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FT-IR studies of the secondary structure of mt-PA6 and mt-PA6 treated with L-arginine, (+)-citrulline, and L-asparagine were carried out in aqueous buffer solution. Spectral subtraction was used to remove the interfering water bands in the amide absorption region, and the amide I absorptions were monitored to investigate changes in the secondary structure of the mt-PA6 induced by the binding of these amino acids. The spectral data showed a narrowing of the amide I absorption of mt-PA6 on treatment with L-arginine, (+)-cirrulline, and L-asparagine. Deconvolution of the amide I absorption revealed vibrational bands characteristic of β-sheet (1632 cm−1), disordered or bound water (1644 cm−1), and turns (1660 cm−1) secondary structures for the mt-PA6. Curve-fitting methods were also used to examine the changes in spectra and secondary structure of the mt-PA6 resulting from amino acid treatment. Analysis of the spectral data shows that loss in intensity of the bands near 1644 and 1660 cm−1 is responsible for the amino acid-induced narrowing of the mt-PA6 amide I absorption. In addition, the spectral data could suggest different binding interactions for L-arginine to mt-PA6 compared to the L-asparagine and (+)-citrulline.

Pinhole magnification imaging is an important technique for practitioners of pediatric nuclear medicine. This article reviews basic principles of pinhole magnification imaging and ways for optimizing image acquisition with this technique. Applications to skeletal scintigraphy, scrotal scintigraphy and renal cortical scintigraphy are discussed and illustrated.

Pinhole magnification scintigraphy is an effective means of evaluating the pediatric skeleton because it provides optimal high-resolution images. This technique is indicated when diagnostic uncertainty persists after high-resolution imaging with parallel hole collimation. Pinhole magnification scintigraphy requires approximately 20 minutes of acquisition time per image and meticulous attention to details such as choice of pinhole insert, collimator positioning, and patient immobilization. However, the technique is superior to planar imaging in demonstrating acute osteomyelitis in bone adjacent to growth centers and epiphyseal involvement that is either primary or the result of local spread of infection. In addition, pinhole imaging has proved highly reliable in the early diagnosis of Legg-Calvé-Perthes disease and is useful in depicting osteonecrosis related to specific causes such as corticosteroid treatment or trauma. Scintigraphic manifestations of femoral head ischemia or infarction and findings indicative of osteomyelitis associated with a hip effusion are well demonstrated with pinhole imaging. This technique also helps characterize osteoid osteomas and may be used intraoperatively to confirm the complete excision of this benign tumor. Finally, pinhole magnification scintigraphy clearly depicts fractures of the femoral neck and allows a high degree of confidence in diagnosing injuries to the small bones of the hands and feet.

A method for performing scatter corrections that would directly use the photopeak information and would be straightforward for use in clinical practice would be attractive in SPECT imaging. The dual-photopeak window method may be such a method. It relates the scatter fraction to the ratio of the lower to the total parts of a split-photopeak window. We investigated the use of this scatter correction method on a dedicated brain camera.Calibration curves for the Ceraspect, a dedicated brain imaging camera, were obtained for four split-window combinations using point sources in air and water. Simulations of the Ceraspect calibration curves at several energy resolution values were obtained using a Monte Carlo simulation of the instrument.The calibration curves, experimental and simulated, revealed an ambiguous and unstable relationship between lower-to-total ratio and scatter fraction.The unsatisfactory calibration curves can be attributed to the limited scatter produced in a brain-sized phantom during the calibration process and inherent stability problems in the calibration process. The dual-photopeak window method is not usable for small-field imaging systems and may even be unstable for larger-field systems.

A method for registering three-dimensional CT, MR, and PET data sets that require no special patient immobilization or other precise positioning measures was adapted to high-resolution SPECT and MRI and was applied in 14 subjects (five normal volunteers, four patients with dementia (Alzheimer's disease), two patients with recurrent glioblastoma, and three patients with focal lesions (stroke, arachnoid cyst and head trauma]. T2-weighted axial magnetic resonance images and transaxial 99mTc-HMPAO and 201Tl images acquired with an annular gamma camera were merged using an objective registration (translation, rotation and rescaling) program. In the normal subjects and patients with dementia and focal lesions, focal areas of high uptake corresponded to gray matter structures. Focal lesions observed on MRI corresponded to perfusion defects on SPECT. In the patients who had undergone surgical resection of glioblastoma followed by interstitial brachytherapy, increased 201Tl corresponding to recurrent tumor could be localized from the superimposed images. The method was evaluated by measuring the residuals in all subjects and translational errors due to superimposition of deep structures in the 12 subjects with normal thalamic anatomy and 99mTc-HMPAO uptake. This method for superimposing magnetic resonance and high-resolution SPECT images of the brain is a useful technique for correlating regional function with brain anatomy.

Sequential thallium-201-chloride and technetium-99m-hexamethylpropyleneamine oxime single-photon emission computed tomography (SPECT) images were obtained in a patient with extracranial metastatic glioblastoma multiforme. Thallium-201 uptake was high (three times the scalp background) in all pathologically confirmed extracranial metastases and moderate (1.6 times scalp background) intracranially, where most biopsy specimens showed gliosis with scattered atypical astrocytes. Technetium-99m-HMPAO uptake was decreased intracranially in the right frontal and parietal lobes which had been irradiated. It was also decreased in one well-encapsulated scalp lesion and high in another scalp mass with less defined borders. Possible mechanisms of tumor uptake of these agents are reviewed.

Myocardial clearance of the new cationic, lypophilic myocardial perfusion agent, Tc-99m-hexakis-2-methoxy-2-methylpropyl isonitrile (MIBI) was studied in nine patients with coronary artery disease. Regional time-activity curves were determined from serial postexercise myocardial SPECT images after a single dose of Tc-99m MIBI. There were significant differences between the clearance rates from normal and ischemic myocardium. Tc-99m MIBI washout from normal myocardium was 27 +/- 8% by 6 hours after injection. Clearance from mild myocardial defects (initial activity greater than 60% of the activity in normal myocardium) was 16% by 6 hours in six patients. No washout was detected by 6 hours in the three patients with severe myocardial defects. The ratio between the activity in ischemic and normal myocardium increased from 0.70 +/- 0.08 to 0.80 +/- 0.13 and 0.84 +/- 0.13 at 4 and 6 hours after injection in the patients with mild defects. In the patients with large defects, the ratio increased from 0.42 +/- 0.09 to 0.54 +/- 0.07 at 6 hours. It is concluded that, while redistribution is substantially slower than with Tl-201, image interpretation and data evaluation should be approached cautiously when imaging is delayed 4 hours or more after injection of Tc-99m MIBI. Quantitative techniques aimed at evaluating the extent and intensity of myocardial ischemia will be particularly affected.

Four 3 beta-hydroxy-delta 5-steroid sulphates were found to be potent and specific inhibitors of the sperm acrosomal proteinase, acrosin. Two of these acrosin inhibitors, desmosteryl sulphate and cholesteryl sulphate, occur naturally in spermatozoa. Desmosteryl sulphate, an inhibitor of the in-vitro capacitation of hamster spermatozoa, has a Ki of 3.5 x 10(-6) M for the inhibition of acrosin. The mechanism of inhibition of sperm capacitation by sterol sulphates is probably due to their inhibition of acrosin.

Interest in international standardization is increasing rapidly in Latin America — to a considerable extent through the efforts of the American Standards Association which has sought ways and means of supplying more adequate American representation and co-operation in the development of standards. The program for the future includes exchange of technical data among the various American republics and development of inter-American standards to the advantage of all the Americas.

A high-pressure gas scintillation proportional chamber has been designed and constructed to image x and gamma rays for medical applications. The chamber contains 4 atm of pure xenon. Ultraviolet light emitted from excited xenon atoms within the detector is collected by a hexagonal array of seven UV-sensitive photomultiplier tubes, which in turn are separated from the pressurized gas by 1-cm-thick fused-silica windows. A model was used to predict the energy resolution of the device as a function of fill-gas pressure, voltage within the detector, and light-collection efficiency. The energy resolution improved with increasing scintillation region voltage from 17% full width at half maximum (FWHM) at 1.9 kV to 10% FWHM at 3.0 kV for 59.5-keV photons; once above 1.5 kV, there was no improvement with increasing drift voltage. The addition of the signals from the peripheral phototubes to that of the center phototube did not substantially improve the energy resolution of the device. This was because the noise that was present yielded a high correlation between the phototubes; when this noise was incorporated into the model, the energy resolution of the multiphototube system was accurately estimated. The energy resolution of the gas scintillation proportional chamber was found to be superior to the sodium iodide Anger camera at 59.5 keV by a factor of 2. Further improvement can be obtained by increasing the scintillation region voltage and by increasing the light-collection efficiency by moving the scintillation region closer to the phototubes.

A technique is described for the anterior and lateral imaging of the thorax during internal mammary lymphoscintigraphy. It permits reliable estimates of lymph-node location to within 3 mm of the actual location. Use of the results from these measurements can be directly applied to radiation portal planning.

A multidetector single photon emission computerized tomographic brain scanner was modified to improve the angular sampling. The detector plate was rotated such that 12, 24, or 36 angular projections could be acquired. Phantom experiments demonstrated that the angular aliasing artifacts seen in images obtained with 12 detectors were eliminated with 36 effective detectors. In addition, the reconstructed image noise in a uniform source was decreased by a factor of 1.7 by the use of 36 instead of 12 angular projections, as predicted by computer simulation.

Acrosin and acrosomal hyaluronidase were inhibited by tetradecyl sodium sulphate (TDSS) in vitro at concentrations of less than 10(-4) M. TDSS prevented the removal in vitro of the cumulus oophorus by testicular hyaluronidase and the zona pellucida by acrosin. TDSS had a contraceptive effect in rabbits when administered intravaginally before coitus or released at levels of 1-3 micrograms/day from intrauterine silicone rubber devices.

Despite its 9.3-min half-life, Ta-178 can be used to produce radiopharmaceuticals for lung and liver imaging. A variety of human serum albumin microspheres and other particulate radiopharmaceuticals were labeled with Ta-178. A period of approximately 10 min was required for their preparation and administration to rats. Extrapolation to the clinical situation suggests that imaging could take place after one half-life of the nuclide has elapsed. We found that satisfactory imaging is possible using Ta-178 radiopharmaceuticals with the Anger camera and a pinhole collimator. Since short imaging times, high spatial resolution, and low patient doses are reasonable objectives in pediatric scintigraphy, these new radiotracers may prove useful for lung and liver imaging in children.

Blood flow can be measured by monitoring the count rate of Krypton-81m after its parent, Rubidium-81 (a potassium analogue), has been deposited in the tissue. The steady-state Kr-81m count rate reflects both production by decay of Rb-81 and washout due to blood flow. Its use is theoretically superior to that of Xenon-133 for quantification of blood flow (cc/min per 100 gm) since: (1) multiple flow measurements can be obtained from a single arterial injection, (2) flow-dependent changes in the count rate of Kr-81m provide a steady-state measure of specific flow, and (3) errors due to uptake in fat are eliminated. The count rate of Kr-81m was measured as a function of flow in a dynamic phantom with a NaI crystal, suing both pure cyclotron-produced Rb-81 and commercially available samples with as much as 25% contamination from Rb-82m. The phantom was calibrated by measuring the flow-rate constants with Xe-133. No significant difference was found between the flow-rate constant measured with three pure samples. The ratio of the zero-flow Kr-81m count rate to the rate observed in the presence of flow showed excellent correlation with calibrated flow over a range of rate constant from 0 to 0.02 sec (-1). This study suggests that regional specific flow can be measured in vivo with currently available Nal detecting systems after the intra-arterial injection of Rb-81.

The detection efficiency of a high-pressure, gas scintillation proportional chamber (GSPC), designed for medical imaging in the 30-150 keV energy range, has been investigated through measurement and Monte Carlo simulation. Measurements were conducted on a GSPC containing 4 atm of pure xenon separated from a hexagonal array of seven ultraviolet-sensitive photomultiplier tubes by 1.27-cm-thick fused-silica windows. Experimental measurements of the photopeak efficiency, fluorescence escape efficiency, and the energy collection efficiency were obtained. Results were also obtained for different photon energies and different values of temporal resolution. The measurements were compared with the results obtained from a Monte Carlo simulation designed specifically for investigating the imaging of low-energy photons (below 150 keV) with a gas-filled detector. The simulation was used to estimate photopeak efficiency, fluorescence escape efficiency, photopeak-to-fluorescence escape peak ratio, quantum interaction efficiency, energy collection efficiency, and local energy collection efficiency. The photopeak efficiency of the GSPC relative to that of a 3-in. (7.62-cm)-thick sodium iodide crystal was measured to be 0.284 +/- 0.001 at 60 keV and 0.057 +/- 0.001 at 140 keV. Of the 60-keV photons incident upon the detector, 70% +/- 4% interacted in the detector, with 28% +/- 1% being in the photopeak, as estimated both by experimentation and through the simulation. The maximum energy collection efficiency was found to be 65% at 60 keV, with 46% being deposited within 0.2 cm of the initial photon interaction. The information gained from this study is being used to design an optimized detector for use in specialized nuclear medicine studies.

Resting computerized transaxial tomography was performed after the i.v. injection of thallium-201 in six normal subjects and in five patients who had had myocardial infarctions 3 mo to 4 yr before scintigraphy. Decreased myocardial activity corresponded to the site of previous infarction in all cases and was clearly separated from adjacent myocardium with normal activity. With tomography, the left ventricle was clearly separated from surrounding structures such as the left-ventricular cavity, the lungs, and the liver. This study demonstrates the feasibility for the assessment of myocardial perfusion using single-photon transaxial emmission computed tomography.

Forty-six patients were studied with N-isopropyl I-123 p-iodoamphetamine (IMP) and the Harvard Scanning Multidetector Brain System. In nine control patients, good differentiation between the gray and white matter of the cerebral cortex and the basal ganglia was evident. Regional uptake was affected by physiologic maneuvers (visual stimulation). In 24 patients studied for stroke, IMP images demonstrated areas that were involved in acute infarction in eight patients whose initial transmission computerized tomography (TCT) was normal; IMP also showed perfusion abnormalities larger than the TCT abnormality in ten patients. Perfusion abnormalities were present in 23/24 of these patients. Seven patients studied with a history of TIA had normal TCT and IMP images. In three patients studied during seizure activity, regions of hyperperfusion corresponded to the EEG seizure focus. Markedly decreased activity was present in three patients with brain tumor and corresponded to the focal abnormality on the TCT study. Our study demonstrates the feasibility of assessing regional brain perfusion using a radiopharmaceutical that is lipid soluble and has a high extraction fraction in the brain, together with single-photon ECT.

A 30 degrees slant-hole collimator was used during radionuclide ventriculography of the cardiac blood pool to improve imaging of the heart in both the modified left anterior oblique (MLAO) and right anterior oblique (RAO) views. In the MLAO view, with the holes slanted caudally, good separation between the left atrium and left ventricle was achieved, and the septum was displayed without foreshortening. In the RAO view with the collimator flat against the chest there was better resolution of the cardiac apex. The results of ejection fraction and wall motion analysis in these patients correlated well with contrast ventriculography (r=0.94). Combination of the slant-hole collimator, in vivo red blood cell labeling with stannous pyrophosphate, simultaneous collection of all phases of the cardiac cycle, and cine mode display, provide a practical system for the noninvasive measurement of left ventricular performance parameters.

The biodistribution of N-isopropyl-p-[123I]iodoamphetamine (I-123 IMP) in the Macaca fascicularis monkey was determined at 15 min and at 1, 4, 24, and 48 hr after intravenous injection. Brain uptake was 7.8% of the injected dose at 1 hr, with little change in concentration between 15 min and 1 hr, falling thereafter. Eye uptake reached a maximum of 0.23% of injected dose at 24 hr, with activity primarily in the pigmented layers. The human absorbed radiation dose was calculated on the basis of biodistribution data. The critical organ is the eye (0.407 rad/mCi of I-123 IMP). The eye dose increased to 1.11 rad/mCi with 4% contamination from I-124 IMP and to 0.535 rad/mCi with 0.4% contamination from I-125 IMP. The absorbed dose to the liver was 0.127 rad/mCi for pure I-123 IMP and the thyroid dose was 0.120 rad/mCi, both increasing with either I-124 or I-125 contamination. While delayed eye uptake has not yet been reported in the human, care should be exercised in limiting the amount of contaminating I-124 or I-125 to the lowest practical level.

In November 1983, the final report for the initial crashworthy cyclic control stick effort was published. The report detailed the development and testing of a purely mechanical self-contained crashworthy cyclic control stick equipped with load-limiting and separating joint. The joint was to limit impact loads transmitted to a crewmember. This report covers the additional development and testing of this concept by Simula Inc. to further delethalize the separating crashworthy cyclic control stick. Using an impact load-limiting grip pad and reduction of the moving mass to reduce the inertial forces, two configurations were subjected to static and dynamic pendululm testings. Additional destructive static tested in a full-scale dynamic test using an anthropomorphic dummy and a vertically stroking UH-60A Black Hawk crewseat. Testing demonstrated that the delethalized stick worked as intended when struck by the dummy. It also showed that the loads transmitted to the dummy were far less than with conventional sticks.

Lipophilic neutral 99mTc complexes of diaminedithiol (DADT) ligands cross the brain-blood barrier. A new derivative of DADT family, 99mTc ethyl cysteinate dimer (ECD) showed high brain uptake in nonhuman primates. We report here the in vivo kinetics and biodistribution results in 16 normal human subjects. Dynamic images of brain obtained for 10 min following an i.v. administration of [99mTc]ECD showed that the maximum 99mTc brain activity reached within 1 min and remained near that level for the next 10 min. The blood clearance of the tracer was very rapid and the activity remaining in blood after 5 min was less than 10%. Within 2 hr 50% of 99mTc activity was excreted in urine. Anterior and posterior total-body images were obtained at 5, 30, 60 min, 2, 4, 24, and 48 hr using a moving table at 20 cm/min. Percent injected dose was calculated for different organs and tissues. The brain uptake was 6.5 +/- 1.9% at 5 min postinjection and remained relatively constant over several hours. Two-compartment analysis of brain time-activity curve showed that 40% of brain activity washed out faster (T 1/2 = 1.3 hr) while the remaining 60% had a slower clearance rate (T 1/2 = 42.3 hr). Some of the tracer was excreted through the hepatobiliary system. Lung uptake and retention of [99mTc]ECD was negligible. Radiation dosimetry is favorable for the administration of up to 20-40 mCi of [99mTc]ECD. These results show that [99mTc]ECD is rapidly extracted and retained by the brain providing favorable conditions for single photon emission computed tomography imaging.

Highly purified acrosin (A), the serine protease of the acrosome; which facilitates penetration of sperm through the zona pellucida, rapidly hydrolyzes tri- and tetrapeptide synthetic substrates relatively specific for thrombin (T) (S2238, chromozym TH, S2160) and factor Xa (Xa) (S2222) but only minimally hydrolyzes plasmin and plasma kallikrein substrates. A shares other biological properties with T and Xa. A slowly converts highly purified fibrinogen to fibrin and rapidly converts purified bovine prothrombin into T in a factor V or phospholipid-independent fashion. A, like T and Xa, is inhibited by antithrombin Ill; the inhibition is enhanced by heparin. A, like T, is inhibited by the pancreatic secretory trypsin inhibitor of Kazal but not by the Kunitz-Northrop trypsin inhibitor. A, unlike T, is not inhibited by hirudin and does not aggregate platelets. As has been reported for T and other serine proteases, A stimulates the growth of cultured fibroblasts in a concentration-dependent fashion. In T3T mouse fib,Vblasts only A stimulated DNA synthesis; T, plasmin and trypsin had no effect. Although the evolutionary and physiologic implications of similarities between A and clotting serine proteases remain unclear, the observed effect of A on cell proliferation may assign a new role for this enzyme in early embryogenesis.

We evaluated a single-photon emission computed tomographic system using ten scanning detectors in a circular array. The system uses focusing collimators that scan radially as well as tangentially. The spatial resolution in the tomographic plane is 2.6 cm FWHM and the axial resolution is 3.3 cm FWHM. The resolution is independent of position within the field of view, and nearly independent of energy through 511 keV. Sensitivity was found to be 4600 cps/muCi-ml for an extended phantom, 20-cm in diameter, filled with Tc-99m; 7200 cps/muCi-ml with TI-201; and 8000 cps/muCi-ml with Ga-67. Investigations of positional uniformity indicated some quantitative distortion of data due to inadequate attenuation correction. Improvement in the attenuation correction is necessary before truly quantitative tracer distribution studies are undertaken.

Tantalum-178 is a short-liver radionuclide (T 1/2 = 9.3 min.) and emits primarily 56- to 64-keV characteristic x-rays. We have determined the imaging characteristics with this radionuclide and a large-field-of-view Anger camera. With a pinhole collimator, good spatial resolution is possible with Ta-178, although the image quality is superior with Tc-99m under comparable conditions. Spatial resolution with parallel-hole or converging collimators was much less satisfactory with Ta-178 because of septal penetration by high-energy photons. Pulmonary perfusion and liver-spleen images of excellent quality were obtained in the rabbit using the pinhole collimator and Ta-178-labeled agents.

The growth of nuclear medicine has paralleled the development and acceptance of gamma cameras, which are stationary instruments that produce an image of an isotope distribution. The most successful gamma camera is based on a large, single crystal of the scintillator sodium iodide coupled to an array of photomultiplier tubes and electronic networks to determine the location of a gamma ray. Current cameras are capable of spatial resolution of 4.0 mm or better. Other types of gamma cameras have been developed, including the multi-crystal camera and a limited number of instruments using gas detectors and semiconductor detectors. The scintillation type of gamma camera will continue to be the dominant camera for the next 5 to 10 years, and will continue to gradually improve. Most significant improvements will result from application of digital electronics to position circuits.

System options for developing landfill gas recovery projects are discussed. The report also presents factors affecting the economics of each option. Sample calculations and worksheets are included to assist in the process of making preliminary judgments about production and revenue potentials for landfill gas recovery at a specific site.

The author has been in the business of constructing rules for war games (i.e., games with human players) for some years. The search for “realism” has been arduous and always frustrating. Since the author must usually adopt a pragmatic attitude towards this elusive property and make do with whatever is at hand, the search for truly general criteria for realism has been sometimes desperate. Over the last several years one such criterion has slowly emerged. It is only a necessary condition, not a sufficient one. Therefore it is only a weak criterion for realism, but appears to be a strong test for a lack of realism. Special purpose games can probably be imagined for which the theorem does not apply.