NMR imaging in theory and in practice

Taylor, David G.; Inamdar, R.; Bushell, M C

doi:10.1088/0031-9155/33/6/001

Cited by 17 publications

(4 citation statements)

References 111 publications

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“…The bound contribution presents a microscopic heterogeneity that is not averaged out on the time scale of measurement, i.e., within milliseconds. Multi-exponential behavior of relaxation that has been reported (Hazlewood et al, 1974;McSweeney et al, 1984;Bottomley et al, 1984), and the reduction in the diffusion coefficient are not explained by the fast exchange model, which holds only for simple solutions such as protein solutions with physiological concentrations (Taylor et al, 1988). The effect of compartmentation however leads to the presence of isolated submagnetizations.…”

Section: Data Evaluationmentioning

confidence: 90%

Anomalous diffusion of water in biological tissues

Köpf¹,

Corinth²,

Haferkamp³

et al. 1996

Biophysical Journal

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This article deals with the characterization of biological tissues and their pathological alterations. For this purpose, diffusion is measured by NMR in the fringe field of a large superconductor with a field gradient of 50 T/m, which is rather homogenous and stable. It is due to the unprecedented properties of the gradient that we are able not only to determine the usual diffusion coefficient, but also to observe the pronounced Non-Debye feature of the relaxation function due to cellular structure. The dynamics of the probability density follow a stretched exponential or Kohlrausch-Williams-Watts function. In the long time limit the Fourier transform of the probability density follows a long-tail Lévy function, whose asymptotic is related to the fractal dimension of the underlying cellular structure. Some of the properties of Lévy walk statistics are discussed and its potential importance in understanding certain biophysical phenomena like diffusion processes in biological tissues are pointed out. We present and discuss for the first time NMR data giving evidence for Lévy processes that capture the essential features of the observed power law (scaling) dynamics of water diffusion in fresh tissue specimens: carcinomas, fibrous mastopathies, adipose and liver tissues.

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Section: Data Evaluationmentioning

confidence: 90%

Anomalous diffusion of water in biological tissues

Köpf¹,

Corinth²,

Haferkamp³

et al. 1996

Biophysical Journal

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“…Introductions to the physical principles of MRI are given e.g. by Taylor et al (1988), Leach (1988) and Brix (1992). The biological effects of the magnetic fields and the radiofrequency radiation applied in MRI have been reviewed comprehensively by Bernhardt (1992).…”

Section: Magnetic Resonance Imagingmentioning

confidence: 99%

Recent developments in breast imaging

1996

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A review of breast imaging has already appeared in 1982 in this journal. Consequently, the present article concentrates on a discussion of only those developments of a more recent nature. Although the emphasis is placed on the physical aspects of the different imaging methods concerned, the essential factors relating to the clinical background and the associated radiation risk are also outlined. The completeness of detail depends on the present clinical importance of the method under discussion. X-ray mammography, which is still the most important breast imaging technique and has proved to be an effective method for breast cancer screening, is therefore treated in greater detail. Since the early 1980s, ultrasound B-mode scanning has evolved to an indispensable adjunct to x-ray mammography. For Doppler sonography, diaphanography, contrast-enhanced MRI, CT and DSA, the visualization of a tumour depends essentially on the enhanced vascularity of the lesion. Whether this will prove to be a reliable indicator for malignancy remains to be shown in controlled clinical studies. Common to all imaging systems is the increasing use of digital methods for signal processing, which also offers the possibility of computer-aided diagnosis by texture analysis and pattern recognition.

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“…the higher energy state. The slight initial excess of nuclei in the lower energy state is the only reason that an NMR signal can be seen at all (Taylor et al 1988).…”

Section: Resonancementioning

confidence: 99%

“…The combination of x and y gradients during read out of the signal can produce projections of the signal intensity at different angles (Taylor et al 1988). Therefore by repeating the sequence of slice selection and using a series of xy gradient combinations that change for each measurement (figure 2.14), a set of projections can be produced.…”

Section: Projection Reconstructionmentioning

confidence: 99%

An investigation into the applications of polymer gel dosimetry in radiotherapy

Farajollahi

1999

Medical Physics

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The verification of complex dose distributions produced using novel techniques in radiotherapy requires measurements in three dimensions with high spatial resolution. Recent developments in polymer gel dosimetry employing MRI suggest this may be the best available method. In this work the properties of BANG (bis, acrylamide, nitrogen, and gelatin) polymer gel were investigated. The gel was found to be tissue equivalent and its response to absorbed dose reproducible to within ±4% and linear up to 10–12 Gy. The response of the gel was also found to be independent of energy and dose rate, but dependent on oxygen contamination and gel temperature during MR imaging. The application of BANG gel in different areas of radiotherapy was investigated. In brachytherapy a comparison of the relative dose rate distributions between gel, calculation, and TLDs agreed to within ±5%. The measured dose distributions from complex brachytherapy and multifield external beam irradiations agreed well with the distribution produced by the Helax‐TMS planning system. For external beam irradiation the depth doses measured in the gel showed good agreement with ion chamber measurements to within ±3%. The gel was also used to verify the absorbed dose distribution produced by intensity modulated beam techniques using compensators. The results agreed well with film dosimetry. BANG gel was also found to be an excellent candidate for dynamic measurements and measurements in areas with restricted access. A novel technique for measurements in boron neutron capture therapy using boron‐loaded gel is also described. It was concluded that gel can be used to verify complex dose distributions. [Copies of the thesis are available from Main Library, University of Leicester, University Road, Leicester, LE1 7RH, England.]

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NMR imaging in theory and in practice

Abstract: This review was completed in February 1988where 7, the gyromagnetic ratio, characterises the species of nuclei (e.g. for protons, y/2.rr = 42.6 MHZ T-').

Cited by 17 publications

References 111 publications

Anomalous diffusion of water in biological tissues

Anomalous diffusion of water in biological tissues

Recent developments in breast imaging

An investigation into the applications of polymer gel dosimetry in radiotherapy

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