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 . <EOS>