Clinical MR Spectroscopy: Techniques and Applications

Clinical MR Spectroscopy - Techniques and Applications explains both the underlying physical principles of MRS and provides a perceptive.
Table of contents

It gives the reader a solid basis for understanding both the techniques and the applications of clinical MRS. The book is organized into 14 chapters. Chapter 1 introduces in vivo MRS, and chapter 2 discusses pulse sequences and protocol design.

Supplemental Content

Chapter 3 addresses spectral analysis methods, quantitation, and common artifacts, and chapter 4 handles normal regional variations, particularly brain development and aging. The rest of the chapters discuss MRS findings in brain tumors; in stroke and hypoxic—ischemic encephalopathy; in infectious, inflammatory and demyelinating lesions; in epilepsy; in neurodegenerative diseases; in traumatic brain injury; in cerebral metabolic disorders; in prostate cancer; in breast cancer; and in musculoskeletal diseases.


  1. So Enchanting.
  2. Clinical Application of MR Spectroscopy and Imaging of Brain Tumor..
  3. An A-Z of Modern America;
  4. Das achte Loch (Die haarsträubenden Fälle des Philip Maloney 14) (German Edition).
  5. Result Filters.

Each chapter begins with key points and ends with recommendations and a conclusion. References are updated and useful. The aim of this book is to serve as a practical reference work that covers all aspects of in vivo human spectroscopy for clinical purposes. The book explains physical principles and provides a comprehensive and perceptive review of clinical applications. Also discussed are the limitations of MRS, such as its low spatial resolution when compared with MRI, common artifacts, and diagnostic pitfalls.

More widespread adoption of MRS into the clinic will lead to better diagnoses and improved outcomes for individual patients. The recent improvements in spatial resolution have been impressive and the technique is slowly becoming more quantitative. Given the flexibility of clinical magnetic resonance techniques, particularly magnetic resonance imaging, it is likely that MRI will be the diagnostic tool of choice in a wider range of diseases, such as multiple sclerosis, stroke, neurodegenerative conditions, sports injuries and in staging malignancies. Since proton magnetic resonance spectroscopy packages have become a routine addition to many MRI systems, it is feasible to select the MRI sequences of most value in highlighting anatomical and pathological abnormalities and to incorporate specifically selected MRS sequences to emphasize biochemical differences.

Improvements in technical methodologies are central to further developments. For example, use of internal coils, such as implantable or endoscopic coils, will enable small regions of tissue to be studied in considerable detail, which may otherwise be inaccessible to measurement. Chemical MRS studies have benefited from the use of higher magnetic fields, and the same may be expected for clinical MRS studies. Whole-body magnets up to 4 T have been used in a few centres, and certainly 3 T systems are becoming more widely available with the recent tremendous interest in functional imaging.

Certainly, better control of artefacts can be expected; for example, improved definition of spectral changes due to voluntary or involuntary movements. Wider use of proton decoupling methods will improve the specificity of the spectra, by allowing definitive assignments of overlapping resonances, as well as the sensitivity. The sensitivity and spatial resolution of MRS is a limiting factor in vivo , but parallel utilisation of in vitro MR spectroscopy of tissue extracts, body fluids and cell lines at much higher magnetic field strengths typically In this article, we aim to equip the clinician with knowledge of the background physics involved in MRS, so that informed decisions can be made for research studies.

Introduction

NMR refers to the behaviour of atoms subjected to a magnetic field. The phenomenon was first described in by Bloch and Purcell. During relaxation following excitation, radiofrequency signals are generated which can be expressed as a frequency spectrum.

Magnetic Resonance Spectroscopy: Principles and Techniques: Lessons for Clinicians

Nuclear resonance occurs because the nuclei of at least one of the isotopes of most elements possess a magnetic moment. When placed in a constant magnetic field, nuclei that possess spin can be excited, the energy of the magnetic moment depends on the orientation of the nucleus with respect to that field. In an applied magnetic field, the magnetic moments of nuclei become oriented relative to the direction of the applied field in a number of ways, determined by the nuclear spin quantum number, I.

Electromagnetic radiation in the radio-frequency range causes transitions between the two energy levels, giving the possibility of 1 H NMR spectra. Resonant absorption by nuclear spin will occur only when electromagnetic radiation of the correct frequency Larmor precession rate is applied to match the energy difference between the nuclear spin levels in a constant magnetic field of appropriate strength.

In a molecule, the magnetic field that a particular proton experiences is influenced by that due to the motions of nearby electrons the chemical environment to which it is subjected. Differently sited protons experience slightly different effective applied fields and resonate at slightly different frequencies; it is this which gives 1 H NMR its diagnostic value, as this property can be used to discern different proton environments within molecules.

Nuclear MRS

Thus, the magnetic environment experienced by each MR sensitive nucleus may be different. Although all nuclei are dominated by the static magnetic field strength, B 0 , and by the applied field B 1 , they will also experience a local magnetic field due to the magnetic fields of the electrons within their immediate chemical environment. Thus, the degree of shielding or enhancement of the local magnetic field by electron currents depends upon the exact electronic environment, which is a function of the precise chemical structure of the molecule.

When protons occur in more than one kind of environment within a molecule, circumstances may allow their spins to interact with one another. The influence of one proton's spin on another is due to the shielding effects of its electrons, which can cause the magnetic energy experienced by a neighbouring proton to be slightly stronger or weaker if the magnetic moment of the neighbouring proton is parallel or perpendicular to the magnetic force applied.

In reality, roughly half of the neighbouring protons are found to be parallel and half perpendicular to the external magnetic field. Therefore, a proton's NMR signal can be found as a split peak, with one peak shifted downfield slightly on NMR and one shifted upfield slightly. This effect is known as spin-spin coupling and it can be seen in different forms in MRS. Its interpretation can allow for finely detailed analysis of the molecular structure being analysed. The rate of signal decay is characterised by both spin lattice T 1 and spin-spin T 2 relaxation times.

Development and applications of in vivo clinical magnetic resonance spectroscopy.

Resonance is obtained by superimposing weak oscillating field B 1 on the field B 0 generated by a receiver coil 5 ; signal production is achieved by applying a short, intense pulse of radiofrequency energy to the sample under test, which is absorbed by the nuclei present. After the applied pulse has terminated, the sample emits signals for a time, while various transitions return to their equilibrium state. Fourier transformation from free induction decay to MR spectrum. The phenomenon of chemical shift therefore gives rise to a MR frequency spectrum consisting of nuclei which resonate at different frequencies.

The frequency depends on the exact magnetic field strength, so it is usually expressed in dimensionless units parts per million, ppm , by reference to a specific material; in 1 H MR spectroscopy, this is often water at 4. Peaks in the MR spectra are also called resonances. Some metabolites may be split into two doublet or more sub-peaks. The area beneath the peak represents the concentration of the metabolite. Absolute quantification of metabolites is theoretically possible, but can be difficult to achieve accurately owing to factors including T 1 and T 2 effects. A number of other techniques can also be employed to increase result reliability.

Protons will resonate in the form of a sine wave and each of these waves will possess a phase. Not all the protons in the samples will possess the same phase. Therefore, when the FID is Fourier transformed, some resonances will display positive peaks, some will display negative peaks and some in between.


  1. Unlocking potential with the best learning and research solutions?
  2. Spiritual Health and Healing: The Art of Living.
  3. $171.00 (G)!
  4. Putin: Russias Choice.
  5. Dead by Any Other Name (A Janets Planet Mystery)!
  6. Clinical Application of MR Spectroscopy and Imaging of Brain Tumor. - PubMed - NCBI.
  7. Truffles by the Sea (Chocolate Series Book 2).

By multiplying the spectrum by a phase correction, which can be applied to the whole spectrum, all peaks can be corrected to positive and symmetrical line shapes. Baseline errors can be corrected using automated or manual software so that all spectra have a baseline starting at a y -value of 0. This has the effect of truncating the FID tail, so that resonances from noise are not Fourier transformed, resulting in an increased signal-to-noise ratio.

The NMR signal is collected as a series of data points by the receiver coil. By adding an equal number of zeros to the original number or data points done simply by the computer , the number of data points increases, which in turn improves line shapes in the resultant NMR spectrum. This manipulation has no effect on signal resolution, and it is purely cosmetic.

Magnetic fields of the strength used for in vitro high resolution NMR spectroscopy can only be generated by superconducting magnets. The field is generated by passing a current through a wire coil. Passing vertically through the centre of the machine is a room temperature zone into which the sample is placed Figure 4. Schematic diagram of a nuclear magnetic resonance system.

MR Spectroscopy in Brain - DRE 10 - Prof. Dr. Mamdouh Mahhfouz

A, outer shell; B, liquid nitrogen; C, liquid helium; D, solenoid wire coil; E, shim coils; F, receiver and radiofrequency pulse coils; G, biofluid sample. To obtain precision, the magnetic field needs to be as homogenous across the sample as possible. The magnet alone, even though it generates a very strong field, is not able to achieve this.

Shim coils are small wire coils placed strategically around the sample, through which current is transmitted, generating small, local magnetic fields which can be individually altered to provide a near homogenous field. This is achieved by continuous monitoring of a designated signal usually deuterated hydrogen and adjusting the field by small amounts to keep this signal at the same frequency.

In vivo , single voxel spectroscopy or chemical shift imaging are most commonly used for MRS. Single voxel spectroscopy defines voxels of interest within an organ using gradients. Voxel size used is predefined by the user. Use of smaller voxels requires a higher number of signal averages to be acquired in order to improve the signal-to-noise ratio, and this leads to a longer scan duration.

Chemical shift imaging CSI uses a matrix of voxels to form the spectra. Theoretically, this can be done in all three directions, but practically, is usually done in one plane, giving 2D single slice CSI. Single voxel spectroscopy creates superior image quality, but CSI allows greater anatomical coverage.

Ideally, when using a clinical whole-body magnet system, signal loss due to T 1 relaxation and T 2 decay should be avoided. A longer TE would attenuate the signal from unwanted macromolecule resonances, such as from lipids. Numerous different in vivo MRS sequences have been developed for clinical whole-body MRS, differing in pulse sequences and localisation methods. Both can now be produced with short echo times.

At high magnetic field strengths, the characteristics of the molecular surrounding of the proton can also be manipulated by using different RF pulse sequences. When interpreting in vivo MRS data, a number of experimental factors contributing data accuracy must be considered: While high resolution MRS obtained on body fluids at high magnetic field strengths will reveal a whole array of metabolites, the most important visible peaks on the cerebral proton MR spectrum in vivo at field strengths of 1.

Using in vivo MRS, metabolite concentrations are expressed as absolute values or ratios. There are some methodological problems with absolute quantification however.