Search

Byline: Ludivine Chalumeau-Lemoine (1), Jean-Luc Baudel (1), Vincent Das (1), Lionel Arrive (2), Beatrice Noblinski (2), Bertrand Guidet (1,3), Georges Offenstadt (1,3), Eric Maury (1,3,4) Keywords: Bedside ultrasonography; Intensive care; Curriculum Abstract: Rationale and objectives To evaluate limited training of ICU physicians without knowledge of ultrasound in performing basic general ultrasonography. Design and setting A prospective, observational, study conducted in a 14-bed MICU. Patients Seventy-seven critically ill patients (38 females) aged 64 +- 16 years, with a SAPS II score of 47 +- 21, 49 of whom (64%) were receiving mechanical ventilation. Methods After 8.5 h of training comprising a 2.5 h didactic course that included essential views of normal and pathologic conditions and three hands-on sessions of 2 h each, one of eight ICU residents and the radiologist on duty performed the same examination in a blind manner. The questions addressed concerned the presence of pleural effusion, intra-abdominal effusion, acute cholecystitis, intrahepatic biliary duct dilation, obstructive uropathy, chronic renal disease, and deep venous thrombosis. Measurements and main results The answers to 129 questions were analyzed. The possible presence of pleural effusion, and arguments for the presence of urinary tract obstruction and chronic renal insufficiency, were the questions most frequently addressed. Residents answered 84.4% of the questions correctly [Kappa: 0.66, CI 95% (0.32--1.12)]. Most of the discrepancies concerned small non-drainable pleural or abdominal effusions. For questions with a potential therapeutic impact, residents answered 95% of the questions correctly [Kappa 0.86, CI 95% (0.75--1.04)]. Residents completed the examination in 37 +- 39 min compared with 296 +- 487 min for the radiologists (P = 0.004). Conclusions These results suggest that after brief focused training, intensive-care unit physicians without previous knowledge of ultrasonography can competently perform basic general ultrasonic examinations. Author Affiliation: (1) Medical Intensive Care Unit, Hopital Saint-Antoine, Assistance Publique-Hopitaux de Paris, Paris, France (2) Radiology Department, Hopital Saint-Antoine, Assistance Publique-Hopitaux de Paris, Paris, France (3) Universite Pierre et Marie Curie-Paris6, INSERM, UMR S-707, 75012, Paris, France (4) Service de Reanimation Medicale, Hopital Saint-Antoine, Assistance Publique-Hopitaux de Paris, 184 rue du Faubourg Saint-Antoine, 75571, Paris, France Article History: Registration Date: 28/05/2009 Received Date: 03/12/2008 Accepted Date: 27/04/2009 Online Date: 16/06/2009

The structural characteristics of a health3 tendon are related to the anisotropic speckle patterns observed in ultrasonic images. This speckle orientation is disrupted upon damage to the tendon structure as observed in patients with tendinopathy. Quantification of the structural appearance of tendon shows promise in creating a tool for diagnosing, prognosing, or measuring changes in tendon organization over time. The current work describes a first step taken towards this goal--classification of Achilles tendon images into tendinopathy anti control categories. Eight spatial frequency parameters were extracted from regions of interest on tendon images, filtered and classified using linear discriminant analysis. Resulting algorithms had better than 80% accuracy in categorizing tendon image kernels as tendinopathy or control. Tendon images categorized wrongly provided for an interesting clinical association between incorrect classification of tendinopathy kernels as control and the symptom and clinical time history based inclusion criteria. To assess intersession reliability of image acquisition, the first 10 subjects were imaged twice during separate sessions. Test-retest of repeated measures was excellent (r = 0.996, ICC (2,1) : 0.73 with one outlier) indicating a general consistency in imaging techniques. Index Terms--Classifier, image analysis, tendinopathy, tendon, ultrasound.

Byline: D. Lichtenstein (1), J.-S. Hulot (1), A. Rabiller (1), I. Tostivint (1), G. Meziere (2) Keywords: Key words Thoracentesis; Pleural effusion; Ultrasound diagnosis; Thorax; ultrasound diagnosis; Lung; ultrasound diagnosis; Intensive care unit Abstract: Objective: Thoracentesis in a ventilated patient is rarely performed because of the risk of pneumothorax. We have evaluated the safety of this procedure when aided by ultrasound. Design: Prospective study. Setting: Medical intensive care unit, university-affiliated hospital. Patients: 45 procedures were performed in 40 consecutive patients with ultrasound signs of pleural effusion, all mechanically ventilated. Interventions: Pleural effusion was defined on ultrasound as a collection of fluid between parietal and visceral pleura leading to variations in interpleural distance during breathing. When the interpleural distance was aY= 15 mm and visible over three intercostal spaces, a needle (16 or 21 G) was inserted after ultrasound localization in a patient in either dorsal or lateral decubitus. Results: No complication occurred in the 45 thoracenteses. Fluid was obtained in 44 of 45 procedures, thus confirming the diagnosis of pleural effusion. The procedure was immediate (less than 10 s) in 40 of 45 cases. It was easy (i. e., keeping the patient supine) in 22 of 45 procedures. In 44 cases where fluid was obtained, only 27 bedside radiographs revealed signs of effusion, whereas 17 showed absence of a visible effusion. Ultrasound thus appeared more efficient than bedside X-ray in detecting pleural effusion. Conclusions: If basic rules are followed, ultrasound localization makes thoracentesis a safe, easy and simple procedure in patients on mechanical ventilation. Author Affiliation: (1) Service de Reanimation Medicale, Hopital Ambroise-Pare, 9 avenue Charles-de-Gaulle, F-92 100 Boulogne (Paris), France Tel. + 33(1)49 09 56 01 Fax + 33(1)49 09 58 92, FR (2) Service de Reanimation Polyvalente, Centre Hospitalier General, Saint-Cloud (Paris), France, FR Article note: Received: 9 November 1998 Final revision received: 24 April 1999 Accepted: 17 May 1999

Ultrasound backscattering is well adapted to study the red blood cell (RBC) aggregation phenomenon and growth of RBC aggregates since the backscattered ultrasonic intensity depends on the sixth power of the mean radius of the scattering centers when considered as spherical. Thus, small variations of aggregate size induce large variations of the backscattered intensity. From measurements of the ultrasonic backscattering coefficient (ultrasonic backscattering cross section per unit volume of suspension), an analytical model describing its variation versus time, for human aggregated red blood cells in sedimentation, is proposed. Results given by the model allow to define three phases in the phenomenon: 1) a starting phase characterized by a duration [t.sub.s]; 2) a stationary final phase beginning at time [t.sub.f]; 3) a growing intermediate phase characterized by its duration [t.sub.f] - [t.sub.s]. The analytical model has been applied to describe RBC aggregation in dextran 70 000 dalton of different concentrations, and at various hematocrits. Knowledge of the durations [t.sub.s], [t.sub.f] and the maximum slope s of the curve during the intermediate phase, determined with the model, allows a means to study RBC aggregate growth. Index Terms - Analytical model, red blood cell aggregation, sedimentation, ultrasound backscattering.

A theoretical and numerical study of the acoustic field intensity within a curved flow conduit having 1) diameter similar to the wavelength of the interrogating frequency and 2) speed of sound mismatch with the surrounding medium is presented. The field intensity is shown to vary significantly and in a monotonic fashion across the flow conduit. The resulting insonation of emboli transiting through the Doppler sample volume is explored with a Monte Carlo study of the behavior of the embolus to blood power ratio (EBR). The numerical simulation findings are shown to be in good agreement with previously reported experimental results. A method is explored for estimating embolus diameter when this refraction artifact is present, and shown to yield excellent results when applied to experimental data. Further work toward clinical application of these results is discussed.

Backscattering of an incident ultrasound beam by blood gives rise to a Doppler spectrum whose characteristics are affected not only by the velocity distribution, but also by certain basic aspects of the RBC's behavior. Starting from fundamental assumptions, an explicit expression is derived for the Doppler spectrum in terms of the variance in the scatterer number density and the backscattering cross section. This shows that the Doppler power at a given frequency is weighted by the backscattering cross section and the manner in which the red blood cells (RBC's) are packed (packing factor). Since spatial variations in the flow field can result in changes in the variance and backscattering cross section, the mean Doppler frequency will not necessarily be proportional to the mean flow through the sample volume. Experimental results for two different flow fields are used to illustrate these effects. The implications of these findings are discussed in relation to volumetric flow estimation and the power mode display used in some color Doppler flow imaging systems.

An experiment to verify a theory describing ultrasound backscattering from emboli in flowing blood is presented. The theoretical predictions for the backscattered power versus embolus size are based on the measurement of the embolus to blood ratio (EBR) of backscattered acoustic power. This tool is necessary for in vivo clinical application because it removes the need to characterize attenuation and reflection loss in heterogeneous tissue. The experiment presented utilizes a customized ultrasound pulse Doppler that is capable of interrogating a sample volume with two different frequencies concurrently. A flow circuit including a 3.6-mm-diameter conduit in polyacrylamide gel in which emboli are observed with the dual frequency Doppler is described. The flow within the circuit has acoustic backscatter coefficient similar to blood due to a calibrated concentration of 31.1-[Mu] diameter polystyrene microspheres. Polystyrene micro-sphere 'emboli' having nominal diameters of 161 and 239 [Mu] are placed in this flow loop and time series Doppler shift signatures are recorded. These signatures are investigated and a refraction artifact hypothesis is proposed to explain systematic deviation of the signatures away from theoretically expected results. Results show that gross discrimination of embolus size is feasible.

A comparison study is reported on the ultrasonic assessment of human trabecular and bovine trabecular bone samples. Both ultrasonic velocity and ultrasonic attenuation were evaluated through a transmission insertion technique and correlated with bone mineral density as determined with single photon absorptiometry. For a 1-MHz ultrasonic transducer pair and the human cancellous bone samples the correlations were 0.91 and 0.89 between density and velocity and attenuation, respectively. For a 500-kHz ultrasonic transducer pair the correlations were 0.89 and 0.81 between density and velocity and attenuation, respectively. For the bovine bone samples, the correlations were 0.90 and -0.31 for the velocity and attenuation, respectively, for the 1 MHz transducer pair. For the 500-kHz transducers, the correlations were 0.85 and -0.17 for the velocity and attenuation, respectively. By combining both velocity and attenuation in a multivariate regression, an improvement was achieved in the estimation of bone density in the human samples for both the 500-kHz and 1-MHz transducer pairs. No significant improvement was achieved in the multivariate regressions for the bovine bone samples. In conclusion, the results indicate that ultrasonic measurements are in general highly correlated with bone mineral density in trabecular bone samples. This correlation is more consistent and strong in relatively low density human samples compared with the higher density bovine samples.

The backscattering coefficient of saline suspensions of porcine red blood cells was measured for hematocrits up to about 90%. It was found that the coefficient peaks at approximately 15%, but then, contrary to what a simple 'gap theory' might suggest, it decays smoothly to zero, without showing another peak at high hematocrits. A one-dimensional (1-D) slab scattering model, in which the number of slabs per unit length represents the hematocrit and whose thickness and acoustical properties are similar to red cells/plasma, was also used to investigate the relation between the backscattered power and hematocrit. Monte-Carlo simulations performed for randomized boundary conditions show a similar relation to that of the 3-D system. The experimental data is compared to the Percus-Yevick theory for the packing of hard spheres, and the simulated data is compared to the Percus-Yevick theory for infinite slabs.