Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2000-03-09
2002-12-31
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S428000
Reexamination Certificate
active
06501979
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods and systems for medical imaging of parts of a patient in which acquisition of data by a medical imaging apparatus for image reconstruction is gated by a combination of electrocardiogram (ECG) and peripheral pulse (PPU) signals from the patient.
2. Description of the Related Art
Many organs and regions of the body of a patient are affected by cardiac and respiratory motions, including, for example, not only the heart, the lungs, and vessels throughout the body, but also abdominal organs, especially upper abdominal organs, and intracranial structures. For the medical imaging of such affected organs, it is often useful, or even necessary, to take these motions into account. On the one hand, in the case of those imaging modalities, such as a conventional x-ray imaging, in which a single image is acquired in a short exposure (for example, a few milliseconds (msec) or less), it is often useful for images to be acquired at known and pre-determined phases of cardiac or respiratory motions.
However, on the other hand, in the case of those imaging modalities which reconstruct a recognizable image from imaging data acquired over a period of time (for example, 100 msec. or more), it is often necessary to take body motion into account in order to avoid motion artifacts that degrade reconstructed images and render them less useful clinically. Currently, important modalities of this nature include magnetic resonance (MR) imaging, computer tomographic (CT) x-ray imaging, and nuclear imaging of particles emitted by radioactive tracers administered to a patient. For many cardiac, vascular, neurologic, and other imaging examinations using such modalities, synchronization of imaging data collection sequences to the intrinsic motion of the heart is crucial to obtain high-quality images without motion artifacts.
For cardiac synchronization of medical imaging data collection, triggering data collection by features recognized in the electrocardiogram (ECG) signal or in the peripheral pulse (PPU) signal from nearly any artery can be utilized. PPU signals, in comparison to ECG signals, are always delayed with respect to the QRS complex of the ECG signal (signifying the onset of ventricular systole), and have a temporal frequency spectrum with significantly lower frequency components. The variable delay can be up to 100-200 msec. or more. Therefore, triggering with ECG signals is generally preferred to achieve triggering that is temporally more precisely defined in time and to enable data collection during early ventricular systole.
However, important medical imaging modalities often introduce noise and distortions into ECG signals measured from a patient during imaging examinations. These noise and distortions are due to various kinds of electromagnetic interference inherently generated during examination by such modalities. In the case of CT and nuclear imaging, electrical interference may be induced in the patient or in affixed ECG leads, and therefore, into resulting ECG signals, either directly from the imaging apparatus itself or secondarily by radiation used in the imaging.
In the case of MR imaging, switched magnetic field gradients, RF pulses, and hydrodynamic flows of blood containing charged ions in the strong static magnetic field present in an MR apparatus induce voltage gradients in a patient that in turn introduce noise and distortions into ECG signals. Since blood flow effects are enhanced during systole, when the blood flows in the aorta and other vessels are increased, introduced ECG artifacts are maximum during ventricular systole. Such artifacts hamper R-wave detection and, thus, successful synchronization of imaging data collection.
For example,
FIG. 2A
illustrates two ECG signals from a healthy volunteer. ECG
80
is recorded in an MR apparatus but without the presence of the static main magnetic field. ECG
81
is recorded in the MR apparatus in the presence of a static field of, for example, 1.5 Tesla (T). Second ECG
81
, recorded in the presence of the static magnetic field, contains several additional signal peaks compared to first ECG
80
, which can lead to erroneous interpretations of the ECG, for example, being recognized as non-physiological, false R-waves.
A method and apparatus that attempts to improve ECG triggering is known from U.S. Pat. No. 5,526,813. In this known method, erroneous determination of ECG features is reduced by filtering and signal processing prior to using the signal for triggering imaging data collection. However, a drawback of this known method is that the filtering and signal processing of the ECG data can be complicated and unreliable, and as a result erroneous triggering of imaging data acquisition may still occur even though the ECG signals have been filtered and processed. Another method and apparatus that also attempts to improve ECG triggering is known from International Application no. PCT/IB98/01062. According to the latter known method, information from a vector ECG (VCG) signal is used to improve recognition of ECG signal features compared to their recognition in a scalar ECG. However, measurement of a vector electrocardiogram signal is also subject to inherent noise and distortions generated by the imaging modalities, and its analysis can also be complex, difficult, and unreliable.
What is needed, therefore, are simple and reliable methods and apparatus for accurately and reliably triggering data acquisition for medical image reconstruction at fixed times with respect to the cardiac cycle.
Citation of a reference herein, or throughout this specification, is not to construed as an admission that such reference is prior art to the Applicants' invention of the invention subsequently claimed.
SUMMARY OF THE INVENTION
The objects of the present invention are to provide methods and apparatus which overcome the above identified problems in, and satisfy the needs of, the current medical imaging art.
As used herein, it is to be understood that a “medical imaging modality” is any imaging modality that acquires imaging data by a process that can be disturbed by body motions, and, therefore, that advantageously takes heart motions into account when imaging organs that are directly or indirectly affected by such heart motions. This invention is most advantageously applied to those imaging modalities the practice of which generates noise and distortions of electrocardiogram (ECG) signals measured from a patient during imaging. Preferably, this invention is applied to magnetic resonance (MR) imaging, or to computer tomographic (CT) x-ray imaging, or to nuclear medicine imaging.
Additionally, as used herein, it is to be understood that “ECG signals” means any representation of the electrical activity of the heart. It includes conventional scalar representations where the time courses of single voltages measured between established positions on the patient are displayed. In these representations, the QRS complex has its well-known form, e.g., as schematically represented by signal
80
in FIG.
2
A. It also includes vector electrocardiogram (VCG) representations, where the time course of the net electrical polarization vector of the heart is displayed in various projections. In these representations, the QRS complex is seen as a loop elongated along one direction. Finally, it is to be understood that “PPU signal” means any representation of the pulsatile flow of blood in an artery. It can be non-invasively measured, for example, by an oximeter, or invasively measured, for example, by arterial pressure, or by other means.
Generally, the objects of this invention are achieved by medical imaging methods according to which information from both ECG signals and from PPU signals are considered together in order to generate reliable synchronization signals for triggering imaging data collection in a medical imaging apparatus. The synchronization signals represent occurrences of pre-determined phases of cardiac motion so that the imaging data collection can be
Botnar Rene M.
Manning Warren J.
Stuber Matthias
Koninklijke Philips Electronics , N.V.
Lateef Marvin M.
Mantis Mercader Eleni
Vodopia John
LandOfFree
Methods and devices for combined ECG and PPU controlled... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Methods and devices for combined ECG and PPU controlled..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Methods and devices for combined ECG and PPU controlled... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2961515