Parallel Imaging

Parallel imaging offers a number of advantages, like faster examination times, when applied to standard MR protocols. Rather than relying on rapid gradient switching to speed acquisition, parallel imaging uses clever algorithms and radiofrequency technology to acquire smaller data sets, specifically by undersam-pling fc-space 30, 54, 56, 66 . The basis of parallel imaging is the use of the spatial information of the radiofrequency field that is associated with the individual elements of an RF...

Endogenous Methods Arterial Spin Labelling

Endogenous tracer methods in perfusion MRI use a model that assumes that the tracer diffuses freely from the intravascular compartment into the tissue com partment. This model is similar to the one used in PET measuring the regional accumulation of the tracer, which is influenced by regional blood flow and its halflife 1 . Arterial spin labelling (ASL), also called arterial spin tagging, is an endogenous tracer perfusion method based on the measurement of the signal loss produced by...

High Field DSC

Currently, most MR perfusion studies are acquired on 1.5 T machines, but MR systems operating at higher field strengths are increasingly becoming available in clinical practice 4, 5, 8 . In general, imaging at higher magnetic field strengths offers at least a linear SNR increase, but its utilization is impaired by problems related to magnetic susceptibility artefacts. Since magnetic susceptibility increases with field strength, at 3.0 T image distortion maybe critical, particularly if EPI pulse...

High Field Strength MRI 30 T or More in White Matter Diseases

The great majority of magnetic resonance imaging (MRI) studies of white matter diseases have been conducted so far on 1.5 T MR scanners. This is likely to change over the next few years with the increased availability of high-field MR scanners. With a magnetic field strength of 3.0 T or higher, a variety of exciting improvements in clinical and research applications are expected. First exclusively employed for research, more than a hundred of these 'new generation' high-field MR scanners are...

References

Alkadhi H, Kollias SS, Crelier GR, et al. (2000) Plasticity of the human motor cortex in patients with arteriovenous malformations a functional MR imaging study. AJNR 21 1423-1433 2. Baxendale S (2002) The role of functional MRI in the presurgical investigation of temporal lobe epilepsy patients a clinical perspective and review. J Clin Exp Neuropsychol 24 664-676 3. Bogomolny DL, Petrovich NM, Hou BL, et al. (2004) Functional MRI in the brain tumor patients. Top Magn Reson Imaging 14 325-335...

Spectral Editing

Even though their concentration levels limit the number of detectable metabolites with in vivo spectroscopy, there are still a dozen or more metabolites contributing to the total spectrum. Due to signal overlaps and complicated spectral patterns, most of these metabolites cannot easily be differentiated from each other, and have to be treated as metabolite groups like the Glx-components glutamine, glutamate and GABA, or just as baseline disturbances like most of the macromolecules. Any...

Other White Matter Diseases

The use of MR systems at 3.0 T or higher is relatively new and although several studies have already been conducted on MS, the literature on the use of higher field MR scanners for the study of other white matter diseases is still scarce. Table 15.1 summarizes some of the recent work that has been done so far to assess white matter damage in diseases such as frontotempo-ral dementia 28 , aging 22, 41 , Alzheimer's disease 21 , and adrenoleukodystrophy 38 with 3.0 or 4.0 T MR scanners. The...

Exogenous Methods Dynamic Susceptibility Contrast

Exogenous tracer methods for perfusion MRI use a model assuming that the tracer is confined to the intra-vascular compartment and does not diffuse to the ex-travascular space 1, 3-5 . Imaging can be obtained either dynamically (rapid imaging over time after a bolus injection) or, less frequently, in the steady state (after constant infusion has achieved an equilibrium concentration of the tracer in the blood) 1-5 . With steady-state techniques, a baseline image is acquired before injection and...

T MRI Studies of Multiple Sclerosis 1521

Multiple sclerosis MS is an idiopathic inflammatory demyelinating disease of the central nervous system CNS characterized by the presence of widely disseminated lesions throughout the brain and spinal cord 11 . Complementary to the clinical assessment, conventional MRI cMRI techniques, such as dual-echo, fluid attenuated inversion recovery FLAIR , and -weighted with and without post-contrast , provide helpful information for the diagnosis and prognosis of MS, as well as for monitoring disease...

MRA Techniques

Phase Contrast Mra Sequence

Although there are several approaches to visualizing the intracranial vessels with MR, the two most widely used techniques are time of flight TOF and phase contrast PC MRA. In TOF MRA, which is usually performed using a flow compensated gradient refocused sequence, stationary tissues are saturated and thus have low signal intensity. However, blood upstream of the imaging volume is unsaturated. When this blood flows into the im aging volume, it is bright compared with the stationary background...

High Field MR in Patients with TBI

Magnetic Resonance Spectroscopy Tbi

The potential advantages of high-field MR in routine clinical practice are increased spatial contrast, and spectral and temporal resolution, which are greater with the more advanced techniques. In principle, the performance of a 3.0 T MR imager should be double that of a 1.5 T machine 23 . However, artefacts and technical limitations do not allow this to be achieved in practice. A greater signal noise ratio SNR , the main advantage of high-field imaging, can be reduced by local magnetic field...

High Field MRI and Safety I Installation1

ScARAbino, V. d'Alesio, M. Tosetti, M. ARmillottA, U. SAlvolini High-field magnetic resonance MR , originally developed in the framework of spectroscopy and functional neuroradiology, is set to become an important diagnostic tool not only in research but also in advanced clinical practice. High magnetic fields afford a better signal noise ratio SNR and consequently better spatial resolution in a shorter acquisition time, even though the diagnostic outcome is then subject to the...

Proton MRS in Neuroradiology

Proton magnetic resonance spectroscopy of the brain reveals specific biochemical information about cerebral metabolites, which may support clinical diagnosis and enhance the understanding of neurological disorders. Analysis of the resonance signals of low-molecular weight brain metabolites concentrations in mmol provides information on metabolite concentrations and makes it possible to correlate their modifications with various pathological conditions. The high diagnostic specificity of MRS...

High Field and Temporal Resolution

The information about neuronal phenomena that fMRI extracts from the BOLD effect represents the convolution of the temporal envelope of local brain activity with the so-called haemodynamic input function 15 . The general effect of this convolution consists in the blurring of the functional information in space and in its dispersion in time. Thus, as is the case for the spatial resolution, the limit of temporal resolution is generally set by factors intrinsic to the local brain haemodyna-mics,...

High Field and BOLD Signal Behaviour

Fmri Signals Motor

It has been clear from the very first experiences that the strength of the main magnetic field B0 is a major factor in determining the amplitude of BOLD dependent fMRI signal changes 33 Fig. 10.3 . The physical reasons for the field dependence are inherent in the mechanisms producing the BOLD effect. In fact, the bulk magnetic susceptibility difference between blood containing paramagnetic deoxyhaemoglobin and surrounding diamagnetic tissue, on which difference the BOLD effect is based,...

List of Contributors

Servizio di Neuroradiologia, Ospedale Bellaria, Bologna, Italy Adriana Aragri Department of Neurological Sciences, II University of Naples, Naples, Italy Michele Armillotta Neuroradiologia, Dipartimento di Scienze Radiologiche, Istituto Scientifico Casa Sollievo della Sofferenza, San Giovanni Rotondo Fg , Italy Servizio di Neuroradiologia, Ospedale Bellaria, Bologna, Italy Alessandro Carriero Radiologia, Universit di Novara, Novara, Italy Domenico Catapano Department of Neurosurgery, Scientific...

Pulse Sequences

Images Grey And White Matter

Anatomical brain scanning essentially relies on proton density, differences in T1 and T2 between regions e.g. cortex vs. subcortical nuclei , and tissue type white matter, grey matter and CSF . Brain images can be acquired using different pulse sequences. A 3.0 T MR system implements all the pulse sequences commonly applied in clinical practice, including SE normal, fast 2D and 3D GE GRASS fast GRASS 2D and 3D, SPGR fast SPGR 2D and 3D EPI single shot multishot 2D and 3D and IR STIR, FLAIR,...