A method of segmenting an image, the method comprising the steps of: generating a first frame of image data representing a plurality of items in an imaging view at a first time, wherein the first frame of image data comprises a first frame of cross-sectional image data generated using an intravascular imaging system; generating a second frame of image data representing a plurality of items in an imaging view at a second time, the second time differing from the first time, wherein the second frame of image data comprises a second frame of cross-sectional image data generated using an intravascular imaging system; selecting a first portion of the first frame, the first portion having a first subset of the image data of the first frame; comparing the selected first portion to image data of the second frame; selecting a second portion of the second frame based on the comparison, the second portion having a second subset of the image data of the second frame; calculating a first displacement vector representing relative movement between the first portion at the first time and the second portion at the second time; selecting a third portion of the first frame, the third portion having a third subset of the image data of the first frame, and wherein the third subset of the image data of the first frame differs from the first subset of the image data of the first frame; comparing the selected third portion to image data of the second frame; selecting a fourth portion of the second frame based on the comparison, the fourth portion having a fourth subset of the image data of the second frame; calculating a second displacement vector representing relative movement between the third portion at the first time and the fourth portion at the second time; and comparing a length of the first displacement vector to a length of the second displacement vector; characterized in that it further comprises the steps of: based on the length of the first displacement vector differing from the length of the second displacement vector, determining that the first portion of the first frame of image data represents blood within a vessel and the third portion of the first frame of image data represents vessel tissue or plaque, and measuring a heart rate of a patient, wherein the first and second times are determined using the measured heart rate of the patient. generating a first frame of image data representing a plurality of items in an imaging view at a first time, wherein the first frame of image data comprises a first frame of cross-sectional image data generated using an intravascular imaging system; generating a second frame of image data representing a plurality of items in an imaging view at a second time, the second time differing from the first time, wherein the second frame of image data comprises a second frame of cross-sectional image data generated using an intravascular imaging system; selecting a first portion of the first frame, the first portion having a first subset of the image data of the first frame; comparing the selected first portion to image data of the second frame; selecting a second portion of the second frame based on the comparison, the second portion having a second subset of the image data of the second frame; calculating a first displacement vector representing relative movement between the first portion at the first time and the second portion at the second time; selecting a third portion of the first frame, the third portion having a third subset of the image data of the first frame, and wherein the third subset of the image data of the first frame differs from the first subset of the image data of the first frame; comparing the selected third portion to image data of the second frame; selecting a fourth portion of the second frame based on the comparison, the fourth portion having a fourth subset of the image data of the second frame; calculating a second displacement vector representing relative movement between the third portion at the first time and the fourth portion at the second time; and comparing a length of the first displacement vector to a length of the second displacement vector; characterized in that it further comprises the steps of: based on the length of the first displacement vector differing from the length of the second displacement vector, determining that the first portion of the first frame of image data represents blood within a vessel and the third portion of the first frame of image data represents vessel tissue or plaque, and measuring a heart rate of a patient, wherein the first and second times are determined using the measured heart rate of the patient. based on the length of the first displacement vector differing from the length of the second displacement vector, determining that the first portion of the first frame of image data represents blood within a vessel and the third portion of the first frame of image data represents vessel tissue or plaque, and measuring a heart rate of a patient, wherein the first and second times are determined using the measured heart rate of the patient.