An exploration of the potential utility of fetal cardiovascular MRI as an adjunct to fetal echocardiography

Objectives: Fetal cardiovascular magnetic resonance imaging (MRI) offers a potential alternative to echocardiography, although in practice, its use has been limited. We sought to explore the need for additional imaging in a tertiary fetal cardiology unit and the usefulness of standard MRI sequences. Methods: Cases where the diagnosis was not fully resolved using echocardiography were referred for MRI. Following a three‐plane localiser, fetal movement was assessed with a balanced steady‐state free precession (bSSFP) cine. Single‐shot fast spin echo and bSSFP sequences were used for diagnostic imaging. Results: Twenty‐two fetal cardiac MRIs were performed over 12 months, at mean gestation of 32 weeks (26–38 weeks). The majority of referrals were for suspected vascular abnormalities (17/22), particularly involving the aortic arch (n = 10) and pulmonary vessels (n = 4). Single‐shot fast spin echo sequences produced ‘black‐blood’ images, useful for examining the extracardiac vasculature in these cases. BSSFP sequences were more useful for intracardiac structures. Real‐time SSFP allowed for dynamic assessment of structures such as cardiac masses, with enhancement patterns also allowing for tissue characterisation in these cases. Conclusions: Fetal vascular abnormalities such as coarctation can be difficult to diagnose by using ultrasound. Fetal MRI may have an adjunctive role in the evaluation of the extracardiac vascular anatomy and tissue characterisation. © 2016 The Authors. Prenatal Diagnosis published by John Wiley & Sons, Ltd

Finite volume analysis of temperature effects induced by active MRI implants with cylindrical symmetry: 1. Properly working devices

BACKGROUND: Active Magnetic Resonance Imaging implants are constructed as resonators tuned to the Larmor frequency of a magnetic resonance system with a specific field strength. The resonating circuit may be embedded into or added to the normal metallic implant structure. The resonators build inductively coupled wireless transmit and receive coils and can amplify the signal, normally decreased by eddy currents, inside metallic structures without affecting the rest of the spin ensemble. During magnetic resonance imaging the resonators generate heat, which is additional to the usual one described by the specific absorption rate. This induces temperature increases of the tissue around the circuit paths and inside the lumen of an active implant and may negatively influence patient safety. METHODS: This investigation provides an overview of the supplementary power absorbed by active implants with a cylindrical geometry, corresponding to vessel implants such as stents, stent grafts or vena cava filters. The knowledge of the overall absorbed power is used in a finite volume analysis to estimate temperature maps around different implant structures inside homogeneous tissue under worst-case assumptions. The "worst-case scenario" assumes thermal heat conduction without blood perfusion inside the tissue around the implant and mostly without any cooling due to blood flow inside vessels. RESULTS: The additional power loss of a resonator is proportional to the volume and the quality factor, as well as the field strength of the MRI system and the specific absorption rate of the applied sequence. For properly working devices the finite volume analysis showed only tolerable heating during MRI investigations in most cases. Only resonators transforming a few hundred mW into heat may reach temperature increases over 5 K. This requires resonators with volumes of several ten cubic centimeters, short inductor circuit paths with only a few 10 cm and a quality factor above ten. Using MR sequences, for which the MRI system manufacturer declares the highest specific absorption rate of 4 W/kg, vascular implants with a realistic construction, size and quality factor do not show temperature increases over a critical value of 5 K. CONCLUSION: The results show dangerous heating for the assumed "worst-case scenario" only for constructions not acceptable for vascular implants. Realistic devices are safe with respect to temperature increases. However, this investigation discusses only properly working devices. Ruptures or partial ruptures of the wires carrying the electric current of the resonance circuits or other defects can set up a power source inside an extremely small volume. The temperature maps around such possible "hot spots" should be analyzed in an additional investigation

The influence of methylphenidate on the power spectrum of ADHD children – an MEG study

BACKGROUND: The present study was dedicated to investigate the influence of Methylphenidate (MPH) on cortical processing of children who were diagnosed with different subtypes of Attention Deficit Hyperactivity Disorder (ADHD). As all of the previous studies investigating power differences in different frequency bands have been using EEG, mostly with a relatively small number of electrodes our aim was to obtain new aspects using high density magnetoencephalography (MEG). METHODS: 35 children (6 female, 29 male) participated in this study. Mean age was 11.7 years (± 1.92 years). 17 children were diagnosed of having an Attention-Deficit/Hyperactivity Disorder of the combined type (ADHDcom, DSM IV code 314.01); the other 18 were diagnosed for ADHD of the predominantly inattentive type (ADHDin, DSM IV code 314.0). We measured the MEG during a 5 minute resting period with a 148-channel magnetometer system (MAGNES™ 2500 WH, 4D Neuroimaging, San Diego, USA). Power values were averaged for 5 bands: Delta (D, 1.5–3.5 Hz), Theta (T, 3.5–7.5 Hz), Alpha (A, 7.5–12.5 Hz), Beta (B, 12.5–25 Hz) and Global (GL, 1.5–25 Hz).). Additionally, attention was measured behaviourally using the D2 test of attention with and without medication. RESULTS: The global power of the frequency band from 1.5 to 25 Hz increased with MPH. Relative Theta was found to be higher in the left hemisphere after administration of MPH than before. A positive correlation was found between D2 test improvement and MPH-induced power changes in the Theta band over the left frontal region. A linear regression was computed and confirmed that the larger the improvement in D2 test performance, the larger the increase in Theta after MPH application. CONCLUSION: Main effects induced by medication were found in frontal regions. Theta band activity increased over the left hemisphere after MPH application. This finding contradicts EEG results of several groups who found lower levels of Theta power after MPH application. As relative Theta correlates with D2 test improvement we conclude that MEG provide complementary and therefore important new insights to ADHD

Ventricular function and signal enhanced imaging with active MR imaging stents

Titelblatt und Inhaltsverzeichnis Einleitung Grundlagen der ventrikulären Funktion Entwicklung der MR - Funktionsdiagnostik Problematiken der Funktionsuntersuchungen Bestimmung der linksventrikulären Funktionsparameter Beurteilung der regionalen linksventrikulären Kinetik Bestimmung der rechtsventrikulären Funktionsparameter Neue Ansätze zur Beurteilung des Stentlumens Diskussion Zusammenfassung LiteraturDie genaue Beschreibung der Ventrikelvolumina sowie der rechts- und linksventrikulären Funktion ist für viele kardiale Erkrankungen bezüglich der Prognose und Therapieentscheidung von eminenter Bedeutung. Die MRT ist in der Lage, mit hoher Genauigkeit die globale und regionale Funktion zu bestimmen. Im Vergleich mit der Elektronenstrahl-Computertomographie (EBT) konnten wir in mehreren Studien eine signifikante Korrelation der MRT bezüglich der rechts- und linksventrikulären Funktionsparameter sowie des Regurgitationsvolumens einer Mitralklappeninsuffizienz zeigen. Die Elektronenstrahl- Computertomographie ist durch die Weiterentwicklungen der Mehrzeilen- Computertomographie (MSCT) weitgehend ersetzt worden und erlaubt die volumendeckende Abbildung des Herzens. Der so gewonnene Datensatz ermöglicht, da er EKG-getriggert akquiriert wird, eine zeitaufgelöste Bildrekonstruktion, die als Grundlage für die Funktionsanalyse der Ventrikel herangezogen werden kann. Wir haben sechs Patienten mit Kardiomegalie vor und nach ventrikelverkleinernder Operation im MRT evaluiert. Die MRT war in der Lage, dem Chirurgen relevante Befunde vor ventrikelverkleinernder Operation zu liefern. In der frühen postoperativen Verlaufsbeurteilung kann sie funktionelle und morphologische Veränderungen zuverlässig darstellen. Unsere Studienergebnisse belegen, dass durch die partielle linksventrikuläre Resektion eine signifikante Reduktion der linksventrikulären Volumina und Verbesserung der biventrikulären Funktion erreicht werden kann. Darüber hinaus kann die regionale Wandbewegung, Wanddicke und Wanddickenzunahme bestimmt werden, die für die Therapieplanung essentiell ist. Die MRT bietet gegenüber der Computertomographie aufgrund der erheblich besseren Zeitauflösung und der Möglichkeit des Taggings grundlegende Vorteile in der Beurteilung regionaler Wandbewegungsstörungen. Das Tagging ermöglicht regionale Wandbewegungsanalysen durch Markieren des Myokards. Wir haben 16 Patienten mit nachgewiesener koronarer Herzkrankheit und stattgehabtem Myokardinfarkt mittels Lävokardiographie, Doppler-Gewebe-Echokardiographie und MR-Tagging untersucht. Alle Patienten wiesen regionale Wandbewegungsstörungen auf. Die Übereinstimmung zwischen MRT und Echokardiographie zeigte einen -Wert von 0,962 und zwischen MRT und Lävokardiographie sowie zwischen Echokardiographie und Lävokardiographie betrug der -Wert 0,602. Das MR-Tagging ermöglichte in unserer Studie im Vergleich zur Echokardiographie mit Gewebe-Doppler- Bildgebung eine zuverlässige Charakterisierung regionaler linksventrikulärer Kinetikstörungen. Die nichtinvasiven schnittbildgebenden Verfahren zeigten an unserem Patientenkollektiv mehr regionale Wandbewegungsstörungen als die Lävokardiographie. Eine wesentliche Limitation der MR-Bildgebung liegt in den lokalen Suszeptibilitätsartefakten begründet, die durch metallhaltiges Material von Fremdkörpern verursacht wird. Metallhaltige Stents können daher eine Darstellung des Stentlumens beeinträchtigen oder sogar vollständig verhindern. In dem zweiten, experimentellen Teil dieser Arbeit haben wir das innovative Konzept der aktiven Visualisierung des Stentlumens in der Magnetresonanztomographie evaluiert. Induktiv gekoppelte Spulen ermöglichen im MRT eine Bildgebung mit erhöhter Signalintensität, ohne dass sie über eine Kabelverbindung mit dem Tomographen verbunden sein müssen. Bildgebung sowie Flussmessungen innerhalb des Stentlumens sind auf diese Weise möglich. Dieses Konzept besitzt das Potenzial, tierexperimentelle nichtinvasive Verlaufsbeurteilungen nach Stentimplantation hochauflösend durchzuführen. Für die klinische Anwendung erscheint eine magnetresonanztomographische Offenheitsbeurteilung bzw. Beurteilung einer möglichen In-Stent-Restenose von MR-aktiven Stents möglich.Magnetic resonance imaging (MRI) is an accurate modality to assess ventricular global and regional function. Assessment of global ventricular function is based on measuring changes in chamber volume using two- and three-dimensional methods. We could show an excellent correlation between MRI and electron beam tomography (EBT) in determining left-ventricular parameters in patients with ischemic and dilated cardiac disease. Both methods are suitable for volumetric assessment of the left ventricle. Additionally, MRI provides relevant information prior to left ventricular reduction surgery and depicts functional changes in the postoperative follow-up in patients undergoing left ventricular reduction surgery. For assessment of regional wall motion abnormalities MR tagging has been introduced. We compared the visual analysis of magnetic resonance imaging with the tagging technique and Doppler tissue echocardiography with invasive ventriculography in detecting and quantifying regional wall motion abnormalities. Agreement between MRI and echocardiography was excellent. MRI and Doppler tissue echocardiography detected more wall motion abnormalities than invasive ventriculography and graded them as more severe. Assessment of right ventricular volumes and function is feasible with MRI as well as with EBT. EBT showed good agreement with a close correlation and an acceptable interobserver variability for right ventricular volumes and global function in a study comprising 27 patients when compared to MRI. However, EBT has been replaced by multislice spiral computed tomography (MSCT) in cardiac imaging. To validate right ventricular measurements we examined 25 patients with MSCT and MRI. A close correlation was found between the two modalities and MSCT seems to be an accurate and reliable non-invasive technique for evaluating tight ventricular measurements. To avoid artifacts form metal containing foreign bodies such as stents we assessed an active MR imaging stent (AMRIS) in an animal model which consists of an inductively coupled coil. This stent prototype is catheter-deployable and allowed for artifact-free imaging with local improvement in signal-to-noise ratio. The stented vessel segment could be examined with enhanced signal intensity on MRI and flow measurements within the stent were feasible. This might be a suitable approach for monitoring in-stent-pathologies and vessel wall alterations by MR imaging in patients having undergone stent placement