An Intravascular Longitudinal Image (L-Mode) is a constrained three-dimensional reconstruction of an IVUS or IVOCT multi-frame image. The Longitudinal Image can be reconstructed from either FOR PROCESSING or FOR PRESENTATION Images. Figure EEE.3-1 is an example of an IVUS cross-sectional image (on the left) with a reconstructed longitudinal view (on the right).
Figure EEE.3-1 - IVUS Image with Vertical Longitudinal View
The Longitudinal reconstruction is comprised of a series of perpendicular cut planes, typically consisting of up to 360 slices spaced in degree increments. The cut planes are perpendicular to the cross-sectional plane, and rotate around the catheter axis (I.e. center of the catheter) to provide a full 360 degrees of rotation. A longitudinal slice indicator is used to select the cut plane to display, and is normally displayed in the associated cross-sectional image (e.g. blue arrow cursor in figure EEE.3-1). A current frame marker (e.g. yellow cursor located in the longitudinal view) is used to indicate the position of the corresponding cross-sectional image, within the longitudinal slice.
When pullback rate information is provided, distance measurements are possible along the catheter axis. The Intravascular Longitudinal Distance (0052,0028) or IVUS Pullback Rate (0018,3101) attributes are used along with the Frame Acquisition DateTime (0018,9074) attribute to facilitate measurement calculations. This allows for lesion, calcium, stent and stent gap length measurements. Figure EEE.3-2 is an example of an IVOCT cross-sectional image (on the top), with a horizontal longitudinal view on the bottom. The following example also illustrates how the tint specified by the Palette Color LUT is applied to the OCT image.
Figure EEE.3-2 - IVOCT Image with Horizontal Longitudinal View
Figure EEE.3-3 - Longitudinal Reconstruction
Figure EEE.3-3 illustrates how the 2D cross-sectional frames are stacked along the catheter longitudinal axis. True geometric representation of the vessel morphology cannot be rendered, since only the Z position information is known. Position (X and Y) and rotation (X, Y and Z) information of the acquired cross-sectional frames is unknown.