Validation of a knowledge-based boundary detection algorithm: a multicenter study.

A completely operator-independent boundary detection algorithm for multigated blood pool (MGBP) studies has been evaluated at four medical centers. The knowledge-based boundary detector (KBBD) algorithm is nondeterministic, utilizing a priori domain knowledge in the form of rule sets for the localization of cardiac chambers and image features, providing a case-by-case method for the identification and boundary definition of the left ventricle (LV). The nondeterministic algorithm employs multiple processing pathways, where KBBD rules have been designed for conventional (CONV) imaging geometries (nominal 45 degrees LAO, nonzoom) as well as for highly zoomed and/or caudally tilted (ZOOM) studies. The resultant ejection fractions (LVEF) from the KBBD program have been compared with the standard LVEF calculations in 253 total cases in four institutions, 157 utilizing CONV geometry and 96 utilizing ZOOM geometries. The criteria for success was a KBBD boundary adequately defined over the LV as judged by an experienced observer, and the correlation of KBBD LVEFs to the standard calculation of LVEFs for the institution. The overall success rate for all institutions combined was 99.2%, with an overall correlation coefficient of r=0.95 (P<0.001). The individual success rates and EF correlations (r), for CONV and ZOOM geometers were: 98%, r=0.93 (CONV) and 100%, r=0.95 (ZOOM). The KBBD algorithm can be adapted to varying clinical situations, employing automatic processing using artificial intelligence, with performance close to that of a human operator.

Clinical applications of nuclear medicine in gastroenterology.

Nuclear medicine (NM) has traditionally been a non-nursing field. This specialty has grown rapidly and continues to expand. Most nurses have had very limited exposure to nuclear medicine, except in the area of patient preparation for the nuclear medicine department. Because this specialty has had significant advances that require patient monitoring in many diagnostic and therapeutic procedures, nurses will benefit by learning more about this field and by equipping themselves to care for pre- and postprocedural patients. This article is an overview of the nuclear medicine process and its most common clinical applications in the GI field as they relate to nursing practice.

Relationship of field dependence/independence with learning styles and locus of control among registered nurses.

This study investigated the relations among scores on field dependence/independence, learning styles, and locus of control for 199 Registered Nurses. Hypotheses were that nurses with higher scores on field independence would score higher on internal locus of control and nurses with scores on concrete learning styles would score higher on field independence and internal locus of control. The Group Embedded Figures Test, Learning Style Inventory, and the Internal-External Scale, and a demographic questionnaire were administered. Analysis showed that nurses were field dependent, used the Reflective Observation mode of learning, displayed abstract and active learning styles, and scored as internal on the measure of locus of control.

Attenuation properties of lead composite aprons.

Traditionally, the absorption properties of protective aprons used in diagnostic radiology have been specified in units of lead equivalent thickness. This is appropriate and accurate when lead is the only high-atomic-numbered component in the apron. In an attempt to manufacture light-weight protective apparel, however, some manufacturers have included other elements with k absorption edges in the energy range of interest, to provide equivalent absorption properties with less weight. With these other high-atomic-numbered elements added, the lead equivalence of the apparel becomes a function of the photon energy. This must be recognized and specified by the supplier, because lead apparel is used in environments other than diagnostic radiology, where the shielding benefits may be substantially less than expected when specifications are based on the diagnostic x-ray energy range.

Stability of fixation in healthy subjects during automated perimetry.

The stability of fixation of 12 healthy young subjects was assessed with a high-resolution eye tracker during automated perimetry. All the subjects exhibited eye movements and fixation shifts during the examination. The average shift in eye position between successive 1-minute intervals ranged from 0.41 degrees to 2.11 degrees, and the average standard deviation of eye position around the average of each interval ranged from 0.56 degrees to 2.55 degrees. In nine of the subjects the eye remained within 3 degrees of centre for 96% or more of the stimuli. The remaining three subjects experienced difficulty maintaining central fixation: the eye was more than 3 degrees away from centre for 28% or more of the stimuli. In the latter subjects the ability to repeatedly stimulate the intended retinal test locations was substantially reduced. The authors discuss the effects of unstable fixation on short-term fluctuation and on fixation loss.

Monocular blurring. A complication of YAG laser iridotomy.

Laser iridotomy is the procedure of choice for primary angle-closure glaucoma. The authors report a new visual disturbance after neodymium (Nd): YAG laser iridotomy. Thirteen patients presented with monocular blurring or a bluish or colored line after the laser procedure. Each eye had a patent iridotomy partially exposed by the upper lid. When the iridotomy was fully covered or fully exposed, symptoms disappeared. Symptoms also were relieved with tinted lenses. The authors suggest close preoperative examination with careful placement of the laser iridotomy entirely under the upper lid to prevent this potential visual disturbance.

Acceptable risk as a basis for regulation.

In recent years, guidelines for radiation protection have increasingly been based on estimates of the risks associated with radiation exposures and judgments regarding acceptable levels of risk. This leads to a more objective basis for regulations if the risk estimates are accurate. However, as enthusiasm for this approach expands, the large uncertainties in the risk estimates are often overlooked, and unreasonable, restrictive applications are possible. Several recent examples of radiation protection guidelines illustrate the risk-based emphasis underlying today's radiation safety philosophy.

Inaccuracies in quantitative radionuclide renal imaging due to patient position or diverging collimation.

Radionuclide renal studies with quantitative measurements in patients confined to intensive care units usually require the use of a 10-inch field-of-view mobile gamma camera and a diverging collimator to image both kidneys simultaneously. The patient must frequently be in the lateral decubitus position so imaging can be performed in the posterior projection. Due to spatial distortion caused by the diverging collimator, variations in detector angulation and kidney depth produce different detection efficiencies for each kidney. Counts in regions of interest over the kidneys were compared as a function of detector angulation and patient position (prone and lateral decubitus). Substantial variations were observed comparing the diverging collimator data to 15-inch field-of view parallel hole acquisitions. Significant variation can also be obtained with parallel hole collimators when the patient's position is changed.

Nuclear magnetic resonance velocity spectra of steady flow.

Nuclear magnetic resonance (NMR) velocity spectra are a compact way to represent the flow information in a velocity-resolved image set. Fully developed steady flow in long tubes gives NMR velocity spectra with average velocities which correlate well with the values derived from the flow rate. The ratio of average velocity to peak velocity correlates well with the Reynolds number. Tubes with compressed cross sections have velocity spectra similar to those of circular tubes. Tubes with irregular walls have velocity spectra in the entrance region that are markedly different from those from smooth-walled tubes.

Characterization of fluid flow using low-spatial-resolution velocity spectra from NMR images.

Flow velocity distributions or spectra may be obtained by NMR imaging using an anisotropic three-dimensional Fourier transform pulse sequence in which the low-resolution direction encodes perpendicular velocity. Velocity spectra from regions of interest covering the entire lumens of pipes in a flow phantom containing straight sections, a jet, and a constriction suggest that velocity spectra provide useful information even when the vessels are not spatially well-resolved. The flow in the phantom was characterized and limited measurements were made.

MR imaging of susceptibility-induced magnetic field inhomogeneities.

A 90 degrees-tau 1-90 degrees-tau 2-image acquisition pulse sequence allows spatial mapping of resonant frequency. This sort of sequence has previously been used for magnet shimming, and its use in chemical-shift imaging has been proposed. The authors used this sequence in magnetic resonance imaging of a phantom to demonstrate the magnetic field gradients arising from susceptibility differences within the phantom and allow those gradients to be measured. Gradients may arise near interfaces between substances that cannot support the same magnetic flux density. The pulse sequence was found to work well in lower-field-strength instruments.

Acceptance testing and quality control of gamma cameras, including SPECT.

The measurement of several performance parameters of a scintillation camera at the time of installation and thereafter at regular intervals is necessary to ensure that the camera is operating within specifications and to detect changes over time that can initiate a request for service. There are varied opinions on what constitutes a satisfactory acceptance test and quality control program. Few individuals would disagree that either an acceptance test or routine quality control measurements are necessary, yet agreement on the contents and frequencies of these tests is lacking. This paper discusses the performance parameters of scintillation cameras that are usually measured for planar imaging and also for SPECT with rotating cameras.

Guidelines for radiation protection.

Guidelines for radiation protection originate from numerous federal, state, and local agencies. Webster defines a guideline as a line by which one is guided, especially as an outline (as by a government) of policy or conduct. Guidelines in radiation protection can be either mandatory or advisory. Regulations by federal, state, and local governments for the use of radioactive materials define operating practices. Adherence to these regulations is required by law and there are penalties for noncompliance. Regulations generally constitute the minimum requirements for good practice and are usually supplemented by less formal recommendations from regulatory agencies and advisory groups. The regulatory guides published by the Nuclear Regulatory Commission (NRC) and by radiation control groups of agreement states are intended to assist the user of radioactive material in maintaining compliance with regulations. These guides recommend good practice but are not mandatory in that the user can propose alternatives to the regulatory agencies to meet the regulations. Many groups serve in an advisory capacity in formulating reports and recommendations for the safe use of radioactive material. The most prominent and influential among these are the National Council in Radiation Protection and Measurements (NCRP) and the International Commission on Radiological Protection (ICRP). Often the recommendations of these advisory groups evolve into either regulatory guidelines or regulations for the use of radioactive materials. At the present time, the backbone of the Nuclear Regulatory Commission's regulations relating to the medical use of radionuclides, "Standards for Protection Against Radiation" (10CFR20) and "Human Use of Byproduct Material (10CFR35), are undergoing extensive review with major revisions anticipated within the very near future. These proposed changes could have a significant impact on the practice of nuclear medicine. The changes will have some influence on radiation safety practice as it relates to the radiation worker, the patient, and the environment.