Vascular phantoms

Details Vascular phantoms Vascular phantoms

1998-12-22

2001-03-27

Noland, Thomas P. (Department: 2856)

Measuring and testing

Specimen model or analog

C073S195000, C430S325000, C434S268000, C600S416000

Reexamination Certificate

active

06205871

ABSTRACT:

FIELD OF THE INVENTION
The invention is in the field of vascular phantoms for modeling fluid flow.
BACKGROUND
Flow studies with models of vascular geometries are useful for analyzing hemodynamics in complex geometries and for development and validations of imaging methodologies. One of the more widely used imaging techniques is angiography, an invasive technique requiring that a catheter be manipulated into the carotid artery and a radio-opaque dye injected. Angiography actually causes stroke in a small group of patients. Non-invasive techniques, such as ultrasound and magnetic resonance angiography (MRA) may also be used to determine the degree of vascular stenosis. However, the results obtained with these modalities may vary widely between laboratories because of differences in both hardware and technical expertise. The result is that vascular laboratories find themselves increasingly in a situation where they have no independent validation method. Several alternative models have been proposed for the calibration of ultrasound equipment, such as restricted surgical tubing (Anthropomorphic Vascular Phantoms, Shelley Medical Imaging Technologies, Ontario, Canada), moving strings (Doppler QA Phantom System, Nuclear Associates, Carle Place, N.Y.) or vibrating plates (Doppler Sensitivity Phantom, Nuclear Associates); however, these modalities do not test the ability of the equipment to measure velocities in flow regimes comparable to those found in vivo. Accordingly, the present invention provides a series of anatomically accurate, clinically relevant stenosis phantoms, which can be transported between centers, allowing assessment of the accuracy of a given laboratory and providing a dramatic effect on the reproducibility of vascular imaging techniques.
Relevant Literature
Imbesi et al. (1998) Am J Neuroradiol 19, 761-766 describe a lost-wax procedure for making a replica of an ulcerated atherosclerotic human carotid bulb.
SUMMARY OF THE INVENTION
The invention provides a system through which blood-mimicking fluid can be pumped to provide a realistic reproduction of flow conditions in the relevant vascular territories. This system can be used in conjunction with radiological imaging modalities, such as Magnetic Resonance Imaging, Doppler Ultrasound, x-ray angiography, etc. In addition, the system can be used with optical imaging methods such as Laser Doppler Velocimetry, Digital Particle Imaging Velocimetry, etc.
The invention provides anatomically accurate, clinically relevant stenosis phantoms, methods of making and using such phantoms, and graded series of such phantoms. In a particular embodiment, the phantoms are silastic molds of artery lumens, made by stereo lithography based upon data from high resolution imaging, such as MRI (e.g. 200 micron resolution) of atherosclerotic plaques or arteries, (e.g. carotid artery, aorta, renal arteries, etc.) excised at surgery. The flow models produced by this method provide features not available in other flow models. There are no limitations on the geometrical configuration of the vessels unlike other models, which require monotonically varying features, i.e. those other models are unable to produce overhangs as occur in realistic vessels. Because of their geometrical accuracy, the flow conditions in these models are realistic representations of flow conditions in vivo. For example, the phantoms may be used in an apparatus which can duplicate particular blood flow patterns, such as the pulsatile flow wave seen at the carotid bifurcation. Hence, true flow conditions (laminar, disordered, turbulent) as found in vivo are readily reproduced. In addition, background material can be adjusted to provide realistic tissue signals, markers can be inserted to help identify ROIs (Regions of Interest), and panels of multiple models to cover a range of geometric configurations such as stenotic conditions or a range of velocities, can be used.
Commercial applications of these phantoms include validation of ultrasound and MRA. The phantoms can be transported between centers, allowing an assessment of the accuracy of a given laboratory and providing a dramatic effect on the overall reproducibility of these imaging techniques. At present there is no available “gold standard” for determining the accuracy of these imaging modalities. Previous attempts at validation have been in reference to angiography: an approach that is fundamentally flawed because it provides a projection view of the vessels which masks many of the detailed features of the vessel surface. Further, the different modalities are inherently unique one from the other and recent data indicate that both ultrasound and MRA may be more accurate than angiography in determining degree of carotid artery stenosis. Thus, the subject phantoms can be used to check imaging equipment for systematic measurement errors, to provide a measurement of random errors arising from scanner imperfections, to train personnel who use the imaging equipment, as a controlled model that can be used for the development and standardization of new imaging methods and hence improve our ability to accurately define vascular disease such as carotid stenosis and risk of stroke.
In a particular embodiment, the model is constructed as follows:
1. The lumen of the vessel is obtained either at surgery or from cadavers. For example, the lumen can be removed during routine endarterectomy surgery to remove atherosclerotic plaque.
2. The lumen and surrounding tissue is imaged, such as with high resolution three-dimensional Magnetic Resonance Imaging. This is accomplished, for example, using a radiofrequency antenna that accommodates a small syringe containing the specimen immersed in high signal fluid that produces high contrast between the tissue and the lumen. Alternatively, fluid producing no MRI signal can be used to give high contrast.
3. The three dimensional data set is postprocessed to produce a binary image.
4. The binary image is converted into a triangulated representation of the surface, in a format (STL) compatible with stereolithography machines.
5. A solid model of the lumen is obtained using commercial stereolithography.
6. The model is encased in rubber and a rubber mold is made.
7. The mold is injected with wax providing a solid model of the lumen in wax.
8. The wax is embedded in transparent silastic.
9. The wax is dissolved leaving a hollow reproduction of the initial vessel.
10. The wax model is connected to a flow circuit that provides a pulsatile waveform. Preferred flow circuits are inexpensive, easy to use systems, such as described herein and providing realistic pulsatility.
11. Translation tables provide reproducible positioning of ultrasound probe.
Accordingly, the invention provides materials and methods for modeling human blood vessels. In a particular embodiment, the invention provides a panel of anatomically accurate vascular phantoms, such as carotid artery phantoms, comprising a range of stenotic conditions from undiseased vessels with no reduction in flow channel to critically stenosed vessels with a reduction in cross sectional area as great as 99%. In another embodiment, the invention provides methods of making anatomically accurate vascular phantoms using stereolithography with an input data set representation of a natural vascular lumenal surface to construct an anatomically accurate vascular phantom comprising a physical representation of said surface. In a more particular embodiment, the input data set representation is of excised atherosclerotic plaques and/or is derived from high-resolution magnetic resonance imaging. The invention also provides methods of using the subject phantoms and panels of phantoms, such as methods of measuring a parameter of fluid flow through a panel of anatomically accurate vascular phantoms comprising a range of stenotic conditions.


REFERENCES:
patent: 2924894 (1960-02-01), Hellund
patent: 2987830 (1961-06-01), Jackson
patent: 4554832 (1985-11-01), Hasegawa et al.
patent: 4855910 (1989-08-01), Bohning
patent: 4974461 (1990-12-01), Smith et al.
patent: 5272909

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