Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2001-04-11
2004-03-16
Wolfe, Willis R. (Department: 3747)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C378S008000, C378S095000
Reexamination Certificate
active
06708052
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to cardiac imaging and, in particular, acquiring cardiac images having minimized motion artifact with high-speed imaging devices. The invention relates to a method and apparatus for acquiring these cardiac images by prospective gating based in part on the length of a cardiac cycle, gender of the subject being imaged and the imaging speed.
BACKGROUND OF THE INVENTION
Acquiring clear images of the heart is typically impeded by cardiac motion and coronary artery motion caused by the rhythmic beating of the heart. The resulting loss of resolution causes blurring or streaking, called motion artifact, which diminishes the diagnostic value of these images.
Efforts have been made to minimize cardiac motion artifact. Scanning protocols may be adapted to attempt to limit the motion reflected in the cardiac image. Alternatively, patients may simply be instructed to lie still and hold their breath during the scan to reduce respiratory motion, or patient restraints and supports may be used to limit general body motion. In addition, some attempts have been made to shorten image acquisition time by actively increasing the subject's heart rate and/or increasing the speed of the image-acquisition scan generated by the cardiac imaging device. As an alternative, ECG gating techniques have developed which involve equipping the cardiac imaging apparatus with an ECG gating device that synchronizes the image-acquisition scans with specific phases of the cardiac cycle.
ECG gating relies on the electrocardiographic signals that represent the rhythmic contraction of the heart's atria and ventricles. These signals originate from electrical pulses of the sinoatrial (SA) node, which spread over the atria and ventricles and cause them to contract, resulting in a complete cycle of the heart's contractions. Thus, a recorded ECG waveform represents the cardiac cycle, and is comprised of a set of discrete electrocardiographic signals corresponding to the muscular contraction and relaxation of the atria and ventricles. Specifically, the R-R interval measures the period of the heart beat, the P-R segment corresponds to the time from the onset of atrial contraction to the onset of ventricular contraction; the R-T segment approximately measures ventricular contraction or systole; and the T-R interval measures ventricular relaxation, or diastole.
Many known ECG gating techniques involve “retrospective triggers” that coordinate the scanning of images with different electrocardiographic signals of the cardiac cycle to obtain a full set of scans over a number of cardiac cycles. Then, the scans are “sorted” by computerized means according to the phase of the cycle during which they were taken to construct separate images of each phase of the cardiac cycle. Thereafter, the technician or physician selects the clearest image from this series with the least motion artifact for diagnostic purposes.
ECG gating techniques also involve efforts to “prospectively trigger” an image-acquisition scan starting with a specific phase of the cardiac cycle, typically at 40-50% of the R-R interval and at 70-80% of the R-R interval. These percentages allegedly correspond to quiescent points of the cardiac cycle where cardiac motion is at a minimum.
There are several problems associated with known ECG gating techniques. First, the traditional techniques generate scan triggers at pre-determined, fixed percentages of the cardiac cycle regardless of the heart rate of the subject being imaged during the scanning procedure. Quiescent points, however, vary with heart rate, so that using a fixed percentage for all subjects regardless of heart rate is ineffective.
Moreover, with many known techniques, the clarity of the resulting images depends on the type of imaging device being used and the speed of the image-acquisition scan it generates. For instance, one ECG gating technique involves using 40-50% of the R-R interval to trigger image-acquisition scan for coronary artery screening or coronary angiography with electron beam tomography (EBT), which has an ultrashort image acquisition time (50-100 ms). This technique may not be as effective with scanning devices having longer acquisition times, such as MRI and spiral CT scanners (100-500 ms).
Finally, because the traditional techniques generate triggers at pre-determined percentages of the R-R interval, the length of each cardiac cycle must be the same during the scanning procedure so that the image-acquisition scan is triggered at precisely the right time for each heart beat. Thus, these techniques produce images with minimized motion artifact only when the heart being imaged has a consistent heart rate, usually measured in beats per minute. ECG gating is not effective for those subjects that have irregular heart rates, or whose heart rates increase or decrease during the imaging procedure, either because of a physical condition or disease or because of stress resulting from the imaging procedure.
Thus, it is an object of the present invention to provide a method and apparatus for acquiring diagnostically valuable cardiac images of the heart having minimized motion artifact via prospective gating by triggering an image-acquisition scan starting at a point of a cardiac cycle, where this point is calculated, in part, by the length of the cardiac cycle. It is yet another object of the present invention to acquire cardiac images having minimized motion artifact with imaging devices having a wide range of scan speeds. Finally, it is an object of this invention to acquire these diagnostically valuable cardiac images in a manner wherein the quality of the resulting images is not dependent on consistent heart rate and, in fact, may dynamically vary as necessary with each heart beat.
SUMMARY OF THE INVENTION
The present invention relates to a method and apparatus for acquiring an image of the heart by triggering an image-acquisition scan starting at a point of the cardiac cycle having minimized motion. The optimal point for triggering an image-acquisition scan is determined by measuring the lengths of the cardiac cycles of the subject being imaged. The optimal trigger point of each cardiac cycle depends on the length of that cycle; thus, this point varies as the length of the cardiac cycle changes. Thus, preferably, the present method and apparatus measures each cardiac cycle during the scanning procedure and dynamically determines and adjusts the optimal trigger point from one heart beat to the next as necessary. Thus, in the preferred embodiment, the diagnostic value of the images obtained pursuant to this invention does not rely on the subject having a constant heart rate throughout the duration of the scanning procedure.
The method disclosed by the present invention acquires a cardiac image with minimized motion artifact by measuring the length of the R-R interval of a particular heart beat, calculating the length of the R-T segment to determine the quiescent segment of the cardiac cycle, identifying an optimal scan starting point of the cardiac cycle, and triggering an image-acquisition scan at this point.
The calculation of the R-T segment length is based in part on the gender of the subject and the length of the R-R interval. For men, the R-T length is calculated by the algorithm 0.143×RR+224.2; for women, the R-T length is calculated by the algorithm 0.157×RR+221.2. In both cases, the R-R interval=1000 ms×60/heart rate (ms). The quiescent segment, which corresponds to the period of minimized cardiac motion velocity, is late systole to early diastole, and approximates the end of the R-T segment.
The optimal scan starting point, which is within the quiescent segment, is based on the image-acquisition scan speed and the subject's heart rate. The present method contemplates the use of scan speeds that fall within the range of about 25 ms to about 250 ms. As an example, the optimal scan starting point is at 25-50 ms before the end of the R-T interval where the speed of the scan protoco
Budoff Matthew J.
Mao Songshou
Harbor UCLA Research and Education Institute
Orrick Herrington & Sutcliffe LLP
Wolfe Willis R.
LandOfFree
Method and apparatus for cardiac imaging with minimized... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for cardiac imaging with minimized..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for cardiac imaging with minimized... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3220005