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

Purpose: Nuclear cardiology plays an important role in clinical assessment and has enormous impact on the management of a variety of cardiovascular diseases. Pediatric patients at different age groups are exposed to a spectrum of radiation dose levels and associated cancer risks different from those of adults in diagnostic nuclear medicine procedures. Therefore, comprehensive radiation dosimetry evaluations for commonly used myocardial perfusion imaging (MPI) and viability radiotracers in target population (children and adults) at different age groups are highly desired. Methods: Using Monte Carlo calculations and biological effects of ionizing radiation VII model, we calculate the S-values for a number of radionuclides (T1-201, Tc-99m, I-123, C-11, N-13, O-15, F-18, and Rb-82) and estimate the absorbed dose and effective dose for 12 MPI radiotracers in computational models including the newborn, 1-, 5-, 10-, 15-yr-old, and adult male and female computational phantoms. Results: For most organs, Tl-201 produces the highest absorbed dose whereas Rb-82 and O-15-water produce the lowest absorbed dose. For the newborn baby and adult patient, the effective dose of Rb-82 is 48% and 77% lower than that of Tc-99m-tetrofosmin (rest), respectively. Conclusions: Rb-82 results in lower effective dose in adults compared to Tc-99m-labeled tracers. However, this advantage is less apparent in children. The produced dosimetric databases for various radiotracers used in cardiovascular imaging, using new generation of computational models, can be used for risk-benefit assessment of a spectrum of patient population in clinical nuclear cardiology practice. (C) 2015 American Association of Physicists in Medicine.

Assessment of radiation dose in nuclear cardiovascular imaging using realistic computational models

Addendum to "Relevance of accurate Monte Carlo modeling in nuclear medical imaging" [Med. Phys. 26, 574-608 (1999)].

Radiation exposure and associated radiation risks are major concerns for fetal development for pregnant patients who undergo radiation therapy or diagnostic imaging procedures. In order to accurately estimate the radiation dose to the fetus and assess the uncertainty of fetal position and rotation, three hybrid computational fetus phantoms were constructed using magnetic resonance imaging (MRI) for each fetus model as a starting point to construct a complete anatomically accurate fetus, gravid uterus, and placenta. A total of 27 fetal organs were outlined from radiological images via the Velocity Treatment Planning System. The DICOM-Structure set was imported to Rhinoceros software for further reconstruction of 3D fetus phantom model sets. All fetal organ masses were compared with ICRP-89 reference data. Our fetal model series corresponds to 20, 31, and 35 weeks of pregnancy, thus covering the second and third trimester. Fetal positions and locations were carefully adapted to represent the real fetus locations inside the uterus for each trimester of pregnancy. The new series of hybrid computational fetus models together with pregnant female models can be used in evaluating fetal radiation doses in diagnostic imaging and radiotherapy procedures.

https://iopscience.iop.org/article/10.1088/1361-6560/ab44f8/pdf

Construction of realistic hybrid computational fetal phantoms from radiological images in three gestational ages for radiation dosimetry applications

The many applications of Monte Carlo modeling in PET arouse to increase the accuracy and computational speed of Monte Carlo codes. The accuracy of Monte Carlo simulations strongly depends on cross-section libraries used for photon transport calculations. Furthermore, large amounts of CPU time are required to obtain meaningful simulated data. We present a comparison of different photon cross-section libraries together with the parallel implementation of the 3D PET Monte Carlo simulator, Eidolon on a MIMD parallel architecture. Different photon cross-section libraries and parametrizations show quite large variations as compared to the most recent EPDL97 nuclear data files for energies from 1 keV to 1 MeV. Together with the optimization of the computing time performances of the Monte Carlo software, photon transport in 3D PET could be efficiently modeled to better understand scatter correction techniques. In implementing Eidolon on a parallel platform, a linear speedup factor was achieved with the number of computing nodes.

Improvement of the performance and accuracy of PET Monte Carlo simulations

Whole-body (WB) PET parametric imaging has recently become clinically feasible with the introduction of multi-bed dynamic acquisition protocols, benefiting from the latest technologies in clinical PET scanners. Currently, Time-of-Flight (TOF) capabilities of modern PET systems allow for more accurate localization of the annihilation position along the line of response (LOR). As a result, TOF can prevent propagation, during image reconstruction, of various resolution degrading factors and noise beyond their origin and across the image space, thus providing i) an inherent correction or contrast recovery mechanism and ii) an effective sensitivity gain relative to non-TOF acquisitions. In addition, the incorporation of the PET system's point spread function (PSF) within the reconstruction system matrix has resulted in i) enhanced contrast and ii) considerably lower image roughness. Recently, we explored the effect of TOF and PSF on WB indirect Patlak imaging. In this work, we systematically investigate the additional benefit of TOF and PSF on clinical studies when reconstructing WB Patlak images directly from projection data. Therefore, we developed a nested direct 4D Patlak WB reconstruction algorithm capable of i) utilizing TOF information, ii) modeling PSF with an effective space-invariant Gaussian resolution kernel and iii) supporting both standard and generalized Patlak analysis. Our clinical evaluation on a set of WB dynamic clinical studies, as acquired with Siemens Biograph mCT TOF scanner, indicated a 15–30% target-to-background (TBR) and contrast-to-noise ratio (CNR) enhancement in all examined regions and for both Patlak methods, when only TOF feature is enabled, with an additional 5–10% improvement when combined with a 4mm FWHM Gaussian PSF kernel. Thus, we have demonstrated the benefits of integrating TOF and PSF features within a clinically adoptable direct 4D WB generalized Patlak reconstruction scheme.

Habib Zaidi

Papers

Assessment of radiation dose in nuclear cardiovascular imaging using realistic computational models

Addendum to "Relevance of accurate Monte Carlo modeling in nuclear medical imaging" [Med. Phys. 26, 574-608 (1999)].

Construction of realistic hybrid computational fetal phantoms from radiological images in three gestational ages for radiation dosimetry applications

Improvement of the performance and accuracy of PET Monte Carlo simulations

Clinical evaluation of direct 4D whole-body PET parametric imaging with time-of-flight and resolution modeling capabilities