Oxidatively stable nanoporous silicon photocathodes with enhanced onset voltage for photoelectrochemical proton reduction.

Stable and high-performance nanoporous "black silicon" photoelectrodes with electrolessly deposited Pt nanoparticle (NP) catalysts are made with two metal-assisted etching steps. Doubly etched samples exhibit an ∼300 mV positive shift in photocurrent onset for photoelectrochemical proton reduction compared to oxide-free planar Si with identical catalysts. We find that the photocurrent onset voltage of black Si photocathodes prepared from single-crystal planar Si wafers by an Ag-assisted etching process increases in oxidative environments (e.g., aqueous electrolyte) owing to a positive flat-band potential shift caused by surface oxidation. However, within 24 h, the surface oxide layer becomes a kinetic barrier to interfacial charge transfer that inhibits proton reduction. To mitigate this issue, we developed a novel second Pt-assisted etch process that buries the Pt NPs deep into the nanoporous Si surface. This second etch shifts the onset voltage positively, from +0.25 V to +0.4 V versus reversible hydrogen electrode, and reduces the charge-transfer resistance with no performance decrease seen for at least two months. PEC performance was stable owing to Pt NP catalysts that were buried deeply in the photoelectrode by the second etch, below a thick surface layer comprised primarily of amorphous SiO2 along with some degree of remaining crystalline Si as observed by scanning and transmission electron micrographs. Electrochemical impedance studies reveal that the second etch leads to a considerably smaller interfacial charge-transfer resistance than samples without the additional etch, suggesting that burying the Pt NPs improves the interfacial contact to the crystalline silicon surface.

Adherent endotoxin on orthopedic wear particles stimulates cytokine production and osteoclast differentiation.

Aseptic loosening of orthopedic implants is thought to be caused primarily by osteoclast differentiation induced by bone resorptive cytokines produced in response to phagocytosis of implant-derived wear particles. This study examined whether adherent endotoxin on the wear particles is responsible for inducing osteoclast differentiation as well as production of interleukin-1beta (IL-1beta), IL-6, and tumor necrosis factor a (TNF-alpha). Removal of adherent endotoxin almost completely inhibited the responses to titanium (Ti) particles by both murine marrow cells and human peripheral blood monocytes. In vivo experiments showed that endotoxin removal reduced particle-induced osteolysis by 50-70%. Addition of lipopolysaccharide (LPS) to the "endotoxin-free" particles restored their ability to induce cytokine production and osteoclast differentiation in vitro. Moreover, marrow cells from mice that are hyporesponsive to endotoxin because of mutation of Toll-like receptor 4 induced significantly less cytokine production and osteoclast differentiation in response to Ti particles with adherent endotoxin than did marrow cells from normoresponsive mice. This mutation also resulted in significantly less particle-induced osteolysis in vivo. Taken together, these results show that adherent endotoxin is involved in many of the biological responses induced by orthopedic wear particles and should stimulate development of new approaches designed to reduce the activity of adherent endotoxin in patients with orthopedic implants.

Localizing infection with a technetium-99m-labeled peptide: initial results.

In vitro-labeled leukocyte imaging is useful for the detection of infection, but an in vivo labeling method is preferable. This study sought to evaluate the safety and efficacy of a leukocyte-avid peptide for the detection of infection, to determine the effects of peptide dose on performance and to compare the peptide with in vitro-labeled leukocytes. A 23-amino acid peptide, P483, containing the platelet factor-4 heparin-binding sequence, was labeled with 99mTc and complexed with heparin (P483H). Thirty patients were injected with 29 microg (n = 11), 145 microg (n = 10) or 290 microg (n = 9) of labeled peptide, and imaged 15 min and 90-120 min later. Early and late images were interpreted individually and jointly. Twenty patients underwent (111)In-labeled leukocyte scintigraphy. Fourteen patients had infection: osteomyelitis (n = 7), vascular graft (n = 2), abscess (n = 2), joint replacement (n = 1), surgical wound (n = 1) and pneumonia (n = 1). There were 10 adverse events in six patients; all were mild and resolved spontaneously, and without any intervention. The sensitivity, specificity and accuracy were the same for both early and late imaging: 0.86, 0.81 and 0.83, respectively. Interpreting early and late images together did not improve the results. No relationship between peptide dose and study accuracy was found. In patients undergoing both examinations, the accuracies of the peptide and in vitro-labeled leukocyte imaging were identical: 0.80. In summary, 99mTc-P483H safely, rapidly and accurately detected focal infection, was comparable with in vitro-labeled leukocyte imaging and therefore merits further investigation.

Radionuclide venography and labeled platelets in deep venous thrombosis.

99mTc-labeled macroaggregated albumin, 99mTc-labeled red blood cell, and 99mTc human serum albumin blood pool venography are simple, noninvasive imaging procedures that provide indirect evidence of deep vein thrombosis. These techniques rely on alterations in the normal venous anatomy. They do not determine the cause of venous obstruction and/or altered anatomy and cannot differentiate between acute and chronic deep venous thrombosis. In vitro labeled platelet scintigraphy provides direct evidence of active or acute thrombosis. Unfortunately, this technique requires a labor-intensive, lengthy labeling process and has a high number of false-negative results in patients who receive heparin therapy.

Comparison of 99mTc-methoxyisobutyl isonitrile and 201Tl scintigraphy for detection of residual thyroid cancer after 131I ablative therapy.

UNLABELLED: In this study, we compared 99mTc-methoxyisobutyl isonitrile (MIBI) with 201Tl scintigraphy for the detection of residual thyroid cancer not found by 131I scans in patients with increased risk of recurrence after 131I therapy. METHODS: 201Tl and MIBI scans were obtained in 54 patients with negative 131I scans 3-25 y (median 7.9 y) after the first postsurgical 131I therapy. Serum thyroglobulin (Tg) levels were measured while patients were receiving thyroid hormone and again 6 wk after withdrawal of hormone therapy. RESULTS: The overall results were the same for both 201Tl and MIBI imaging, with a sensitivity of 19 of 36 (53%), specificity of 17 of 17 (100%) and accuracy of 36 of 54 (69%). Planar images missed residual cancer in high cervical lymph nodes adjacent to salivary gland activity, in small nodes (<1 cm) deep in the neck or chest and with diffuse pulmonary micrometastases. Serum Tg was elevated in 24 of 36 (67%) patients with residual cancer; 201Tl detected tumor sites in 13 of 24 (54%) of these patients, and MIBI detected tumor sites in 14 of 24 (58%) of these patients. Of the 12 patients who had residual cancer and false-negative serum Tg levels, 6 had true-positive 201Tl and 5 had true-positive MIBI scans. CONCLUSION: 201Tl and MIBI planar imaging yield the same high specificity and positive predictive value for residual thyroid cancer in patients with high-risk profiles and negative radioiodide scans. Both imaging agents detected residual cancer in more than half of the patients in whom conventional staging techniques did not reliably detect either the presence or the extent of residual thyroid cancer and changed the management in patients with surgically resectable cancer.

Imaging techniques for evaluation of postoperative orthopedic infections.

Labeled leukocyte scintigraphy is the preferred imaging technique for the evaluation of suspected postoperative orthopedic infections. Labeled leukocyte localization returns to a normal pattern faster than MRI after bone trauma, surgical procedures, and treatment of osteomyelitis. 99mTc HMPAO labeled leukocyte scintigraphy is useful, particularly in children, because less peripheral blood volume is required for labeling. However, delayed 16-20 hour imaging is usually needed to detect low-grade osteomyelitis, and 111In WBC usually provides better images in adults. Combined 111In WBC/99mTc sulfur colloid marrow images improve the specificity for detection of osteomyelitis in regions containing active bone marrow. Simultaneous 111In leukocyte/99mTc bone SPECT imaging is usually necessary in regions such as the skull, spine, and hips, where there is overlapping bone, and soft tissues.

Diagnostic imaging of lower limb deep venous thrombosis.

Lower limb deep venous thrombosis is a common clinical disorder that can lead to fatal pulmonary emboli and postphlebitic syndrome. The clinical evaluation for deep venous thrombosis has been found to be useful in nonhospitalized patients, but a low-cost, easily available technique to confirm the presence of lower limp thrombi is still needed. Doppler ultrasound examination with compression has emerged as the diagnostic imaging study of choice for most patients. Contrast venography, magnetic resonance imaging or radionuclide scintigraphy may be useful in selected patients.

Emission-based attenuation correction of myocardial perfusion studies.

BACKGROUND: Nonuniform attenuation in the thorax can generate artifacts in single-photon emission computed tomographic myocardial perfusion studies that mimic coronary artery disease. In this article we present both phantom and simulation data, as well as clinical data, in support of an emission-based method that provides reliable correction for attenuation effects without the need for a transmission measurement. METHODS AND RESULTS: The attenuation map is derived from the measured distribution of 99mTc-labeled macroaggregated albumin in the lungs and a radioactive binder wrapped about the thorax. This information is acquired as part of a dual-isotope acquisition during the rest 201Tl study. Segmentation is used to define the interiors of lung and body compartments, which are assigned a single attenuation coefficient for each of the two tissue types. The appropriateness of this approach was investigated by examining the measured attenuation coefficients in a group of 80 individuals (40 male, 40 female) from positron emission tomographic transmission studies. The correction technique was evaluated with computer simulations, a physical phantom, and clinical data acquired from 20 patients. Analysis of the positron emission tomographic data found a small SD in the mean attenuation coefficients for the body (<5%) and lungs (<15%). The application of emission-based attenuation-correction technique produced a substantial reduction in the magnitude of the attenuation artifact in images obtained from both the phantom and the simulation studies. The emission-based attenuation-correction technique was easily applied to myocardial perfusion studies, where it had a significant effect, resulting in changes in interpretation for nine of 20 patients. CONCLUSIONS: The results of this study provide strong support for the concept that an attenuation map can be generated with fixed attenuation values in place of those that are directly measured. Thus the emission-based attenuation-correction technique can be considered an inexpensive alternative to transmission-based correction methods. Because the emission-based correction technique does not require any additional hardware, it has the major advantage of being applicable to all single-photon emission computed tomographic systems.

Four- to twenty-four-hour uptake ratio: an index of rapid iodine-131 turnover in hyperthyroidism.

UNLABELLED: Rapid thyroidal iodine turnover may contribute to 131I therapy failure in patients with hyperthyroidism. The utility of a 4- to 24-hr 131I uptake ratio was evaluated as an index of thyroidal iodide retention in hyperthyroid patients. METHODS: In 433 hyperthyroid patients, the success of 131I therapy was correlated with the following factors: gender, pretreatment with antithyroid drugs, clinical diagnosis, magnitude of early and late thyroidal 131I uptake values, and the 4- to 24-hr 131I uptake ratio. RESULTS: Of the 433 patients, 362 patients (84%) had a successful outcome after a single therapeutic dose of 131I while 71 (16%) did not. Multiple linear regression analysis revealed that the highest statistically significant predictor of outcome was the 4- to 24-hr 131I uptake ratio (p-value < 0.001); all other factors showed a weaker association. An 131I uptake ratio of > 1 was found in 67 (15%) patients. Thirty-two of these 67 patients (48%) failed 131I therapy, whereas those patients with uptake ratios of < 1.0, only 39/366 (11%) failed 131I therapy. CONCLUSION: The 4- to 24-hr 131I thyroidal uptake ratio is a practical substitute for exact determination of the effective half-life. It identifies patients who are likely to have a rapid 131I turnover without the need for extended thyroid uptake measurements. An 131I uptake ratio of > or = 1 was found in 15% of hyperthyroid patients and was associated with a near 50% 131I therapy failure rate.

Cranial osteomyelitis: diagnosis and follow-up with In-111 white blood cell and Tc-99m methylene diphosphonate bone SPECT, CT, and MR imaging.

PURPOSE: To assess the usefulness of indium-111 white blood cell and technetium-99m methylene diphosphonate bone single photon emission computed tomography (SPECT), computed tomography (CT), and magnetic resonance (MR) imaging in cranial osteomyelitis. MATERIALS AND METHODS: Twenty-six cases (25 patients: 13 male, 12 female; mean age, 55 years) of suspected osteomyelitis were evaluated. Sixteen were postoperative. Final diagnosis was established by means of bone culture in 18 cases and clinical follow-up in eight. RESULTS: Of 35 CT scans, 10 were true-positive (TP); three false-negative (FN); 13, true-negative (TN); one, false-positive (FP); and eight, equivocal. Of 36 SPECT scans, 19 were TP; 13, TN; one, FP; one, FN; and two, equivocal. Of 11 MR images four were TP; five, TN; and two, FN. CONCLUSION: CT is best for differentiation between soft-tissue and bone infection. MR imaging is best for assessment of the calvaria and skull base. SPECT is best for assessment of altered bone and may be the best technique for follow-up.

Evaluation of temporal and facial osteomyelitis by simultaneous In-WBC/Tc-99m-MDP bone SPECT scintigraphy and computed tomography scan.

A reliable imaging technique is needed for follow-up of patients with temporal and facial osteomyelitis. Clinical outcome in 20 patients with suspected osteomyelitis of the temporal/mastoid, calvarium, and mandible facial bones was evaluated with 30 combined In-WBC/Tc-99m MDP bone single photon emission computed tomographic (SPECT) scans and 27 computed tomographic scans. Simultaneous dual-tracer 25-minute SPECT scans were acquired 18 to 20 hours after radiotracer injection by use of a three-detector system. Diagnosis of the 20 patients (age range, 3 to 74 years) included 8 with facial osteomyelitis, 6 with malignant otitis externa, 3 with mandibular osteomyelitis, and 3 with calvarial osteomyelitis. Diagnosis was confirmed by biopsy/culture results in 18 patients and by endoscopic and clinical evaluation in 2 patients with initial negative scans. Of the 30 In-WBC/MDP scans, 15 were true-positive, 13 true-negative, 1 false-negative, and 1 equivocal. Of a total of 27 CT scans, 9 were true-positive, 5 false-negative, and 1 equivocal in patients with biopsy-proven osteomyelitis. Three computed tomographic scans were false-positive and 1 was equivocal in patients without osteomyelitis, because of concurrent postoperative bone abnormalities. Additionally, 8 computed tomographic scans were true-negative. These results suggest that dual In-WBC/Tc-99m MDP bone SPECT scintigraphy provides an accurate imaging modality for diagnosis and follow-up of temporal and facial osteomyelitis when existing clinical or postoperative bone changes make it difficult to detect active osteomyelitis by computed tomographic scan.

Utility of Tc-99m mebrofenin scintigraphy in the assessment of infantile jaundice.

Technetium-99m mebrofenin hepatobillary excretory patterns were assessed in 36 infants with hyperbilirubinemia. Phenobarbital was administered to 22 patients before imaging. Final diagnoses included: intrahepatic cholestasis (14 patients), neonatal hepatitis (nine patients), biliary atresia (eight patients), alpha-1-antitrypsin deficiency (two patients), Alagille's syndrome (two patients), and cystic fibrosis (one patient). No patient with biliary atresia showed bowel activity by 24 hours. Of the 28 infants without biliary atresia, 23 (82%) had bowel activity visualized by 6-8 hours and 26 (90%) had bowel activity by 24 hours. Two had no bowel activity at 24 hours: one had cystic fibrosis and one had neonatal hepatitis. Of the 26 patients with bowel visualization, the time to visualize bowel did not differ between patient groups with and without phenobarbital induction. All of the patients with hepatitis, including those with marked dysfunction, showed good hepatic uptake. Mebrofenin scintigraphy is an important imaging technique in the diagnostic evaluation of infants with hyperbilrubinemia. In addition to biliary atresia, intrahepatic cholestasis due to cystic fibrosis and severe neonatal hepatitis may also cause bowel nonvisualization up to 24 hours. The results of this study suggest phenobarbital induction may not be needed when Tc-99m mebrofenin scintigraphy is used for the assessment of infantile jaundice.

Colonic localization of labeled leukocytes in critically ill patients. Scintigraphic detection of pseudomembranous colitis.

This study assesses the causes of colonic localization of labeled white blood cells (WBCs) in critically ill patients who had undergone leukocyte scintigraphy for suspected infection. Forty-two patients showed abdominal or pelvic WBC localization; 20 of these had a pattern of colonic localization, and some also showed a pattern of small bowel activity. Eight of the 20 patients had documented gastrointestinal bleeding. White blood cell scintigraphy in these eight patients showed a pattern of multifocal and/or regional bowel activity that changed in intensity and location from early (3-5-hour) to delayed (18-28-hour) images. In contrast, 5 of the 6 patients with documented pseudomembranous colitis (PMC) showed intense WBC localization involving most of the colon. In 3 of these 5 patients, early and delayed images were acquired and showed a relatively constant pattern of WBC localization. The sixth PMC patient had been treated with vancomycin before leukocyte scintigraphy and showed minimal distal small bowel activity on early images and only mild regional colonic activity on delayed images. As in the patients with gastrointestinal bleeding, the remaining six patients showed either focal or regional activity of variable intensity that changed over time. In critically ill patients, gastrointestinal bleeding and PMC accounted for 14 of the 20 patients in which labeled leukocyte scintigraphy exhibited colonic activity. A pattern of diffuse, intense colonic radiotracer activity which persists from early to delayed imaging strongly suggests the presence of PMC in this patient population.(ABSTRACT TRUNCATED AT 250 WORDS)

Tc-99m MIBI scintigraphic detection of metastatic insular thyroid carcinoma.

Thallium-201 and, recently, Tc-99m MIBI have been used in conjunction with I-131 scintigraphy for follow-up of patients with well-differentiated thyroid cancer. Insular carcinoma of the thyroid is a fairly aggressive thyroid neoplasm that is believed to arise from follicular cells and usually concentrates I-131. The authors report a patient with recurrent insular thyroid carcinoma in whom bilateral adrenal and lung metastatic lesions developed 3 years after ablative I-131 therapy for cervical lymph node and skeletal metastases. Tc-99m MIBI planar and SPECT images demonstrated these new lesions better than pretherapy I-131 scintigraphy and affords an imaging technique for post-I-131 therapy follow-up that does not require withholding thyroid hormone suppression.