放射線画像の物理的画質―基礎的概念と理論―

放射線画像診断において，X 線画像の物理的画質は正確な確定診断に影響を与える。高画質になるほど，診断の精度は上がる。X 線画像の画質は，三つの画質因子，すなわち，コントラスト，解像度（鮮鋭度），ノイズ（X線画像モトル）に影響されることはよく知られている。これら三つの因子は，物理的画質の基本的要素を構成する。撮像システムのコントラストは，通常X 線画像コントラストといわれるが，被写体（放射線）コントラスト，フィルムコントラスト（グラディエント）と一次線（散乱線）含有率に関係している。解像特性は，modulation transfer function (MTF)，またはline spread function (LSF) あるいは point spread function (PSF) で，また，画像ノイズ特性は，Wiener spectrum あるいは自己相関関数によって定量的に評価されている。本稿では，X 線撮像システムの画像コントラスト，MTF およびウィナースペクトルの基礎的概念と理論を解説した。In diagnostic radiologic examinations, diagnostic accuracy or correct diagnosis is influenced by the physical imagequality of radiographic images. As the physical image quality improves, the diagnostic accuracy is increased. It is known that the physical image quality is affected by three fundamental factors, namely, contrast, resolution (or sharpness), and noise (or radiographic mottle) of imaging systems. These three parameters constitute the fundamental components of physical imagequality. The contrast of an imaging system, commonly referred to as radiographic contrast (or image contrast), is related to the subject contrast (or radiation contrast), film contrast (or gradient), and primary (or scatter) fraction. The resolution of imaging systems has been determined by means of the modulation transfer function (MTF), line spread function (LSF),or point spread function (PSF). The image noise has been quantifi ed in terms of the Wiener spectrum or autocorrelation function. This article describes basic concept and theory for the radiographic contrast, MTF, and Wiener spectrum of radiographic systems.総

Concept of Formation Length in Radiation Theory

The features of electromagnetic processes are considered which connected with finite size of space region in which final particles (photon, electron-positron pair) are formed. The longitudinal dimension of the region is known as the formation length. If some external agent is acting on an electron while traveling this distance the emission process can be disrupted. There are different agents: multiple scattering of projectile, polarization of a medium, action of external fields, etc. The theory of radiation under influence of the multiple scattering, the Landau-Pomeranchuk-Migdal (LPM) effect, is presented. The probability of radiation is calculated with an accuracy up to "next to leading logarithm" and with the Coulomb corrections taken into account. The integral characteristics of bremsstrahlung are given, it is shown that the effective radiation length increases due to the LPM effect at high energy. The LPM effect for pair creation is also presented. The multiple scattering influences also on radiative corrections in a medium (and an external field too) including the anomalous magnetic moment of an electron and the polarization tensor as well as coherent scattering of a photon in a Coulomb field. The polarization of a medium alters the radiation probability in soft part of spectrum. Specific features of radiation from a target of finite thickness include: the boundary photon emission, interference effects for thin target, multi-photon radiation. The experimental study of LPM effect is described. For electron-positron colliding beams following items are discussed: the separation of coherent and incoherent mechanisms of radiation, the beam-size effect in bremsstrahlung, coherent radiation and mechanisms of electron-positron creation.Comment: Revised review paper, 96 pages, 28 figures. Description of SLAC E-146 experiment removed, discussion of CERN SPS experiment adde

HR: A System for Machine Discovery in Finite Algebras

We describe the HR concept formation program which invents mathematical definitions and conjectures in finite algebras such as group theory and ring theory. We give the methods behind and the reasons for the concept formation in HR, an evaluation of its performance in its training domain, group theory, and a look at HR in domains other than group theory

The minimum flux corona; theory or concept

The reply to the criticisms of the minimum flux theory is discussed. These criticisms are correct in substance, as well as in detail. Counter arguments that the minimum flux corona theory is untenable, because of errors in its formulation, are presented