
1032 MJvanderBomet al
Introduction
Three-dimensional (3D) anatomical information can be of great value during many image-
guided interventions. However, in most cases only two-dimensional (2D) x-ray projection
images can be acquired during the intervention. For this reason, registration of pre-treatment
3D volume data to 2D x-ray images during clinical procedures is considered beneficial in a
variety of clinical applications. For instance, the registration of portal images to 3D volume
data can provide assistance in treatment planning and patient positioning for radiotherapy
(Bijhold 1993, Gilhuijs et al 1996, Murphy 1997,Siroiset al 1999,Kimet al 2001, Clippe
et al 2003,Jinet al 2006, Jans and Syme 2006, Khamene et al 2006, Munbodh et al 2006,
Chen et al 2008). In the fields of minimally invasive and computer-aided surgery (Lemieux
et al 1994,Lavall
´
ee and Szeliski 1995, Feldmar et al 1997, Weese et al 1997,Gu
´
eziec et al
1998, Kita et al 1998,Liuet al 1998, Maurer et al 1998, Hamadeh et al 1998, Penney et al
1998, 2001, Rohlfing and Maurer 2002, Benameur et al 2003,Toma
ˇ
zevi
ˇ
c et al 2003, Livyatan
et al 2003, Birkfellner et al 2003,Kimet al 2005, Rohlfing et al 2005, Russakoff et al 2005,
Turgeon
et al 2005, McLaughlin et al 2005, Birkfellner et al 2005, Dey and Napel 2006,
Toma
ˇ
zevi
ˇ
c et al 2006, Aouadi and Sarry 2008, Fu and Kuduvalli 2008,Markeljet al 2008,van
der Bom et al 2010), navigation of medical devices can be performed using volumetric data
acquired prior to the procedure, offering 3D insight into the patient’s anatomy. A great variety
of 2D–3D registration methods have been developed of which most are applicable only for
the registration of computed tomography (CT) to x-ray images. Because both these imaging
modalities use x-rays, their visual content in terms of tissue contrast is rather similar. These
similarities are well exploited in various registration methods proposed (Bijhold 1993, Gilhuijs
et al 1996, Murphy 1997,Siroiset al 1999,Kimet al 2001, Clippe et al 2003,Jinet al 2006,
Jans and Syme 2006, Khamene et al 2006, Munbodh et al 2006, Chen et al 2008, Lemieux
et al 1994,Lavall
´
ee and Szeliski 1995, Feldmar et al 1997, Weese et al 1997,Gu
´
eziec et al
1998, Kita et al 1998,Liuet al 1998, Maurer et al 1998, Hamadeh et al 1998, Penney et al
1998, 2001, Rohlfing and Maurer 2002
, Benameur et al 2003, Livyatan et al 2003, Birkfellner
et al 2003,Kimet al 2005, Rohlfing et al 2005, Russakoff et al 2005, Turgeon et al 2005,
McLaughlin et al 2005, Birkfellner et al 2005, Dey and Napel 2006, Aouadi and Sarry 2008,
Fu and Kuduvalli 2008, van der Bom et al 2010, Maes et al 1997, Hill et al 2001, Pluim et al
2003).
However, for some applications additional images providing adequate soft tissue contrasts
may be of great value. This soft tissue contrast can be useful during endovascular
interventions like embolization of arteriovenous malformations or orthopedic interventions
like vertebroplasty. Registration of x-ray images to magnetic resonance imaging (MRI) data
may provide such complementary soft tissue contrast which is lacked by x-ray images.
Registering x-ray to MRI data is technically very challenging because fundamental
differences in imaging physics and contrast mechanisms lead to very different tissue contrasts.
Rohlfing and Maurer (2002) proposed a similarity measure that uses the distributions of MRI
intensities along rays. Subsequently, these distributions are compared to the pixel intensities
of the x-ray image in a manner that is similar to mutual information. A quantitative evaluation
of this method has so far not been reported. Toma
ˇ
zevi
ˇ
c et al (2003) have developed a method
that registers the bony edges of vertebral bodies extracted from 3D volume data to the high
intensity gradients in the x-ray images. Because the method uses gradient information it is
applicable for the registration of x-ray to CT and MR. A drawback of this method is that
the extraction of bone edges in MRI data is not an easy task. Furthermore, Toma
ˇ
zevi
ˇ
c et al
propose a method that registers a coarse 3D reconstruction, generated from two or more
oblique x-ray images, to MRI data (Toma
ˇ
zevi
ˇ
c et al 2006). Like the gradient-based method