Magnetic-resonance imaging

ASTM F2052-00 Standard Test Method for Measurement of Magnetically Induced Displacement Force on Passive Implants in the Magnetic Resonance Environment ASTM F2119-01 Standard Test Method for Evaluation of MRl Artifacts From Passive Implants 

The ACR has made safety recommendations for the use of MRl machines. The new recommendations include restricting access to MRl rooms, appointing a special director of hospital MRl 

Even when steps such as these are taken, heating can occur during an MRI scan, so MRI technicians must ask patients to signal if they feel undue heat during the scan. 

The analytical and diagnostic applications of NMR in biochemistry and medicine have developed very rapidly in recent years. The techniques employed fall broadly into two categories (1) nuclear magnetic resonance imaging (NMRl) (usually known simply as magnetic resonance imaging (MRI)), and (2) nuclear magnetic resonance spectroscopy (NMRS), or simply MRS (Chapter 14.2). 

Most development work to date has utilised H and C NMR which are capable of producing sharper and better-defined images of soft body tissues than are obtainable with x-rays. MRI techniques are somewhat less sensitive to than to H distribution, because of the generally lower concentration of the former. This is offset, however, by the significance and medical importance of the various P-containing metabolic compounds which are always present in living organisms. 

MRI is much more sensitive to the phosphorus in ATP and other mobile metabolites than it is to the P atoms in bone. It is therefore particnlarly suitable for the study of soft tissues. Excellent pictures have been obtained of such organs as brain, heart and kidney. Whole-body scanning is now a practicable technique. Some P compounds can be used as contrast agents [70], for example, (12.142) (see 7.305). 

The principles that govern the NMR experiments described throughont this textbook have applications in the field of medicine. A very important diagnostic tool in medicine is a technique known as magnetic resonance imaging (MRI). In the space of only a few years, MRI has found wide use in the diagnosis of injuries and other forms of abnormality. It is qnite common for sports fans to hear of an athlete who has sustained a knee injnry and had it examined via an MRI scan. 

The nuclei of water molecules that are not bonnd within living cells have a relaxation time differ- 

FIGURE 9.19 MRI scan of a skull showing soft tissues of the brain and eyes. 

Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or dnpUcated, in whole or in part. 

The MRI method is not limited to the study of water molecules. Pulse sequences designed to study the distribution of lipids are also used. 

The MRI technique has several advantages over conventional X-ray or CAT scan techniques it is better suited for studies of abnormalities of soft tissue or of metabolic disorders. Furthermore, unlike other diagnostic techniques, MRI is noninvasive and painless, and it does not require the patient to be exposed to large doses of X-rays or radioisotopes. 

616 Nuclear Magnetic Resonance Spectroscopy Part Five Advanced NMR Techniques 

No change in populations of the two spin states is involved in this type of relaxation, so no energy is transferred from the spins to the sin-roundings. 

Similar equations maybe written for gradients along the x- andy-directions. Exposure of the sample to radiation of frequency v z) results in a signal with an intensity that is proportional to the number of protons at the position z. This procedure is an example of slice selection, the use of radiofrequency radiation that excites nuclei in a specific region, or slice, of the sample. It follows that the intensity of the NMR signal will be a projection of the number of protons on a line parallel to the field gradient. The image of a three-dimensional object such as a flask of water can be obtained if the slice selection technique is applied at different orientations (Fig. 13.28). In projection reconstruction, the projections can be analyzed on a computer to reconstruct the three-dimensional distribution of protons in the object. 

FIGURE 19.8 A 2D 7 spectrum. The ID proton spectrum is overlaid on a 2D 7 spectrum. 

Some of the most extensively used two-dimensional NMR are as follows  

Three and four-dimensional NMRs are also available. They are more complicated than one- and two-dimensional NMR, but the underlying general principles are about the same. The three- and four-dimensional NMRs are useful for the determination of stmctmes of larger proteins and protein complexes. 

Magnetic resonance imaging (MRI) is the NMR used for diagnosing certain diseases such as those in the brain and spinal cord. A patient is placed inside the 

Let 5( Bi,( 2) be the desired image of the object and P a , p) be a projection obtained by applying a gradient in the direction tp. In correspondence with the projection P a, cp) there is a one-dimensional Fourier transformation to C(f, (p). That is, there are relations 

MRI generates high-resolution images of the body s soft tissue. It is based on the principle of NMR, and employs the protons present in water, abundant in the human body, as contrast agent. MRI can be used to visualise other natural or injected nuclei in the body, such as P and E The first MRI image was published in 1973 [103], and the inventors of MRI, Lauterbur and Mansfield, were rewarded with the Nobel Prize in Physiology or Medicine in 2003. Development of the instruments has 

Superparamagnetic nanoparticles (SPION) are negative contrast agents that can be used in MRI imaging, and in a range of other biomedical applications including magnet-assisted transfection, hypothermia induction, and cell separation. The 

Reproduced with permission from H. Kobayashi, S. Kawamoto, S.K. Jo, H.L. Bryant, M.W. Brechbiel, and R.A. Star, Bioconjugate Chemistry, 2003, 14, 2, 388. 

There are a number of important MRl techniques that are applicable to the study of granular materials. All are based on combining NMR with linear field gradients to encode spatial information into the frequency of precession. 

When a nucleus with a magnetic moment, or spin, is placed in a magnetic field, the magnetic moment precesses about the magnetic field direction with a frequency uoi proportional to the field strength. For example, for protons in Ho = 2 T magnetic field. 

If a magnetic field gradient in the x-direction Gx, is applied during a free induction decay or a spin echO then for times short compared to T, the signal 

NMR signals are usually measured using quadrature demodulation at so S t) = S t)exp -io)it) contains both the real and imaginary parts of (2.15). S(t) can be recast as the kx component of the Fourier transform of the spin density n(x), 

Many different methods exist to sample fc-space including radial sampling spiral sampling and raster sampling. For more details see, for example, [277]. Once sufficient sampling is complete, the spin density n x) is recovered by Fourier transform. 

The increased brightness of T2-weighted MR images also contributed to the potential development of this agent for MR angiography. Moreover, Cu-NPs with a diameter of 23.5 run proved to be only moderately toxic [76]. 

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The great diversity of applications of magnetic resonance imaging (MRI) has resulted in a plethora of teclnhques which at first sight can seem bemusmg. However, at heart they are built on a series of connnon... 

The classical description of magnetic resonance suffices for understanding the most important concepts of magnetic resonance imaging. The description is based upon the Bloch equation, which, in the absence of relaxation, may be written as... 

Morris P G 1986 Nuclear Magnetic Resonance Imaging in Medicine and Biology (Oxford Ciarendon)... 

Stehiing M K, Turner R and Mansfieid P 1991 Echo-pianar imaging magnetic-resonance-imaging in a fraction of a second Science 254 43-50... 

McDonald P J 1997 Stray field magnetic resonance imaging Prog. Nucl. Magn. Reson. Spectrosc. 30 69-99... 

Ahn C B and Cho Z H 1989 A generalized formulation of diffusion effects in pm resolution nuclear magnetic-resonance imaging Med. Rhys. 16 22-8... 

Tzalmona A, Armstrong R L, Menzinger M, Cross A and Lemaire C 1990 Detection of chemical waves by magnetic resonance imaging Chem. Rhys. Lett. 174 199-202... 

Liquid helium s use in magnetic resonance imaging (MRI) continues to increase as the medical profession accepts and develops new uses for the equipment. This equipment has eliminated some need for exploratory surgery by accurately diagnosing patients. Another medical application uses MRE to determine (by blood analysis) whether a patient has any form of cancer. 

Magnetic resonance imaging (MRI) (Section 13 13) A diag nostic method in medicine in which tissues are examined by NMR... 

Ring Currents Aromatic and Antiaromatic Magnetic Resonance Imaging Spectra by the Thousands Gas Chromatography GC/MS and MS/MS... 

Future Applications. The use of gadolinium complexes as contrast agents in magnetic resonance imaging (mri) is growing (40). 

Mag netic Resonance Magnetic resonance imaging (MRI) is a tomographic imaging modaHty. The basis of MRI, equation 6,... 

D. D. Stark and W. G. Bradly, Magnetic Resonance Imaging Mosby, Lanham, Md., 1988. 

The resolution of the y-camera is determined by both the collimator and the crystal/photomultipher tube combination. In general, the resolution is significantly poorer than that of other modaUties such as magnetic resonance imaging (mri) and x-ray computerized tomography (ct). For single-photon... 

Sucralfate [54182-58-0] an aluminum salt of sucrose octasulfate, is used as an antacid and antiulcer medication (59). Bis- and tris-platinum complexes of sucrose show promise as antitumor agents (60). Sucrose monoesters are used in some pharmaceutical preparations (21). A sucrose polyester is under evaluation as a contrast agent for magnetic resonance imaging (mri) (61). Oral adrninistration of this substance opacifies the gastrointestinal tract and eliminates the need for purging prior to mri. 

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