Patent Application
20060280284
The present invention is directed to an imaging control method and an X-ray CT (computed tomography) apparatus, more specifically to a method of controlling the timing of start of imaging of the X-ray CT apparatus, and an X-ray CT apparatus for controlling the timing of start of imaging.
When imaging a heart by means of an X-ray CT apparatus, the heart is imaged while collecting the electrocardiogram signal, a predetermined number of view data around the desired view in the electrocardiogram phase is used to reconstruct an image. The imaging is conducted in helical scan or the like, while the patient is directed to hold the breath during imaging, and the data collection is conducted by an X-ray detector of multi slice type and the like (see for example patent reference 1)
[Patent reference 1] JP-A-2004-275440 (pp. 3 & 5, FIGS. 1, 2, 8, and 9)
In order to obtain a reconstructed image of better quality, it is necessary to image when the heart rate is stably settled. However the heart rate is in general start changing since the start of breath holding and is not well settled immediately. The time needed until the heart rate is settled and the extent of variation of heart rate is dependent on patients. An image of better quality cannot be obtained if the imaging is started at the same time that the breath is held.
Therefore, an object of the present invention is to provide an imaging control method, which allows cardiac imaging of better quality, and an X-ray CT apparatus for controlling imaging as such.
(1) In an aspect of the present invention for solving the problem as have been described above, the present invention provides an imaging control method, for controlling the start timing of imaging by an X-ray CT apparatus, comprising the steps of: computing heart rate of a subject; and starting imaging when the heart rate is settled.
(2) In another aspect of the present invention for solving the problem as have been described above, the present invention provides an ray CT apparatus including an electrocardiogram signal collector device for collecting electrocardiographic signals of a subject, a data collector device for collecting data after imaging the subject by means of X-ray beam, a controller device for controlling the data collector device, and an image reconstruction device for reconstructing an image based on the data, the controller device comprising: a computer means for computing a heart rate based on the electrocardiogram signal; and a controller means for starting imaging when the heart rate is settled.
Preferably, the computation of heart rate is conducted on the heartbeats during a breath holding period, in order to prevent the breathing from affecting.
Preferably, the start of imaging is automatically conducted when the heart rate is settled within a predetermined range in order to automate the start of imaging.
Preferably, the start of imaging is manually conducted when the heart rate is settled within a predetermined range, in order to manually conduct the start of imaging.
Preferably, the manual start of imaging is conducted based on the indication that the heart rate is settled within the predetermined range, in order to facilitate the manual start of imaging.
Preferably, the manual start of imaging is conducted based on the indication of the transition of the heart rate or stability thereof, in order to facilitate the manual start of imaging.
Preferably, the stability is indicative of standard deviation of heartbeats in order to express the stability more precisely.
Preferably, the stability is indicative of differential of heartbeats in order to simplify the indication of stability.
The present invention in accordance with several aspects described above, starts imaging when the heart rate is settled by computing the heartbeats of the subject in order to control the start timing of imaging by the X-ray CT apparatus, allowing to achieve an imaging control method allowing cardiac imaging of better quality as well as an X-ray CT apparatus allowing control of imaging as such.
Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings.
The best mode for carrying out the present invention will be described in greater details herein below with reference to accompanying drawings. It should be understood that the present invention is not intended to be limited to the best mode for carrying out the present invention disclosed herein. Now referring to
As shown in
The data collected by the gantry 100 is input to the operator console 300. The operator console 300 also receives the electrocardiogram signal from the electrocardiograph 400. The electrocardiograph 400 is an exemplary embodiment of the electrocardiogram signal collector device in accordance with the present invention. The operator console 300 incorporates a data processing unit such as for example a computer, and the input data and electrocardiogram signals are stored in its memory. The operator console 300 reconstructs an image based on the data and electrocardiogram signals. The operator console 300 is an exemplary embodiment of the image reconstruction device in accordance with the present invention.
The reconstruction of an image is conducted by means of data for a half scan or a full scan around the view of desired electrocardiogram phase. Thus reconstructed image will be displayed on a display 302.
The operator console 300 controls the gantry 100 and the table 200. Under the control of the operator console 300, the gantry 100 images in a predetermined imaging condition, while the table 200 positions the subject 10 in an imaging field so as to be able to scan a predetermined part thereof. The operator console 300 is an exemplary embodiment of the control device in accordance with the present invention. The operator console 300 is also an exemplary embodiment of the computing means and of the control means as well in accordance with the present invention.
The positioning of the subject 10 is performed by means of the built-in position adjustment mechanism, which adjusts the vertical height of the top plate 202, and the lateral displacement of a cradle 204 on the top plate 202. The height adjustment of the top plate 202 is performed by swingingly pivoting a stem 206 on the center of attachment to its base 208.
An axial scan can be conducted by scanning while the cradle 204 stops. On the other hand a helical scan is conducted by scanning with the cradle 204 continuously displaced.
Now referring to
The X-ray radiation and detection device 110 revolves around the center axis passing through the image center or namely the isocenter O. The center axis is in parallel to the center axis of partial cylinder formed by the X-ray detector 150. By defining the direction of revolving center axis as z axis, the direction connecting the isocenter O with the focal point 132 as y direction, and the direction perpendicular to both z direction and y direction as x direction. The x-, y-, and z-axes are three axes of a revolved coordinate system around the center axis on z-axis.
Now referring to
Each of detector cells 154 forms a detector channel of the X-ray detector 150. The X-ray detector 150 thus is a multi-channel X-ray detector. The detector cells 154 may be formed by a combination of a scintillator and a photodiode.
The X-ray detector 150 as have been described above is also referred to as a multi-column X-ray detector or a multi-slice type X-ray detector. As the X-ray detector 150 is a multi-column X-ray detector, data for a plurality of slices can be obtained at once, allowing imaging of higher efficiency.
Cardiac imaging is conducted with the subject 10 holding the breath. The heart rate of the subject 10 during breath holding period transits in general as shown in
Now referring to
Alternatively, the stability of the heart rate may be indicated by the differential between heartbeats, instead of the standard deviation. The differential is a difference between the maximum heart rate and the minimum heart rate in successive adjoining plural heartbeats. The combination of successive adjoining plural heartbeats is movingly altered for each heartbeat. When indicating the transition of the heart rate as shown in
In view of the change in the heart rate as have been described above, it is preferable to conduct the imaging during the period in which the heart rate is settled. In the apparatus therefore, the timing of imaging is controlled so as to start imaging when the heart rate is stably settled. The control is performed in the operator console 300.
Now referring to
In step 403, the stability of the heart rate is computed. As the index of stability of the heart rate, the standard deviation for example is computed. The differential between heartbeats may be computed instead of or in addition to the standard deviation.
In step 407, it is determined whether or not the stability of the heart rate is within the tolerance range. The tolerance of the heart rate stability is predefined. The upper limit of the tolerance in the standard deviation may be defined as 1 or 2. The upper and lower limit of the tolerance in the differential may be ±1. If the heart rate stability is not within the tolerance, the process will proceed back to step 401. While the heart rate stability is not fallen within the tolerance, the system will iteratively repeat the operation of steps 401 to 407.
When the heart rate stability falls within the tolerance, then the imaging is conducted in step 411. More specifically, the operator console 300 issues an imaging instruction to the gantry 100, which, in response to the instruction, images the subject 10. Since the X-ray detector 150 is a multi-column X-ray detector which may obtain the data for a plurality of slices at once, the heart may be entirely scanned while the heart rate is being stably settled. In this manner, images of better quality can be obtained without being affected by the fluctuation of heart rate at the beginning of breath holding period.
Now referring to
In step 407, it is determined whether or not the heart rate stability is fallen within the tolerance. If the heart rate stability is not within the tolerance then the process proceeds back to step 401. While the heart rate stability is not fallen within the tolerance, the process will iteratively repeat the operation of steps 401 to 407.
Once the heart rate stability falls within the tolerance, in step 409, an imaging button is lit. The imaging button is an illuminated operable button provided on the operator console 300. The operator is informed that the imaging is enabled when the imaging button is lit.
The operator pushes the button in correspondence with the notification, the subject is imaged in step 411. In these manner images of better quality can be obtained without being affected by the fluctuation of heart rate at the beginning of breath holding period.
Now referring to
In step 405 the computation result of the heart rate stability is displayed. The result is displayed on the display 302. The contents of the display includes the transition of the standard deviation or differential values, a graph as shown in
In step 407, it is determined whether or not the heart rate stability is fallen within the tolerance range. The determination may be conducted by the operator monitoring the display 302. While the heart rate stability is not within the tolerance, the system will iteratively repeat the operation of steps 401 to 407.
The operator pushes the imaging button when he/she decides that the heart rate stability is well within the tolerance. Responsively the imaging will be conducted in step 411. In this manner, images of better quality can be obtained without being affected by the fluctuation of heart rate at the beginning of breath holding period.
Since the transition of the heart rate during the breath holding period may vary dependent on a personal error, it is preferable to recognize in advance the way of individual transition by conducting a dry rehearsal with the subject of breath holding to determine the standard deviation and the differential, in order to effectively run the imaging.
In case of imaging with the compensation for the body movement due to breathing, the breath holding during imaging session is not needed. However the imaging in that case requires the heart rate to be stably settled. The control of imaging timing in the manner as have been described above allows images of better quality to be obtained.
Many widely different embodiments of the invention may be configured without departing from the spirit and the scope of the present invention. It should be understood that the present invention is not limited to the specific embodiments described in the specification, except as defined in the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-168221 | Jun 2005 | JP | national |
