Court Opinion

ID: 211778
Source: CourtListenerOpinion
Date Created: 2011-03-13 08:31:30+00
Date Added: 2024-06-11T17:28:08.551560
License: Public Domain

NOTE: Pursuant to Fed. Cir. R. 47.6, this disposition
                      is not citable as precedent. It is a public record.

United States Court of Appeals for the Federal Circuit

                                           04-1546

                               TRANSONIC SYSTEMS, INC.,

                                                         Plaintiff -Appellant,

                                              v.

              NON-INVASIVE MEDICAL TECHNOLOGIES CORPORATION
                 (doing business as In-Line Diagnostics Corporation),

                                                         Defendant-Appellee.

                                _______________________

                                 DECIDED: July 25, 2005
                                _______________________

Before SCHALL, GAJARSA, and PROST, Circuit Judges.

GAJARSA, Circuit Judge.

         Transonic Systems, Inc. appeals from the district court’s judgment of no

infringement, in favor of Non-Invasive Medical Technologies Corporation, on claims 1,

9, 24, and 32 of U.S. Patent No. 5,685,989 (issued Nov. 11, 1997). Transonic Sys., Inc.

v. Non-Invasive Medical Techs. Corp., No. 1:99cv41 B, 1:00cv46 ST (D. Utah Aug. 9,

2004).

         The district court erred in construing, and applying, the claim term “calculating”.

As set forth herein, the court reverses the district court’s claim construction, vacates the
judgment of no infringement, and remands for further proceedings concerning both the

“Delta H” and “Go / No-Go” methods, and NMT products, at issue. The district court

further determined that Transonic was estopped from asserting infringement under the

doctrine of equivalents for all four claims. We vacate the district court’s prosecution

history estoppel ruling and remand for further proceedings.

       Finally, we clarify that the “calculating means” in claims 24 and 32 require the

function of “calculating” as defined in claims 1 and 9. On remand the district court

should evaluate the means-plus-function terms in claims 24 and 32 for infringement

using a section 112, paragraph 6 analysis, in light of the meaning of “calculating” as

explained herein.

                                            I.

       Transonic Systems, Inc. (“Transonic”) and Non-Invasive Medical Technologies

Corporation (“NMT”) make kidney dialysis equipment. Transonic owns U.S. Patent No.

5,685,989 (“the ’989 patent”) to a “Method and Apparatus to Measure Blood Flow and

Recirculation In Hemodialysis Shunts.”

       A dialysis machine takes blood from a surgically implanted shunt, cleans it, and

returns the blood to the body. The shunt eventually suffers from clotting or clogging; if

allowed to progress past a certain point, the normal blood flow through the shunt is

impaired and the dialysis is subject to “recirculation.” Recirculation means that blood is

drawn in multiple passes through the dialysis machine. The effect of recirculation is to

reduce the machine’s efficiency, because the recirculation displaces blood that needs

dialysis.   Eventually a new shunt must be implanted, but the number of times and

places this can be done is limited.

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                                          -2-
       The ’989 patent addresses this problem by teaching methods, and devices, for

ascertaining the blood flow through the shunt. If reduced blood flow is identified early

enough, doctors can intervene and address the reduced flow before a new shunt is

required. The patent approaches this problem by a method termed “dilution,” which

relates the observable properties of volume, concentration, and measurable duration of

an “indicator” to the shunt blood flow of interest. An indicator is a substance that alters

a measurable property of blood, added during flow through the dialysis loop. The ’989

patent describes eight equations setting forth specific relations between these

observables – or measures derived from observable parameters – and the shunt blood

flow of interest. Independent claims 1 and 9 are directed to processes for ascertaining

the blood flow through a shunt, and independent claims 24 and 32 are directed to

devices for doing the same.

       NMT makes a “Crit-Line Monitor” that monitors patient’s blood during dialysis.

NMT further teaches two methods for ascertaining shunt blood flow. The first, “Delta H”,

relates to the hematocrit (red blood cell concentration) in dialyzed blood as a function of

varying the dialysis filtration rate. The second, “Go / No-Go”, calls for comparing one

measured parameter, called “reverse-line recirculation” (the percentage of treated blood

that recirculates through the dialyzer when blood flow through the dialyzer is reversed),

to a reference (33%). If greater than 33%, the method teaches that shunt blood flow

has fallen below 600 ml / min, indicating a problem.

       Transonic sued NMT for infringing claims 1, 9, 24, and 32 of the ’989 patent. The

disputed claim term is “calculating.”     This court has, on two occasions, already

addressed the meaning of “calculating.” First, in Transonic Sys., Inc. v. Non-Invasive

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                                           -3-
Medical Techs. Corp., 10 Fed. Appx. 928 (Fed. Cir. 2001) (“Transonic I”), the court

vacated and remanded the grant of preliminary injunction for Transonic. In Transonic I,

the court explained that “calculating . . . must be construed as requiring the use of at

least one of the equations set forth in the specification of the ’989 patent.” Id. at 934.

Second, in Transonic Sys., Inc. v. Non-Invasive Medical Techs. Corp., 75 Fed. Appx.

765 (Fed. Cir. 2003) (“Transonic II”), the court vacated and remanded the district court’s

summary judgment for NMT of non-infringement. Id. at 778. The court clarified its claim

construction and further directed the district court to consider the doctrine of equivalents

in view of the intervening Supreme Court decision in Festo Corp. v. Shoketsu Kinzoku

Kogyo Kabushiki Co., 535 U.S. 722 (2002). Id. at 775-79.

       On remand the district court interpreted this court’s clarification of “calculating” in

Transonic II as meaning “requir[ing] calculation of a dilution curve.” Turning to the

“Delta H” method, the district court found no literal infringement of method claims 1 or 9.

The court further determined that, as to “calculating means” under device claims 24 and

32, “NMT technology does not use the mathematical principles disclosed in the

Transonic patent.” The court understands this as a ruling that the accused devices lack

an identical function, namely, “calculating” as defined in claims 1 and 9. Turning to the

“Go / No-Go” method, the court found no evidence that the method “used” an equation

relating to the teachings of the ’989 patent, and implicated by the term “calculating.”

Finally, the district court determined that “the difference between [Delta H] and the ’989

patent is substantial” and found Transonic barred from asserting infringement under the

doctrine of equivalents.

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                                            -4-
       On August 6, 2004, the district court granted partial summary judgment of no

infringement for Transonic on all four claims. Transonic filed its notice of appeal on

August 17, 2004, asserting jurisdiction under 28 U.S.C. § 1292(c)(1). On March 18,

2005, the parties stipulated to final judgment in the trial court, nunc pro tunc to August 6,

2004. The court has jurisdiction under 28 U.S.C. § 1295(a)(1).

                                             II.

                                             A.

       The court reviews de novo the district court’s grant of partial summary judgment.

The court will affirm the partial summary judgment of no infringement in favor of NMT if,

drawing all reasonable factual inferences in favor of Transonic, the court concludes that

the district court made the proper legal determinations and no genuine issue of fact

prevented the determination of no infringement. Fed. R. Civ. P. 56(d); Anderson v.

Liberty Lobby, Inc., 477 U.S. 242, 255 (1986).

       The infringement analysis follows two well-traveled steps. First, the court must

review the district court’s reading of “calculating”. See Cybor Corp. v. FAS Techs., Inc.,

138 F.3d 1448, 1454 (Fed. Cir. 1998) (en banc). This is a legal issue reviewed de novo.

Id. Second, the court reviews the district court’s application of the properly construed

claims to the accused product. The comparison is a factual issue. See Teleflex, Inc. v.

Ficosa North America Corp., 299 F.3d 1313, 1323 (Fed. Cir. 2002). Reviewing partial

summary judgment of literal infringement this court assesses, de novo, whether the

district court correctly found no genuine issue of material fact precluding the judgment of

no infringement.

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                                            -5-
                                           B.

                                            1.

      In Transonic II this court examined the relation between the “dilution principles”

discussed in the ’989 patent specification, the equations set forth in that specification,

and the meaning of “calculating” and “determining” in the asserted claims. Rejecting the

notion that infringement lay only in solving for shunt blood flow using the “exact

equations” in the ’989 patent specification, this court recognized that the specific

arguments of the various equations might vary depending on the choice of indicator and

the properties inspected to ascertain indicator density at any given time. As the court

explained,

      [T]he specification is always highly relevant to the claim construction
      analysis. Usually, it is dispositive; it is the single best guide to the
      meaning of a disputed term.” Vitronics Corp. v. Conceptronic, Inc., 90
      F.3d 1576, 1582 (Fed. Cir. 1996). In this case, the patentee’s statements
      made in the SUMMARY OF THE INVENTION, and reproduced in
      pertinent part below, are instructive:

             Blood flow, Q, measured by the dilution method (A.C.
             Guyton Textbook of Medical Physiology, Sixth Edition, p.
             287, 1981) is given by:

                                      Q=V/S (Eq.1)

             where V is the amount of injected indicator and S is the area
             under a dilution curve and is equal to the average
             concentration of indicator in the blood for the duration of the
             curve, multiplied by the duration of the curve.

                                         * * *
             The change of characteristics is measured by known
             sensors, such as sound velocity sensors, electrical
             impedance sensors, optical sensors, thermal sensors,
             isotope sensors, or the like, and the blood flow relationships
             are calculated in accordance with the foregoing equations.

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                                          -6-
       ’989 patent, col. 1, ll. 56-61 & col. 4, ll. 26-27. . . . [T]he specification [of
       the ’989 patent] does not disclose “calculating” or “determining” without
       the use of one of the disclosed relationships.

                                            * * *

       During prosecution of the ’989 patent, in response to an Office Action
       rejecting the pending claims, Transonic identified several “primary features
       of the invention.” Included in these features was “the calculation of shunt
       blood flow (line blood flow) from the sample via dilution principles as is
       taught in the present application.”         As discussed above, the only
       “calculation . . . via dilution principles” taught in the specification of the
       ’989 patent revolves around the disclosed equations. In the same
       response, Transonic argued that the disclosed equations are critical to
       achieving the purpose of the invention and are novel over the prior art. It
       stated in pertinent part as follows:

                 The purpose of the invention is to measure shunt (blood line)
                 blood flow, and for this purpose the application sets out the
                 flow relationships which permit calculation of the line blood
                 flow from other measurements. These relationships are not
                 taught in the prior art. . . .

       Moreover, Transonic distinguished a prior art reference during prosecution
       by explaining that, “in the present invention[,] shunt flow is calculated from
       a dialysis flow and a concentration curve measurement.” Based upon the
       claim, the specification, and the prosecution history, we again conclude
       that Transonic “disclaimed any interpretations of the terms ‘calculating’
       and ‘determining’ that do not reflect the stated significance of the
       disclosed equations to the invention as a whole.”

Transonic II, 75 Fed. Appx. at 775-76.

       The court concluded:

       [T]he terms “calculating” and “determining” must use at least one of the
       equations set forth in the specification of the ’989 patent, i.e., “Q = V/S”,
       but that the claims also cover the use of indicators other than saline. In
       other words, the elements of the equation, “V” and “S”, may be altered to
       account for the characteristics of different indicators, such as saline,
       temperature, etc., so long as the relationships set forth in the equations in
       the specification are still expressed.

Id. at 776-77.

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                                             -7-
                                             2.

       Although the court explained that “calculating” or “determining” required the “use

of at least one equation” set forth in the ’989 patent specification, it did not delve into

what it meant to “use” an equation or relation. Based on the ’989 patent specification’s

frequent reference to dilution curves, on remand following Transonic II the trial court

concluded that “calculating” means that the accused infringer has to “calculate a dilution

curve.”

       Transonic contends that the trial court erred in this claim construction.          In

particular, Transonic contends that the construction is not required by the plain

language of the claims, and, indeed, violates the canon of claim differentiation by

making superfluous the specific reference to dilution curves in claim 18. Nor is the trial

court’s reading compelled by the ’989 patent’s written description, which discusses

dilution curves in the context of explaining various mathematical relations but does not

suggest that a curve must actually be drawn, or the area under a curve must be

measured from a graph, in order to make use of the relations set forth in the

specification. Finally, Transonic maintains that the trial court erred in ignoring the effect

of a broadening amendment during prosecution, in which specific reliance on dilution

curves was moved to issued claim 18 as a special case of the asserted claims. As set

forth below, we agree with Transonic.

                                             3.

       For this analysis the court focuses on language, and prosecution history, of

issued claims 1, 9, and 18. See Vitronics Corp. v. Conceptronic, Inc., 90 F.3d 1576,

04-1546
                                            -8-
1582 (Fed. Cir. 1996); Bell Communications Research, Inc. v. Vitalink Communications

Corp., 55 F.3d 615, 619-20 (Fed. Cir. 1995).

       As originally filed, claim 1 required:

       [1] measuring the [a] amount and [b] duration of said changed physical
       property in said arterial line and [2] producing a dilution curve from said
       measurement; and

       [3] determining from the area of said dilution curve the blood flow in said
       arterio-venous shunt.

(ll. 21-25).

       Responding to a June 19, 1996 Office Action (and examiner interview), the

inventors cancelled original claim 1 and added new independent claims (43 and 52) that

issued as independent claims 1 and 9.                 The inventors explained that the new

independent claim 43 was “revised to more clearly highlight the features of the invention

which distinguish it over the prior art of record[.]” Arguing that new independent claims

43 and 52 (issued as 1 and 9) “define the primary features of the invention,” the

inventors defined those features as:

       - “The sampling of the mixture downstream in the shunt using the intake of the
       hemodialysis circulating system;” and

       - “The calculation of shunt blood flow (line blood flow) from the sample via
       dilution principles as is taught in the present application.”

       As issued, claim one requires:

       measuring the amount of distinguishable blood characteristic in said
       removed portion of mixed blood; and

       calculating the rate of flow of said shunt blood flow in said arterio-venous
       shunt from said measured amount of distinguishable blood characteristic.

’989 patent, col. 8, ll. 51-55 (emphases added). For this analysis, claim 9 differs only by

reciting “determining” instead of “calculating.”

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                                                -9-
       The district court, Transonic argues, limited “calculating” in a manner consistent

with the originally filed claim, but inconsistent with the broadened language that actually

issued in claims 1 and 9.

       By comparison, Transonic points to issued claim 18. It reads:

       18. The process of claim 9, further including:

       [1] producing from the changed parameter measurement an indicator
       dilution curve representing said distinguishable blood characteristic; and

       [2] determining from said indicator dilution curve said blood flow rate in
       said shunt.

’989 patent, col. 10, ll. 9-13 (emphases added). As Transonic argues, issued claim 18

basically appends to claim 9 (which, with issued claim 1, replaced original claim 1) the

limitations from original claim 1.

       In view of this record, two long-standing principles of claim construction support

the view that “calculating” is not limited to “producing a dilution curve,” nor to

“calculating a dilution curve.”      First, this court’s case law precludes a reading that

restricts “calculating” to the limitations removed by broadening amendment. See United

States v. Telectronics, Inc., 857 F.2d 778, 783 (Fed. Cir. 1988) (“[C]ourts are not

permitted to read back into the claims limitations which were originally there and were

removed during prosecution of the application through the Patent Office.” [cit. omitted]);

Kistler Instrumente AG v. United States, 628 F.2d 1303, 1308 (Ct. Cl. 1980) (“It is

significant that none of the claims in the patent which ultimately issued contain the

narrow limitation of original claim . . . . It must be concluded that the Patent Office did

not feel that this was a critical limitation. Thus, defendant's insistence upon this court's

reading back into the claims limitations which were originally there and were removed

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                                             - 10 -
during prosecution of the application through the Patent Office cannot be permitted.”).

Thus, “calculating” in issued claim 1 is broader than “calculating” in originally filed claim

1. The district court’s construction is consistent with the plain language of the originally

filed claim, but not the issued claim.

       Second, by the doctrine of claim differentiation the court presumes that

“determining” in claim 9 must have a different scope from the narrow limitations set forth

in claim 18. See Liebel-Flarsheim Co. v. Medrad, Inc., 358 F.3d 898, 910 (Fed. Cir.),

cert. denied, 125 S. Ct. 316 (2004) (“[T]he presence of a dependent claim that adds a

particular limitation raises a presumption that the limitation in question is not found in

the independent claim.”). “There is presumed to be a difference in meaning and scope

when different words or phrases are used in separate claims. To the extent that the

absence of such difference in meaning and scope would make a claim superfluous, the

doctrine of claim differentiation states the presumption that the difference between

claims is significant.” Tandon Corp. v. United States Int'l Trade Comm'n, 831 F.2d

1017, 1023 (Fed. Cir. 1987).       Claim 18 plainly requires “producing … an indicator

dilution curve” and “determining” the shunt blood flow from it.          By straightforward

application of this doctrine, “determining” in claim 9 (and “calculating”) has broader

scope; it does not require “producing an indicator dilution curve.”         Although claim

differentiation is only an interpretative presumption, NMT identifies no substantive

reason to foreclose its application here. Cf. Comark Communications, Inc. v. Harris

Corp., 156 F.3d 1182, 1187 (Fed. Cir. 1998).

       The ’989 patent specification is fully consistent with a reading of “calculating” or

“determining” that does not require creating a dilution curve or measuring the area

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                                           - 11 -
underneath it. In the Summary of Invention, Transonic introduces its use of dilution

methods to ascertain shunt blood flow.       Discussing blood flow Q as a function of

indicator volume V and defined variable “S”, the specification explains:

        S is the area under a dilution curve and is equal to the average
        concentration of indicator in the blood for the duration of the curve,
        multiplied by the duration of the curve.

’989 patent, col. 1, ll. 62-65. As this passage explains, the area under a dilution curve

can be ascertained without actually drawing such a curve and measuring the area under

it.   Put differently, the parameter relevant to the claims at bar, “S”, represents the

product of average indicator concentration over a specific interval, and the duration of

that interval. In short, although “S” may have meaning as an area in the context of a

dilution curve, charting indicator concentration over time, the fact that S may be

graphically illustrated does not require that an infringer actually plot the curve. Aside

from claim 18, which specifically requires “producing … an indicator dilution curve,” the

claims at bar do not so require. The ’989 patent specification, both at claim 18 and the

written description explaining dilution principles, thus does not support the district

court’s analysis. The trial court erred in reading “calculating” and “determining” to mean

“calculation of a dilution curve.”

        As this court explained in Transonic II, an infringer “calculates” or “determines”

shunt flood blow within the meaning of the asserted claims by “using” at least one

equation set forth in the ’989 patent. A method or device “calculates” shunt blood flow

within the meaning of the asserted claims if it solves for the flow as a function of the

parameters set forth in the relevant question.

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                                          - 12 -
       For example, the ’989 patent expresses the basic relation between shunt blood

flow (Q) and ‘dilution’ as a ratio of indicator volume (V) and the product of a measuring

interval and the average indicator concentration over that interval (S). I.e., Q = V / S.

This expression captures an intuitive relationship in which a high blood flow rate

suggests a briefer interval over which indicator can be detected, or a lower average

concentration as the indicator rapidly dissipates in the presence of a high blood flow

rate (and vice versa). A method or device that solves for shunt blood flow by measuring

or deriving indicator volume, identifying a measuring interval over which the indicator is

detectable, and obtaining the average indicator concentration over that interval, and

combining this information according to a relation described in the ’989 patent, therefore

“uses” that relation. A method that obtains S by plotting a dilution curve and measuring

the area beneath it provides one way of “using” this relation or equation, but the

asserted claims are not limited to that approach.

       The court further reaffirms the analysis in Transonic II, where the court held that

such “use” of an equation set forth in the ’989 patent includes varying the specific

parameters at issue to account for different indicators or different indicator or blood

properties that are inspected to ascertain indicator density. That is, “the elements of the

equation, ‘V’ and ‘S’, may be altered to account for the characteristics of different

indicators . . . so long as the relationships set forth in the equations in the specification

are still expressed.” 75 Fed. Appx. at 777. The elements of the equation may be

altered to account for use of a different indicator, a different way of introducing that

indicator to the bloodstream at the upstream location, and a different changed blood

characteristic measured at the downstream location, so long as the resulting equation

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                                           - 13 -
utilizes indicator dilution principles to estimate shunt blood flow. Thus, so long as an

equation that embodies indicator dilution principles is used to estimate shunt blood flow,

use of a different indicator, a different way of introducing the indicator to the blood, and

a different changed blood characteristic do not mean that shunt blood flow is not

“determined” or “calculated.”

       In sum, the court reverses the trial court’s claim construction.      The asserted

claims do not require “producing a dilution curve.” Instead, “calculating” in claim 1, and

“determining” in claim 9, means solving or estimating shunt blood flow, using at least

one of the equations set forth in the ’989 patent. A method or device “uses” an equation

in the ’989 patent when it solves for shunt blood flow by combining measured

parameters according to a particular relation specified in a relevant equation from the

’989 patent.

                                            C.

       The court next considers whether, under the proper claim construction, the

district court properly granted judgment of no infringement.         The partial summary

judgment is proper only when no reasonable trier of fact could find that every limitation

recited in a properly construed claim is found in the accused device or method either

literally or under the doctrine of equivalents. See Bai v. L & L Wings, Inc., 160 F.3d

1350, 1353-54 (Fed. Cir. 1998).

                                             1.

       The district court stated that “[b]ecause indicator dilution equations are not the

relationship contemplated by the Federal Circuit, the court need not consider whether

∆H equations are indicator dilution equations.”       Under this court’s construction of

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                                           - 14 -
“calculating” and “determining,” however, the fact-finder must consider whether the

Delta H method utilizes an equation that embodies indicator dilution principles. Upon

review of the evidence, we conclude that a summary judgment was improper. With this

record a reasonable fact-finder could find that determining shunt blood flow using the

Delta H method is “calculating” or “determining” shunt blood flow within the meaning of

the asserting claims.

       As noted above, the Delta H method calls for assessing shunt blood flow by

analyzing hematocrit as a function of a dialysis ultrafiltration rate. One of Transonic’s

experts, Dr. Spergel, explained in more detail how Delta H method works:

       [I]n order to measure [shunt] blood flow, the clinician sets the ultrafiltration
       rate in the dialyzer first at a minimum speed, then at a maximum speed,
       and then at a minimum speed at very precise time intervals. It is my
       understanding that changing the ultrafiltration rate changes the hematocrit
       (i.e., the percentage of red blood cell mass in the blood). The CRIT-LINE
       reads the hematocrit at each speed. Then the clinician reverses the lines,
       and repeats the same procedure with the lines in the reversed position.
       From these various hematocrit levels, [shunt] blood flow would be
       manually calculated using a complicated formula provided by NMT in its
       literature.

(J.A. at 936). This “complicated formula” appears in one of NMT’s Technical Notes:

ABF = (UFRmax x Rmax) / (∆HR – ∆HN), where ∆HR = Rmax – [(R1 + R2) / 2)] and ∆HN =

Nmax – [(N1 + N2) / 2)].

       Importantly, the NMT Technical Note defines ∆HR in terms of three

measurements of hematocrit when the lines of the dialyzer are reversed: (1) Rmax, which

is a measurement of hematocrit at maximum ultrafiltration speed; (2) R1, which is a first

measurement of hematocrit at minimum ultrafiltration speed; and R2, which is a second

measurement of hematocrit at the minimum ultrafiltration speed. By comparing Rmax to

the average of R1 and R2, the formula appears to take into account the change in

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                                            - 15 -
hematocrit when the lines of the dialyzer are reversed. Moreover, according to the

Technical Note, these measurements of hematocrit are made at four minute intervals,

which seemingly correspond to the “very precise time intervals” referred to by

Dr. Spergel. In light of this evidence, we cannot say that a reasonable jury could not

conclude that the Delta H method measures a changed blood characteristic over time

and utilizes a formula that mathematically relates particular variables according to

indicator dilution principles.

       Thus, the question of whether the Delta H method infringes the claims of the ’989

patent must be remanded for further proceedings consistent with this court’s claim

construction.

                                                2.

       The district court also granted judgment that NMT’s “Go / No-Go” method does

not infringe the asserted claims of the ’989 patent. The trial court relied on an absence

of any genuine issue of fact concerning whether the NMT method “uses” a specific

equation from the ’989 patent relating reverse-line recirculation to shunt blood flow. In

particular, Transonic argued that NMT’s “Go / No-Go” method relies on the relation Qa =

Qb (1 / Rrev – 1), the relation between shunt blood flow (Qa), dialyzer blood flow (Qb),

and reversed-line recirculation or percentage of recirculation with reversed lines (Rrev),

that NMT discloses in material describing its “saline dilution” method. Transonic further

argued that this relation is “mathematically equivalent” to “the equations disclosed” in

the ’989 patent. The trial court focused on equation 5 from the ’989 patent. That

equation provides:

                           Qshunt = Qdial (Vven / Vcal * Scal / Sart – 1)

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                                              - 16 -
’989 patent, col. 2, l. 67. The equation expresses shunt blood flow (Qshunt) as a function

of dialyzer blood flow (Qdial), the volume of indicator injected into the venous line (Vven),

the quantity of indicator used in a calibration injection (Vcal), the area under the diluation

curve generated by a calibration (Scal), and the “absolute concentration of indicator in

the arterial blood line” (Sart). Id. at ll. 18-64. The district court characterized Transonic’s

infringement argument as resting on mere “assumption” that the latter equation restates

equation 5 in the ’989 patent, and further determined that Transonic “has not

established the use of this equation in the ‘Go-No Go method’.” Finding no genuine

issue of fact, the trial court granted summary judgment for NMT.

       Transonic argues that the trial court misread the record and ignored genuine

issues of fact supporting infringement. We agree. First, there is no genuine dispute

that NMT’s “Go / No-Go” method is a special case of NMT’s “saline dilution” method in

which the dialyzer blood flow (Qb) is simply fixed at 300 ml / min, and the calculated

shunt blood flow is simply compared to a reference point of 600 ml / min. NMT’s own

documents indicate that NMT drew its shunt blood flow relation, for the saline dilution

method, from a 1995 article by Krivitski. In a tech note describing its “Go / No-Go”

screening criteria, NMT explained that

       Review of published data proves that at a dialyzer blood flow rate of 300
       ml / min, a reversed-line recirculation [Rrev] of approximately 33% is
       equivalent to an Access Blood Flow [shunt blood flow] of 600 ml / min.

       Using the tech note as a starting point, Transonic’s expert opined that the only

“published data” establishing a “quantitative relationship between access blood flow,

dialyzer blood flow rate, and reversed-line recirculation” was the “formula recited” in

NMT’s literature concerning its “saline dilution” method. In view of this evidence, NMT’s

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                                            - 17 -
argument that “the [saline dilution] equation cited by Transonic never appears in any

literature describing or promoting the Go/No Go method” is misplaced.

       Second, Transonic’s expert further opined that NMT’s reversed-line recirculation

equation, for the “saline” method, and the relations set forth in the ’989 patent, were

“equivalent.”   Notwithstanding the trial court’s characterizing this evidence on

equivalence as a mere “assumption,” we find the expert testimony sufficient to raise a

genuine issue of material fact resisting summary judgment.

       In short, a reasonable fact-finder could find that NMT’s “Go / No-Go” method

infringes the asserted claims by “calculating” or “determining” shunt blood flow on the

basis of relations set forth in the ’989 patent. The trial court erred in granting judgment

of no infringement on NMT’s “Go / No-Go” method.

                                            D.

       The court further notes that claims 24 and 32 both include limitations subject to

the requirements of 35 U.S.C. § 112, ¶ 6 that are affected by our construction of the

term “calculating.”   “Literal infringement of a § 112, ¶ 6 limitation requires that the

relevant structure in the accused device perform the identical function recited in the

claim and be identical or equivalent to the corresponding structure in the specification.”

Odetics, Inc. v. Storage Tech. Corp., 185 F.3d 1259, 1267 (Fed. Cir. 1999). As the

court explained in Transonic II, the functions of both “means for calculating” in claim 24

and “calculator means” in claim 32 require “calculating.”        75 Fed. Appx. at 778.

Therefore, on remand the district court should reassess infringement of claims 24 and

32 under the construction of “calculating”, as clarified above. If the district court finds

that the accused devices perform the identical function of “calculating” shunt blood flow,

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then the district court must ascertain whether the structures of those devices are

identical or equivalent to the corresponding structure disclosed in the ‘989 patent. See

Odetics, 185 F.3d at 1267.

                                          E.

      Finally, the district court determined that Transonic was estopped from asserting

infringement under the doctrine of equivalents. We find this determination unsupported

by the analysis in the district court’s opinion. As explained by the Supreme Court in

Festo, a narrowing amendment made to satisfy any requirement of the Patent Act

invokes a presumption that the patentee surrendered all subject matter between the

broader and the narrower claim language.          535 U.S. at 740.   To overcome the

presumption of surrender, the patentee bears the burden of proving whether an

exception applies. See id. at 740-41 (“The equivalent may have been unforeseeable at

the time of the application; the rationale underlying the amendment may bear no more

than a tangential relation to the equivalent in question; or there may be some other

reason suggesting that the patentee could not reasonably be expected to have

described the insubstantial substitute in question.”). From the district court’s partial

summary judgment order we are unable to ascertain: (1) what amendment is at issue;

(2) what claim scope was deemed to be surrendered; (3) what arguments Transonic

made to overcome any presumption of surrender; and (4) why any such arguments

were insufficient. Accordingly, we vacate the ruling on prosecution history estoppel and

remand for analysis under Festo.

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                                             III.

      The district court’s construction of “calculating” was in error. The court reverses

the district court’s claim construction, and construes the claim as set forth in this

opinion. The infringement analysis depending on this claim construction is flawed, and

must be undertaken anew. Furthermore, the district court failed to conduct a proper

Festo analysis. Therefore, we vacate the judgment of no infringement, and the ruling on

prosecution history estoppel, and remand for proceedings consistent with this opinion.

      Each side shall bear its own costs.

                 REVERSED-IN-PART, VACATED AND REMANDED.

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