In the field of medical technology, image output devices are used to display for a user volume data images, particularly slice images, derived from volume data of a target tissue region. By way of example, such volume data can be obtained with the aid of tomography devices, such as computed tomography scanners, magnetic resonance imaging scanners, or else other imaging devices such as ultrasound installations. There are different display modes for such volume data images obtained from volume data. For example, they show different slice or sectional perspectives of the imaged tissue region in different projections or display depths. These include the multiplanar reconstruction (MPR) and the maximum intensity projection (MIP). The multiplanar reconstruction is a sectional imaging method in which the hollow organ is placed into a plane in a virtual fashion and shown with depth resolution in a virtually three-dimensional fashion. By contrast, the maximum intensity projection is a sectional imaging method in which sections of a tissue region, situated one behind the other or one above the other, are illustrated in a two-dimensional fashion. In the process, superimposed structures are illustrated together and a contrast is formed where that part of the tissue volume which causes the greatest measurement intensity in the imaging measurement produces the highest degree of coloring in the projection illustration. Like a back projection onto a focusing screen, structures positioned behind one another can in this fashion be illustrated in a plane.
An important field of application which uses volume data images generated by the abovementioned imaging devices is the diagnosis of hollow organs or hollow organ sections, e.g. vessels, in particular coronary vessels on the heart or vessels in the brain, or other tubular hollow organs such as the colon or the bronchi. In particular, a problem in diagnosing such structures lies in the fact that lesions can usually be found in edges of the hollow structure or in the walls of the hollow organ. A typical example of such a lesion is a stenotic region in a vessel section.
These days, such hollow organ sections are usually diagnosed using a pre-calculated profile line through the hollow organ. In the following text, a “profile line” is a line which follows the profile of the observed hollow organ. This generally is a central line running right through the middle of the hollow organ, the so-called “centerline”. The literature already discloses different relevant methods for pre-calculating such centerlines. Likewise, within the scope of computer aided diagnosis methods, there already are different methods for automatically selecting slice planes through the hollow organ such that possible lesions are illustrated in the view suitable for a post-evaluation. Thus, EP 0 961 993 B1 (=WO 98/37517) describes a method in which regions of an intestine with an abnormal wall thickness are automatically recognized as possible lesions and are then visualized in a particularly marked fashion in a wire model. In the process, slices are also generated along the profile line such that the lesions are clearly identifiable. U.S. Pat. No. 6,643,533 B2 suggests placing slice images along the profile plane through a blood vessel such that in a narrowing the smallest diameter of the blood vessel lies in the slice plane, i.e. the slice plane is selected such that the slice image shows the smallest lumen dimension. In the case of dilation, the slice image can be placed along the profile plane such that the largest diameter of the blood vessel is situated in the slice plane.
During the conventional diagnosis by an expert at an image output device, this centerline is used as a path for a virtual movement through the hollow organ section. Depending on the type of profile line or centerline calculation, this can consist of a number of individual points aligned next to one another, or else it can be constructed as a continuous line or a polygonal chain. During a virtual movement through the hollow organ along the centerline, different slice images can then be displayed on a diagnosis workstation at different observation points which can, for example, be the individual points from which the “centerline” is composed or, in the case of a continuous “centerline”, points at a certain step-size and can be observed by the user.
A typical screen surface for such diagnosis is illustrated in FIG. 1. On the left-hand side there is an image display field BF in which four different illustrations of the hollow organ section HO of interest, in this case the right coronary artery, are illustrated. To the right thereof there is a parameter display bar PL, acting as a user interface, on which the observer can adjust certain parameters with the aid of mouse clicks. In this case, a three-dimensional volume image VR of the heart, in which the relevant coronary artery is clearly visible, is displayed at the bottom on the right-hand side of the image display field BF. To the left thereof an orthogonal slice OS is shown at a certain point on the “centerline” along the coronary artery (the “centerline” itself is not illustrated in this case). The two upper images show two tangential slice images TS1, TS2. The orthogonal slice plane and the tangential slice planes are selected such that they respectively are mutually perpendicular. Here, the orthogonal slice plane is situated perpendicular to the profile line at a given point on the profile line and the tangential slice planes correspond to longitudinal slices along the hollow organ section and can be tangent to the profile line at e.g. this point, or can comprise this point. When moving along the “centerline” from one observation point to the next, a new orthogonal slice, which is perpendicular to the “centerline” at the respective observation point, and the two tangential slice images TS1, TS2 perpendicular thereto are illustrated at all observation points. By moving forward and backward along the “centerline”, for example by operating virtual pushbuttons on the parameter display bar with the aid of the mouse pointer, the complete hollow organ section can be successively observed within the scope of this profile display.
However, the problem with such a conventional procedure is that there are very big jumps in the tangential planes, particularly in the case of strongly curved structures and/or in the case of structures with frequent changes in curvature. When passing through the structure along the profile line, this leads to a bumpy, very vigorously “shaking” display of the tangential slice images. This harbors the risk of the observer easily losing the focus and the orientation in the image. This can lead to relevant structural changes being overlooked.