Multi-frequency detection of a dielectric object using flexible contactless RF sensors for tissue diagnosis.

The aim of this paper is to experimentally assess the capacity of radio-frequency flexible sensors to localize a dielectric object inside a fluid, which could be used as a non contact sensor detected to the detection or the monitoring a local modification of a tissue, such as a tumor or a lesion. The used sensor is an MRI-like antenna, which consists in a flat, flexible and low cost multi-turn split resonator (MTLR), which features a geometrically pre-determined resonance frequency. The MTLR is used here as a transmit and receive sensor monitored by a distant loop coil. The complex impedance changes observed at the ends of the monitoring coil is known to be linked to the dielectric properties of the resonator environment. If a dielectric object is placed close to the resonator, the complex impedance is altered. In this work, an experimental set up is used to assess the relevance of such a measurement scheme to detect the presence of a dielectric inclusion embedded in another dielectric medium. The setup includes a spherical object of 1.5 cm diameter filled with various NaCl solutions moved vertically inside a tank filled with deionized water by means of a three axis robotic arm, to create an electrical conductivity contrast between the inclusion and the media, and three 2 cm diameter MTLR sensors featuring 30, 47 and 70 MHz resonance frequencies, respectively. The sensors are operated through the use of monitoring coils connected to a network analyzer, and measurements are carried out at each position of the spherical object. The resulting sensor responses are plotted and used for the assessment of sensor performances. In addition, a method to combine the multi-frequency data provided by the three different sensors is proposed. Two different metrics regarding the spatial resolution (SR) and the peak signal to noise ratio (PSNR) are computed to characterize the single sensor performances, as well as the enhancement provided by the proposed multi-frequency approach.

Imaging of a dielectric inclusion using a contactless radio-frequency inductive probe for tissue diagnosis.

In this paper, a contactless radio-frequency (RF) inductive probe is used to spatially localize and characterize a complex dielectric organic inclusion in a fluid. The effect of dielectric properties (DP) of this organic material is investigated experimentally and by numerical computations.The used RF probe is a 135 MHz 3 cm diameter and 10 cm long, cylindrical bracelet resonator, placed close to a water tank filled with deionized water which includes a 1.5 cm diameter inclusion filled of air or NaCl solutions and placed in arbitrary positions. The water tank and the inclusion are used to model an organic material including a tumor. The RF probe is used as a transmit and receive sensor. It induces a magnetic field inside the water tank, which, by reciprocity, conveys information about the DP of the investigated material. The impedance changes at the end of the RF probe are directly related to the modifications of the magnetic field, and are measured by means of a network analyzer. A complex fit of the impedance frequency response around the resonance frequency gives access to two quantities proportional to the electrical conductivity and dielectric constant of the inclusion. The inclusion is moved into the water tank along the three axes by means of a robotic arm, so that two three dimensional maps of the equivalent dielectric quantities in function of the inclusion position are sensed by the probe. Then, the inclusion is filled with different conductive NaCl solutions from 0.1 to 1.1 S/m in order to test the ability of the probe to sense the modifications of the dielectric properties of the inclusion. Experimental as well as computation results obtained using the Distributed Point Source Method (DPSM) validate the ability of the proposed probe to localize the inclusion as deep as 1 cm into the water, and the ability of the probe to sense the dielectric property changes of the inclusion.

[Perioperative management of a patient with an acquired von Willebrand syndrome]. / Gestion périopératoire d'un patient porteur d'un syndrome de von Willebrand acquis.

We report the case of a man suffering from a monoclonal gammapathy with an acquired von Willebrand disease in a perioperative context. This pathology is rare, but is important to diagnose because of the possible haemorrhagic complications encountered. We describe the main therapeutic options available today to prevent bleeding during major surgery.

[Cerebral monitoring with somatosensory evoked potentials in carotid surgery. A review of 141 carotids]. / Monitorage cérébral par potentiels évoqués somesthésiques en chirurgie carotidienne. A propos d'une série de 141 carotides opérées.

OBJECTIVE: To evaluate postoperative and mid-term results of carotid surgery (CS) with somatosensory evoked potentials (SEP) monitoring. METHODS: Between 1998 and 2006, 141 CS in 124 patients were performed under general anesthesia. Selective shunting was based on SEP abnormality. Shunting criteria were: reduction up to 50% of the amplitude or latency increasing up to 10%. Early results and follow-up data are analyzed retrospectively. RESULTS: Shunting rate was 6%, 3 strokes (two transient strokes) occurred and one patient died of perioperative myocardial ischemia. The cumulative stroke and death rate at 30 days was 1.4%. CONCLUSIONS: Intra-operative SEP monitoring with selective shunting may be safely performed in carotid surgery.

[BIS monitoring may allow the detection of severe cerebral ischemia]. / Intérêt potential du BIS pour détecter une souffrance cérébrale importante.

PURPOSE: To show that the bispectral index (BIS) is not only a monitor of the depth of anesthesia but that acute decreases of the index may be related to severe cerebral ischemia. CLINICAL FEATURES: Several clinical observations suggest that an unexplained fall of the BIS may be the result of cerebral ischemia. Somatosensory evoked potentials decreased in parallel to the decrease in BIS during carotid clamping in a 58-yr-old patient undergoing carotid endarterectomy. In a 62-yr-old patient undergoing resection of an aortic aneurysm, the BIS decreased from 40-50% to 8% as the cardiac index and central venous O(2) saturation decreased. The BIS returned to normal values when the low cardiac output was corrected pharmacologically. CONCLUSION: While the BIS is a well accepted monitor of the depth of anesthesia, several factors, unrelated to anesthesia, can modify the index. Thus, to adjust the level of anesthesia based solely on the BIS could be inappropriate. While the sensitivity and specificity of the BIS for this indication have not been determined, we suggest that the BIS may be useful to detect severe cerebral ischemia.

[Continuous infusion of vancomycin in post-neurosurgical staphylococcal meningitis in adults]. / Vancomycine en perfusion continue dans les méningites à staphylocoques post-neurochirurgicales de l'adulte.

Eight adult patients with post-surgery meningitis caused by methicillin-resistant staphylococci were treated with continuous intravenous infusion of vancomycin in mean doses of 50 mg/kg/day. This treatment, which lasted 3 to 6 weeks, was well tolerated by the kidneys and resulted in cure in all cases; its effect on the ear was not evaluated. Stable concentrations of 4 to 7 mg/l in cerebrospinal fluid were obtained after the 48th hour of treatment.

[The value and limitations of autotransfusion in traumatology]. / Intérêt et limites de l'autotransfusion en traumatologie.

29 autotransfusions were realised in severe cases of trauma (20% of a sample of 143 traumatic emergencies). The recovery of haemothorax blood as well as the peroperative collection by a Cell Saver allowed the retransfusion of 1989 +/- 1,838 ml (225-7070 ml) of autologous blood, amounting to 56% of the average blood loss. A total of 69% of the patients received homologous blood. Eight patients (where the haemorrhage amounted to 143% of the blood volume) showed some coagulation troubles. Autotransfusion assures the immediate availability of blood while reducing the immunological and viral transfusion risks. Therefore haemothorax autotransfusion should be used systematically. Peroperative recollection by a cell-separator works well but is technically more tedious.