TABLE 1.

Definitions of Quantitative MRCP+ Biliary Dilatation Metrics

Quantitative MRCP Metrics	Definition
Individual dilatation metrics
Candidate dilatation	Bile duct dilatation with at least 1 mm absolute increase and at least 30% relative increase in diameter compared to its closest (in diameter) neighboring local minimum
Relative severity of candidate dilatation	$\frac{\text{Maximum dilatation diameter −}\text{Nearest local minimum diameter}}{\text{Nearest local minimum diameter}}$
Length of candidate dilatation (mm)	Full width at half maximum of candidate dilatation diameter profile
Dilatation score (mm)	$\text{Length of candidate dilatation}\times \text{Relative severity of dilatation}$
Tree dilatation metrics*
Biliary tree length (m)	Total length of the biliary tree modeled by MRCP+
Number of dilatations, DilatNum (m−1)	$\frac{\text{Total number of candidate dilatations}}{\text{Total length of measured biliary tree in meters}}$
Sum of relative severity of dilatations, SumRelSevDilat (m−1)	$\frac{\text{Sum of relative severity of all candidate dilatations}}{\text{Total length of measured biliary tree in meters}}$
Proportion of tree dilated, DilatTreeProp (%)	$\frac{\text{Sum of lengths of candidate dilatations in meters}}{\text{Total length of measured biliary tree in meters}}\times 100$
Tree dilatation score, TreeDilatScore	$\frac{\text{Sum of candidate dilatation scores in meters}}{\text{Total length of measured biliary tree in meters}}$
Volume metrics
Biliary tree volume,* TreeVol (mL m−1)	$\frac{\text{Total measured biliary tree volume}}{\text{Total length of measured biliary tree in meters}}$
Gallbladder volume (mL)	Fasted volume of the segmented gallbladder

^*These metrics were normalized to the total length of the measured biliary tree to account for variable lengths of the biliary tree modeled on MRCP+ among participants.