Temporal SNR characteristics in segmented 3D-EPI at 7T.

Three-dimensional segmented echo planar imaging (3D-EPI) is a promising approach for high-resolution functional magnetic resonance imaging, as it provides an increased signal-to-noise ratio (SNR) at similar temporal resolution to traditional multislice 2D-EPI readouts. Recently, the 3D-EPI technique has become more frequently used and it is important to better understand its implications for fMRI. In this study, the temporal SNR characteristics of 3D-EPI with varying numbers of segments are studied. It is shown that, in humans, the temporal variance increases with the number of segments used to form the EPI acquisition and that for segmented acquisitions, the maximum available temporal SNR is reduced compared to single shot acquisitions. This reduction with increased segmentation is not found in phantom data and thus likely due to physiological processes. When operating in the thermal noise dominated regime, fMRI experiments with a motor task revealed that the 3D variant outperforms the 2D-EPI in terms of temporal SNR and sensitivity to detect activated brain regions. Thus, the theoretical SNR advantage of a segmented 3D-EPI sequence for fMRI only exists in a low SNR situation. However, other advantages of 3D-EPI, such as the application of parallel imaging techniques in two dimensions and the low specific absorption rate requirements, may encourage the use of the 3D-EPI sequence for fMRI in situations with higher SNR.

Intravascular ultrasound underestimates vessel dimensions.

The information gathered with intravascular ultrasound (IVUS) are of great value in endovascular techniques. The aim of this study was to evaluate the reliability of IVUS when measuring vessel dimensions by comparison with an established reference method. The left carotid artery was exposed in 4 pigs (45-55 kg) and two piezoelectric crystals were sutured on the adventitia in the same cross-sectional plane. The distance between them was measured either by IVUS and by sonomicrometers. The mean distance between the two crystals calculated by the sonomicrometer was 4.7+/-0.4 mm (mean systolic distance was 4.9+/-0.2 mm, mean diastolic distance was 4.6+/-0.1 mm). The mean distance between the two targets calculated by IVUS was 4. 5+/-0.2 mm (mean systolic distance was 4.6+/-0.2 mm and mean diastolic 4.4+/-0.2 mm). Regression analysis of the two series of data shows a R(2)=0.9984. IVUS measurements are an average 5% smaller than sonomicrometer measurements (3.6% up to 8.3%) and the difference is statistically significant ( p <0.05). The underestimation of IVUS measurements will affect the accuracy, and probably the long-term outcome, of endovascular procedures.

Creación de una demo 3D mediante gráficos procedurales

Aquest projecte consisteix en el desenvolupament d’una demo 3D utilitzant exclusivament gràfics procedurals per tal d’avaluar la seva viabilitat en aplicacions més complexes com els videojocs. En aquesta aplicació es genera un terreny aleatori explorable amb vegetació i textures creades proceduralment.

Intracellular nanomanipulation by a photonic-force microscope with real-time acquisition of a 3D stiffness matrix.

A traditional photonic-force microscope (PFM) results in huge sets of data, which requires tedious numerical analysis. In this paper, we propose instead an analog signal processor to attain real-time capabilities while retaining the richness of the traditional PFM data. Our system is devoted to intracellular measurements and is fully interactive through the use of a haptic joystick. Using our specialized analog hardware along with a dedicated algorithm, we can extract the full 3D stiffness matrix of the optical trap in real time, including the off-diagonal cross-terms. Our system is also capable of simultaneously recording data for subsequent offline analysis. This allows us to check that a good correlation exists between the classical analysis of stiffness and our real-time measurements. We monitor the PFM beads using an optical microscope. The force-feedback mechanism of the haptic joystick helps us in interactively guiding the bead inside living cells and collecting information from its (possibly anisotropic) environment. The instantaneous stiffness measurements are also displayed in real time on a graphical user interface. The whole system has been built and is operational; here we present early results that confirm the consistency of the real-time measurements with offline computations.

Prenatal exposure to traffic-related air pollution and ultrasound measures of fetal growth in the INMA Sabadell cohort

Background: Few studies have used longitudinal ultrasound measurements to assess the effect of traffic-related air pollution on fetal growth.Objective: We examined the relationship between exposure to nitrogen dioxide (NO2) and aromatic hydrocarbons [benzene, toluene, ethylbenzene, m/p-xylene, and o-xylene (BTEX)] on fetal growth assessed by 1,692 ultrasound measurements among 562 pregnant women from the Sabadell cohort of the Spanish INMA (Environment and Childhood) study.Methods: We used temporally adjusted land-use regression models to estimate exposures to NO2 and BTEX. We fitted mixed-effects models to estimate longitudinal growth curves for femur length (FL), head circumference (HC), abdominal circumference (AC), biparietal diameter (BPD), and estimated fetal weight (EFW). Unconditional and conditional SD scores were calculated at 12, 20, and 32 weeks of gestation. Sensitivity analyses were performed considering time–activity patterns during pregnancy.Results: Exposure to BTEX from early pregnancy was negatively associated with growth in BPD during weeks 20–32. None of the other fetal growth parameters were associated with exposure to air pollution during pregnancy. When considering only women who spent 2 hr/day in nonresidential outdoor locations, effect estimates were stronger and statistically significant for the association between NO2 and growth in HC during weeks 12–20 and growth in AC, BPD, and EFW during weeks 20–32.Conclusions: Our results lend some support to an effect of exposure to traffic-related air pollutants from early pregnancy on fetal growth during mid-pregnancy.

Patient-specific computational hemodynamics of intracranial aneurysms from 3D rotational angiography and CT angiography: an in vivo reproducibility study

Patient-specific simulations of the hemodynamics in intracranial aneurysms can be constructed by using image-based vascular models and CFD techniques. This work evaluates the impact of the choice of imaging technique on these simulations

Estimation of the viscoelastic properties of vessel walls using a computational model and Doppler ultrasound

Human arteries affected by atherosclerosis are characterized by altered wall viscoelastic properties. The possibility of noninvasively assessing arterial viscoelasticity in vivo would significantly contribute to the early diagnosis and prevention of this disease. This paper presents a noniterative technique to estimate the viscoelastic parameters of a vascular wall Zener model. The approach requires the simultaneous measurement of flow variations and wall displacements, which can be provided by suitable ultrasound Doppler instruments. Viscoelastic parameters are estimated by fitting the theoretical constitutive equations to the experimental measurements using an ARMA parameter approach. The accuracy and sensitivity of the proposed method are tested using reference data generated by numerical simulations of arterial pulsation in which the physiological conditions and the viscoelastic parameters of the model can be suitably varied. The estimated values quantitatively agree with the reference values, showing that the only parameter affected by changing the physiological conditions is viscosity, whose relative error was about 27% even when a poor signal-to-noise ratio is simulated. Finally, the feasibility of the method is illustrated through three measurements made at different flow regimes on a cylindrical vessel phantom, yielding a parameter mean estimation error of 25%.

Ex-vivo ultrasound control of resection margins during partial nephrectomy

Introduction: Surgery represents the treatment of choice for localized renal cell neoplasia. Partial nephrectomy (PN) has widened its indications over the past two decades and has shown oncological results equivalent to radical nephrectomy for small tumors. The role of negative surgical margins has been widely debated. Intraoperative fresh frozen section analysis is shown to be unreliable, expensive, time-consuming and not well correlated to final pathology. The goal of the present study was to assess the feasibility of intraoperative ex-vivo ultrasound (US) control of resection margins and its correlation to margin status at definitive pathology in patients undergoing PN.Material and Methods: The study was carried out in our institution from February 2008 to March 2010. Patients undergoing PN for T1-T2 renal tumors were included. Ex vivo US was performed by one single senior radiologist. Considering its availability, not all consecutive eligible patients were included. PN was undertaken in a standardized technique applying the "minimal healthy tissue margin" technique. Once resected, the specimen was kept in a saline solution and ex-vivo US was performed to evaluate the whole tumor pseudocapsule.Results: Twelve patients (five women, age (mean}SD) 65}11 years) were included. Intraoperative ex-vivo US showed negative surgical margin in all cases. US duration ranged from 1 to 4 minutes, with a median time of 1 minute. Definitive histological analysis confirmed the presence of two angiomyolipoma, eight pT1a tumors, of which seven were clear cell carcinoma and one was a type II papillary tumor, one pT1b clear cell carcinoma and one pT2 chromophobe carcinoma (size 2.9}2.3 cm). Final pathology revealed R0 margins.Conclusion: Intraoperative ex-vivo US control of resection margins in patients undergoing PN is feasible, time-efficient and well correlated to definitive pathological examination with regards to margin status.

Magnetization transfer-based 3D visualization of foot peripheral nerves.

PURPOSE: To investigate magnetization transfer (MT) effects as a new source of contrast for imaging and tracking of peripheral foot nerves. MATERIALS AND METHODS: Two sets of 3D spoiled gradient-echo images acquired with and without a saturation pulse were used to generate MT ratio (MTR) maps of 260 μm in-plane resolution for eight volunteers at 3T. Scan parameters were adjusted to minimize signal loss due to T2 dephasing, and a dedicated coil was used to improve the inherently low signal-to-noise ratio of small voxels. Resulting MTR values in foot nerves were compared with those in surrounding muscle tissue. RESULTS: Average MTR values for muscle (45.5 ± 1.4%) and nerve (21.4 ± 3.1%) were significantly different (P < 0.0001). In general, the difference in MTR values was sufficiently large to allow for intensity-based segmentation and tracking of foot nerves in individual subjects. This procedure was termed MT-based 3D visualization. CONCLUSION: The MTR serves as a new source of contrast for imaging of peripheral foot nerves and provides a means for high spatial resolution tracking of these structures. The proposed methodology is directly applicable on standard clinical MR scanners and could be applied to systemic pathologies, such as diabetes.

3D-partikkelit aloittelijoille : tarkastelussa 3D-Kalevala-projekti

Opinnäytteeni teososana on 3D-Kalevala projektinimellä tunnetun animaation partikkeliefektit. Tarkastelen tarkemmin elokuvan Lumi-, Kylä-, Paja- ja Luola-kohtauksia. 3D-Kalevala on tietokoneella tehty animaatio, joka kertoo Suomen kansalliseepoksen Kalevalan päähenkilöstä Väinämöisestä. Elokuvassa vanha Väinämöinen muistelee nuoruutensa tapahtumia. 3D-Kalevala-projekti käynnistettiin vuonna 2003, mutta sen alkuperäiset tekijät eivät saaneet sitä valmiiksi, ja projektin teko keskeytettiin vuonna 2005. Vuoden 2006 keväällä projektiin perustettiin uusi kahden verkkoviestinnän opiskelijan projektiryhmä, jonka tehtävänä oli saada elokuva valmiiksi vuoden 2007 kevääseen mennessä. Kun aloitimme projektin tekemisen, olin kolmiulotteisessa mallinnuksessa aloittelija. Tästä johtuen opinnäytteen kirjallinen osa on opas aloittelijoille partikkelien maailmaan. Selvitän raportissani miten elokuvan partikkeliefektit rakennettiin, mitä niiden tekeminen minulta vaati ja miten ne loppujen lopuksi mielestäni onnistuivat. Elokuvan efektit tehtiin 3D Studio Max-ohjelman versiolla 6.0, ja tämän takia kirjoitankin efektien rakentamisesta kyseisen ohjelman keinoin. Projektin suuruuden vuoksi molemmat tekijät pääsivät tekemään monenlaisia töitä, mutta päävastuualueet olivat selvät. Minun osani oli tehdä elokuvaan efektejä. Partikkeliefektit ovat proseduraalisia efektejä, joiden avulla on mahdollista tehdä aidon näköisiä luonnonilmiöitä, kuten tulta, savua, kipinöitä ja veden roiskeita. Koska partikkeliefektit mallintavat reaalimaailman ilmiöitä, on tekijän hyvä olla kiinnostunut selvittämään ilmiöiden käyttäytymistä luonnossa. Raportoin myös projektin aikana huomaamistani hyvistä tavoista opiskella itsenäisesti partikkelien rakentamiseen käytettyjä tekniikoita. On hyvä lukea 3D Studio Maxin tasokasta käyttöohjesovellusta, tutustua Internetissä löytyviin 3D-aiheisiin foorumeihin, käydä aiheesta tutoriaaleja läpi sekä tutustua ohjelman ominaisuuksiin kokeilemalla ja tutkimalla itsenäisesti. Elokuvan efektit onnistuivat mielestäni kiitettävästi ottaen huomioon lähtötasoni. Löysin tapoja kehittää itseäni ja helppoja keinoja toteuttaa realistista jälkeä efektien rakentamisessa. Toivon, että raportistani olisi jollekin 3D-partikkeliefekteistä kiinnostuneelle hyötyä.

Keskeytyneen uusmediatuotannon jatkaminen : kohteena 3D-Kalevala

Opinnäytetyöni aiheena on keskeytyneen uusmediatuotannon jatkaminen. Monimuototyön työosana toteutettiin 7-minuuttinen 3D animaatio, joka kertoo Suomen kansalliseepoksen Kalevalan taruhahmosta Väinämöisestä, muistelemassa menneitä. Projekti käynnistettiin alun perin vuonna 2003, mutta resurssien vähetessä se keskeytyi vuoden 2005 loppupuolella. Keväällä 2006 projekti käynnistettiin uuden projektiryhmän voimin, jossa olin itse mukana vastaten muun muassa tuotannonohjauksesta ja hahmoanimoinneista. Uusi projektiryhmä oli henkilöstöresursseiltaan pieni, joten vastuualueet olivat monipuolisia. Keskeytyneen projektin jatkamisen ja haltuunoton haasteellisuus sai minut kiinnostumaan tutkia aihetta tarkemmin. Tuotannonohjaajana vastasin hyvin pitkälle tuotannon uudesta käynnistämisestä ja projektin saattamisesta vihdoin loppuun. Keskeytyneen projektin haltuunotto oli tilanteena kaikille uusi, mikä heijastui vaikeuksina uudelleen käynnistettyyn tuotantoon. Raportin tarkoituksena ei ole olla projektinhallinnallinen käsikirja, sillä käsittelen vain tämän projektin jatkolle oleellisina pidettyjä asioita. Projekti toivottavasti kuitenkin antaa kuvan huolellisen projektinhallinnan ja onnistuneen tuotannonohjauksen tärkeydestä. Jokainen keskeytynyt projekti ei ole aina välttämättä elvytettävissä - ainakaan alkuperäisessä muodossaan. Projektin jatkamista tulisi katsoa aina tapauskohtaisesti. Keskeytymiseen on useimmiten syynsä, joten ongelmien selvittäminen ja niihin puuttuminen on tärkeää ennen jatkopäätöksen tekemistä. Myös projektityöskentelytavat kehittyvät ja pohdin työssäni uusien projektinhallintatapojen, kuten wikien käyttöä projektinhallinnan työkaluna ja projektiyhteisön välistä viestintää edistävänä työkaluna.