Elsevier

European Journal of Radiology

Volume 93, August 2017, Pages 30-39
European Journal of Radiology

Research papers
Liver MRI: From basic protocol to advanced techniques

https://doi.org/10.1016/j.ejrad.2017.05.028Get rights and content

Highlights

  • Liver MR is a well-established multiparametric imaging modality.

  • Standard protocol includes T1, T2, diffusion and contrast-enhanced sequences.

  • High field strength (3T) exams require adaptations to the imaging protocol.

  • Advanced MR techniques can give new valuable information.

Abstract

Liver MR is a well-established modality with multiparametric capabilities. However, to take advantage of its full capacity, it is mandatory to master the technique and optimize imaging protocols, apply advanced imaging concepts and understand the use of different contrast media. Physiologic artefacts although inherent to upper abdominal studies can be minimized using triggering techniques and new strategies for motion control. For standardization, the liver MR protocol should include motion-resistant T2-w sequences, in-op phase GRE T1 and T2-w fast spin echo sequences with fat suppression. Diffusion-weighted imaging (DWI) is mandatory, especially for detection of sub-centimetre metastases. Contrast-enhanced MR is the cornerstone of liver MR, especially for lesion characterization. Although extracellular agents are the most extensively used contrast agents, hepatobiliary contrast media can provide an extra-layer of functional diagnostic information adding to the diagnostic value of liver MR. The use of high field strength (3T) increases SNR but is more challenging especially concerning artefact control. Quantitative MR belongs to the new and evolving field of radiomics where the use of emerging biomarkers such as perfusion or DWI can derive new information regarding disease detection, prognostication and evaluation of tumour response. This information can overcome some of the limitations of current tests, especially when using vascular disruptive agents for oncologic treatment assessment. MR is, today, a robust, mature, multiparametric imaging modality where clinical applications have greatly expanded from morphology to advanced imaging. This new concept should be acknowledged by all those involved in producing high quality, high-end liver MR studies.

Introduction

MR is a well-established liver imaging modality that has been subject to continuous improvement, through advances in hardware, software and contrast agent development [1], [2]. It provides a comprehensive assessment of tissue characteristics through its multiparametric capabilities, providing accurate qualitative and quantitative data [3], [4].

When compared to its main competitor CT, MR has a higher contrast-to-noise ratio (CNR), lack of ionizing radiation exposure and uses contrast agents with the ability to explore both extracellular and hepatocellular compartments [2], [3], [5].

There are however some constraints, like higher cost, longer acquisition time, greater need for patient collaboration and individual patient limitations, like claustrophobia, presence of pacemakers and poor renal function, the latter specifically for contrast-enhanced MR (DCE-MR) [5].

In order to use the abilities of liver MR to its full extent, performing high quality efficient exams, it is mandatory to use the best imaging protocol, to optimize the technique, to minimize artefacts and to select the most adequate type of contrast agent [4].

Patients should receive general instructions regarding the magnetic field, highlighting the importance of immobilization throughout the entire exam and the need for a shallow, regular breathing motion, crucial for free-breathing and respiratory-triggering techniques [6], [7]. Breath-hold acquisitions should also be explained at the beginning of the exam [6]. Placing the patient in a comfortable supine position, which may include knee support by a foam pad, is important for immobilization and compliance to other instructions [6], [7]. Placing an abdominal cushion may be useful to minimize dielectric effect observed on 3T magnets [8], [9].

Section snippets

Standard liver protocols

An adequate MRI protocol has to be short, comprehensive and standardized to allow reproducibility and consistency of image quality and diagnostic information. It allows evaluation of the liver parenchyma, vasculature and biliary system [2]. Examples of sequence parameters are displayed in Table 1.

Liver MR at 1.5T and 3T

Scanners operating at a 3T magnetic field have been introduced and rapidly evolved over the last decade. These scanners take advantage of the increased SNR provided by 3T fields relative to 1.5T, which is used to improve spatial resolution, to lower the acquisition time or a combination of the two [8], [11], [17].

In most tissues, T1 relaxation times are generally longer at 3T compared to 1.5T, while T2 relaxation times are almost unaffected. There is also greater fat and water spectral

Perfusion MR

In recent years there has been an increasingly wide use and development of vascular targeting agents, such as antiangiogenic drugs and vascular disruption agents (VDAs), for clinical use in the treatment of cancer as well as in clinical trials [22], [23], [24], [25]. Considering the cytostatic nature of vascular targeting agents it has been suggested that the effect of vascular targeting therapies may be better assessed by evaluating the functional changes in tumour tissue than by observing the

Conflicts of interest

The authors have no conflicts of interest to disclose.

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