What is HU unit of measure?
Hounsfield units (HU) are a dimensionless unit universally used in computed tomography (CT) scanning to express CT numbers in a standardized and convenient form. Hounsfield units are obtained from a linear transformation of the measured attenuation coefficients 1.
How is Hu calculated?
The linear attenuation coefficient for each material at the selected effective energy was converted to CT numbers Hounsfield units using the standard equation: HU = (µmaterial–µwater)/(µwater) × 1000.
What is HU value in CT?
The Hounsfield unit (HU) is a relative quantitative measurement of radio density used by radiologists in the interpretation of computed tomography (CT) images. The absorption/attenuation coefficient of radiation within a tissue is used during CT reconstruction to produce a grayscale image.
How is Hu measured in CT scan?
The Hounsfield scale of CT is set around water measuring 0 HU. By altering the attenuation level (mid-HU value) and range (extent of gray scale) at which the image is viewed, the tissue to be displayed can be determined. To view bone, the window level is set at about 250 HU with a wide window width (1000 HU).
What does low density mean on a brain CT scan?
Tissues like air and water have little attenuation and are displayed as low densities (dark), whereas bone has high attenuation and is displayed as high density (bright) on CT. Among pathologic conditions, high density lesions are often seen with freshly clotted blood, hyperemia and with the use of contrast.
What does low attenuation on a CT scan mean?
Attenuation is a feature of CT, and low attenuation means that a particular area is less intense than the surrounding. All of the malignant nodules confirmed by biopsy have low attenuation, with the exception of two which have a mixture of high and low attenuation.
What is CT number in CT scan?
Computed tomography (CT) number is a calculated value reflecting the X-ray attenuation coefficient in an image voxel, generally expressed in Hounsfield units (HU), where the CT number of water is 0 HU.
What is the CT number of water?
CT number = 1000 × ( μ − μ water ) / μ water. (1) The unit for CT numbers is Hounsfield units (HU); from the definition, water is zero HU and air is − 1000 HU . CT manufacturers typically release specifications on tolerance for CT numbers.
What are Hounsfield units in kidney cyst?
Homogeneous simple renal cysts can have mean attenuation values of up to 30 HU, as determined by contrast-enhanced CT, whereas homogeneous RCCs have mean attenuation values as low as 42 HU, with no overlap occurring between the two groups.
What does low density mean?
1. low-density – having low relative density or specific gravity. light – of comparatively little physical weight or density; “a light load”; “magnesium is a light metal–having a specific gravity of 1.74 at 20 degrees C” 2. low-density – having low concentration; “low-density urban areas”