High-resolution Doppler Imaging Research Articles

TOBE-Costas arrays for fast high-resolution 3D power Doppler imaging.

2D sparse arrays and row-column arrays are both alternatives to 2D fully-addressed arrays with lower channel counts. Row-column arrays have recently demonstrated fast 3D structural and flow imaging but commonly suffer from high grating lobes or require multiplexing to achieve better quality. 2D sparse arrays enable full-volume acquisitions for each to transmit event, but plane-wave transmissions with them usually lack quality in terms of uniformity of wavefronts. Here, we propose a novel architecture that combines both types of these arrays in one aperture, enabling imaging using row-column or sparse arrays alone or a hybrid imaging scheme where the row-column array is used in transmission and a 2D sparse array in reception. This hybrid imaging scheme can potentially solve the shortcomings of each of these approaches. The sparse array layout chosen is a Costas array, characterized by having only one element per row and column, facilitating its integration with row-column (TOBE) arrays. We simulate images acquired with TOBE-Costas arrays using the hybrid imaging scheme and compare them to row-column and sparse spiral arrays of equivalent aperture size (128λ×128λ at 7.5 MHz) in ultrafast plane-wave imaging of point targets and 3D power Doppler imaging of synthetic flow phantoms. Our simulation results show that TOBE-Costas arrays exhibit superior resolution and lower side lobe levels compared to plane-wave compounding with row-column arrays. Compared to density-tapered spiral arrays, they provide a larger field of view and finer resolution.

Comparing Non-Stress Test versus Umbilical Artery Doppler Velocimetry among Aample of High-risk Pregnant Women in Erbil City

Background: The mainstay of care for lowering maternal and perinatal mortality and morbidity is antepartum foetal surveillance. Numerous techniques are used, including fetal movements, Vibroacoustic stimulation tests, contraction stress tests, biophysical profiles of the fetus, modified biophysical profiles, non-stress testing and Doppler Umbilical artery of the fetus's. The fetal heart reaction to internal and extrinsic stimuli is seen on electronic fetal monitoring devices. The benefit of high resolution dynamic ultrasonography and Doppler imaging is that it allows for the visualization of the fetus and its surroundings as well as the monitoring of fetal health by measuring utero-placental circulation. Patients and techniques: The cross-sectional investigation including 120 pregnant women who visited the Maternity Teaching Hospital between 26 June and 31 August 2022 and complained of decreased uterine contractions have been included. The questionnaire included sociodemographic data, obstetrical data, information on the fetal outcome and method of delivery. In accordance with the American Academy of Obstetricians and Gynecologists, cardiotopography was utilized to conduct a non-stress test, and the outcomes were categorized as reactive and non-reactive. Cardiotopography was used to perform a non-stress test, and the results were classified as reactive or non-reactive in accordance with the American Academy of Obstetricians and Gynecologists. Also, during 32 weeks or more of gestation, the inferior vena cava was not compressed by the gravid uterus during ultrasonography of the umbilical arteries, which was performed in a semi-recumbent position with a slight lateral tilt. Result: Based on NST and Doppler velocimetry of the umbilical artery, all cases were classified into two groups. The outcomes of the two tests didn't significantly differ from one another. The rate of Cesarean section (CS) was 46.1% among women with non-reactive (abnormal) CTG, compared with 25% among women with normal CTG (p = 0.0316). Only one neonate (1.3%) died among women with normal CTG, while none of the neonates died among women with abnormal CTG. The rate of CS among women with abnormal ultrasonography was 80% compared to women (11%) with normal ultrasonography. Furthermore, one neonate (2.1%) in the group of abnormal doppler, compared with 0% in the normal group. Conclusion: NST and umbilical artery Doppler of are sensitive and specific tests with strong positive prognostic value to suggest a poor prognosis for the newborn. Doppler velocimetry of umbilical artery is more important than a non-stress test because it lowers the likelihood of a CS birth in non-reactive non-stress test situations without increasing the risk of perinatal morbidity and mortality. Bangladesh Journal of Medical Science Vol.22 (Special Issue) 2023 p.10-17

Repeatability of high-resolution laser Doppler images of the hands in patients with systemic sclerosis and secondary Raynaud's phenomenon.

The objective of the study was to establish the repeatability of baseline diagnostic images of the dorsum of the hands acquired using a high-resolution laser Doppler imager in patients with Raynaud's phenomenon secondary to systemic sclerosis (SSc). The dorsal side of the hands of 22 patients (8 male 14 female), age range 29-73, median 62, with SSc and secondary Raynaud's phenomenon were imaged over two consecutive days at approximately the same time using a Moor Instruments' high-resolution laser Doppler imaging unit. The images were analysed by taking regions of interest at discrete locations in the images to calculate dimensionless values of flux (PU). Repeatability of the diagnostic investigation was assessed using methods described by Bland and Altman and by also plotting the results from visit 1 against visit 2 and calculating the line of best fit. Based on the criteria that 95% of all measurement differences should be within a factor of 1.96 of the standard deviations of the mean values, then high-resolution laser Doppler imaging technique is probably repeatable when acquiring and analysing baseline images of patients with Raynaud's phenomenon secondary to SSc. However, a larger study with more patients is required to prove this conclusively-as only data from 19 patients were analysed (3 patients were not included due to technical issues)-and was therefore susceptible to marked clinical variations in patients presenting on different days for the investigations.

Helium diffusion in magnetic stellar atmospheres of early B-type stars

Context. The treatment of diffusion in stellar atmospheres of chemically peculiar stars is complex and difficult to model and has been treated mainly in A-type and late B-type stars. Vertical stratification is very often fixed from ad hoc chemical distribution profiles obtained by combining high-resolution spectropolarimetric observations and magnetic Doppler imaging techniques. Aims. Our goal is to improve the modelling of diffusion in magnetic B-type stars and reproduce non-homogeneous surface distributions in helium-peculiar stars. Moreover, we aim to predict the photospheric vertical stratification by self-consistently calculating atomic diffusion in the presence of magnetic fields. Methods. We solved the flow equations that describe gravitational settling along with thermal and chemical diffusion in stellar atmospheres under the influence of magnetic fields. We based the atomic diffusion on a previous treatment, which considers a mix of gases with various relative velocities. We took advantage of calculations from the literature on the stellar evolution of white dwarf stars. In this study, we neglected the effect of the radiative acceleration. Results. We described the helium abundance with latitude and depth in hot and intermediate spectral B-type stars considering diffusion processes with and without magnetic fields. We found variations in the number density of atoms between the magnetic pole and the equator that depend on the direction of the Lorentz force. This effect leads to under- or over-abundances in helium, giving the appearance of rings (equator) or spots (pole). However, the chemical profile found does not reproduce the strength of the helium lines. Conclusions. We concluded that the resulting chemical profiles computed with diffusion processes under the approximation of effective atoms describe the behaviour observed in the helium lines in He peculiar stars but it does not explain the observed strength. Other mechanisms in addition to diffusion, such as stellar winds, should be explored in detail.

High Resolution Doppler Imaging for Stepped Multiple Frequency Rader

High Resolution Doppler Imaging for Stepped Multiple Frequency Rader

Role of high-resolution sonography and doppler imaging in detecting nerve damage in leprosy patients

Leprosy is the chronic infectious disease-causing peripheral nerve damage leading to functional impairment of limbs, ulcer formation, and deformities. Pathological findings of leprosy are nerve enlargement and inflammation, with the help of high-resolution sonography and color Doppler (CD) imaging to demonstrate nerve enlargement and inflammation. Aims: To assess the role of high-resolution sonography in detecting nerve damage in leprosy patients. Methods and Materials: The study group of 30 cases of leprosy performed on e Soate My lab 40 and evaluated bilateral US of the ulnar (UN), lateral popliteal (LP), and posterior tibial (PT) nerves compared this with the sonographic findings in 30 healthy controls. Results and Conclusions: The nerves were significantly thicker in the leprosy patients as compared with healthy controls (P

Spectroscopic transit search: a self-calibrating method for detecting planets around bright stars

Aims. We aim to search for transiting exoplanets around the star β Pictoris using high-resolution spectroscopy and Doppler imaging that removes the need for standard star observations. These data were obtained on the VLT with UVES during the course of an observing campaign throughout 2017 that monitored the Hill sphere transit of the exoplanet β Pictoris b. Methods. We utilized line profile tomography as a method for the discovery of transiting exoplanets. By measuring the exoplanet distortion of the stellar line profile, we removed the need for reference star measurements. We demonstrated the method with white noise simulations, and then looked at the case of β Pictoris, which is a δ Scuti pulsator. We describe a method to remove the stellar pulsations and perform a search for any transiting exoplanets in the resultant data set. We injected fake planet transits with varying orbital periods and planet radii into the spectra and determined the recovery fraction. Results. In the photon noise limited case we can recover planets down to a Neptune radius with an ~80% success rate, using an 8 m telescope with a R ~ 100 000 spectrograph and 20 min of observations per night. The pulsations of β Pictoris limit our sensitivity to Jupiter-sized planets, but a pulsation removal algorithm improves this limit to Saturn-sized planets. We present two planet candidates, but argue that their signals are most likely caused by other phenomena. Conclusions. We have demonstrated a method for searching for transiting exoplanets that (i) does not require ancillary calibration observations, (ii) can work on any star whose rotational broadening can be resolved with a high spectral dispersion spectrograph, and (iii) provides the lowest limits so far on the radii of transiting Jupiter-sized exoplanets around β Pictoris with orbital periods from 15 days to 200 days with >50% coverage.

Angiopoietin/Tie2 Axis Regulates the Age-at-Injury Cerebrovascular Response to Traumatic Brain Injury.

Although age-at-injury influences chronic recovery from traumatic brain injury (TBI), the differential effects of age on early outcome remain understudied. Using a male murine model of moderate contusion injury, we investigated the underlying mechanism(s) regulating the distinct response between juvenile and adult TBI. We demonstrate similar biomechanical and physical properties of naive juvenile and adult brains. However, following controlled cortical impact (CCI), juvenile mice displayed reduced cortical lesion formation, cell death, and behavioral deficits at 4 and 14 d. Analysis of high-resolution laser Doppler imaging showed a similar loss of cerebral blood flow (CBF) in the ipsilateral cortex at 3 and 24 h post-CCI, whereas juvenile mice showed enhanced subsequent restoration at 2-4 d compared with adults. These findings correlated with reduced blood-brain barrier (BBB) disruption and increased perilesional vessel density. To address whether an age-dependent endothelial cell (EC) response affects vessel stability and tissue outcome, we magnetically isolated CD31+ ECs from sham and injured cortices and evaluated mRNA expression. Interestingly, we found increased transcripts for BBB stability-related genes and reduced expression of BBB-disrupting genes in juveniles compared with adults. These differences were concomitant with significant changes in miRNA-21-5p and miR-148a levels. Accompanying these findings was robust GFAP immunoreactivity, which was not resolved by day 35. Importantly, pharmacological inhibition of EC-specific Tie2 signaling abolished the juvenile protective effects. These findings shed new mechanistic light on the divergent effects that age plays on acute TBI outcome that are both spatial and temporal dependent.SIGNIFICANCE STATEMENT Although a clear "window of susceptibility" exists in the developing brain that could deter typical developmental trajectories if exposed to trauma, a number of preclinical models have demonstrated evidence of early recovery in younger patients. Our findings further demonstrate acute neuroprotection and improved restoration of cerebral blood flow in juvenile mice subjected to cortical contusion injury compared with adults. We also demonstrate a novel role for endothelial cell-specific Tie2 signaling in this age-related response, which is known to promote barrier stability, is heightened in the injured juvenile vasculature, and may be exploited for therapeutic interventions across the age spectrum following traumatic brain injury.

Abstract 131: Effect of Fetal Alcohol Exposure on Stroke Severity and Blood Flow in Adult Mice

Background and Purpose: Metabolic and cardiovascular disease in later life may have developmental origins. The present study specifically tested the hypothesis that fetal alcohol exposure (FAE) will persistently influence blood flow in adulthood and result in greater impairment following ischemic stroke. Methods: Timed-pregnant C57Bl/6 female mice (GD12) were intragastrically gavaged with ethanol (3g/kg/bwt) or water twice per day from GD12 through 15. At 3 months of age, FAE and control males and females were subject to high-resolution ultrasound pulsed-wave Doppler imaging to record blood flow in carotid, abdominal, renal and femoral arteries. Blood flow was quantified. Thereafter, mice were subjected to middle cerebral artery occlusion (MCAo) using an intraluminal filament and sacrificed at 24 h post-stroke. Stroke induced brain damage was assessed by behavioral assays (adhesive tape test), neurological score and infarct volume. Results: Blood flow measurements indicated that fetal alcohol exposure increased acceleration in renal lobar arteries of ethanol exposed females (P<0.003), indicating that alcohol exposure may lead to impairment vascular tone and early signs of hypertension in end organs like kidney. In animals subject to MCAo, FAE adults exhibited greater neurological deficits at 24h post-stroke, as determined by their higher scores on a combination of different parameters of motor impairment and behavioral measures (neurologic score) compared to controls (P<0.0004). Sensorimotor deficits assessed by sticky tape test also showed that fetal alcohol exposed animals were severely affected (p<0.05) indicating that developmental alcohol exposure can impair adaptation in adult brain to an acute neural damage. There is also a significant correlation between the neurological scores and infarct volume in FAE females (p<0.05) but not FAE males, suggesting sex differences in response to FAE modify the relationship between stroke and outcomes. Conclusions: Our findings support a hypothesis that fetal alcohol exposure has long lasting and sexually dimorphic effects on adult health, resulting in impaired renal blood flow and poor stroke outcomes.

Combined Persistent Fetal Vasculature: A Classification Based on High-Resolution B-Mode Ultrasound and Color Doppler Imaging

The purpose of this study was to classify combined persistent fetal vasculature (PFV) on the basis of the ultrasonographic and Doppler characteristics. The potential clinical significance for both surgery design and prognosis determination was discussed. A cross-sectional case series. The eyes of 54 children diagnosed with unilateral combined PFV were evaluated using B-mode ultrasound and color Doppler imaging (CDI). Each participant's age at first presentation, diagnosis for referral, gender, family history, and systemic or other ocular anomalies were recorded. Retinal detachment, optic nerve abnormalities, and macular dislocation were also recorded in detail according to the RetCam (Clarity Medical Systems, Pleasanton, CA), ultrasound, and Doppler findings. The PFV eyes were divided into 4 groups on the basis of the ultrasound and CDI findings. Intergroup analysis was performed. Overall and intergroup analyses of the demographic features of the children with PFV were performed. The axial length, depth of the anterior chamber, and lens thickness were compared between the affected eyes and the fellow healthy eyes among the 4 groups. Some 22.2%, 18.5%, 33.3%, and 25.9% of the eyes were grouped into type I ("I" shape), II ("Y" shape), III (inverted "Y" shape), and IV ("X" shape) combined PFV, respectively. The age at first presentation for type I was older than that for the other groups (P= 0.014). The axial length was reduced (P= 0.012) and the anterior chamber more shallow (P= 0.011) than in fellow healthy eyes for type IV eyes, but not for the other 3groups. Ultrasound and CDI are informative screening and diagnostic tools that show characteristic flow patterns in the 4 types of combined PFV. This novel classification system provides new and important information for the diagnosis of PFV and, if validated, may play a role in guiding treatment recommendations in the future.

STARSPOT DISTRIBUTIONS ON FULLY CONVECTIVE M DWARFS: IMPLICATIONS FOR RADIAL VELOCITY PLANET SEARCHES

Since M4.5 - M9 dwarfs exhibit equatorial rotation velocities of order 10 km/s on average, radial velocity surveys targeting this stellar population will likely need to find methods to effectively remove starspot jitter. We present the first high resolution Doppler images of the M4.5 dwarf, GJ 791.2A, and the M9 dwarf, LP 944-20. The time series spectra of both objects reveal numerous line profile distortions over the rotation period of each star which we interpret as starspots. The transient distortions are modelled with spot/photosphere contrast ratios that correspond to model atmosphere temperature differences of Tphot-Tspot = 200 and 300 K. GJ 791.2A is a fully convective star with vsini = 35.1 km/s. Although we find more starspot structure at high latitudes, we reconstruct spots at a range of phases and latitudes with a mean spot filling of ~3%. LP 944-20 is one of the brightest known late-M dwarfs, with spectral type M9V and vsini = 30.8 km/s. Its spectral time series exhibits two dominant transient line distortions that are reconstructed as high latitude spots, while a mean spot filling factor of only 1.5% is found. The occurrence of low-contrast spots at predominantly high latitudes, which we see in both targets here, is in general likely to be responsible for the low amplitude photometric variability seen in late-M dwarfs. For GJ 791.2A, the radial velocities induced by the starspot features yield an rms velocity variability of 138 m/s, which can be reduced by a factor of 1.9 using our reconstructed surface brightness distributions.

High-resolution tissue Doppler imaging of the zebrafish heart during its regeneration.

The human heart cannot regenerate after injury, whereas the adult zebrafish can fully regenerate its heart even after 20% of the ventricle is amputated. Many studies have begun to reveal the cellular and molecular mechanisms underlying this regenerative process, which have exciting implications for human cardiac diseases. However, the dynamic functions of the zebrafish heart during regeneration are not yet understood. This study established a high-resolution echocardiography for tissue Doppler imaging (TDI) of the zebrafish heart to explore the cardiac functions during different regeneration phases. Experiments were performed on AB-line adult zebrafish (n=40) in which 15% of the ventricle was surgically removed. An 80-MHz ultrasound TDI based on color M-mode imaging technology was employed. The cardiac flow velocities and patterns from both the ventricular chamber and myocardium were measured at different regeneration phases relative to the day of amputation. The peak velocities of early diastolic inflow, early diastolic myocardial motion, late diastolic myocardial motion, early diastolic deceleration slope, and heart rate were increased at 3 days after the myocardium amputation, but these parameters gradually returned to close to their baseline values for the normal heart at 7 days after amputation. The peak velocities of late diastolic inflow, ventricular systolic outflow, and systolic myocardial motion did not significantly differ during the heart regeneration.

Multi-wavelength analysis of active regions using ring-diagram technique

With the availability of high-cadence and high-resolution Doppler and intensity images from the Solar Dynamics Observatory's Helioseismic Magnetic Imager (HMI) and Atmospheric Imager Assembly (AIA), we analyze the characteristics of high-degree solar acoustic modes in active regions. We apply the ring-diagram technique to Doppler, continuum intensity measurements from HMI, and intensity images from AIA 1600 Å and 1700 Å passband to examine the high-degree mode parameters and sub-surface horizontal flows.

Abstract 4359: Use of high resolution Doppler imaging for non-invasive, quantitative evaluation of hypoxia-driven neovascularization following surgical ligation of the femoral artery

Abstract A tumor's growth is inextricably linked with its vascularization. Rapidly growing tumors outstrip their blood supply, creating hypoxia. To compensate, tumor cells release angioproliferative factors that stimulate endothelial cell proliferation. Proliferating endothelial cells contribute to the formation of new blood vessels that promote tumor perfusion and stimulate further tumor growth. The close link between tumor growth and neovascularization makes it difficult to study either process in the absence of the other. To address this we have adapted a mouse model used in the study of peripheral arterial disease. Ischemia was induced by surgical ligation and excision a 3-5mm portion of the femoral artery, vein, and all nearby arterial branches in the right hindlimb of 10-12 week old athymic nude mice. Limb perfusion was measured prior to surgery and 1, 7, 14, 21, and 28 days post-surgery. A 7mm portion of hindlimb perfusion was quantified using Power Doppler mode on the VisualSonics Vevo 770 High Resolution micro Ultrasound system. Morphological changes were observed by histology and immunohistochemistry using antibodies against CD31 and F4/80. Based on quantified Doppler ultrasound data, limb perfusion was reduced as much as 80% within 24 hrs of ligation. Blood flow was restored over the course of the next 7 days. However, re-perfused limbs showed a diffuse pattern of blood flow in comparison to control limbs. Loss of perfusion was accompanied by muscle atrophy and the accumulation of intra-fasicular fat deposits. IHC revealed a marked increase of F4/80 and CD31 staining in ligated limbs. Similar changes were not observed in contralateral limbs that were not operated on or in sham-ligated hind limbs. Our data is consistent with the interpretation that femoral artery ligation causes acute loss of perfusion that is compensated for by macrophage recruitment and disseminated neovascularization. This model provides a novel opportunity to study neovascularization in the absence of tumor growth that will complement ongoing studies using tumor-based models of angiogenesis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4359. doi:1538-7445.AM2012-4359

Recent Developments on High-Power Gyrotrons—Introduction to This Special Issue

Gyrotrons with output powers of several 100 kW are mainly used as high-power millimeter (mm)-wave sources for electron cyclotron resonance heating (ECRH), electron cyclotron current drive (ECCD), stability control and diagnostics of magnetically confined plasmas for generation of energy by controlled thermonuclear fusion. Other applications include ECR ion sources, materials processing and plasma chemistry, high-resolution Doppler radar, radar ranging and imaging in atmospheric and planetary science, active denial systems, as well as detection of concealed radioactive materials. The present review summarizes the status of recent developments on high-power gyrotrons and introduces this Special Issue on Gyrotrons.

SEISMIC DETECTION OF SOLAR MESOGRANULAR-SCALE FLOW

Helioseismic correlation data computed from the Solar and Heliospheric Observatory/Michelson Doppler Imager high-resolution Doppler images were inverted for solar flows of horizontal scale between 5 and 45 Mm. The photospheric Doppler velocity inferred from the inversions was compared with the original Doppler images at each scale. For horizontal scales greater than about 15 Mm, the seismically inferred and directly observed flow maps look similar, as has been seen in studies of supergranular flow. At smaller scales, the similarity disappears, but regression analysis reveals significant correlation between the maps, demonstrating that solar p- and f-mode oscillations contain useful information about these flows. The slope of the computed regression plots is close to unity, indicating that mesogranular-scale flows extend at least a megameter below the photosphere.

High-resolution sonography: a new technique to detect nerve damage in leprosy.

BackgroundLeprosy is the most common treatable peripheral nerve disorder worldwide with periods of acute neuritis leading to functional impairment of limbs, ulcer formation and stigmatizing deformities. Since the hallmarks of leprosy are nerve enlargement and inflammation, we used high-resolution sonography (US) and color Doppler (CD) imaging to demonstrate nerve enlargement and inflammation.Methology/Principal FindingsWe performed bilateral US of the ulnar (UN), median (MN), lateral popliteal (LP) and posterior tibial (PT) nerves in 20 leprosy patients and compared this with the clinical findings in these patients and with the sonographic findings in 30 healthy Indian controls.The nerves were significantly thicker in the leprosy patients as compared to healthy controls (p<0.0001 for each nerve). The two patients without nerve enlargements did not have a type 1 or type 2 reaction or signs of neuritis. The kappa for clinical palpation and nerve enlargement by sonography was 0.30 for all examined nerves (0.32 for UN, 0.41 for PN and 0.13 for LP). Increased neural vascularity by CD imaging was present in 39 of 152 examined nerves (26%). Increased vascularity was observed in multiple nerves in 6 of 12 patients with type 1 reaction and in 3 of 4 patients with type 2 reaction. Significant correlation was observed between clinical parameters of grade of thickening, sensory loss and muscle weakness and US abnormalities of nerve echotexture, endoneural flow and cross-sectional area (p<0.001).Conclusions/SignificanceWe conclude that clinical examination of enlarged nerves in leprosy patients is subjective and inaccurate, whereas sonography provides an objective measure of nerve damage by showing increased vascularity, distorted echotexture and enlargement. This damage is sonographically more extensive and includes more nerves than clinically expected.

A Pictorial Review of Sonographically Detected Intra-Testicular Lesions

Ultrasound is the optimal imaging modality for evaluation of the scrotum. The combination of high-resolution, gray-scale, and color Doppler and spectral Doppler imaging provides excellent depiction of the testicular parenchyma and the extra-testicular, intrascrotal structures and their vascularity, respectively. Advantages of ultrasound include its lack of ionizing radiation, portability, relative low cost, and diagnostic utility when marked pain or swelling limits physical examination. Various neoplastic, inflammatory, congenital, infectious, and vascular processes can affect the testes.

Following the Flow in Chambers

This article summarizes the current progress in imaging the sequence of blood flow inside the cardiac chambers. Observations from experimental models and computational fluid dynamics have been compared with in vivo findings from phase contrast MRI, high-resolution Doppler imaging, and echo particle imaging velocimetry. The discussion includes chamber and valve geometry and its role in asymmetric flow propagation with an emphasis on the cardiac mechanical sequence that helps stabilize the redirected blood streams. Mapping intracardiac flow patterns in health and disease provides a rich and challenging field of research that warrants careful application in future investigations.

X‐Ray Spectroscopic Signatures of the Extended Corona of FK Comae

High-resolution Chandra X-ray spectra and surface Doppler images obtained from optical spectra of the rapidly rotating giant FK Com have been analyzed in order to investigate links between coronal and surface magnetic structures. Net redshifts were detected at the 3 σ level in the light of Ne λ12.13 amounting to ~140 km s−1. Smaller shifts of ~60 km s−1 at the ~2 σ level are seen in the X-ray spectrum as a whole, while the observed position of O VIII λ18.97, the second strongest line in the spectrum after Ne X, is also consistent with its rest wavelength. There is no statistical difference between redshifts during the first and second halves of the observation. Spectral line widths are most consistent with thermal broadening combined with rotational broadening at a scale height of ~1R, although they are also statistically consistent with surface rotational broadening. We interpret the results as indicative of hot plasma predominantly residing in extended structures centered at phase = 0.75 with a size similar to that of the star itself. The contemporaneous Doppler images of the surface of FK Com reveal active longitudes at phases ~ 0.6 and 0.9. We speculate that extended coronal structures correspond to magnetic fields joining the two active longitudes, which theoretical models predict are of opposite magnetic polarity. Such structures are supported by coronal potential field extrapolations of typical theoretical model surface magnetic field distributions. This study was based on a relatively short 40 ks Chandra observation. A much longer observation of FK Com with the HETGS, combined with contemporaneous Zeeman-Doppler imaging, would be of great value for constraining magnetospheric structure and dynamo models of rapidly rotating stars.