Recently, we proposed marginal space learning (MSL) as
a generic approach for automatic detection of 3D anatom-
ical structures in many medical imaging modalities. To
accurately localize a 3D object, we need to estimate nine
parameters (three for position, three for orientation, and
three for anisotropic scaling). Instead of uniformly search-
ing the original nine-dimensional parameter space, only
low-dimensional marginal spaces are uniformly searched
in MSL, which significantly improves the speed. In many
real applications, a strong correlation may exist among pa-
rameters in the same marginal spaces. For example, a large
object may have large scaling values along all directions.
In this paper, we propose constrained MSL to exploit this
correlation for further speed-up. As another major contri-
bution, we propose to use quaternions for 3D orientation
representation and distance measurement to overcome the
inherent drawbacks of Euler angles in the original MSL.
The pro...