counting the clock pulses from the trigger device 7 with a counter 6, and is determined by a signal generated from a trigger device 7.

FIG. 2 shows a time chart of the ECG signal and the NMR pulse sequence, and the operation of the embodiment of the present invention will be explained based on this diagram. In this example, we will discuss the case where the NMR signal is read using the inversion recovery method.The NMR pulse sequence will differ slightly depending on the method of reconstructing the image, but here we will discuss the case where the NMR signal is read using the inversion recovery method. A case will be described in which a method of detecting signals and performing imaging is adopted. Although this NMR pulse sequence is well known, the hour wheel will be explained below.

A trigger is output when an R wave of the ECG signal occurs. After the trigger output, a preset delay time tgd
Activation of one cycle of the pulse sequence is applied to f&. First, a 180° pulse is applied, followed by a preset inversion recovery time t.

A 90° pulse is applied after . This 90°
The echo generated by reversing the gradient magnetic field at the time of pulse generation is detected after a predetermined time ted determined by the time function of the static magnetic field.

When an echo is generated by such a pulse sequence, the solution of Bloch's equation after applying the 18° pulse is corrected for the decrease in intensity due to repetition, and the T2 (transverse relaxation time) due to the echo is also corrected. Taking this into account, the magnetization parallel to the direction of the static magnetic field (can be expressed as longitudinal), where MO is the initial value of the longitudinal magnetic strength, T is the pulse sequence period, and (τl + τ2) is the magnetic gradient applied by the gradient magnetic field. The time corresponds to tea in the figure. Since T takes a constant value in normal NMR imaging, T1 can be immediately calculated by treating the term T2 as a constant.

As mentioned above, in electrocardiographic gated NMR imaging, since the period T of the pulse sequence is different each time, it is not possible to calculate an accurate T1 value using Equation 11.

In the embodiment of the present invention, the pulse sequence period Tl'' that changes each time is determined and memorized by actually measuring 6 pulse periods from the ECG signal, and each raw sampling data of the NMR signal is measured by the corresponding T)''. to correct.

In equation (2) and FIG. 2, tQ, tgd,
Since ted(-τ1+τ2) is a constant during measurement, the only variable is T4. For example, T −tl+t
Calculate the error-free Tl value by adding t4 +t5 +ta to the 2+t3 T1 piece and storing it, and using this to correct the data for each sampling using equation (2) and subtracting the T1 value. If the calculation results are used for imaging, the resulting image will be accurate.

In addition, in the above embodiment, the correction method was explained when the NMR signal is read by the inversion recovery method, but even if the saturation recovery method is used, the period TA of the pulse sequence obtained by actually measuring the time interval of 6 beats. Of course, it is possible to correct by using .

Effect) As explained above, according to the present invention, electrocardiogram gated NMR
Even if there is a change in the 6 beats of the subject in the imaging method, the time interval of the 6 beats is actually measured and stored, and the detected data is corrected using that time and used to reconstruct the image. , it is possible to obtain more accurate images with no errors compared to conventional methods.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram of an electrocardiogram gated NMR imaging apparatus, and FIG. 2 is an operational explanatory diagram showing a time chart of an ECG signal and an NMR pulse sequence when an embodiment of the present invention is applied to an inversion recovery method. 1- Shield room 2-E CG cable device 3-・ECG device 4-Computer system 5- Sequencer 7-) Riga device Patent applicant Shimadzu Corporation representative Patent attorney Arata Nishida Figure 1

Claims (1)

[Claims] In a method for obtaining an NMR image of a subject's heart by generating an NMR excitation pulse in synchronization with the 6 beats of the subject and sampling the NMR signal excited by the pulse, each of the 6 beats at the time of sampling is The interval is actually measured and memorized, the intensity of the data obtained by the above sampling is corrected using the corresponding predetermined interval, and the corrected data is used to construct an image of the subject's heart. Characteristic electrocardiogram-gated NMR imaging method.