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.

Protective and cellular immune responses to idiotypic determinants on cells from a spontaneous lymphoma of NZB-NZW F1 mice.

A spontaneous lymphoma (141) producing monoclonal IgM is established in NZB/NZW F(1) (B/W) mice who spontaneously develop an autoimmune disease. Idiotypic determinants of 141 IgM are present on the lymphoma cell surface as shown by indirect immunofluorescence and specific cytotoxicity with rabbit anti-idiotypic antiserum. Fluorescence and cytotoxicity are inhibited by 141 IgM but not by 104E IgM, a monoclonal IgM produced by a BALB/c plasmacytoma. Immunization of B/W mice with 141 IgM before transplantation of lymphoma 141 confers protective immunity. No such protection occurs after immunization with 104E IgM or other unrelated proteins. Protected mice contain spleen cells cytotoxic for 141 lymphoma cells. This cytotoxicity is blocked by incubation of spleen cells with 141 IgM but not with 104E IgM. Moreover, splenic lymphocytes from protected mice are stimulated to synthesize DNA by 141 IgM but not by 104E IgM. These results suggest that specific cellular immune responses to idiotypic determinants may participate in the observed protection against challenge with the corresponding B-cell tumor.

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.

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.

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.

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.

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.

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.

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.

Septic arthritis in sickle-cell thalassemia. Pathophysiology of impaired response to infection.

The knee of a boy with sickle-cell thalassemia became infected with Salmonella enteritidis, sensitive to ampicillin. Doses of ampicillin that achieved anti-bacterial titers of 32 in synovial fluid failed to eradicate the organism. The synovial fluid exhibited severe hypoxia, hypercapnia, and lactic acidosis. Methods were developed to estimate the oxygen saturation of blood in regional venous capillaries, the degree of periarticular sickling, changes in the viscosity of local blood, and the articular ratio of blood flow to oxygen utilization. The results suggest that local vascular insufficiency associated with sickling may affect host response to infection and efficacy of antibiotics. The Salmonella C1 readily transformed to an L form on hypertonic medium, thus acquiring resistance to ampicillin and other cell-wall inhibitors.

Septic arthritis and Reiter's syndrome in sickle cell disorders: case reports and implications for management.

Two patients with sickle cell disorders developed gram-negative septic arthritis and responded poorly to conventional managment. Unfavorable factors included (1) confusion with the nonseptic arthropathy of a sickle crisis; (2) impaired articular perfusion, perhaps related to local sickling; (3) conversion of an infecting organism to an L-form in the presence of cell-wall inhibitors; and (4) interference with cultures and antibacterial titrations of synovial fluid caused by intro-articular administration of antibiotics. Prolonged treatment with very high doses of antibiotics was required to eradicate infection in both patients. Because sickling and local hypoxia apparently interfere with defenses against infection, anemia should be corrected by transfusion. One patient had had Reiter's syndrome; the dysenteric form of this disease may be a cause of arthritis in some sicklemic patients.

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.

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.

Clearance of calcium pyrophosphate dihydrate crystals in vivo. I. Studies using 169Yb labeled triclinic crystals.

Synthetic triclinic calcium pyrophosphate dihydrate crystals were uniformly trace-labeled with Ytterbium-169 (169Yb), a pure gamma-emitting isotope with a halflife of 31 days. The solubility of the labeled crystals was similar to that of cold synthetic crystals. The clearance rate of labeled sterile crystals, sieved to obtain the desired size, was determined after injection of microgram quantities into 4 arthritic huuman and 3 normal adult rabbit joints and corrected by the observed rate of clearance of free 169Yb. The derived rate constants were then used to calculate the time required for half of the injected dose of CPPD to be cleared from the joint. Crystal clearance was found in all instances. Crystal removal from normal rabbit joints was much more rapid than from the much larger human arthritic joints and was inversely proportional to the size of the crystals injected.

Evidence for an abnormal microenvironment in the thymus of New Zealand black mice.

The proliferative response of NZB and DBA/2 thymocytes and spleen cells to allogeneic cells and mitogens was studied in intact and lethally irradiated bone marrow-repopulated syngeneic recipients. The major findings were complete recovery of function in NZB spleen cells and premature recovery in thymocytes compared to the control DBA/2 strain. This recovery was not influenced by the administration of thymosin to the recipients, and was not due to functional thymocytes present in the donor marrow inoculum. These results suggest normal or increased support of T cell differentiation by the radioresistant thymus in 4-month-old NZB mice. Thymic epithelial cell products regulating T cell maturation may be disordered or unbalanced but do not appear to be broadly deficient at this age.

CLearance of calcium pyrophosphate dihydrate crystals in vivo. II. Studies using triclinic crystals doubly labeled with 45Ca and 85Sr.

The clearance rate of isotopically labeled synthetic triclinic calcium pyrophosphate dihydrate (CPPD) crystals injection into rabbit joints was estimated by serial counting. Kinetic analysis using a four compartment model showed that half of the injected dose was cleared from 4 rabbit knee joints in 19.1 +/- 0.42 (SEM) days. Profound hypomagnesemia, produced in 2 rabbits with a low magnesium diet, did not affect the rate of crystal clearance detectably. Lavage of joints with solutions known to promote CPPD crystal solubility failed to remove detectable radioactivity. The previous finding of CPPD crystals in synovial phagocytes by electron microscopy, together with the finding of nuclide activity in the synovium and the failure to remove such activity by joint lavage, suggests that endocytosis by synovial cells is an important, effective mechanism controlling the synovial fluid concentration of crystals in patients with CPPD crystal deposition disease.

Hyperactive T-cell function in young NZB mice; increased proliferative responses to allogenic cells.

The one-way mixed lymphocyte reaction was employed to study proliferative responses to antigens by mature, immunocompetent T cells from NZB mice 3 weeks to 4 months old. Compared to cells from control mice of the same H-2 type, thymus, spleen and lymph node cells from NZB mice were hyperactive in this response. The results are discussed in relation to possible effects of chronic stimulation by endogenous type C leukaemia virus upon differentiation of functional T cells or upon regulation by T cells of other T-cell functions, including augmentation of antibody responses.

Lymphocytes binding polyriboadenylic acid and synthesizing antibodies to nucleic acids in autoimmune and normal mice.

Splenic lymphocytes from both normal and autoimmune mice bind significant quantities of polyriboadenylic acid (poly rA) when incubated with radiolabeled poly rA for 40 min at 37 degrees C. This poly rA binding is specifically inhibited by an excess of nonradioactive poly rA and by anti-mouse immunoglobulin. Poly rA binding is decreased by exposing spleen cells to Pronase and is restored by subsequent culture for 18 to 72 hr. Poly rA-binding activity is associated more with bone marrow-derived than with thymus-derived lymphocytes. These results suggest the presence of autoantigen-binding lymphocytes in normal as well as autoimmune mice. Furthermore, spleen cells from normal and autoimmune mice cultured for 72 hr synthesize and secrete antibodies to poly rA and DNA. These antibodies can be recovered from the culture supernatants by a solid immunoadsorbent technique and antibody immunoprecipitation. The synthesis of antibodies to nucleic acids by normal spleen cells suggests that autoreactive lymphocytes may be released from normal immunoregulatory control during in vitro culture conditions.