Differential changes in bone mineral density of the appendicular and axial skeleton with aging: relationship to spinal osteoporosis.

Patterns of bone loss in the axial and the appendicular skeleton were studied in 185 normal volunteers (105 women and 82 men; age range, 20--89 yr) and in 76 women and 9 men with vertebral fractures due to osteoporosis. Bone mineral density was measured in vivo at the lumbar spine (predominantly trabecular bone) by dual photon absorptiometry and at the midradius (greater than 95% cortical bone) and distal radius (75% cortical and 25% trabecular bone) by single photon absorptiometry. In normal women, bone diminution from the vertebrae began in young adulthood and was linear. In the appendicular skeleton, bone diminution did not occur until age 50 yr, was accelerated from aged 51 to 65 yr, and then decelerated somewhat after age 65 yr. Overall bone diminution throughout life was 47% for the vertebrae, 30% for the midradius, and 39% for the distal radius. In normal men, vertebral and appendicular bone diminution with aging was minimal or insignificant. Mean bone mineral density was lower in patients with osteoporosis than in age- and sex-matched normal subjects at all three scanning sites, although spinal measurements discriminated best; however, there was considerable overlap. By age 65 yr, half of the normal women (and by age 85 yr, virtually all of them) had vertebral bone mineral density values below the 90th percentile of women with vertebral fractures and, thus, might be considered to have asymptomatic osteoporosis. For men, the degree of overlap was less. The data suggest that disproportionate loss of trabecular bone from the axial skeleton is a distinguishing characteristic of spinal osteoporosis.

Changes in bone mineral density of the proximal femur and spine with aging. Differences between the postmenopausal and senile osteoporosis syndromes.

We measured bone mineral density (BMD) of the proximal femur, lumbar spine, or both by dual photon absorptiometry in 205 normal volunteers (123 women and 82 men; age range 20 to 92 yr) and in 31 patients with hip fractures (26 women and 5 men; mean age, 78 yr). For normal women, the regression of BMD on age was negative and linear at each site; overall decrease during life was 58% in the femoral neck, 53% in the intertrochanteric region of the femur, and 42% in the lumbar spine. For normal men, the age regression was linear also; the rate of decrease in BMD was two-thirds of that in women for femoral neck and intertrochanteric femur but was only one-fourth of that in women for lumbar spine. This difference may explain why the female/male ratio is 2:1 for hip fractures but 8:1 for vertebral fractures. The standard deviation (Z-score) from the sex-specific age-adjusted normal mean in 26 women with hip fracture averaged -0.31 (P < 0.05) for the femoral neck, -0.53 (P < 0.01) for the intertrochanteric femur, and +0.24 (NS) for the lumbar spine; results were similar for 5 men with hip fractures. By contrast, for 27 additional women, ages 51-65 yr, with only nontraumatic vertebral fractures, the Z-score was -1.92 (P < 0.001) for the lumbar spine. Thus, contrary to the view that osteoporosis is a single age-related entity, our data suggest the existence of two distinct syndromes. One form, "postmenopausal osteoporosis," is characterized by excessive and disproportionate trabecular bone loss, involves a small subset of women in the early postmenopausal period, and is associated mainly with vertebral fractures. The other form, "senile osteoporosis," is characterized by proportionate loss of both cortical and trabecular bone, involves essentially the entire population of aging women and, to a lesser extent, aging men, and is associated with hip fractures or vertebral fractures or both.

On X-ray back-scattering to detect hidden cracks in multi-layer structures.

A method that uses X-ray scanning to detect subsurface cracks is described. The method deals with samples typical of aircraft structures for which access is limited to one surface and a crack is hidden within the first substrate layer beneath the surface layer. A single-scatter model for the total response due to all X-rays that scatter once in one of the substrate layers and then pass through the top surface of the crack region and escape the target is developed. In this model, the crack is treated as a region of lower average density, and hence interaction coefficient, than the unaffected bulk material. The EGS4 Monte Carlo code also is used to estimate multiple-scattering response assuming the crack region is a thin void. These two models provide consistent results which indicate that properly designed X-ray back-scatter scanners can identify the presence of hidden cracks that extend through the substrate layer and are greater than about 1 cm in length.

Quality control of bone densitometry in a national health survey (NHANES III) using three mobile examination centers.

A quality control (QC) program for bone mineral measurements at the proximal femur by dual-energy x-ray absorptiometry (DXA) was designed for the osteoporosis component of the Third National Health and Nutrition Examination Survey (NHANES III). Major elements of the QC program are (1) a QC center for review of all scans, (2) setup procedures for and continuous monitoring of daily QC procedures, (3) reference standards for cross-calibration, (4) longitudinal studies for assessment of instrument stability, (5) monitoring of technologist performance, and (6) training. This report describes the results of the QC program of the first half of this 6 year study, which began in 1988. Measurements were performed on 7376 subjects in three mobile examination centers, which traveled to a new location about every 3 months, a total of 44 locations. A small percentage (3.5%) of all scans were rejected, mostly because of patient motion during scanning, but 33% of the remaining scans required reanalysis at the QC center to refine the location of the regions of interest. Precision in spine and hip phantoms was below 1% at all ROIs. In 535 subjects with duplicate scans, age 20-91 of both sexes, examined in a blinded review, precision for BMD at the femur neck ROI was 3.2% (CV) and 5.1% for Ward's triangle BMD. The central review improved scan quality, increased the number of usable scans, and reduced significantly the range of the mean percentage difference in the duplicate scans. Minor alterations in machine function were observed and corrected. QC results on phantoms were similar to those obtained with stationary instruments in dedicated laboratories. Retrospective analysis of the regression slopes from QC records did not show a need for correction of the data base, indicating that the instruments were stable during the course of the study.

Prevalence of low femoral bone density in older U.S. women from NHANES III.

Data on the number of U.S. women with low femoral bone mineral density (BMD) are currently available only from indirect estimates. We used dual-energy X-ray absorptiometry (DXA) measurements of femoral BMD from phase 1 of the third National Health and Nutrition Examination Survey (NHANES III, 1988-1991) to estimate prevalences of low femoral BMD in women ages 50 years and older using an approach proposed recently by an expert panel of the World Health Organization (WHO). Cutpoints for low BMD were derived from BMD data of 194 non-Hispanic white (NHW) women aged 20-29 years from the NHANES III dataset. The prevalence of older U.S. women with femoral osteopenia (BMD between 1 standard deviation [SD] and 2.5 SD below the mean of young NHW women) ranged from 34-50% in four different femur regions, which corresponds to approximately 12-17 million women. The prevalence with osteoporosis (BMD > 2.5 SD below the mean of young NHW women) ranged from 17-20%, or approximately 6-7 million women. Prevalences were 1.3-2.4 times higher in NHW women than non-Hispanic black women (NHB), and 0.8-1.2 times higher in NHW versus Mexican American (MA) women. The estimated numbers of NHW, NHB, and MA women with osteopenia were 10-15 million, 800,000-1.2 million, and 300,000-400,000, respectively; corresponding figures for osteoporosis were 5-6 million, 200,000-300,000, and 100,000 respectively. Thus, the first data on BMD from a nationally representative sample of older women show a substantial number with low femoral BMD.(ABSTRACT TRUNCATED AT 250 WORDS)

Prevalence of low femoral bone density in older U.S. adults from NHANES III.

Most estimates of osteoporosis in older U.S. adults have been based on its occurrence in white women, even though it is known to affect men and minority women. In the present study, we used dual-energy X-ray absorptiometry measurements of femoral bone mineral density (BMD) from the third National Health and Nutrition Examination Survey (NHANES III, 1988-1994) to estimate the overall scope of the disease in the older U.S. population. Specifically, we estimate prevalences of low femoral BMD in women 50 years and older and explore different approaches for defining low BMD in older men in that age range. Low BMD levels were defined in accordance with an approach proposed by an expert panel of the World Health Organization and used BMD data from 382 non-Hispanic white (NHW) men or 409 NHW women ages 20-29 years from the NHANES III dataset. For women, estimates indicate 13-18%, or 4-6 million, have osteoporosis (i.e., BMD > 2.5 standard deviations [SD] below the mean of young NHW women) and 37-50%, or 13-17 million, have osteopenia (BMD between 1 and 2.5 SD below the mean of young NHW women). For men, these numbers depend on the gender of the reference group used to define cutoff values. When based on male cutoffs, 3-6% (1-2-million) of men have osteoporosis and 28-47% (8-13 million) have osteopenia; when based on female cutoffs, 1-4% (280,000-1 million) have osteoporosis and 15-33% (4-9 million) have osteopenia. Most of the older U.S. adults with low femur BMD are women, but, regardless of which cutoffs are used, the number of men is substantial.

Biodistribution and dosimetry results from a phase III prospectively randomized controlled trial of Zevalin radioimmunotherapy for low-grade, follicular, or transformed B-cell non-Hodgkin's lymphoma.

UNLABELLED: Radiation dosimetry studies were performed in patients with non-Hodgkin's lymphoma (NHL) treated with 90Y Zevalin (90yttrium ibritumomab tiuxetan, IDEC-Y2B8) on a Phase III open-label prospectively randomized multicenter trial. The trial was designed to evaluate the efficacy and safety of 90Y Zevalin radioimmunotherapy compared to rituximab (Rituxan, MabThera) immunotherapy for patients with relapsed or refractory low-grade, follicular, or transformed NHL. An important secondary objective was to determine if radiation dosimetry prior to 90Y Zevalin administration is required for safe treatment in this patient population. METHODS: Patients randomized into the Zevalin arm were given a tracer dose of 5 mCi (185 MBq) (111)In Zevalin (111indium ibritumomab tiuxetan) on Day 0, evaluated with dosimetry, and then administered a therapeutic dose of 0.4 mCi/kg (15 MBq/kg) 90Y Zevalin on Day 7. Both Zevalin doses were preceded by an infusion of 250 mg/m(2) rituximab to clear peripheral B-cells and improve Zevalin biodistribution. Following administration of (111)In Zevalin, serial anterior and posterior whole-body scans were acquired and blood samples were obtained. Residence times for 90Y were estimated for major organs, and the MIRDOSE3 computer software program was used to calculate organ-specific and total body radiation absorbed dose. Patients randomized into the rituximab arm received a standard course of rituximab immunotherapy (375 mg/m(2) weekly x 4). RESULTS: In a prospectively defined 90 patient interim analysis, the overall response rate was 80% for Zevalin vs. 44% for rituximab. For all patients with Zevalin dosimetry data (N=72), radiation absorbed doses were estimated to be below the protocol-defined upper limits of 300 cGy to red marrow and 2000 cGy to normal organs. The median estimated radiation absorbed doses were 71 cGy to red marrow (range: 18-221 cGy), 216 cGy to lungs (94-457 cGy), 532 cGy to liver (range: 234-1856 cGy), 848 cGy to spleen (range: 76-1902 cGy), 15 cGy to kidneys (0.27-76 cGy) and 1484 cGy to tumor (range: 61-24274 cGy). Toxicity was primarily hematologic, transient, and reversible. The severity of hematologic nadir did not correlate with estimates of effective half-life (half-life) or residence time of 90Y in blood, or radiation absorbed dose to the red marrow or total body. CONCLUSION: 90Y Zevalin administered to NHL patients at non-myeloablative maximum tolerated doses delivers acceptable radiation absorbed doses to uninvolved organs. Lack of correlation between dosimetric or pharmacokinetic parameters and the severity of hematologic nadir suggest that hematologic toxicity is more dependent on bone marrow reserve in this heavily pre-treated population. Based on these findings, it is safe to administer 90Y Zevalin in this defined patient population without pre-treatment (111)In-based radiation dosimetry.

A new histochemical method for the identification and visualization of both side chain acylated and nonacylated sialic acids.

A new histochemical method is described for the differentiation of mucins that utilizes two different Schiff reagents and allows single section identification of side chain O-acylated, and nonacylated, sialic acids in contrasting colors. In the event of mucins containing only one type of sialic acid, it may allow their specific identification (e.g., C7 or C8 side chain O-acylated). It has been shown to be useful in the identification of some metastases from adenocarcinomas of colon (where the primary is potassium hydroxide/periodic acid-Schiff positive) and should prove of great value in the investigation of diseases of the gastrointestinal tract and particularly those of the colon. It should also be valuable in the general field of epithelial mucin histochemistry, particularly for those mucins of the salivary and parotid glands, etc.

A histochemical method for the identification of 9-O-acyl sialic acid. An investigation of bovine submaxillary gland and intestinal mucins.

Prolongation of the initial periodate oxidation step of the periodate-borohydride technique/potassium hydroxide/periodic acid-Schiff and periodic acid-Thionin Schiff/potassium hydroxide/periodic acid-Schiff sequences produced little or no change in the diagnostic staining for the potassium hydroxide/periodic acid-Schiff effect, exhibited by the colonic epithelial mucins of man and rat and the Brunner's gland mucin of rabbits. In contrast, there was a gradual, but clear decrease in the intensity of such staining of bovine submaxillary gland mucins. It was concluded that, in the intestinal mucins studied the potassium hydroxide/periodic acid-Schiff effect was due to sialic acids bearing O-acyl substitutents at positions C7 and/or C8 whereas in bovine submaxillary gland mucin the potassium hydroxide/periodic acid-Schiff effect is probably due, at least in part, to the presence of 9-O-acyl sialic acids. This investigation has led to the development of a technique which can be used to identify 9-O-acyl sialic acids.

A correlative chemical and histochemical study of the O-acetylated sialic acids of human colonic epithelial glycoproteins in formalin fixed paraffin embedded tissues.

Procedures are described for the isolation and identification of epithelial glycoproteins from formalin fixed, paraffin embedded specimens of human large intestine. The side chain O-acetylation patterns of the sialic acids of these glycoproteins were surprisingly similar to those of purified glycoproteins prepared from epithelial cells obtained from the same tissue before fixation. These results were consistent with those obtained by histochemical procedures performed on representative sections taken from the same tissue blocks. The methodology described permits a direct correlation of chemical and histochemical results obtained from the study of colonic epithelial glycoproteins of both normal and diseased tissues. It eliminates some of the difficulties associated with interpretation of the results by either discipline and may provide new information which would be unavailable by either chemistry or histochemistry alone.

Differences between the O-acetylated sialic acids of the epithelial mucins of human colonic tumors and normal controls: a correlative chemical and histochemical study.

Chemical analyses, together with histochemical assessments, were carried out on specimens of adenocarcinoma of the colon and histologically normal colonic epithelium (from resection margins from cases of carcinoma of the colon). In the epithelial glycoproteins of the normal tissue, both chemical and histochemical investigations indicated that the great majority of the sialic acids contained a side-chain O-acyl substituent located at position C8, whereas the side-chain substitution of the sialic acids of tumor glycoproteins was markedly reduced. Chemical analysis of the normal glycoproteins indicated that the great majority of the sialic acids were resistant to digestion with Vibrio cholerae neuraminidase, presumably due to an ester substituent at C4. The sialic acids of the tumor glycoproteins were significantly different from normal, in that they were less resistant to digestion with neuraminidase (p greater than 0.01), and therefore had a lower percentage of substitution at C4 (p greater than 0.01).

Errors in longitudinal measurements of bone mineral: effect of source strength in single and dual photon absorptiometry.

The effect of changing strength during the useful life of a radiation source was evaluated in studies performed on four dual photon (DPA) and two single photon (SPA) bone absorptiometry instruments. Two DPA units and one SPA unit did not show any systematic dependence of measured bone mineral content or bone mineral areal density (BMD) on source activity when evaluated over an entire source life. One DPA and one SPA instrument, however, showed significant time trends associated with source activity. The fourth DPA instrument had a significant linear decrease in BMD over a source life in the automatic mode but performed better in the manual mode.

Performance evaluation of xenon-133 inhalation rebreathing systems for regional blood flow measurements.

A quality-control phantom is described which is capable of testing the performance of inhalation rebreathing systems for measurements of regional cerebral blood flow (rCBF). The phantom is designed so that data similar to those from a patient study are obtained. The standard rCBF data-processing algorithm is used for the calculation of phantom study results. Malfunctions were induced to simulate instrument malfunction, and their effects on detector and air curves were evaluated. The use of this phantom is recommended prior to a patient study if the rCBF instrument is used infrequently or after service for routine maintenance or malfunction.

Assessment of bone mineral. Part 2.

A number of different techniques are available to study bone mineral. Those based on radiographs are helpful as an initial approach to the symptomatic patient with advanced disease, but they do not have the sensitivity to detect early bone loss, to assist in the estimation of fracture risk, or to monitor effects of treatment in controlled drug studies. A radiograph of the spine and hip, however, should be the first step before other tests are ordered. Photon absorptiometry methods or CT-based tests are currently most attractive as second-line approaches. Of these, photon absorptiometry is more widely tested clinically and allows studies of predominantly cortical or trabecular bone sites and total skeletal calcium. Although all of this cannot be done reliably with one instrument under routine laboratory conditions at present, it may well become possible in the near future. Of the CT-based procedures, the forearm scanner is very attractive because of its high precision and accuracy and the fact that it allows measurement of trabecular bone only. The technique is restricted to the forearm and may not be versatile enough for modern clinical requirements. A similar comment may be applicable to neutron-activation techniques of the hand, forearm, or spine. Low-level counting and the handling of neutron sources are not widely known techniques in many laboratories, and this will restrict their use in clinical practice. At this time there is no optimal technique available for mass screening for early osteoporosis. Dual-photon absorptiometry of the spine has been in use in our institution as the method of choice in selected patients for early detection of osteoporosis. However, for screening purposes the radius is still a very attractive bone to measure. At the currently used measuring sites, however, it does not have the sensitivity required to indicate spinal bone loss. Perhaps measurements closer to the distal end, where the trabecular-to-cortical bone ratios approach that in the spine, could be more sensitive. The difficulty of relocating the arm for photon absorptiometry can perhaps be solved for photon absorptiometry, or may be resolved by CT of the forearm. Correlation of the extreme distal radius with the spine is necessary to answer this question.

Bone scintigraphy evaluated in diagnosing and staging Langerhans' cell histiocytosis and related disorders.

UNLABELLED: An analysis of patients with proven Langerhans' cell histiocytosis (LCH) was undertaken with the aim of evaluating the role of bone scintigraphy in the diagnosis and staging of LCH. METHODS: Radiographic skeletal surveys and whole-body bone scintigraphy study results were reviewed for all patients treated at the Mayo Clinic in Rochester, Minnesota during 1965-1994 with histologic proven LCH. All available studies were then reported in a randomized and blinded fashion. RESULTS: Of the 73 patients with the histologic diagnosis, 56 (76%) had a definite lesion reported on radiographs and subsequent biopsy-proven bone involvement. For this population, the sensitivity and specificity of radiographic survey were 100% and 61%, respectively, compared to 91% and 55% for bone scintigraphy. Solitary bone lesions were reported on 21 radiographic surveys and 24 bone scintigrams. For solitary lesions, radiograph sensitivity and specificity were 95% and 73%, respectively, compared to 88% and 77% for bone scintigraphy. Bone scintigraphy receiver operating characteristic curves showed the region of greatest diagnostic accuracy to be skull, facial bones and mandible (88% sensitivity, 52% specificity). Radiation dosimetry to adult reproductive organs was less favorable for radiographic skeletal survey compared to bone scintigraphy. CONCLUSION: Our results support the use of radiographic skeletal survey in the initial diagnosis of LCH. Bone scintigraphy may have a role in monitoring a patient's progress in which the initial scintigram and radiographic survey show good correlation.

Filtered technetium-99m-sulfur colloid evaluated for lymphoscintigraphy.

UNLABELLED: Several 99mTc-labeled radiopharmaceuticals have been developed for lymphoscintigraphy of the extremities. In the United States, however, these agents are not widely used clinically. This study evaluates the use of smaller particle sizes ( < 0.1 micron) of 99mTc-sulfur colloid (99mTc-SC) for lymphoscintigraphy. METHODS: The 99mTc-SC was prepared by kit, and the final preparation was filtered through a sterile 0.1-micron filter. The radiochemical purity (RCP) of the filtered 99mTc-SC was determined before administration. Nineteen patients with suspected lymphedema were injected with 18.5 MBq (500 muCi) filtered 99mTc-SC intradermally in each foot, and whole-body images were obtained immediately and 1, 3, 6 and 24 hr later. Local views over the inguinal or axillary lymph nodes were also obtained every 5 min for the first hour. RESULTS: The average RCP value was 93.4% +/- 4.2% (n = 19), and the RCP difference pre- and postfiltration of the 99mTc-SC preparation was -1.7% +/- 1.4% (n = 40). Evaluation of the particle size with the polycarbonate filter showed that 89.9% +/- 4.5% (n = 28) of particles were less than 50 nm, and the particle size was further determined by electron microscopy to be 38.0 +/- 3.3 nm (n = 202). The mean particle sizes of two peaks measured by laser light scattering techniques were 7.5 and 53.9 nm (major peak). Clinical studies with filtered 99mTc-SC demonstrated similar lymphoscintigrams compared with those obtained with 99mTc antimony sulfide colloid (99mTc-ATC). Filtered 99mTc-SC showed a faster transport rate to the inguinal lymph nodes and lower radiation dosimetry for liver, spleen and whole body compared with 99mTc-ATC. CONCLUSION: Filtered 99mTc-SC can be easily prepared and is readily available for routine clinical use in lymphoscintigraphic studies.

Noninvasive bone mineral measurements.

Single and dual photon absorptiometry are now available to aid the physician in diagnosis and management of generalized bone diseases. Both methods are reviewed in detail. They allow an accurate and reproducible assessment of bone mineral at predominantly cortical (appendicular skeleton) and trabecular (axial skeleton) bone sites. Newer findings show that cortical and trabecular bone behave differently and that the effect of endocrine dysfunction on bone appears to be both disease and site specific. These qualitative and quantitative differences in cortical and trabecular bone loss require that an optimal sampling site has to be found for a given bone problem if maximum benefit is to be derived from these tests.

Technical pitfalls in image acquisition, processing, and display.

Optimal image quality is an ideal in nuclear medicine that is not always realized, being subject to a variety of conditions that can act, either singly or in combination, to undermine its accomplishment. These conditions include potential defects and limitations in both the hardware and software used for the acquisition and reconstruction of nuclear medicine images. Factors relating to individual patients can contribute to these obstacles, including limitations in mobility and compliance. Importantly, suboptimal or erroneous technique is a common source of poor imaging results, with loss of diagnostic efficacy. Appropriate test selection and careful attention to patient preparation and procedural details are essential elements in avoiding image flaws and artifacts in nuclear medicine.

Comparison of dual-energy x-ray absorptiometry and dual photon absorptiometry for bone mineral measurements of the lumbar spine.

A new x-ray-based (dual-energy x-ray absorptiometry [DEXA]) instrument for measurement of bone mineral in the spine and hips (QDR-1000, Hologic, Inc.) was compared with a commercial dual photon absorptiometry (DPA) instrument that uses a 153Gd source (DP3, Lunar Radiation Corporation). Measurements were made on phantoms and lumbar spines of patients to study accuracy, precision, limitations, and compatibility of results between instruments. Both instruments measure bone mineral of integral bone in terms of area bone density with an entrance exposure of less than 5 mR. For spinal bone mineral measurements, the DEXA instrument had a shorter scanning time and higher resolution images than the DPA system. The DEXA instrument also showed better precision in a spine phantom and reduced influence of thickness for patient measurement. For bone mineral content, accuracy was about equal for both instruments; for measurements of the area of the region of interest, accuracy was better with the DEXA instrument. With both instruments, fat had little effect on bone mineral density in bone phantom studies. Measurements on both instruments were influenced by the location of a bone phantom within the photon beam. Results in patients showed good correlation (r = 0.988) for bone mineral density. Measurements of bone mineral density in patients were consistently lower with the DEXA instrument because of better accuracy in area measurements. The new x-ray-based instrument is a major advance in bone mineral absorptiometry and provides improved, yet less expensive, measurements in research and clinical applications.

Comparison of three platelet markers for measurement of platelet survival time in healthy volunteers.

We studied mean platelet survival times in healthy volunteers with use of [51Cr]disodium chromate, 111In-oxine (in a solution of acid-citrate-dextrose [ACD] and saline), and 111In-tropolone (in ACD-plasma) as markers. Differences found between the 51Cr and 111In labels probably can be attributed to a variation in localization of the label on the cell and of renal handling of the free label after release. The mean platelet survival time with 51Cr was slightly longer than the survival time with both indium labels and showed a sex difference not seen with 111In-oxine. Protein-bound plasma 51Cr was lower than plasma 111In and remained constant throughout the study. Plasma 111In increased with time. For survival time calculations, no correction for free 51Cr is necessary, but correction should routinely be performed when 111In markers are used. Both 111In markers gave similar results with respect to platelet survival time. The somewhat more elaborate plasma labeling procedure with tropolone shows no measurable advantage over the original 111In-oxine method. 111In-tropolone labeling takes less time and maintains platelets in the physiologic environment of plasma during incubation. Biodistribution studies show no difference between the two 111In markers.