Ab initio studies of fluorine passivation on the electronic structure of the NV- defect in nanodiamond.

We have investigated using density functional theory the effect of fluorine termination of a (001) diamond surface on the electronic energy levels of an NV- centre buried beneath the surface. We find that, like OH termination, fluorine passivates the surface and reduces the influence of the surface on the electronic properties of the NV- centre. The results have significance for the optical properties of NV- defects in nanodiamonds.

E center in silicon has a donor level in the band gap.

It has been an accepted fact for more than 40 years that the E center in Si (the group-V impurity--vacancy pair)--one of the most studied defects in semiconductors--has only one energy level in the band gap: namely, the acceptor level at about 0.45 eV below the conduction band. We now demonstrate that it has a second level, situated in the lower half of the band gap at 0.27 eV above the valence band. The existence of this level, having a donor character, is disclosed by a combination of different transient-capacitance techniques and electronic-structure calculations. The finding seriously questions some diffusion-modeling approaches performed in the past.

Degradation of boron-doped Czochralski-grown silicon solar cells.

The formation mechanism and properties of the boron-oxygen center responsible for the degradation of Czochralski-grown Si(B) solar cells during operation is investigated using density functional calculations. We find that boron traps an oxygen dimer to form a bistable defect with a donor level in the upper half of the band gap. The activation energy for its dissociation is found to be 1.2 eV. The formation of the defect from mobile oxygen dimers, which are shown to migrate by a Bourgoin mechanism under minority carrier injection, has a calculated activation energy of 0.3 eV. These energies and the dependence of the generation rate of the recombination center on boron concentration are in good agreement with observations.

Generation of inorganic pyrophosphate from extracellular adenosine triphosphate by human serum and plasma.

OBJECTIVE: To quantify inorganic pyrophosphate (PPi) production from extracellular adenosine triphosphate (ATP) by human serum or plasma. METHODS: Serial measurements of ATP hydrolysis (t1/2) were performed by the luciferase method from a starting concentration of 1 microM in serum or platelet-poor plasma incubated under physiologic conditions. ATP was then pumped into another sample of each specimen using the rate constant derived from the ATP t1/2 of that specimen. Trace (32P) gamma ATP was added at the start of the infusion; conversion to (32P) inorganic orthophosphate (Pi) and to (32P) PPi was determined by precipitation of Pi as reduced phosphomolybdate before and after treatment with yeast pyrophosphatase. RESULTS: ATP was hydrolyzed by all serum and plasma specimens; the rate of hydrolysis in serum and plasma from the same blood sample was nearly identical. PPi was the major product, averaging 71%. CONCLUSION: PPi is the major product of ATP catabolism in serum and platelet-poor plasma.

Diagnostic reliability of radionuclide ventriculography in detecting left ventricular hypertrophy. Echocardiographic and ECG correlations.

Left ventricular hypertrophy (LVH) is frequently present in patients referred for radionuclide ventriculography (RVG) for evaluation of left ventricular function. During interpretation of these studies, the nuclear medicine physician may have the subjective impression that increased septal thickening is present because of the abnormally prominent separation of the right and left ventricular blood pools. To examine the diagnostic reliability of this finding, we retrospectively reviewed the RVG studies of 43 consecutive patients and correlated the finding of subjectively increased septal thickness with established echocardiographic (ECHO) criteria and commonly used electrocardiographic (ECG) indices of LVH. Using standard ECHO measurements of septal thickness as a gold standard, RVG interpretation of septal thickening demonstrated a sensitivity of 0.69, specificity of 0.70, and accuracy of 0.70. When compared with standard ECG criteria for LVH, RVG performed quite favorably in the diagnosis of LVH confirmed by ECHO left ventricular mass index. We conclude that scintigraphic evidence of LVH should be reported when RVG studies are interpreted.

Accuracy and precision of radionuclide measurement of CSF oscillation in the spine.

A technique for simultaneously measuring pulsation, translation and diffusion of a radioactive tracer in the spinal cerebrospinal fluid (CSF) has been described. To evaluate the accuracy and precision of this method for measuring CSF oscillation in the spine, an apparatus was designed that moved a radioactive source sinusoidally with known amplitude along a line. With list mode acquisition of radioactive emissions, the amplitude of oscillation was measured for a series of peak-to-peak amplitudes ranging from 0.01 mm to 3.8 mm. For oscillations larger than 0.35 mm peak-to-peak, measured values were within 6.1 percent of the expected values. For the spinal CSF, oscillation larger than 0.4 mm should be measured accurately with this technique.

Alzheimer disease: quantitative analysis of I-123-iodoamphetamine SPECT brain imaging.

To enable a more quantitative diagnosis of senile dementia of the Alzheimer type (SDAT), the authors developed and tested a semiautomated method to define regions of interest (ROIs) to be used in quantitating results from single photon emission computed tomography (SPECT) of regional cerebral blood flow performed with N-isopropyl iodine-123-iodoamphetamine. SPECT/IMP imaging was performed in ten patients with probable SDAT and seven healthy subjects. Multiple ROIs were manually and semiautomatically generated, and uptake was quantitated for each ROI. Mean cortical activity was estimated as the average of the mean activity in 24 semiautomatically generated ROIs; mean cerebellar activity was determined from the mean activity in separate ROIs. A ratio of parietal to cerebellar activity less than 0.60 and a ratio of parietal to mean cortical activity less than 0.90 allowed correct categorization of nine of ten and eight of ten patients, respectively, with SDAT and all control subjects. The degree of diminished mental status observed in patients with SDAT correlated with both global and regional changes in IMP uptake.

Measurement of cerebrospinal fluid movement in the spine. An experimental technique.

The authors devised a new technique for measuring cerebrospinal fluid movement in the spine. With gated list mode acquisition of radioactive emissions, bulk flow, oscillations, and dispersion of a bolus of isotope can be measured. The accuracy of the technique was measured in a simulation in which fluid oscillated at 71 cycles/minute and displaced at 6.5 cm/minute. With this method, the measured oscillation frequency and amplitude and the rate of translation were within 10% of actual values.

Comparison of technetium-99m pyrophosphate and technetium-99m DTPA aerosols for SPECT ventilation lung imaging.

Although [99mTc] diethylenetriaminepentaacetic acid (DTPA) is currently the most widely used radioaerosol, rapid alveolar clearance limits its usefulness for single photon emission computed tomography (SPECT) ventilation lung imaging. Previous research has shown that [99mTc]phosphate compounds have high alveolar deposition and slow clearance and thus provide suitable aerosols for pulmonary ventilation studies. We have compared the pulmonary retention and blood levels of [99mTc]pyrophosphate (PYP) and [99mTc]DTPA in eight normal nonsmoking male volunteers. These two radioaerosols have comparable pulmonary deposition. Technetium-99m PYP, however, has a much slower pulmonary clearance which allows sufficient time (20 or more minutes) for SPECT data acquisition using a single-headed rotating gamma camera. While the radiation absorbed dose to the lungs for [99mTc]PYP (0.31 rad/mCi) is greater than for [99mTc]DTPA (0.11 rad/mCi), it is at a clinically acceptable and safe level.

Comparison of single-photon emission computed tomography with [123I]iodoamphetamine and xenon-enhanced computed tomography for assessing regional cerebral blood flow.

Regional CBF (rCBF) images obtained from xenon-enhanced computed tomography (XeCT) and single-photon emission computed tomography (SPECT) with N-isopropyl-p-[123I]iodoamphetamine (IMP) done with a rotating gamma-camera were compared in nine patients. Both XeCT and SPECT/IMP demonstrated flow abnormalities at all sites of infarction identified by CT, while detecting reduced rCBF in areas normal by CT in eight of the nine patients. All areas that were abnormal on XeCT were abnormal on the comparable SPECT/IMP images. The major advantages of XeCT are its greater resolution and potential for noninvasive quantitation of rCBF, while the major advantage of SPECT/IMP is its visualization of the entire brain on transverse, coronal, and sagittal sections.

A simple method to quantitate iodine-124 contamination in iodine-123 radiopharmaceuticals.

Iodine-123 (123I) produced by the 124Te(p,2n)123I reaction contains several percent 124I radionuclidic contamination at the time of imaging. Since 124I degrades the quality of the images and causes unnecessary radiation absorbed dose to the patient, it is important to know the amount present in radiopharmaceuticals at the time of administration. A simple approach is described which uses a radionuclide dose calibrator and lead shield. The sample is assayed both shielded and unshielded and the ratio of readings depends uniquely upon the percent 124I present. The technique can be adopted for any type of dose calibrator, sample container, and Pb shield, but use of the numeric constants reported here should be restricted to the specified equipment.

Radioisotope measurement of the velocity of tracheal mucus.

A radioisotope scanning technique for measuring the velocity of tracheal mucus has been developed utilizing a canine model. A solution of stannous phytate labeled with 99mTc is introduced percutaneously into the lower trachea and the upward movement of the leading edge of the radioactivity is followed by repeat scanning at 2-minute intervals using a modified rectilinear scanner, thus allowing calculation of the velocity of the mucus. It is believed that this technique may be of value in studying the effect of experimentally induced tracheal injuries on mucus velocity. Possible applications of the technique for the study of the velocity of mucus in the human trachea are discussed.

Gamma camera energy windows for Tc-99m bone scintigraphy: effect of asymmetry on contrast resolution. Work in progress.

By raising the lower threshold of the Tc-99m energy window, rejection of scattered photons can be made more efficient. Unfortunately, with most gamma cameras significant nonuniformities are produced when the window is changed to an asymmetric setting. Recently introduced designs with gain stabilization of the photomultiplier tubes and improved energy correction maintain field uniformity even for an asymmetric window. To assess the impact of an asymmetric energy window on clinical images, 33 Tc-99m-MDP scintigrams of the lumbar spine were taken with symmetrical (126-154 keV) and asymmetric windows (135-154 keV). Bone:soft tissue ratios improved with the asymmetric window, and the resulting images were preferred by the physicians questioned.

Clearance of 85Sr-labeled calcium phosphate crystals from rabbit joints.

The clearance of basic calcium phosphate crystals from rabbit joints was studied using synthetic crystals with characteristics similar to natural joint fluid mineral phase. Addition of strontium 85 during synthesis resulted in uniform trace-labeling. Crystals were rapidly taken up by synovial lining cells after intrasynovial injection. The time for clearance of one-half of the injected basic calcium phosphate crystal mass was 6.7 days, approximately 3 times faster than found previously for the much larger calcium pyrophosphate dihydrate crystals.

Gastric emptying in patients with diabetes mellitus.

We evaluated whether chronic nausea and vomiting in diabetic patients correlate with abnormal gastric emptying of liquid or solid, or both liquid and solid, radiolabeled meals and recorded the acute effects of metoclopramide. last, we compared several methods of analyzing gastric emptying data obtained using the gamma-camera. Eighteen healthy control subjects and 16 insulin-dependent diabetics with neuropathy were investigated. Ten of the patients suffered from chronic nausea and vomiting; the remaining 6 served as disease controls. Gastric emptying of solid and liquid meals could best be described by the slopes of two linear components and their intercept. Liquid meals generally were handled normally, while solid meals were emptied slowly by both groups of diabetics. A single dose of metoclopramide frequently corrected the delayed onset of the second, more rapidly emptying phase, that is, the major abnormality of solid emptying. The radiologic findings during a barium meal did not distinguish symptomatic from asymptomatic patients. We conclude that abnormal gastric motor function, manifested by delayed emptying of a solid meal or barium suspension, or both, is common in diabetics with neuropathy and that this motor abnormality is not the only cause of chronic vomiting. The beneficial, often short-term symptomatic effects of metoclopramide in these patients appear to be mediated by a combination of normalization of gastric emptying and a central antiemetic action.

Effect of esophageal emptying and saliva on clearance of acid from the esophagus.

We studied clearance of acid from the esophagus and esophageal emptying in normal subjects. A 15-ml bolus of 0.1 N hydrochloric acid (pH 1.2) radiolabeled with [99mTc]sulfur colloid was injected into the esophagus, and the subject swallowed every 30 seconds. Concurrent manometry and radionuclide imaging showed nearly complete emptying of acid from the esophagus by an immediate secondary peristaltic sequence, although esophageal pH did not rise until the first swallow 30 seconds later. Esophageal pH then returned to normal by a series of step increases, each associated with a swallow-induced peristaltic sequence. Saliva stimulation by an oral lozenge shortened the time required for acid clearance, whereas aspiration of saliva from the mouth abolished acid clearance. Saliva stimulation or aspiration did not affect the virtually complete emptying of acid volume by the initial peristaltic sequence. We conclude that esophageal acid clearance normally occurs as a two-step process: (1) Virtually all acid volume is emptied from the esophagus by one or two peristaltic sequences, leaving a minimal residual amount that sustains a low pH, and (2) residual acid is neutralized by swallowed saliva.

Internal derangement of the temporomandibular joint: detection by single-photon emission computed tomography. Work in progress.

The diagnostic accuracy of both planar and single-photon emission computed tomography (SPECT) bone scintigraphy, radionuclide angiography, arthrography, and conventional radiography was evaluated in 36 patients with temporomandibular joint (TMJ) dysfunction undergoing preoperative testing. The sensitivity of SPECT bone scintigraphy (0.94) was comparable with arthrography (0.96) and significantly better than planar bone scintigraphy (0.76), radionuclide angiography (0.35), and transcranial lateral radiographs (0.04). While data for a larger asymptomatic control population are needed, preliminary results give SPECT a diagnostic specificity of 0.70 for internal derangements of the TMJ requiring surgical correction. It is concluded that SPECT bone scintigraphy is a useful noninvasive imaging test to screen for internal derangement of the TMJ.

Internal mammary lymphoscintigraphy in patients with breast cancer. Correlation with computed tomography and impact on radiation therapy planning.

Twenty patients with Stage I or II breast cancer, all of whom had undergone radiation therapy planning, were examined with internal mammary lymphoscintigraphy (IMLS) and computed tomography (CT). Based on the results of IMLS, radiation fields were revised in 12 cases (60%). The mean number of nodes identified by IMLS in each patient was 7.8, which is in agreement with previously published autopsy and scintigraphic data. CT identified 243 possible nodes of normal size, but only 49 of them were within 10 mm of regions shown to be positive on the scintigram. The authors conclude that IMLS is the method of choice for defining parasternal lymphatic drainage and identifying those internal mammary nodes that are normal in both size and function.

Clearance of calcium pyrophosphate dihydrate crystals in vivo. III. Effects of synovial hemosiderosis.

Synthetic triclinic calcium pyrophosphate dihydrate crystals, uniformly labeled with 85Sr and 45Ca, were injected into the knee joints of 2 normal adult rabbits and 2 rabbits previously injected repeatedly with autologous blood. The "half clearance time" of the injected crystal mass was 20.4 and 19 days from control joints, nearly identical to previously reported values in 6 rabbits (19.1 +/- 1.4), and 28.8 and 34 days from the joints injected with blood, a significant difference (P less than 0.05). Iron stains showed hemosiderin granules in the superficial synovium in these joints. Electron microscopy showed crystals with a molar calcium/phosphorus ratio of 1.0 and particles containing iron within synovial cells. We hypothesize that the decreased clearance rate from hemosiderotic synovium is due to inhibition of one or more intracellular pyrophosphatases by iron.