High Frequency Doppler Research Articles

Perioperative Detection of Cerebral Fat Emboli From Bone Using High-Frequency Doppler Ultrasound

ObjectiveFat embolism syndrome and cerebral fat emboli are rare yet serious conditions arising from systemic distribution of bone marrow emboli. Emboli are known to produce high-intensity transient signals (HITS) in a Doppler signal. We hypothesized that both intramedullary nailing in pigs and median sternotomy in human infants cause bone marrow release, that some of these cause cerebral emboli, and that these were detectable by a new cerebral doppler ultrasound monitoring system (NeoDoppler). We also aimed to describe the intensity of HITS generated during these procedures. MethodsSpecific pathogen-free Norwegian landrace pigs were allocated to either bilateral femoral nailing or injection of autologous bone marrow (positive controls). Testing was carried out under continuous Doppler monitoring. Presence of cerebral emboli was confirmed with histology. NeoDoppler data from infants undergoing sternotomy prior to cardiac surgery were investigated for comparison. ResultsEleven of twelve pigs were monitored with cerebral Doppler ultrasound during femoral surgery. HITS were seen in five (45%). Brain biopsies demonstrated bone marrow emboli in 11 of the 12 (92%). Four positive control pigs received intraarterial injections of bone marrow, saline, or contrast, and strong HITS were detected in all pigs (100%). Median sternotomy in eight human infants was associated with a significant increase in embolic burden; the HITS intensity was lower than HITS in pigs. ConclusionHigh-frequency cerebral Doppler ultrasound is a valuable tool for perioperative monitoring that can detect emboli in real-time, but sensitivity and specificity for bone marrow emboli may be limited and size-dependent.

Ionospheric signatures from 2 years continuous monitoring of the equatorial ionosphere over Nigeria with HF Doppler sounder

A receiver that measures and logs Doppler shifts of high frequency (HF) radio signals reflected from the ionosphere was installed in Lagos (geographic: 6.48°N, 3.27°E; dip latitude −4.66°), Nigeria in March 2011. However, continuous monitoring of the ionosphere was facilitated by the installation of a transmitter in Abuja (geographic: 8.99°N, 7.39°E; dip latitude 1.01°), Nigeria in July 2019, dedicated to transmitting HF signals for this remote sensing system. This provided the opportunity to study ionospheric signatures in HF Doppler data obtained from an equatorial location. This paper presents a summary of key findings from analysis of data from the instrument during the first 28 months of operation from July 2019 to November 2021. In this work, a statistical analysis of two main daytime features in the Doppler data is presented. The first feature is irregularities that appear as spreading of the Doppler trace, while the second feature is wave structures consistent with travelling ionospheric disturbances (TIDs). In order to highlight trends in the data, the events were separated into morning (occurring from sunrise to 1159 LT) and afternoon (occurring from 1200 LT to sunset) events. The results showed that occurrences of either type of features were more frequent during the afternoon compared with morning hours. The occurrences of irregularities that appeared as a spread in the Doppler trace peaked in the month of July in the morning, while, in the afternoon these occurrences peaked in the month of March. The duration of most of these irregularities was ≥60 min. A peak in occurrences of TIDs was observed in the morning and afternoon epochs during the March equinox. It was also observed that over 80 % of occurrences of spreading in the Doppler trace during the equinoxes were associated with the occurrences of TIDs. In the month of July, despite a paucity of TIDs, there was a peak in occurrences of spreading in the Doppler trace. Overall, the lowest number of occurrences of both types of features was recorded in the month of August. Detailed analysis of selected events showed that the morning occurrences of spreading in the Doppler trace were mostly remnants of post-midnight spread F, while the afternoon occurrences were due to either TIDs or severe E-layer irregularities. The results from this study show the potential of the low-cost HF Doppler instrument as a real-time monitor of space weather activity at equatorial latitudes. However, further work will be required to establish what percentage of daytime spreading in the F-layer is caused by the remnants of nocturnal plasma bubbles, TIDs, or irregularities in the E-layer.

Simultaneous observations of equatorial plasma bubbles with an all-sky airglow imager and a HF Doppler sounding system in Taiwan

High-Frequency Doppler (HFD) sounders at low-latitudes often detect characteristic oblique spreading Doppler traces in the spectrogram, known as Oblique Spread Structure (OSS). OSS has been expected to be generated by the dispersion of radio wave reflection due to equatorial plasma bubbles (EPBs). However, it has not yet been confirmed whether OSS is surely a manifestation of EPB by conducting simultaneous observations of EPB and OSS with different observational techniques. Additionally, it remains unclear what kinds of properties of EPB are reflected in the fine structure of OSS. In this study, we investigated three cases of OSSs and EPBs simultaneously observed by a HFD sounding system and an all-sky airglow imager in Taiwan. For the three cases presented here, the timing of OSS occurrence in the HFD data well coincided with that of the EPB appearance in the airglow data. The frequency shift of OSS is quantitatively explained assuming a radio wave reflection at 250–300 km altitudes. These results strongly indicate that OSS is formed by electron density variations at F-region altitudes accompanying EPB; thus, OSS is a manifestation of EPB in the HFD observations. Furthermore, it was suggested that the fine structure of OSS reflected the branching structure of EPB when the multiple branches of EPB reached the intermediate reflection point of the HFD observation. The detection of EPB occurrence and its fine structure using HFD observation enables monitoring of EPB regardless of weather conditions, which will contribute to monitoring the space weather impact of EPBs, for example, on GNSS navigation, in a wide area.Graphical

The CNES Solutions for Improving the Positioning Accuracy with Post-Processed Phase Biases, a Snapshot Mode, and High-Frequency Doppler Measurements Embedded in Recent Advances of the PPP-WIZARD Demonstrator

For many years, the navigation team at the French Space Agency (CNES) has been developing its Precise Point Positioning project. The goal was initially to promote a technique called undifferenced ambiguity resolution. One of the main characteristics of this technique is the capability for a user receiver to perform centimeter-level accuracy in real time. To do so, a demonstrator has been built. Its architecture is composed of three main elements: a correction processing software called the server part, a means to transmit the corrections using standardized messages, and a user software capable of handling the corrections to compute an accurate positioning at the user level. In this paper, we present the recent advances in the CNES precise point positioning demonstrator. They are composed of some evolution of the network of stations and server software, the implementation of the new state space representation standard, a new method for instantaneous ambiguity resolution using uncombined four-frequency signals, its implementation in real-time at the server and the user level, and the use of high-rate Doppler measurements to improve the accuracy of the solution in harsh urban environments. On top of that, the computation of high-accuracy post-processed phase biases with the majority of current GNSS signals supported, compatible with the uncombined method and a new online positioning service to demonstrate the capacity of the user software, is demonstrated.

Assessment of High Frequency Imaging and Doppler System for the Measurements of the Radial Artery Flow-Mediated Dilation

Objectives: In the article we describe the new, high frequency, 20 MHz scanning/Doppler probe designed to measure the flow mediated dilation (FMD) and shear rate (SR) close to the radial artery wall. Methods: We compare two US scanning systems, standard vascular modality working below 12 MHz and high frequency 20 MHz system designed for FMD and SR measurements. Axial resolutions of both systems were compared by imaging of two closely spaced food plastic foils immersed in water and by measuring systolic/diastolic diameter changes in the radial artery. The sensitivities of Doppler modalities were also determined. The diagnostic potential of a high frequency system in measurements of FMD and SR was studied in vivo, in two groups of subjects, 12 healthy volunteers and 14 patients with stable coronary artery disease (CAD). Results: Over three times better axial resolution was demonstrated for a high frequency system. Also, the sensitivity of the external single transducer 20 MHz pulse Doppler proved to be over 20 dB better (in terms of a signal-to-noise ratio) than the pulse Doppler incorporated into the linear array. Statistically significant differences in FMD and FMD/SR values for healthy volunteers and CAD patients were confirmed, p-values < 0:05. The areas under Receiver Operating Characteristic (ROC) curves for FMD and FMD/SR for the prediction CAD had the values of 0.99 and 0.97, respectively. Conclusions: These results justify the usefulness of the designed high-frequency scanning system to determine the FMD and SR in the radial artery as predictors of coronary arterial disease.

Software-defined radio-based HF doppler receiving system

High-frequency Doppler (HFD) sounding is one of the major remote sensing techniques used for monitoring the ionosphere. Conventional systems for HFDs mainly utilize analog circuits. However, existing analog systems have become difficult to maintain as the number of people capable of working with analog circuits has declined. To solve this problem, we developed an alternate HFD receiver system based on digital signal processing. The software-defined radio (SDR) technique enables the receiver to be set up without the knowledge of analog circuit devices. This approach also downsizes the system and reduces costs. A highly stabilized radio system for both the transmitter and receiver is necessary for stable long-term observations of various phenomena in the ionosphere. The global positioning system disciplined oscillator with an accuracy of {10}^{-11} compensates for the frequency stability required by the new receiving system. In the new system, four frequencies are received and signal-processed simultaneously. The dynamic range of the new system is wider (> 130 dB) than that of the conventional system used in HFD observations conducted by the University of Electro-Communications in Japan. The signal-to-noise ratio significantly improved by 20 dB. The new digital system enables radio waves to be received with much smaller amplitudes at four different frequencies. The new digital receivers have been installed at some of the stations in the HFD observation network in Japan and have already captured various ionospheric phenomena, including medium-scale traveling ionospheric disturbances and sudden commencement induced electric field fluctuations, which indicates the feasibility of SDR for actual ionospheric observations. The new digital receiver is simple, inexpensive, and small in size, which makes it easy to deploy new receiving stations in Japan and elsewhere. These advantages of the new system will help drive the construction of a wide HFD observation network.Graphical

Estimating Coastal Winds by Assimilating High-Frequency Radar Spectrum Data in SWAN.

Many activities require accurate wind and wave forecasts in the coastal ocean. The assimilation of fixed buoy observations into spectral wave models such as SWAN (Simulating Waves Nearshore) can provide improved estimates of wave forecasts fields. High-frequency (HF) radar observations provide a spatially expansive dataset in the coastal ocean for assimilation into wave models. A forward model for the HF Doppler spectrum based on first- and second-order Bragg scattering was developed to assimilate the HF radar wave observations into SWAN. This model uses the spatially varying wave spectra computed using the SWAN model, forecast currents from the Navy Coastal Ocean Model (NCOM), and system parameters from the HF radar sites to predict time-varying range-Doppler maps. Using an adjoint of the HF radar model, the error between these predictions and the corresponding HF Doppler spectrum observations can be translated into effective wave-spectrum errors for assimilation in the SWAN model for use in correcting the wind forcing in SWAN. The initial testing and validation of this system have been conducted using data from ten HF radar sites along the Southern California Bight during the CASPER-West experiment in October 2017. The improved winds compare positively to independent observation data, demonstrating that this algorithm can be utilized to fill an observational gap in the coastal ocean for winds and waves.

Multi‐Position Facility for HF Doppler Sounding of Ionospheric Inhomogeneities in Ukraine

AbstractThis paper describes a system for multi‐position Doppler ionosphere sounding implemented at the beginning of 2018 in the Kharkiv region of Ukraine, the data processing technique and initial results of data analysis. The system comprises a high frequency (HF) transmitter and three receiving sites making almost a right triangle with catheti of 32.8 and 58 km. The transmitter continuously emitting a monochromatic signal of a ∼20 W power at a frequency in most cases slightly lower than foF2 is located in the city of Kharkiv. The foF2 value was permanently controlled by the ionosonde installed in about 45 km from the transmitter. We report and discuss the initial results of traveling ionospheric disturbances (TIDs) observations for three years since January 2018 until December 2020. Statistical distributions of the frequency of appearance, periods, horizontal speeds, and propagation directions of TIDs are presented. The range of their most probable wavelengths is from 120 to 260 km, while their propagation velocities are from 80 to 220 m/s. The preferred direction of the TID propagation changes during the daytime and shows a tendency to rotate clockwise in azimuth. Notably, such regular long‐term measurements in the Eastern Europe have been carried out for the first time.

History of the Super Dual Auroral Radar Network (SuperDARN)-I: pre-SuperDARN developments in high frequency radar technology for ionospheric research and selected scientific results

Abstract. Part I of this history describes the motivations for developing radars in the high frequency (HF) band to study plasma density irregularities in the F region of the auroral zone and polar cap ionospheres. French and Swedish scientists were the first to use HF frequencies to study the Doppler velocities of HF radar backscatter from F-region plasma density irregularities over northern Sweden. These observations encouraged the author of this paper to pursue similar measurements over northeastern Alaska, and this eventually led to the construction of a large HF-phased-array radar at Goose Bay, Labrador, Canada. This radar utilized frequencies from 8–20 MHz and could be electronically steered over 16 beam directions, covering a 52∘ azimuth sector. Subsequently, similar radars were constructed at Schefferville, Quebec, and Halley Station, Antarctica. Observations with these radars showed that F-region backscatter often exhibited Doppler velocities that were significantly above and below the ion-acoustic velocity. This distinguished HF Doppler measurements from prior measurements of E-region irregularities that were obtained with radars operating at very high frequency (VHF) and ultra-high frequency (UHF). Results obtained with these early HF radars are also presented. They include comparisons of Doppler velocities observed with HF radars and incoherent scatter radars, comparisons of plasma convection patterns observed simultaneously in conjugate hemispheres, and the response of these patterns to changes in the interplanetary magnetic field, transient velocity enhancements in the dayside cusp, preferred frequencies for geomagnetic pulsations, and observations of medium-scale atmospheric gravity waves with HF radars.

Development of remote HF wave receiver in the backlobe direction of the SuperDARN Hokkaido East radar: Initial observations

We have been operating remote high frequency (HF) wave receivers for the SuperDARN Hokkaido East radar in Nagoya (1092 km away from the radar) and Rikubetsu (a few tens of m away from the radar antenna) since 2014 to monitor the ionospheric environment and its changes. One receiver set consists of a USRP-N210 receiver unit, Ubuntu Linux PC and dipole/loop antenna. Using the remote receiver data it is possible to monitor the upward/downward motion of the ionosphere at the ionospheric reflection point of the HF radar backlobe beams emitted toward the Nagoya area. The usage of the SuperDARN (backlobe) beams has the following advantages over other instruments such as HF Doppler systems: (1) SuperDARN Backlobe beams also have high directivity, so that it is possible to observe strong echoes at the remote area more than 1000 km away from the radar. (2) Since the SuperDARN radars emit pulse waves instead of continuous waves, it is possible to identify the travel time from the radar to the receiver. The initial results of the observation of ionospheric perturbations using the remote HF wave receiver of the SuperDARN Hokkaido East radar are described.

Observations of long period HF Doppler oscillations over the dip equatorial ionosphere in the Indian longitudinal sector

Background/ Objective: The signatures of long period High Frequency Doppler (HFD) oscillations over a dip equatorial station, Trivandrum (8.33◦N, 77◦E, dip 0.4◦N) in the Indian longitudinal sector have been investigated. Methods: High cadence vertical plasma drift measurements obtained using a Multi frequency HF Doppler Radar over Trivandrum along with ground based magnetometer observations over several latitudes/longitudes have been used to address this very aspect. Findings: It has been observed that long period (~15 min.) oscillations of high latitude origin can instantaneously reflect over the equatorial latitudes in the form of coherent HFD oscillations. The study is very important as it provided a unique opportunity not only to understand various characteristics of HFD oscillations, but also expected to have significant implications in the understanding of equatorial ionospheric variability in context of solar wind-magnetosphere-ionosphere coupling. Novelty: In a complementary point of view, the study also highlights the potential of HF Doppler measurements to capture such transient events originating from interplanetary medium with an unprecedented temporal resolution. Keywords: HF Doppler radar; equatorial ionosphere; HF Doppler oscillations

Barotropic and baroclinic tides in Panay Strait, Philippines

The Panay Strait constitutes a bathymetrically complex system with intense tidal currents. The four major tidal constituents in the total energy spectra inferred from sea level and current profiles are K1, O1, M2, and S2. Spatially, O1 and M2 dominate over K1 and S2, respectively. The diurnal tide accounts for highest amplitude variability over the shallow shelf while semi-diurnal tides over the deeper channel of the strait. Rotary spectra of surface currents shows inertial frequency peaks and exhibit an unusually broad peak in both the clockwise (CW) and counterclockwise (CCW) rotating components, indicating frequency shift by the vorticity of sub-inertial currents prevalent in the region. Vertically, variance of the horizontal velocity explained by the major tidal constituents peaks in two distinct depth bands; the upper layer centered at 110 m (11% variance) dominated by semi-diurnal tide (M2) and the lower layer at 470 m (26% variance) dominated by diurnal tides (O1). Semi-diurnal tidal current ellipses (M2 and S2) exhibit a dominance of CW motions at near-surface depth (110 m), indicative of downward energy propagation and implying a surface energy source. These features from Acoustic Doppler Current Profiler (ADCP) deployed close to the sill is consistent with the dominant semi-diurnal tide (M2) over the channel of the strait from the High Frequency Doppler Radar (HFDR). Comparison of incoherent to coherent tidal energy shows K1 dominated the incoherent tidal band. Spatially, incoherent energy is dominant over the channel particularly near the sill and the constricted part of the strait. The incoherent portion of the tide is presumably attributable to the surface expression of the internal tide which seems to be generated near the sill and then topographically steered west over the edge of the shallow shelf where incoherent energy is dominant.

Comparative Usefulness of High-frequency Doppler Ultrasonography, Serum PSA Density, and Free to Total Serum PSA Ratio in the Prediction of Prostate Cancer

Comparative Usefulness of High-frequency Doppler Ultrasonography, Serum PSA Density, and Free to Total Serum PSA Ratio in the Prediction of Prostate Cancer

Real-time Measurement of Projectile Velocity in a Ballistic Fabric with a High-frequency Doppler Radar

Because of technical limitations, most experimental studies on the energy-absorbing properties of ballistic fabrics are limited to discrete evaluations based on impact and residual velocities. Consequently, the continuous interaction between a projectile and a target material is still commonly assessed with analytical models or numerical simulations, the validation of which is based on the aforementioned discrete values. The present document aims at describing and validating a new experimental method to make it possible to evaluate the continuous evolution of the projectile velocity during penetration into a fabric material. The method is based on the Doppler effect and a specific and complex nonstationary signal treatment. A high-frequency continuous-wave Doppler radar was adapted to assess the continuous evolution of the velocity of a projectile penetrating a fabric material. Based on two ballistic-grade fabric configurations, a perforating and a nonperforating case were described and evaluated. The instantaneous Doppler frequency was extracted based on the Hilbert-Huang transform. A validation of the proposed method was performed based on high-speed camera images, giving the displacement of the apex of the deformation pyramid of the fabric with time. Additionally, a Weibel® Doppler radar was used to measure the impact velocity. Based on instantaneous frequencies deduced from the high-frequency radar signal analysis, Doppler theory and high-speed camera images, velocity–time and displacement–time plots were obtained. Additionally, the evolution of the fabric deformation (pyramid morphology) was recorded from the high-speed camera images. Comparisons between the data assessed with the high-frequency Doppler radar and those deduced from the high-speed camera indicated that good agreement exists between the two methods. The new Doppler radar method seems to be a promising complementary tool for measuring the continuous interaction between a projectile and a fabric target material.

Evaluation of EAR Spaced Antenna Performance Using Multiple Receiving Antennas Orientations

AbstractEquatorial Atmosphere Radar (EAR) is a very high frequency (VHF) Doppler radar with an active phased array antenna system operating at 47 MHz. It had originally been equipped with a single receiving channel system since its establishment in 2001 at the equator in Kototabang, West Sumatra, Indonesia (0.20°S, 100.32°E). Recent progress has enabled the implementation of a spaced antenna (SA) method on the EAR through the development of a multichannel receiver using Universal Software Radio Peripheral (USRP) and GNU Radio. However, this approach exhibits limited height observation and horizontal wind estimation accuracy. Here, we present comparison and analysis of EAR SA performance with five different orientations, taking into consideration the size of the receiving antennas and their separation distance. Experiments with the chosen configurations were carried out between April and September 2019, and the horizontal wind profiles were estimated using full correlation analysis (FCA) and compared with the EAR standard data. In addition, FCA with the least squares method is carried out for all configurations with the aim of improving the estimation accuracy. Based on the results, the configuration with the largest aperture shows a clear advantage over the other four configurations but with limited improvement in terms of maximum observable height.

Determination of the Level of Hypocoagulation to Change the Parameters of Microcirculation in the Treatment of Deep Vein Thrombosis

Introduction - Venous thromboembolic complications are recognized as one of the main causes of death. The leading place in diagnosis of deep vein thrombosis (DVT) belongs to the colored ultrasound duplex screening (CDS). However there is no information in the periodical literature on the possibilities of the study of microcirculation (MC) at the height of DVT treatment with anticoagulants (AC), which could early recognize unsufficient level of hypocoagulation. Despite the widespread introduction of oral AC into clinical practice, the choice of clinicians is not always associated with their priority appointment, due to the risk of bleeding in special groups of patients, especially patients with reduced glomerular filtration rate. Timely determine the choice of AK and dosage, reliably providing a sufficient level of hypocoagulation is very important. Methods - There were examined in 98 patients with DVT of the lower limbs, confirmed by CDS, including 35 men and 63 women ranging in age 31 -89 and median age 65 years. In all patients, the thrombus was tightly fixed to the wall, had no signs of flotation. In the primary treatment has produced CDS with the determination of the level of occlusion. Parameters of MC were measured using high–frequency Doppler ultrasound "minimax-Doppler K" in the nail bed of the 1st finger of the upper limb by 15MHz ultrasound transducer. Analysis of dopplerograms was performed according to the shape and spectrum of curves. Control examination was performed after the appointment of AK therapy in 2, 4, 8 weeks. I group - 69 patients were prescribed rivaroxaban 15 mg twice a day for 3 weeks and then 20 mg a day, and II group - 29 patients with reduced glomerular filtration rate (lower than 50ml/min) recived rivaroxaban 20 mg for 3 weeks, followed by a transition to 15 mg a day. The obtained data were compared with the results of CDS – and percent of recanalizaton in dynamics. Results - In the evaluation of recanalization of thrombus in the I group in 1 month revealed an average of 64 % , in the II group an average of 50%, and 2 months from the start of treatment in the I group 78%, and in the second 56%. There is a tendency to a direct correlation of MC parameters and recanalization of the thrombus according to the CDS, due to the insufficient level of hypocoagulation with reduced dosage of rivaroxaban, which particularly affected the results of controlled after 2 months treatments. Conclusion - MC indicators correlate well with CDR data. The reduced dosage of rivaroxabane no soo effective as a full dose. Monitoring of the state of MC in patients with outpatient care allows during suspected insufficient level of hypocoagulation, which may be useful for further tactics of conducting these patients.

Development of Software‐Defined Multichannel Receiver for EAR

AbstractThe Equatorial Atmosphere Radar (EAR) is a very high frequency Doppler radar operated with an active phased‐array antenna system at 47 MHz. It is located at the equator in Kototabang, West Sumatra, Indonesia (0.20°S, 100.32°E) and was established with a single receiving channel. Here, we present the development of a multichannel receiver system for EAR using a combination of the Universal Software Radio Peripheral X300 (USRP X300) series and GNU Radio software. Two USRP X300 devices, corresponding to four receiving channels, were synchronized using 10‐MHz reference clocks and a one‐pulse per second signal. Received signals were collected by the existing EAR antennas, fed to the USRPs for digital conversion, and then stored on a hard disk drive. Signal postprocessing was carried out to estimate wind velocity profiles. Wind profiles estimated using full correlation analysis indicate that the spaced antenna method from multichannel receivers agrees well with EAR standard observational data.

Surface waves magnitude estimation from ionospheric signature of Rayleigh waves measured by Doppler sounder and OTH radar

Surface waves emitted after large earthquakes are known to induce atmospheric infrasonic waves detectable at ionospheric heights using a variety of techniques, such as high frequency (HF) Doppler, global positioning system (GPS), and recently over-the-horizon (OTH) radar. The HF Doppler and OTH radar are particularly sensitive to the ionospheric signature of Rayleigh waves and are used here to show ionospheric perturbations consistent with the propagation of Rayleigh waves related to 28 and 10 events, with a magnitude larger than 6.2, detected by HF Doppler and OTH radar respectively. A transfer function is introduced to convert the ionospheric measurement into the correspondent ground displacement in order to compare it with classic seismometers. The ground vertical displacement, measured at the ground by seismometers, and measured at the ionospheric altitude by HF Doppler and OTH radar, is used here to compute surface wave magnitude. The ionospheric surface wave magnitude (Msiono) proposed here introduces a new way to characterize earthquakes observing the signature of surface Rayleigh waves in the ionosphere. This work proves that ionospheric observations are useful seismological data to better cover the Earth and to explore the seismology of the Solar system bodies observing the ionosphere of other planets.

Observation and analysis of electrical structure change and diversity in thunderstorms on the Qinghai-Tibet Plateau

A comprehensive observation on thunderstorms was conducted in the Qinghai area by using a very high frequency three-dimensional lightning mapping system and Doppler radar. The spatio-temporal evolution of the charge structure of the isolated thunderstorm was analyzed according to the developing process of thunderstorm, and the reasons for the change in charge structure diversity were studied. During the initial developing and mature stages of the thunderstorm, the charge structure was a steady negative dipole polarity, i.e., the negative charge region was above the positive charge region. Furthermore, the total number of flashes was lower during these two stages. During the thunderstorm's dissipation stage, the charge structure was varied and complicated, with a positive dipole, negative dipole, and a tripole charge structure changing and coexisting during this stage. This charge structure diversity was primarily caused by the collision and merging of two local thunderstorm cells, leading to a charge rearrangement and distribution and the formation of a new charge structure. The frequency of the negative cloud-to-ground and intracloud flashes increased sharply in the dissipation stage, reaching a maximum value. The increase in frequency of negative cloud-to-ground was mainly caused by the lower positive charge weakening during the dissipation stage. In addition, the relationship between charging regions and temperature layers was analyzed by combining sounding temperature data with the theory of a non-inductive charging mechanism.

English

INTRODUCTION: In community, population older than fifty years of age, about 50% develop thyroid nodules. Among them 5% of these nodules are malignant, But it does not eliminate the need to screen benign nodules and differentiate it from malignant nodules. Ultrasonography of neck in general population detects 15 to 90%, having Thyroid nodules. Thyroid scan-B mode shows characters like dimension, contour, echogenicity, presence and type of peripheral halo. It also demonstrates the number of nodules. But, usual B mode USG cannot differentiate benign nodules from malignant nodules. In evaluation of thyroid swelling, FNAC plays a vital role. But, FNAC is not always diagnostic (eg. suspicious findings, insufficient materials, false positive or non diagnostic results). This can occur up to about 28% of samples. Moreover FNAC cannot differentiate follicular adenoma from follicular carcinoma. These limitations can be bridged by using high frequency Doppler scan that can detect blood flow in thyroid gland and other superficial tissues. It is based on the simple principle that increase in vascularity is associated with increased proliferation of cells. Doppler USG provides information about nodule vascularisation and is useful in identification of at risk nodules for malignancy by analyzing various parameters like resistance index, pulsatility index and filling patterns. AIM OF THE STUDY: 1. To Evaluate that Doppler USG is useful in diagnosing thyroid nodules at risk for malignancy, more importantly in differentiating benign follicular neoplasm from malignant follicular neoplasm. 2. It aids in management of patients with solitary nodule of thyroid with high risk for malignancy that they may directly undergo total thyroidectomy rather than going for hemithyroidectomy and later for second stage completion thyroidectomy. MATERIALS AND METHODS: In my study One hundred seventy seven patients with solitary thyroid nodule were analysed, sex distribution found to be 171 women & 6 men at our hospital. Age distribution found to be 15 to 75 years (mean 42 years). Once the presence of thyroid nodules were confirmed clinically, FNAC was done. These people were subjected to ultrasound neck along with Doppler imaging, We included only the nodules for which representative cytological material was available in FNAC. Ethical committee clearance was obtained and patients were enrolled for study after getting informed consent. All Doppler scans were performed with Siemens accuson, high frequency variable linear transducer, frequency used is 10 MHz (7.5MHz to 10MHz). Microscopic study of the FNAC specimens demonstrated that 119 of the 177 nodules were benign, 29 had indeterminate cytology (follicular cells/neoplasm) and 29 were malignant. In 29 patients with follicular cytology, 27 were proceeded with surgery and post op biopsy revealed 19 patients with benign disease and 8 patients with malignant disease. In this group of patients preoperative Doppler studies were correlated with post operative biopsy. In other patients Doppler studies were compared with FNAC CONCLUSION: USG evaluation of thyroid nodules by using power doppler can effectively differentiate nodules with high risk for malignancy from benign nodules. Power Doppler and RI have a high sensitivity and specificity in detecting malignancy. Patients showing follicular cells in FNAC can reliably be differentiated in to benign and malignant groups using Doppler sonogram, which can bridge the limitation of FNAC which cannot identify malignant follicular neoplasm