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Biomedical subjects

C H Cunningham

Publications and source records attributed to C H Cunningham.

At least 19 recordsLinked to original sources
PubMed2001

Partial discrete Fourier transform (PDFT) multiband encoding.

For conventional multiband encoding techniques such as Hadamard encoding, scan time scales linearly with the number of slices encoded simultaneously. In this work, a new multiband encoding technique called partial discrete Fourier transform (PDFT) encoding is introduced, which overcomes this restriction. This technique incorporates the principle of partial Fourier imaging, allowing the tradeoff of SNR and imaging time without changing the number of slices. The theory behind PDFT encoding and its inherent sensitivity to phase errors are outlined. The theory was validated through simulations, showing that phase errors result in degraded slice localization. The feasibility of PDFT encoding of 12 slices was tested with experimental excitation profile measurements and heart images of a human subject using commercial MRI equipment. Imaging time was reduced to 66% with SNR reduced to 82%. Magn Reson Med 45:118-127, 2001.

Computer Simulation↗
PubMed1999

Method for improved multiband excitation profiles using the Shinnar-Le Roux transform.

A method to design multiband RF pulses for magnetic resonance imaging is described. The method is based on the Shinnar-Le Roux transform and involves a phase correction that provides control over the phase of the excited bands. The theory behind the method and this phase correction is outlined. The method is demonstrated with the design of RF pulses for Hadamard encoding and Haar wavelet encoding. Experimentally measured excitation profiles and images for RF pulses designed with the new method are compared to those designed by the conventional method. The conventional method is shown to result in distortion of the excitation profile when the bands are closely spaced. A 78% reduction in this distortion is attributed to the new method. This translates into a 52% reduction of out-of-slice signal in Haar wavelet encoding. Magn Reson Med 42:577-584, 1999.

Algorithms↗
PubMed1976

Avian infectious bronchitis vaccine: primordial or derived virus?

Vaccine formulations of virulent, modified/attenuated, or inactivated mono- or multivalent types of chicken embryo-propagated avian infectious bronchitis virus (IBV) at different passage levels and administered by non-parenteral routes have been used for immunization of chickens against the disease. Two doses of vaccines are generally used: 1) high level virus of lessened virulence, antigenicity and immunogenicity as "derived" from its parental virus via serial passage in and selective adaptation to the chicken embryo, and 2) low passage level virus with the above properties more closely related to the greater potency of the "primordial" parental virus in nature. The efficacy of vaccines with contemporary or candidate virus has been interpreted from a variety of criteria among which are: 1) clinical response, residence and dissemination of virus, 2) in vivo and in vitro local tissue response of tracheal epithelium, 3) protection against virulent homologous or heterologous types of IBV, and 4) induced secretory and humoral antibody. Vaccines have been economically useful and of epizootiological value but the greatest difficulty is the uncertainty of protection because of the changing antigenic, immunogenic and other properties of existing virus and of newly emerging types. With a complex virus such as IBV, the opportunities for natural selection and evolution of new or modified antigens via association with antibody of immune or of partially immune hosts are as enormous as antigenic lability resulting from fragmentation of the primordial genome under natural and/or artificial environmental stress. The present day IBV might be progeny from a unique pool of primordial genome via mutation and host-induced variation, or even persistence of primordial virus as an infinitesimal portion of the population.

Animals↗
PubMed1975

Coronaviridae.

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Coronaviridae↗
PubMed1975

Immunity to avian infectious bronchitis.

Avian infectious bronchitis is recognized clinically as a respiratory disease in its only natural host,the chicken, but the virus is disseminated throughout other systems by a viraemia with localization especially in the kidney and oviduct. The sensitivity or instability of the antigenic and immunogenic properties of the virus under laboratory stress or natural influences complicates the selection of seed virus for vaccines. Modified or attenuated active virus vaccines induce greater protection against subsequent infection than do inactive virus vaccines. Maternal antibody is effective in providing passive immunity for about two weeks after the chick is hatched. Immunoglobulins induced by primary infection or by vaccination are IgG effective for neutralization of virus by circulating antibody, and presumably secretory IgA in the respiratory tract, with the latter being more effective as evidenced by protection of the trachea against reinfection. The level of humoral antibody is not necessarily correlative with immunity based on chicken protection tests against challenge with virulent virus. A true carrier status apparently does not result from primary infection but it has been suggested that the chicken may possibly become an immune carrier.

Animals↗
PubMedDate not supplied

Differentiation of avian infectious bronchitis virus isolates by thermal sensitivity.

Six isolates of avian infectious bronchitis virus (IBV) at different passage levels in the chicken embryo were tested for sensitivity at 56 C, with the following results: 1) isolates differed in thermal sensitivity; 2) virus was inactivated in a first-order exponential-kinetics 2-component fashion indicative of a heterogeneous population with a preponderance, 98% or more, of thermal-sensitive (S) virions over thermal-resistant (R) virons; 3) R virions 2-component populations were inactivated; 4) recovered R virions could be maintained in continuous passage in the chicken embryo as a one-component population by the limiting-dilution technique, although there was a progressive parallel increase in thermal sensitivity associated directly with the continuous passage; 5) growth curves of isolated one-component populations of R virions were quantitatively and in time sequence similar to curves of 2-component populations of continuous-passage virus.

Animals↗