Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2000-03-24
2003-02-04
Jaworski, Francis J. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S443000, C600S455000
Reexamination Certificate
active
06514208
ABSTRACT:
I. FIELD OF THE INVENTION
This invention relates to estimating the amount of blood flowing to the tissues of the kidney. More particularly, the invention is related to analyzing obtained power Doppler ultrasound images taken of the kidney and even more specifically of the kidney cortex tissue to produce a numerical value that correlates to the blood flow.
II. BACKGROUND OF THE INVENTION
Patients suffering from shock have impaired blood flow to the vital organs. The kidney is one such organ. A goal of therapy is to restore blood flow to these organs, including the kidney and in particular the cortex thereof.
Pulmonary artery catheters are often placed during complicated resuscitations, but they carry finite risks such as pneumothorax, pulmonary artery laceration, pulmonary infarction, and line sepsis. Also, data derived from pulmonary artery catheters, arterial blood gases, and so forth address global perfusion but not regional organ perfusion, whereas the latter may be more important in resuscitation.
Shock may result from a burn. Most thermally injured patients respond to standard resuscitation regimens, in which a physiologic crystalloid solution is infused at a rate dictated by total burn surface area and weight, with titration of that rate based primarily on the adequacy of the urine output. However, this approach fails on occasion, particularly in massively burned patients. A recent review at the U.S. Army Institute of Surgical Research Burn Center revealed that 12 of 93 nonsurviving burn patients (13 percent) were resuscitation failures, in whom hemodynamic stability could not be achieved as discussed by Cioffi et al. in “Cause Of Mortality in Thermally Injured Patients,”
Die Infektion beim Brandverletzten: Proceedings of the “Infektionsprophylaxe und Infektionshekampfung beim Brandverletzten” International Symposium,
ed. S. Lorenz & P.-R. Zellner, Darmstadt: Steinkopff Verlag, 1993, pp. 7-11. To salvage these high risk patients, new monitoring devices that accurately assess tissue perfusion may be necessary.
Furthermore, in patients with acute renal failure—whether oliguric or non-oliguric—urine output does not necessarily reflect renal perfusion. This is likewise true of patients who have received a diuretic, whose urine output is driven by glycosuria or nitrogen metabolites, or those in whom alcohol has inhibited antidiuretic hormone. Also, an intervention intended to improve renal blood flow, such as the institution of an inotropic agent or a bolus of an intravenous crystalloid solution, may affect urine output in delayed fashion. Clinicians frequently estimate kidney blood flow by measuring the amount of urine produced per hour. However, in several classes of patients—to include those with acute renal failure and those who have received drugs, which artificially increase the production of urine—urine output measurements are not reliable indicators of kidney blood flow.
No device or technique exists rapidly and reliably to measure kidney blood flow at the level of the small blood vessels of the renal cortex in humans.
One noninvasive tool that has been tried is color Doppler ultrasound (CDUS), which displays mean velocity data and is useful in the study of large vessel blood flow. The slowest flow velocity detectable using color Doppler ultrasound is approximately 4 cm/sec. The ability to detect blood flow in smaller vessels did not exist until the advent of power Doppler ultrasound (PDUS), which provides spectral analysis of the received sound and integration of the resulting amplitude-frequency function to permit display of a perfusion index for each pixel as discussed by Rubin et al. in an article entitled “Power Doppler US: A Potentially Useful Alternative to Mean Frequency-based Color Doppler US,”
Radiology,
190:853-6 (1994) and Bude et al. in an article entitled “Power Versus Conventional Color Doppler Sonography: Comparison In The Depiction Of Normal Intrarenal Vasculature,”
Radiology,
192:777-80 (1994). PDUS is likely to be able to detect blood flow velocity of less than 1 cm/sec in ultrasound images.
In the PDUS mode, the ultrasound processor performs spectral analysis of the reflected sound, e.g., via fast Fourier transform. The amplitude (or power) of each received frequency is proportional to the number of red blood cells (RBCs) which are reflecting at that frequency. Frequency, in turn, is proportional to the velocity of the RBCs. Thus, a large number of RBCs moving at a low velocity should generate a high-power, low-frequency signal, whereas a smaller number of RBCs moving at high velocity should generate a low-power, high-frequency signal. The processor then integrates the power of the received signal over frequency to obtain a perfusion index for each pixel as discussed by Dymling et al. in an article entitled “Measurement of Blood Perfusion in Tissue Using Doppler Ultrasound,”
Ultrasound in Medicine and Biology,
1991:433-44 (1991).
In vitro phantom studies have shown that PDUS image intensity depends, as expected, on both the velocity and the concentration of reflecting particles. Commercially available ultrasound devices translate this numerical data into color output, in which the magnitude of the perfusion index is represented by color intensity. This color information is superimposed on the gray scale ultrasound image as illustrated by Parro et al. in an article entitled “Amplitude Information from Doppler Color Flow Mapping Systems: A Preliminary Study of the Power Mode,”
J Am Coll Cardiol,
18:997-1003 (1991).
Another advantage of PDUS is that it is not subject to aliasing (a signal wrap-around phenomenon seen in CDUS). The relative angle-independence of PDUS makes it less sensitive to inaccurate flow information based on an improper angle of insonation. One disadvantage of PDUS is a longer scanning time, which makes it more susceptible to motion and flash artifacts.
Clinical and animal studies employing PDUS have, as in a study conducted by the inventors and discussed later, demonstrated its utility in imaging the kidneys. Bude et al. demonstrated the increased sensitivity of PDUS over CDUS in depicting intrarenal and renal cortical flow in normal human kidneys, describing the latter as a non-pulsatile “blush.” Durick et al. in an article entitled “Renal Perfusion: Pharmacologic Changes Depicted with Power Doppler US in an Animal Model,”
Radiology,
197:615-7 (1995), used an image analysis procedure to quantify changes in total renal perfusion as depicted by PDUS, following infusion of epinephrine and then papaverine into the renal artery of swine. Taylor et al., as discussed in an article entitled “Renal Cortical Ischemia in Rabbits Revealed by Contrast-Enhanced Power Doppler Sonography,”
American Journal of Roentgenology,
170:417-22 (1998), used contrast-enhanced PDUS to measure renal cortical perfusion during hemorrhagic hypotension in rabbits. The Taylor 5 et al. study found good correlation with blood flow as measured by radiolabelled microspheres; in contrast to the study conducted by the inventors, this correlation was not found when ultrasonographic contrast injection was not performed.
Akiyama et al. In their article entitled “Hemodynamic Study of Renal Transplant Chronic Rejection Using Power Doppler Sonography,”
Transplant Proc,
28:1458-60 (1996) proposed the use of power Doppler ultrasonography to represent blood flow; which however, offered no evidence that a power Doppler image would represent microvascular blood flow. They discussed the use of a power Doppler image focused on three areas of the kidney (the interlobar artery, the interlobular artery, and a portion of the outer cortex) to compare well functioning kidneys (S—Cr≦2.0 mg/dL) and poorly functioning kidneys (S—Cr>2.0 mg/dL) after a kidney transplant operation. The problem with this analysis, in part, is that going into the study it was known which kidneys were accepted and which kidneys were rejected by transplant patients. An explanation for the selection of these three locations is that Akiyama et al. assumed that these three areas would be more i
Cancio Leopoldo C.
Kuwa Toshiyuki
Matylevitch Natalia P.
Arwine Elizabeth
Jaworski Francis J.
Patel Maulin
The United States of America as represented by the Secretary of
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