Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2001-07-31
2003-07-15
Jaworski, Francis J. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S466000, C600S461000
Reexamination Certificate
active
06592520
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to ultrasound devices and methods for imaging internal portions of the human body, and more particularly, to interventional intravascular or intracardiac imaging using catheters with multi-element transducer arrays.
BACKGROUND OF THE INVENTION
Ultrasound imaging has been widely used to observe tissue structures within a human body, such as the heart structures, the abdominal organs, the fetus, and the vascular system. Ultrasound imaging systems include a transducer array connected to multiple channel transmit and receive beamformers applying electrical pulses to the individual transducers in a predetermined timing sequence to generate transmit beams that propagate in predetermined directions from the array. As the transmit beams pass through the body, portions of the acoustic energy are reflected back to the transducer array from tissue structures having different acoustic characteristics. The receive transducers (which may be the transmit transducers operating in the receive mode) convert the reflected pressure pulses into corresponding RF signals that are provided to the receive beamformer. Due to different distances to the individual transducers, the reflected sound waves arrive at the individual transducers at different times, and thus the RF signals have different phases. The receive beamformer has a plurality of processing channels with compensating delay elements connected to a summer. The receive beamformer uses a delay value for each channel and collect echoes reflected from a selected focal point. Consequently, when delayed signals are summed, a strong signal is produced from signals corresponding to this point, but signals arriving from different points, corresponding to different times, have random phase relationships and thus destructively interfere. Furthermore, the beamformer selects the relative delays that control the orientation of the receive beam with respect to the transducer array. Thus, the receive beamformer can dynamically steer the receive beams that have desired orientations and focus them at desired depths. In this way, the ultrasound system acquires echo data.
Invasive, semi-invasive and non-invasive ultrasound systems have been used to image biological tissue of the heart and the vascular system. Doppler ultrasound imaging systems have been used to determine the blood pressure and the blood flow within the heart and the vascular system. The semi-invasive systems include transesophageal imaging systems, and the invasive systems include intravascular imaging systems. A transesophageal system has an insertion tube with an elongated semi-flexible body made for insertion into the esophagus. The insertion tube is about 110 cm long, has about a 30 F diameter and includes an ultrasonic transducer array mounted proximate to the distal end of the tube. The transeophageal system also includes control and imaging electronics including the transmit beamformer and the receive beamformer connected to the transducer array. To image the heart, the transmit beamformer focuses the emitted pulses at relatively large depths, and the receive beamformer detects echoes from structures located 10-20 cm away, which are relatively far in range.
The intravascular imaging systems use an intravascular catheter that requires different design considerations from a transeophageal catheter. The design considerations for an intravascular catheter are unique to the physiology of the vascular system or to the physiology of the heart. The intravascular catheter has an elongated flexible body about 100-130 cm long and about 8F to 14F in diameter. The distal region of the catheter includes an ultrasonic transducer mounted proximate of the distal end. To image the tissue, several mechanical scanning designs have been used. For example, a rotating transducer element or a rotating ultrasound mirror is used to reflect the ultrasound beam in a sweeping arrangement. Furthermore, catheters with several transducer elements have been used, wherein different transducer elements are electronically activated to sweep the acoustic beam in a circular pattern. This system can perform cross-sectional scanning of arteries by sweeping the acoustic beam repeatedly through a series of radial positions within the vessel. For each radial position, the system samples the scattered ultrasound echoes and stores the processed values. However, these ultrasound systems have a fixed focal length of the reflected acoustic beam. The fixed focal length significantly limits the resolution to a fixed radius around the catheter.
Furthermore, intravascular ultrasound imaging has been used for determination of the positions and characteristics of stenotic lesions in the arteries including the coronary arteries. In this procedure, a catheter with a transducer located on the tip is positioned within an artery at a region of interest. As the catheter is withdrawn, the system collects ultrasound data. The imaging system includes a catheter tracking detector for registering the position and the velocity of the transducer tip. The imaging system stacks two-dimensional images acquired for different positions during the transducer withdrawal. An image generator can provide three-dimensional images of the examined region of the blood vessel or the heart, but these images usually have low side penetration.
Recently, ultrasound catheters with the above-described mechanical, rotating transducer designs have increasingly been used in the assessment and therapy of coronary artery diseases. These catheters have a larger aperture, giving rise to deeper penetration depths, which allows imaging of tissue spaced several centimeter away from the transducer, such as the right atrium of the human heart. These images can assist in the placement of electrophysiology catheters. However, these devices still do not provide high quality, real time images of selected tissue regions since they have somewhat limited penetration, a limited lateral control and a limited ability to target a selected tissue region. In general, the produced views are predominantly short axis cross-sectional views with a low side penetration.
Currently, interventional cardiologists rely mainly on the use of fluoroscopic imaging techniques for guidance and placement of devices in the vasculature or the heart as performed in a cardiac catheterization laboratory (Cathlab) or an electrophysiology laboratory (Eplab). A fluoroscope uses X-rays on a real-time frame rate to give the physician a transmission view of the chest cavity, where the heart resides. A bi-plane fluoroscope, which has two transmitter-receiver pairs mounted at 90° to each other, provides real time transmission images of the cardiac anatomy. These images assist the physician in positioning the catheters by providing him (or her) with a sense of the three-dimensional geometry in his (or her) mind that already understands the cardiac anatomy. While fluoroscopy is a useful technique, it does not provide high quality images with real tissue definition. The physician and the assisting medical staff need to cover themselves with a lead suit and need to limit the fluoroscopic imaging time when ever possible to reduce their exposure to X-rays. Furthermore, fluoroscopy may not be available for some patients, for example, pregnant women, due to the harmful effects of the X-rays. The transthoracic and transesophageal ultrasound imaging techniques have been very useful in the clinical and surgical environments, but have not been widely used in the Cathlab or Eplab for patients undergoing interventional techniques.
What is needed, therefore, is an ultrasound system and method for effective intravascular or intracardiac imaging that can visualize three-dimensional anatomy of a selected tissue region. Such system and method would need to use an imaging catheter that enables easy manipulation and positional control. Furthermore, the imaging system and method would need to provide convenient targeting of the selected tissue and good side penetration allowing imaging of near and more
Beck Heather
Miller David G.
Peszynski Michael
Jaworski Francis J.
Koninklijke Philips Electronics , N.V.
Patel Maulin
Vodopia John
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