**2.2 Radiography vs. tomosynthesis**

Anteroposterior (AP) radiograph of these joints demonstrate the excellent visualization of the prostheses in this view. AP radiograph is difficult to visualize 3D information in an AP radiograph as shown (Fig.4). An alternative approach to tomosynthesis imaging is to determine the number of views that can be acquired given imaging constraints (e.g., time restrictions from patient motion, dose restrictions of the detector). The tomographic angle can be selected to yield images with an acceptable level of artifacts. This is certainly the case with FBP algorithm and is suspected to be the case with simple backprojection (or the SAA algorithm). It is possible, however, that this restriction could be reduced by the use of an alternative reconstruction scheme.

X-Ray Digital Linear Tomosynthesis Imaging of Arthoroplasty 99

Methods for reduction of metal artifacts aim to improve the quality of images affected by these artifacts. In recent years, modified iterative (Wang et al 1996 , 1999 , 2000 , Man et al 2000) or wavelet reconstruction techniques have produced promising results. However, these methods cannot be combined with the fast and robust FBP algorithm, which is the standard

Digital linear tomosynthesis using the FBP algorithm shows adequate overall performance, but its effectiveness depends strongly on the region of the image. Digital linear tomosynthesis using FBP algorithm images gives good results independent of the type of metal present in the patient and shows good results for the removal of noise artifacts, especially at greater distances from metal objects. Application of digital linear tomosynthesis to the imaging of hip prostheses appears promising. In addition, flexibility in the choice of digital linear tomosynthesis imaging parameters based on the desired final

In Fig.4, Coronal slice images (multi-planar reconstruction; MPR) of the hip prosthesis at center heights on metal artifact reduction (MAR) CT (MAR-CT) and non MAR-CT scans at approximately the same level. Remarkable metal artifacts can be seen occurring in the neighborhood of the hip prosthesis. However, MAR-CT processing reduced the metal artifacts. Tomosynthesis images of the prostheses at center heights at the same level. The new diagnostic information that could not be acquired from CT images is provided. Reduction in metal artifacts was obtained in the images as shown here. The use of tomosynthesis allowed better visualization of the prosthesis caused by the blurring of

The FBP tomosynthesis was compared to MAR CT, and non-MAR CT scans of a prosthesis case. The effectiveness of this method in enhancing visibility of a prosthesis case was quantified in terms of the signal-to-noise ratio (SNR), and removal of ghosting artifacts in a prosthesis case was quantified in terms of the artifact spread function (ASF). The SNR in the

pixel value in the region of interest (ROI) within the object, *N0* is the mean pixel value in the

object, in addition to photon statistics and electronic noise. Wu et al. proposed an ASF metric to quantify artifacts observed in planes outside the focus image plane (Wu et al 2003). The artifacts are generated from real features located in the focus image plane, and resemble the real feature. The artifacts exhibited in image planes are defined by the ASF as

the location of the off-focus plane, and *Nartifact* (*z0*) and *NBG* (*z0*) are the average pixel intensities of the feature and the image background in the in-focus plane, respectively, *Nartifact*(*z*) and *NBG* (*z*) are the average pixel intensities of the artifact and the image

The effectiveness of this method in enhancing visibility of a prosthesis case was quantified in terms of the SNR, and removal of ghosting artifacts in a prosthesis case was quantified in terms of the ASF. In the near in-focus plane, the contrast is greater in the MAR CT or FBP

, where *z0* is the location of the in-focus plane of the real feature, *z* is

0 *N N* 

0 is the standard deviation of pixel values in the

0 includes structure noise that can obscure the

, where *N1* is the mean

reconstruction technique (Robertson et al 1997) implemented in modern CT scanners.

images and generation of high quality images may be beneficial.

anatomic structures above and below the visualized planes.

ROI in a background area, and

0 0 () () () ()

*artifact BG artifact BG N zN z N z Nz* 

background ROI. Throughout these results,

background in the off-focus plane, respectively.

tomosynthesis relative to the non-MAR CT (Fig.5).

prosthetic case was determined. The SNR is defined as 1 0
