What is the importance of density on the radiograph?
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Show AbstractWhen x-ray movies were first taken at the University of California Medical School in San Francisco in about 1950, it became apparent immediately that the dose to the patient was an important limiting factor. Since a movie is simply a series of still films, the problem of patient dose in movies is actually related to the whole problem of patient dose in radiography. In this study the aim is to understand the conditions which give the required information on the film with the least patient dose. Our first studies dealt with ordinary radiography. In order that there may be information on a radiograph, there must be a “picture” of an object having a certain density and certain light transmission with a surround of a different density and different light transmission through the roentgenogram. What we actually see when viewing a film are areas with various brightnesses. The density of the object and of the surround obviously depends upon the exposure of the film in these areas. This in turn is affected by the amount of radiation incident on the body and transmitted to the film through the various objects which it must traverse. The quality of the radiation used to make the radiograph affects the fraction of the radiation transmitted through the object and its surround, the contrast between them on the roentgenogram, and the ratio of the skin dose to the film dose and density. The appearance of the radiograph will be dependent upon the brightness of the light by which it is viewed. These considerations led to the study of: (a) quality and quantity of radiation as a function of voltage and filtration; (b) density of film in cassettes with screens versus exposure of cassette front at various qualities; (c) absorption of radiation by the cassette front and screen; (d) usual density of radiographs; (e) factors affecting contrast on radiographs; (f) patient exposure required to produce given densities and contrasts on a radiograph as a function of quality; (g) transmission of radiation of several qualities through various materials of clinical interest; (h) appearance of radiographs as a function of view-box brightness. The studies were applicable particularly to films of the abdomen although the basic principles are of general application. The abdomen was chosen for study because (a) it is a relatively homogeneous area of soft tissue, (b) a high patient dose is necessary in obtaining its films, and (c) there is a present interest in gonadal exposure. Significant reduction in the patient exposure required for abdominal films will be the most effective way of reducing gonadal exposure in medical radiography. Certain assumptions were made to simplify the studies in an attempt to arrive at some useful concepts. Article HistoryAccepted:
July 1962 BASIC RADIOLOGICAL DENSITIES DENSIDADES RADIOLÓGICAS BÁSICASApril 17, 2018 | Translate Conventional radiology is a medical image that provides us a great piece of information about the estate of our inner structures, those which we are not able to see with a naked eye. However, how is it possible to contradistinguish these structures? On which is conventional radiography based? What occurs when we do a simple radiography of chest or abdomen? All this procedure is explained through the interaction of the radiation on the tissues. The emitted radiation are the x-rays, which will traverse the patient and they will provide an image of their inside once they traverse the different tissues. This beam of electromagnetic radiation can be absorbed or scattered in its trajectory, resulting a decrease in the original intensity of the X-rays and the atoms of the substance where the beam of radiation is incident. There are several factors which determine that this radiation would be more or less absorbed and/or scattered: the atomic number of the irradiated atom, the thickness of the traversed material, the density of the given material (in our case body tissue) and the energy that the radiation beam has (wavelength of incident radiation). This is going to provoke that the initial radiation, while it traverses each part of our body (each tissue with different characteristics), the intensity of the final radiation would be different from the initial one and different depending on the traversed materials or tissues. This means that in the plate of the radiography different contrasts are seen in the grayscale obtaining radiopacity depending on the final intensity that reaches each point of it after crossing the human body. These possible results are known as radiological densities, and they are going to allow us to identify the nature of each structure in the radiography. This effect of absorption, dispersion and penetration causes that in the human body we can find 5 fundamental densities, with which we will be able to interpret an x-ray. Of these densities, four belong to the human economy, and only one of them is external in nature. Air Density: It is the density of less absorption, because when the X-rays pass through the tissues with this density there is no resistance that opposes them; So all the radiation will be reflected in the radiographic plate. This density is easily identified as being black. It will occur in lungs or digestive tract, among others. Density Fat: Tissues with this density absorb a minimum of radiation, but somewhat higher than air. For this reason it is visualized as a faint whitish gray color. It is characteristic of fat or muscles, being able to find it also surrounding the abdomen and intra-abdominal structures. Water Density: The tissues which exhibit the characteristics of this density have a high aqueous content. The amount of absorbed X-rays is greater than in the two previous densities. This is why gray films are displayed on the radiographs. They own soft tissue such as muscles, intestine with own content or blood vessels. Density Calcium (or bone): In this case there is great absorption because the X-rays find great resistance to their passage. That is why little radiation from the incident will reach the plate and we will see that white tissue. It is the proper density of the bones. However, it can also occur in some calcified cartilages, vascular calcifications or lithiasis. [Hueso (calcio): bone (calcium); Aire: air; Metal: metal; grasa: fat; Tejidos blandos (agua): soft tissues (water)]. Metal Density: It naturally does not exist in the body. These materials will absorb even more radiation than those with calcium or bone density. On the plate you will see a very intense white color. This density can be easily observed in the presence of surgical material, pacemakers (as can be seen in the photograph), prostheses, oral or intravenous contrasts, or pellets. Bibliography:
Made by: Simón García Maldonado. Alicia García Martínez. Alba Mª Moreno del Salto. La radiografía convencional es una imagen médica que nos proporciona una gran información acerca del estado de nuestras estructuras internas, aquellas que no somos capaces de ver a simple vista. Pero, ¿cómo es posible diferenciar estas estructuras entre sí? ¿En qué se basa la radiografía convencional? ¿Qué ocurre cuando nos hacemos una radiografía simple de tórax o abdomen? Todo este procedimiento se explica a través de la interacción de la radiación sobre los tejidos. La radiación emitida son los rayos X, que atravesarán al paciente y nos darán una imagen de su interior una vez atravesados sus diferentes tejidos. Este haz de radiación electromagnética puede ser absorbida o dispersada en su trayectoria, dando como resultado una disminución en la intensidad original de los rayos. La absorción o dispersión es debida a la interacción de los rayos X y los átomos de la materia donde incide el haz de radiación. Hay varios factores que van a determinar que esta radiación sea más o menos absorbida y/o dispersa: el número atómico del átomo irradiado, el espesor del material atravesado, la densidad de dicho material (en nuestro caso tejido corporal) y la energía que posea el haz de radiación (longitud de onda de la radiación incidente). Esto va a provocar que de la radiación inicial, al atravesar cada parte de nuestro cuerpo (cada tejido con características distintas), la intensidad de radiación final sea diferente a la inicial y diferente en función de los materiales o tejidos atravesados. Esto conlleva que en la placa de la radiografía se vean distintos contrastes en escala de grises obteniendo radiolucidez o radiopacidad en función de la intensidad final que llega a cada punto de la misma después de atravesar el cuerpo humano. A estos posibles resultados es a lo que llamamos densidades radiológicas, y es lo que nos va permitir identificar la naturaleza de cada estructura en la radiografía. Este efecto de absorción, dispersión y penetración hace que en el cuerpo humano podamos encontrar 5 densidades fundamentales, con las cuales vamos a poder interpretar una radiografía. De estas densidades, cuatro pertenecen a la economía humana, y sólo una de ellas es de naturaleza externa. Densidad Aire: Es la densidad de menor absorción, debido a que cuando pasan los rayos X a través de los tejidos con esta densidad no hay resistencia que se oponga a los mismos; por lo que toda la radiación se plasmará en la placa radiográfica. Esta densidad se identifica fácilmente por ser de color negro. Se va a dar en pulmones o tubo digestivo, entre otros. Densidad Grasa: Los tejidos con esta densidad absorben un mínimo de radiación, pero algo mayor que el aire. Por ello se visualiza como un tenue color gris blanquecino. Es propia de la grasa o los músculos, pudiendo encontrarla también rodeando el abdomen y las estructuras intraabdominales. Densidad Agua: Los tejidos que muestran las características propias de esta densidad tienen un alto contenido acuoso. La cantidad de rayos X absorbidos es mayor que en las dos densidades anteriores. Por ello en las radiografías se visualiza de color gris. Propio de tejidos blandos como músculos, intestino con contenido propio o vasos sanguíneos. Densidad Calcio ( o hueso ): En este caso hay gran absorción debido a que los rayos X encuentran gran resistencia a su paso. Es por ello que poca radiación de la incidente llegará a la placa y veremos ese tejido de color blanco. Es la densidad propia de los huesos. No obstante, también puede darse en algunos cartílagos calcificados, calcificaciones vasculares o litiasis. Densidad Metal: De forma natural no existe en el organismo. Estos materiales absorberán aún más radiación que los que presentan densidad calcio o hueso. En la placa se verá de color blanco muy intenso. Esta densidad puede observarse fácilmente en presencia de material quirúrgico, marcapasos (como puede observarse en la fotografía), prótesis, contrastes orales o intravenosos, o perdigones. Bibliografía:
Realizado por: Simón García Maldonado. Alicia García Martínez. Alba Mª Moreno del Salto. What is the importance of image quality in radiography?The quality of a radiographic image influences diagnostic accuracy and subsequent clinical management of the patient [1]. A radiographic image is accepted as good quality when certain technical qualities are satisfied, and the image considered of diagnostic value [2].
What is density on a radiograph?Radiographic Density - the overall amount / degree of darkening on a radiograph. In routine radiography, the useful range of density varies from 0.3 to 2.0 density. The density below 0.3 is due to the density produced by the base and by some fog on the film (base plus fog).
How does density affect radiographic image?Radiographic density is the amount of overall blackness produced on the image after processing. Black on a film is the most exposed portion because the metallic silver turns black when exposed to radiation. Too white means not enough density or underexposure. Too black means too much density or overexposure.
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