A few words about...
(DTS) is referred to as the limited angle technique, which allows the reconstruction of
tomographic planes on the basis of the information contained within the images acquired
during one tomographic acquisition step. DTS is a project that we started in 1988 .
Our preliminary investigations has clearly demonstrated that DTS can be successfully used
with digitized fluoroscopic data to produce three-dimensional information and it can be
applied to Isocentric Rotational (IR) units such as the Radiotherapy Simulator or the
Angiographic units without necessitating any modifications to equipment.
The Multiple Projection Algorithm
We have introduced the Multiple Projection Algorithm (MPA) which performs DTS tomogram
of various orientations from projection images . The principle of
image reconstruction is given in the next figure:
Fig.1: A flowchart of the MPA algorithm 
The MPA algorithm has been implemented into a clinical prototype imaging system comprising
a digital chain that is interfaced with an IR fluoroscopic unit to form an integrated DTS
facility for three-dimensional visualization of patient anatomy .
Fig.2: The Digitomo process 
Reconstruction times of few seconds per plane have been achieved. The
region of interest can be approached by tracking through cross-sections with user-selected
Fig.3: The DTS reconstruction 
The Noise Removal
The image quality of the DTS tomograms was found to be primarily
influenced by the quality of projection images but also by the inherent tomographic noise
characteristic to a limited angle reconstruction method. The extensive technological
development on detectors such as flat-panel detectors (already available on the market)
may ensure high quality of projection images. The tomosynthetic noise removal was a
subject of our extensive research that was summarized in two published papers [4,5].
of a noise mask 
It involves the reconstruction and subtraction of blur from the plane of interest (see fig.4).
Fig.4: DTS Angiographic tomograms : (a) original, (b) denoised
wavelet based method 
The comparison of 3 successive DTS planes can provide a noise map which is
subsequently used to remove the blur from the middle plane, by wavelet filtering (see fig.5).
Fig.5: DTS Angiographic tomograms : (a) original, (b) denoised
DTS for Artero Venous Malformations
The potential benefits that could occur from the application of DTS in
treatment planning for stereotactic radiotherapy of artero venous malformations (AVMs)
were also presented in a published paper .
The DTS Localization Tool
The next step in our DTS project consisted in trying to localize
brachytherapy implanted wires and seeds using a DTS-based localization tool. The
localization method involves the identification of a point of interest on a DTS
reconstructed anatomical cross-section of arbitrary orientation, the calculation of its
position within the treatment co-ordinate system, the verification of this position on two
selected projection radiographs and the system feedback on the necessary corrective
actions if this trial has been unsuccessful. The interaction with simultaneous reference
to projection and tomographic data allows the user to verify his perception of spatial
relationships and ensures a high degree of localization accuracy of 1.2 mm and a precision
of 0.4 mm. [7,8]
Fig.5: DTS Localization 
The DTS -Cone Beam CT approach
Present research is directed towards a combined DTS-Cone Beam CT
approach for image reconstruction. Both Digital Tomosynthesis (DTS) and Cone Beam CT
(CBCT) reconstruction algorithms are based on backprojection and use cone beam projection
data as input. The relationship between the two reconstruction methods was analytically
explored. The effect of the reconstruction arc on the spatial resolution, slice thickness,
contrast sensitivity, shape distortion and artifacts, was also experimentally studied .
Fitered DTS with isocentric rotational units, such as radiotherapy simulators or
angiographic units, may be regarded as a limited angle equivalent of CBCT where only a
subset of projection data is used for reconstruction.
applications in Orthopedics, Dental and Mammographic Imaging
Pre-planning of orthopedic interventional procedures are mostly performed using 3D imaging, while in-theater imaging still employs 2D
projections. However tomographic data can be obtained also in-theater, using a motorized fluoroscopic C-arm and algorithms for
tomographic reconstruction such as Digital Tomosynthesis (DTS) or Cone Beam CT
(CBCT). We worked on the developments of a software tool used with an existing DTS based 3D imaging system
and applied for intramedullary nailing in computer assisted orthopedic surgery
DTS based CAOS system for intramedullary
Tomographic systems for dental applications based on CBCT and using isocentric rotational
fluoroscopic machines has already been proposed. Collecting, however, projection data over 360 degrees as
required by CBCT is not always desirable due to radiation protection considerations. Limited arc methods for tomographic reconstruction such as
methods for tomographic reconstruction such as Digital Tomosynthesis (DTS), could
be used prior to dental surgery .
DTS based dental imaging system 
Planar mammography is inherently limited to representing 3D information in 2D space. In order to improve the image visualization, a tomographic
modality such as tomosynthesis could be used. We investigated the
image quality in tomosynthetic tomographic imaging using various noise
removal algorithms. 
Noise removal in Tomosynthetic Mammographic
Following the above considerations we may conclude that:
Over the course of the project we witnessed the possibility of enhancing
the image quality based on technological improvements.
We are convinced that DTS can effectively improve the non-CT based
treatment planning in radiotherapy and especially add value in the following areas: ·
source localization in Brachytherapy ( a user friendly and highly accurate tool) · long
term evaluation of the treatment based on follow-up and study of complications arising
from the possibility to relate dose distribution to anatomy if combined with depth dose
data. · cost-effectiveness of Treatment Planning for clinics by integration of data
acquisition and Treatment Planing process.
By combining the DTS and CBCT techniques the system can be expanded to
broader area of clinical cases and add value to the simulator. Very promising
applications prove to be in Computed Assisted Orthopedic Surgery,
Tomographic Dental Imaging and Mammography.
The new research results are providing promising outlook. It is obvious that for this type
of research it is necessary to assume good collaboration with simulator manufacturers and
In this point we search clinical partners and we are ready to
talk to industrial partners. We would be interested to form a 3 members consortium to
investigate the industrial opportunities for this project.
A list of publications...
. Kolitsi Z, , Panayiotakis G, Pallikarakis
N,.Simulator based Cross-sectional Imaging Using a Digital Tomosynthesis Technique in
Proc. V International Conference on Biomedical Engineering Singapore,1988,pp.105-108.
. Kolitsi, Z.; Panayiotakis, G; Anastassopoulos, V.; Skodras, A.;
Pallikarakis, N. A multiple projection method for digital tomosynthesis. Med. Phys. 19(4):
. Kolitsi, Z.; Yoldassis, N.; Siozos, T.; Pallikarakis,
N. Volume Imaging in Fluoroscopy, A clinical prototype system based on a generalized
digital tomosynthesis technique. Acta Radiologica 37:741-748 ; 1996.
. Kolitsi Z, Panayiotakis G, Pallikarakis N, A method for selective
removal of out-of-plane structures in digital tomosynthesis. Med Phys 1993
. Badea C, Kolitsi Z, Pallikarakis N, A wavelet-based
method for removal of out-of-plane structures in digital tomosynthesis. Comput Med Imaging
Graph 1998 Jul-Aug;22(4):309-15 [Pdf]
. Kosta M. Kolitsi Z, Pallikarakis N, Can DTS benefit
stereotactic radiothrepay of artero venious malformations? A feasibility report, Physica
Medica-Vol XIV, N.3, July-September 1998).
. Messaris G, Kolitsi Z, Badea C, Pallikarakis N,
Three-dimensional localisation based on projectional and tomographic image correlation: An
application for digital tomosynthesis, Med Eng Phys. 1999 Mar;21(2):101-9
. Badea C., Kolitisi Z., Pallikarakis N. "An
automated Localisation Method in Brachytherapy using Digital Tomosynthesis" presented
in the World Congress in Medical Physics and Biomedical Engineering" , Chicago 2000.
[Abstract] [Ph.D Thesis: chapter]
 C. Badea: "Volume Imaging Using a Combined Cone Beam CT -DTS Approach",
Doctorate Thesis in Biomedical Engineering, University of Patras,
Greece, 2000; [Pdf_zip]
. C. Badea, Z. Kollitsi ,N. Pallikarakis: "Image quality in
Extended arc Filtered Digital Tomosynthesis " Acta Radiologica, Vol. 42, issue 2
. D. Soimu, C. Badea, Z. Kolitsi : " A Software Tool for a DTS-based Imaging System used in Intramedullary Nailing",
In Proceedings of the Third European Symposium in BME and MP, Patras,
2002 [ Pdf ]
. C. Badea, Z. Kollitsi ,N. Pallikarakis, :"A 3D Imaging
System for Dental Imaging based on Digital Tomosynthesis and Cone Beam
CT", in Proceedings of Medicon Conference, Pula, Croatia, 2001; [Pdf]
. C.Badea, K. Bliznakova, Z.Kolitsi, N.
Pallikarakis: "Noise Removal in Tomosynthetic Mammographic
Imaging" to appear in Proceedings of the EMBEC Conference, Vienna,
. D. Soimu, Z. Kolitsi, N.
Pallikarakis: “A Multiple Projection Algorithm With Noise
Removal of Out-of-Plane Structures for Digital Tomosynthesis using a
Stationary Detector”,4rd European Symposium
in Biomedical Engineering and Medical Physics, Patras, Greece,
25-27.06, 2004 [pdf]
Pallikarakis N, Comment on "Tomosynthesis-based localization of
radioactive seeds in prostate brachytherapy" MEDICAL PHYSICS, Vol 32,
Iss 1, pp 300, 2005
K., Kolitsi, Z., Speller, R.D., Horrocks, J.A., Tromba, G.,
Pallikarakis, N. Evaluation of digital breast tomosynthesis
reconstruction algorithms using synchrotron radiation in standard
geometry Medical Physics, 37 (4), pp. 1893-1903 (2010)