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Biomedical subjects

T W Redpath

Publications and source records attributed to T W Redpath.

14 recordsLinked to original sources
PubMed1992

Noise correlation in multicoil receiver systems.

When two or more rf coils are used to receive NMR signals from the same part of the patient, the overall sensitivity of an image formed from some combination of these signals may be degraded if noise voltages in the coils are correlated. Whereas it is straightforward to calculate correlation caused by noise sources in the coils themselves, there is disagreement about noise correlation when that noise arises from thermally driven currents within the body itself. A general analysis based on the principles of reciprocity, superposition, and energy conservation yields an equation for sample-induced noise correlation in terms of circuit impedances. Furthermore, the analysis yields a very simple expression for the total noise correlation (i.e., noise from patient and coil elements) between the coils. This latter expression is applicable to any two-port receiver coil assembly, including single coils with two modes, such as a birdcage coil, and in general, to any two ports of an n-port receiver system.

Artifacts↗
PubMed1992

Magnetic resonance imaging of pulsatile cerebrospinal fluid flow by spatial modulation of magnetization.

Various orders of binomial spatial modulation of magnetization sequences up to (1 4 6 4 1) have been tested to find the optimum sequence for clinical application. Stripe width, stripe sharpness and the tolerance of the sequences to radiofrequency non-linearity have been investigated. The (1 3 3 1) sequence was found to be a good compromise between competing design criteria, and its application to viewing pulsatile cerebrospinal fluid motion is described.

Cerebrospinal Fluid↗
PubMed1989

Low-field cine magnetic resonance imaging in aortic valve disease.

Cine magnetic resonance imaging (MRI) holds considerable promise as a means of detecting abnormal blood flow patterns with the heart and great vessels. To date, the majority of techniques employed have required moderate to high field strengths. We describe a novel, low-field-strength approach that is technically undemanding and faster than conventional methods, which we have applied to the detection of aortic valve disease. A series of 26 patients with aortic stenosis or aortic regurgitation was compared with 21 normal subjects. All 20 patients with aortic stenosis and 15 of 16 patients with aortic regurgitation were identified. There were four false positives in the aortic stenosis group; all these patients had significant aortic regurgitation. There were no false positives in the aortic regurgitation group. Low-field cine MRI is a practical and useful technique for the detection of aortic valve disease.

Adolescent↗
PubMed1988

FADE--a new fast imaging sequence.

A series of rapid, equally spaced rf pulses of constant amplitude produces two distinct components of transverse magnetization. FADE (fast acquisition double echo) is a new Fourier steady-state free precession (SSFP) imaging sequence which images both components separately in each interpulse interval. The first component gives more signal than the second but lacks contrast while the second is strongly T2 weighted.

Fourier Analysis↗
PubMed1988

Magnetic resonance image synthesis from an interleaved saturation recovery/inversion recovery sequence.

An interleaved saturation recovery/inversion recovery (SR/IR) pulse sequence allows the sign of the IR signal to be retained even if images are formed from the magnitude of the two-dimensional complex Fourier transforms of the raw data. Synthesis of images by a linear combination of SR and signed IR pixel values has proved a valuable method of relaxation time (T1) contrast manipulation without the need to re-image the slice. Linear combination has also allowed IR images with a wide range of time-to-inversion (TI) values to be synthesized from an SR/IR pair obtained with TI = 200 ms and time-to-recovery (TR) = 1000 ms, thus avoiding the need for computationally intensive calculations based on complicated relaxation equations.

Computer Simulation↗
PubMed1988

Magnetic resonance imaging of the orbits using a binocular surface coil.

Sixty subjects, including 12 normal volunteers, have been studied using the Aberdeen 0.08 T magnetic resonance imager. A wide range of pathological conditions, including both ocular and and orbital disease, have been examined using a specialized binocular surface coil. The images produced using this coil are superior to those made with a head coil and have the advantage of demonstrating both eyes simultaneously. Each patient has been studied using a pulse sequence combining alternate saturation-recovery and inversion-recovery pulses. The resultant short time-to-inversion inversion-recovery and saturation-recovery images have been shown to be accurate in demonstrating the normal anatomy of the globe and orbit and for the demonstration of a wide range of disease states.

Abscess↗
PubMed1985

The nuclear magnetic resonance appearances of neuroblastoma.

In addition to being a non-ionising method of imaging, nuclear magnetic resonance has the ability to demonstrate the body organ using different radio pulse sequences in order to highlight different tissues. Neuroblastomas are best demonstrated using proton spin lattice relaxation time (T1) weighted images such as inversion recovery or calculated T1, rather than proton density. The ability to produce sections in the sagittal and coronal as well as the axial plane allows for accurate tumour localisation and management planning. The appearances of primary neuroblastoma and metastatic spread to bone are described in three cases of neuroblastoma.

Adolescent↗
PubMed1984

Estimating patient dielectric losses in NMR imagers.

Dielectric losses in the patient may impair radiofrequency receiver coil sensitivity, and transmitter coil efficiency, in nuclear magnetic resonance (NMR) imagers. The frequency dependence of this loss mechanism is derived. Patient losses in a solenoidal head coil used for imaging heads were simulated by a cylindrical saline phantom. The frequency dependence of the loss introduced by the phantom can indicate whether dielectric losses in the patient will be significant compared to eddy current losses. The detuning caused by the phantom is used to calculate an upper limit for the distributed stray capacitance between coil and patient. Given the approximate conductivity of the patient, an upper limit for the dielectric loss can be estimated. Some methods of reducing patient dielectric losses are suggested.

Electric Conductivity↗