Dr. Farhad A. Ghelmansarai Profile

Dr. Farhad A. Ghelmansarai

Sr. Staff Scientist

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Publications (3)

Proceedings Article | 20 April 2005 Paper

Soft tissue visualization using a highly efficient megavoltage cone beam CT imaging system

Farhad Ghelmansarai, Ali Bani-Hashemi, Jean Pouliot, Ed Calderon, Paco Hernandez, Matthias Mitschke, Michelle Aubin, Kara Bucci

Proceedings Volume 5745, (2005) https://doi.org/10.1117/12.602148

KEYWORDS: Receptors, Image filtering, Tissues, Digital filtering, X-ray computed tomography, Imaging systems, Signal to noise ratio, Sensors, Photons, Image quality

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Proceedings Article | 5 June 2003 Paper

High-resolution video-based EPID for cone beam CT

Farhad Ghelmansarai, Ali Bani-Hashemi, Juan Celi, Paco Hernandez, Ed Calderon, Matthias Mitschke

Proceedings Volume 5030, (2003) https://doi.org/10.1117/12.480484

KEYWORDS: Amorphous silicon, Signal to noise ratio, Sensors, Cameras, Imaging systems, Scintillators, Video, Spatial resolution, Computed tomography, Electronic imaging

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Proceedings Article | 5 June 2003 Paper

Electronic readout of a-Si EPIDs for optimum signal-to-noise ratio

Farhad Ghelmansarai, Satrajit Misra, Jean Pouliot

Proceedings Volume 5030, (2003) https://doi.org/10.1117/12.480481

KEYWORDS: Signal to noise ratio, Sensors, Amorphous silicon, Photodiodes, Computed tomography, X-rays, 3D acquisition, Imaging systems, Radiotherapy, Lanthanum

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Three acquisition schemes for a-Si flat panels are described for radiation therapy imaging. The goal of all three acquisition modes is to acquire images with the highest achievable SNR (signal to noise ratio). The acquisition modes are Single mode for low dose acquisition (used for patient positioning), external continuous mode used for patient treatment (verification), and Cone Beam mode for mega-voltage computed tomography (MVCT). During single mode acquisition, a few frames are readout prior to the start of irradiation. During this cycle, the accumulated dark current and residual data are cleared. During the radiation delivery no readout occurs, and the signal is integrated over the entire exposure period. After the irradiation readout occurs. The advantages of this readout scheme are to reduce the effects of readout noise and eliminate the linear accelerator (linac) pulsing effects on the final image. There is no readout during the exposure; therefore, no beam pulsing artifacts occur. Since the signal is integrated during the exposure time and the readout is performed after the exposure, this improves the SNR compared to acquiring a few frames during the radiation and averaging these frames to create the final image. The single mode acquisition is used clinically routinely and allows the acquisition of clinical images with a small amount of exposure (<=2 MU). During external trigger continuous mode, the linear accelerator pulsing artifacts are removed by synchronizing the frame readout with linear accelerator pulses. The pulsing artifacts reduce the signal to noise ratio. This degradation is in the range of 70% for a single frame acquisition with 6MV, 300MU/min X-ray beam. Frame averaging reduces the degradation. The Cone beam acquisition mode is used to perform volume MVCT in the cone beam geometry to visualize 3D (three dimensional) anatomy during patient positioning. In this mode the image acquisition is synchronized with the linear accelerator, which enables the imager to remove linear accelerator pulsing artifacts from the image and also provides the charge integration during low dose imaging. This synchronization improves the SNR.

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