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At least 109 records · Page 6Linked to original sources
PubMed1986

Basic physics of nuclear magnetic resonance.

This review of basic physics of nuclear magnetic resonance (NMR) discusses precession of magnetic nuclei in a static external field, introduces the concept of the rotating frame, and describes excitation of nuclei by an RF field. Treats subject of T1 and T2 relaxation from the dual viewpoints of (1) phenomena of relaxation times for both the longitudinal and transverse magnetization and (2) relaxation resulting from local field fluctuations. It describes practical ways in which T1 and T2 are measured (i.e., inversion recovery and spin-echo) and gives the value of the nuclear magnetization in thermodynamic equilibrium with a static external field. It discusses the reduction of NMR signal resulting from saturation. These concepts are related to clinical use with a set of four spin-echo images of a human head.

Astrocytoma↗
PubMed2006

Alfred Nier and the sector field mass spectrometer.

Science and technology are intimately related, and advances in science often become possible with the availability of new instrumentation. This has certainly been the case in mass spectrometry, which is used in so many scientific disciplines. Originally developed as an instrument for research in physics it was used in the discovery of isotopes, their recognition as the fundamental species comprising the elements, and the investigation of elemental isotopic composition. Isotope ratio mass spectrometry is a metrological technique of the highest order, and has been widely used in chemical, biochemical, cosmochemical, environmental, geological, physical, and nuclear research. Mass spectrometry presently plays a key role not only in scientific research, but also in industrial operations. This paper highlights the role that Alfred Otto Carl Nier played in bringing mass spectrometry into the mainstream of science. Nier's career spanned a remarkable period in science, and he made crucial contributions to atomic weights, geochronology, isotope geochemistry, nuclear physics, and space science. He is widely viewed as the 'father of modern mass spectrometry', because of his genius with instrumentation, his innovations, and the generosity with which he shared his ideas and designs. It is timely to remember his fundamental work in mass spectrometry, particularly the development of the sector field mass spectrometer, which is still the instrument of choice for many isotope scientists some 66 years after its first appearance in 1940.

Journal Article↗
PubMed1996

Pierre Auger--a life in the service of science.

A short biography of Pierre Auger, the discoverer of the atomic auger electron effect, is given. Professor Auger's outstanding professional career covered physics, nuclear power and space research, organization and administration of research, diplomatic services and pedagogics but also extended into modern biology, humanistic sciences, poetry and arts. Part of a speech in Paris of professor Auger held in 1989 on the theme 'Research and Creativity' at an international symposium on the auger effect is included in this biography as well as one of his poems.

Biophysics↗
PubMed2005

An improved photo-absorption cross section model for the physics models regime in MCNPX.

The photo-nuclear physics model capabilities utilising the CEM2k model implemented in the MCNPX code were improved > 100 MeV photon energy by basing the photon transport on experimental photo-absorption cross sections of nuclides rather than on free nucleon cross sections. Below 100 MeV, the photo-nuclear physics model now uses isotope-specific giant dipole resonance (GDR) photo-absorption cross sections that are provided to the code in a parameterised form on a data file. Adjustments of the photo-fission cross sections were implemented to match the BOFOD evaluated data through a CEM2k internal parameter. The physics models with these improvements are better equipped to supplement the tabulated data based photo-nuclear MCNPX capability for isotopes with missing tabulated data evaluations especially in the GDR region, and has improved its predictive power at energies above the GDR resonances.

Absorption↗
PubMed1979

Physiology and physics of nuclear cardiology.

This chapter is a primer on the physics of radionuclide detection, flow physiology, and methods of in vivo evaluation of myocardial metabolism and intercavitary flow by noninvasive methods of intravenous isotope injection. This summary presents key concepts for the application of currently available instrumentation as well as future directions of nuclear cardiology. 1. Quantitative information is obtained in nuclear cardiology at the cost of high resolution imaging for two reasons: (a) the intrinsic resolution of the detecting systems is limited by available technology, and (b) the statistics required to achieve a high resolution image necessitate doses and imaging times far in excess of those which can be tolerated. Image resolution for both projection images as well as transverse sections are limited to the range of 5 to 20 mm, depending upon the configuration and instrument involved. 2. The second important concept is the fact that nuclear cardiology gives quantitative information regarding the amount of radiopharmaceutical which has accumulated in or is flowing through the cardiovascular system. This information allows one to deduce the dynamics of flow as well as actual metabolic rates. 3. The major emphasis for future work might well lie in the multiple transverse section imaging of the myocardium using both rotating and static devices. The key feature of this approach is the fact that the volume of interest can be localized and actual concentrations of radiopharmaceuticals can be measured by external detection using reconstruction tomography images. 4. Quantitative data on the distribution of a metabolite which accumulates in the myocardium is of little value if regional blood flow is not also known. 5. Finally, it is shown in this chapter that specific volume flow can be evaluated using short half-life isotopes and equations derived from the principle of conservation of mass. In principle it is now possible to obtain quantitative values delineating endo- and epicardial flow for the heart of man without invasive catheterization or high radiation doses. These procedures involve constant inhalation of carbon dioxide labeled with 15O which converts to labeled water and can be used for evaluating myocardial perfusion; bolus injection of 82Rb, a short half-life analogue of potassium, for repeated (every 5 min) imaging of the evolution of myocardial infarction size; evaluation of the accumulation of labeled fatty acids, amino acids, and sugars in the myocarium; presentation of images which reflect the magnitude of ejection fraction; and noninvasive evaluation of cardiac shunts. It is now possible to perform on the same patient during a few hours the following studies of myocardium: cation perfusion evaluation; water perfusion; uptake of fatty acids, amino acids, and glucose; oxygen utilization of the myocardium; and even measurement of the quantity of lung water. We now have the tools and methods to evaluate the in vivo biochemistry of the ischemic, 128 infarcting, repairing, and hypertrophic myocardium.

Blood Flow Velocity↗
PubMed2004

X-ray imaging physics for nuclear medicine technologists. Part 1: Basic principles of x-ray production.

The purpose is to review in a 4-part series: (i) the basic principles of x-ray production, (ii) x-ray interactions and data capture/conversion, (iii) acquisition/creation of the CT image, and (iv) operational details of a modern multislice CT scanner integrated with a PET scanner. Advances in PET technology have lead to widespread applications in diagnostic imaging and oncologic staging of disease. Combined PET/CT scanners provide the high-resolution anatomic imaging capability of CT with the metabolic and physiologic information by PET, to offer a significant increase in information content useful for the diagnostician and radiation oncologist, neurosurgeon, or other physician needing both anatomic detail and knowledge of disease extent. Nuclear medicine technologists at the forefront of PET should therefore have a good understanding of x-ray imaging physics and basic CT scanner operation, as covered by this 4-part series. After reading the first article on x-ray production, the nuclear medicine technologist will be familiar with (a) the physical characteristics of x-rays relative to other electromagnetic radiations, including gamma-rays in terms of energy, wavelength, and frequency; (b) methods of x-ray production and the characteristics of the output x-ray spectrum; (c) components necessary to produce x-rays, including the x-ray tube/x-ray generator and the parameters that control x-ray quality (energy) and quantity; (d) x-ray production limitations caused by heating and the impact on image acquisition and clinical throughput; and (e) a glossary of terms to assist in the understanding of this information.

Humans↗
PubMed2005

The American Board of Radiology Maintenance of Certification (MOC) Program in Radiologic Physics.

Maintenance of Certification (MOC) recognizes that in addition to medical knowledge, several essential elements involved in delivering quality care must be developed and maintained throughout one's career. The MOC process is designed to facilitate and document the professional development of each diplomate of The American Board of Radiology (ABR) through its focus on the essential elements of quality care in Diagnostic Radiology and its subspecialties, and in the specialties of Radiation Oncology and Radiologic Physics. The initial elements of the ABR-MOC have been developed in accord with guidelines of The American Board of Medical Specialties. All diplomates with a ten-year, time-limited primary certificate in Diagnostic Radiologic Physics, Therapeutic Radiologic Physics, or Medical Nuclear Physics who wish to maintain certification must successfully complete the requirements of the appropriate ABR-MOC program for their specialty. Holders of multiple certificates must meet ABR-MOC requirements specific to the certificates held. Diplomates with lifelong certificates are not required to participate in the MOC, but are strongly encouraged to do so. MOC is based on documentation of individual participation in the four components of MOC: (1) professional standing, (2) lifelong learning and self-assessment, (3) cognitive expertise, and (4) performance in practice. Within these components, MOC addresses six competencies: medical knowledge, patient care, interpersonal and communication skills, professionalism, practice-based learning and improvement, and systems-based practice.

Certification↗
PubMed2002

Development of technetium-99m-based CNS receptor ligands: have there been any advances?

By virtue of its ideal nuclear physical characteristics for routine nuclear medicine diagnostics and its ready availability, technetium-99m is of outstanding interest in the development of novel radiopharmaceuticals. The potential for the development of 99mTc-based radioligands for the study the receptor function in the central nervous system (CNS) is also well recognised despite the difficulties to be overcome. A fundamental challenge is the pharmacologically acceptable integration of the transition metal technetium, with its specific coordination chemistry, into the molecular entity of CNS receptor ligands. Conceptually, the ligand molecule can be assembled by three building blocks: a small neutral chelate unit, an organic linker that may also serve as a pharmacological modifier and a receptor-binding region derived from selective receptor antagonists. The recent introduction of novel technetium chelate units, particularly mixed-ligand complexes and low-valency organometallic compounds of technetium, provides an impetus for the further development of CNS receptor ligands. Moreover, progress in receptor pharmacology and the experience gained with positron emission tomography radiotracers have facilitated the design of numerous 99mTc-based CNS receptor ligands. The formidable challenge of developing 99mTc probes as single-photon emission tomography imaging agents targeting CNS receptors can be viewed with optimism given the successful development of [99mTc]TRODAT-1 as a 99mTc complex for imaging dopamine transporters in the brain, although there are a number of receptor-specific imaging agents that have so far resisted all efforts to develop them. This review presents recent advances and discusses the remaining hurdles in the design of 99mTc-based CNS receptor imaging agents.

Blood-Brain Barrier↗