A collimator assembly, comprising: a collimator, comprising: a honeycomb structure having walls defining and separating apertures, wherein the apertures include: a first plurality of apertures in a central region having a first aspect ratio; a second plurality of apertures in a peripheral region having a second aspect ratio less than the first aspect ratio; and a third plurality of apertures in a transitional region disposed between the central region and the peripheral region, wherein the walls defining the third plurality of apertures of the transitional region form a conical shape surrounding the central region, and a shield portion coupled with the collimator, the shield portion comprising: a top ring; a support ledge below the top ring, the support ledge extending radially outward; and a cylindrical band extending downward from the support ledge, wherein the cylindrical band comprises: a first substantially vertical portion; and a radially inward sloped portion extending downward from the first substantially vertical portion, wherein the radially inward sloped portion extends across a portion of the second plurality of apertures in the peripheral region. a collimator, comprising: a honeycomb structure having walls defining and separating apertures, wherein the apertures include: a first plurality of apertures in a central region having a first aspect ratio; a second plurality of apertures in a peripheral region having a second aspect ratio less than the first aspect ratio; and a third plurality of apertures in a transitional region disposed between the central region and the peripheral region, wherein the walls defining the third plurality of apertures of the transitional region form a conical shape surrounding the central region, and a honeycomb structure having walls defining and separating apertures, wherein the apertures include: a first plurality of apertures in a central region having a first aspect ratio; a second plurality of apertures in a peripheral region having a second aspect ratio less than the first aspect ratio; and a third plurality of apertures in a transitional region disposed between the central region and the peripheral region, a first plurality of apertures in a central region having a first aspect ratio; a second plurality of apertures in a peripheral region having a second aspect ratio less than the first aspect ratio; and a third plurality of apertures in a transitional region disposed between the central region and the peripheral region, wherein the walls defining the third plurality of apertures of the transitional region form a conical shape surrounding the central region, and a shield portion coupled with the collimator, the shield portion comprising: a top ring; a support ledge below the top ring, the support ledge extending radially outward; and a cylindrical band extending downward from the support ledge, wherein the cylindrical band comprises: a first substantially vertical portion; and a radially inward sloped portion extending downward from the first substantially vertical portion, wherein the radially inward sloped portion extends across a portion of the second plurality of apertures in the peripheral region. a top ring; a support ledge below the top ring, the support ledge extending radially outward; and a cylindrical band extending downward from the support ledge, wherein the cylindrical band comprises: a first substantially vertical portion; and a radially inward sloped portion extending downward from the first substantially vertical portion, wherein the radially inward sloped portion extends across a portion of the second plurality of apertures in the peripheral region. a first substantially vertical portion; and a radially inward sloped portion extending downward from the first substantially vertical portion, wherein the radially inward sloped portion extends across a portion of the second plurality of apertures in the peripheral region.