There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Co-Planar Stereotaxic Atlas of the Human Brain—3-Dimensional Proportional System: An Approach to Cerebral Imaging, J. Talairach, P. Tournoux. Georg Thieme Verlag, New York (1988), 122 pp., 130 figs. DM 268

“Unpaired Image-to-Image Translation using Cycle-Consistent Adversarial Networks”の学習報告

NOTE The report of the Committee without its annexes appears as Official Records of the General Assembly, Sixty-third Session, Supplement No. 46. The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the Secretariat of the United Nations concerning the legal status of any country, territory, city or area, or of its authorities, or concerning the delimitation of its frontiers or boundaries. The country names used in this document are, in most cases, those that were in use at the time the data were collected or the text prepared. In other cases, however, the names have been updated, where this was possible and appropriate, to reflect political changes. Scientific Annexes Annex A. Medical radiation exposures Annex B. Exposures of the public and workers from various sources of radiation INTROdUCTION 1. In the course of the research and development for and the application of atomic energy and nuclear technologies, a number of radiation accidents have occurred. Some of these accidents have resulted in significant health effects and occasionally in fatal outcomes. The application of technologies that make use of radiation is increasingly widespread around the world. Millions of people have occupations related to the use of radiation, and hundreds of millions of individuals benefit from these uses. Facilities using intense radiation sources for energy production and for purposes such as radiotherapy, sterilization of products, preservation of foodstuffs and gamma radiography require special care in the design and operation of equipment to avoid radiation injury to workers or to the public. Experience has shown that such technology is generally used safely, but on occasion controls have been circumvented and serious radiation accidents have ensued. 2. Reviews of radiation exposures from accidents have been presented in previous UNSCEAR reports. The last report containing an exclusive chapter on exposures from accidents was the UNSCEAR 1993 Report [U6]. 3. This annex is aimed at providing a sound basis for conclusions regarding the number of significant radiation accidents that have occurred, the corresponding levels of radiation exposures and numbers of deaths and injuries, and the general trends for various practices. Its conclusions are to be seen in the context of the Committee's overall evaluations of the levels and effects of exposure to ionizing radiation. 4. The Committee's evaluations of public, occupational and medical diagnostic exposures are mostly concerned with chronic exposures of …

sources and effects of ionizing radiation

Aim We sought to investigate the feasibility of 18F-FDG-leukocyte imaging to detect islet rejection. Methods Two thousand Sprague-Dawley (SD, syngeneic group) or Lewis (allogeneic group) islet equivalents were intraportally injected into SD rat recipients. Four and 7 days after transplantation, 108 18F-FDG–labeled splenocytes were injected into the jugular vein. Splenocytes were harvested from naive or sensitized (12 days after intraportal transplantation of 2000 Lewis IEQ) SD rats. Positron emission tomography (PET) imaging was started 5 minutes after splenocyte infusion and performed hourly for 4 hours. Results One hour after splenocyte injection, FDG was mainly detected in the heart and lungs. It was then further distributed to other organs, and from the second hour, the highest tracer concentration was located in the abdomen. Liver FDG uptake was similar between syngeneic, allogeneic, and sensitized allogeneic groups at 4 and 7 days after islet transplantation. Discussion No islet rejection was detected by 18F-FDG-leukocyte imaging. The amount of transplanted tissue was only few millilitres and the additional related inflammation in case of rejection is small and difficult to detect. The liver showed a relatively high spontaneous tracer uptake; the related background prevented detection of a potential increase in tracer uptake in cases of islet rejection.

Assessment of 18F-FDG-leukocyte imaging to monitor rejection after pancreatic islet transplantation.

123I neuroligands allow SPECT imaging of dopaminergic and benzodiazepine systems in various movement disorders including Parkinson’s disease, Huntington’s disease, progressive supranuclear palsy, multiple system atrophy and Wilson’s disease. Cocaine analogs with high affinity and selectivity for dopamine transporter (DAT) sites in the putamen and the caudate nucleus such as 123I-CIT [1], 123I-Altropane [2], and 123I-FPCIT [3] allow SPECT imaging of the DAT system. Likewise, dopamine transporters can be imaged with SPECT using 123I neuroligands such as 123IBZM [4], 123IBF [5], etc. Significant progress has been made in the design of high-resolution SPECT cameras dedicated for brain imaging. Also, improved physical compensation and reconstruction algorithms have been proposed, and some have been incorporated into commercial software supplied by vendors to end-users. However, in spite of advances in algorithmic designs allowing improved quantitative accuracy, absolute quantitation of DAT or D2 has been and is still very challenging with SPECT, unlike PET, due to the difficulty to accurately and simply compensate for image degrading factors such as attenuation, scatter, limited spatial resolution and low sensitivity [6]. Sensitivity is an important impediment against dynamic brain SPECT imaging which is required to achieve absolute quantitation of the distributions of many of these neuroligands. Photon attenuation and contributions from scattered photons reduce the accuracy of measured activities and activity concentrations. In addition, limited spatial resolution causes a “hot” object that is less than 2–3 times the system’s resolution in a “colder” background to appear blurred with reduced activity concentration (partial volume effect). While the total reconstructed counts within the object are conserved, the count density is decreased from the true value because the data are distributed over a larger area than the object’s true activity distribution.

/pdf/is-absolute-quantification-of-dopaminergic-neurotransmission-4xjxuqtl7t.pdf

Is absolute quantification of dopaminergic neurotransmission studies with 123I SPECT ready for clinical use

Design of a benchmark platform for evaluating PET-based contouring accuracy in oncology applications

Accurate scatter correction is one of the major problems facing quantitative 3D PET and many methods have been developed for the purpose of reducing the resultant degradation of image contrast and loss of quantitative accuracy. A new scatter correction method called Statistical Reconstruction-Based Scatter Correction (SRBSC) is proposed in this paper and evaluated using Monte Carlo simulations, experimental phantoms and clinical studies. For accurate modeling, the scatter fraction and scatter response function for uniformly attenuating media are parametrised using Monte Carlo simulations.

Statistical reconstruction-based scatter correction: a new method for 3D PET

Continuous bed motion (CBM) has been recently introduced in the clinic as an alternative PET acquisition mode with respect to the traditional time-discretized step-and-shoot (SS) multi-bed acquisitions. In CBM mode, each slice can be considered as a different bed, since it is scanned over a different acquisition window. By reducing scan time discretization from a whole bed down to a single slice, the CBM acquisition offers additional degrees of freedom when designing acquisition protocols and thus larger margins for their optimization. Therefore, CBM mode could be particularly important for protocols of higher complexity, such as whole-body (WB) dynamic PET acquisitions. However, only a few studies have quantitatively validated the 2 modes on clinical data. In this work, we evaluate CBM vs. SS quantitative performance on a set of clinical data acquired over a 0–60min period using a WB dynamic PET acquisition protocol with a Biograph mCT TOF scanner. The TOF resolution (580ps) of the scanner allowed selecting faster CBM speeds (4.2mm/sec) and equivalent SS frames (30sec/bed), eventually permitting acquisition of 12 WB total passes of which half were performed in CBM mode and half in SS mode. The two modes were alternated between successive passes to allow a balanced interleaving of post-injection time between them to ensure an objective comparison. The evaluation of the 2 modes in terms of target-to-background (TBR) contrast and contrast-to-noise ratio (CNR) has been conducted for various noise levels by gradually adding all respective passes from each mode as well as in the parametric images after applying post-reconstruction WB Patlak analysis. Our results indicate a bias of ∼10% between the 2 modes for the low count frames, reducing to <3% as we gradually add all respective frames. In addition, a small bias of <10% was observed in Patlak images at overlapped slices between beds, which is attributed to the non-uniformity of the axial sensitivity profile of SS mode.

Habib Zaidi

Papers

Assessment of 18F-FDG-leukocyte imaging to monitor rejection after pancreatic islet transplantation.

Is absolute quantification of dopaminergic neurotransmission studies with 123I SPECT ready for clinical use

Design of a benchmark platform for evaluating PET-based contouring accuracy in oncology applications

Statistical reconstruction-based scatter correction: a new method for 3D PET

Continuous bed motion Vs. step-and-shoot acquisition on clinical whole-body dynamic and parametric PET imaging