SPECT images using a multislice fan beam collimator

Several methods to improve the image resolution of single photon emission computed tomography (SPECT) occur to us. It is one method to use multislice fan beam collimators which have the parallel collimation along the cephalic-caudul axis of a patient and the conversing collimation within planes parpendicular to that axis. It is impossible to obtain corrective image when we used the algorithm which is commonly used for reconstruction of SPECT images. We proposed a reconstruction algorithm for multislice fan beam collimator in this paper. An interpolation method developed for fan beam type X-ray CT was modified to reconstruct images from SPECT with multislice fan beam collimator. This algorithm was confirmed by means of computer simulation studies. Beside improving the system resolution by effectively reducing the intrinsic resolution of the cameras, this collimator also increases the system sensitivity by utilizing a large fraction of the crystal area. We have thought that to use multislice fan beam collimator is beneficial for SPECT images.     

Experimental study on the collimator for increasing the resolution of N-isopropyl-p-(123I)iodoamphetamine (IMP) SPECT imaging of the brain

This study was carried out to design a new collimator for the present 123I-IMP SPECT imaging of the brain, which is hindered by the contamination of 124I and 126I. In this study we intended to increase spacial resolution along the transaxial direction and, at the same time, to compensate for the decrease of sensitivity by sacrificing the resolution along the axial direction to some extent. For this purpose, we developed 4 kinds of slat type units; ultrahigh resolution (UHR), high resolution (HR), high sensitivity (HS), and ultrahigh sensitivity (UHS). In practice, either UHR or HR is set to the detector together with either HS or UHS. After testing 4 kinds of combinations, we found that the combination of UHR-HS gave us far better images than those obtained with the conventional medium energy parallel hole collimator and was best suited for 123I-IMP SPECT imaging of the brain at present. We are now thinking of fusing these two units together into one collimator.     

Evaluation of gamma camera collimator for regional cerebral blood flow measurements using a 133Xe inhalation method

In the measurements of regional cerebral blood flow (rCBF) using inhalation of 133Xe gas, the activity present is generally limited in lower levels than those of usual brain scintigraphy. Measurements with low count-rate are usually resulted in diminishing the accuracies of results obtained. Therefore, it is necessary to make measurements using a high sensitive collimator for getting as much count-rate as possible when a gamma camera is used. The relationships among sensitivity and structures of multi-parallel collimator were mathematically analyzed. The results of analysis suggested that sensitivity usually increased by using a collimator with holes of reduced height and diameter. A prototype multi-parallel collimator with holes of low height and small diameter was made in our laboratory for testing sensitivity and resolution. The collimator possessing 1141 holes of 6 mm phi in hole diameter, 1.5 cm is hole height and septal thickness of 1 mm lead showed 24 times more sensitive than those of a general all purpose collimator supplied by the manufacturer. However, resolution measured in FWHM was of 9 to 14 mm at the collimator face and of 29 to 38 mm at 5 cm from the face. The results indicated that this collimator was useful enough in rCBF measurements with 133Xe inhalation using a gamma camera. The mathematical analysis however, suggested that optimum collimator for rCBF measurements was approximate 4.5 mm phi in hole diameter and 1.0 cm in hole height.     

A cooperative group study of clinical efficacy of the liver SPECT

The purpose of this study is to evaluate the clinical efficacy of the liver SPECT about detectability of SOLs (space occupying lesion). The images were interpreted with the planar scintigram (PS) only and combination of PS and SPECT (single photon emission computed tomography) by 11 physicians. Changes of false positive and false negative rate were calculated to evaluate the influence of the diffuse parenchymal liver disease and the localization of the SOLs. Addition of SPECT to PS in the cases who are suspected SOLs is effective in right hepatic lobe (right anterior and posterior segment) to detect the SOLs, but not effective in left lateral segment. Addition of SPECT to PS in the cases with diffuse parenchymal liver disease and SOLs increases the false positive rate.     

Theoretical study of the ethane ionization spectra within the correlation hole model

This work is an extension of a previous study on the assignment of the peaks of the photoionization spectrum of C₂H₆ [1]. The model of the correlation hole is reconsidered in order to carry out a new study of the states² A _1g ,² E _g ,² E _u and² A _2u of the C₂H ₆ ⁺ The qualitative relations which the average mass of the electrons in the Coulomb hole must have for the four states of the C₂H ₆ ⁺ , lead to a new criterion for the assignation of the peaks of the spectrum. The arrangement obtained for the two lower peaks is in agreement with those obtained previously [1].     

Results obtained from the group study on the clinical efficacy of SPECT of the liver

The influence of SPECT over the detectability of SOL in the liver was evaluated by the Subcommittee on Efficacy Study, which belongs to Medical and Pharmaceutical Committee of Japan Radioisotope Association, under the participation of 9 hospitals including some university hospitals. In this study segmental reading of the SOL was requested. The film reading was performed twice on the different patient-groups and the results from well-experienced doctors (11 doctors) were summarized, indicating a slight increase in sensitivity as a whole although there were some doctors showing a reverse effect in each performance. Sensitivity was determined in the patient-group without SOL, which showed a slight decrease as a whole, indicating that SPECT had some possibility of increasing false positive cases. In the study of SOL detectability based on its segmental location, a marked positive effect of SPECT was noted in the right anterior and right posterior segments whereas a marked negative effect in the left lateral segment. The left medial segment also showed a slight decrease in the detectability of SOL.     

Monte Carlo study of the translocation of a polymer chain through a hole

The translocation of a polymer chain through a narrow hole in a rigid obstacle has been studied by the static Monte Carlo simulations. A modified self-avoiding walk on a cubic lattice has been used to model the polymer in an athermal solution. The entropy of the chain before, in the course, and after the translocation process has been estimated by the statistical counting method. The thermodynamic generalized forces governing the translocation have been calculated. The influence of the system geometry on the entropic barrier landscape is discussed.     

Impact of dose rates on the position accuracy of multi-leaf collimator

PurposeTo study the impact of dose rates on the position accuracy of a Varian multi-leaf collimator (MLC) in dynamic IMRT.MethodsFour nasopharyngeal carcinoma (NPC) patients who received dynamic IMRT were chosen. The dosimetric verification at different dose rates (400–600 MU/min) was performed using a PTW 2D ion chamber Array in a Varian Clinac iX linear accelerator. Meanwhile, the actual MLC leaf position data was taken by the MLC controller. The passing ratios of dosimetric verification were compared at different dose rates, and the MLC leaf position deviations were evaluated through the parameters of Error Histogram and Error RMS.ResultsThe passing ratios of dosimetric verification both of the criteria of 3%/3 mm and 2%/2 mm did not show statistical differences between two dose rates (P>0.05). But using the criteria of 2%/1 mm, significant differences were observed between two dose rates (P<0.05). Moreover, according to the analysis of the Error Histogram and Error RMS, the MLC leaf position deviations were higher with the increase of dose rate, and the differences between 400 and 600 MU/min were statistically significant (P<0.05).ConclusionsThe higher dose rate will affect the accuracy of MLC leaf position in dynamic IMRT.     

Increasing the speed limit for hole transport in DNA

Transport of positive charge or holes in DNA occurs via a thermally activated multi-step hopping mechanism. The fastest hopping rates reported to date are those for repeating poly(purine) sequences in which hopping occurs via a random walk mechanism with rate constants of k(hop) = 4.3 × 10(9) s(-1) for poly(dG) and 1.2 × 10(9) s(-1) for poly(dA). We report here the dynamics of charge separation in DNA conjugates possessing repeating 7-deazaadenine (dzA) sequences. These data provide an estimated value of k(hop) = 4.2 × 10(10) s(-1) for poly(dzA), an order of magnitude faster than for poly(dG).     

Topography and field effects in the inner side of microvia hole using ToF‐SIMS

We have developed a simple and powerful method, which is called ‘angled sample holder method’, to characterize a topographic structured sample such as microsized via hole of ball grid array using time‐of‐flight SIMS. The diameter of via holes was 100 µm and the depth was 70 µm. To remove the shaded area by incidence primary ion beam and to extract secondary ions from the bottom of a via hole, several types of angled sample holders with compensation steering plate were applied on the basis of simulation results using SIMION code. And the analyses using angled sample holder method enabled us to characterize the bottom and side wall of a via hole in clear. Copyright © 2014 John Wiley & Sons, Ltd.     

Direct measurement of free-volume hole distributions in polymers by using a positronium probe

We have directly measured the free-volume hole distributions in semicrystalline polypropylene by positron lifetime annihilation spectroscopy. A Laplace inversion technique was engaged to analyze the positron lifetime spectra measured under quasi-isotropic external pressures of 0, 4.2, and 14.7 kbar into continuous lifetime distributions. The hole radii distributions as determined from the ortho-positronium lifetime distributions are found to be between 4.0 and 0.5 Å and to have maxima at 3.0, 1.9, and 1.1 Å under the external pressures of 0, 4.2, and 14.7 kbar, respectively. © 1992 John Wiley & Sons, Inc.     

Measurement of free-volume hole size distribution in Nafion-117 using positron annihilation spectroscopy

We report a new result of free-volume hole size distribution in water and ethanol-swollen Nafion-117 polymer. With the increase in water content, free-volume hole size decreases, but overall the volume fraction increases. The hole size distribution in dry polymer is seen to be distinctly different from hydrated membranes. The narrow and symmetric distribution in hydrated membrane as compared to dry membrane is believed to be a consequence of crosslinking due to cluster formation. In alcohol-swollen membranes, on the other hand, not only are the free-volume size and fraction seen to be higher, the hole size distribution is seen to be broader compared to dry or hydrated membranes, indicating the effect of penetration of alcohol into the hydrophobic backbone region. We have also examined our results vis-a-vis reported gas diffusion studies in Nafion in the framework of existing free-volume model. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 983–989, 1998     

Fundamental study for SPECT imaging with 123I produced by (p, 5n) reaction

The effects of higher-energy photon from 123I (p, 5n) on the SPECT image quality were evaluated. The quality was evaluated by image contrast and %rms. Image contrast had similar tendency to planar and SPECT FWHM value. %rms was affected by septal penetration. Using 140 keV high resolution collimator (140 keV HR), image contrast was superior to that for 300 keV medium energy collimator (300 keV ME), but septal penetration rate (SPR) was 18% and %rms was 10.5. When quantitation is required, the collimator with less SPR than 18% is recommended for SPECT imaging. Using 300 keV ME, SPR was 0.05%, but spatial resolution and image contrast were inferior to that for 140 keV HR.     

CASSCF/CAS-PT2 study of hole transfer in stacked DNA nucleobases

CASSCF and CAS-PT2 calculations are performed for the ground and excited states of radical cations consisting of two and three nucleobases. The generalized Mulliken-Hush approach is employed for estimating electronic couplings for hole transfer in the pi-stacks. We compare the CASSCF results with data obtained within Koopmans' approximation. The calculations show that an excess charge in the ground and excited states in the systems is quite localized on a single base both at the CASSCF level and in Koopmans' picture. However, the CASSCF calculations point to a larger degree of localization and, in line with this, smaller transition dipole moments. The agreement between the CAS-PT2 corrected energy gaps and the values estimated with Koopmans' theorem is better, with the CAS-PT2 calculations giving somewhat smaller gaps. Overall, both factors result in smaller CASSCF/CAS-PT2 couplings, which are reduced by up to 40% of the couplings calculated using Koopmans' approximation. The tabulated data can be used as benchmark values for the electronic couplings of stacked nucleobases. For the base trimers, comparison of the results obtained within two- and three-state models show that the multistate treatment should be applied to derive reliable estimates. Finally, the superexchange approach to estimate the donor acceptor electronic coupling in the stacks GAG and GTG is considered.     

Testing performance of the improved pinhole collimator and its application to small animals

Testing performance of the improved pinhole collimator of 1.5 mm aperture attached to the gamma camera was carried out with three kinds of radionuclides, 99mTc, 67Ga and 131I, using a hand-made phantom. The results obtained in this experiment were compared to those obtained with a human pinhole collimator of 4 mm aperture. Those were nearly understood by taking account of the effective aperture of a pinhole collimator for each effective photon energy. And all scintigrams obtained from rats with various scintigraphy showed high resolution images.