Transient Respiratory-motion Artifact and Scan Timing during the Arterial Phase of Gadoxetate Disodium-enhanced MR Imaging: The Benefit of Shortened Acquisition and Multiple Arterial Phase Acquisition

Abstract

Purpose: To investigate whether shortened acquisition or multiple arterial phase acquisition improves image quality of the arterial phase compared with conventional protocol.

Methods: This retrospective study was approved by the relevant Institutional Review Board. A total of 615 consecutive patients who underwent gadoxetate disodium-enhanced MRI including one of the following three sequences in three different periods were included: (i) conventional liver acquisition with volume acceleration (LAVA) (between October 2014 and January 2015, n = 149), (ii) Turbo-LAVA (between March and August 2016, n = 216), and (iii) differential sub-sampling with Cartesian ordering (DISCO) (between January and September 2015, n = 250). We monitored the respiratory bellows waveform during breath holding for each patient and recorded breath-hold fidelity of the patients. Two radiologists independently evaluated the degree of respiratory artifact and scan timing on the arterial phase and compared them between the three protocols (i.e., conventional LAVA, Turbo-LAVA, and DISCO), with conventional LAVA as control.

Results: The ratio of patients with breath-hold failure was not significantly different among the three protocols (P = 0.6340 and 0.1085). Respiratory artifact was significantly lower in DISCO than in conventional LAVA (P = 0.0424), while there was no significant difference between Turbo-LAVA and conventional LAVA (P = 0.2593). The ratio of adequate scan timing and diagnosable image defined as no or mild artifact and adequate scan timing were higher in DISCO than in conventional LAVA (P = 0.0025 and 0.0019), while there was no significant difference between Turbo-LAVA and conventional LAVA (P = 0.0780 and 0.0657).

Conclusion: Compared with conventional protocol, multiple arterial phase acquisition (DISCO) obtained a higher number of diagnosable images by reducing respiratory motion artifact and optimizing the scan timing of arterial phase.

Keywords: artifacts; gadoxetate disodium; image reconstruction; liver; magnetic resonance imaging.

Fig. 1

Classification of breath-hold status. Breath-hold status was assessed by using respiratory bellows monitors for precontrast and arterial phase acquisitions. Breath-hold success was defined as a straight or slowly varying trace during the image acquisition (left). Breath-hold failure was defined as a jagged trace during the image acquisition or the onset of sudden pronounced oscillations (right).

Fig. 2

Sample images of respiratory artifact grading. Respiratory artifact was assessed using a 4-point visual score (1, no artifact; 2, mild = respiratory artifact is present but not interfering with the depiction of intrahepatic structures; 3, moderate = respiratory artifact is present and interfering with the depiction of intrahepatic structures; 4, severe = non-diagnostic images with marked artifact).

Fig. 3

Sample images of scan timing of arterial phase grade. Scan timing of arterial phase was assessed as adequate or not. Adequate timing was defined as images with appropriate enhancement of hepatic artery and portal vein (arrow) without enhancement of hepatic vein (dotted arrow). Too early [without enhancement of portal vein (arrow)] and too late [enhancement of hepatic vein (dotted arrow)] scan timing were considered as inadequate scan timing.

Fig. 4

Relationship between breath-hold failure and diagnosable image in each sequence. Diagram shows overlap of breath-holding failure and diagnosable image. In DISCO, diagnosable images were obtained in 71.2% (37/52) of breath-hold failure cases, while in conventional LAVA, diagnosable images were obtained in only 33.3% (7/21) of breath-hold failure cases. In Turbo-LAVA, diagnosable images were obtained in 50.0% (13/26) of breath-hold failure cases. DISCO, differential sub-sampling with Cartesian ordering; LAVA, liver acquisition with volume acceleration.

Fig. 5

Example of images in each acquisition sequence. Arterial phase images obtained by conventional LAVA (66-year-old man with hepatitis C, left), Turbo-LAVA (66-year-old woman with hepatitis C, middle), and DISCO (67-year-old man with hepatitis B, right). All of them show no respiratory artifact and adequate scan timing defined as diagnosable images. DISCO, differential sub-sampling with Cartesian ordering; LAVA, liver acquisition with volume acceleration.

Fig. 6

Representative magnetic resonance images of the breath-hold failure case. A 63-year-old woman with hepatitis C showed breath-hold failure. Various grades of respiratory motion artifacts were observed in DISCO sequence (mild in third phase, moderate in fourth phase, and severe in fifth and sixth phases). However, diagnosable images (no or mild artifact and adequate scan timing of arterial phase) were obtained in the first, second, and third phases. DISCO, differential sub-sampling with Cartesian ordering.