Patent Application
20080177181
The operation of the heart of a patient can be monitored in vivo using a variety of approaches. One commonly used approach for monitoring the operation of the heart is an electrocardiogram (ECG or EKG) which is a graphical representation of the electrical activity of the heart over time. Another commonly used approach for monitoring the operation of the heart is the echocardiogram, which is typically used to generate a two dimensional moving video image of the heart in real time, while the heart is beating. Each of these approaches provides a different set of information about the operation of the heart, in real time.
ECG data and ultrasound data are synchronized by adding a marker to both sets of data, then detecting the position of the markers in the data, and using the detected positions to align the two sets of data in time. This enables an operator to visualize which frame of ultrasound data corresponds in time to which portion of the ECG waveform.
The inventor has recognized that significant advantages can be obtained by synchronizing ECG data and ultrasound data so that the operator can visualize which frame of ultrasound data corresponds in time to which portion of the ECG waveform, and the present invention relates to synchronizing or registering ECG and ultrasound data. While the primary intended application is in the field of cardiac ultrasound, it can be used in numerous other applications as well.
In one preferred implementation, synchronization is provided by simultaneously generating (a) a first signal that can be detected by an ECG machine; and (b) a second signal that can be detected by an ultrasound machine. One suitable set of such signals is depicted in
For the signal that is detectable by the ECG machine, a short, positive-going pulse of current from the baseline for the ECG signal is suitable. For the signal that is detectable by the ultrasound machine, a short burst of ultrasound RF is suitable, with the RF carrier preferably close to the operating frequency of the transducer (e.g., 6 MHz). Preferably, the signal should be at least as long as the frame-to-frame interval of the ultrasound system. For example, a 20 mS pulse would be suitable for a system that is imaging at 50 frames per second. Preferably, the rise and fall times of the pulse should be much shorter than the frame-to-frame interval (e.g., less than 1 mS).
The burst of RF is synchronized with the pulse that is applied to the ECG machine, e.g., as shown in
The required synchronized pulses can be generated with the circuit depicted in
Switch 3 may be a manually operated switch that, when actuated, passes the output of the signal generator 1 to the rest of the circuit. Alternatively, it may be an electronic switch that is closed for a predetermined period of time (e.g., between about 10 and about 50 mS, and preferably about 10 mS), under control of a suitable circuit (e.g., a one-shot).
Resistor 4 (e.g., 100Ω) and back to back diodes 5 and 6 form a protective circuit to limit the voltage that is applied to the ECG system. Diode 7 half-wave rectifies the AC, and capacitor 8 (e.g., 1000 pF) captures the peaks. The capacitor 8 is discharged through resistor 9 (e.g., 3 kΩ) and the track of potentiometer 10 (e.g., 10Ω), and the output voltage is set to match the ECG system by adjusting the position of the wiper of the potentiometer 10. Taken together, Diode 7, capacitor 8, resistor 9, and potentiometer 10 operate as an envelope detector.
To adjust the circuit for operation, the ultrasound box is set up for imaging, and the antenna is placed near the ultrasound probe or near the connector to the ultrasound box. (A physical connection to the ultrasound box is not required to couple the signal into the ultrasound box.) Closing switch 3 sends RF to the antenna, and the signal generator output level and/or antenna position is adjusted until the ultrasound image appears noticeable whiter than it was when the switch 3 was open. This increase in whiteness serves as a marker or artifact in the ultrasound image. Next, the output from the envelope detector is connected to the ECG machine. One suitable way to make this connection is by connecting the output from the envelope detector to the RA input of the ECG machine and connecting the ground to the other leads of the ECG machine, but other lead connection arrangements may also be used, as will be apparent to persons skilled in the relevant arts. Pulses are then generated by closing and opening the switch 3, and adjusting potentiometer 10 until a satisfactory signal appears on the ECG, in the form of the leading edge of a positive going pulse, analogous to the upstroke of an R-wave. This pulse serves as a marker or artifact in the electrocardiogram.
After the adjustment, the ultrasound system and the ECG system are operated simultaneously to capture images and an electrocardiogram of the subject. While this is happening, pulses may be generated by closing and opening S3, and the ultrasound images and the electrocardiogram are recorded. Afterwards, the ultrasound image is played back frame by frame, and the appearance of the marker in the ultrasound images is compared to the appearance of the marker in the electrocardiogram. A timing relationship between the ultrasound image and the electrocardiogram can then be determined. Alternatively, a pulse train generator may be used to generate pulses at regular intervals, and a timing relationship between the ultrasound image and the electrocardiogram may then be determined using the pulse repetition rate.
Once the timing relationship between the two systems has been established, it can be calculated for subsequent times by tracking the amount of time elapsed in both systems. Since only one frame of an ultrasound image is typically displayed at any given instant, and an electrocardiogram displays a number of seconds of data all at once, one suitable user interface for indicating the timing relationship between the ultrasound images and the electrocardiogram is to colorize the spot on the electrocardiogram trace that corresponds to the frame of ultrasound that is being displayed at any given instant. When the ultrasound image is played back, the colorized spot would then move along the electrocardiogram trace. Alternatively, if the current time corresponds to a fixed position on the electrocardiogram display screen, the fixed position could be marked on the screen using a vertical line, and the ultrasound frame that corresponds to whatever portion of the electrocardiogram is at that fixed position at any given instant could be displayed. A wide variety of alternative user interfaces for displaying both sets of information and indicating the timing relationship between them can be readily envisioned.
Synchronizing the ultrasound image with the ECG can be especially important in cardiac resynchronization therapy (CRT). In CRT one is interested the use of bi-ventricular pacemakers to overcome problems in the timing of cardiac wall movement—dyssynchrony. In particular, one would like to know that contraction is appropriately synchronous throughout the left ventricle—except for a smooth gradient from apex to base. Ultrasound data accurately timed with respect to the ECG and in particular the R-wave, for example, in the form of CINE loops, could be used to assess the appropriateness of the placement of pacemaker leads and the timing of pacemaker impulses.
This application claims the benefit of U.S. provisional application No. 60/886,483, filed Jan. 24, 2007, which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60886483 | Jan 2007 | US |
