Fast 3D Isotropic Proton Density-Weighted Fat-Saturated MRI of the Knee at 1.5 T with Compressed Sensing: Comparison with Conventional Multiplanar 2D Sequences

Abstract

Purpose Compressed sensing (CS) is a method to accelerate MRI acquisition by acquiring less data through undersampling of k-space. In this prospective study we aimed to evaluate whether a three-dimensional (3D) isotropic proton density-weighted fat saturated sequence (PDwFS) with CS can replace conventional multidirectional two-dimensional (2D) sequences at 1.5 Tesla.

Materials and Methods 20 patients (45.2 ± 20.2 years; 10 women) with suspected internal knee damage received a 3D PDwFS with CS acceleration factor 8 (acquisition time: 4:11 min) in addition to standard three-plane 2D PDwFS sequences (acquisition time: 4:05 min + 3:03 min + 4:46 min = 11:54 min) at 1.5 Tesla. Scores for homogeneity of fat saturation, image sharpness, and artifacts were rated by two board-certified radiologists on the basis of 5-point Likert scales. Based on these ratings, an overall image quality score was generated. Additionally, quantitative contrast ratios for the menisci (MEN), the anterior (ACL) and the posterior cruciate ligament (PCL) in comparison with the popliteus muscle were calculated.

Results The overall image quality was rated superior in 3D PDwFS compared to 2D PDwFS sequences (14.45 ± 0.83 vs. 12.85 ± 0.99; p < 0.01), particularly due to fewer artifacts (4.65 ± 0.67 vs. 3.65 ± 0.49; p < 0.01) and a more homogeneous fat saturation (4.95 ± 0.22 vs. 4.55 ± 0.51; p < 0.01). Scores for image sharpness were comparable (4.80 ± 0.41 vs. 4.65 ± 0.49; p = 0.30). Quantitative contrast ratios for all measured structures were superior in 3D PDwFS (MEN: p < 0.05; ACL: p = 0.06; PCL: p = 0.33). In one case a meniscal tear was only diagnosed using multiplanar reformation of 3D PDwFS, but it would have been missed on standard multiplanar 2D sequences.

Conclusion An isotropic fat-saturated 3D PD sequence with CS enables fast and high-quality 3D imaging of the knee joint at 1.5 T and may replace conventional multiplanar 2D sequences. Besides faster image acquisition, the 3D sequence provides advantages in small structure imaging by multiplanar reformation.

Key Points: 

• 3D PDwFS with compressed sensing enables knee imaging that is three times faster compared to multiplanar 2D sequences

• 3D PDwFS with compressed sensing provides high-quality knee imaging at 1.5 T

• Isotropic 3D sequences provide advantages in small structure imaging by using multiplanar reformations

Citation Format

• Endler CH, Faron A, Isaak A et al. Fast 3D Isotropic Proton Density-Weighted Fat-Saturated MRI of the Knee at 1.5 T with Compressed Sensing: Comparison with Conventional Multiplanar 2D Sequences. Fortschr Röntgenstr 2021; 193: 813 – 821

Zusammenfassung

Ziel Compressed Sensing (CS) ist eine Signalverarbeitungstechnik, mithilfe derer man durch Unterabtasten des k-Raums weniger Daten akquirieren und so MRT-Aufnahmen beschleunigen kann. Ziel dieser prospektiven Studie war die Klärung der Frage, ob eine 3-dimensionale (3D) isotrope protonengewichtete fettgesättigte Sequenz (PDwFS) mit CS konventionelle multidirektionale 2-dimensionale (2D) Sequenzen bei 1,5 T ersetzen kann.

Material und Methoden 20 Patienten (45,2 ± 20,2 Jahre; 10 Frauen) mit Verdacht auf Kniebinnenschaden erhielten am 1,5T-MRT zusätzlich zu den konventionellen, in 3 Ebenen angefertigten 2D-PDwFS (Akquisitionszeit: 4:05min + 3:03min + 4:46min = 11:54 min) eine 3D-PDwFS mit CS-Beschleunigungsfaktor 8 (Akquisitionszeit: 4:11 min). Die Homogenität der Fettunterdrückung, die Bildschärfe und Artefakte wurden anhand von 5-Punkt-Likert-Skalen durch 2 erfahrene Radiologen beurteilt. Anhand der so vergebenen Punkte wurde die Gesamtbildqualität ermittelt. Zusätzlich wurden quantitative Kontrastverhältnisse für die Menisken (MEN), das vordere (ACL) und das hintere Kreuzband (PCL) im Vergleich zum Musculus popliteus errechnet.

Ergebnisse Die Gesamtbildqualität wurde in der 3D-PDwFS höher als in den 2D-PDwFS-Sequenzen bewertet (14,45 ± 0,83 vs. 12,85 ± 0,99; p < 0,01), insbesondere aufgrund weniger Artefakte (4,65 ± 0,67 vs. 3,65 ± 0,49; p < 0,01) und einer homogeneren Fettunterdrückung (4,95 ± 0,22 vs. 4,55 ± 0,51; p < 0,01). Die Bildschärfe ergab keinen signifikanten Unterschied (4,80 ± 0,41 vs. 4,65 ± 0,49; p = 0,30). Die quantitativen Kontrastverhältnisse waren in den 3D-PDwFS für alle gemessenen Strukturen höher als in den 2D-PDwFS (MEN: p < 0,05; ACL: p = 0,06; PCL: p = 0,33). In einem Fall konnte ein Meniskusriss lediglich mithilfe einer multiplanaren Reformatierung der 3D-PDwFS diagnostiziert werden und wäre auf den konventionellen multiplanaren 2D-Sequenzen übersehen worden.

Schlussfolgerung Eine isotrope fettgesättigte 3D-PD-Sequenz mit CS ermöglicht eine schnelle und qualitativ hochwertige 3D-Bildgebung des Kniegelenks bei 1,5 T und könnte konventionelle multiplanare 2D-Sequenzen ersetzen. Neben einer schnelleren Bildakquise bietet die 3D-Sequenz Vorteile in der Bildgebung kleiner Strukturen.

Kernaussagen: 

• 3D-PDwFS mit Compressed Sensing ermöglicht eine 3-fach schnellere Knie-Bildgebung verglichen mit multiplanaren 2D-Sequenzen.

• 3D-PDwFS mit Compressed Sensing ermöglicht eine qualitativ hochwertige Knie-Bildgebung bei 1,5 T.

• Isotrope 3D-Sequenzen bieten Vorteile in der Darstellung kleiner Strukturen durch die Möglichkeit der multiplanaren Reformation.

Key words

3D sequence - knee imaging - MRI - meniscal tear - compressed sensing

Publication History

Received: 15 October 2020

Accepted: 09 December 2020

Article published online:
03 February 2021

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