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THREE-DIMENSIONAL SYSTEM FOR
ABDOMINAL AORTIC ANEURYSM
This invention relates generally to a system for ultrasound imaging of the descending abdominal aorta artery, and more specifically concerns such a system in which the ultrasound data is acquired and analyzed without the aid of a skilled sonographer.
BACKGROUND OF THE INVENTION
The aorta artery in the abdomen carries blood from the 15 heart to the abdominal region. One disorder of the abdominal aorta is known as an abdominal aortic aneurysm, which is a permanent localized dilation of the arterial wall of the abdominal aorta. When dilation of the arterial wall is greater than 1.5 times the typical, i.e. nominal, diameter, it is 20 referred to as an aneurysm. A normal abdominal aorta is shown in FIG. 1. FIG. 1A shows a typical aortic aneurysm at 16. An aortic aneurysm is usually located below the renal arteries 18 and the kidney arteries 20 and above the aortailiac bifurcation 22. Below the aortic-iliac bifurcation 22 are 25 additional arteries. Abdominal aortic aneurysms are a fairly common disorder, occurring in approximately 5-7% of the population over age 60. Abdominal aortic aneurysms, depending upon their size, result in pressure on adjacent tissue structure and organs, causing potential embolization 30 and/or thrombosis in those tissues/organs. Rupture of the aneurysm typically results in death, and comprises approximately 2% of all deaths in men over 60 years of age.
Accurate diagnosis of an abdominal aortic aneurysm is important in preventing rupture, as well as in controlling the 35 expansion of the aneurysm. Convention two-dimension B-mode ultrasound scan devices are currently used to produce measurements of aortic aneurysms, both axially (longitudinally) along the aorta and laterally (radially) across the aorta. Typically, the accuracy is within three 40 millimeters of the actual size of the aneurysm, using conventional CT or MRI processing. These conventional systems, whoever, are very expensive, both to purchase/ lease and to maintain. Further, a trained sonographer is necessary to interpret the results of the scans. This results in 45 many aneurysms going undetected and/or being not consistently monitored after discovery, until rupture and resulting death of the patient.
Hence, it would be desirable to have a low-cost yet
accurate system to detect and measure abdominal aortic aneurysms. In particular, it would be useful to a primary care physician or emergency personnel to have a low-cost device which provides accurate information concerning aortic aneurysms, without the necessity of a trained technician to ^ interpret the scan results.
SUMMARY OF THE INVENTION
Accordingly, the present invention is a system and corresponding method for abdominal aortic aneurysm evalua- 60 tion and monitoring, which comprises a data collection device/method step for obtaining three-dimensional ultrasound scan information of a selected portion of an abdominal aorta, in the form of a plurality of scan line planes; a processor/step for converting the scan line plane information 65 into coordinates in which the converted scan line planes slice approximately perpendicularly through the aorta; a
processor/step for determining aorta boundary information from the converted scan information; and a calculation circuit/step for calculating the diameter of the aorta from the boundary information, wherein diameter information from the aorta at a plurality of locations therealong is useful in determining the existence of an aneurysm in the abdominal aorta artery.
Another aspect of the invention is a system for abdominal aortic aneurysm monitoring, comprising: an apparatus for obtaining three-dimensional ultrasound information for a selected portion of an abdominal aorta and for processing said ultrasound information to determine aorta boundaries; and a processor for compounding the boundary information to produce a visual representation of the aorta, surfacerendered to produce a realistic representation of the aorta.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 and 1A are simplified drawings showing the aortic artery, without and with an aortic aneurysm.
FIGS. 2 and 2A are diagrams showing a 3-D scan using ultrasound with plane coordinates.
FIG. 3 is a drawing showing the arrangement of five scanheads for adequate coverage of the abdominal aorta area.
FIG. 4 is a diagram of a portion of the system of the present invention.
FIG. 5 shows the scan planes as they intersect the aorta after conversion to spherical coordinates.
FIGS. 6 and 7 are flow charts showing the function of the system of the present invention, including software portions thereof.
FIGS. 8A-8D are diagrams showing the result of the various steps in the boundary determining portion of the system of the present invention.
FIG. 9 is a diagram showing the overlapping coverage of the ultrasound scans of the system of the present invention.
FIG. 10 shows quadrature demodulation using synchronous sampling.
BEST MODE FOR CARRYING OUT THE
As briefly discussed above, an abdominal aortic aneurysm is defined as a dilation of the wall of the abdominal aorta. The average aorta diameter is two centimeters (somewhat greater in men and somewhat less in women). Since the definition of an aneurysm is 1.5 times the average aortic diameter, an aorta diameter greater than three centimeters is an indication of an aneurysm. Aneurysm diameters of between three centimeters and five centimeters should be monitored regularly, while an aneurysm greater than five centimeters in diameter should have prompt surgical treatment to prevent rupture and resulting probable death.
In the present invention, generally, a conventional ultrasound transducer, which in operation transmits and receives back an ultrasound beam, is positioned by an operator on a patient approximately over the abdominal aorta. This is explained in more detail below. The device first produces an ultrasound signal which is processed by Doppler techniques relative to the blood flow through the artery to produce an audible sound based on blood flow. The operator uses the Doppler sound to accurately position the device relative to the aorta.
The device is then operated to produce a threedimensional scan by generating a plurality of individual scan
lines at successive angles of rotation. The resulting threedimensional scan will encompass the descending aorta. This operation of the ultrasound transducer device can be readily carried out by emergency personnel; a trained sonographer or ultrasound technician is not necessary. The resulting data 5 can then be processed, either locally or remotely, to produce an indication of the existence of an aneurysm and the extent of the aneurysm. In selected cases, an actual image of the aneurysm can be displayed for evaluation by a trained sonographer. However, this is typically not necessary with the present invention, i.e. numerical information over a selected portion of the aorta is sufficient.
Referring now to FIGS. 2 and 2A, an ultrasound beam is generated and transmitted in conventional fashion by one or more ultrasound transducers in a hand-held scanner appa- 15 ratus. In the embodiment shown, each transducer operates at a frequency of 3.7 MHz, producing a beam 30 approximately 15 centimeters deep and 0.04 radians wide. Each transducer includes a motor, which tilts the transducer through a 120° angle (0) by moving the transducer first 60° 20 clockwise and then 60° counter-clockwise. The depth of the beam is indicated by the designation r. This produces a two-dimensional single sector (plane) image of selected depth. A second motor then rotates the transducer in the embodiment shown approximately 15° (angle 9), and 25 another 120° scan plane image is produced, by action of the first motor. This process is repeated until the transducer is rotated in the angle 9 dimension to 180°, resulting in a cone-shaped, three-dimensional image data set comprising 12 individual planes or sectors of data of a selected known 30 depth.
FIG. 2 shows a single plane or sector of radius r and angle 0 120°, while FIG. 2A shows 12 planes of data arranged to give a three-dimensional cone-shaped coverage, with each plane/sector separated in angle 9 by 15°. In this 35 arrangement, the range r (depth) for a scan, the scan or tilt angle 0 and the rotation angle 9 completely identifies each point in the three-dimensional data set. These are generally referred to as plane coordinates.
One important aspect of the present invention is the initial 40 positioning, i.e. aiming, of the scanner prior to the full capture of the data needed to produce the abdominal diagnosis. The scan signals at this point are in a single dimension, with rotational angle 9 being zero. The transducer is positioned at an angle over the aorta such that the 45 resulting one-dimensional scan line will intersect the body at an angle of 25°, although this can be varied to some extent, so that the flow of blood through the aorta will have an advancing component of its velocity vector relative to the transducer. This will cause the Doppler backscatter to be 50 shifted to the upper side band of the transmitted signal spectrum. The resulting audio Doppler signal is provided through a speaker in the scanner. The scanner is moved around by the operator to the point where the maximum sound is heard, indicating the point of maximum blood flow. 55 The scanner is then considered to be centered on the aorta. This arrangement makes the initial positioning, i.e. aiming, of the scanner simple and straightforward, without requiring trained personnel.
Hence, the data collection device, i.e. scanner, can be 60 properly positioned on the patient without the necessity of an image, i.e. it is a "blind" positioning. When the audible sounds of blood flow are heard, the operator initiates the regular capture mode of the scanner by depressing a scan button on the device. The instrument then "captures" a 65 three-dimensional scan cone with B-mode image data covering a portion of the aorta. In the present embodiment, the
scan data is interpreted by algorithms to produce information concerning the aorta walls, which permits the determination of aortic diameter, for instance.
One cone-shaped, three-dimensional scan typically will not cover the entire abdominal aorta to include the renal artery, the iliac bifurcation and the superior mesenteric artery. Several approaches are used to cover the large field of view.
In one embodiment, five individual transducers 32—32 are arranged linearly, with a physical separation between the scanheads, as shown in FIG. 3. In this case, the separation is five centimeters, although this can be varied. Typically, the five scanhead arrangement will cover the abdominal region to provide scan coverage of the desired portion of the aorta. In this embodiment, ultrasound signals are generated in parallel with an identical motion in such a way that they do not interfere with each other. Since the geometry of the plurality of scan cones is fixed, this embodiment has the best cone-to-cone coordination. This is the fastest system but also the most hardware-intensive and expensive. The resulting data can be sent by the internet for remote processing.
Other arrangements and numbers of transducers can, however, be used. The geometry of movement of the transducers in the scanner can be arranged to reduce the computational requirements of the system. For instance, the individual transducers can be sequentially energized so that the information from only one scanhead at a time is being processed. The resulting information can then be combined to produce comprehensive scan information concerning the abdominal aorta.
In one such additional arrangement, multiple scans using a single ultrasound scan cone are made. The user takes multiple single cone scans of the aorta area, repositioning the instrument each time along a straight line down the patient's abdomen. The data for all the scans is stored and then sent via the internet for remote processing.
In still another embodiment, using a single scan cone and a single scan, the aortic diameter is displayed on the instrument following a scan. The user moves the instrument around on the abdomen to find the largest diameter, which is calculated either from a full three-dimensional scan cone or a single two-dimensional power Doppler plane.
If a single two-dimensional power Doppler plane is used, the diameter information is presented faster, the user looks for the maximum aorta diameter, and when that is determined, pushes a button, which results in the device taking a full three-dimensional scan. The three-dimensional scan produces a more accurate maximum diameter, and the resulting three-dimensional image is stored for later upload to the web server. In this approach, however, the user must orient the instrument such that the two-dimensional plane cuts across a true cross-section of the aorta. The Doppler audio aiming feature is not utilized, since power Doppler includes this same information.
The use of a three-dimensional scan cone removes this orientation requirement, permitting the user to position the device in any orientation. The user simply takes several three-dimensional image scans, moving along the patient's abdomen. When not doing a full three-dimensional image, the device outputs Doppler-audio to guide the user aiming the device. After each scan, the diameter of the section of the aorta covered by that scan is displayed and the image is stored if the diameter from the new scan is larger than any previous diameter. The image produced in this embodiment, whether it be from two-dimensional power Doppler plane or three-dimensional scan cone, can be optimally transmitted via the internet for remote enhanced processing and rendering.