Computed tomography dose index

The computed tomography dose index (CTDI) is a commonly used radiation exposure index in X-ray computed tomography (CT), first defined in 1981. The unit of CTDI is the gray (Gy) and it can be used in conjunction with patient size to estimate the absorbed dose. The CTDI and absorbed dose may differ by more than a factor of two for small patients such as children. The computed tomography dose index (CTDI) is a commonly used radiation exposure index in X-ray computed tomography (CT), first defined in 1981. The unit of CTDI is the gray (Gy) and it can be used in conjunction with patient size to estimate the absorbed dose. The CTDI and absorbed dose may differ by more than a factor of two for small patients such as children. Because CT scanners typically acquire multiple slices during a single rotation with a single beam, the CTDI is calculated by integrating over the dose profile for a single axial rotation, then dividing by the nominal beam width: C T D I = 1 n T ∫ − z + z D ( z ) d z {displaystyle CTDI={frac {1}{nT}}int _{-z}^{+z}{D(z){ ext{d}}z}} where n {displaystyle n} is the number of slices acquired per single axial rotation, T {displaystyle T} is the width of a single acquired slice (and thus n {displaystyle n} T {displaystyle T} is the nominal beam width) and D ( z ) {displaystyle D(z)} is the radiation dose measured at position z {displaystyle z} along the scanner's main axis - the dose profile.