Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2000-03-01
2001-07-31
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
Reexamination Certificate
active
06267727
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to high resolution intravascular imaging and more particularly to intravascular ultrasound imaging and techniques for enhancing image quality.
In intraluminal or intravascular ultrasound (also referred to as “IVUS”) imaging, the production of high resolution images of vessel wall structures requires imaging at high ultrasound frequencies. IVUS imaging systems may utilize electronic scanners or mechanical scanners. IVUS systems utilizing electronic scanning typically include in the distal end of a catheter an array of ultrasound transducers which are sequentially excited so as to electronically scan an ultrasonic beam. IVUS systems utilizing mechanical scanning (one example of such a system being shown in
FIG. 1
) may use a single rotating transducer
1
in the distal end of a catheter
3
that enters the blood vessel
20
, with a drive shaft
5
coupling the transducer
1
to a motor (not shown) coupled to the catheter
3
at its proximal end. IVUS systems using mechanical scanning have wider applications, mainly due to the smaller size of the mechanical scanner in comparison with electronic scanner, that advantageously allow the system to be used for smaller blood vessels as well as larger blood vessels.
The present invention relates to IVUS imaging systems with mechanical scanning. In these types of IVUS systems, an ultrasonic unidirectional exciter/detector (e.g., transducer) within a catheter probe positioned within a blood vessel is used to acquire signal data from echoes of the emitted ultrasonic energy off the interior of the blood vessel. Specifically, vectors are created by directing focused ultrasonic pressure waves
2
radially from a transducer in a catheter and collecting echoes
4
at the same transducer from the target area, as seen in FIG.
1
. In an exemplary IVUS system with mechanical scanning, the transducer is mechanically rotated at a uniform speed with multiple firings of ultrasonic excitation in order to obtain a plurality of equally spaced radial vectors from the collected echoes. The plurality of radial vectors from the rotated transducer comprises an image frame. A signal processor then performs image processing (e.g., stabilization of a moving image, temporal filtering for blood speckle, and other image enhancement techniques) on the acquired data in order to provide a display of the corrected and filtered intravascular image on a raster-scan display monitor. Signal processing in an intravascular ultrasound imaging system utilizing a mechanically rotated transducer operates under the assumption that the transducer is rotated at a uniform speed. However, this assumption is often violated as the catheter traverses the blood vessel. Specifically, the friction between the catheter and the vessel walls and/or the flexing of the vessel walls causes binding and/or whipping of the catheter, which translates into non-uniform rotation of the transducer. The system thus inaccurately reads the reflected echoes from blood/vessel structure/blood vessel as being received from an incorrect location, as the assumption of uniform rotational speed is violated. Therefore, it is desirable to detect and quantize the non-uniform rotation in order to correct for the image distortion caused by non-uniform rotation, and thereby provide an intravascular image display with enhanced accuracy.
Some conventional techniques used to detect non-uniform rotation of the transducer in intravascular ultrasound imaging involve calibrating the catheter
3
with landmarks or beacons
7
, whether active or passive, generally located at various points (circumferentially or helically) along the perimeter of sheath
9
of the catheter
3
, as seen in FIG.
1
. Each beacon's position relative to the catheter is known. Passive beacons act as reflectors of ultrasound transmitted by the catheter and may undesirably cause reflective bright spots on the image which shadow points in the intravascular field behind the spots. Active beacons transmit ultrasonic energy (characterized by phase, amplitude, frequency and/or pulse repetition rate so as to identify the particular beacon) in the direction of the rotating transducer so that the imaging system may identify the particular beacon in order to determine the angular position of the transducer. However, such conventional techniques using passive or active beacons are not always effective because the beacons may cause shadowing of tissue behind the beacons or may introduce artifacts adversely affecting the imaging of the anatomical structures.
From the above, it can be seen that alternative methods and apparatus are needed for detecting non-uniform rotation distortion to allow enhanced display of intravascular ultrasound images.
SUMMARY OF THE INVENTION
The present invention provides methods and apparatus which detect non-uniform rotation in an improved manner without using beacons which may create shadowing of tissue behind the beacons or other undesired artifacts in the image. In specific embodiments, the present invention may provide a particularly simple and useful solution for addressing the problem of non-uniform rotation distortion in intravascular ultrasound imaging in systems which use mechanical scanning.
According to a specific embodiment, the present invention provides a method for detecting non-uniform rotation distortion in an intravascular ultrasound blood vessel image. The method includes the step of providing a catheter probe within a blood vessel, where the catheter probe includes a sheath and a transducer substantially centrally located within the sheath. The transducer is mechanically controlled and the catheter probe also includes a bubbly liquid between the sheath and the transducer. The method also includes the steps of emitting an ultrasonic beam to produce echoes reflected from the bubbly liquid and the sheath to obtain a given image vector, and sampling the echoes in multiple time windows for the given image vector. In addition, the method includes the step of correlating the sampled echoes in the multiple time windows to determine existence of non-uniform rotational speed of the transducer.
According to another specific embodiment, the present invention provides a method for detecting non-uniform rotation distortion in an intravascular ultrasound blood vessel image. The method provides a catheter probe within a blood vessel, where the catheter probe has a transducer substantially centrally located therein and the transducer is mechanically controlled. The method also provides steps of emitting multiple ultrasonic beams to produce echoes reflected from a blood region within the blood vessel to obtain multiple successive image vectors, and sampling the echoes at a predetermined range (r
p
) for each of the successive image vectors. The r
p
for each of the successive image vectors is located within the blood region. The method further includes obtaining correlation coefficients for the sampled echoes at r
p
between each of the successive image vectors to determine changes in a rotational speed of the transducer.
According to another specific embodiment, the present invention provides related apparatus and other methods for detecting non-uniform rotation distortion in an intravascular ultrasound blood vessel image utilizing correlation. These and other embodiments of the present invention, as well as its advantages and features, are described in more detail in conjunction with the text below and attached figures.
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Petros Maragos, “Morphological Correlation and Mean Absolute Error Criteria,”IEE
Lateef Marvin M.
Patel Maulin
Sci-Med Life Systems, Inc.
Townsend and Townsend / and Crew LLP
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