Determination of arbitrary cardiac phases using...

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Reexamination Certificate

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Reexamination Certificate

active

06771999

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to gating for medical imaging, and more particularly, this invention relates to a method and system of selecting an arbitrary cardiac phase in physiological, non-electrical signals for cardiac gating.
In many applications, it is often desirable to obtain an image at a particular point in a variable cycle, such as a peak of the variable cycle, to analyze behavior at that peak. In the medical field, imaging systems are often used to obtain internal physiological information of a subject. For example, a medical imaging system may be used to obtain images of the bone structure, the brain, the heart, the lungs, and various other features of a subject. Medical imaging systems include magnetic resonance imaging (MRI) systems, computed tomography (CT) systems, x-ray systems, ultrasound systems, and various other imaging modalities.
Gating is essential for characterizing different attributes of a dynamic organ during imaging. The most common techniques of gating including cardiac, respiratory, and peripheral pulse gating have uses in numerous medical applications across diagnostic modalities including CT, MR, X-Ray, Ultrasound, and PET-CT.
Cardiac gating is an essential component of cardiac imaging while using imaging modalities such as CT, magnetic resonance (MR) to minimize motion related artifacts. Current cardiac imaging tools utilize simultaneously collected EKG data to tag CT projection data with cardiac phase information. Essentially, the R-wave of the EKG is used for this purpose. Heart functions are characterized by two distinct periods called systole and diastole. In systole, the heart-muscle is contracting the volume of the left ventricle to pump the contents out through the aortic valve. During the diastole, or diastolic period, the left ventricle is filling through the mitral valve. At the end of the systole, the left ventricle has its smallest volume since it has been contracted to pump blood out. The end of the diastole is the point at which the left ventricle has its largest volume since it is filled with blood ready to be pumped out. During the diastolic period the heart is relatively motion-free allowing images generated from data collected during this period to be clearer as a result of the limited movement.
FIG. 1
illustrates one cardiac cycle of an EKG signal waveform, including a systole condition, or period, and a diastole condition, or period, of the heart. The portions of the EKG signal labeled Q, R and S are referred to as the QRS complex, in which the R-feature, or R-wave, is the most prominent, highest amplitude, feature of the entire EKG signal. The cardiac cycle is typically defined as beginning with an R-wave and continuing until the occurrence of a next R-wave.
EKG gating selects times when a best image of the heart is available. An EKG machine is connected to a patient. A cardiac cycle period is determined, for example, as a time between R-peaks of the EKG. One of the common applications is to use an R-peak as a reference along with the determined cardiac cycle period, to acquire gated images during periods of a cardiac cycle for which the heart is nearly stationary, or during periods for which imaging is desired.
Turning now to
FIG. 2
, two of the commonly used approaches, shown collectively at
130
, for determining the diastole and systole phases in a cardiac cycle using an EKG signal are shown. In waveform
132
, the systolic
134
and diastolic
136
phases are centered at x % and y %, respectively in a cardiac cycle. In waveform
140
, the systolic phase
142
is certain delay from the previous R-peak
146
. Similarly, the systolic phase
144
is certain delay from the previous R-peak
148
. The diastolic phase
152
is certain advance from the next R-peak
148
, and similarly, the diastolic phase
154
is certain advance from the next R-peak
150
. These approaches
130
are based on an assumption that the cardiac phases would occur at a certain time interval during the cardiac cycle. This assumption may not necessarily be accurate for every cardiac cycle and for every individual in a population.
Once the location for the systolic and diastolic phases are made or estimated using one of the approaches described above in
FIG. 2
, image reconstruction may be performed.
FIG. 3
shows half scan and multi-sector image reconstruction where “I” represents the image reconstructed from a single cycle and two consecutive cycles respectively. In waveform
122
of EKG waveforms
120
, projections
126
from a single cardiac cycle, also known as half-scan reconstruction, for a dataset for reconstruction. In waveform
124
, subsets
128
of projections
126
from multiple cardiac cycles are blended, also known as sector based reconstruction, to form a complete dataset for reconstruction.
BRIEF SUMMARY OF THE INVENTION
The above discussed and other drawbacks and deficiencies are overcome or alleviated by a method of selecting an optimal trigger point in a cardiac cycle, the method including providing an input signal including non-electrical cardiac related data, analyzing the input signal to detect candidate features, sorting through the candidate features to select optimal features, and selecting an optimal trigger point.
In another embodiment, a method of selecting an arbitrary cardiac phase for cardiac gating includes identifying a trigger point identifying onset of a systole or diastole phase on a signal, the trigger point existing at time t
1
, specifying a time &dgr; t before the trigger point and extending from a time t
0
to a time t
1
, wherein time t
0
is earlier than time t
1
, and selecting a time interval T over which an image will be reconstructed, wherein the time interval T extends from time t
0
to a time t
2
, wherein time t
2
is later than time t
0
.
In another embodiment, a method of image reconstruction using cardiac gating includes providing a signal indicative of a plurality of consecutive cardiac cycles, for each cardiac cycle, the method further including identifying a trigger point identifying onset of a systole or diastole phase, the trigger point existing at time t
1
, specifying a time &dgr; t before the trigger point and extending from a time t
0
to a time t
1
, wherein time t
0
is earlier than time t
1
, selecting a time interval T over which an image will be reconstructed, wherein the time interval T extends from time t
0
to a time t
2
, wherein time t
2
is later than time t
0
, and reconstructing an image over at least one time interval T.
In another embodiment, a storage medium is encoded with a machine readable computer program code, the code including instructions for causing a computer to implement a method for selecting an optimal trigger point in a cardiac cycle, the method including providing an input signal including non-electrical cardiac related data, analyzing the input signal to detect candidate features, sorting through the candidate features to select optimal features, and selecting an optimal trigger point.
In another embodiment, a storage medium is encoded with a machine readable computer program code, the code including instructions for causing a computer to implement a method for selecting an arbitrary cardiac phase for cardiac gating, the method including identifying a trigger point identifying onset of a systole or diastole phase on a signal, the trigger point existing at time t
1
, specifying a time &dgr; t before the trigger point and extending from a time t
0
to a time t
1
, wherein time t
0
is earlier than time t
1
, and selecting a time interval T over which an image will be reconstructed, wherein the time interval T extends from time t
0
to a time t
2
, wherein time t
2
is later than time t
0
.
In another embodiment, a system for selecting an optimal trigger point in a cardiac cycle includes a non-electrical sensor sensing mechanical vibrations of the heart, a processing circuit coupled to the mechanical sensor, the processing circuit processing a signal sent by the mechanical sensor, analyzing the signal to detect candidate features, sort

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