Citations

Background: Medication use in the intensive care unit (ICU) depends on creatinine-based glomerular filtration rate (GFR) estimates. Urine output deterioration may precede the creatinine rise resulting in delayed recognition of GFR reductions. Our objective was to quantify the disparity between estimated GFR (eGFR) and true GFR in ICU patients with hospital-acquired oligoanuric acute kidney injury (hAKI). Methods: This single-center cohort study examined adults who met the Acute Kidney Injury Network stage III urine output criterion ≥48 hours after ICU admission. True GFR was ≤15 mL/min/1.73 m 2 , and eGFR was described by 6 different creatinine-based equations. True GFR and eGFR were compared on the day of hAKI diagnosis and followed for 4 days using multivariable linear regression with generalized estimating equations, adjusting for day and method. Results: Of the 691 patients screened, we enrolled 61 patients. After adjustment for multiple comparisons and day, there were significant differences in eGFR between the estimation methods and true GFR ( P < .001). After day adjustment, eGFR overestimated true GFR by 17 to 50 mL/min/1.73 m 2 and overestimation persisted through the fourth day of hAKI ( P ≤ .001). Conclusion: Creatinine-based equations overestimated GFR in ICU patients with hAKI. This study highlights a population at risk of medication misadventures in whom systems optimization should be considered.

In this work, a numerical technique suitable for evaluating the ultrasonic scattering from a three-dimensional poroelastic material is presented. Following Biot’s derivation of the macroscopic governing equations for a fluid saturated poroelastic material, the predicted two propagating wave equations are formulated in terms of displacement and pressure. Assuming that porosity variations on a microscopic scale have a cumulative effect in generating a scattered field, the scattering attenuation coefficient of a Biot medium can be determined. The scattered fields of the wave equations are numerically evaluated as Neumann series solutions of the Kirchhoff-Helmholtz integral equation. A Padé approximant technique is employed to extrapolate beyond the Neumann series’ radius of convergence (weak scattering regime). In the case of bovine trabecular bone, the relationship between the scattering attenuation coefficient and the structural and mechanical properties of the trabecular bone is of particular interest. The results demonstrate the validity of the linear frequency-dependent assumption of attenuation coefficient n the low frequency range. Further comparisons, between measured observations and the numerical results will be discussed.

In this work, the generation of difference frequency waves arising from the interaction of dual-incident beams on a solid sphere is considered. The high-frequency incident beams induce a radiation force onto the fluid-saturated sphere causing the scatterer to vibrate. An analysis on the contribution between the difference frequency sound and radiation force pressure is of particular interest. The scattered pressure due to the two primary waves are obtained as solutions to the Kirchhoff–Helmholtz integral equation for the fluid–solid boundary. Due to the contrasting material properties between the host fluid and solid sphere, high-order approximations are used to evaluate the integral equation.

In this work, the results from our Comb Push Ultrasound Shear Elastography (CUSE) assessment of suspicious breast lesions are presented. The elasticity value of the breast lesions are correlated to histopathological findings to evaluate their diagnostic value in differentiating between malignant and benign breast lesions. A total of 44 patients diagnosed with suspicious breast lesions were evaluated using CUSE prior to biopsy. All patient study procedures were conducted according to the protocol approved by Mayo Clinic Institutional Review Board (IRB). Our cohort consisted of 27 malignant and 17 benign breast lesions. The results indicate an increase in shear wave velocity in both benign and malignant lesions compared to normal breast tissue. Furthermore, the Young’s modulus is significantly higher in malignant lesions. An optimal cut-off value of the Young’s modulus ≥ 80 kPa was observed for the receiver operating characteristic (ROC) curve. This is concordant with the published cut-off values of elasticity for suspicious breast lesions. [This work is supported in part by the grant 3R01CA148994-04S1 and 5R01CA148994-04 from NIH.]

Green’s functions effectively simulate shear waves produced by an applied acoustic radiation force in elastic and viscoelastic soft tissue. In an effort to determine the optimal parameters for these simulations, the convergence of Green's function-based calculations is evaluated for realistic spatial distributions of the initial radiation force “push.” The input to these calculations is generated by FOCUS, the “Fast Object-oriented C + + Ultrasound Simulator,” which computes the approximate intensity fields generated by a Phillips L7-4 ultrasound transducer array for both focused and unfocused beams. The radiation force in the simulation model, which is proportional to the simulated intensity, is applied for 200 μs, and the resulting displacements are calculated with the Green's function model. Simulation results indicate that, for elastic media, convergence is achieved when the intensity field is sampled at roughly one-tenth of the wavelength of the compressional component that delivers the radiation force “push.” Aliasing and oscillation artifacts are observed in the model for an elastic medium at lower sampling rates. For viscoelastic media, spatial sampling rates as low as two samples per compressional wavelength are sufficient due to the low-pass filtering effects of the viscoelastic medium. [Supported in part by NIH Grants R01EB012079 and R01DK092255.]

Acoustic radiation force (ARF) provides a simple and yet non-invasive mechanism to induce a localized stress inside human body. The response to this excitation is used to estimate the mechanical properties of the targeted tissue in vivo. This talk covers an overview of three studies that use ARF for estimation of elastic properties of thyroid, breast, and the bladder in patients. The studies on thyroid and breast were aimed at differentiating between malignant and benign nodules. The study on the bladder was aimed at indirect evaluation of bladder compliance; hence, only a global measurement was needed. The study on breast showed that 16 out of 18 benign masses and 21 out of 25 malignant masses were correctly identified. The study on 9 thyroid patients with 7 benign and 2 malignant nodules showed all malignant nodules were correctly classified and only 2 of the 7 benign nodules were misclassified. The bladder compliance study revealed a high correlation between our method and independent clinical measurement of compliance (R-squared of 0.8–0.9). Further investigations on larger groups of patients are needed to fully evaluate the performances of the methods.

In conventional shear wave elastography materials are assumed to be linear, elastic, homogeneous, and isotropic. These assumptions are important to account for in certain tissues because they are not always appropriate. Many tissues such as skeletal muscle, the kidney, and the myocardium are anisotropic. Shear waves can be used to investigate the directionally dependent mechanical properties of anisotropic media. To study these tissues in a systematic way and to account for the effects of the anisotropic architecture, laboratory-based phantoms are desirable. We will report on several phantom-based approaches for studying shear wave anisotropy, assuming that these materials are transversely isotropic. Phantoms with embedded fibers were used to mimic anisotropic tissues. Homogeneous phantoms were compressed to induce transverse isotropy according to the acoustoelastic phenomenon, which is related to nonlinear behavior of the materials. The fractional anisotropy of these phantoms was quantified to compare with measurements made in soft tissues. In addition, soft tissues are also viscoelastic, and we have developed a method to model viscoelastic transversely isotropic materials with the finite element method (FEM). The viscoelastic property estimation from phantom experiments and FEM simulations will also be discussed.

AbstractWe developed and implemented a ‘CPOE-QT Alert’ system, that is, clinical decision support integrated in the computerized physician order entry system (CPOE), in 2011. The system identifies any attempts to order medications with risk of torsade de pointes (TdP) for patients with a history of significant QT prolongation (QTc ≥500 ms) and alerts the provider entering the order. We assessed its impact by comparing orders and subsequent medication administration before and after activation of the system. We found a significant decrease in the proportion of completed order per ordering attempt after system activation (94% (1293/1379) vs 77% (1888/2453), difference 16.8%; p&lt;0.001). This resulted in a 13.9% reduction in the administration of those medications to patients. A significant decrease was observed across all provider types, educational levels, and specialties. The CPOE-QT Alert system successfully reduced exposure to QT-prolonging medications in high risk patients.

Marfan syndrome is the most common inherited disorder of connective tissue affecting multiple organ systems. Identification of the facial, ocular and skeletal features should prompt referral for aortic imaging since sudden death by aortic dissection and rupture remains a major cause of death in patients with unrecognized Marfan syndrome. Echocardiography is recommended as the initial imaging test, and once a dilated aortic root is identified magnetic resonance or computed tomography should be done to assess the entire aorta. Prophylactic aortic root replacement is safe and has been demonstrated to improve life expectancy in patients with Marfan syndrome. Medical therapy for Marfan syndrome includes the use of beta blockers in older children and adults with an enlarged aorta. Addition of angiotensin receptor antagonists has been shown to slow the progression of aortic root dilation compared to beta blockers alone. Lifelong and regular follow up in a center for specialized care is important for patients with Marfan syndrome. We present a case of a patient with clinical features of Marfan syndrome and discuss possible therapeutic interventions for her dilated aorta.