Retrograde hemodialysis access flow during dialysis as a predictor of access pathology.

We have detected retrograde flow by Doppler ultrasound within the hemodialysis access of 10 patients during routine dialysis. Nine of these accesses were prosthetic grafts, and 1 was an autogenous fistula. All 9 of the grafts had access pathology demonstrated by angiography. The single patient with the fistula exhibiting reversed access flow had a poorly developed access with no focal stenoses on angiogram, but 18% recirculation by ultrasound dilution. All patients with retrograde flow had access flow rates below 650 mL/min. While 3 of these patients had substantial access recirculation (2 grafts, 12% and 40%; and 1 fistula, 18%) 2 of these patients had 3% recirculation (2 needle urea method), and 4 patients had 0% access recirculation (ultrasound dilution and 2 needle urea method). We report that retrograde access flow during dialysis may be a specific indicator of access dysfunction. These findings further suggest that retrograde access flow develops before access recirculation, indicating that this finding is more sensitive than recirculation for detecting access dysfunction. Further study is needed to determine the utility of this finding in access surveillance.

Ultrasound detection of microembolic signals in hemodialysis accesses.

Microembolic signals (MES) detected by ultrasound, thought to be of gaseous or solid origin, have been described with decompression illness and in the intracranial and cardiopulmonary circulation. We describe the first reported cases of MES occurring in hemodialysis accesses. Two hemodialysis patients, one with a synthetic graft and one with an arteriovenous fistula, showed MES during a dialysis session detected by duplex ultrasound. We postulate that these MES represent cavitation bubbles developing from turbulent blood flow around the venous needle in the access. However, other potential causes exist, including air introduced into the circulation from the dialysis circuit or microemboli arising from thrombus or atheroma.

Analysis of variable flow Doppler hemodialysis access flow measurements and comparison with ultrasound dilution.

The variable flow (VF) Doppler method determines access blood flow from the pump speed-induced change in Doppler signal between the arterial and venous needles. This study evaluated 35 patients in two analyses to assess VF Doppler measurement reproducibility (54 paired measurements) and compared VF Doppler and ultrasound dilution flow measurements (24 paired measurements). VF Doppler measurement variations were 4% for access flow less than 800 mL/min (n = 17), 6% for access flow of 801 to 1,600 mL/min (n = 22), and 11% for access flow greater than 1,600 mL/min (n = 15). The mean measurement coefficient of variation was 7% for VF Doppler compared with 5% for ultrasound dilution. Correlation coefficients (r) between VF Doppler and ultrasound dilution access flow measurements were 0.79 (n = 24; P < 0.0001), 0.84 for access flow less than 2,000 mL/min (n = 20; P < 0.0001), and 0.91 for access flow less than 1,600 mL/min (n = 18, P < 0.0001). VF Doppler measurements using indicated versus measured pump flow rates correlated highly (r = 0.99; P < 0.0001). VF Doppler therefore yields reproducible access volume flow measurements that correlate with ultrasound dilution measurements. The VF Doppler method is dependent on the pump-induced change in access Doppler signal and therefore is inherently most accurate and reproducible at lower access blood flow rates. This method appears capable of determining access flow rates in the clinically useful range.

1978 memorial award paper: a computer-aided technique for overlaying cerebral angiograms onto computed tomograms.

We have developed a method which uses a digital computer to combine angiographic images of the cerebral vasculature with a computed tomogram of the brain. The procedure is simple and could be implemented in any radiology department equipped with both a CT scanner and a bi-plane angiography suite. We have performed the entire process in prototype on phantoms and on a patient and have produced images that appear accurate and informative.

Ultrasound detection of differences in density. Explanation of the ureteric jet phenomenon and implications for new ultrasound applications.

Flow of urine from the ureter into the bladder can be encountered during routine sonographic examination of the pelvis. The findings include a stream of hyperechogenic foci spurting into the bladder in real time with the production of a frequency shift during Doppler examination. We have demonstrated that visualization of this phenomenon, at least in part, reflects differences in density and associated compressibility changes between urine in the bladder and in the ureter, and need not be dependent upon flow velocity or other previously hypothesized parameters. The clinical utility of these reproducible and measurable phenomena is explored.

Three-dimensional left ventricular wall motion in man. Coordinate systems for representing wall movement direction.

We have studied the three-dimensional (3D) motion of left ventricular (LV) epicardial points by tracking one to three dozen coronary artery bifurcations in eleven human subjects. Wall motion was analyzed using several different coordinate systems: (1) cylindrical centered about the LV long axis, (2) spherical with origin at the LV center-of-gravity (COG), and (3) spherical with origin at the LV center-of-contraction (COC), the best-fit 3D point toward which the wall moves. The coordinate systems were studied both fixed and moving with time. Three-dimensional motions were decomposed into three directional components, with high radial (in and out) percentages being regarded as the figure-of-merit of a given coordinate system. Average percentage radial motions were fixed cylindrical 16%, fixed spherical COG 35%, fixed spherical COC 47%, moving cylindrical 17%, moving spherical COG 30%, moving spherical COC 91%. Spherical systems were generally better than cylindrical systems, with the COC representing a better origin than the COG. Moving systems were appreciably better than fixed only for the COC model, indicating that the COC, which traverses up and down the LV midline, moves significantly while the other systems are more stationary. At each instant in time, almost all (91%) of the 3D motion of the entire heart wall is directed toward a single moving 3D point, the COC. Thus, there exists in principle a near-perfect 3D heart wall motion model. Approximately 25% of 3D wall motion is unseen in conventional monoplane views. Also, any model that represents 3D wall motion only along fixed straight 3D lines (eg, end-diastole to end-systole) necessarily ignores 27% of the true 3D heart wall motion.

Laminar submerged jets by color Doppler ultrasound. A model of the ureteral jet phenomenon.

RATIONALE AND OBJECTIVES: The authors developed and tested a technique to noninvasively measure ureterovesical junction (UVJ) pressure gradients. Such a technique could be used to evaluate ureteral reflux and obstruction. METHODS: Color Doppler ultrasound measurements of an in vitro model of the ureteral jet were performed. RESULTS: The authors show that the orificial rate of momentum transfer of the ureteral jet (from which the intraluminal pressure in the ureter can be calculated) can be determined to within 45% to 94% of its true value depending primarily on the flow sensitivity of the color flow imager. Marked improvement in the momentum calculation (> 80%) is achieved when a low-flow sensitivity is used. CONCLUSION: Such noninvasive measurements could replace more invasive techniques (eg, the Whitaker test or cystoscopy with or without ureteral cannulation), which seriously perturb the system of interest.

The use of ultrasound mean acoustic attenuation to quantify bone formation during distraction osteogenesis performed by the Ilizarov method. Preliminary results in five dogs.

RATIONALE AND OBJECTIVES: Management of distraction during Ilizarov limb lengthening remains primarily clinical and empirical. Estimates of tissue acoustic attenuation were evaluated for their ability to quantify bone formation within the distraction gap. METHODS: Five dogs had tibias lengthened by the method of Ilizarov. Mean acoustic attenuation measurements at multiple positions across the distraction gap were compared with corresponding x-ray computed tomography attenuation measurements. RESULTS: Computed tomography and ultrasound attenuation displayed similar quantitative behavior across the gap. Linear correlation between them ranged from R2 = .878 to R2 = .131. Fibrous interzone width estimates based on computed tomography and ultrasound attenuation measurements were correlated, based on our preliminary data with R2 = .519. These estimates are independent of the width of distraction. CONCLUSIONS: Ultrasound parallels computed tomography as a measure of bone formation within the distraction gap. Future studies are needed to improve acoustic attenuation data acquisition techniques and to evaluate their potential as a tool for optimizing early distraction rates in patients at risk for rate-related complications.

Methods for evaluating cardiac wall motion in three dimensions using bifurcation points of the coronary arterial tree.

An accurate three-dimensional (3D) representation of heart wall motion would be an important means of evaluating cardiac function. To accomplish this, we have developed an interactive computer graphics system designed to enter the time-dependent 3D positions of bifurcations of the coronary arterial tree. These bifurcations are precise markers of the epicardial surface, and their motions accurately represent the motion of the underlying heart wall. We demonstrate techniques for calculating local wall motion, including displacement and velocity, for determining a time-dependent center-of-contraction point towards which the epicardium tends to move and for tracking the mechanical contraction wave using cross-correlation methods. We have applied these techniques to study seven patients with normal left ventriculograms and coronary arteriograms. We have found these methods to be generally applicable and to provide information not obtainable without 3D analysis.

Pre- to postnatal reduction in ultrasound attenuation coefficient of the liver.

A recent study showed the ultrasound attenuation coefficient of fetal liver between 26 and 40 weeks of gestation to be 26% higher than after birth. To test the hypothesis that ultrasound attenuation is sensitive to fetal liver glycogen concentration, the livers of 24 fetuses were examined at 5 MHz just prior to and just after birth. The mean pre- to post-delivery reduction in attenuation coefficient was 0.08 dB cm-1 MHz-1 +/- 0.02 (SEM), or 17% of the post-delivery mean. This is consistent with the increase in attenuation measured by others in liver homogenate when glycogen was added. An increase in measurement accuracy, correlation with glycogen content, and, possibly, control for biological variability will be required to make predictions in individual cases, as opposed to these averages. A simple test of glycogen content would be of value scientifically and in prenatal and postnatal management.

Transcutaneous interruption of ultrasound contrast agents for blood flow evaluation.

RATIONALE AND OBJECTIVES: The ability to create short boluses in targeted arteries with rapid rise times is limited by the transport of bubbles from the venous to arterial portion of the circulation. Acoustic interruption of contrast agent in arteries may create the short boluses necessary for simple wash-in/wash-out measures of blood flow. METHODS: An ultrasound contrast agent was used with spectral Doppler ultrasound to observe contrast interruption in femoral arteries and VX2 carcinoma in a rabbit model. At an upstream location in the femoral artery, single, sinusoidal ultrasound tone bursts at 1.8 MHz with durations of 0.25 to 1 seconds were applied to interrupt the flow of contrast agent injected intravenously. RESULTS: In VX2 carcinoma, bursts as short as 40 cycles produced contrast interruption lasting only one cardiac cycle within the tumor periphery and I(SPPA) <3 W/cm2 produced measurable interruptions. CONCLUSIONS: Acoustic fields applied transcutaneously interrupted flow of contrast agents to form temporally short negative boluses.

Dilated renal collecting systems: differentiating obstructive from nonobstructive dilation using duplex Doppler ultrasound.

Two patients with ileal loop urinary diversions, studied with real-time and Doppler sonography ("duplex sonography") of the kidneys, were shown to have dilated intrarenal collecting systems. Resistive index measurements calculated from the Doppler signal correctly identified obstructive dilatation in 1 case and nonobstructive dilatation in the other.

Increases in ornithine decarboxylase activity in the positive inotropism induced by androgens in isolated left atrium of the rat.

It is well established that the intracellular receptors of androgens act as transcription factors upon their activation by androgen binding. However, a growing number of studies have associated androgens with rapid biological responses independent of their classical action mechanism. In this sense, 5alpha- and 5beta-dihydrotestosterone elicited a rapid positive inotropism in the isolated left atrium of the rat via cAMP-dependent mechanisms that may involve genomic effects. In addition, polyamines are mediators of several biological actions including those acute and long-term effects induced by androgens in the heart. The present study analyzed the role of polyamine synthesis in the cardiotonic effect of androgens in the left atrium of male Wistar rats, electrically stimulated (0.5 Hz, 5 ms and supramaximal voltage) and placed in an organ bath in 10 ml of Tyrode's solution. Incubation in the organ bath with an inhibitor of ornithine decarboxylase activity, alpha-difluoromethylornithine 10 mM, significantly decreased the positive inotropism induced by 5alpha- and 5beta-dihydrotestosterone (0.1-100 microM). This suggests that ornithine decarboxylase seems to be involved in androgen-induced positive inotropism. Furthermore, 6-min exposure to 5alpha- or 5beta-dihydrotestosterone significantly increased the activity of ornithine decarboxylase from 61.81+/-7.53 (control) to 93.28+/-9.45 and 80.28+/-12 pmol/h/mg of protein, respectively. Northern blot analysis showed that 5alpha- and 5beta-dihydrotestosterone did not modify the level of expression of the ornithine decarboxylase gene. Therefore, our results suggest that polyamine synthesis might be involved in the positive inotropism elicited by androgens through the stimulation of ornithine decarboxylase activity without changes in the expression of the ornithine decarboxylase gene.

Clinical applications of combined cerebral angiograms and brain CT scans.

This paper illustrates the clinical value of a computer technique for superimposition of two different kinds of imaging procedures. The initial application was to overlay cerebral angiograms onto computed tomograms of the brain. Case material from three patients with intracerebral abnormalities is presented. The sum of information from the combined studies exceeds that from either study alone and has value for both diagnosis and treatment of head lesions.

Characterization of transmitted motion in fetal lung: quantitative analysis.

A simple two-dimensional analytic model is evaluated for transmitted cardiac motion in fetal lung. The model treats the latter as being an incompressible viscoelastic medium. The mean radial deformation in an elastic medium is demonstrated to depend on a length parameter l approximately square root of mu/rho omega 2, where mu, rho, and omega correspond to elastic shear modulus, mass density, and frequency of cardiac motion, respectively. Digitized M-mode images are demonstrated as a feasible method to measure such deformations in vivo. Data for two patients are presented to illustrate the technique.

Spinal ultrasonography. Intraoperative and pediatric applications.

Ultrasonography has had limited usefulness in the diagnosis of diseases of the spine and spinal cord in older children and adults. However, its use intraoperatively in patients of all ages, and nonoperatively in infants and young children, is finding increased application. The authors, who perform and rely on spinal sonography in both clinical situations, present an overview of technique, normal anatomy, and selected pathologic entities based on their experience and the literature.

Ultrasound-guided periventricular stereotaxis.

Intraoperative ultrasound can aid the biopsy of deep intracranial lesions. It is, perhaps, less clear whether ultrasound could be useful in functional neurosurgery, where the target is not abnormal in echogenicity. As an example, we chose to investigate in a dog model the periventricular gray target, which is frequently the choice for the placement of electrodes to control intractable pain. Autopsies showed the placement of our electrodes with less than 1 mm of error in four of five brains and a 1.5-mm error in the fifth brain. The largest error was seen to occur on the video screen and was due to our failure to tighten the guide properly. The potential advantages of this technique over conventional stereotaxis include the avoidance of: ventricular catheterization, the injection of contrast agent into the ventricles, the necessity for a stereotactic frame, and multiple x-ray exposures. Also, with real time scanning the surgeon has instant visual confirmation of electrode placement and can observe quickly any significant hematoma formation.

A cannula for use in ultrasonically guided biopsies of the brain. Technical note.

The authors describe a cannula that has been modified to improve its visibility during ultrasonically guided biopsies of the brain. To enhance the echogenicity of the tip of the cannula, six parallel rings, 0.25 to 0.30 mm deep and 0.40 to 0.50 mm apart, were etched into the tip of the cannula. The cannula was also lengthened to approximately 19 cm to permit its unencumbered passage through any biopsy guidance device that may be employed. Detailing the precise location of the tip of the biopsy cannula is most important. The tip of this modified probe is much more echogenic and hence more easily seen ultrasonically than it would be otherwise, both in vivo and in vitro. This modified cannula is useful in any ultrasonically guided intracranial biopsy procedure.

Intraoperative ultrasonic evaluation of spinal cord motion.

The spinal canals of 11 patients with various pathological conditions, both benign and malignant, were examined intraoperatively using real-time ultrasonography. The spinal cords in eight of these patients with lesions causing cord compression were seen to oscillate rhythmically over each mass with a frequency corresponding to the patient's arterial pulsations. The majority of the observed motion was transmitted or extrinsically induced from compression of the anterior spinal artery. In one case, after resection of an anterior cervical neurofibroma, these oscillations diminished markedly. Spinal cord motion, as described, has important implications for neurosurgery, since it contradicts the previously held belief that oscillations of the spinal cord or dura mater imply a "free" or noncompressed spinal cord. Furthermore, spinal cord motion may play a role in the degradation of computerized tomography images of the cord, since these movements are maximized at the areas with the most severe pathology.