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CNR (imaging)
Contrast resolution is the ability to distinguish between differences in intensity in an image. The measure is used in medical imaging to quantify the quality of acquired images. It is a difficult quantity to define because it depends on the human observer as much as the quality of the actual image. For example, the size of a feature affects how easily it is detected by the observer. One definition of image contrast is: : C = \frac where SA and SB are signal intensities for signal-producing structures A and B in the region of interest. A disadvantage of this definition is that the contrast ''C'' can be negative. An alternative definition is: : C = \frac where Sref is a reference signal intensity, which is independent of the type of signal-producing structure under investigation. In MRI, determining contrast is of high importance for calibration because the operator has a high degree of control of how the signal intensities of various structures vary in the images by using diff ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Medical Imaging
Medical imaging is the technique and process of imaging the interior of a body for clinical analysis and medical intervention, as well as visual representation of the function of some organs or tissues (physiology). Medical imaging seeks to reveal internal structures hidden by the skin and bones, as well as to diagnose and treat disease. Medical imaging also establishes a database of normal anatomy and physiology to make it possible to identify abnormalities. Although imaging of removed organs and tissues can be performed for medical reasons, such procedures are usually considered part of pathology instead of medical imaging. Measurement and recording techniques that are not primarily designed to produce images, such as electroencephalography (EEG), magnetoencephalography (MEG), electrocardiography (ECG), and others, represent other technologies that produce data susceptible to representation as a parameter graph versus time or maps that contain data about the measurement loca ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hounsfield Units
The Hounsfield scale , named after Sir Godfrey Hounsfield, is a quantitative scale for describing radiodensity. It is frequently used in CT scans, where its value is also termed CT number. Definition The Hounsfield unit (HU) scale is a linear transformation of the original linear attenuation coefficient measurement into one in which the radiodensity of distilled water at standard pressure and temperature (STP) is defined as 0 Hounsfield units (HU), while the radiodensity of air at STP is defined as −1000 HU. In a voxel with average linear attenuation coefficient \mu, the corresponding HU value is therefore given by: HU = 1000\times\frac where \mu_ and \mu_ are respectively the linear attenuation coefficients of water and air. Thus, a change of one Hounsfield unit (HU) represents a change of 0.1% of the attenuation coefficient of water since the attenuation coefficient of air is nearly zero. Calibration tests of HU with reference to water and other materials may be done to ensu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Contrast-to-noise Ratio
Contrast-to-noise ratio (CNR) is a measure used to determine image quality. CNR is similar to the metric signal-to-noise ratio (SNR), but subtracts a term before taking the ratio. This is important when there is a significant bias in an image, such as from haze. As can be seen in the picture at right, the intensity is rather high even though the features of the image are washed out by the haze. Thus this image may have a high SNR metric, but will have a low CNR metric. One way to define contrast-to-noise ratio is: :C = \frac where ''S''''A'' and ''S''''B'' are signal intensities for signal producing structures ''A'' and ''B'' in the region of interest and ''σ''o is the standard deviation of the pure image noise. See also *Contrast resolution Contrast resolution is the ability to distinguish between differences in intensity in an image. The measure is used in medical imaging to quantify the quality of acquired images. It is a difficult quantity to define because it depends o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
American College Of Radiology
The American College of Radiology (ACR), founded in 1923, is a professional medical society representing nearly 40,000 diagnostic radiologists, radiation oncologists, interventional radiologists, nuclear medicine physicians and medical physicists. The ACR has 54 chapters in the United States, Canada and the Council of Affiliated Regional Radiation Oncology Societies (CARROS). Medical imaging accreditation The ACR has accredited more than 39,000 medical imaging facilities in 10 imaging modalities since 1987, including: * Breast MRI * Breast Ultrasound * Computed Tomography * Mammography * Magnetic Resonance Imaging *Nuclear Medicine * Positron Emission Tomography *Radiation Oncology Practice * Stereotactic Breast Biopsy *Ultrasound ACR Appropriateness Criteria The ACR Appropriateness Criteria (ACR AC) are evidence-based guidelines that assist referring physicians and other providers in making the most appropriate imaging or treatment decision for a specific clinical condition. The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Contrast-to-noise Ratio
Contrast-to-noise ratio (CNR) is a measure used to determine image quality. CNR is similar to the metric signal-to-noise ratio (SNR), but subtracts a term before taking the ratio. This is important when there is a significant bias in an image, such as from haze. As can be seen in the picture at right, the intensity is rather high even though the features of the image are washed out by the haze. Thus this image may have a high SNR metric, but will have a low CNR metric. One way to define contrast-to-noise ratio is: :C = \frac where ''S''''A'' and ''S''''B'' are signal intensities for signal producing structures ''A'' and ''B'' in the region of interest and ''σ''o is the standard deviation of the pure image noise. See also *Contrast resolution Contrast resolution is the ability to distinguish between differences in intensity in an image. The measure is used in medical imaging to quantify the quality of acquired images. It is a difficult quantity to define because it depends o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spatial Resolution
In physics and geosciences, the term spatial resolution refers to distance between independent measurements, or the physical dimension that represents a pixel of the image. While in some instruments, like cameras and telescopes, spatial resolution is directly connected to angular resolution, other instruments, like synthetic aperture radar or a network of weather stations, produce data whose spatial sampling layout is more related to the Earth's surface, such as in remote sensing and satellite imagery. See also * Image resolution * Ground sample distance * Level of detail * Resel In image analysis, a resel (from ''res''olution ''el''ement) represents the actual spatial resolution in an image or a volumetric dataset. The number of resels in the image may be lower or equal to the number of pixel/voxels in the image. In an act ... References Accuracy and precision {{physics-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
