A method of modeling comprising: acquiring scan data, wherein the scan data comprises data associated with a plurality of x-ray projections of an item; determining a first maximum area based on the data associated with the plurality of x-ray projections; determining at least one edge of the first maximum area; determining an outer closed boundary curve associated with the item based on the at least one edge of the first maximum area; determining a second maximum area based on the data associated with the plurality of x-ray projections, wherein the second maximum area is less than the first maximum area; determining at least one edge of the second maximum area; determining an inner closed boundary curve associated with the item based on the at least one edge of the second maximum area; generating a model of the item using the outer closed boundary curve, the inner closed boundary curve and a set of material specific parameters comprising a first material specific parameter associated with a material between the outer closed boundary curve and the inner closed boundary curve and a second material specific parameter associated with a material within the inner closed boundary curve; utilizing the model to generate computed scan data; comparing the computed scan data to the scan data and determining a goodness of fit; and adjusting the model of the item by altering the outer closed boundary curve, the inner closed boundary curve and the first and second material specific parameters by: determining a cost function and a cost function gradient associated with the outer closed boundary curve, the inner closed boundary curve and the first and second material specific parameters; and altering the outer closed boundary curve, the inner closed boundary curve and the first and second material specific parameters based on the cost function gradient. acquiring scan data, wherein the scan data comprises data associated with a plurality of x-ray projections of an item; determining a first maximum area based on the data associated with the plurality of x-ray projections; determining at least one edge of the first maximum area; determining an outer closed boundary curve associated with the item based on the at least one edge of the first maximum area; determining a second maximum area based on the data associated with the plurality of x-ray projections, wherein the second maximum area is less than the first maximum area; determining at least one edge of the second maximum area; determining an inner closed boundary curve associated with the item based on the at least one edge of the second maximum area; generating a model of the item using the outer closed boundary curve, the inner closed boundary curve and a set of material specific parameters comprising a first material specific parameter associated with a material between the outer closed boundary curve and the inner closed boundary curve and a second material specific parameter associated with a material within the inner closed boundary curve; utilizing the model to generate computed scan data; comparing the computed scan data to the scan data and determining a goodness of fit; and adjusting the model of the item by altering the outer closed boundary curve, the inner closed boundary curve and the first and second material specific parameters by: determining a cost function and a cost function gradient associated with the outer closed boundary curve, the inner closed boundary curve and the first and second material specific parameters; and altering the outer closed boundary curve, the inner closed boundary curve and the first and second material specific parameters based on the cost function gradient. determining a cost function and a cost function gradient associated with the outer closed boundary curve, the inner closed boundary curve and the first and second material specific parameters; and altering the outer closed boundary curve, the inner closed boundary curve and the first and second material specific parameters based on the cost function gradient.