Biomedical Image Technologies (BIT)

Research: High Resolution Imaging

The aim of this activity is to contribute to the design and implementation of high resolution Positron Emission Tomography (PET) scanners. These scanners require to detect and identify pairs of photons coming from the same annihilation positron-electron. The identification of these pairs of almost simultaneous photons is the key to obtain information on the spatial distribution of the radiopharmaceutical emitting positrons. A new research line has been started on Optical Tomography.

The main activities are:

Design of acquisition modules with programmable logic By continuously sampling the signal provided by the detectors, the acquisition module has to identify the detection of an annihilation photon and to characterize it in terms of energy, spatial position and time of detection. This last feature has to be very accurate as it is the key to identify pairs of detections in coincidence. In this work we have designed an acquisition module based on programmable devices (FPGA). Schematic of PETonCHIP architecture: event and coincidence detection on a single FPGA

Characterization & simulation of new detectors & architectures By means of simulations, the performance of different architectures and detectors has been characterized. Rotating or static architectures have been studied with different number of detectors blocks in order to get the best compromise in terms of cost, spatial resolution and sensitivity. Other detector crystals like CZT are also been simulated to determine the feasibility of their use in PET scanners. This could have a high interest to build combined PET/MRI scanners. A new line has been started on Monte Carlo simulations for turbid media light propagation to assess optical tomography reconstruction. Tomographic reconstruction Efficient 2D & 3D iterative reconstruction algorithms (OSEM) to obtain the best possible images that each scanner can produce have been developed. These algorithms need a system matrix that relates the scanner geometry with the acquired data. We have simulated the system matrix with Monte Carlo techniques. The simulator also allows including in the reconstruction process effects like the probability of detection in the scintillator crystals, probability of Compton scattering and others.

FEM simulation for the computation of weighting potential within a 32 mm thick CZT slab 18F rat study. FORE + 2D OSEM fast reconstruction

Collaborations

• Unidad de Medicina y Cirugía Experimental. Hospital G.U. Gregorio Marañón.
• SEDECAL - Sociedad Española de Electromedicina y Calidad S.A. (formerly SUINSA Medical Systems).
• Joint Department of Physics. Royal Marsden NHS Foundation Trust / Institute of Cancer Research. London (UK)
• Functional Imaging and Instrumentation Group. Department of Physics "E. Fermi". Università degli Studi di Pisa (Italy).

Some publications

(more can be found on the Publications page)

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• Gómez-Valverde, J.J., Sinz, C., Rank, E., Chen, Z., Santos, A., Drexler, W., Ledesma-Carbayo, M.J. "Adaptive compounding speckle-noise-reduction filter for optical coherence tomography images". J. Biomed. Opt., 26(6):065001. 2021 (doi: 10.1117/1.JBO.26.6.065001).
• Gómez-Valverde, J.J., Antón, A., Fatti, G., Liefers, B., Herranz, A., Santos, A., Sánchez, C.I., Ledesma-Carbayo, M.J. "Automatic glaucoma classification using color fundus images based on convolutional neural networks and transfer learning". Biomed. Opt. Express, 10(2):892-913. 2019.
• Zorraquino, C., Bugalho, R., Rolo, M., Silva, J.C., Vecklans, V., Silva, R., Ortigão, C.; Neves, J.A., Tavernier, S., Guerra, P., Santos, A., Varela, J. "Asymmetric Data Acquisition System for an Endoscopic PET-US Detector". IEEE Trans. Nucl. Sci., 63(1):213-221. 2016.
• Guerra, P., Valverde, J.J., Martin, A., Ledesma, M.J., Rubio-Guivernau, J.L., Santos, A. "Real Time Signal Processing and Data Handling with dedicated hardware in handheld OCT Device". J. Instrum., 10(11):C11001. 2015.
• Sportelli, G., Ortuño, J.E., Vaquero, J.J., Desco, M., Santos, A. "Massively parallelizable list-mode reconstruction using a Monte Carlo-based elliptical Gaussian model". Med. Phys., 40(1):012504. 2013.
• Sportelli, G., Belcari, N., Guerra, P., Santos, A. "Low-resource synchronous coincidence processor for positron emission tomography". Nucl. Instrum. Methods Phys. Res. Sect. A-Accel. Spectrom. Dect. Assoc. Equip., 648: S199-S201. 2011.
• Sportelli, G., Belcari, N., Guerra, P., Spinella, F., Franchi, G., Attanasi, F., Moehrs, S., Rosso, V., Santos, A., Del Guerra, A. "Reprogrammable Acquisition Architecture for Dedicated Positron Emission Tomography". IEEE Trans. Nucl. Sci.., 58(3): 695-702. 2011.
• Ortuño, J.E., Kontaxakis, G., Rubio, J.L., Guerra, P., Santos, A. "Efficient methodologies for system matrix modellig in iterative image reconstruction for rotating high resolution PET". Phys. Med. Biol., 55(7): 1833-1861. 2010
• Guerra, P., Santos, A, Darambara, D.G. "An investigation of performance characteristics of a pixellated room-temperature semiconductor detector for medical imaging". J. Phys. D-Appl. Phys., 42: 175101 (11pp). Sep. 2009.
• Guerra, P., Ortuño, J.E., Kontaxakis, G., Ledesma-Carbayo, M.J., Vaquero, J.J., Desco, M., Santos, A. "Real-Time Digital Timing in Positron Emission Tomography". IEEE Trans Nucl Sci, 55(5):2531-2540. 2008.
• Guerra, P., Santos, A., Darambara, D. "Development of a simplified simulation model for performance characterization of a pixellated CdZnTe multimodality imaging system". Phys Med Biol, 53(4):1099-1113. 2008.
• Guerra, P., Rubio, J.L., Ortuño, J.E., Kontaxakis, G., Ledesma, M.J., Santos, A. "Performance Analysis of a Low-Cost Small Animal PET/SPECT scanner". Nucl Instrum Methods Phys Res Sect A, 571(1-2):98-101. 2007.
• Guerra, P., Rubio, J.L., Kontaxakis, G., Ortuño, J.E., Ledesma, M.J., Santos, A. "Programmable electronics for low-cost small animal PET/SPET imaging". Nucl Instrum Methods Phys Res Sect A, 569(2):162-166. 2006.
• Ortuño, J.E., Guerra-Gutiérrez, P., Rubio, J.L., Kontaxakis, G., Santos, A. "3D-OSEM iterative image reconstruction for high resolution PET using precalculated system matrix". Nucl Instrum Methods Phys Res Sect A, 569(2):440-444. 2006.
• Guerra, P., Espinosa, J., Ortuño, J.E., Kontaxakis, G., Vaquero, J.J., Desco, M., Santos, A. "New Embedded Digital Front-End for High Resolution PET Scanner". IEEE Trans Nucl Sci, 53(3): 770-775. 2006.
• Guerra, P., Ortuño, J.E., Vaquero, J.J., Kontaxakis, G., Desco, M., Santos, A. "Modeling the Acquisition Front-End in High Resolution Gamma-Ray Imaging". IEEE Trans Nucl Sci, 53(3): 1150-1155. 2006.