Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2000-09-07
2001-11-27
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S447000
Reexamination Certificate
active
06322509
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to the imaging of moving ultrasound scatterers. In particular, the invention relates to methods for positioning the gate or sample volume (hereinafter “sample gate”) in medical diagnostic ultrasound imaging.
BACKGROUND OF THE INVENTION
Premium medical diagnostic ultrasound imaging systems require a comprehensive set of imaging modes. These are the major imaging modes used in clinical diagnosis and include timeline Doppler, color flow Doppler, B mode and M mode. In the B mode, such ultrasound imaging systems create two-dimensional images of tissue in which the brightness of a pixel is based on the intensity of the echo return. Alternatively, in a color flow imaging mode, the movement of fluid (e.g., blood) or tissue can be imaged. Measurement of blood flow in the heart and vessels using the Doppler effect is well known. The phase shift of backscattered ultrasound waves may be used to measure the velocity of the backscatterers from tissue or blood. The Doppler shift may be displayed using different colors to represent speed and direction of flow. In the spectral Doppler imaging mode, the power spectrum of these Doppler frequency shifts are computed for visual display as velocity-time waveforms.
One of the primary advantages of Doppler ultrasound is that it can provide noninvasive and quantitative measurements of blood flow in vessels. Given the angle between the insonifying beam and the flow axis (hereinafter referred to as the “Doppler angle”), the magnitude of the velocity vector can be determined by the standard Doppler equation:
v=cf
d
/(2
f
0
cos &thgr;) (1)
where c is the speed of sound in blood, f
0
is the transmit frequency and f
d
is the motion-induced Doppler frequency shift in the backscattered ultrasound signal.
In conventional ultrasound spectral Doppler imaging, the operator is required to manually position the sample gate to the measurement location in a two-dimensional image with or without color flow data. The operator also needs to manually adjust the sample gate size relative to the diameter of the vessel to be studied. From the acoustic data acquired over many transmit firings, Doppler frequency spectral data is obtained via standard Fast Fourier Transform (FFT) spectral analysis.
For a given measured Doppler frequency shift f
d
, the flow velocity (speed) v is calculated using Eq. (1). The ideal Doppler angle is zero, i.e., when the beam is aligned in the direction of blood flow. Unfortunately, Doppler angles that can be formed in practice tend to be larger, and as they approach 90 degrees, a small error in the angle estimate can lead to a large error in v. For this reason, it is generally recommended that the Doppler beam be steered to form Doppler angles of no greater than about 60 degrees for reliable velocity measurements. Angle steering is another adjustment the operator needs to make manually in conventional Doppler systems.
In an attempt to minimize manual Doppler adjustments when the spectral Doppler mode is activated, conventional scanners generally provide presets for the Doppler sample gate position and size, and for the beam steering angle. However, such presets have limited benefits because the vessel depth, size and orientation relative to the probe can vary a great deal from one case study to the next.
U.S. Pat. No. 5,365,929 describes the use of multiple range gates and multiple Doppler beams to scan a region of interest. By comparing some signal characteristic, such as total power or maximum velocity, of the multiple sample volumes, the scanner automatically selects the best sample gate for full spectral analysis and display. It will appear to the user that the scanner has automatically positioned the sample gate at a location where the Doppler signal is optimal in some sense.
European Patent Application No. 0 842 638 A2 describes a method of tracking vessel walls in the B-mode image, and then automatically adjusting the sample volume size to ensure the entire vessel diameter is covered. While this may be useful for volume flow measurements, the user is still expected to first manually position the sample volume and vessel wall markers at the correct locations. Also, in Doppler exams that do not involve volume flow measurements, different clinics may follow different practices in terms of sample gate size relative to the vessel diameter.
European Patent Application No. 0 985 380 A1 describes a method for automatic positioning of the Doppler sample gate based on bloodstream or color flow information. Among various specific applications, this method can be used to automatically set the sample gate cursor at an optimal position when the sample gate is first brought up in the image, or when it is being moved. The optimal position may be defined by a color flow pixel showing the highest velocity, or the center point of the largest flow segment, or the center point of the next best flow segment etc.
U.S. Pat. No. 5,690,116 describes a method of estimating the orientation (slope) of the vessel axis based on gray-scale image data, and then computing the Doppler angle.
U.S. Pat. No. 6,068,598 describes a robust method for detecting the vessel walls based on B-mode and/or color flow data, estimating the vessel orientation based on the best vessel edge data, and then computing the Doppler angle.
U.S. Pat. No. 4,937,797 describes a method of adjusting the transducer array beamforming delays to automatically steer the Doppler beam to achieve a target Doppler angle such as 60 degrees (or less). This method, however, requires the user to first manually rotate an angle cursor on the B-mode image to define the vessel orientation or flow direction.
There is a need for an automatic method of initializing and adjusting the Doppler sample gate position and size settings and the beam steering angle setting based on actual vessel image data, with the goal of improving the efficiency of the Doppler study above and beyond what can be achieved using presets.
SUMMARY OF THE INVENTION
The present invention is directed to a method and an apparatus which provides automatic initialization and adjustment of the Doppler sample gate position and size settings, and of the beam steering angle setting based on actual vessel image data. This capability is presented as an aid or “smart feature” to the user when either one of the two following conditions is met: (1) when the sample gate cursor is first activated or brought up in the image (before or upon spectral Doppler mode activation); or (2) when the sample gate cursor is being moved. Both of these conditions are normally monitored automatically by the master controller of the system. In accordance with the preferred embodiment of the invention, if either condition is detected, the following functions are automatically performed: (1) the “morphologically best” or nearest vessel segment within a target search region in the two-dimensional image is found; (2) the sample gate is placed at or near the center of the targeted vessel segment; (3) the sample gate size is adjusted in relation to the vessel size; and (4) the best available steering angle that minimizes the Doppler angle is selected. All four features are intended to provide a good but initial adjustment to the sample gate position and size and to the beam steering angle, which should facilitate further manual adjustments by the user. It is not generally possible to predict exactly which vessel or vessel portion the user wants to study, but by setting up the Doppler sampling parameters according to the best image data available, this invention will improve examination speed and/or ease of use.
The vessel segment search method (step 1 above) in accordance with the preferred embodiment of the invention employs an object search technique based solely on geometric and morphological information in a binarized vessel image obtained from either B-mode or color flow image data. The vessel extraction method disclosed herein is not based on comparing Doppler signal characteristics from multiple sample vo
Dong Fang
Mo Larry Y. L.
Pan Lihong
Washburn Michael J.
Flaherty Dennis M.
GE Medical Systems Global Technology Company LLC
Lateef Marvin M.
Patel Maulin
Vogel Peter J.
LandOfFree
Method and apparatus for automatic setting of sample gate in... 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 automatic setting of sample gate in..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for automatic setting of sample gate in... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2579422