Research papersLiver MRI: From basic protocol to advanced techniques
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.
References (61)
- et al.
New imaging techniques for liver diseases
J. Hepatol.
(2015) - et al.
Hepatic MR imaging techniques, optimization, and artifacts
Magn. Reson. Imag. Clin. N. Am.
(2014) - et al.
The ins and outs of liver imaging
Clin. Liver Dis.
(2015) - et al.
Magnetic resonance imaging of the liver: sequence optimization and artifacts
Magn. Reson. Imag. Clin. N. Am.
(2010) - et al.
Liver MR imaging: 1.5T versus 3T
Magn. Reson. Imag. Clin. N. Am.
(2007) - et al.
Diffusion-weighted imaging of the liver: techniques and applications
Magn. Reson. Imag. Clin. N. Am.
(2014) Magnetic resonance contrast agents for liver imaging
Magn. Reson. Imaging Clin. N. Am.
(2014)- et al.
The role of hepatocyte-specific contrast agents in hepatobiliary magnetic resonance imaging
Semin. Ultrasound CT MRI
(2013) - et al.
Monitoring the treatment efficacy of the vascular disrupting agent CA4P
Eur. J. Cancer
(2007) Technical aspects of MR perfusion
Eur. J. Radiol.
(2010)