GB2107553A - Pulse gated system for x-ray generation and image acquisition - Google Patents

Abstract

An improvement in an x-ray apparatus used to obtain diagnostic x-ray images is described. The improvement includes a monitoring means, 10, for monitoring a physiological process such as cardiac or respiratory cycles. A signal generating means, 12, is used to generate signals in response to the monitored physiological process. Signals from the signal generating means are coupled to a control means, 14, which in turn controls the generation of x-rays within the x-ray apparatus. In this manner x-ray images are only acquired for pre-determined events in the physiological process. Fewer images are acquired thus reducing the patient's exposure to x-rays and reducing the processing and storage requirements. <IMAGE>

Description

SPECIFICATION Pulse gated system for x-ray generation and image acquisition 1. Field of the Invention.

The invention relates to the field of x-rays for medical diagnostics and more particularly, xray diagnostics where a plurality of images are used to obtain a "differenced" image.

2. Prior Art.

It is well-known in the art of x-ray diagnostics to take a series of images and then to obtain differenced images to highlight, for example, the cardiovascular system. In some cases, the images are taken before and after the administration of a radiographic contrast media. In other cases, the images are taken at different energy levels, such as below and above the K absorption edge of iodine. The tissue under consideration absorbs more of the media than surrounding tissue. In theory, the image resulting from the substraction will show only the media absorbent tissue. Various techniques are known for obtaining the differenced images, including techniques using digital technology. See U.S. Patent Nos.

3,894,181; 3,974,386; 4,204,226 and 3,854,049.

Some digital fluoroscopy (DF) systems utilize periodic pulses of x-rays which are evenly spaced in time. The data acquired at these periodic intervals may not correspond to a desired event in a physiologic process. For example, in a substraction intravenous arteriogram, the images may not correspond to the same point in the cardiac cycle. Therefore, when the images are substracted from one another they will not show a given artery or cardiac chamber in precisely the same position or state. The sampling pulse intervals of the DF system may literally be out of phase with the physiologic process being investigated, resulting in poorer quality images than might otherwise be possible to obtain.

Other DF systems use a continuous x-ray beam. The x-ray data can thus be retrospectively sorted into intervals corresponding to physiologic events, such as a precise point within a cardiac cycle. However, this approach results in an inefficient use of the x-ray dose available to the patient, and the patient is exposed to relatively high x-ray doses for the amount of data actually used.

As will be seen, the present invention synchronizes x-ray generation and data acquisition to predetermined physiological events.

For example, data is acquired only at a predetermined point or event in a cardiac cycle. By synchronizing the sampling pulses the radiation exposure is minimized to the patient and high quality images are assured. Moreover, the throughput data rate for the system is reduced for DF systems and the storage and retrieval of the digital information becomes significantly more manageable. In addition, the requirements of real-time digital image processing and image storage can be eliminated for examination of the cardiac chambers using the present invention.

SUMMARY OF THE INVENTION: An improvement in an x-ray apparatus used for obtaining diagnostic x-ray images is described. The improvement includes a monitoring means for monitoring a physiologic process such as cardiac or respiratory cycles. A signal generation means is used to generate signals in response to the monitored physiologic process. Signals from the signal generatiion means are coupled to a control means which in turn controls the generation of x-rays within the x-ray apparatus. In this manner, xray images are only acquired forSpredeter- mined events in the physiologic fiprocess.

According to the present invention there is provided an improvement in an x-ray apparatus for obtaining diagnostic x-ray images, comprising: monitoring means for monitoring a physiologic process; signal generation means for generating signals in response to said physiologic process, said signal generation means coupled to said monitoring means; and control means for controlling the generation of x-rays in said x-ray apparatus, said control means coupled to said signal generation means; whereby x-ray images are acquired only for predetermined events in said physiologic process.

BRIEF DESCRIPTION OF THE DRAWINGS: Figure I is a block diagram illustrating the overall operation of the invention.

Figure 2 is a block diagram illustrating a system for controlling the acquisition of images upon coincidence of predetermined events in two physiologic processes.

Figure 3 is a block diagram generally illustrating the presently preferred embodiment of the invented improvement in an x-ray imaging apparatus.

DETAILED DESCRIPTION OF THE INVEN TION: An improvement in a diagnostic x-ray imaging apparatus is described. In particular, the improvement is most useful in digital fluoroscopy (DF) where the difference of images are obtained. As is commonly done, images are taken before and after the administration of a radiographic contrast media or at energy levels above and below the K absorption edge of a contrast media.

In the following description well-known xray apparatuses and DF processors are not described in detail in order not to obscure the present inventiion in unnecessary detail. The best references known by Applicant on this subject include the above mentioned three patents and Kruger, Mistretta, Houk, et al, "Computerized Fluoroscopy in Real-Time for Noninvasive Visualization of the Cardiovascular System", Radiology, 130:49-57, January 979; Ovitt, Capp, Fisher, et al, "Development of a Digital Video Subtraction System for Intravenous Arteriography", SPIE, 206:73, 1979; W.J. Maclntyre, W. Pavlicek, J.H.

Gallagher, 'imaging Capability of an Experimental Digital Subtraction Angiography Unit," Radiology, 139:307-313, May 1981.

In the present invention, x-ray images are only acquired at predetermined events in a physiologic process. Consider a substraction system for DF images of blood vessels where images are taken before and after the administration of radiographic contrast media. Because of Cardiac pulsations, a random image obtained after contrast will not necessarily depict the cardiac system in the same position as the image obtained prior to the injection of the contrast media. Ideally both images should be obtained during the same interval of the cardiac cycle. With the present invention, the x-ray pulses are gated by the patient's electrocardiogram (or by other physiologic process) thereby insuring that the images occur at the same point in the cardiac cycle.

Referring first to Fig. 1, the overall x-ray system includes an x-ray generator 14 which projects x-rays through a patient 15 onto an xray detector 16 which typically includes means for image acquisition. The data thus obtained is coupled to an image processor 18 and from there the data is stored as indicated by the image storage means 20. The digital or analog data can be stored on any one of a plurality of well-known means such as discs, tapes or in semiconductor memories. The generator 14, detector 16, processor 18 and image storage means 20 are all well-known in the art. In the prior art, as previously mentioned, the x-ray generator 14 and the x-ray detector 16 provide continuous images or time-based, periodic images.

In the present invention, the x-ray generator 14 and x-ray detector and image acquisition means 16 are activated by signals from a trigger generator 12. The trigger generator receives signals associated with a physiologic process, in particular from the patient physiologic monitor 10. The monitor 10 could monitor a cardiac cycle in which event the monitor 10 can be an ordinary EKG apparatus. The trigger generator 12 generates pulses during the same interval of each EKG cycle. Therefore, images taken before the administration of a contrast media can be more readily matched with images taken after the administration of the media since the images will occur during the same interval of the physiologic process. In practice, fewer images need be taken to obtain a high contrasting difference image, thus reducing the x-ray dosage to the patient.In addition, since the number of images required is reduced fewer images need be processed by the image processor 18, thereby reducing the electronics hardware required and enabling processing with less expensive computers. Moreover, fewer images need be stored, thus allowing the image storage means 20 to have less memory capacity and therefore be less costly.

Referring to Fig. 3, in the presently preferred embodiment, the improvement includes an EKG monitor or other transducer such as those used to monitor a respiratory cycle. The EKG monitor 22 provides an EKG signal to peak detector 24. A typical EKG signal is shown on line 23. The peak detector 24 which may be an ordinary peak detection circuit, detects the peak of the EKG signal, in particular the QRS complex. The output from the peak detector 24 is shown on line 25.

The output of the peak detector 24 can be coupled through switch 42 directly to a trigger buffer 34. Trigger buffer 34 may be any one of a plurality of well-known trigger generators or buffers required to generate appropriate pulses to control the x-ray generator 14 of Fig. 1 and/or the x-ray detector and image acquisition means 16 of Fig. 1. Each time a pulse occurs from buffer 34 an image is obtained.

In some cases, it may be necessary to obtain images not at the QRS, but rather, at some predetermined time following the QRS.

If this is necessary, switch 42 is opened and, for example, switch 36 is closed. Delay means 26 provides a time delay "A". With switch 36 closed and switches 38, 40 and 42 opened, an output will occur from the trigger buffer 34 after a delay "A" following the QRS. Of course, the delay means 26 can be a variable delay means so that the time delay "A" can be adjusted.

In other cases, it may be necessary to take a plurality of images between each of the QRS pulses. This can be done by opening switch 42 and closing switches 36, 38 and 40. Assume that the delay means 28 provides a delay of "B" where "B" is greater than "A", and further assume that delay means 30 provides a delay of time "C" and that "C" is greater than "B". Also, to prevent ambiguity it must be assumed that the delay "C" is not as great as the period between the QRS pulses. After each QRS pulse three triggers will occure from the trigger buffer 34, causing three images to be obtained following each QRS.

For the switch position where switches 38, 40 and 42 are closed and switch 36 opened, a a trigger pulse occurs on each QRS, followed by a trigger pulse after a delay "B". The resultant waveform is shown on line 35.

The steering diode 32 prevents signals from the outputs of the delay means 26, 28 and 30 from being fed back into the delay means when the switch 42 is closed.

It will be apparent to one skilled in the art that other physiologic processes or functions may be monitored and signals generated from the monitored process or function to trigger the x-ray generator and image acquisition means. Also, it is apparent that the number of delays and the manner in which they are obtained are not critical to the present invention.

In some instances, the quality of an image may be affected by more than one physiologic process. For example, breathing can affect the difference images, as well as heartbeat. In an alternate embodiment of the present invention, images are taken only upon the simultaneous occurrence of predetermined events in two physiologic processes.

Referring to Fig.2, the EKG monitor 22 is again illustrated. The output of this monitor is coupled to a trigger generator 44 which may be fabricated with the teachings of Fig. 3. The output of the generator 44 is a series of pulses as shown on line 35. A second monitor 46 which, for example, monitors respiration is used. The output of the monitor 46 is coupled to a generator 48. This generator may be identical to the generator 44 or it may be a generator which generates pulses (as shown in line 49) which are wider than the pulses on line 35. The generator 48, by way of illustration, generates relatively wide pulses at each exhalation. Ordinary circuit means quite similar to those shown in conjunction with Fig. 3 can be used to generate the pulses on line 49.

The resulting waveforms from the generators 44 and 48 are compared. A simple AND gate 50 is used to provide signals on line 52 only when a coincidence occurs between the pulses on lines 35 and 49. Note that each of the waveforms when considered alone are somewhat periodic, however, relative to one another the signals are asynchronous. Thus, several respiratory cycles may be required before an image is acquired.

Thus, an improvement in an x-ray imaging apparatus has been described. The improvement enables the acquisition of x-ray images at proper times with respect to physiologic processes, thereby reducing the overall number of images required. The present invention reduces the patient's exposure to x-rays and reduces the amount of data which needs to be processed and stored.

Claims (16)

1. An improvement in an x-ray apparatus for obtaining diagnostic x-ray images, comprising: monitoring means for monitoring a physiologic process; signal generation means for generating signals in response to said physiologic process, said signal generation means coupled to said monitoring means; and, control means for controlling the generation of x-rays in said x-ray apparatus, said control means coupled to said signal generation means; whereby x-ray images are acquired only for predetermind events in said physiologic process.

2. The improvement defined by Claim 1 wherein said monitoring means comprises means for monitoring cardiac cycles.

3. The improvement defined by Claim 2 wherein said signal generation means includes peak detection means for detecting the peaks of signals.

4. The apparatus defined by Claim 3 wherein said signal generation means generates trigger pulses used for controlling said generation of x-rays.

5. The improvement defined by Claim 1 wherein said monitoring means monitors respiratory cycles.

6. The improvement defined by Claim 1 wherein said signal generation means includes delay means for delaying a signal.

7. An improvement in an x-ray appartus for obtaining x-ray images, comprising: first monitoring means for monitoring a first physiologic process; second monitoring means for monitoring a second physiologic process; first signal generation means for generating signals in response to said first physiologic process, said first signal generation means coupled to said first monitoring means; second signal generation means for generating signals in response to said second physiologic process, said second signal generation means coupled to said second monitoring means; comparator means for comparing signals, said comparator means coupled to said first and second signal generation means;; whereby the output from said comparator means is used to control the acquisition of xray images, thereby allowing images to be taken during the simultaneous occurrence of two predetermined physiologic events of said physiologic processes.

8. The improvement defined by Claim 7 wherein said first monitoring means monitors cardiac cycles.

9. The improvement defined by claim 8 wherein said second monitoring means monitors respiratory cycles.

10. The improvement defined by Claim 7 wherein said comparator means is a circuit means for detecting the coincidence of two signals.

11. An improvement in an x-ray apparatus for providing a differenced x-ray image for controlling the time at which images are acquired, comprising: monitoring means for monitoring a physiologic process; signal generation means for generating signals in response to said physiologic cycle, said signal generation means being coupled to said monitoring means; and, control signal generation means for providing control signals to control the time at which images are acquired, said control means being coupled to said signal generation means; whereby images are only acquired at peredetermined events in said process.

12. The improvement defined by Claim 11 wherein said signal generation means generates at least one delayed signal for controlling said acquisition of images.

13. The improvement defined by Claim 11 wherein two physiologic cycles are monitored and wherein images are acquired upon the coincidence of predetermined events in each of said processes.

14. The improvement defined by Claim 11 wherein said monitoring means monitors cardiac cycles.

15. The improvement defined by Claim 12 wherein said monitoring means monitors respiration cycles.

16. An improvement in an x-ray apparatus for obtaining diagnostic x-ray images substanially as herinbefore described with reference to and as illustrated in the accompanying drawings.