Herbert Bruder, Presenter: Employee, Siemens AG

Martin Ulrich Sedlmair MS, Abstract Co-Author: Employee, Siemens AG

Karl Stierstorfer PhD, Abstract Co-Author: Employee, Siemens AG

Thomas G. Flohr PhD, Abstract Co-Author: Employee, Siemens AG

We present an iterative reconstruction scheme - High Definition extended Field of View (HD FOV) reconstruction - for CT imaging in radiation therapy and nuclear medicine.

The accuracy of line integrals needed for dose estimation in radiation therapy or attenuation correction in nuclear medicine depends on the precision of the reconstructed patient contour and attenuation. In case of obese patients and/or special positioning of the patient, parts of the patient might be outside the Scan Field of View (SFOV). Consequently, a portion of the CT raw data is truncated at the edges of the SFOV. Mathematically speaking, there is no unique solution; a good way to solve the problem is to use prior knowledge. Our new approach attempts an estimate of both the contour and the attenuation outside the SFOV. A good estimate for the contour of the patient beyond the SFOV is obtained by thresholding the image data of a standard extended FOV reconstruction, e.g. based on the adaptation of the slope of projection data and extended model data. After detecting the contour, the tissue area inside is filled with constant (typically soft tissue) attenuation. Applying this procedure, we obtain an intermediate image volume which is forward projected into raw data space using a model of the CT acquisition, covering the entire extended FOV. As a result, synthetic raw data are obtained, containing line integrals covering the constant attenuation outside the SFOV. Measurement data and projected data are linearly combined, filtered and back projected to obtain the final image volume covering the extended FOV.  

Based on phantom and clinical data, we demonstrate that our approach gives a good estimate of patient geometry outside the SFOV and good stability of attenuation values. In typical clinical situations, a +/- 50 HU stability of is maintained within a 65 cm FOV.

Using prior knowledge of contour and attenuation a highly accurate reconstruction of image signals beyond the standard FOV is feasible. Precise dose estimation in radiation therapy and attenuation correction in nuclear medicine is guaranteed in a 65 cm FOV.

HD FOV reconstruction extends the SFOV in CT imaging with high accuracy, thus improving dose estimation in radiation therapy and attenuation correction in nuclear medicine.  

Bruder, H, Sedlmair, M, Stierstorfer, K, Flohr, T, High Definition Extended Field of View (HD FOV) Reconstruction in CT.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11015308.html