Table 1:

Formulas for CTDI and its variations

Dose Index	Formula	Notes
CTDI	$\mathrm{CTDI}=\frac{1}{T}{\displaystyle {\int }_{-\infty }^{+\infty }D\left(z\right)}\mathrm{dz}$	T is the nominal width of a section and D(z) is the dose at point z parallel to the z-axis
CTDI measured >100 mm	$\mathrm{CTD}{I}_{100}=\frac{1}{\mathrm{NT}}{\displaystyle {\int }_{-50\mathrm{mm}}^{+500\mathrm{mm}}D\left(z\right)}\mathrm{dz}$	N is the number of acquired sections per scan, T is the nominal width of each acquired section, and D(z) is the dose at point z parallel to the z-axis
Weighted CTDI	$\mathrm{CTDIw}=\frac{1}{3}\mathrm{CTD}{I}_{100,\mathrm{center}}+\frac{2}{3}\mathrm{CTD}{I}_{100,\mathrm{periphery}}$	CTDI100,center is the CTDI100 measured at the center of the standard CTDI phantom and CTDI100,periphery is the CTDI100 measured at the periphery of the phantom
CTDIvol	$\mathrm{CTDIvol}=\frac{\mathrm{CTDIw}}{\mathrm{pitch}}$	Pitch is table travel distance per rotation divided by nominal beam width