Energy dispersive CdTe and CdZnTe detectors for spectral clinical CT and NDT applications.

We are developing room temperature compound semiconductor detectors for applications in energy-resolved high-flux single x-ray photon-counting spectral computed tomography (CT), including functional imaging with nanoparticle contrast agents for medical applications and non destructive testing (NDT) for security applications. Energy-resolved photon-counting can provide reduced patient dose through optimal energy weighting for a particular imaging task in CT, functional contrast enhancement through spectroscopic imaging of metal nanoparticles in CT, and compositional analysis through multiple basis function material decomposition in CT and NDT. These applications produce high input count rates from an x-ray generator delivered to the detector. Therefore, in order to achieve energy-resolved single photon counting in these applications, a high output count rate (OCR) for an energy-dispersive detector must be achieved at the required spatial resolution and across the required dynamic range for the application. The required performance in terms of the OCR, spatial resolution, and dynamic range must be obtained with sufficient field of view (FOV) for the application thus requiring the tiling of pixel arrays and scanning techniques. Room temperature cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe) compound semiconductors, operating as direct conversion x-ray sensors, can provide the required speed when connected to application specific integrated circuits (ASICs) operating at fast peaking times with multiple fixed thresholds per pixel provided the sensors are designed for rapid signal formation across the x-ray energy ranges of the application at the required energy and spatial resolutions, and at a sufficiently high detective quantum efficiency (DQE). We have developed high-flux energy-resolved photon-counting x-ray imaging array sensors using pixellated CdTe and CdZnTe semiconductors optimized for clinical CT and security NDT. We have also fabricated high-flux ASICs with a two dimensional (2D) array of inputs for readout from the sensors. The sensors are guard ring free and have a 2D array of pixels and can be tiled in 2D while preserving pixel pitch. The 2D ASICs have four energy bins with a linear energy response across sufficient dynamic range for clinical CT and some NDT applications. The ASICs can also be tiled in 2D and are designed to fit within the active area of the sensors. We have measured several important performance parameters including; the output count rate (OCR) in excess of 20 million counts per second per square mm with a minimum loss of counts due to pulse pile-up, an energy resolution of 7 keV full width at half maximum (FWHM) across the entire dynamic range, and a noise floor about 20keV. This is achieved by directly interconnecting the ASIC inputs to the pixels of the CdZnTe sensors incurring very little input capacitance to the ASICs. We present measurements of the performance of the CdTe and CdZnTe sensors including the OCR, FWHM energy resolution, noise floor, as well as the temporal stability and uniformity under the rapidly varying high flux expected in CT and NDT applications.

Hemodynamic effect of sustained pulmonary hyperinflation in patients after cardiac surgery: open vs. closed chest.

BACKGROUND: In a previous study, we showed that sustained pulmonary hyperinflation, i.e. a lung recruitment maneuver, after closure of the chest in patients undergoing cardiac surgery had significantly negative effects on the central hemodynamics. As elevated pleural pressure is believed to be a major cause of this cardiovascular impairment, we hypothesized that performing the sustained pulmonary hyperinflation under open chest conditions would affect the circulation less. METHODS: Patients undergoing cardiac by-pass surgery were included and sustained pulmonary hyperinflations (40 cmH(2)O airway pressure for 15 s) were performed immediately before and after closure of the sternum. Pulse contour cardiac output, heart rate, mean arterial pressure and pulse pressure variation were measured before, during and 1 min after the hyperinflations. Left ventricular dimensions were measured using trans-esophageal echocardiography. RESULTS: Cardiac output (CO) and mean arterial blood pressure (MAP) decreased significantly during the sustained pulmonary hyperinflation both with an open and closed chest (in parenthesis): CO by 50 (45)% and MAP by 19 (24)%. The left ventricular end-diastolic area was significantly reduced by 24 (33)%. One minute after the hyperinflation, all measured variables had returned to baseline values. No significant differences in the measured variables were found between the two conditions before, during or 1 min after the hyperinflation. CONCLUSION: Contrary to our hypothesis, sustained pulmonary hyperinflations with the chest open, i.e. before sternal closure, had similar negative effects on central hemodynamics as those performed with the chest closed, i.e. after sternal closure.

Both lung recruitment maneuver and PEEP are needed to increase oxygenation and lung volume after cardiac surgery.

BACKGROUND: Patients ventilated after cardiac surgery commonly have impaired oxygenation, mainly due to lung collapse. We have previously found that PaO2 and end-expiratory lung volume (EELV) were increased by a lung recruitment maneuver (LRM) followed by positive end-expiratory pressure (PEEP). The aim of this study was to evaluate whether only PEEP or only a LRM could give similar effects. METHODS: Thirty circulatory stable patients (aged 55-79 years) mechanically ventilated after cardiac surgery were randomized to receive LRM (four 10-s insufflations to an airway pressure of 45 cmH2O) and zero end-expiratory pressure (LRM-group), PEEP 12 cmH2O (PEEP-group) or LRM in combination with PEEP 12 cmH2O (LRM + PEEP-group). The set end-expiratory pressure was kept for 75 min. Before, during and after the intervention, EELV (SF6 washout technique) and blood gases were measured. RESULTS: Initial EELV and PaO2 were similar in all groups. In the LRM-group, PaO2 and EELV increased transiently (P < 0.0001), but returned at 5 min to the initial values. In the PEEP-group, PaO2 did not change but EELV increased to 155 +/- 27% of the initial value (P < 0.0001). In the LRM+PEEP-group, PaO2 and EELV increased to 212 +/- 66% and 178 +/- 31% of the initial values (P < 0.0001), respectively, and were maintained during PEEP application. CONCLUSION: In patients ventilated after cardiac surgery: (1) PEEP increased lung volume but not PaO2, (2) a lung recruitment maneuver without subsequent PEEP had no sustained effect, and (3) both a lung recruitment maneuver and PEEP were needed to increase and maintain the increased lung volume and PaO2.

Thoracic sympatholysis with epidural blockade assessed by quantitative measurement of cutaneous blood flow.

BACKGROUND: Quantifying sympathetic activity is difficult. Direct measurement is possible and superior to indirect techniques, but nerves to internal organs are not accessible in humans. Recently, we validated a quantitative technique for measurement of cutaneous blood flow using heat as an indicator. The aim of the study was to investigate whether sympatholysis during thoracic epidural blockade (TEA) may be documented by changes in regional cutaneous blood flow. A secondary aim was to assess whether, during TEA, local heating itself enhances regional blood flow. METHODS: Six patients scheduled for elective coronary artery bypass grafting (CABG) were studied. An epidural catheter was inserted at the T2-3 interspace. Measurements were performed with an electrode, which can measure the local temperature of the skin. The probe is covered with a thermostatically controlled cap to avoid a thermic gradient to air. As a result of the cap, a change in temperature of the central disc depends almost solely on the blood flow in the underlying tissue. Regional cutaneous blood flow rates were measured before and after epidural anesthesia with and without local heating. RESULTS AND COMMENTS: All patients had a sensory blockade covering at least T1-5. Cutaneous blood flow increased in all six patients after blockade (13.6 ml/min/100 g, range 10.6-14.6 vs. 18.4 ml/min/100 g, range 13.9-24.5; P<0.05). Local heating did not further enhance blood flow. CONCLUSION: High TEA is associated with a uniform increase in thoracic cutaneous blood flow, and is suggestive of regional sympatholysis. Quantitative measurements of skin blood flow appear promising for documenting regional sympatholysis during TEA.

Racemization kinetics of aspartic acid in fish material under different conditions of moisture, pH, and oxygen pressure.

The racemization kinetics of aspartic acid in heat-treated whole herring have been studied under conditions of treatment comparable to those that may occur in processing of fish meal. D-Aspartic acid content in the samples has been measured by RP-HPLC with precolumn automatic derivatization. The major parameters affecting the rate of racemization of aspartic acid k(Asp) have been demonstrated to be temperature (elevation of temperature from 95 to 120 degrees C resulted in an increase of k(Asp) from 0.46 to 3.39x10(-3) min(-1)), moisture of the raw material (reduction of the moisture content of the raw material from 80 to 15% lowered k(Asp) measured at 95 degrees C from 0.46 to 0.06x10(-3) min(-1)), and to a lesser extent, pH (k(Asp) at 95 degrees C was lowered from 0.46 to 0.37x10(-3) min(-1) following a decrease of pH from 7.0 to 4.0). No significant effects on the racemization rate of aspartic acid was observed for reducing the oxygen pressure to 0.8%. The results from the present study show that the content of D-aspartic acid in fish material is a function of heat exposure and may be used to predict the thermal history of fish meal.

Epidural anesthesia in cardiac surgery: is there an increased risk?

OBJECTIVE: To assess the risk of hemorrhagic complications associated with epidural anesthesia in patients undergoing coronary artery bypass grafting. DESIGN: A prospective study. SETTING: A cardiac surgical center associated with a university. PARTICIPANTS: Five hundred fifty-eight consecutive patients scheduled for coronary artery bypass surgery. INTERVENTIONS: A Tuohy 18G epidural catheter was inserted the day before surgery in all patients. MEASUREMENTS AND MAIN RESULTS: Preoperative coagulation tests, such as platelet count and prothrombin time, were performed. No patient was on oral anticoagulation therapy or had coagulation disorders. Four hundred three (72%) patients were on antiplatelet therapy, which was terminated at least 1 week before surgery. The epidural catheter was left in situ for up to 5 days. All patients were observed daily for signs of spinal cord compromise, such as radicular back pain or progressive sensory or motor deficits. There were no documented spinal hematomas. CONCLUSION: By following certain guidelines, the risk for the development of epidural hematoma is not increased in patients undergoing epidural anesthesia during cardiac surgery.

[Perioperative risk in heart surgery. An original material and review of difficulties in correct comparisons with other materials]. / Perioperativ risiko ved hjerteoperationer. Et originalmateriale og en gennemgang af vanskelighederne ved korrekt sammenligning med andre materialer.

The purpose of this study was to present data concerning morbidity and mortality after cardiac surgery and to establish a method to make the presentation comparable to other reports. The main difficulty in comparing results of surgery of one institution with those of another is the lack of a simple and widely acceptable quantification of risk. A preoperative risk classification of patients requires readily available and objective data. The shortage of standardized criteria for comparing outcome was obvious as only a few comprehensive reports regarding preoperative predictors were found in the literature. The method of Tuman et al is based on 12 preoperative risk factors that are reasonably free of observer bias and practically obtainable. This method was used to report the results of 628 consecutive patients undergoing coronary revascularization or valvular surgery. Total in-hospital morbidity was 3.5% and mortality 1.0%. The most important predictors for postoperative morbidity were valvular surgery, advanced age, renal dysfunction, recent myocardial infarction and pulmonary hypertension. The system is most useful in predicting good outcome in low-risk patients. The identification of high-risk patients is valuable in spite of the limited predictive ability, by allowing special attention to be directed to the patient at risk.

Effect of nitrous oxide and volatile anaesthetics on platelet function in man.

Twelve otherwise healthy male volunteers scheduled for arthroscopy of the knee were studied. The influence in vivo of nitrous oxide (N2O) per se and the addition of a halogenated volatile anaesthetic (halothane or isoflurane) on ADP-induced platelet aggregation and release of beta-thromboglobulin into plasma was evaluated. All measurements were made before surgery. We found that N2O increased platelet aggregation. Adding a halogenated anaesthetic reversed the relative hyperaggregation induced by N2O. The concentrations in plasma of the platelet release product beta thromboglobulin were not influenced by the anaesthetics.

[Acute surgery-requiring mitral valve insufficiency caused by rupture of the chordae tendineae]. / Akut operationskraevende mitralinsufficiens forårsaget af ruptur af chordae tendineae.

The etiology of acute severe mitral incompetence resulting from rupture of the chordae is presented and is illustrated by four case reports. The condition was incorrectly diagnosed and treated primarily as pneumonia or obstructive pulmonary disease. The correct diagnosis was established primarily by echocardiography. Treatment was surgical with implantation of a mitral valvular prosthesis. In three out of four patients, myxomatously degenerated tissue and balooning of the edges of the cups, compatible with the diagnosis of the mitral prolapse syndrome were found. The pathogenesis appears to be primarily dysplasia of the chordae with a component of mechanical wear and tear with physical exertion as the factor precipitating the rupture. The diagnosis of severe mitral incompetence resulting from rupture of the chordae should be borne in mind in cases of acutely developing dyspnoea.

[Cannulation of the radial artery. Risks, effective examination methods and monitoring of the circulation in the hand during the procedure]. / Kanylering af a. radialis. Risici, relevante undersøgelsesmetoder og monitorering af håndens kredsløb i forbindelse med proceduren.

Cannulization of the radial artery with the object of continuous measurement of the blood pressure or repeated analyses of the arterial blood gases is an easy and relatively safe procedure. Thrombosis is observed in 25-40% of the cases. The frequency depends upon the condition of the patient, the cannula and technique of cannulization and duration of this. Permanent ischaemic damage resulting from thrombosis is, however, rare. Other complications of clinical significance are infections and vascular lesions which are, similarly, rare. Allen's test for assessing the collateral circulation of the hand has a high negative predictive value while the positive predictive value is so low that a positive test result does not exclude cannulization. In these cases, better assessment of the perfusion of the hand may be obtained by combining the test with pletysmography. After cannulization, it should be possible to monitor perfusion distal to the site of cannulization employing more recent pulse oximeters with the aid of the pletysmographic curve.

Rectal induction of anaesthesia in children. A comparison between ketamine-midazolam and halothane for induction and maintenance of anaesthesia.

Thirty children were randomly allocated to one of three anaesthetic techniques. Rectal anaesthesia induction with a mixture of ketamine 10 mg.kg-1 BW and midazolam 0.2 mg.kg-1 BW and maintenance of anaesthesia with either intravenous ketamine or halothane were compared to induction and maintenance with halothane. Rectal induction was found reliable and useful. The frequency of side effects, the recovery time, and the time until the child could be discharged were similar in the groups maintained with halothane, whereas recovery was prolonged when intravenous ketamine was used for maintenance.