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Earlybird: A new approach to vascular assessment
Get PDFThe aim of the thesis was to explore and identify possible clinical applications within vascular health for a novel, high-sensitivity, ultrasound Doppler system (earlybird). The unit was developed by Professor Hans Torp, at the Department of Circulation and Imaging, NTNU. Earlybird consists of an ultrasound probe with a relatively large area, scanner, and a customized user interface. The device is designed to monitor peripheral blood flow simultaneously and continuous in a depth down to 40 mm. It allows easy placement over vessel structures of interest. The Earlybird project is part of a larger innovation and commercialization process of the underlying ultrasound technology, which includes other clinical applications.
In a proof-of-concept study (study I, paper I), it was demonstrated that earlybird correlates well with laser Doppler flowmetry and pulsed-wave Doppler to assess microcirculatory function in healthy subjects 3. This study validates earlybird’s ability to assess peripheral blood circulation.
The second study (study II, paper II and III) includes an innovational treatment-device (FlowOx™) for patients with peripheral arterial disease. A proportion of patients with intermittent claudication, are not able to participate in exercise programs due to lack of motivation or comorbidity. FlowOx™ incorporates intermittent negative pressure (INP) to increase peripheral blood circulation. In a randomized sham-controlled trial, patients with intermittent claudication were treated for 12 weeks with either 40 mmHg or 10 mmHg INP. A mean treatment effect of increase in pain-free walking distance of 50 meters was found, in favor of the 40 mmHg INP treatment group (paper II) 4. Earlybird-recordings were used to explore secondary outcomes (paper III). An immediate increase in blood flow velocities was observed during the INP treatment. Analyses of flowmotion characteristics of endothelial, sympathetic, and myogenic activity, showed a difference in change of myogenic activity between the groups after 12 weeks of treatment with INP. This finding suggests an involvement of vascular smooth muscle cells of the arterioles, and it may contribute to the understanding of the mechanism of action of INP. The ability of earlybird to monitor and assess blood flow velocities, was confirmed in patients with peripheral arterial disease.
In a pilot study (study III, congress abstract I) blood flow velocities were monitored during an endovascular procedure. Earlybird detects changes in blood flow velocities in real-time. Earlybird could be a valuable tool for periprocedural decision making, to guide the clinician in what extent to revascularize a limb 5. Further studies are needed to determine hemodynamic properties that can be associated with clinical endpoints.
Although controversial, the surveillance of volume flow rate (VFR) in arteriovenous fistulas (AVF) for hemodialysis could increase their patency. Earlybird’s ability to be a potential future tool for surveillance of VFR in AVFs was evaluated in an experimental and clinical setting (study IV, paper IV). VFR-measurements were automatically derived from earlybird’s flow velocity recordings, and was compared to duplex ultrasound, and calibrated VFR. Earlybird was found to be a feasible tool for evaluating VFR in AVFs, with a strong correlation and good agreement between the methods used 6. Further development, especially to overcome the limitations with angle dependency, may increase user-friendliness and further improve the accuracy. Earlybird could be a potential valuable tool for surveillance of VFR.
FlowOx™ is a promising device, supplementary to standard care of peripheral arterial disease. Earlybird has been demonstrated to be a feasible device to assess blood flow in healthy individuals, as well as in patients with a range of clinical challenges within the broad segment of vascular disease. Earlybird could be a future tool for clinical decision making during endovascular treatment and a future promising tool for surveillance of hemodialytic vascular access. Further technical and software development of earlybird, may increase user-friendliness and allow for a wide range of clinical applications.Norsk sammendrag
Formålet med doktorgradsarbeidet var å utforske mulige kliniske bruksområder innenfor karhelse for et nyutviklet, høy-sensitivt, ultralyd Doppler system (earlybird). Enheten er utviklet ved Institutt for sirkulasjon og bildediagnostikk, NTNU, ved professor Hans Torp. Earlybird består av ulike ultralydprober med et relativt stort areal, en skanner og et tilpasset brukergrensesnitt. Egenskapene gjør den enkel å plassere over karstrukturer av interesse. Earlybird-prosjektet er del av en større innovasjon- og kommersialiserings-prosess av den underliggende ultralyd-teknologien, som omfatter andre kliniske bruksområder.
I studie I ble earlybird sammenlignet med laser og pulset Doppler. Friske personer ble utsatt for ulike fysiologiske tester som igangsetter en vasomotorisk respons. Det ble funnet en god overenstemmelse mellom de ulike målemetodene (artikkel I). Earlybird virker til å kunne fange opp endringer i perifer blodgjennomstrømning hos friske personer.
I studie II, inkluderte man en behandlingsmetode som tar i bruk intermitterende undertrykk (FlowOx™) for å behandle pasienter med redusert blodgjennomstrømning til beina. En del av pasientene med anstrengelsesutløste gangsmerter er ikke i stand til å delta i anbefalte treningsprogram, og det er derfor interessant å vurdere ikkeinvasive behandlingsmetoder. I denne randomiserte studien var 63 pasienter tilgjengelige for vurdering etter endt oppfølgingstid. Det ble funnet at pasienter som ble behandlet i 12 uker med 40 mmHg intermitterende undertrykk hadde 50 meter gjennomsnittlig økning i smertefri gangdistanse, sammenlignet med de som ble behandlet med 10 mmHg (artikkel II). For å vurdere sekundære utfall av studien (artikkel III) ble målinger av blodstrømshastigheter, målt med earlybird, gjennomført før og etter den 12-ukers lange behandlingsperioden. Man fikk gode og pålitelige målinger av blodgjennomstrømningen. Dette viser at earlybird også kan måle endring i blodsirkulasjon hos pasienter med perifer arteriell sykdom. Målingen ble brukt til å analysere effekter på blodstrømmen, forårsaket av behandling med intermitterende undertrykk. Det ble bekreftet at intermitterende undertrykksbehandling gir en umiddelbar økning i blodstrømshastigheten. Det kan også virke som om den positive effekten sett ved behandling med FlowOx™, delvis kan forklares av økt aktivitet av glattmuskulatur i karveggen tilsvarende arteriolene.
Blodstrømshastigheter ble overvåket i sanntid med earlybird i det aktuelle beinet som gjennomgikk endovaskulær behandling (studie III, kongress abstrakt I). Først etter ballong-dilatasjon av en stent, plassert i en bekkenokklusjon, får man en økning i blodstrøm. Earlybird kan være et nyttig verktøy for peroperativ klinisk beslutningsstøtte. Imidlertid er det nødvendig med flere studier for å vurdere hvilke hemodynamiske parametere og terskelverdier som kan forutsi kliniske endepunkter.
I studie IV har man vist at earlybird kan være et fremtidig verktøy til å måle blodstrøm i arteriovenøse fistler til bruk for hemodialyse (artikkel IV). Selv om det er vist at overvåkning av arteriovenøse fistler kan redusere tromboseringsraten, diskuteres nytteverdien av slike overvåkningsregimer. Det er foreslått at analyse av blodstrømstrender kan være nyttige. Den største begrensningen til earlybird vil være at den ikke tillater vinkelkorrigering av blodstrømshastigheten. Videreutvikling av earlybird, spesielt med tanke på å gjøre den vinkeluavhengig, vil kunne øke brukervennligheten og forbedre nøyaktigheten.
Earlybird har vist seg å kunne måle og overvåke perifer blodsirkulasjon. Earlybird kan være et potensielt fremtidig verktøy for klinisk beslutningsstøtte under endovaskulære behandling og for overvåkning av arteriovenøse fistler brukt som tilgang til
hemodialyse. Ytterligere utvikling av den underliggende teknologien og programvare vil kunne øke brukervennligheten og medføre tilpasning av earlybird til et bredt spekter av kliniske bruksområder
Continuous cerebral Doppler monitoring in infants with congenital heart disease
Get PDFEnglish summary
Continuous cerebral Doppler monitoring in infants with congenital heart disease Congenital heart disease is the most prevalent congenital malformation, seen in approximately 1% of all newborns. About a quarter of these children need surgery within the first year of life. Children with complex heart defects have an increased risk of delays in cognitive and motor skills, as well as learning difficulties and concentration problems. The causes of brain injuries in these children are multifactorial and complex, with factors from before birth, before surgery, and after surgery. However, we do know that surgery and interventions pose significant risk for the developing brain, and therefore are potential targets for modification.
Neuroprotection – protecting the brain – and neuroprotective strategies are important. As of today, there are no good direct methods for monitoring cerebral circulation. Optimization of cerebral blood flow and circulation is based on indirect parameters such as CO2, blood pressure, saturation measurements, and heart rate. Near-infrared spectroscopy (NIRS), a venous weighted oxygenation index, is used to some extent in children with congenital heart disease. Direct, continuous measurement of cerebral blood flow could enable clinicians to optimize the factors known to affect cerebral blood flow, thereby ensuring stable perfusion of the brain during vulnerable periods of the treatment process.
In this project, we have utilized a new ultrasound technology, NeoDoppler, which allows for continuous monitoring of cerebral blood flow over time in newborns and infants. This has been a collaborative project between St. Olav’s Hospital, the Norwegian University of Science and Technology (NTNU), and Oslo university hospital (OUS). The technology was developed at NTNU with Professor Emeritus Hans Torp at the forefront, in close collaboration with the clinical environment at St. Olav’s Hospital. In partnership with the pediatric cardiology department at Rikshospitalet, we included newborns and infants undergoing transcatheter interventions and heart surgery with cardiopulmonary bypass. The main questions we wanted to answer in this project were: Is it feasible to monitor infants with congenital heart disease during transcatheter interventions and heart surgery with cardiopulmonary bypass? Can NeoDoppler provide us with new and useful information on cerebral circulation during these procedures?Norsk sammendrag
Kontinuerlig cerebral Doppler-overvåking hos spedbarn med hjertefeil
Medfødt hjertefeil er den vanligste medfødte misdannelsen og sees omtrent hos 1 % av alle nyfødte barn. Rundt en fjerdedel av disse barna har en hjertefeil som krever kirurgi i løpet av første leveår. Barn med komplekse hjertefeil har økt risiko for forsinkelser i kognitive og motoriske ferdigheter, samt lærevansker og konsentrasjonsvansker. Årsaken til hjerneskader hos disse barna skyldes mange ulike faktorer, som forhold før fødsel, før operasjon og etter operasjon. Kirurgiske inngrep og intervensjoner utgjør en klar risiko for en hjerne i utvikling. Optimal håndtering er derfor viktig.
Nevroproteksjon – å beskytte hjernen - er avgjørende hos disse barna, men i dag finnes det ingen gode direkte metoder for overvåkning av hjernesirkulasjon. Optimalisering av hjerneblodstrøm baserer seg i stor grad på indirekte mål som CO2, blodtrykk, metningsmålinger og hjertefrekvens. Nær-infrarød spektroskopi (NIRS) som er en venøst vektet oksygeneringsindeks brukes noe hos hjertebarn, men gir ingen sikker informasjon om hjerneblodstrøm. Direkte, kontinuerlig måling av hjerneblodstrøm vil kunne gi klinikere mulighet til å optimalisere faktorer som påvirker hjerneblodstrøm, og dermed sikre god blodtilførsel og oksygenmetning av hjernevev i sårbare perioder av behandlingsforløp.
I dette doktorgradsprosjektet har vi brukt, NeoDoppler, en ny ultralydteknologi for kontinuerlig overvåkning av hjerneblodstrøm hos nyfødte og spedbarn. Prosjektet er et samarbeid mellom St Olavs hospital, Norges teknisk-naturvitenskapelige universitet (NTNU) og Oslo universitetssykehus (OUS). Teknologien er utviklet ved NTNU med Professor emeritus, Hans Torp, i nært samarbeid med det kliniske miljøet ved St Olavs hospital. I samarbeid med barnekardiologisk avdeling ved Rikshospitalet har vi inkludert spedbarn som har gjennomgått kateterbaserte hjerteintervensjoner og hjertekirurgi med hjertelungemaskin. De sentrale spørsmålene vi ønsket å besvare i dette prosjektet var: Er det mulig å overvåke hjerneblodstrøm hos hjertebarn under kateterintervensjoner og åpen hjertekirurgi? Kan NeoDoppler gi oss ny og nyttig informasjon om hjernens sirkulasjon under disse prosedyrene?digital fulltext is not availabl
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Methods for improving quality and efficiency in quantitative echocardiography: Aspects of using high frame rate
Get PDFUltralyd er i dag et standardverktøy innen hjertediagnostikk. Analyse av ventrikkelfunksjon gjøres subjektivt ved å se på gråskala ultralydopptak av hjertet. Dette gjør dokumentasjon og opplæring vanskelig. Det er derfor ønskelig med kvantitative mål på ventrikkelfunksjon. Kvantitative metoder kan benytte høy tidsoppløsning og dermed også registrere flere detaljer.
To teknikker for kvantitativ ventrikkelanalyse er vevs-Doppler og speckle tracking (mønsterfølging). Ved bruk av disse teknikkene er det viktig å sikre kvaliteten av resultatene samtidig som analyseprosessen kan gjennomføres så effektivt som mulig. I denne avhandlingen presenteres flere metoder for å sikre kvalitet og øke effektivitet ved kvantitativ ventrikkelanalyse som alle er relatert til bruk av høy tidsoppløsning.
For å kunne gjøre effektiv ventrikkelanalyse behøves analyseverktøy. Et slikt verktøy som fungerer med både vevs-Doppler og speckle tracking presenteres i denne avhandlingen. Dette verktøyet har gjort flere store kliniske studier mulig. Ved analyse av hendelsene som skjer innen en hjertesykel er det viktig å dele opp hjertesykelen i ulike faser. Venstre ventrikkels tømmingsfase avsluttes ved at aortaklaffen lukkes, og denne hendelsen må derfor bestemmes før kvantitative parametre i slutten av tømmingsfasen og i overgangen til fyllingsfasen kan bestemmes. I denne avhandlingen vurderes og testes ulike kandidater for bestemmelse av lukkingen. To gunstige kandidater i hastighetskurver fra basale deler av ventrikkelen ble funnet: andre nullkryssing etter tømming og høyeste positive akselerasjon etter tømming før fylling. Et eget bidrag viser at den siste av disse kan bestemmes automatisk. For å oppnå høy tidsoppløsning kreves høy datarate. En populær metode for å øke datarate er flere parallelle mottaksstråler for hver sendestråle. I vanlig gråtoneavbilding av hjertet er det imidlertid observert at dette medfører uønskede linjelignende strukturer i bildet. I denne avhandlingen vises det at årsaken til dette er at de parallelle strålene deformeres når de passerer strukturene mellom hjertet og proben. Avhandlingen inneholder også et bidrag som viser hvordan bruk av parallelle mottakstråler kan medføre at vevs-Doppler kurver blir hentet fra et annet sted i hjertet enn det intensjonen var. Samlet er avhandlingen et bidrag til fortsatt utvikling og forbedring av kvantitative ultralydmetoder innen hjertediagnostikk.PhD i medisinsk teknologiPhD in Medical Technolog
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
3D Ultrasound for Quantitative Echocardiography
Get PDFMedical ultrasound imaging is widely used to diagnose cardiacdiseases. The recent availability of real time 3D ultrasound posesseveral interesting challenges and opportunities, and the work of thisthesis is devoted to both challenges and opportunities.
One of the key benefits of ultrasound imaging is that its images arereal time. This has been challenged with the recent introduction of 3Dimages, where the number of ultrasound beams is squared compared totraditional 2D images. One common way to alleviate this is byreceiving several closely spaced ultrasound beams from each pulsetransmission, which increases acquisition speed but affects the imagequality. Specifically, B-mode images are irregularly sampled and losespatial shift invariance while a bias in the Doppler velocityestimates causes a discontinuity in the velocity estimates in colorflow images. We have found that these artifacts can be reducedsignificantly by interpolation of the beamformed data from overlappingbeams, with the limitation of requiring at least twice the number ofbeamformers.
We have also found that valvular regurgitation is one of thecardiac diseases that can benefit greatly from quantification ofseverity using 3D ultrasound. We have devised a modality that useshigh pulse repetition frequency 3D Doppler to isolate thebackscattered signal power from the vena contracta of a regurgitantjet. This measure is calibrated with a narrow reference beam insidethe jet to estimate the cross-sectional area of the vena contracta. Wehave validated this method with computer simulations, with an in vitrostudy and finally in vivo with 27 patients who had mitralregurgitation. We found that the cross-sectional area and regurgitantvolume of the vena contracta could be quantified without bias as long as the orifice was sufficiently large for a calibration beam tofit inside it. The severity of smaller regurgitations will beoverestimated, but this does not pose a clinical problem, as thesepatients can easily be identified by standard 2D Doppler examination and donot typically need further quantification.
Finally, we have developed a new, fast 3D ultrasound simulation methodthat can incorporate anisotropic scattering from cardiac muscle cells. This approach is three orders of magnitudefaster than the most commonly used simulation methods, making it wellsuited for the simulation of dynamic 3D images for development and testingof quantitative diagnostic methods such as 3D speckle tracking andvolumetric measurements.PhD i medisinsk teknologiPhD in Medical Technolog
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
3D Ultrasound for Quantitative Echocardiography
No full textMedical ultrasound imaging is widely used to diagnose cardiacdiseases. The recent availability of real time 3D ultrasound posesseveral interesting challenges and opportunities, and the work of thisthesis is devoted to both challenges and opportunities. One of the key benefits of ultrasound imaging is that its images arereal time. This has been challenged with the recent introduction of 3Dimages, where the number of ultrasound beams is squared compared totraditional 2D images. One common way to alleviate this is byreceiving several closely spaced ultrasound beams from each pulsetransmission, which increases acquisition speed but affects the imagequality. Specifically, B-mode images are irregularly sampled and losespatial shift invariance while a bias in the Doppler velocityestimates causes a discontinuity in the velocity estimates in colorflow images. We have found that these artifacts can be reducedsignificantly by interpolation of the beamformed data from overlappingbeams, with the limitation of requiring at least twice the number ofbeamformers. We have also found that valvular regurgitation is one of thecardiac diseases that can benefit greatly from quantification ofseverity using 3D ultrasound. We have devised a modality that useshigh pulse repetition frequency 3D Doppler to isolate thebackscattered signal power from the vena contracta of a regurgitantjet. This measure is calibrated with a narrow reference beam insidethe jet to estimate the cross-sectional area of the vena contracta. Wehave validated this method with computer simulations, with an in vitrostudy and finally in vivo with 27 patients who had mitralregurgitation. We found that the cross-sectional area and regurgitantvolume of the vena contracta could be quantified without bias as long as the orifice was sufficiently large for a calibration beam tofit inside it. The severity of smaller regurgitations will beoverestimated, but this does not pose a clinical problem, as thesepatients can easily be identified by standard 2D Doppler examination and donot typically need further quantification. Finally, we have developed a new, fast 3D ultrasound simulation methodthat can incorporate anisotropic scattering from cardiac muscle cells. This approach is three orders of magnitudefaster than the most commonly used simulation methods, making it wellsuited for the simulation of dynamic 3D images for development and testingof quantitative diagnostic methods such as 3D speckle tracking andvolumetric measurements
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