How do you calculate noise index in CT?
Noise in CT is measured via the signal to noise ratio (SNR); comparing the level of desired signal (photons) to the level of background noise (pixels deviating from normal).
The higher the ratio, the less noise is present in the image..
How do you measure volume on a CT?
Volume calculations
The ABC/2 volume estimation is based on a simplification of the ellipsoid volume equation.
As described by Kothari et al.,6 to estimate ICH volume, A=maximum length (in cm), B=width perpendicular to A on the same head CT slice, and C=the number of slices multiplied by the slice thickness (Fig. 1)..
How is CTDI calculated?
The CTDI calculation assumes that the radiation decreases linearly from the outside to the center and is calculated as CTDI = (1/3) * radiationcenter + (2/3) * radiationperiphery.
It is then divided by the length of the scan to give a CTDI per slice..
How is CTDI measured?
To measure the CTDI, the radiation dose from a single CT scan is collected by a 100-mm- long ionization chamber, and then the integrated dose is normalized to the nominal beam width.
Hence, CTDI is not a dose to a point, but rather an average dose over a volume..
How is DLP related to CTDI Vol?
CTDIvol represents the average radiation dose of a standard phantom under a given scan parameter, and is highly susceptible to the scanning protocol.
DLP is calculated based on the CTDIvol, which is the product of the CTDIvol and the scan range length.Jan 3, 2019.
What is a volume scan in CT?
Volumetric computed tomography (VCT) is a technology in which area detectors are used for imaging large volumes of a subject with isotropic imaging resolution..
What is CT noise index?
Increasing the Noise Index (NI) means higher noise in the image which means decreasing mA resulting in decreased CTDIvol.
Noise Index will vary based on the slice thickness selected due to the difference in image noise relative to slice thickness.
The same NI should never be used across all slice thicknesses..
What is CTDI and DLP?
Dose length product (DLP) measured in mGy*cm is a measure of CT tube radiation output/exposure.
It is related to volume CT dose index (CTDIvol), but CTDIvol represents the dose through a slice of an appropriate phantom.
DLP accounts for the length of radiation output along the z-axis (the long axis of the patient)..
What is volume scanning in CT?
Volumetric computed tomography (VCT) is a technology in which area detectors are used for imaging large volumes of a subject with isotropic imaging resolution..
- CTDIvol represents the average radiation dose of a standard phantom under a given scan parameter, and is highly susceptible to the scanning protocol.
DLP is calculated based on the CTDIvol, which is the product of the CTDIvol and the scan range length.Jan 3, 2019 - CTDIvol = (1/pitch) x CTDIw
Therefore CTDIw represents the average radiation dose over the x and y direction whereas CTDIvol represents the average radiation dose over the x, y and z directions. - Dose length product (DLP) measured in mGy*cm is a measure of CT tube radiation output/exposure.
It is related to volume CT dose index (CTDIvol), but CTDIvol represents the dose through a slice of an appropriate phantom.
DLP accounts for the length of radiation output along the z-axis (the long axis of the patient). - Hounsfield units (HU) are used in computed tomography (CT) to represent CT numbers in a standardised format of the resultant image.
HU is derived from a linear transformation of the measured attenuation coefficients based on arbitrarily assigned air and pure water densities. - The CTDI measures the radiation dose within the primary beam, and the MSAD represents the average dose received during an examination.
Importantly, these doses represent actual tissue exposure rather than the skin entrance doses commonly used with conventional radiography.
