Non-enhanced T1-weighted liver vessel imaging at 7 Tesla.

Anja Fischer,Lale Umutlu,Michael Forsting,Stefan Maderwald,Thomas C Lauenstein,Mark E Ladd,Karsten Beiderwellen,Oliver Kraff,Jeroen Hendrikse

doi:10.1371/journal.pone.0097465

Abstract

ObjectivesAim of the study was to assess the feasibility and to compare three non-enhanced T1-weighted (w) sequences for liver vessel imaging at 7 Tesla (T).Material and Methods12 healthy volunteers were examined on a 7 T whole-body MR-system. The following non-enhanced sequences were acquired: T1w 2D FLASH, T1w 3D FLASH and Time of flight (TOF)-MRA. Qualitative image analysis was performed by two radiologists including over all image quality as well as vessel delineation of the liver arteries, liver veins and portal vein and the presence of artifacts using a five-point scale (5 = excellent vessel delineation to 1 = non-diagnostic). Contrast ratios (CR), SNR und CNR of the above named vessels in correlation to adjacent liver tissue were calculated for quantitative assessment. For statistical analysis, a Wilcoxon Rank Test was applied.ResultsAll three sequences provided a homogenous hyperintense delineation of the assessed liver vessels. Qualitative image analysis demonstrated the superiority of TOF-MRA, providing best overall image quality (TOF 4.17, 2D FLASH 3.42, 3D FLASH 3.46; p<0.01) as well as highest image quality values for all analyzed liver vessel segments. TOF-MRA was least impaired by B1 inhomogeneity (4.13) and susceptibility artifacts (4.63) out of all three sequences (p<0.01). Quantitative image analysis confirmed the superiority of TOF MRA showing significant higher CR values for all liver vessels (e.g. right hepatic artery TOF 0.47, 2D FLASH 0.09, 3D FLASH 0.11 with p = 0.02 and 0.01, respectively). Providing the lowest standard deviation in noise, TOF showed highest values for SNR and CNR.ConclusionsNon-enhanced T1w imaging in general and TOF MRA in particular, appear to be promising techniques for high quality non-enhanced liver vessel assessment at 7 T.

Highlights

Over the last decades, contrast-enhanced CT angiography and MR angiography (MRA) have been established as the imaging techniques of choice to assess liver vessel anatomy prior to hepatectomy or liver transplantation [1,2]
Quantitative image analysis confirmed the superiority of Time of flight (TOF) MRA showing significant higher Contrast ratios (CR) values for all liver vessels
As CT angiography deploys ionizing radiation and the application of contrast agent in general bears the potential of side effects and is restricted in case of renal insufficiency [3], the focus of scientific research has shifted towards non-enhanced MRA techniques within the last few years

Summary

Introduction

Contrast-enhanced (ce) CT angiography and MR angiography (MRA) have been established as the imaging techniques of choice to assess liver vessel anatomy prior to hepatectomy or liver transplantation [1,2]. Several studies at lower field strength (1.5 Tesla) have demonstrated the diagnostic potential of non-contrast-enhanced liver vessel imaging, utilizing true steady-state free-precession sequences and time-spatial labeling inversion pulses. Shimada et al reported initial results of 3D true SSFP imaging utilizing a spatial labeling inversion pulse to visualize hepatic arterial and venous vasculature, selectively achieving high arterial and venous vessel contrast and good suppression of the portal veins and surrounding static tissue [4,5,6]. The increase of the magnetic field strength to 3 T has been proven beneficial in terms of achieving higher spatiotemporal resolution, as well as enabling comparable or improved delineation of vessel structures [7]. With SSFP and T2 TSE imaging being restricted at ultra-high-field strength, most studies on 7 Tesla non-enhanced MRA have focused on T1-weighted imaging, utilizing the inherently hyperintense vessel signal at 7 T

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