Dr. Niko Pagoulatos Profile

Dr. Niko Pagoulatos

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Publications (7)

Proceedings Article | 11 April 2002 Paper

Intensity-based image registration for 3D spatial compounding using a freehand 3D ultrasound system

Niko Pagoulatos, David Haynor, Yongmin Kim

Proceedings Volume 4687, (2002) https://doi.org/10.1117/12.462184

KEYWORDS: Image registration, 3D acquisition, 3D image processing, Data acquisition, 3D image reconstruction, Chromium, In vivo imaging, Ultrasonography, Sensors, Image quality

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3D spatial compounding involves the combination of two or more 3D ultrasound (US) data sets, acquired under different insonation angles and windows, to form a higher quality 3D US data set. An important requirement for this method to succeed is the accurate registration between the US images used to form the final compounded image. We have developed a new automatic method for rigid and deformable registration of 3D US data sets, acquired using a freehand 3D US system. Deformation is provided by using a 3D thin-plate spline (TPS). Our method is fundamentally different from the previous ones in that the acquired scattered US 2D slices are registered and compounded directly into the 3D US volume. Our approach has several benefits over the traditional registration and spatial compounding methods: (i) we only peform one 3D US reconstruction, for the first acquired data set, therefore we save the computation time required to reconstruct subsequent acquired scans, (ii) for our registration we use (except for the first scan) the acquired high-resolution 2D US images rather than the 3D US reconstruction data which are of lower quality due to the interpolation and potential subsampling associated with 3D reconstruction, and (iii) the scans performed after the first one are not required to follow the typical 3D US scanning protocol, where a large number of dense slices have to be acquired; slices can be acquired in any fashion in areas where compounding is desired. We show that by taking advantage of the similar information contained in adjacent acquired 2D US slices, we can reduce the computation time of linear and nonlinear registrations by a factor of more than 7:1, without compromising registration accuracy. Furthermore, we implemented an adaptive approximation to the 3D TPS with local bilinear transformations allowing additional reduction of the nonlinear registration computation time by a factor of approximately 3.5. Our results are based on a commercially available tissue-mimicking abdominal phantom and in-vivo muscle data.

Proceedings Article | 28 May 2001 Paper

Real-time 3D ultrasound imaging on a next-generation media processor

Niko Pagoulatos, Frederic Noraz, Yongmin Kim

Proceedings Volume 4319, (2001) https://doi.org/10.1117/12.428084

KEYWORDS: 3D image processing, Reconstruction algorithms, 3D image reconstruction, Algorithm development, Position sensors, Ultrasonography, 3D acquisition, Visualization, 3D visualizations, Data processing

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Proceedings Article | 18 April 2000 Paper

New spatial localizer based on fiber optics with applications in 3D ultrasound imaging

Niko Pagoulatos, Robert Rohling, Warren Edwards, Yongmin Kim

Proceedings Volume 3976, (2000) https://doi.org/10.1117/12.383088

KEYWORDS: Sensors, 3D image processing, Fiber optics sensors, Position sensors, Ultrasonography, 3D acquisition, 3D metrology, 3D modeling, Fiber optics, Computing systems

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Proceedings Article | 18 April 2000 Paper

Image-based registration of ultrasound and magnetic resonance images: a preliminary study

Niko Pagoulatos, David Haynor, Yongmin Kim

Proceedings Volume 3976, (2000) https://doi.org/10.1117/12.383037

KEYWORDS: Image registration, Magnetic resonance imaging, Surgery, Position sensors, Transmitters, Detection and tracking algorithms, Magnetism, Ultrasonography, Visualization, Medical imaging

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A number of surgical procedures are planned and executed based on medical images. Typically, x-ray computed tomography (CT) and magnetic resonance (MR) images are acquired preoperatively for diagnosis and surgical planning. In the operating room, execution of the surgical plan becomes feasible due to registration between preoperative images and surgical space where patient anatomy lies. In this paper, we present a new automatic algorithm where we use ultrasound (US) 2D B-mode images to register the preoperative MR image coordinate system with the surgical space which in our experiments is represented by the reference coordinate system of a DC magnetic position sensor. The position sensor is also used for tracking the position and orientation of the US images. Furthermore, we simulated patient anatomy by using custom-built phantoms. Our registration algorithm is a hybrid between fiducial- based and image-based registration algorithms. Initially, we perform a fiducial-based rigid-body registration between MR and position sensor space. Then, by changing various parameters of the rigid-body fiducial-based transformation, we produce an MR-sensor misregistration in order to simulate potential movements of the skin fiducials and/or the organs. The perturbed transformation serves as the initial estimate for the image-based registration algorithm, which uses normalized mutual information as a similarity measure, where one or more US images of the phantom are automatically matched with the MR image data set. By using the fiducial- based registration as the gold standard, we could compute the accuracy of the image-based registration algorithm in registering MR and sensor spaces. The registration error varied depending on the number of 2D US images used for registration. A good compromise between accuracy and computation time was the use of 3 US slices. In this case, the registration error had a mean value of 1.88 mm and standard deviation of 0.42 mm, whereas the required computation time was approximately 52 sec. Subsampling the US data by a factor of 4 X 4 and reducing the number of histogram bins to 128 reduced the computation time to approximately 6 sec. with a small increase in the registration error.

Proceedings Article | 26 May 1999 Paper

PC-based system for 3D registration of ultrasound and magnetic resonance images based on a magetic position sensor

Niko Pagoulatos, Warren Edwards, David Haynor, Yongmin Kim

Proceedings Volume 3658, (1999) https://doi.org/10.1117/12.349473

KEYWORDS: Image registration, Magnetic resonance imaging, Transmitters, Position sensors, Magnetism, Receivers, Transducers, Ultrasonography, Brain, 3D image processing

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Proceedings Article | 26 June 1998 Paper

Calibration and validation of freehand 3D ultrasound systems based on DC magnetic tracking

Niko Pagoulatos, Warren Edwards, David Haynor, Yongmin Kim

Proceedings Volume 3335, (1998) https://doi.org/10.1117/12.312541

KEYWORDS: Calibration, Receivers, Ultrasonography, 3D image processing, Transmitters, Tin, Position sensors, Magnetic tracking, Sensors, Magnetism

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Proceedings Article | 11 December 1996 Paper

Photoacoustic location of optical absorbers in phantom tissue

Christoph Hoelen, G. Hamhuis, Niko Pagoulatos, Iris van den Ham, Frits de Mul, Jan Greve

Proceedings Volume 2927, (1996) https://doi.org/10.1117/12.260657

KEYWORDS: Tissue optics, Signal detection, Sensors, Photoacoustic spectroscopy, Blood, Optical fibers, Capillaries, Blood vessels, Scattering, Near field optics

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Pulsed photoacoustic (PA) signals may be used for the detection and imaging of blood vessels in tissue. A relatively strong absorption by red blood cells and low absorption by the surrounding tissue, combined with a reasonable penetration depth of the light is found at a wavelength of ca. 577 nm. Experiments were performed with a pulsed frequency doubled Nd:YAG laser which delivered 10 ns pulses at 532 nm wavelength. Ten percent dilutions of India ink and 50% suspensions of red blood cells in PBS were used as optical absorbers. Blood vessels were simulated by hollow nylon fibers with an inner diameter of ca. 250 micrometer through which these suspensions flow. The optical scattering of the surrounding tissue was simulated by a 12% dilution of Intralipid-10% to get a solution with a reduced scattering coefficient of 1.8 mm^-1. The PA signals were detected with a hydrophone that contained four wide band piezoelectric transducers made of 9 micrometer thick PVdF film with an effective diameter of 200 micrometers. Laser pulses with energies up to 8 microjoules were delivered to the sample by a 50 or 100 micrometer core diameter glass fiber. Pulsed optical heating of red blood cells up to 30 - 35 degrees for more than 12,000 times did not affect the photoacoustic response of the cells. If a single fiber is used to illuminate the sample, then even at a depth of 1 mm the PA signals show that the volume that is effectively illuminated is laterally restricted to a diameter of ca. 1 mm. Vessels with blood or ink dilutions were detected up to a depth of more than 1 mm in the scattering medium. Monte- Carlo (MC) simulations were used to simulate the spatial distribution of light absorption in phantom tissue. From this distribution the PA response of blood vessels was simulated. A delay-and-sum beam forming algorithm was developed for 3-D near field configurations and applied to a PA image reconstruction program. The images based on MC simulations as well as experimental data show that the side of larger vessels that is facing the illuminating fiber can be located with a resolution that depends on the configuration and varies between 0.1 and 1 time the inner vessel diameter. This shows the principle and the feasibility of three dimensional photoacoustic dermal tissue imaging.

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