Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2000-11-17
2003-03-04
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S473000, C600S476000, C600S478000, C600S481000, C600S500000, C382S128000, C382S130000
Reexamination Certificate
active
06529770
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to the imaging of body passage surfaces through body fluids and, in particular, to a novel technique for imaging cardiovascular surfaces through blood. The invention also relates to an apparatus for carrying out a method of such kind. Such method and apparatus can be advantageously used in examination of cardiovascular surfaces and conducting minimally invasive procedures in cardiovascular surgery.
BACKGROUND OF THE INVENTION
Direct visualization of body passages has become a routine procedure now. Modern endoscopic technique is used for viewing and imaging different body passages, such as gastrointestinal tract, bronchial passages, joints, cardiovascular system. Most of the passages are filled with body fluids, such as blood, urine, stomathic fluids which are opaque for illumination and prevent visualization of the passage's surfaces. For passages not filled with blood it is not a problem because in such body cavities as stomach or esophagus the fluid can be evacuated to clear the visualization field. Similar technique is used in angioscopy. Sterile saline flush solution is introduced into the vessel continuously or periodically for blood evacuation (U.S. Pat. No. 4,998,972 issued Mar. 3, 1991 to Chin Albert K. et. al,; U.S. Pat. No. 4,175,545 issued November 1979 to Termanini). Such procedure provides user with very short time of vision determined by the length of irrigation period. It is particularly difficult to perform this procedure in arterial system where pressure and flow rate of blood are much higher than in veins. It makes difficult to obtain enough clear bloodless field for visualization of the cardiovascular surfaces.
Ability to see through blood would enable revolutionary new approaches in diagnosis and treatment of cardiac, arterial, and venous diseases.
In standard angioscopy procedure a light delivered into a lumen of a cardiovascular passage irradiates the interior. Only backscattered and reflected light is available for imaging. Radiation being reflected and scattered by the surface structure at least partly is detected and intensity signals are used to produce image signals. High concentration of blood cells along with discontinuing in the index of refraction at the interface between plasma and cells make blood a multiply scattering and absorbing medium. Thus, imaging through blood is imaging of diffused and reflected by the surface structure light being scattered many times before it reaches the detector. Because of that the radiation detected at any location of back-scattered flux contains a contribution of scattering from all regions of the irradiated interior resulting in a strong background presence in the detected signals. The background masks the actual intensity signals containing imaging information about the cardiovascular surface. Along with decreasing the contrast of an image signal the scattering attenuates signal itself and limits the optical path length (OPL) in blood. One of the most difficult aspects of imaging through blood is to obtain maximal image signal contrast at maximal optical path length.
With taking into account that only the radiation collected within a field of view of the acquiring optical system is detected and that the angle of view of the cardiovascular surface, &phgr;, is different from the angle of view of the interior, &phgr;, the detected part of incident radiation I
0
is described by equation
I=I
0
[&tgr;
2
&rgr;
s
&phgr;
s
+&rgr;
b
&phgr;] (1)
where &tgr; is the blood transmittance at the wavelength of irradiation and &rgr;
s
is the surface reflectance, &rgr;
b
is the blood diffuse reflectance.
For intraluminal irradiation, the blood can be considered as a semi-infinite medium and the term “diffuse reflectance” characterizes the light emergent the semi-infinite medium back to irradiating side due to scattering. The transmittance and diffusive reflectance in eq. (1) are determined by blood optical properties characterized by an absorption coefficient, &mgr;
a
and reduced scattering coefficient (coefficient of scattering back), &mgr;′
s
per unit length. In diffusion approximation of a semi-infinite cardiovascular interior the radiation backscattered by blood can be characterized by a diffuse reflection [S. Jacques, Diffuse reflectance from a semiinfinite medium. OMC & Report, May 1998] and approximated by expression:
&rgr;
d
∞
=exp
(
−A
/{square root over (3(
1
+N
))})
and the equation (1) can be re-written in form:
I
=
I
0
[
ρ
s
ϕ
s
exp
(
-
2
3
μ
a
μ
t
l
)
+
ϕ
exp
(
-
A
3
(
1
+
N
′
)
)
]
(
2
)
with a total attenuation coefficient &mgr;
t
=&mgr;
a
+&mgr;′
s
and diffuse reflectance characterizing parameter
N
′
=
μ
s
′
μ
a
Here l is the optical path length, and the factor
A
=
-
ln
(
l
l
0
)
The value of A depends on reflectance parameter N′ and refractive index mismatch at the blood-air interface. As it is seen from eq. (2), the primary component of the detected intensity signals is a strong background not containing information about the vessel surface. Such strong background extremely decreases contrast of the intensity signals and dramatically shortens the viewing distance through blood. Once the radiation being diffused back by blood (the second term in eq. (2)) and reflected by the vessel surface (the first term in eq. (2)) are specified, one can calculate the contrast of the intensity signal:
K
=
ρ
d
ρ
s
=
exp
[
-
A
-
3
μ
t
l
3
μ
t
μ
a
]
Optical properties of blood are dependent on wavelength and, therefore, total attenuation and diffuse reflection are also wavelength depend. As a result the intensity signal and its contrast strongly vary with wavelength. That makes attractive to enhance the intensity signal and improve the contrast at the same time simply by selecting an “optimal” wavelength. International patent application WO 00/24310 published in May 2000 discloses a device and method for imaging through body fluids simply by using the radiation of mid Infrared (IR) spectrum regions (1.4 to 1.8 mkm, 2.1 to 2.4 mkm, 3.7 to 4.3 mkm, 4.6 to 5.4 mkm, and 7 to 14 mkm). Blood has obviously reduced scattering in mid IR region. As per inventors' statement the absorption is also extremely low at mid IR wavelengths because water as the main part of blood has optical windows at these wavelengths. However, modern experimental data shows that radiation of above mentioned wavelengths is strongly absorbed by blood glucose [Jason J. Bumeister and Mark A. Arnold
Spectroscopic considerations for noninvasive blood glucose measurements with near infrared spectroscopy,
Infrared Spectroscopy, p. 2, 1999] and other blood components [A. Roggan et. al.
Optical properties of circulating blood in the wavelength range
400-2500
nm,
J. of Biomedical Optics, Vol. 4, pp. 36-46, 1999] resulting in an unacceptably short OPL. Total attenuation and diffuse reflectance spectra derived from published data are shown in FIG.
1
. It is seen that total attenuation in and diffuse reflectance from blood have different spectra and at the wavelength of the signal contrast improvement (mid IR) the total attenuation is unacceptably high.
Numerous techniques for optical imaging based on special processing the detected signals are known in the art. Most of them use a transmission mode imaging. The term “transmission mode” is regarded to detecting the radiation passed through the turbid medium. Methods of this kind are known from the article B. Chance et. al.
Highly sensitive object location in tissul models with linear m. phase and anti
-
phase multielement optical arrays in one and
2
dimersoons,
Proc. of the National Academy of Science USA, Vol. 90 (1993) 3423-3427 and U.S. Pat. No. 5,807,262 issed Sep. 15, 1998 to Papaioannou Dimitoios. By transilluminating the turbid medium with a set of couples
Lateef Marvin M.
Lin Jeoyuh
Zborovsky I.
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