James Ng | PubMed Health

PubMed2006

Modeling ultrasound imaging as a linear, shift-variant system.

We solve the equation that governs acoustic wave propagation in an inhomogeneous medium to show that the radio-frequency (RF) ultrasound signal can be expressed as the result of filtering the scatterer field with a point-spread function. We extend the analysis to make the link between the RF ultrasound signal and the representation of ultrasound scatterers as vectors with small magnitude and random phase in the complex plane. Others have previously performed parts of this analysis. The contribution of the present paper is to provide a single, coherent treatment emphasizing the assumptions that have to be made and the physical consequences of the models derived. This leads to insights into the interaction of monopole and dipole scattering, useful techniques for simulating and analyzing speckle statistics in the complex plane and a new expression for the normalized covariance of the analytic RF ultrasound signal in terms of the complex envelope of the point-spread function.

Algorithms↗

PubMed2005

Evaluation of hydrogel tissue sealant in porcine laparoscopic partial-nephrectomy model.

BACKGROUND AND PURPOSE: Laparoscopic partial nephrectomy (LPN) is technically challenging with a steep learning curve, primarily because techniques used to control bleeding on the cut surface of the kidney can be ineffective, inconsistent, or challenging. Hemostatic techniques can include intracorporeal suturing, vascular coagulation (argon-beam coagulator, bipolar cautery, laser), and application of various tissue sealants. There is no uniformity of opinion regarding which hemostatic technique is optimal for this application. CoSeal, a hydrogel (Baxter Healthcare Corp, Deerfield, IL), has been effective following vascular surgery but has not been applied to a partial-nephrectomy model. We evaluated the effectiveness of this hydrogel in controlling bleeding and sealing the collecting system by comparing it with intracorporeal suturing and fibrin sealant (Tisseel; Baxter) in a porcine laparoscopic partial-nephrectomy model. MATERIALS AND METHODS: Bilateral synchronous upper-pole partial nephrectomies were performed in two groups of 18 farm pigs, and the three hemostatic techniques (suturing, Tisseel, CoSeal) were applied. In the first group, partial nephrectomies were performed and the pigs sacrificed 3 days postoperatively (acute group). In the second group, the pigs were euthanized 6 weeks postoperatively (chronic group). In both groups, weight, blood pressure, estimated blood loss, weight of the partial and completion nephrectomy specimen, presence/ absence of urinary leak on retrograde study, histopathologic findings, and complications were recorded. RESULTS: The mean weight, blood pressure, estimated blood loss, histopathology findings, and weight of the partial and completion nephrectomy specimens were similar in the three groups. CoSeal did not adhere well to the renal parenchyma compared with Tisseel. All three animals in the acute CoSeal group and three of the six pigs in the sutured group had small urinary leaks during retrograde ureteral study, whereas none of the pigs in the fibrin-glue cohort had urinary leaks. There was one complication (urinary leak) in the CoSeal group, necessitating sacrifice of the animal on postoperative day 8 because of sepsis. CONCLUSIONS: CoSeal is not as effective as fibrin glue in adhering to the cut renal surface and sealing the collecting system during laparoscopic partial nephrectomy.

Animals↗