According to various embodiments, apparatus and methods disclosed herein may be implemented in a digital communication receiver, and relate to minimizing noise in an estimated channel frequency response at the receiver for the purposes of channel equalization. The device includes an elongate member having a lumen to receive a fluid, and a structure deployable from a distal portion of the elongate member to channel blood flowing in the vessel. The first band-pass filter is disposed directly beneath the cold shield aperture when the cold shield aperture is switched to the first diameter or the second diameter. 5% by atom and B in an amount of 5.