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Iridium-191m is an attractive radionuclide for first-pass radionuclide angiography, but development of an 191Os/191mIr generator with high 191mIr yield has proven difficult. The use of trans-dioxobisoxalatoosmate(VI) as a parent species results in a higher initial yield (20 to 25%/mL), but the yield decreases over time. Using an anion-exchange column of tridodecylmethylammonium chloride-treated silica gel and AG MP-1 resin, we have developed an improved 191Os/191mIr generator with higher initial yield (25 to 30%/mL) and a slower rate of decrease than the previous design.

Deconvolution is a mathematical technique used to improve radionuclide angiocardiography after suboptimal injection of radiopharmaceutical. A new deconvolution algorithm designed to be relatively insensitive to the random errors that occur in experimental data was tested. First-pass radionuclide angiocardiography using iridium-191m was performed to quantitate left-to-right shunting in normal dogs and dogs with atrial septal defects. Deconvolution was used to correct for injection shape. Four quantitation techniques were studied (good injection/no deconvolution, good injection/deconvolution, fragmented injection/no deconvolution, fragmented injection/deconvolution). The mean (p less than .001) and standard deviation (p less than .0001) of the fragmented injection/no deconvolution technique were significantly different from the other three techniques, which were not significantly different from each other (mean or standard deviation) at the p = 0.05 level. This deconvolution method made it possible to accurately quantitate left-to-right shunts even with fragmented injections.

Thallium-201 emission computed tomography (ECT) was performed in 3 pediatric patients in whom conventional scintigraphy was normal but there was a strong clinical suspicion of myocardial disease. Abnormalities in the distribution of myocardial perfusion appeared sharply. Single photon ECT provides a three dimensional reconstruction which results in greater enhancement since activity in overlying structures does not interfere. Its widespread use is limited only by the cost of the imaging device.

Sprague Dawley rats were divided into two groups. Ten were kept in room air and 10 in hypobaric hypoxia (air at 380 mm Hg). After two weeks all were injected intravenously with 50 muCi of 201Tl and sacrificed. The right and left ventricles were separated, weighed, and measured for radioactivity in a gamma well counter. Left and right ventricular mass ratios (MR) correlated with 201Tl radioactivity ratios (TAR) in both control and hypoxic rats: r = 0.962 where MR = 0.863 TAR + 0.27. Myocardial 201Tl uptake reflects and quantitates normal and abnormal ventricular mass, the abnormal mass in this model consisting of right ventricular hypertrophy associated with hypoxic pulmonary hypertension.

A new osmium-191 leads to iridium-191m generator suitable for first-pass radionuclide angiocardiography has been developed. This generator system allows repeated elutions of 4.96-sec iridium-191m from its 15.4-day Os- 191 parent. The Os-191 is loaded on an anion-exchange column (AGMP-1) and Ir- 191m eluted with 0.9% NaCl at pH 1. Each elution (0.6 to 1 ml) of the generator yields about 7 to 10% Ir-191m and gives 0.003-0.008% of Os-191 breakthrough. Toxicity studies of the generator eluate carried out in animals support the safety of using iridium-191m in humans. The long shelf-life of the generator (approximately equal to 2 wk) will allow medical centers to use Ir- 191m for routine clinical diagnosis. Iridium-191m obtained by this method should find additional useful applications in nuclear medicine.

Iridium-191m is a potential tracer for angiocardiography and may be of particular value in the evaluation of heart disease in children. It possesses a short half-life (4.9 sec), suitable photon energy (129 keV) and may be obtained as a generator product by decay of its long lived (15.3 day) parent 191 Os. An 191Os leads to 191mIr generator capable of providing 15 mCi of 191mIr in 1.5 ml of eluant is described. The separation of 191mIr from 191Os is achieved by absorbing 191OsC16-2 on an anion exchange resin. The generator employs an additional resin column which is replaced to prevent 191Os breakthrough to become excessive. By this procedure, the breakthrough may be kept below 0.001% over a period of at least one month and after multiple elutions.

Krypton-81m, an inert, radioactive gas with a physical half-life of 13 seconds was used to evaluate regional lung ventilation in 25 pediatric patients. The results suggest that Kr-81m has several advantages over previous methods employing xenon-133. These include: more favorable physical characteristics for imaging with present scintillation cameras; ease of performance of the examinations; improved resolution and multiple views with better detection and localization of abnormalities; and a much lower dose to the patient.

Tantalum-178 is a potential tracer for the first transit studies of the heart. It has a short physical half-life (9.3 minutes) and is obtained as a generator product from its long-lived (21.3 days) parent, tungsten-178. First transit studies were performed in the monkey and dog following the intravenous injection of 20 mCi (740 MBq) of tantalum-178. Imaging was performed with a large field of view single crystal camera and a multicrystal camera. Pulmonary dilution curves were derived for the analysis of left-to-right intracardiac shunting and high temporal resolution studies were obtained to assess left ventricular function and to measure left ventricular ejection fraction. The short physical half-life of tantalum-178 permits fraction. The short physical half-life of tantalum-178 permits multiple sequential studies with reduced patient radiation dose compared to the current radionuclide of choice, technetium-99m.

A 191Os----191mIr generator has been developed that has higher 191mIr yield and lower 191Os breakthrough than previous designs. These improvements have been realized through the use of the osmium chelate complex trans-dioxobismalonatoosmate(VI) as the parent species on the generator. The new generator provides an initial 191mIr yield of 40%/mL and 191Os breakthrough of 2-3 X 10(-3)% when eluted with a solution of 0.05 M malonic acid/0.10 M sodium chloride at pH 4. Other advantages of the new design include faster clearance of the 191Os breakthrough products and simpler assembly.

Scintigraphy with Gallium 67 is frequently used in the evaluation of children with fever of unknown origin (FUO). Its usefulness in this setting, however, has not been definitely established. We reviewed the clinical records and imaging studies of 30 children with FUO who had Gallium scans. We defined FUO as a febrile illness of greater than two weeks duration which remained undiagnosed after initial clinical, laboratory and radiographic evaluation. 4 of 30 children had positive Gallium scans. Of 25 children with only systemic signs and symptoms in addition to fever, 1 had a positive scan. Of 5 children with more focal complaints, 3 had positive studies: all had localized infections which had remained occult despite imaging with other modalities. We conclude that in most children with FUO, who have only systemic complaints, Gallium scanning is rarely useful. It may be very helpful, however, when there is a suspicion of localized infection, even if other imaging studies are negative. [ABSTRACT FROM AUTHOR]

Estimates of radiation absorbed dose to organs of the nuclear medicine patient are a requirement for administered activity optimization and for stochastic risk assessment. Pediatric patients, and in particular the newborn child, represent that portion of the patient population where such optimization studies are most crucial owing to the enhanced tissue radiosensitivities and longer life expectancies of this patient subpopulation. In cases where whole-body CT imaging is not available, phantom-based calculations of radionuclide S values-- absorbed dose to a target tissue per nuclear transformation in a source tissue-- are required for dose and risk evaluation. In this study, a comprehensive model of electron and photon dosimetry of the reference newborn child is presented based on a high-resolution hybrid-voxel phantom from theUniversity of Florida (UF) patient model series. Values of photon specific absorbed fraction (SAF) were assembled for both the reference male and female newborn using the radiation transport code MCNPX v2.6. Values of electron SAF were assembled in a unique and time-efficient manner whereby the collisional and radiative components of organ dose--for both self- and cross-dose terms-- were computed separately. Dose to the newborn skeletal tissues were assessed via fluence-to-dose response functions reported for the first time in this study. Values of photon and electron SAFs were used to assemble a complete set of S values for some 16 radionuclides commonly associated with molecular imaging of the newborn. These values were then compared to those available in the OLINDA/EXM software. S value ratios for organ self-dose ranged from 0.46 to 1.42, while similar ratios for organ cross-dose varied from a low of 0.04 to a high of 3.49. These large discrepancies are due in large part to the simplistic organ modeling in the stylized newborn model used in the OLINDA/EXM software. A comprehensive model of internal dosimetry is presented in this study for the newborn nuclear medicine patient based upon the UF hybrid computational phantom. Photon dose response functions, photon and electron SAFs, and tables of radionuclide S values for the newborn child--both male and female--are given in a series of four electronic annexes available at stacks.iop.org/pmb/57/1433/mmedia. These values can be applied to optimization studies of image quality and stochastic risk for this most vulnerable class of pediatric patients. [ABSTRACT FROM AUTHOR]

Gallium-67 has been extensively used to diagnose and localize adult and pediatric inflammatory, infectious and malignant disease. Its mechanism of localizing in pathologic foci, although the subject of numerous studies both in vitro and in vivo, has not been clearly understood yet. The presence of normal polymorphonuclear leukocytes has been reported to be important in the accumulation of the tracer in inflammatory sites. We reviewed our experience with Gallium scintigraphy in three children with chronic granulomatous disease, an entity characterized by defective neutrophils and recurrent infection. Radiogallium was found to localize in inflammation in these patients. Hematologic disorders with specific structural or biochemical defects in their polymorphonuclear leukocytes may provide important information as to how these cells contribute to the accumulation of Gallium-67 in inflammation. [ABSTRACT FROM AUTHOR]

Abstract. A study of radionuclide bone scintigraphy in adolescents was conducted to evaluate the pattern of stress-related abnormalities and their correlation with both symptoms and roentgenography. In 26 episodes of stress-related abnormal scintigraphy, 12 (46%) had a multifocal pattern of abnormalities. Forty foci were identified by scintigraphy, with 11 (28%) exhibiting abnormal roentgenograms. These multiple abnormalities were frequently unsuspected clinically, and studies limited to symptomatic areas would have failed to detect them. It is recommended that patients with stress-related symptoms be screened utilizing radionuclide bone scintigraphy to facilitate the early detection of abnormalities in bone prior to the development of cortical disruption, thereby preventing increased morbidity and possible disabling sequelae. [ABSTRACT FROM AUTHOR]