contrast

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Related to negative contrast: positive 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 ?
The purpose of the second experimental condition, FR 1, was to determine whether an increase in the rate of reinforcement in the varied component resulted in decreases in responding in the target components (i.e., negative contrast).
Cyproheptadine prevents the initial occurrence of Successive Negative Contrast. Pharmacology, Biochemistry & Behavior, 40, 433442.
Correlation of corticosterone elevation and negative contrast varies as a function of postshift day.
Successive negative contrast after partial reinforcement in the consummatory behavior of rats.
"Can Contextual Cues Control Consummatory Successive Negative Contrast?".
The tests include reading tests, LogMAR reading test, LogMAR near charts, task images (books and newspapers), binocular vision tests (fixation disparity, binocularity, suppression, steropsis), Duochrome (dots, letters, rings), Amsler (positive and negative contrast, draw directly on charts) and fixation targets.
Emphasis is placed on recent developments in the study of consummatory successive negative contrast. Amsel's model of psychobiological research involves an integration of behavioral theory with neurobiological and developmental approaches.
At times, I found myself thinking: "Yes, Schillebeeckx levels that same critique." Or, "What you are saying here is a clear illustration of Schillebeeckx's notion of negative contrast experience." (1) But, the strongest evocations of Schillebeeckx I found in Gebara's work were actually my own experiences of negative contrast.
Contrast can be classified into two primary categories; positive and negative contrast. 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.
Both positive and negative contrast were larger for longer (i.e.
(23-26) For the majority of our studies, an oral preparation using 300 mL Gastromark (Mallinckrodt Medical, St Louis, MO) and 300 mL Readi-cat 2 (Bracco Diagnostics, Princeton, NJ) given 1.5 hours prior to examination was used to provide negative contrast within the bowel lumen without substantial susceptibility effect.