Outracing Lung Signal Decay – Potential of Ultrashort Echo Time MRI

Mark Oliver Wielpütz; Simon M. F. Triphan; Yoshiharu Ohno; Bertram J. Jobst; Hans-Ulrich Kauczor

doi:10.1055/a-0715-2246

RöFo - Fortschritte auf dem Gebiet der Röntgenstrahlen und der bildgebenden Verfahren, Table of Contents

Rofo 2019; 191(05): 415-423
DOI: 10.1055/a-0715-2246

Review

Outracing Lung Signal Decay – Potential of Ultrashort Echo Time MRI

Dem Signalzerfall in der Lunge zuvorkommen – Potenzial der Ultrashort-Echo-Time-MRT

Mark Oliver Wielpütz

¹Department of Diagnostic and Interventional Radiology, Subdivision of Pulmonary Imaging, University Hospital of Heidelberg, Heidelberg, Germany

²Translational Lung Research Center Heidelberg (TLRC), German Lung Research Center (DZL), Heidelberg, Germany

³Department of Diagnostic and Interventional Radiology with Nuclear Medicine, Thoraxklinik at the University Hospital of Heidelberg, Heidelberg, Germany

,

Simon M. F. Triphan

¹Department of Diagnostic and Interventional Radiology, Subdivision of Pulmonary Imaging, University Hospital of Heidelberg, Heidelberg, Germany

²Translational Lung Research Center Heidelberg (TLRC), German Lung Research Center (DZL), Heidelberg, Germany

³Department of Diagnostic and Interventional Radiology with Nuclear Medicine, Thoraxklinik at the University Hospital of Heidelberg, Heidelberg, Germany

,

Yoshiharu Ohno

⁴Advanced Biomedical Imaging Research Center, Kobe University Graduate School of Medicine, Kobe, Japan

,

Bertram J. Jobst

¹Department of Diagnostic and Interventional Radiology, Subdivision of Pulmonary Imaging, University Hospital of Heidelberg, Heidelberg, Germany

²Translational Lung Research Center Heidelberg (TLRC), German Lung Research Center (DZL), Heidelberg, Germany

³Department of Diagnostic and Interventional Radiology with Nuclear Medicine, Thoraxklinik at the University Hospital of Heidelberg, Heidelberg, Germany

,

Hans-Ulrich Kauczor

¹Department of Diagnostic and Interventional Radiology, Subdivision of Pulmonary Imaging, University Hospital of Heidelberg, Heidelberg, Germany

²Translational Lung Research Center Heidelberg (TLRC), German Lung Research Center (DZL), Heidelberg, Germany

³Department of Diagnostic and Interventional Radiology with Nuclear Medicine, Thoraxklinik at the University Hospital of Heidelberg, Heidelberg, Germany

› Author Affiliations

Abstract

Background Magnetic resonance imaging (MRI) of the pulmonary parenchyma is generally hampered by multiple challenges related to patient respiratory- and circulation-related motion, low proton density and extremely fast signal decay due to the structure of the lungs evolved for gas exchange.

Methods Systematic literature database research as well as annual participation in conferences dedicated to pulmonary MRI for more than the past 20 years by at least one member of the author team.

Results and Conclusion The problem of motion has been addressed in the past by developments such as triggering, gating and parallel imaging. The second problem has, in part, turned out to be an advantage in those diseases that lead to an increase in lung substance and thus an increase in signal relative to the background. To reduce signal decay, ultrashort echo time (UTE) methods were developed to minimize the time between excitation and readout. Having been postulated a while ago, improved hardware and software now open up the possibility of achieving echo times shorter than 200 µs, increasing lung signal significantly by forestalling signal decay and more effectively using the few protons available. Such UTE techniques may not only improve structural imaging of the lung but also enhance functional imaging, including ventilation and perfusion imaging as well as quantitative parameter mapping. Because of accelerating progress in this field of lung MRI, the review at hand seeks to introduce some technical properties as well as to summarize the growing data from applications in humans and disease, which promise that UTE MRI will play an important role in the morphological and functional assessment of the lung in the near future.

Key Points:

Ultrashort echo time MRI is technically feasible with state-of-the-art scanner hardware.
UTE MRI allows for CT-like image quality for structural lung imaging.
Preliminary studies show improvements over conventional morphological imaging in lung cancer and airways diseases.
UTE may improve sensitivity for functional processes like perfusion and tissue characterization.

Citation Format

Wielpütz MO, Triphan SM, Ohno Y et al. Outracing Lung Signal Decay – Potential of Ultrashort Echo Time MRI. Fortschr Röntgenstr 2019; 191: 415 – 423

Zusammenfassung

Hintergrund Die Herausforderungen der Magnetresonanztomografie (MRT) des Lungenparenchyms liegen in der Herz- und Atembewegung der Patienten, niedrigen Protonendichte und vor allem dem extrem schnellen Signalabfall. Dieser entsteht durch die für den Gasaustausch optimierte Lungenstruktur.

Methoden Diese Übersicht basiert auf systematischer Literaturrecherche sowie jährlicher Teilnahme an Konferenzen zum Thema Lungen-MRT über mehr als 20 Jahre durch mindestens einen Autor.

Ergebnisse und Schlussfolgerung Das Problem der Bewegung wurde durch Entwicklungen wie Triggering, Gating und parallele Bildgebung angegangen. Das Problem der geringen Protonendichte hat sich bei Krankheiten, die zu einer Zunahme an Gewebedichte und damit Signal relativ zum Hintergrund, teilweise als Vorteil erwiesen. Um den Signalabfall auszugleichen, wurden ultrashort-echo-time (UTE)-Methoden entwickelt, um die Zeit zwischen Anregung und Auslese zu minimieren. Während diese bereits vor längerer Zeit postuliert wurden, erlauben verbesserte Scanner-Hard- und -Software jetzt Echozeiten unterhalb von 200µs und damit ein signifikant höheres Signal aus der Lunge. Indem man so dem Signalabfall zuvorkommt, lässt sich das Signal der wenigen verfügbaren Protonen effizienter ausnutzen. Solche UTE-Techniken können nicht nur die morphologische Bildgebung in der Lunge verbessern, sondern auch die Möglichkeiten der funktionellen Bildgebung erweitern, einschließlich Ventilations- und Perfusions-Bildgebung sowie der Quantifizierung anderer Parameter. Dem wachsenden Fortschritt in der Lungen-MRT folgend, zeigt diese Übersicht technische Möglichkeiten und liefert einen Überblick über aufkommende Anwendungen am Menschen bzw. Krankheiten. Diese zeigen, dass die UTE-MRT in naher Zukunft eine wichtige Rolle in der morphologischen und funktionellen bildgestützten Untersuchung der Lunge spielen wird.

Kernaussagen:

Ultrashort-echo-time (UTE)-MRT ist auf modernen Scannern technisch machbar und verfügbar.
UTE-MRT erlaubt CT-artige Bildqualität für die morphologische Darstellung der Lunge.
Vorläufige Studien zeigen Verbesserungen gegenüber konventionellen Echozeiten für die morphologische Bildgebung von Lungenkrebs und Atemwegserkrankungen.
UTE-MRT könnte die Sensitivität funktioneller Prozesse wie Perfusionsquantifizierung und Gewebscharakterisierung erhöhen.

Key words

ultrashort TE - lung imaging - functional lung imaging - lung MRI

Full Text

References

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