Prostate brachytherapy involves permanent implantation of radioactive sources into the prostate gland. Since
fluoroscopy and transrectal ultrasound (TRUS) imaging modalities currently complement each other by providing good
visualization of seeds and soft tissue, respectively, the registration of these two imaging modalities could lead to the
intraoperative dosimetry analysis of brachytherapy procedures, thus improving patient outcome and reducing costs.
Although it is desirable to register TRUS and fluoroscopy images by using the implanted seeds as fiducial markers, an
operator, based on our experience, can locate only a small fraction of implanted seeds in axial TRUS images. Therefore,
to perform TRUS-fluoroscopy registration in a clinical setting, there is a need for (1) a new method that can reliably
perform registration at low seed detection rates and (2) a new imaging technique to enhance the seed visibility. We
previously developed iterative optimal assignment (IOA), which can perform registration at seed detection rates below
20%, to address the former. In this paper, we present a new TRUS acquisition method where we acquire images of the
prostate by rotating the longitudinal transducer of a biplanar probe in the clockwise/counter-clockwise direction. We
acquired post-implant fluoroscopy and TRUS images from 35 patients who underwent a seed implant procedure. The
results show that the combined use of IOA and rotational images makes TRUS-fluoroscopy registration possible and
practical, thus our goal of intraoperative dosimetry can be realized.
Currently available seed reconstruction algorithms are based on the assumption that accurate information about the imaging geometry is known. The assumption is valid for isocentric x-ray units such as radiotherapy simulators. However, the large majority of the clinics performing prostate brachytherapy today use C-arms for which imaging parameters such as source to axis distance, image acquisition angles, central axis of the image are not accurately known. We propose a seed reconstruction algorithm that requires no such knowledge of geometry. The new algorithm makes use of perspective projection matrix, which can be easily derived from a set of known reference points. The perspective matrix calculates the transformation of a point in 3D space to the imaging coordinate system. An accurate representation of the imaging geometry can be derived from the generalized projection matrix (GPM) with eleven degrees of freedom. In this paper we show how GPM can be derived given a theoretical minimum number of reference points. We propose an algorithm to compute the line equation that defines the backprojection operation given the GPM. The algorithm can be extended to any ray-tracing based seed reconstruction algorithms. Reconstruction using the GPM does not require calibration of C-arms and the images can be acquired at arbitrary angles. The reconstruction is performed in near real-time. Our simulations show that reconstruction using GPM is robust and accuracy is independent of the source to detector distance and location of the reference points used to generate the GPM. Seed reconstruction from C-arm images acquired at unknown geometry provides a useful tool for intra-operative dosimetry in prostate brachytherapy.
KEYWORDS: Digital watermarking, Computer security, Telecommunications, Medical imaging, Information security, Data communications, Databases, Data storage, Network security, Symmetric-key encryption
Privacy protection of medical records has always been an important issue and is mandated by the recent Health Insurance Portability and Accountability Act (HIPAA) standards. In this paper, we propose security architectures for a tele-referring system that allows electronic group communication among professionals for better quality treatments, while protecting patient privacy against unauthorized access. Although DICOM defines the much-needed guidelines for confidentiality of medical data during transmission, there is no provision in the existing medical security systems to guarantee patient privacy once the data has been received. In our design, we address this issue by enabling tracing back to the recipient whose received data is disclosed to outsiders, using watermarking technique. We present security architecture design of a tele-referring system using a distributed approach and a centralized web-based approach. The resulting tele-referring system (i) provides confidentiality during the transmission and ensures integrity and authenticity of the received data, (ii) allows tracing of the recipient who has either distributed the data to outsiders or whose system has been compromised, (iii) provides proof of receipt or origin, and (iv) can be easy to use and low-cost to employ in clinical environment.
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