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The recent technological developments in nuclear magnetic resonance (NMR) have made it possible to extend the use of this methodology to the formation of body images (MRI), as well as to the in vivo detection of metabolites in tissues and organs, by means of localized magnetic resonance spectroscopy (MRS). After presenting a brief semi-classical introduction to the NMR phenomenon, this article illustrates the principles of MRI, starting from phase encoding to the most commonly used pulse sequences. The main techniques of localized MRS are then introduced, with particular attention to their major advantages and limitations. The last session is devoted to the schematic description of a system for magnetic resonance imaging and spectroscopy.

This chapter summarizes requirements, rationale and main steps in the recent evolution of protocols adopted at international level for quality controls in clinical magnetic resonance imaging (MRI) and spectroscopy (MRS). An accurate assessment of instrumental performance in MRI and MRS is essential for enhancing the clinical value of these methodologies, both in terms of anatomical and physio-pathological information. In the field of MRI, a series of Concerted Actions, carried out in the frame of the medical and health research programmes of the European Economic Communities (EEC), led to the definition of standardized methodologies and to the construction of five test objects for assessing the quality of fourteen instrumental parameters, inherent to: signal uniformity and linearity; geometry; slice position and thickness; spatial resolution; signal-to-noise and contrast-to-noise ratios; T1 and T2 precision and accuracy. The first part of this paper devotes particular attention to the protocols adopted by the EEC Concerted Actions and by the National Electrical Manufacturers Association (NEMA, US), for assessing signal uniformity, geometric distortion and signal-to-noise ratio in MRI. A brief description is also given of the rationale and protocols for measuring other MRI parameters. The second part is devoted to describe eleven parameters of instrumental performance, two test objects and the measuring protocols recently proposed by the EEC Concerted Actions for quality control in single-volume localized MRS, following their validation in a series of experimental multi-centre trials.

This review summarizes experimental bases, limitations and rationale of guide-lines and recommendations adopted by national health authorities for the safety of patients exposed to the magnetic fields utilized during magnetic resonance (MR) examinations: static magnetic field (B0); time-varying magnetic field gradients (dB/dt) and radiofrequency magnetic fields. Although the mechanisms of interaction of these fields with the living matter are today sufficiently understood to identify the main categories of potentially associated health hazards, epidemiological studies and dosimetric concepts are still far from the levels of definition of protection standards adopted in the field of ionizing radiations. The definition of safety thresholds and levels of exposure to magnetic fields during MR examinations has evolved in the last decade and the matter is still under study today. This article summarizes the main steps in this continuous updating process and discusses limitations and criteria, which recently suggested the adoption in some Countries (including Italy) of a two-tier system for the levels of exposure of patients to the magnetic fields generated by clinical MR equipment.

Recent technological developments extended the use of nuclear magnetic resonance to clinical imaging (MRI), as well as to in vivo metabolic studies on tissues and organs by means of localized spectroscopy (MRS). The quantitative determination of absolute metabolic concentrations by in vivo MRS still represents a challenge for technological efforts and biochemical investigations. In fact, the different methodologies today available for spectral acquisition from localized regions within a body organ or pathological lesion should ideally lead to a complete suppression of signals from surrounding tissues, without any appreciable signal loss from the volume of interest. Accurate assessment of deviations of the real from the ideal case represents an essential requirement for either relative or absolute quantification of in vivo localized MR spectra. A review will be presented of the most utilized MRS methodologies, together with a discussion on their potentialities and limitations. Techniques have been classified according to the use of either r.f. (B1) and/or static magnetic field (B0) gradients. The last session will be devoted to the presentation of some results obtained in our laboratory on the use of a particular test-object (constructed at the Deft Institute of Technology) for assessing signal localization efficiency provided by a surface coil in a small scale MRS/MRI equipment (for in vivo biochemical studies on small animals). The surface coil was used in conjunction with a number of sequence (t1-90 degrees-acq; 1-D "chemical shift imaging"; "depth") of either square or adiabatic r.f. pulses. The results allow the selection, on a quantitative basis, of the most appropriate pulse sequence(s) to be used for metabolic studies on superficial experimental tumours (implanted s.c. in small animals), according to the mean area and thickness of the neoplastic lesion. The latter parameters can be non-invasively assessed by previous MRI analysis of the tumour. This study was carried out in the frame of the EC COMAC-BME Concerted Research Project on Tissue Characterization by MRS and MRI.

Nuclear magnetic resonance (NMR) and positron emission tomography (PET) are among the most advanced methodologies providing, with different physical approaches, diagnostic images of the body. In this framework, NMR and PET are particularly well known, not only for the high quality of their present results, but also for the expectations of further developments at clinical and diagnostic level. Common feature of NMR and PET is the capability of associating the anatomical image with information on the physico-chemical and/or biochemical properties of tissues. NMR imaging (MRI) is in fact based upon the acquisition of signals, whose intensities indirectly but closely depend upon particular physico-chemical and biophysical properties of biological tissues. NMR spectroscopy (MRS) and PET allow, on the other hand, quantitative studies on metabolic reactions, as they occur in intact tissues, in vivo and in situ. This review is aimed at summarizing the basic principles of tissue characterization by NMR and PET and discussing their perspectives of clinical application. Emphasis will be given to the special requirements of tissue characterization by these methodologies, referring to the need of improving accuracy and precision of measurements, as well as at evaluating, on a quantitative basis, the performance of the equipment.