Side Holes Research Articles

Catheter-related blood stream infection in hemodialysis patients with symmetric tunneled non-side-hole hemodialysis catheters.

Tunneled hemodialysis catheter-related bloodstream infection is a major cause of morbidity and mortality in end-stage renal disease patients. Side holes positioned near the tip of catheters have been linked to formation of thrombi, which, in turn, have been implicated in predisposition to infection. In addition, side holes allow spillage of catheter locking solution, including antibiotics, thereby minimizing the lock solution's effect on the catheter tip. This study assessed the infection events that occurred in a series of hemodialysis patients using a non-side-hole catheter. Over a period of 2 years, a novel symmetric-tip non-side-hole catheter was placed in 60 patients. Hemodialysis was performed thrice weekly. Prescribed dialyzer flows were 300-350 mL/min. Catheters were routinely locked with heparin 5000 units/mL between treatments. Patients were followed up for any catheter related complications, specifically infection events. Seven events of catheter-related bloodstream infection occurred for a rate of 0.76 events per 1000 catheter-days, with the first event occurring 9 weeks after insertion. These events were treated by locking the affected catheter with 2 g of clindamycin in 2 mL of heparin 1000 units/mL and administration of intravenous antibiotics, in most cases, for 7-14 days. Two catheters were removed due to infection. Catheter-related bloodstream infections with non-side-hole hemodialysis catheters do occur at a relatively low rate and in this initial preliminary study it seems that most of these infections can be successfully treated without removal of the affected catheters.

Turbine endwall cooling and heat transfer characteristics under slashface leakage interacted with nearby discrete-hole injections

A novel turbine endwall cooling structure is modeled by placing discrete holes individually on the pressure or suction side endwall near slashface gap. By solving the Reynolds-averaged Navier-Stokes (RANS) equations and SST k-ω turbulence model, the strong interactions between slashface coolant leakage with nearby discrete hole injections are studied under three blowing ratios (M = 0.5, 1.0, and 1.5), and its effect on gas turbine endwall aerothermal characteristics is numerically investigated. The results indicate that the pressure and suction side holes all largely increase the cooling effectiveness in the throat region. The hole injections are most effective when M = 0.5 in terms of cooling the upstream part endwall with an increased cooling effectiveness of 0.2 in the vicinity. The pressure-side hole injection can elevate the fluid near the endwall and isolate the slashface leakage from passage crossflow, and it can prevent the slashface leakage from lifting off when flowing over the slashface. The spreading of the coolant along slashface suction side edge on the downstream part endwall is interrupted by the pressure-side hole injection. However, the suction-side holes can help the slashface leakage to have a higher lift height and reattach on the endwall further downstream. The endwall along the slashface suction side edge is continuously protected with the help of six suction-side holes when M = 1.5, and the averaged cooling effectiveness between 0.1 < z/Cax < 0.9 is increased by 0.05–0.15. The heat transfer downstream of the holes is largely enhanced by the coolant injection, especially for the region near blade shoulder that directly suffers from flow acceleration. However, the suction-side hole injection can reduce the area of the wedge-shaped high Nu region near passage throat. The averaged Nu in the vicinity of the holes is increased from 1500 to 3000–4000. The net heat flux reduction is decreased by the pressure-side hole injection but the protection effect is strengthened by the suction-side hole injection at low blowing ratios (M = 0.5 and 1.0). The results can help the gas turbine designers to further understand the flow physics of endwall coolant ejection as well as controlling them for a better protection effect.

Staphylococcus aureus accumulation at the tip of hemodialysis catheters with or without tip side holes in catheter related bloodstream infection in a large animal.

Eighty percent of hemodialysis patients start their dialysis with a tunneled hemodialysis catheter. Catheter related bacteremia is the second most common cause of death in these patients. Side holes near the tips of the tunneled cuffed central venous catheters are associated with accumulation of thrombus, which can lead to catheter dysfunction and, possibly, also to catheter-related infection. To assess the hypothesis that a catheter without side holes would be associated with less bacterial growth, this study compared the susceptibility of a side-hole-free catheter to accumulation of pathogenic bacteria at the catheter tip with that of two catheters which have side holes. Eight tunneled cuffed double-lumen central venous catheters were inserted into both jugular veins of four sheep; one side-hole-free and one control catheter with side holes at the tip in each animal. Staphylococcus aureus bacteria were then infused intravenously to cause bacteremia. Six hours later, the catheters were removed, the clots that accumulated in their tips were collected and cultured, and the bacterial colonies were counted after additional 12 h of incubation. Bacteria grew on culture plates seeded with the clot homogenate obtained from the tips of all catheters. The colony counts from the catheters with side holes at the tip exceeded the colony counts of bacteria accumulated in the tips of the side-hole-free hemodialysis catheters by one or more orders of magnitude, with a difference of at least two orders of magnitude observed in three of the four intra-animal comparisons. In paired intra-animal post-inoculation comparison made in this limited study, fewer colony forming units of pathogenic bacteria accumulated at the tip of the side-hole-free catheters than at the tips of the catheters which have side holes. This may translate to a decreased rate of catheter-related blood stream infections in the side-hole-free catheters.

Electrospray Ionization Inside the Ion Inlet Tube: Multijet Mode Operation.

We investigated the electrospray ionization inside the narrow channel of the ion inlet tube. An insulating emitter capillary made of fused silica with a 0.2 mm outer diameter was inserted into the ion inlet tubes with a 0.5 and 0.6 mm inner diameter to aspirate all the charged droplets. A custom-made ion inlet tube with two side holes near its entrance is used to observe the spraying condition. The spray current is measured and monitored during the MS acquisition using isolation amplifiers. Because the emitter is cylindrically surrounded in close proximity by the metallic inner wall, it is difficult to obtain a stable and symmetric Taylor cone with its apex at the center of the emitter. Instead, a stable operation under a flow rate of 1-4 μL/min is found to be in the form of a multicone-jet mode with two or more Taylor cones anchoring around the rim of the emitter. The emitted charged droplet jets are dragged from hitting the wall by the fast-flowing air inside the inlet tube. Comparison with the typical cone-jet and multijet mode operated several millimeters outside the inlet capillary shows signal enhancements for protein standards.

Compulsory drainage of inferior vena cava to obtain bloodless field in minimally invasive mitral valve surgery.

Gaining bloodless field in minimally invasive mitral valve surgery is crucial for a successful surgery. We here demonstrate a simple method to obtain bloodless field in minimally invasive mitral valve surgery with only single venous cannula through the femoral vein. A dual-stage venous cannula is inserted through the femoral vein, with its tip located deep in superior vena cava. After establishing full flow, the inferior vena cava (IVC) was snared. Returning blood from the IVC was blocked at the snare, and drained through the side holes at the midportion of the cannula. This technique collapsed the right atrium, and made the left atrium almost bloodless. Pressures of the femoral vein measured in 28 patients were 9.5 ± 4.1mmHg before bypass, 6.8 ± 4.8mmHg before snaring IVC, and 7.2 ± 4.8mmHg after snaring. By blocking returning blood from the lower body, venous congestion of the lower body did not occur.

Effectiveness analysis of abrasive flow polishing S-shaped elbow with side holes based on large eddy simulation

Effectiveness analysis of abrasive flow polishing S-shaped elbow with side holes based on large eddy simulation

A Novel Fat Making Strategy With Adipose-Derived Progenitor Cell-Enriched Fat Improves Fat Graft Survival.

A low survival rate is one of the main challenges in fat grafting. This study aimed to evaluate whether microfat obtained by a novel strategy promoted the survival and retention of fat grafts. A 5-mm-diameter blunt tip cannula with large side holes (~30 mm2/hole) was used to obtain macrofat. A novel strategy based on a newly invented extracorporeal cutting device was then used to cut the macrofat into microfat, which was named adipose-derived progenitor cell enrichment fat (AER fat); Coleman fat was used as the control. Aliquots (0.5 mL) of both types of fat were transplanted into 10 nude mice and analyzed 10 weeks later. Western blotting, flow cytometry, and immunofluorescence were performed to assess the AER fat characteristics and underlying mechanisms. The retention rate of fat grafts in AER fat-treated animals was significantly higher than that in the Coleman group (mean [standard deviation] 54.6% [13%] vs 34.8% [9%]; P < 0.05) after 10 weeks. AER fat contained more dipeptidyl peptidase-4-expressing progenitor cells (3.3 [0.61] × 103 vs 2.0 [0.46] × 103 cells/mL; P < 0.05), adipose-derived plastic-adherent cells (6.0 [1.10] × 104 vs 2.6 [0.17] × 104 cells/mL; P < 0.001), and viable adipocytes than Coleman fat. Moreover, histologic analysis showed that AER fat grafts had better histologic structure and higher capillary density. AER fat transplantation is a potential strategy to improve the survival and long-term retention of fat grafts. AER fat contained more dipeptidyl peptidase-4-expressing progenitor cells.

Heat transfer improvement in a tube by inserting perforated conical ring and wire coil as turbulators

AbstractIn the present study, two various passive methods for heat transfer enhancement, including conical ring and wire coil are placed in a tube as turbulators. Four conical rings with four side holes are utilized with the same distance. The wire coil is employed at the center of the tube. The considered Reynolds numbers are between 4000 and 10,000. The studied geometrical parameters contain the pitch and diameter of a wire coil. Four different pitches of wire coil, including 10, 12, 14, and 16 mm, are evaluated. Furthermore, four values of wire coil diameter such as 2, 4, 6, and 8 mm are certain. The obtained numerical results displayed that by declining the pitch of a wire coil (37.5%), the average Nusselt number increases by about 143%. Also, augmentation in wire coil diameter by 300% leads to a growth in average Nusselt number by about 131%. Moreover, owing to utilizing two various turbulators, the pressure drop is significantly high in comparison with the bare tube. At Re = 10,000, growth in the inner diameter of the wire coil by 300% leads to an increase in thermal performance by about 36.12%. Moreover, as the pitch of the wire coil rises by 60%, the thermal performance declines by about 35.71%.

Improved Drainage Cannula Design to Reduce Thrombosis in Veno-Arterial Extracorporeal Membrane Oxygenation.

Thrombosis is a potentially life-threatening complication in veno-arterial extracorporeal membrane oxygenation (ECMO) circuits, which may originate from the drainage cannula due to unfavorable blood flow dynamics. This study aims to numerically investigate the effect of cannula design parameters on local fluid dynamics, and thus thrombosis potential, within ECMO drainage cannulas. A control cannula based on the geometry of a 17 Fr Medtronic drainage cannula concentrically placed in an idealized, rigid-walled geometry of the right atrium and superior and inferior vena cava was numerically modeled. Simulated flow dynamics in the control cannula were systematically compared with 10 unique cannula designs which incorporated changes to side hole diameter, the spacing between side holes, and side hole angles. Local blood velocities, maximum wall shear stress (WSS), and blood residence time were used to predict the risk of thrombosis. Numerical results were experimentally validated using particle image velocimetry. The control cannula exhibited low blood velocities (59 mm/s) at the cannula tip, which may promote thrombosis. Through a reduction in the side hole diameter (2 mm), the spacing between the side holes (3 mm) and alteration in the side hole angle (30° relative to the flow direction), WSS was reduced by 52%, and cannula tip blood velocity was increased by 560% compared to the control cannula. This study suggests that simple geometrical changes can significantly alter the risk of thrombosis in ECMO drainage cannulas.

Temperature sensing by hybrid interferometer based on Vernier like effect

A temperature sensitive hybrid interferometer is developed and tested experimentally. The hybrid interferometer consists of a Michelson interferometer (MI) cascaded with a Fabry-Perot interferometer (FPI). It is fabricated by successively fusion splicing a single-mode fiber (SMF), a small section of multi-mode fiber (MMF), double side hole fiber (DSHF) and hollow Core fiber (HCF) together. The end of the HCF is filled with a thermosensitive polymer to form a reflecting surface of the FPI. The free spectral range of the MI and the FPI are designed to similar so that the Vernier-like effect can be generated. The Vernier Effect and the high thermal expansion coefficient of the polymer filled into the HCF enhance the temperature sensitivity of the hybrid interferometer. The maximum temperature sensitivity of 710.9 pm/°C has been achieved through experiments, which is much higher than silica-based temperature sensors.

Continuous Negative Pressure Drainage with Intermittent Irrigation Leaded to a Risk Reduction of Perineal Surgical Site Infection Following Laparoscopic Extralevator Abdominoperineal Excision for Low Rectal Cancer.

PurposeHigh rate of perineal surgical site infection (SSI) is the most common complication following abdominoperineal resection (APR), especially for extralevator abdominoperineal excision (ELAPE). The purpose of this study was to investigate the effect of continuous negative pressure drainage combined with intermittent irrigation (CNPDCII) in the presacral space on the perineal SSI following laparoscopic ELAPE for low rectal cancer.Patients and MethodsThe clinical data of 99 patients with low rectal cancer who underwent laparoscopic ELAPE surgery were retrospectively analyzed. Among the 99 patients, 46 patients received CNPDCII and 53 patients received conventional drainage in the presacral space after ELAPE. Self-made irrigation drainage tube: took a silicone drainage tube, cut 3 side holes at every 2cm intervals at the front end, and fixed a flexible tube of an intravenous needle at the front end of the silicone drainage tube. The conventional drainage tube or self-made irrigation drainage tube was placed in the presacral space and poked out from the inside of the ischial tuberosity. The incidence of SSI and other perioperative indicators between the two groups was compared within 30 days after surgery.ResultsThere was no statistical difference in clinicopathological features between the two groups of patients (p>0.05). A statistically lower rate of SSI was found in CNPDCII group (17.4%, 8/46) than the conventional drainage group (35.8%, 19/53). The drainage tube retention time (7.8±1.2 d VS 9.4±1.6 d) and the postoperative hospital stay (9.7±1.4 d VS 11.9±2.3 d) in CNPDCII group were significantly shortened than the conventional drainage group. There was no statistical difference in operating theatre time and intraoperative blood loss between the two groups. Multivariate analysis confirmed that CNPDCII was an independent protective factor for SSI after ELAPE.ConclusionCNPDCII can effectively reduce the incidence of SSI following laparoscopic ELAPE, which is simple, safe and effective.

A Novel Suction-and-Irrigation Laparoscopic Surgical Instrument: Internal Design and Preclinical Performance Evaluation

Abstract Objective: Laparoscopic instruments with suction and irrigation functions often lead to tissue damage during removal of the aspirated tissues, owing to the presence of aspiration into the side holes of their catheters. To address this problem, we designed a novel irrigation-and-suction catheter and assessed its preclinical efficacy. Methods: We made structural improvements to the irrigation-suction catheter to prevent tissue aspiration through its side holes. We ran a simulation program to perform experimental assessments before printing out the catheter tip models using a three-dimensional (3D) printer. Model 1 was the control, and Models 2, 3, and 4 were the improved models. Using these, we performed 10 repetitions of 15-s suction followed by 15-s irrigation, for a total of 5 times per model. We recorded the number of aspirations that occurred through the side holes and analyzed each model using nonparametric methods. Results: Models 2 and 3 showed fewer aspirations because the velocity and pressure around their side holes were lower than those of Model 1; this was statistically significant. On the other hand, Model 4 had a lesser preventive effect against aspiration due to higher velocity and pressure around its side holes. Interpretation of Results: We confirmed that side-hole aspiration can be prevented with an internal structure that completely separates the irrigation and suction paths. Even if the irrigation and suction paths are not completely separated, adding a septal structure at the distal end of the catheter may prevent aspiration.

High-amplitude sound propagation in acoustic transmission-line metamaterial

We report experiments on high-amplitude sound wave propagation in an acoustic metamaterial composed of an air-filled waveguide periodically side-loaded by holes. In addition to the linear viscothermal and radiation losses, high amplitude sound waves at the locations of the side holes introduce nonlinear losses. The latter result in an amplitude-dependent reflection, transmission, and absorption, which we experimentally characterize. First, we evidence that nonlinear losses change the nature of the device from a reflective to an absorbing one, showing the possibility to use the system as a nonlinear absorber. Second, we study the second-harmonic generation and its beating phenomenon both experimentally and analytically. We find that when considering the propagation of both the fundamental and the second harmonic, nonlinear losses cannot be neglected. Our results reveal the role of nonlinear losses in the proposed device and also provide a quite accurate analytical model to capture the effect of such losses.

Novel Dual-Lumen Drainage Catheter to Enhance the Active Evacuation of Complex Fluid Collections

PurposeTo compare the performance of a dual-lumen flushable drainage catheter to a conventional catheter for complex fluid collection drainage. MethodsTwo prototype catheters (20- and 28-F) were created by incorporating a customized infusion lumen within the wall of a large-bore conventional drainage catheter, which facilitated simultaneous irrigation of the drainage lumen and the targeted collection via inward- and outward-facing infusion side holes. These were tested against unaltered 20- and 28-F conventional catheters to determine if the injection of a dedicated flush lumen improved rapidity and completeness of gravity drainage. In vitro models were created to simulate serous fluid, purulent/exudative fluid, particulate debris, and acute hematoma. ResultsIn the purulent model, mean drainage rate was 19.9 ± 8.0 and 9.5±1.4 mL/min for the 20-F prototype and control (P < .001) and 63.9 ± 4.3 and 35.4 ± 3.4 mL/min for the 28-F prototype and control (P = .006), respectively, with complete drainage achieved in all trials. In the particulate model, mean drainage rate was 24.5 ± 9.7 and 12.0 ± 12.5 mL/min for the 28-F prototype and control (P = .003), respectively, with 69.0% versus 41.1% total drainage achieved over 24 minutes (P = .029). In the hematoma model, mean drainage rate was 22.7 ± 4.6 and 4.8 ± 4.3 mL/min for the 28-F prototype and control (P = .022), respectively, with 80.3% versus 20.1% drainage achieved over 15 minutes (P = .003). Particulate and hematoma 20-F prototypes and conventional trials failed due to immediate occlusion. ConclusionsThe proposed dual-lumen drainage catheter with irrigation of a dedicated flush lumen improved evacuation of complex fluid collections in vitro.

Failure of ureteral stents subject to extrinsic ureteral obstruction and stent occlusions

To quantify the occurrence of stent failure and the dynamic behavior of urine flow in ureter-stent systems, including the relative flow in the ureter and stent lumina, subject to various degrees of ureter and stent blockage. Numerical simulations based on computational fluid dynamics (CFD) were used to quantify urine flow behavior in stented ureters, in the presence of extrinsic ureteral obstruction (EUO) and stent occlusions. Two stented ureter configurations were considered, one with circumferential occlusion of the ureter and the second with pressure on one side of the ureter wall. The pressure within the renal unit for different degrees of ureter closure and stent lumen occlusion was determined systematically. Onset of stent failure and the distribution of urine flow between stent and ureter lumina were determined. In the case of EUO completely encircling the ureter, causing 100% obstruction of the ureter lumen, pressure in the renal unit is essentially unaffected until the stent lumen reaches ~ 90% occlusion, and fails only with > 95% occlusion. Occlusions of 50% in stent side holes in the vicinity of the EUO only alter local flow patterns but have no significant influence on renal unit pressure. For EUO deforming and compressing the ureter from one side, with ~ 50% reduction in ureter lumen, urine drainage proceeds with negligible increase in renal pressure even with 100% occlusion in the stent lumen. CFD simulations show that stent failure under EUO tends to occur suddenly, only when both ureter and stent lumina become almost fully blocked.

Low gas pressure sensor based on a polymer optical fiber grating.

A fiber Bragg grating (FBG) inscribed Zeonex-based novel, to the best of our knowledge, side hole polymer optical fiber (SHPOF) is proposed and demonstrated for low gas pressure measurement above and below the atmospheric pressure. Two different grades of Zeonex have been used to fabricate the core and cladding of this fiber, thereby making it dopant free. The side hole introduced in the cladding is parallel to the fiber core. A few ultrashort pulses with nanosecond duration have been used to write the FBG in the core of this fiber. The incorporation of the side hole leads to enhancement of pressure sensitivity as well as low hysteresis and performance repeatability compared to Zeonex-based conventional polymer optical fiber (CPOF). Above the atmospheric pressure, the proposed probe shows a pressure sensitivity of 0.47 pm/kPa, which is 80% more compared to the Zeonex-based CPOF and 0.48 pm/kPa for regime below atmospheric pressure. The sensor has a resolution of 2.12 kPa and exhibited very low hysteresis.

A new perspective on pore growth in anodic alumina films

In this study, we use advanced analysis techniques to examine the nanostructures of anodic films formed on aluminum in various electrolytes, including oxalic acid and sulfuric acid, in the original state (without being chemically dissolved) and reveal that pores grow with radially branched nanopores. Nanopores are generated in the main pores for the same reason that initial small pores are generated on the film surface: nanopores are created when the electric field is reduced due to the presence of a thick barrier layer. These radially branched nanopores appear in a form characteristic of a film formed in chromic acid, producing a feather-like pore wall. As a representative model, the atypical porous structures created in the film formed in chromic acid were classified into five categories: initial small pores, branched pores, side holes, spherical voids, and radially branched nanopores. We demonstrate that these structures are not unique to chromic acid films but are a universal phenomenon, particularly radial nanobranching, which occurs naturally during the anodizing of most electrolytes.

Comparison of Microfat, Nanofat, and Extracellular Matrix/Stromal Vascular Fraction Gel for Skin Rejuvenation: Basic Research and Clinical Applications.

Over the past 2 decades, fat grafting has been extensively applied in the field of tissue regeneration. The aim of this study was to investigate the therapeutic potential of microfat, nanofat, and extracellular matrix/stromal vascular fraction gel (SVF-gel) in skin rejuvenation. Microfat was harvested by a cannula with multiple 0.8-mm smooth side holes and processed with a fat stirrer to remove fibers. Nanofat and SVF-gel were prepared according to previously reported methods, and their structure and viability were evaluated. Then, SVF cells from the 3 types of samples were isolated and characterized, and the cell viability was compared. The microstructure of the 3 samples showed distinct differences. The microfat group showed a diameter of 100 to 120.0 μm under the microscope and presented a botryoid shape under calcein acetoxymethyl (calcein-AM)/propidium iodide staining. Scanning electron microscopy analysis showed that the microfat maintained an integral histologic structure. In the nanofat group, no viable adipocytes and no normal histologic structure were observed, but high levels of free lipids were noted. The SVF-gel group showed uniform dispersion of cells with different sizes and parts of the adipose histologic structure. Cell count and culture revealed that the number of viable SVF cells decreased distinctly in the nanofat group compared with the microfat group. In contrast, the number of viable SVF cells in the SVF-gel group increased moderately. Clinical applications with microfat showed marked improvements in skin wrinkles. Microfat can preserve the integrity of the histologic structure and presents the advantages of subcutaneous volumetric restoration and improvement of skin quality in skin rejuvenation compared with the nanofat and SVF-gel.

Spatiotemporal Monitoring and Evaluation Method for Sand-Filling of Immersed Tube Tunnel Foundation

The sand-filling method has been widely used in immersed tube tunnel engineering. However, for the problem of monitoring during the sand-filling process, the traditional methods can be inadequate for evaluating the state of sand deposits in real-time. Based on the high efficiency of elastic wave monitoring, and the superiority of the backpropagation (BP) neural network on solving nonlinear problems, a spatiotemporal monitoring and evaluation method is proposed for the filling performance of foundation cushion. Elastic wave data were collected during the sand-filling process, and the waveform, frequency spectrum, and time–frequency features were analysed. The feature parameters of the elastic wave were characterized by the time domain, frequency domain, and time-frequency domain. By analysing the changes of feature parameters with the sand-filling process, the feature parameters exhibited dynamic and strong nonlinearity. The data of elastic wave feature parameters and the corresponding sand-filling state were trained to establish the evaluation model using the BP neural network. The accuracy of the trained network model reached 93%. The side holes and middle holes were classified and analysed, revealing the characteristics of the dynamic expansion of the sand deposit along the diffusion radius. The evaluation results are consistent with the pressure gauge monitoring data, indicating the effectiveness of the evaluation and monitoring model for the spatiotemporal performance of sand deposits. For the sand-filling and grouting engineering, the machine-learning method could offer a better solution for spatiotemporal monitoring and evaluation in a complex environment.

Full waveform inversion for bore reconstruction of woodwind-like instruments

The internal geometry of a wind instrument can be estimated from acoustic measurements. For woodwind instruments, this involves characterizing the inner shape (bore) but also the side holes (dimensions and location). In this study, the geometric parameters are recovered by a gradient-based optimization process, which minimizes the deviation between simulated and measured linear acoustic responses of the resonator for several fingerings through an observable function. The acoustic fields are computed by solving a linear system resulting from the 1D spectral finite elements spatial discretization of the wave propagation equations (including thermo-viscous effects, radiation and side holes). The “full waveform inversion” (FWI) technique exploits the fact that the gradient of the cost function can be computed by solving the same linear system as that of the direct problem but with a different source term. The gradient is computed with better accuracy and less additional cost than with finite-difference. The dependence of the cost function on the choice of the observed quantity, the frequency range and the fingerings used, is first analyzed. Then, the FWI is used to reconstruct, from measured impedances, an elementary instrument with 14 design variables. The results, obtained in about 1 minute on a laptop, are in excellent agreement with the direct geometric measurements.