Exposures of individuals to ionizing radiation have been restricted for many years by a number of guidelines and rules developed by various advisory and regulatory groups. Accompanying these restrictions has been an evolving principle that exposures to individuals and groups should be kept "as low as reasonably achievable" (ALARA), consistent with provision of the benefits of radiation use to society. Although the ALARA concept is a laudable goal in principle, its implementation in a clinical facility has not been a straightforward process. Problems of implementing ALARA have been confounded further by the efforts of regulatory agencies to incorporate the ALARA concept into regulations governing radiation exposures. To facilitate the implementation of ALARA as a workable construct in a clinical facility, guidelines are needed for its application to both individual and collective exposures to radiation. The provision of such guidelines, including action and inaction levels for both individual and collective exposures, are presented here.

Dose-Response Relationship, Radiation↗

PubMed1986

Disposal of low-level radioactive wastes.

The generation of low-level radioactive waste is a natural consequence of the societal uses of radioactive materials. These uses include the application of radioactive materials to the diagnosis and treatment of human disease and to research into the causes of human disease and their prevention. Currently, low level radioactive wastes are disposed of in one of three shallow land-burial disposal sites located in Washington, Nevada, and South Carolina. With the passage in December 1980 of Public Law 96-573, "The Low-Level Radioactive Waste Policy Act," the disposal of low-level wastes generated in each state was identified as a responsibility of the state. To fulfill this responsibility, states were encouraged to form interstate compacts for radioactive waste disposal. At the present time, only 37 states have entered into compact agreements, in spite of the clause in Public Law 96-573 that established January 1, 1986, as a target date for implementation of state responsibility for radioactive wastes. Recent action by Congress has resulted in postponement of the implementation date to January 1, 1993.

Radioactive Waste↗

PubMed1986

Management of individuals accidentally exposed to radiation or radioactive materials.

Sources of ionizing radiation are being used with increasing frequency in a wide spectrum of applications in society. These uses are accompanied by the possible occurrence of accidents resulting in persons exposed to radiation and contaminated with radioactivity. These persons pose a risk to facilities and attending personnel upon their arrival at the hospital. This risk can be minimized without compromising the quality of patient care only if careful planning for such patients has been conducted by the hospital. Planning should include identification of a radiation emergency area within the hospital, delineation of a radiation emergency response team of individuals knowledgeable about radiation and radioactivity, and development of protocols for the medical care and decontamination of patients involved in radiation accidents. Various agencies, including the Joint Commission on Accreditation of Hospitals, have stressed the need for preparation and periodic testing of radiation emergency response plans for hospitals.

Accidents↗

PubMed1986

Radiopharmaceutical dosage selection for pediatric nuclear medicine.

To identify the most rational method for adjusting adult radiopharmaceutical dosages for children, four methods of dosage computation were examined from the perspectives of diagnostic adequacy and radiation absorbed dose. For static imaging, information density is the most important factor in study quality, and adjustment of dosage by body weight (Wt) for "thick" organs, and body surface area (BSA) for "thin" organs is recommended. Compared with adults, small children receive less radiation exposure if radiopharmaceutical dosages are adjusted by Wt, and slightly greater exposure if dosages are adjusted by BSA. For dynamic imaging studies, dosage requirements are governed by the spatial resolution needed for region of interest assignment, and the statistical reliability of the time-activity data. For dynamic renal imaging, renograms of similar quality are obtained if dosages are adjusted by height (Ht). Dynamic cardiac studies might appear to require dosages even larger than those adjusted by Ht which would result in higher radiation absorbed doses to pediatric patients. However, smaller dosages can be used in children by prolonging the imaging time and accepting lower temporal resolution. Dosage requirements for dynamic studies depend on which physiologic characteristics are measured from the time-activity data. Since the measurements of some characteristics demand higher count rates than others, dosage requirements ultimately depend on which measurements are clinically necessary. Close attention to the factors that determine these requirements may yield significant reduction in dosages, and thus in radiation exposure, for patients of all ages.

Adolescent↗

PubMed1985

The perception of radiologic image information. Report of an NCI workshop on April 15-16, 1985.

Explore the source record for details and available documents.

Cognition↗

PubMed1985

MR imaging technology: maximizing the signal-to-noise ratio from a single tissue.

The pulse-sequence equations for spin-echo magnetic resonance imaging were used to determine interpulse delay times that give the highest signal-to-noise ratio from a single tissue. This theoretical result was then verified experimentally using 1-, 2-, and 5-mM/l copper sulfate solutions imaged on a 0.15-T resistive system. Theoretical analysis determined the spin-echo interpulse delay times that maximize the signal-to-noise ratio from a single tissue as TEopt = TEmin, the minimum echo delay time permitted by the system, and, to a good approximation, TRopt = 1.27 T1 + 1.90 TEmin, with T1 the longitudinal magnetic relaxation time of the tissue. Phantom measurements of the signal-to-noise ratio in a typical imaging system confirmed the theoretically determined TRopt values to within 7%.

Humans↗

PubMed1985

Basic principles of magnetic resonance imaging--an update.

Magnetic resonance (MR) imaging technology has undergone many technologic advances over the past few years. Many of these advances were stimulated by the wealth of information emerging from nuclear magnetic resonance research in the areas of new and optimal scanning methods and radio-frequency coil design. Other changes arose from the desire to improve image quality, ease siting restrictions and generally facilitate the clinical use of MR equipment. Many questions, however, remain unanswered. Perhaps the most controversial technologic question involves the optimal field strength required for imaging or spectroscopic applications or both. Other issues include safety and clinical efficacy. Technologic issues affect all aspects of MR use including the choice of equipment, examination procedure and image interpretation. Thus, an understanding of recent changes and their theoretic basis is necessary.

Image Enhancement↗

PubMed1985

Clinical applications of magnetic resonance imaging--current status.

Magnetic resonance imaging has far-reaching real and possible clinical applications. Its usefulness has been best explored and realized in the central nervous system, especially the posterior fossa and brain stem, where most abnormalities are better identified than with computed tomography. Its lack of ionizing radiation and extreme sensitivity to normal and abnormal patterns of myelination make magnetic resonance imaging advantageous for diagnosing many neonatal and pediatric abnormalities. New, reliable cardiac gating techniques open the way for promising studies of cardiac anatomy and function. The ability to image directly in three orthogonal planes gives us new insight into staging and follow-up of pelvic tumors and other pelvic abnormalities. Exquisite soft tissue contrast, far above that attainable by other imaging modalities, has made possible the early diagnosis of traumatic ligamentous knee injury, avascular necrosis of the hip and diagnosis, treatment planning and follow-up of musculoskeletal neoplasms.

Bone Diseases↗

PubMed1984

Optimizing tissue contrast in magnetic resonance imaging.

Magnetic resonance imaging demands that tissue contrast and signal-to-noise advantages be sought in each component of the imaging system. One component of magnetic resonance imaging in which contrast and signal-to-noise ratios are easily manipulated is in the choice of pulse sequences and interpulse delay times. This article provides a general method for determining the best choices of interpulse delay times in pulse sequences and applies that method to saturation recovery, inversion recovery, and spin-echo sequences. Saturation recovery and inversion recovery sequences with rephasing pulses, and tissues with unequal hydrogen densities are considered. Optimization of pulse sequences is carried out for the two distinct cases of (a) a fixed number of sequence repetitions and (b) a fixed total imaging time. Analytic expressions are derived or approximate expressions are provided for the interpulse delay times that optimize contrast-to-noise ratios in each pulse sequence. The acceptable range of interpulse delay times to obtain reasonable contrast using each pulse sequence is discussed.

Animals↗

PubMed1984

Phase detection and contrast loss in magnetic resonance imaging.

Several recent articles have assessed the relative efficiency of nuclear magnetic resonance (NMR) pulse sequences. One consideration that has received little attention is the effect on image contrast of displaying images without information on the sign of the reconstructed signals. The radiofrequency receivers currently used on most NMR imaging systems are quadrature detectors that preserve both the magnitude and sign of the NMR signal. Usually, however, sign or phase information is not used in the final image presentation. We point out that in imaging sequences that may have negative signals, such as inversion recovery, this loss of sign information produces a reduction in contrast between some tissues in an NMR image. We discuss the tissue parameters and interpulse delay times that result in contrast loss in inversion recovery and indicate the extent of contrast loss. We point out that for some tissues with unequal hydrogen spin densities, the region of contrast loss coincides with the region where maximum contrast would occur if sign information were preserved.

Brain↗

PubMed1984

Selection of pulse sequences producing maximum tissue contrast in magnetic resonance imaging.

The importance of spin density [N(H)] and spin-lattice (T1) and spin-spin (T2) relaxation in the characterization of tissue by nuclear magnetic resonance (NMR) is clearly recognized. This work considers which optimized pulse sequences provide the best tissue discrimination between a given pair of tissues. The effects of tissue spin density and machine-imposed minimum rephasing echo times (TEMIN) for achieving maximum signal tissue contrast are discussed. A long TEMIN sacrifices T1-dependent contrast in saturation recovery (SR) and inversion recovery (IR) pulse sequences so that spin-echo (SE) becomes the optimum sequence to provide tissue contrast, due to T2 relaxation. Pulse sequences providing superior performance may be selected based on spin density and T1 and T2 ratios for a given pair of tissues. Selection of the preferred pulse sequence and interpulse delay times to produce maximum tissue contrast is strongly dependent on knowledge of tissue spin densities as well as T1 and T2 characteristics. As the spin density ratio increases, IR replaces SR as the preferred sequence and SE replaces IR and SR as the pulse sequence providing superior contrast. To select the optimal pulse sequence and interpulse delay times, an accurate knowledge of tissue spin density, T1 and T2 must be known for each tissue.

Animals↗

PubMed1984

Magnetic resonance imaging. Part I--physical principles.

Magnetic resonance (MR) imaging is the most complex imaging technology available to clinicians. Whereas most imaging technologies depict differences in one, or occasionally two, tissue characteristics, MR imaging has five tissue variables-spin density, T(1) and T(2) relaxation times and flow and spectral shifts-from which to construct its images. These variables can be combined in various ways by selecting pulse sequences and pulse times to emphasize any desired combination of tissue characteristics in the image. This selection is determined by the user of the MR system before imaging data are collected. If the selection is not optimal, the imaging process must be repeated at a cost of time and resources. The optimal selection of MR imaging procedures and the proper interpretation of the resultant images require a thorough understanding of the basic principles of MR imaging. Included in this understanding should be at least the rudiments of how an MR imaging signal is produced and why it decays with time; the significance of relaxation constants; the principles of scanning methods such as saturation recovery, inversion recovery and spin echo; how data obtained by these methods are used to form an image, and how the imaging data are complied by multi-slice and volumetric processes. In selecting an MR imaging unit, information about different magnet designs (resistive, superconductive and permanent) is useful. Although no bioeffects are thought to be associated with an MR imaging examination, some knowledge of the attempts to identify bioeffects is helpful in alleviating concern in patients.

Humans↗

PubMed1984

Magnetic resonance imaging. Part II--Clinical applications.

Magnetic resonance (MR) imaging is the most promising new technology to appear in the clinical imaging arena since the advent of x-ray transmission computed tomography in the early 1970s. Five independent tissue characteristics (spin density, spin-lattice and spin-spin relaxation times, flow and spectral shift information) are accessible to MR imaging, and their relative influence in the magnetic resonance image can be varied by appropriate selection of pulse sequences and pulse times. All major organ systems appear to be amenable to MR imaging, and some are revealed with superior definition compared with their appearance in images obtained by alternate imaging technologies. Of particular interest is the superior contrast resolution in MR images of the brain and spinal cord, and the absence of bone- and motion-induced artifacts in images of the abdomen and pelvis. Applications of MR imaging to the heart and great vessels are just developing, as are new types of contrast agents for use in MR imaging. In vivo chemical spectroscopic measurements by magnetic resonance are heralded by some investigators as the most significant contribution that magnetic resonance will make ultimately to clinical diagnosis. At present, the number of MR imaging units is extremely low, and clinical studies are proceeding at a slow rate. Nevertheless, it is possible to provide a preliminary evaluation of the usefulness of MR imaging in a variety of clinical applications. This article is such an evaluation, tempered by the acknowledgement that much additional work remains to be done.

Brain Diseases↗

PubMed1984

Practicality of NEMA performance specification measurements for user-based acceptance testing and routine quality assurance.

National Electrical Manufactures Association ( NEMA ) performance specifications provide the only standardized and traceable measurements of scintillation-camera performance that are widely accepted by manufacturers. The NEMA publication describing the performance specifications suggests that elaborate equipment beyond a standard imaging computer is required for the measurements. For this reason the tests are currently unsuitable for both user-based acceptance testing and daily quality assurance. We have implemented five of the eight NEMA performance measurements as routine quality-assurance procedures on our computerized scintillation cameras. In addition, we have shown that seven of the eight NEMA measurements can be performed in a manner traceable to NEMA , with energy resolution as the single exception. With a standard imaging computer, NEMA phantom, and minor modification to NEMA collection and analysis constraints, we have analyzed images for intrinsic uniformity, resolution, linearity, and multiple-window spatial registration as well as for system spatial resolution both with and without scatter.

Computers↗