Journal ArticleDOI
The intrinsic signal-to-noise ratio in NMR imaging.
TLDR
The intrinsic and system SNR is applied to predict image SNR and has found satisfactory agreement with measurements on images, which indicates that the initial choice of pixel size is crucial in NMR.Abstract:
The fundamental limit for NMR imaging is set by an intrinsic signal-to-noise ratio (SNR) for a particular combination of rf antenna and imaging subjects. The intrinsic SNR is the signal from a small volume of material in the sample competing with electrical noise from thermally generated, random noise currents in the sample. The intrinsic SNR has been measured for a number of antenna-body section combinations at several different values of the static magnetic field and is proportional to B0. We have applied the intrinsic and system SNR to predict image SNR and have found satisfactory agreement with measurements on images. The relationship between SNR and pixel size is quite different in NMR than it is with imaging modalities using ionizing radiation, and indicates that the initial choice of pixel size is crucial in NMR. The analog of "contrast-detail-dose" plots for ionizing radiation imaging modalities is the "contrast-detail-time" plot in NMR, which should prove useful in choosing a suitable pixel array to visualize a particular anatomical detail for a given NMR receiving antenna.read more
Citations
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Journal ArticleDOI
The rician distribution of noisy mri data
Hakon Gudbjartsson,Samuel Patz +1 more
TL;DR: The image intensity in magnetic resonance magnitude images in the presence of noise is shown to be governed by a Rician distribution and low signal intensities (SNR < 2) are therefore biased due to the noise.
Journal ArticleDOI
The NMR phased array.
TL;DR: Methods for simultaneously acquiring and subsequently combining data from a multitude of closely positioned NMR receiving coils are described, conceptually similar to phased array radar and ultrasound and hence the techniques are called the “NMR phased array.”
Journal ArticleDOI
Sequence-independent segmentation of magnetic resonance images.
Bruce Fischl,Bruce Fischl,David H. Salat,Andre van der Kouwe,Nikos Makris,Florent Ségonne,Brian T. Quinn,Anders M. Dale,Anders M. Dale +8 more
TL;DR: A set of techniques for embedding the physics of the imaging process that generates a class of magnetic resonance images (MRIs) into a segmentation or registration algorithm results in substantial invariance to acquisition parameters, as the effect of these parameters on the contrast properties of various brain structures is explicitly modeled in the segmentation.
Journal ArticleDOI
Functional Magnetic Resonance Imaging
TL;DR: FMRI reveals short-term physiological changes associated with active brain functioning, and in this way, fMRI can identify different parts of the brain where particular men-tal processes occur and can characterize the patterns of acti-vation associated with those processes.
Journal ArticleDOI
7T vs. 4T: RF power, homogeneity, and signal-to-noise comparison in head images.
J. T Vaughan,Michael Garwood,Christopher M. Collins,Wanzhan Liu,Lance DelaBarre,Gregor Adriany,Peter Andersen,Hellmut Merkle,Rainer Goebel,Michael B. Smith,Kamil Ugurbil +10 more
TL;DR: Signal‐to‐noise ratio (SNR), RF field (B1), and RF power requirement for human head imaging were examined at 7T and 4T magnetic field strengths and were consistent with calculations performed using a human head model and Maxwell's equations.
References
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Book
Image reconstruction from projections
TL;DR: The article addresses the design, implementation, evaluation, and application of computer algorithms for solving the reconstruction problem in various biomedical areas and emphasizes the essential role of computers.
Journal ArticleDOI
A review of normal tissue hydrogen NMR relaxation times and relaxation mechanisms from 1-100 MHz: dependence on tissue type, NMR frequency, temperature, species, excision, and age.
TL;DR: The longitudinal (T1) and transverse (T2) hydrogen (1H) nuclear magnetic resonance (NMR) relaxation times of normal human and animal tissue are compiled and reviewed as a function of tissue type, NMR frequency, temperature, species, in vivo versus in vitro status, time after excision, and age.
Journal ArticleDOI
The Sensitivity Performance of the Human Eye on an Absolute Scale
TL;DR: It is argued that the phenomenon of dark adaptation can be ascribed only in small part to thePrimary photo-process and must be mainly controlled by a variable gain mechanism located between the primary photo- process and the nerve fibers carrying pulses to the brain.
Journal ArticleDOI
Spin warp NMR imaging and applications to human whole-body imaging.
Abstract: Describes a new nuclear magnetic resonance (NMR) imaging technique which the authors call 'spin warp imaging' and gives examples of its application to human whole-body imaging. The apparatus is based on a four-coil, air cored magnet (made by the Oxford Instrument Company) capable of accepting the whole human body. The magnet produces a static field of 0.04 T giving a proton NMR frequency of 1.7 MHz. The maximum field inhomogeneity is about 6*10-4 at a radius of 0.23 m, approximately twice the amount theoretically attainable with this configuration. The pulse sequence used is shown.
Journal ArticleDOI
The sensitivity of the zeugmatographic experiment involving human samples
D.I Hoult,Paul C. Lauterbur +1 more
TL;DR: In this paper, an attempt is made to remove some of the uncertainty surrounding the sensitivity of an NMR experiment involving human samples, and it is shown that noise may be associated not only with the receiving coil resistance, but also with dielectric and inductive losses in the sample.