contrast

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Related to positive contrast: negative contrast

con·trast

(kon'trast),
1. A comparison in which differences are demonstrated or enhanced.
2. In radiology, the difference between the image densities of two areas is the contrast between them; this is a function of the number of x-ray photons transmitted or the strength of the signals emitted by the two regions and the response of the recording medium.
4. Performed with a contrast medium.
[L. contra, against, + sto, pp. status, to stand]

contrast

Imaging An MRI term for the relative difference of signal intensities in two adjacent regions of an image. Image contrast heavily depends on the chosen imaging technique (i.e., TE, TR, TI), and reflects such parameters as proton density and T1 or T2 relaxation times.

con·trast

(kon'trast)
1. A comparison in which differences are demonstrated or enhanced.
2. radiology The difference between the image densities of two areas.
[L. contra, against, + sto, pp. status, to stand]

Contrast (agent, medium)

A substance injected into the body that illuminates certain structures that would otherwise be hard to see on the radiograph (film).

contrast 

1. Subjective sense: subjective assessment of the difference in appearance of two parts of a field of view seen simultaneously or successively. Hence, luminosity contrast, lightness contrast, colour contrast, simultaneous contrast, successive contrast.
2. 
Objective sense: quantities defined by the formulae for luminance contrast.
Note: Example (c) is better known as luminance ratio (CIE). L2 is the maximum luminance and L1 is the minimum luminance. See spatial frequency; contrast sensitivity; differential threshold.
brightness contrast The enhanced apparent darkening of an area when viewed near, or following a lighter stimulus (or lightening, near or after a darker stimulus).
colour contrast 1. A difference in the appearance of surfaces based on hue or saturation. 2. The enhanced difference in the colour of two surfaces induced by their proximity (simultaneous colour contrast) or successive stimulation (successive colour contrast). The appearance of the smaller area shifts towards the complementary colour of the surround or background. Example: a yellow area appears reddish when surrounded by a green background.
contrast sensitivity function See contrast sensitivity function.
contrast sensitivity test See contrast sensitivity chart; contrast sensitivity.
simultaneous contrast A difference in the appearance of two adjacent areas occurring at the same time.
successive contrast A difference in the appearance of stimuli following each other.
contrast threshold See contrast sensitivity; differential threshold.

con·trast

(kon'trast)
1. A comparison in which differences are demonstrated or enhanced.
2. In radiology, the difference between the image densities of two areas is the contrast between them.
3. Contrast medium.
4. Performed with a contrast medium.
[L. contra, against, + sto, pp. status, to stand]

Patient discussion about contrast

Q. Has anyone had an allergic reaction to gadolinium dye, MRI contrast agents, I have had a severe reaction. I would like to know the long term effects of this dye. And if anyone else has had or heard of problems and reactions to it. Please answer me. Thank you

A. In 1969 I almost died from the IVP dye. I had no idea I was allergic and when I awoke I was in a "recovery room." The doctor told me to always tell any physicians/paramedics etc of my allergy status regarding the dye. I now have chronic back pain, have a history of cancer in the family and the doctor wants to do a scan (including dye) but when I emphasized that I was allergic he backed off. Now I am wondering if there is anything else that can be done to test the bone (scan) without the dye. Any answers? Thanks

More discussions about contrast
References in periodicals archive ?
In the first three sessions of extinction (top left-hand panel), Lucy was the only subject to demonstrate an effect consistent with positive contrast, and in Component A only (the following-schedule effect).
O'Dowd supporters proved a pretty positive contrast to their anti-whatever agendas," said the director.
To say this firmly is not to indulge in political correctness, but to give expression to the liberal values that represent the best of Wales and Britain and which mark a positive contrast to the repressive regimes of past centuries.
One advantage to this hodgepodge of diversity is that several of the articles, particularly those with economics as a sub-theme, stand out in positive contrast. Nick Cullather's article on Taiwan's industrial "miracle" and Darlene Rivas's piece on Nelson Rockefeller's involvement in Venezuela in the postwar period were welcome reading, although one has to slog through to the end to meet up with them.
The black object has a negative contrast of 37% against the background of sand and seawater, and the gray object has a positive contrast of 35%.
In this case we have the negative: positive contrast. The Lion, being a tyrant, represents cruelty and boastfulness; the Traveller, on the other hand, is an idealist trying to convince his interlocutor about the necessity of merciful and caring rule, thus representing a complex of features, such as mellowness, wisdom and justice.
The percentage of monolingual Spanish-speaking patients doubled, length of time in therapy increased, and "therapists have openly commented on the surprising and positive contrast between working with trained versus untrained interpreters" (p.
In positive contrast, the Rosas' NIA Technique teaches, applies and reinforces values that decrease stress and promote longevity, pleasure and insight into stress-free living, not just stress-free fitness.
CECT with oral positive contrast:-thin band of contrast circumscribing the peripheral part of lesion (Axial & coronal reformation).
Artifacts from oral positive contrast agents can also arise where there are focal concentrations of high-density contrast, such as barium.
Positive contrast is an increase in the rate of responding in one setting as a result of a decrease in reinforcement (or an increase in punishment) in another setting.