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R J Ordidge

Publications and source records attributed to R J Ordidge.

At least 55 records · Page 3Linked to original sources
PubMed1991

Observation of cerebrospinal fluid flow with echo-planar magnetic resonance imaging.

Using echo-planar (EP) magnetic resonance imaging (MRI), cerebrospinal fluid (CSF) flow patterns have been demonstrated in the normal subject and patients with pathological conditions including communicating hydrocephalus, aqueduct stenosis and syringohydromyelia. Snap-shot imaging times of 128 ms allow detailed demonstration of transient intraventricular CSF flow patterns, which is not possible with conventional MRI. The potential of EPI as a method for qualitative and quantitative assessment of CSF dynamics is illustrated.

Cerebral Aqueduct↗
PubMed1990

Echo-planar imaging of the human fetus in utero.

We have demonstrated that echo-planar imaging can be used to produce high-quality snapshot images of the human fetus in utero in a fraction of a second. These images are free of motional artifact or blurring and allow detailed depiction of fetal structures in normal and pathological pregnancies.

Fetal Heart↗
PubMed1990

Inversion-recovery echo-planar imaging (IR-EPI) at 0.5 T.

Echo-planar imaging is used in combination with a spin preparation phase to produce a T1-weighted image. The small additional time penalty in this procedure does not detract significantly from the ultrahigh-speed imaging capability of EPI, allowing a rapid real-time optimization of tissue parameters in the image display. Results obtained on a head demonstrate this technique.

Electron Spin Resonance Spectroscopy↗
PubMed1990

High-speed multislice T1 mapping using inversion-recovery echo-planar imaging.

Tissue contrast in MR images is a strong function of spin-lattice (T1) and spin-spin (T2) relaxation times. However, the T1 relaxation time is rarely quantified because of the long scan time required to produce an accurate T1 map of the subject. In a standard 2D FT technique, this procedure may take up to 30 min. Modifications of the echo-planar imaging (EPI) technique which incorporate the principle of inversion recovery (IR) enable multislice T1 maps to be produced in total scan times varying from a few seconds up to a minute. Using IR-EPI, rapid quantification of T1 values may thus lead to better discrimination between tissue types in an acceptable scan time.

Fourier Analysis↗
PubMed1990

Study of internal structure of the human fetus in utero by echo-planar magnetic resonance imaging.

The ultrafast echo-planar magnetic resonance imaging technology, developed and built in Nottingham, has been used to produce the first snapshot images of the human fetus in utero. The imager, operating at a proton resonance frequency of 22 MHz, produces transaxial views in 64 or 128 milliseconds. These images comprise either 64 x 128 or 128 x 128 pixels with an in-plane resolution of 3 x 3 mm2. The slice thickness is 10 mm. Fetal scans of up to 32 contiguous slices are produced in a few minutes. These have been used to study the internal structure of the uterus and the fetus in a range of cases with gestations ranging from 26 weeks to term. Echo-planar imaging seems particularly suitable as an imaging modality since its high speed obviates image blurring arising from fetal motion.

Fetal Diseases↗
PubMed1990

Ultrafast magnetic resonance scanning of the liver with echo-planar imaging.

Echo-planar imaging (EPI) is a magnetic resonance imaging (MRI) technique which provides MR images in, typically, 50-100 ms. The potential of EPI as an imaging modality for the liver has been investigated in volunteers and patients with liver disease. Images with improved quality are presented. Obtained at a field strength of 0.52 Tesla, these true unaveraged snap-shot images have larger data arrays, comprising 128 X 128 pixels.

Aged↗
PubMed1990

Echo planar imaging of the human fetus in utero at 0.5 T.

The snap-shot capability of the echo-planar imaging technique is used to freeze motion effectively in human fetal studies in utero. These first results obtained at 0.5 T demonstrate diagnostic quality images without the need for averaging. Although averaging improves the image signal to noise ratio, it is shown that significant image blurring is produced even when only eight separate images are averaged over a period of a few seconds. Results are presented showing anatomical detail of the internal organs of the fetus. Some pathology is also demonstrated. These results were obtained using the modulus blipped echo-planar single-pulse technique (MBEST). Running at 10 frames/second, the modulus version of the fast low-angle excitation echo-planar technique (FLEET) is used to produce ungated fetal cardiac movies.

Female↗
PubMed1989

Snapshot imaging at 0.5 T using echo-planar techniques.

Echo-planar imaging using a magnetic field strength of 0.5 T has resulted in an improvement in image quality compared with recent images published at 0.1 T. The sensitivity of the technique to main magnetic field inhomogeneity and transient eddy currents has necessitated innovations in gradient and radiofrequency coil design. These improvements are described, and new variations in the echo-planar pulse sequence which provide better contrast and allow separate imaging of water and fat distributions are presented.

Abdomen↗
PubMed1989

PEEP--a rapid chemical-shift imaging method.

The phase-encoded echo-planar (PEEP) technique, a variant of echo-planar imaging, is used to achieve simultaneous high-speed spatial and chemical-shift data acquisition. This technique is the 2DFT equivalent of the projection reconstruction echo-planar method for chemical-shift imaging. Examples of images and spectra obtained using the PEEP method are presented.

Magnetic Resonance Imaging↗
PubMed1989

Whole-body echo-planar MR imaging at 0.5 T.

The ultra-high-speed echo-planar imaging technique produces instant snapshot magnetic resonance images in exposure times ranging from approximately 10 to 100 msec. A particular variant, the modulus blipped echo-planar single-pulse technique (MBEST), possesses two advantages: First, it makes the technique experimentally more robust; second, it introduces inherent T2 weighting in the images. The authors have used MBEST with an exposure time of 64 msec to explore the potential range of clinical applications in a series of normal volunteers. Applications include evaluation of the heart, renal function, and gastrointestinal tract. All images were obtained with proton resonances at 22 MHz.

Abdomen↗
PubMed1989

Gastrointestinal tract: dynamic MR studies with echo-planar imaging.

Gastrointestinal (GI) tract motility was depicted in four human volunteers with the high-speed echo-planar imaging technique: modulus blipped echo-planar single-pulse technique (MBEST). Data acquisition times of 64 and 128 msec obviate image degradation due to motion without the need for gut paralysis and allow imaging of the GI tract in real time. Peristaltic patterns of the gastric antrum and proximal small intestine were depicted for fasting and fed subjects and subjects in whom peristalsis had been pharmacologically stimulated. The potential for quantitative measurements of GI tract motion with this new technique was demonstrated.

Adult↗
PubMed1988

Snapshot head imaging at 0.5 T using the echo planar technique.

The echo planar imaging (EPI) method and related variants of this technique can produce complete two-dimensional images from the data collected in a single experiment lasting a fraction of a second. EPI methods are used at 0.5 T to produce snapshot images of the human head with a spatial resolution of less than 2 mm.

Head↗
PubMed1988

A general approach to selection of multiple cubic volume elements using the ISIS technique.

The ISIS method is used regularly for the selection of a single cubic volume of tissue for in vivo investigation by high-resolution NMR spectroscopy. This technique has been extended on a theoretical basis to include the simultaneous selection of a number of cubes, the signals from which can be either assessed individually or in certain circumstances coadded to produce improvement in signal-to-noise ratio. The modification requires additional selective RF pulses in the spatial encoding prepulse period, and spatially localized spectra are produced by addition and subtraction of NMR signals in a manner similar to the original ISIS technique.

Humans↗
PubMed1988

Improvements in snap-shot nuclear magnetic resonance imaging.

New variants of the ultra-high-speed echo-planar imaging technique have been used to obtain snap-shot images of adult patients and volunteers at 0.1 T. Modified pulsed-gradient sequences together with non-linear signal sampling and activity screened gradients have greatly improved the image quality obtainable by single-shot methods. A particular variant, modulus blipped echo-planar single-pulse technique (MBEST), although slightly slower than the blipped echo-planar single-pulse technique (BEST), is experimentally more robust and incorporates intrinsic T2 weighting. An account of these improvements together with some experimental results is presented.

Adult↗
PubMed1987

Spin echo imaging of multiple chemical shifts.

A method to obtain separate cross-sectional NMR images of chemically different species on the basis of their difference in chemical shift is presented. The total experiment time is no longer than that required for a conventional image and the method retains the full sensitivity of a spin-echo 2DFT imaging experiment. Simple addition of the chemical-shift selective images produces an image free from chemical-shift artifacts. Results of an in vivo experiment on a human subject are presented.

Body Water↗
PubMed1987

Random noise selective excitation pulses.

Several methods for the spatial localization of NMR signals from well-defined regions of tissue within extended specimens have been proposed. Most of these techniques are prone to signal error which can arise from large volumes of sample that surround the region of interest. These errors can theoretically be reduced by several orders of magnitude by the application of a radiofrequency prepulse. The pulse acts to randomize the unwanted spin magnetization prior to the application of a spatial localization technique.

Magnetic Resonance Spectroscopy↗