Magnetic Resonance Imaging: Principles and Techniques: Lessons for Clinicians

Abstract

The development of magnetic resonance imaging (MRI) for use in medical investigation has provided a huge forward leap in the field of diagnosis, particularly with avoidance of exposure to potentially dangerous ionizing radiation. With decreasing costs and better availability, the use of MRI is becoming ever more pervasive throughout clinical practice. Understanding the principles underlying this imaging modality and its multiple applications can be used to appreciate the benefits and limitations of its use, further informing clinical decisionmaking. In this article, the principles of MRI are reviewed, with further discussion of specific clinical applications such as parallel, diffusion-weighted, and magnetization transfer imaging. MR spectroscopy is also considered, with an overview of key metabolites and how they may be interpreted. Finally, a brief view on how the use of MRI will change over the coming years is presented. ( J CLIN EXP HEPATOL 2015;5:246-255) T he nuclear magnetic resonance (NMR) phenomenon was first described experimentally by both Bloch and Purcell in 1946, for which they were both awarded the Nobel Prize for Physics in 1952.1,2 The technique has rapidly evolved since then, following the introduction of wide-bore superconducting magnets (approximately 30 years ago), allowing development of clinical applications. The first clinical magnetic resonance images were produced in Nottingham and Aberdeen in 1980, and magnetic resonance imaging (MRI) is now a widely available, powerful clinical tool. 3,4 This article covers a brief synopsis of basic principles in MRI, followed by an overview of current applications in medical practice.All atomic nuclei consist of protons and neutrons, with a net positive charge. Certain atomic nuclei, such as the hydrogen nucleus, 1 H, or the phosphorus nucleus, 31 P, possess a property known as ''spin'', dependent on the number of protons. This can be conceived as the nucleus spinning around its own axis although this is a mathematical analogy. The nucleus itself does not spin in the classical meaning but by virtue of its constituent parts induces a magnetic moment, generating a local magnetic field with north and south poles. The quantum mechanical description of this dipolar magnet is analogous to classical mechanics of spinning objects. The dipole itself is analogous to a bar magnet, with magnetic poles aligning along its axis of rotation (Figure 1 , ). 5Application of a strong, external magnetic field (B 0 ) aligns the nucleus either in parallel with or perpendicular to the external field. A liquid solution containing many nuclear spins, placed within the B 0 field, will contain nuclear spins in one of two energy states: a low-energy state (oriented parallel to the magnetic field) or a high-energy state (orientated perpendicular to the magnetic field direction). In solids or liquids, there would tend to be an excess of spins in the same direction as B 0 . Although a bar magnet would orientate completely parallel or antiparallel to the field, the nucleus has an...

Dendrimer-Trastuzumab Contrast Agent Improves Imaging of Magnetic Resonance Imaging (MRI) On Her2 Positive Breast Cancer Cell Line HCC-1954 in Apple Scaffold

“…The advantage of MRI imaging compared to CT scan are a non-ionizing radiation imaging, multiple image/multiplanar drawing images, good spatial resolution, no bone artifact, noninvasive and superior able to assess soft tissues such as breast cancer [1]. The general approach to MRI data analysis involves the extraction of signals from a given area.…”

“…The general approach to MRI data analysis involves the extraction of signals from a given area. The use of ROI analysis becomes standard practice across all MRI imaging [1,2].…”

Fetal magnetic resonance imaging and ultrasound

“…Optimal application of MRI is fostered by manufacturing of MRI machines that have stronger field strengths. Improvement of MRI image acquisition is a result of ultrafast sequence protocols and better postacquisition image processing and rendering [3]. Fetal MRI technologies, in addition to rapid progressions in prenatal molecular genetics diagnosis and the availability of in utero intervention, have revolutionized obstetric practice.…”

Detection of Prostate Cancer Metastasis by Whole Body Magnetic Resonance Imaging Combined with Bone Scintigraphy and PSA Levels

“…MRI therein applies electromagnetic waves emitted by gradient magnetic field to visualize the internal structure of objects, and it is advantageous in multiplanar imaging and tissue characterization [7,8]. The advent of MRI has been greatly valued clinically, including diagnosing and predicting prognosis of heart disease, lung cancer and gastric carcinoma [9][10][11].…”

“…The advent of MRI has been greatly valued clinically, including diagnosing and predicting prognosis of heart disease, lung cancer and gastric carcinoma [9][10][11]. As a kind of MRI technique, diffusion-weighted imaging (DWI) was firstly introduced to examine intensive brain ischemia and other symptoms like multiple sclerosis and cerebral cancer in the early 1990s [8,12,13]. DWI distinguished tumor tissues from normal tissues through quantification of water molecule diffusion, which was particularly manifested as restricted water molecule movements within tumor tissues in comparison to those within normal tissues [14,15].…”