Digital Tomosynthesis (DTS)

A few words about...
The Multiple Projection Algorithm
The Noise Removal Algorithms
DTS for Artero Venous Malformations (AVMs)
The DTS Localization Tool 
The DTS -Cone Beam CT approach
The new applications in Orthopedics, Dental and Mammographic Imaging 
Conclusions


 
A few words about...

Digital Tomosynthesis (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 [1].

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 [2]. The principle of image reconstruction is given in the next figure:

Fig.1: A flowchart of the MPA algorithm [2]


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 [3]. 

Fig.2: The Digitomo process [4]

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 orientations. 




Fig.3: The DTS reconstruction [3]

 

The Noise Removal Algorithms

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].

        Subtraction of a noise mask [3]

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 image [4]

         A wavelet based method [5]

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 image [5]

 

DTS for Artero Venous Malformations (AVMs)

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 [6]. 

 

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 [7]

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.[9]

  New applications in Orthopedics, Dental and Mammographic Imaging

Orthopedics

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
(CAOS). [11]

DTS based CAOS system for intramedullary nailing[11]

 

Dental Imaging

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 [12].

 DTS based dental imaging  system [12]

Mammography

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. [13]

Noise removal in Tomosynthetic Mammographic Imaging [13]

 

 

Conclusions 

Following the above considerations we may conclude that: 

  1. Over the course of the project we witnessed the possibility of enhancing the image quality based on technological improvements. 

  2. 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. 

  3. 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 clinical partners. 

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...

[1]. 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. 

[2]. Kolitsi, Z.; Panayiotakis, G; Anastassopoulos, V.; Skodras, A.; Pallikarakis, N. A multiple projection method for digital tomosynthesis. Med. Phys. 19(4): 1045-1050; 1992.  

[3]. 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.  

[4]. Kolitsi Z, Panayiotakis G, Pallikarakis N, A method for selective removal of out-of-plane structures in digital tomosynthesis. Med Phys 1993 Jan-Feb;20(1):47-50. 

[5]. 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]

[6]. 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).  

[7]. 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  [Pdf]

[8]. 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]

[9] C. Badea: "Volume Imaging Using a Combined Cone Beam CT -DTS Approach", Doctorate Thesis in Biomedical Engineering, University of Patras, Greece, 2000; [Pdf_zip]

[10]. C. Badea, Z. Kollitsi ,N. Pallikarakis: "Image quality in Extended arc Filtered Digital Tomosynthesis " Acta Radiologica, Vol. 42, issue 2 (2001);244-9;.  [Pdf]

[11]. 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 ]

[12]. 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]

[13]. C.Badea, K. Bliznakova, Z.Kolitsi, N. Pallikarakis: "Noise Removal in Tomosynthetic Mammographic Imaging" to appear in Proceedings of the  EMBEC Conference, Vienna, 2002, [Pdf]

[14]. 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]

[15] Pallikarakis N, Comment on "Tomosynthesis-based localization of radioactive seeds in prostate brachytherapy" MEDICAL PHYSICS, Vol 32, Iss 1, pp 300, 2005

[16] Bliznakova, 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)

 

[home] [Medical Imaging]