4992736 Radio frequency receiver for a NMR instrument

Stormont, Robert S; Anas, Michael C; Pelc, Norbert J.

doi:10.1016/0730-725x(92)90540-g

Cited by 3 publications

(3 citation statements)

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“…An intermediate frequency of 1.25 MHz was employed, with subsampling using an A/D conversion rate of 4/5 of the intermediate frequency, i.e., 1 MHz (28,29). Odd digitized words provide inphase information, and even digitized words provide in-quadrature information.…”

Section: Scannermentioning

confidence: 99%

Single‐shot halfk‐space high‐resolution gradient‐recalled EPI for fMRI at 3 tesla

Jeśmanowicz

Bandettini

Hyde

1998

Magnetic Resonance in Med

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Half k-space gradient-recalled echo-planar imaging (GR-EPI) is discussed in detail. T2* decay during full k-space GR-EPI gives rise to unequal weighting of the lines of k-space, loss of signal intensity at the center of k-space, and a point-spread function that limits resolution. In addition, the long readout time for high-resolution full k-space acquisition gives rise to severe susceptibility effects. These problems are substantially reduced by acquiring only half of k-space and filling the empty side by Hermitian conjugate formation. Details of the pulse sequence and image reconstruction are presented. The point-spread function is 3(1/2) times narrower for half than full k-space acquisition. Experiments as well as theoretical considerations were carried out in a context of fMRI using a whole-brain local gradient and an RF coil at 3 Tesla. Using a bandwidth of +/-83 kHz, well-resolved single-shot images of the human brain, as well as good quality fMRI data sets were obtained with a matrix of 192 x 192 over 16 x 16 cm2 FOV using half k-space techniques. The combination of high spatial resolution using the methods presented in this article and the high temporal resolution of EPI opens opportunities for research into fMRI contrast mechanisms. Increase of percent signal change as the resolution increases is attributed to reduction of partial volume effects of activated voxels. Histograms of fMRI pixel responses are progressively weighted to higher percent signal changes as the resolution increases. The conclusion has been reached that half k-space GR-EPI is generally superior to full k-space GR-EPI and should be used even for low-resolution (64 x 64) EPI.

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Section: Scannermentioning

confidence: 99%

Single‐shot halfk‐space high‐resolution gradient‐recalled EPI for fMRI at 3 tesla

Jeśmanowicz

Bandettini

Hyde

1998

Magnetic Resonance in Med

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“…As an alternative, this work presents the use of undersampling or passband sampling techniques, initially proposed by Pérez et al [7] and Green et al [8], which have been successfully applied in electron paramagnetic resonance detection [9], in radio communications, in what has been called 'software radio' [10], and in nuclear magnetic resonance signal processing [11]. This last reference is a particular case of the more general theory described in this work.…”

Section: Introductionmentioning

confidence: 99%

Potential use of the undersampling technique in the acquisition of nuclear magnetic resonance signals

Pérez

2001

Magnetic Resonance Materials in Biology, Physics, and Medicine

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This communication reviews the use of undersampling techniques to acquire NMR signals. Undersampling transforms bandpass free induction decay (FID) signals, centered at high frequencies, into lowpass signals or bandpass signals centered at much lower frequencies. Consequently, the analog electronic stages that perform the demodulation can be eliminated, gaining in stability and reducing the phase distortion while maintaining an equivalent or better signal to noise ratio when an adequate sampling rate is chosen. The technique has been tested on a BRUKER BIOSPEC BMT 47/40, and the results show that undersampling could be used to process NMR and MRI signals, extending the range of applications of the 'digital radio' techniques to NMR and MRI apparatus.

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“…As an alternative, the use of undersampling for handling NMR signals has been proposed by Pérez et al [5], Green and Balcom [6] and Stortmont et al [7], and has been successfully applied in electron paramagnetic resonance detection [8], and in radio communications, in what has been called 'software radio' [9]. In these papers, it has been shown that undersampling can be used to move a bandpass signal at a highfrequency to a lower frequency without loss of information if the process of sampling satisfies the bandpass sampling theorem [10,11].…”

Section: Introductionmentioning

confidence: 99%