[Innovative Ultrasound: Contrast-Enhanced Ultrasound of the Kidneys]. / Innovativer Ultraschall: Kontrastverstärkter Ultraschall der Nieren.

Ultrasound examination of the kidneys with grey-scale imaging and colour Doppler ultrasound is the most common renal imaging modality. A few years ago, contrast-enhanced ultrasound (CEUS) emerged as a non-invasive perfusion imaging modality to evaluate the renal vessels and microvascularisation. These contrast media contain intravenous microbubbles (sulfur hexafluoride), which have no deleterious effect on renal function. Being free of iodine, they also pose no risk for the thyroid gland. CEUS of the kidneys is mainly used for the evaluation of renal cysts and the analysis of renal lesions suspicious for malignancy. Also this method is used to visualise inflammation as well as renal perfusion after trauma or infarction.

Evaluación funcional de la etapa faríngea de la deglución utilizando sonar Doppler. Revisión crítica de la literatura / Functional assessment of pharyngeal phase of swallowing with sonar Doppler. Critic revision of the literature

El sonar Doppler es una herramienta que permite captar lo que sucede durante la etapa faríngea de la deglución, siendo el sonido percibido y observado un reflejo parcial de la actividad motora que se desencadena. El presente trabajo indaga acerca de las posibilidades del sonar Doppler y su aplicación en la evaluación funcional de la deglución. Se desarrolla un diseño de investigación observacional y retrospectivo, bajo la metodología de revisión sistemática a partir de material bibliográfico, investigaciones y publicaciones de artículos de revistas en inglés, portugués y español, consultando las bases de datos PubMed, SciELO, EBSCO Host, Scopus, Springer, Cochrane, además de revistas especializadas en ASHA, MedLine, CEFAC y Redalyc. Aunque la fiabilidad y validez en el uso del sonar Doppler para la evaluación funcional de la etapa faríngea de la deglución no están aseguradas, podría llegar a brindar enorme ayuda en el diagnóstico de las aspiraciones y/o penetraciones durante el proceso deglutorio. Se insiste en una constante revisión de la metodología para la detección correcta de los sonidos de la deglución y su posterior análisis e interpretación clínica (AU)

Sonar Doppler is a tool that can capture what happens during the pharyngeal stage of swallowing, being the sound perceived and the noting a partial reflection of the motor activity that is triggered. This paper focuses on the possibilities of sonar Doppler and its application in functional assessment of swallowing. The design of this research is retrospective and observational, developed under the systematic review methodology, from bibliographical material, pieces of research and publications of journal articles in English, Portuguese and Spanish, taking the databases of PubMed, SciELO, EBSCO Host, Scopus, Springer, Cochrane, besides specialized magazines in ASHA, MedLine, CEFAC and Redalyc. Although the reliability and validity in the use of sonar Doppler for the functional evaluation of the pharyngeal stage of swallowing are uncertain, it could provide enormous help in diagnosing aspirations and/or penetrations during the swallowing process. We insist on a constant review of the methodology for the correct detection of sounds of swallowing and subsequent analysis and clinical interpretation (AU)

Efficiency of U.S. Tissue Perfusion Estimators.

We measure the detection and discrimination efficiencies of conventional power-Doppler estimation of perfusion without contrast enhancement. The measurements are made in a phantom with known blood-mimicking fluid flow rates in the presence of clutter and noise. Efficiency is measured by comparing functions of the areas under the receiver operating characteristic curve for Doppler estimators with those of the ideal discriminator, for which we estimate the temporal covariance matrix from echo data. Principal-component analysis is examined as a technique for increasing the accuracy of covariance matrices estimated from echo data. We find that Doppler estimators are <50% efficient at directed perfusion detection between 0.1 and 2.0 mL/min per 2 cm(2) flow area. The efficiency was 20%-40% for the task of discriminating between two perfusion rates in the same range. We conclude that there are reasons to search for more efficient perfusion estimators, one that incorporates covariance matrix information that could significantly enhance the utility of Doppler ultrasound without contrast enhancement.

Evolution of Hemodynamic and Functional Human Kidney Graft Dose Response to Dopamine Using an Implantable Doppler Device.

OBJECTIVES: The relation between dopamine infusion and renal hemodynamics and function has not been studied in renal allografts during early recovery. We analyzed the dose response of dopamine infusion on renal blood flow and function in human kidney transplant recipients at reperfusion and during early graft recovery. MATERIALS AND METHODS: Phasic and mean renal blood flow was measured by the pulsed Doppler technique using implantable Doppler microprobes in contact with the graft artery. Systemic and renal parameters were recorded on dopamine infusion (0, 3, 5, and 10 µg·kg⁻¹·min⁻¹) immediately after transplant (day 0) in 13 patients and at day 6 in 7/13 patients with early graft recovery. Results are expressed as median and interquartile range between the 25th and 75th percentiles. RESULTS: At day 0, 3 µg·kg⁻¹·min⁻¹) dopamine did not increase mean renal blood flow over baseline (580 mL/min [219-663 mL/min] vs 542 mL/min [207-686 mL/min]; P = .84). There was an absence of effect with higher dopamine doses, whereas cardiac output, heart rate, and systolic and mean arterial pressure were significantly increased. Urinary sodium excretion, creatinine clearance, and urine output increased dose dependently, with a positive correlation between the increase in urine output and mean arterial pressure (r = 0.48, P < .001). At day 6, 3 µg·kg⁻¹·min⁻¹ dopamine increased mean renal blood flow over baseline (318 mL/min [234-897 mL/min] vs 191 mL/min [173-706 mL/min]; P = .016), with no further increase at higher doses. CONCLUSIONS: Immediately after transplant, kidney grafts with ischemic-reperfusion injury are fully dilated and do not respond to dopamine. The specific renal effects observed are due to systemic hemodynamic status. Vascular responsiveness to a "renal dopamine dose" returns on graft recovery.

Tumores glómicos digitales y extradigitales. Utilidad de la ecografía cutánea / The Usefulness of Ultrasound Imaging in Digital and Extradigital Glomus Tumors

En los últimos años se ha observado un aumento del uso de la ecografía cutánea en el campo de la dermatología, al proporcionar detalles estructurales y/o vasculares que con la simple exploración física no se pueden apreciar. Los tumores glómicos extradigitales son lesiones poco frecuentes en la práctica clínica y pueden suponer un reto diagnóstico para el dermatólogo. Presentamos 4 pacientes con sospecha clínica de tumor glómico extradigital y un paciente con sospecha de tumor glómico subungueal. A cada paciente se le realizó exploración ecográfica en modo B, doppler color y doppler pulsado, exéresis quirúrgica y análisis histológico que confirmó el diagnóstico sospechado. El uso de la ecografía cutánea añadida a los datos clínicos permitió de una manera sencilla e inocua evitar retrasos diagnósticos y determinar la localización exacta para una adecuada exéresis quirúrgica

Recent years have witnessed an increase in the use of ultrasound imaging of the skin in the field of dermatology, as the technique reveals details of vessels and other structures that cannot be detected on physical examination. Extradigital glomus tumors are rarely seen in clinical practice and can pose a diagnostic challenge for dermatologists. We report on 4 patients with a clinical suspicion of extradigital glomus tumor and on 1 patient with a clinical suspicion of subungual glomus tumor. All 5 patients underwent ultrasound examination in B mode and color and pulsed-wave Doppler prior to surgical excision of the tumor and histologic examination, which confirmed the diagnosis in each case. Ultrasound imaging of the skin, combined with clinical findings, provided a simple, noninvasive way of making a prompt diagnosis and identifying the exact location of the lesion for surgical removal

Fetal echocardiography and pulsed-wave Doppler ultrasound in a rabbit model of intrauterine growth restriction.

Fetal intrauterine growth restriction (IUGR) results in abnormal cardiac function that is apparent antenatally due to advances in fetoplacental Doppler ultrasound and fetal echocardiography. Increasingly, these imaging modalities are being employed clinically to examine cardiac function and assess wellbeing in utero, thereby guiding timing of birth decisions. Here, we used a rabbit model of IUGR that allows analysis of cardiac function in a clinically relevant way. Using isoflurane induced anesthesia, IUGR is surgically created at gestational age day 25 by performing a laparotomy, exposing the bicornuate uterus and then ligating 40-50% of uteroplacental vessels supplying each gestational sac in a single uterine horn. The other horn in the rabbit bicornuate uterus serves as internal control fetuses. Then, after recovery at gestational age day 30 (full term), the same rabbit undergoes examination of fetal cardiac function. Anesthesia is induced with ketamine and xylazine intramuscularly, then maintained by a continuous intravenous infusion of ketamine and xylazine to minimize iatrogenic effects on fetal cardiac function. A repeat laparotomy is performed to expose each gestational sac and a microultrasound examination (VisualSonics VEVO 2100) of fetal cardiac function is performed. Placental insufficiency is evident by a raised pulsatility index or an absent or reversed end diastolic flow of the umbilical artery Doppler waveform. The ductus venosus and middle cerebral artery Doppler is then examined. Fetal echocardiography is performed by recording B mode, M mode and flow velocity waveforms in lateral and apical views. Offline calculations determine standard M-mode cardiac variables, tricuspid and mitral annular plane systolic excursion, speckle tracking and strain analysis, modified myocardial performance index and vascular flow velocity waveforms of interest. This small animal model of IUGR therefore affords examination of in utero cardiac function that is consistent with current clinical practice and is therefore useful in a translational research setting.

The analysis of the artifacts due to the simultaneous use of two ultrasound probes with different/similar operating frequencies.

The ultrasound imaging has the potential to become a dominant technique for noninvasive therapies and least invasive surgeries. Few cases may require using multiple probes of different units with different modes of ultrasound on the same patient. It generates imaging artifacts, which makes it complicated to gather information from the acquired image. This study was to identify and analyse the artifacts which are produced by simultaneous use of two probes with different/same operating frequencies. Six imaging studies were performed. First of all, the imaging artifacts of the 3.5 MHz and 6 MHz center frequencies with similar (longitudinal) positions of the probes. Secondly, with similar operating frequencies the 6 MHz probe changed from longitudinal to transverse placement to analyse the resulting artifacts. The third study was done with transverse placement of 3.5 MHz probe. The rest of the three cases were just the repetition with common pulse frequencies. Such artifacts in 3D ultrasound images are more obscure than the other artifacts associated and reported.

Post-operative assessment of perfusion of Deep Inferior Epigastric Perforator (DIEP) free flaps via Pulsatility Index (PI) using a portable colour Doppler sonogram device.

INTRODUCTION: PI as an independent indicator of resistance to flow is a widely-accepted alternative index to measurement of flow volume in vessels. This study aimed to determine the normal values and chronological trend of PI of abdominal wall free flaps in breast reconstruction and to revalidate its clinical relevance in post-operative monitoring of these flaps. MATERIALS AND METHODS: 47 patients with breast reconstruction using DIEP, MS-TRAM and bi-pedicled DIEP flaps were assessed for PI of the supplying perforator vessels using a hand-held colour Doppler ultrasound device over 6 post-operative days. Triplicate measurements were obtained by one operator once daily concurrently with haemodynamic parameters. RESULTS: DIEP flaps demonstrate a descending trend of PI and resistance to blood flow post-operatively (p=0.005) similar to non-perforator free flaps. MS-TRAM flaps show higher initial PI values and vascular resistance compared to DIEP flaps (p=0.038). PI values show no correlation with haemodynamic parameters (r=0.2, n=38). Flaps with venous insufficiency demonstrate significantly higher values of PI (p=0.03). CONCLUSIONS: PI is an objective, non-invasive, efficient, easy-to-measure, reproducible and quickly-responsive indicator of perfusion of DIEP flaps.

An in vitro phantom study on the influence of tear size and configuration on the hemodynamics of the lumina in chronic type B aortic dissections.

OBJECTIVE: Management and follow-up of chronic aortic dissections continue to be a clinical challenge due to progressive dilatation and subsequent rupture. To predict complications, guidelines suggest follow-up of aortic diameter. However, dilatation is triggered by hemodynamic parameters (pressures/wall shear stresses) and geometry of false (FL) and true lumen (TL), information not captured by diameter alone. Therefore, we aimed at better understanding the influence of dissection anatomy on TL and FL hemodynamics. METHODS: In vitro studies were performed using pulsatile flow in realistic dissected latex/silicone geometries with varying tear number, size, and location. We assessed three different conformations: (1) proximal tear only; (2) distal tear only; (3) both proximal and distal tears. All possible combinations (n = 8) of small (10% of aortic diameter) and large (25% of aortic diameter) tears were considered. Pressure, velocity, and flow patterns were analyzed within the lumina (at proximal and distal sections) and at the tears. We also computed the FL mean pressure index (FPI(mean)%) as a percentage of the TL mean pressure, to compare pressures among models. RESULTS: The presence of large tears equalized FL/TL pressures compared with models with only small tears (proximal FPI(mean)% 99.85 ± 0.45 vs 92.73 ± 3.63; distal FPI(mean)% 99.51 ± 0.80 vs 96.35 ± 1.96; P < .001). Thus, large tears resulted in slower velocities through the tears (systolic velocity <180 cm/s) and complex flows within the FL, whereas small tears resulted in lower FL pressures, higher tear velocities (systolic velocity >290 cm/s), and a well-defined flow. Additionally, both proximal and distal tears act as entry and exit. During systole, flow enters the FL through all tears simultaneously, while during diastole, flow leaves through all communications. Flow through the FL, from proximal to distal tears or vice versa, is minimal. CONCLUSIONS: Our results suggest that FL hemodynamics heavily depends on cumulative tear size, and thus, it is an important parameter to take into account when clinically assessing chronic aortic dissections.

Design and implementation of a smartphone-based portable ultrasound pulsed-wave Doppler device for blood flow measurement.

Blood flow measurement using Doppler ultrasound has become a useful tool for diagnosing cardiovascular diseases and as a physiological monitor. Recently, pocket-sized ultrasound scanners have been introduced for portable diagnosis. The present paper reports the implementation of a portable ultrasound pulsed-wave (PW) Doppler flowmeter using a smartphone. A 10-MHz ultrasonic surface transducer was designed for the dynamic monitoring of blood flow velocity. The directional baseband Doppler shift signals were obtained using a portable analog circuit system. After hardware processing, the Doppler signals were fed directly to a smartphone for Doppler spectrogram analysis and display in real time. To the best of our knowledge, this is the first report of the use of this system for medical ultrasound Doppler signal processing. A Couette flow phantom, consisting of two parallel disks with a 2-mm gap, was used to evaluate and calibrate the device. Doppler spectrograms of porcine blood flow were measured using this stand-alone portable device under the pulsatile condition. Subsequently, in vivo portable system verification was performed by measuring the arterial blood flow of a rat and comparing the results with the measurement from a commercial ultrasound duplex scanner. All of the results demonstrated the potential for using a smartphone as a novel embedded system for portable medical ultrasound applications.

Accurate guidance of a catheter by ultrasound imaging and identification of a catheter tip by pulsed-wave Doppler.

BACKGROUND: With the advent of numerous minimally invasive medical procedures, accurate catheter guidance has become imperative. We introduce and test an approach for catheter guidance by ultrasound imaging and pulsed-wave (PW) Doppler. METHODS: A steerable catheter is fitted with a small piezoelectric crystal at its tip that actively transmits signals driven by a function generator. We call this an active-tip (AT) catheter. In a water tank, we immersed a "target" crystal and a rectangular matrix of four "reference" crystals. Two-dimensional (2D) ultrasound imaging was used for initial guidance and visualization of the catheter shaft, and then PW Doppler mode was used to identify the AT catheter tip and guide it to the simulated target that was also visible in the 2D ultrasound image. Ten guiding trials were performed from random initial positions of the AT catheter, each starting at approximately 8 cm from the target. RESULTS: After the ten navigational trials, the average final distance of the catheter tip from the target was 2.4 ± 1.2 mm, and the range of distances from the trials was from a minimum of 1.0 mm to a maximum of 4.5 mm. CONCLUSIONS: Although early in the development process, these quantitative in vitro results show promise for catheter guidance with ultrasound imaging and tip identification by PW Doppler.

Cardiac output monitoring devices: an analytic review.

To evaluate cardiac output (CO), both invasive and semi-invasive monitors are used in critical care medicine. The pulmonary artery catheter is an invasive tool to assess CO with the major criticism that the level of its invasiveness is not supported by an improvement in patients' outcomes. The interest in a lesser invasive techniques is high. Therefore, alternative techniques have been developed recently, and are used frequently in critical care medicine. Cardiac output can be monitored continuously by different devices that analyze the stroke volume and CO. The purpose of this review is to understand these new technologies and their applications and limitations.

Development of a vessel-mimicking material for use in anatomically realistic Doppler flow phantoms.

Polyvinyl alcohol cryogel (PVA-C) is presented as a vessel-mimicking material for use in anatomically realistic Doppler flow phantoms. Three different batches of 10% wt PVA-C containing (i) PVA-C alone, (ii) PVA-C with antibacterial agent and (iii) PVA-C with silicon carbide particles were produced, each with 1-6 freeze-thaw cycles. The resulting PVA-C samples were characterized acoustically (over a range 2.65 to 10.5 MHz) and mechanically to determine the optimum mixture and preparation for mimicking the properties of healthy and diseased arteries found in vivo. This optimum mix was reached with the PVA-C with antibacterial agent sample, prepared after two freeze/thaw cycles, which achieved a speed of sound of 1538 ± 5 m s(-1) and a Young's elastic modulus of 79 ± 11 kPa. This material was used to make a range of anatomically realistic flow phantoms with varying degrees of stenoses, and subsequent flow experiments revealed that higher degrees of stenoses and higher velocities could be achieved without phantom rupturing compared with a phantom containing conventional wall-less vessels.

Convolutional modeling of diffraction effects in pulse-echo ultrasound imaging.

A model is presented for pulse-echo imaging of three-dimensional, linear, weakly-scattering continuum media by ultrasound array transducers. The model accounts for the diffracted fields of focused array subapertures in both transmit and receive modes, multiple transmit and receive focal zones, frequency-dependent attenuation, and aberration caused by mismatched medium and beamformer sound speeds. For a given medium reflectivity function, computation of a B-scan requires evaluation of a depth-dependent transmit/receive beam product, followed by two one-dimensional convolutions and a one-dimensional summation. Numerical results obtained using analytic expressions for transmit and receive beams agree favorably with measured B-scan images and speckle statistics.

A critical review of the ability of continuous cardiac output monitors to measure trends in cardiac output.

Numerous cardiac output (CO) monitors have been produced that provide continuous rather than intermittent readings. Bland and Altman has become the standard method for validating their performance against older standards. However, the Bland and Altman method only assesses precision and does not assess how well a device detects serial changes in CO (trending ability). Currently, there is no consensus on how trending ability, or trend analysis, should be performed. Therefore, we performed a literature review to identify articles published between 1997 and 2009 that compared methods of continuous CO measurement. Identified articles were grouped according to measurement technique and statistical methodology. Articles that analyzed trending ability were reviewed with the aim of finding an acceptable statistical method. Two hundred two articles were identified. The most popular methods were pulse contour (69 articles), Doppler (54), bioimpedance (38), and transpulmonary or continuous thermodilution (27). Forty-one articles addressed trending, and of these only 23 provided an in-depth analysis. Several common statistical themes were identified: time plots, regression analysis, Bland and Altman using change in CO (ΔCO), and the 4-quadrant plot, which used direction of change of ΔCO to determine the concordance. This plot was further refined by exclusion of data when values were small. Receiver operating characteristic curves were used to define the exclusion zone. In animal studies, a reliable reference standard such as an aortic flowprobe was frequently used, and regression or time plots could be used to show trending. Clinical studies were more problematic because data collection points were fewer (8-10 per subject). The consensus was to use the 4-quadrant plot with exclusion zones and apply concordance analysis. A concordance rate of >92% when using a 15% zone indicated good trending. A new method of presenting trend data (ΔCO) on a polar plot is proposed. Agreement was shown by the angle with the horizontal axis and ΔCO by the distance from the center. Trending can be assessed by the vertical limits of the data, similar to the Bland and Altman method.

The leicester Doppler phantom--a digital electronic phantom for ultrasound pulsed Doppler system testing.

Doppler flow and string phantoms have been used to assess the performance of ultrasound Doppler systems in terms of parameters such as sensitivity, velocity accuracy and sample volume registration. However, because of the nature of their construction, they cannot challenge the accuracy and repeatability of modern digital ultrasound systems or give objective measures of system performance. Electronic Doppler phantoms are able to make use of electronically generated test signals, which may be controlled precisely in terms of frequency, amplitude and timing. The Leicester Electronic Doppler Phantom uses modern digital signal processing methods and field programmable gate array technology to overcome some of the limitations of previously described electronic phantoms. In its present form, it is able to give quantitative graphical assessments of frequency response and range gate characteristics, as well as measures of dynamic range and velocity measurement accuracy. The use of direct acoustic coupling eliminates uncertainties caused by Doppler beam effects, such as intrinsic spectral broadening, but prevents their evaluation.

Extracorporeal bubbles: a word of caution.

OBJECTIVES: Gaseous microemboli (GME) are a cause of neurocognitive deficit postcardiac surgery with cardiopulmonary bypass. However, the measurement of microbubbles during cardiopulmonary bypass is not easy, because blood is an opaque fluid and contains microparticles. Recently, two new microbubble counters, the Gampt BC200 and the emboli detection and classification (EDAC) quantifier, were developed for use during cardiac surgery. The accuracy of both devices was validated against industrial standards. METHODS: A clear blood analogue (30%/70% glycerol-water) was pumped, by means of a rollerpump out of a partially filled arterial line screen filter with a nominal pore size of 20 microm. Downstream the pump, all test sensors and an optical cuvette, were inserted in a vertically mounted 3/8 inch tubing. Measurements were taken at flows of 405, 1080, 3000 and 6000 ml/min. Backlight shadowgraphy and optical counting were used as industrial reference techniques for measuring size and counts. RESULTS: On average the EDAC quantifier underestimates average bubble diameter by 35+/-1%, 13+/-8%, 71+/-7% and 33+/-4% at 405, 1080, 3000 and 6000 ml/min, respectively. The Gampt BC200 has good sizing agreement at 1080 ml/min (+5+/-17%) and 3000 ml/min (+33+/-6%) but overestimates average diameter by 220+/-40% and 295+/-49% at 405 and 6000 ml/min, respectively. Both devices only partially count the number of microbubbles at higher flows. At 3 l/min the EDAC counts 38%, the Gampt 18% of total counts and at 6 l/min both the EDAC and Gampt only count 3% of total counts. CONCLUSIONS: Both the EDAC and Gampt can be used in a clinical setting for monitoring basal GME production. However, both devices have some major limitations when used for studying 'worst case' scenarios. One should take great caution when correlating measured data with neurocognitive outcome. Finally, results obtained by one device in a first study cannot be compared nor exchanged with results from the other device in a second study.