contrast


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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 ?
Iohexol, the most widely-used injectable diagnostic contrast agent for imaging procedures, has global sales exceeding USD 500m.
Contrast induced nephropathy is the acute deterioration of renal function after parenteral administration of radiocontrast media in the absence of other causes.
Neuroimaging paired with known exposure to a contrast agent is the key for suspecting the diagnosis of CIE.
However, fatal outcomes of contrast aspiration are very rare and are usually due to the lack of specific therapy, elderly age, and serious comorbidities.
The contrast agent studied was iodixanol, an iodine-containing nonionic radiocontrast agent with a molecular weight of 1550.20 and iodine content of 49.1.
Lowering the tube potential from [greater than or equal to]100 kV to 70 kV while using an injection of 50 mL and 40 mL of contrast media allowed for high-quality coronary and aortic CT angiography, respectively, (corresponding to 17.5g and 14g of iodine, respectively).
Radiography employing a contrast medium can be extremely useful for diagnosis and demonstration of surgical conditions involving the bovine mammary gland and teat (Clifford, 1972).
Keywords: Contrast sensitivity, age, visual function, photopic
Excellent tissue contrast mainly depends on the best selection of suitable pulse sequences, each pulse sequence possessing different qualities.1,3 The choice of the pulse sequences and the compatibility of appropriate parameters with the selection of examining tissues are the crucial concern for the contrast between tissues.
Major players operating in the global contrast media injectors market and included in this report are Bracco Imaging S.p.A., Medrad, Inc.