Andrew Karellas

Interests

Teaching

I have extensive experience in teaching Physics of Medical Imaging to Residents in Medical Imaging. This year I initiated a lecture series for residents and I am working towards establishing a course curriculum. I also interact with members of our research team (postdoctoral fellows or graduate students) in my lab. One postdoctoral fellow graduated from my lab in the past 2 years.

Research

- Detection and diagnostic imaging of the breast by tomographic x-ray imaging (breast CT, tomosynthesis) - Image quality and radiation dosimetry in Computed Tomography- Molecular imaging with x-ray fluorescence tomography- Development and evaluation of x-ray imaging detectors

Courses

Scholarly Contributions

Chapters

• Karellas, A. (2020). Clinical Mammography Physics: Emerging Practice. In Clinical Medical Imaging Physics: Current and Emerging Practice. In Clinical Imaging Physics: Current and Emerging Practice(p. 107). Wiley, Ehsan Samei (Editor), Douglas E. Pfeiffer (Editor).
• Vedantham, S., & Karellas, A. (2020). Clinical Mammography Physics: Emerging Practice. In Clinical Medical Imaging Physics: Current and Emerging Practice (E Samei, DE Pfeiffer, Eds.)(p. 107). John Wiley & Sons.

Journals/Publications

• Fu, Z., Tseng, H. W., Vedantham, S., Karellas, A., & Bilgin, A. (2020). A Multi-Slice Residual Dense Network Assisted Sparse-view Reconstruction for Breast Computed Tomography. Scientific Reports.
• Fu, Z., Tseng, H. W., Vedantham, S., Karellas, A., & Bilgin, A. (2020). A residual dense network assisted sparse view reconstruction for breast computed tomography. Scientific reports, 10(1), 21111.
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  To develop and investigate a deep learning approach that uses sparse-view acquisition in dedicated breast computed tomography for radiation dose reduction, we propose a framework that combines 3D sparse-view cone-beam acquisition with a multi-slice residual dense network (MS-RDN) reconstruction. Projection datasets (300 views, full-scan) from 34 women were reconstructed using the FDK algorithm and served as reference. Sparse-view (100 views, full-scan) projection data were reconstructed using the FDK algorithm. The proposed MS-RDN uses the sparse-view and reference FDK reconstructions as input and label, respectively. Our MS-RDN evaluated with respect to fully sampled FDK reference yields superior performance, quantitatively and visually, compared to conventional compressed sensing methods and state-of-the-art deep learning based methods. The proposed deep learning driven framework can potentially enable low dose breast CT imaging.
• Tseng, H. W., Vedantham, S., & Karellas, A. (2020). Cone-beam breast computed tomography using ultra-fast image reconstruction with constrained, total-variation minimization for suppression of artifacts. Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Association of Biomedical Physics (AIFB), 73, 117-124.
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  Compressed sensing based iterative reconstruction algorithms for computed tomography such as adaptive steepest descent-projection on convex sets (ASD-POCS) are attractive due to their applicability in incomplete datasets such as sparse-view data and can reduce radiation dose to the patients while preserving image quality. Although IR algorithms reduce image noise compared to analytical Feldkamp-Davis-Kress (FDK) algorithm, they may generate artifacts, particularly along the periphery of the object. One popular solution is to use finer image-grid followed by down-sampling. This approach is computationally intensive but may be compensated by reducing the field of view. Our proposed solution is to replace the algebraic reconstruction technique within the original ASD-POCS by ordered subsets-simultaneous algebraic reconstruction technique (OS-SART) and with initialization using FDK image. We refer to this method as Fast, Iterative, TV-Regularized, Statistical reconstruction Technique (FIRST). In this study, we investigate FIRST for cone-beam dedicated breast CT with large image matrix. The signal-difference to noise ratio (SDNR), the difference of the mean value and the variance of adipose and fibroglandular tissues for both FDK and FIRST reconstructions were determined. With FDK serving as the reference, the root-mean-square error (RMSE), bias, and the full-width at half-maximum (FWHM) of microcalcifications in two orthogonal directions were also computed. Our results suggest that FIRST is competitive to the finer image-grid method with shorter reconstruction time. Images reconstructed using the FIRST do not exhibit artifacts and outperformed FDK in terms of image noise. This suggests the potential of this approach for radiation dose reduction in cone-beam breast CT.
• Tseng, H., Karellas, A., & Vedantham, S. (2020). Sparse-view, short-scan, dedicated cone-beam breast computed tomography: image quality assessment. Biomedical Physics & Engineering Express, 6, 065015. doi:https://doi.org/10.1088/2057-1976/abb834
• Vedantham, S., Tseng, H. W., Konate, S., Shi, L., & Karellas, A. (2020). Dedicated cone-beam breast CT using laterally-shifted detector geometry: Quantitative analysis of feasibility for clinical translation. Journal of X-ray science and technology, 28(3), 405-426.
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  High-resolution, low-noise detectors with minimal dead-space at chest-wall could improve posterior coverage and microcalcification visibility in the dedicated cone-beam breast CT (CBBCT). However, the smaller field-of-view necessitates laterally-shifted detector geometry to enable optimizing the air-gap for x-ray scatter rejection.
• Deng, L., Yasar, S., Ahmed, M. F., Jayarathna, S., Feng, P., Wei, B., Vedantham, S., Karellas, A., & Cho, S. H. (2019). Investigation of transmission computed tomography (CT) image quality and x-ray dose achievable from an experimental dual-mode benchtop x-ray fluorescence CT and transmission CT system. Journal of X-ray science and technology, 27(3), 431-442.
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  To investigate the image quality and x-ray dose associated with a transmission computed tomography (CT) component implemented within the same platform of an experimental benchtop x-ray fluorescence CT (XFCT) system for multimodal preclinical imaging applications.
• Karellas, A. (2019). Challenges in Dosimetry and Radiation Dose Trends. Radiology, 294(2), 360-361.
• Tseng, H. W., Vedantham, S., Cho, S. H., & Karellas, A. (2019). Joint optimization of collimator and reconstruction parameters in x-ray fluorescence computed tomography using analytical point spread function and model observer. IEEE transactions on bio-medical engineering.
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  To jointly optimize collimator design and image reconstruction algorithm in X-ray Fluorescence Computed Tomography (XFCT) for imaging low concentrations of high atomic number (Z) elements in small animal models.
• Tseng, H. W., Vedantham, S., Cho, S., & Karellas, A. (2019). Joint optimization of collimator and reconstruction parameters in x-ray fluorescence computed tomography using analytical point spread function and model observer.. IEEE Trans Biomed Eng., doi: 10.1109/TBME.2019.2963040. [Epub ahead of print] PMID: 31899411. doi:10.1148/radiol.2019192414
• Karellas, A. (2018). The role of off-focus radiation in scatter correction for dedicated cone beam breast CT. Medical Physics, 45(1), 191-201. doi:10.1053
• O'Connell, A. M., Karellas, A., Vedantham, S., & Kawakyu-O'Connor, D. T. (2018). Newer Technologies in Breast Cancer Imaging: Dedicated Cone-Beam Breast Computed Tomography. Seminars in ultrasound, CT, and MR, 39(1), 106-113.
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  Dedicated breast computed tomography (CT) is the latest in a long history of breast imaging techniques dating back to the 1960s. Breast imaging is performed both for cancer screening as well as for diagnostic evaluation of symptomatic patients. Dedicated breast CT received US Food and Drug Administration approval for diagnostic use in 2015 and is slowly gaining recognition for its value in diagnostic 3-dimensional imaging of the breast, and also for injected contrast-enhanced imaging applications. Conventional mammography has known limitations in sensitivity and specificity, especially in dense breasts. Breast tomosynthesis was US Food and Drug Administration approved in 2011 and is now widely used. Dedicated breast CT is the next technological advance, combining real 3-dimensional imaging with the ease of contrast administration. The lack of painful compression and manipulation of the breasts also makes dedicated breast CT much more acceptable for the patients.
• Vedantham, S., & Karellas, A. (2018). Emerging Breast Imaging Technologies on the Horizon. Seminars in ultrasound, CT, and MR, 39(1), 114-121.
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  Early detection of breast cancers by mammography in conjunction with adjuvant therapy has contributed to reduction in breast cancer mortality. Mammography remains the "gold-standard" for breast cancer screening but is limited by tissue superposition. Digital breast tomosynthesis and more recently, dedicated breast computed tomography have been developed to alleviate the tissue superposition problem. However, all of these modalities rely upon x-ray attenuation contrast to provide anatomical images, and there are ongoing efforts to develop and clinically translate alternative modalities. These emerging modalities could provide for new contrast mechanisms and may potentially improve lesion detection and diagnosis. In this article, several of these emerging modalities are discussed with a focus on technologies that have advanced to the stage of in vivo clinical evaluation.
• Karellas, A. (2017). Reduced Patient Radiation Exposure during Neurodiagnostic and Interventional X-Ray Angiography with a New Imaging Platform. American Journal of Neuroradiology.
• Shi, L., Vedantham, S., Karellas, A., & Zhu, L. (2017). X-ray scatter correction for dedicated cone beam breast CT using a forward-projection model. Medical Physics, 44(6), 2312-2320.
• Shrestha, S., Vedantham, S., & Karellas, A. (2017). Towards standardization of x-ray beam filters in digital mammography and digital breast tomosynthesis: Monte Carlo simulations and analytical modelling. Physics in Medicine and Biology, 62(5), 1969-1993.
• van der Marel, K., Vedantham, S., van der Bom, I. M., Howk, M., Narain, T., Ty, K., Karellas, A., Gounis, M. J., Puri, A. S., & Wakhloo, A. K. (2017). Reduced Patient Radiation Exposure during Neurodiagnostic and Interventional X-Ray Angiography with a New Imaging Platform. AJNR. American journal of neuroradiology, 38(3), 442-449.
• Michaelsen, K. E., Krishnaswamy, V., Shi, L., Vedantham, S., Karellas, A., Pogue, B. W., Paulsen, K. D., & Poplack, S. P. (2016). Effects of breast density and compression on normal breast tissue hemodynamics through breast tomosynthesis guided near-infrared spectral tomography. Journal of biomedical optics, 21(9), 91316.
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  Optically derived tissue properties across a range of breast densities and the effects of breast compression on estimates of hemoglobin, oxygen metabolism, and water and lipid concentrations were obtained from a coregistered imaging system that integrates near-infrared spectral tomography (NIRST) with digital breast tomosynthesis (DBT). Image data were analyzed from 27 women who underwent four IRB approved NIRST/DBT exams that included fully and mildly compressed breast acquisitions in two projections—craniocaudal (CC) and mediolateral-oblique (MLO)—and generated four data sets per patient (full and moderate compression in CC and MLO views). Breast density was correlated with HbT (r=0.64, p=0.001), water (r=0.62, p=0.003), and lipid concentrations (r=?0.74, p
• Shi, L., Vedantham, S., Karellas, A., & Zhu, L. (2016). Library based x-ray scatter correction for dedicated cone beam breast CT. Medical physics, 43(8), 4529.
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  The image quality of dedicated cone beam breast CT (CBBCT) is limited by substantial scatter contamination, resulting in cupping artifacts and contrast-loss in reconstructed images. Such effects obscure the visibility of soft-tissue lesions and calcifications, which hinders breast cancer detection and diagnosis. In this work, we propose a library-based software approach to suppress scatter on CBBCT images with high efficiency, accuracy, and reliability.
• Vedantham, S., Shrestha, S., Karellas, A., Shi, L., Gounis, M. J., Bellazzini, R., Spandre, G., Brez, A., & Minuti, M. (2016). Photon-counting hexagonal pixel array CdTe detector: Spatial resolution characteristics for image-guided interventional applications. Medical physics, 43(5), 2118.
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  High-resolution, photon-counting, energy-resolved detector with fast-framing capability can facilitate simultaneous acquisition of precontrast and postcontrast images for subtraction angiography without pixel registration artifacts and can facilitate high-resolution real-time imaging during image-guided interventions. Hence, this study was conducted to determine the spatial resolution characteristics of a hexagonal pixel array photon-counting cadmium telluride (CdTe) detector.
• Zygmanski, P., Shrestha, S., Briovio, D., Karellas, A., & Sajo, E. (2016). Prototypes of self-powered radiation detectors employing intrinsic high-energy current. Medical physics, 43(1), 16.
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  The authors experimentally investigate the effect of direct energy conversion of x-rays via selfpowered Auger- and photocurrent, potentially suitable to practical radiation detection and dosimetry in medical applications. Experimental results are compared to computational predictions. The detector the authors consider is a thin-film multilayer device, composed of alternating disparate electrically conductive and insulating layers. This paper focuses on the experiments while a companion paper introduces the fundamental concepts of high-energy current (HEC) detectors.
• Elshahat, B., Gill, H. S., Filipyev, I., Shrestha, S., Hesser, J., Kumar, J., Karellas, A., Zygmanski, P., & Sajo, E. (2015). Technical Note: Nanometric organic photovoltaic thin film detectors for dose monitoring in diagnostic x-ray imaging. Medical physics, 42(7), 4027-32.
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  To fabricate organic photovoltaic (OPV) cells with nanometric active layers sensitive to ionizing radiation and measure their dosimetric characteristics in clinical x-ray beams in the diagnostic tube potential range of 60-150 kVp.
• Goertz, L., Tsiamas, P., Karellas, A., Sajo, E., & Zygmanski, P. (2015). Monte Carlo simulation of a prototypical patient dosimetry system for fluoroscopic procedures. Physics in medicine and biology, 60(15), 5891-909.
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  The purpose of this study is to investigate feasibility of a novel real-time dosimetry method for fluoroscopically guided interventions utilizing thin-film detector arrays in several potential locations with respect to the patient and x-ray equipment. We employed Monte Carlo (MC) simulation to establish the fluoroscopic beam model to determine dosimetric quantities directly from measured doses in thin-film detector arrays at three positions: A-attached to the x-ray source, B-on the couch under the patient and C-attached to the fluoroscopic imager. Next, we developed a calibration method to determine skin dose at the entry of the beam ([Formula: see text]) as well as the dose distribution along each ray of the beam in a water-equivalent patient model. We utilized the concept of water-equivalent thickness to determine the dose inside the patient based on doses measured outside of the patient by the thin-film detector array layers: (a) A, (b) B, or (c) B and C. In the process of calibration we determined a correction factor that characterizes the material-specific response of the detector, backscatter factor and attenuation factor for slab water phantoms of various thicknesses. Application of this method to an anthropomorphic phantom showed accuracy of about 1% for [Formula: see text] and up to about 10% for integral dose along the beam path when compared to a direct simulation of dose by MC.
• Michaelsen, K. E., Krishnaswamy, V., Shi, L., Vedantham, S., Poplack, S. P., Karellas, A., Pogue, B. W., & Paulsen, K. D. (2015). Calibration and optimization of 3D digital breast tomosynthesis guided near infrared spectral tomography. Biomedical optics express, 6(12), 4981-91.
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  Calibration of a three-dimensional multimodal digital breast tomosynthesis (DBT) x-ray and non-fiber based near infrared spectral tomography (NIRST) system is challenging but essential for clinical studies. Phantom imaging results yielded linear contrast recovery of total hemoglobin (HbT) concentration for cylindrical inclusions of 15 mm, 10 mm and 7 mm with a 3.5% decrease in the HbT estimate for each 1 cm increase in inclusion depth. A clinical exam of a patient's breast containing both benign and malignant lesions was successfully imaged, with greater HbT was found in the malignancy relative to the benign abnormality and fibroglandular regions (11 μM vs. 9.5 μM). Tools developed improved imaging system characterization and optimization of signal quality, which will ultimately improve patient selection and subsequent clinical trial results.
• Noo, F., & Karellas, A. (2015). Introduction: Advances and trends in image formation in X-ray computed tomography. Medical physics, 42(5), 2656.
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  Short Editorial/Introduction
• Vedantham, S., Karellas, A., Vijayaraghavan, G. R., & Kopans, D. B. (2015). Digital Breast Tomosynthesis: State of the Art. Radiology, 277(3), 663-84.
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  This topical review on digital breast tomosynthesis (DBT) is provided with the intent of describing the state of the art in terms of technology, results from recent clinical studies, advanced applications, and ongoing efforts to develop multimodality imaging systems that include DBT. Particular emphasis is placed on clinical studies. The observations of increase in cancer detection rates, particularly for invasive cancers, and the reduction in false-positive rates with DBT in prospective trials indicate its benefit for breast cancer screening. Retrospective multireader multicase studies show either noninferiority or superiority of DBT compared with mammography. Methods to curtail radiation dose are of importance. (©) RSNA, 2015.
• Zygmanski, P., Shrestha, S., Elshahat, B., Karellas, A., & Sajo, E. (2015). Dosimetric properties of high energy current (HEC) detector in keV x-ray beams. Physics in medicine and biology, 60(7), N121-9.
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  We introduce a new x-ray radiation detector. The detector employs high-energy current (HEC) formed by secondary electrons consisting predominantly of photoelectrons and Auger electrons, to directly convert x-ray energy to detector signal without externally applied power and without amplification. The HEC detector is a multilayer structure composed of thin conducting layers separated by dielectric layers with an overall thickness of less than a millimeter. It can be cut to any size and shape, formed into curvilinear surfaces, and thus can be designed for a variety of QA applications. We present basic dosimetric properties of the detector as function of x-ray energy, depth in the medium, area and aspect ratio of the detector, as well as other parameters. The prototype detectors show similar dosimetric properties to those of a thimble ionization chamber, which operates at high voltage. The initial results obtained for kilovoltage x-rays merit further research and development towards specific medical applications.

Proceedings Publications

• Karellas, A., Tseng, H., & Vedantham, S. (2021, 07/Summer). Image Quality Evaluation of a Compressed-Sensing Algorithm for Image Reconstruction in Dedicated Cone-Beam Breast CT Using Offset-Detector. In 63rd Annual Meeting of the American Association of Physicists in Medicine (AAPM), 48.
• Vedantham, S., Karellas, A., & Tseng, H. (2021, 07/Summer). Dedicated Cone-Beam Breast CT with Offset-Detector: Estimates of Mean Glandular Dose (MGD) with Heterogeneous Tissue Distribution and Real Breast Shapes from Clinical Datasets. In 63rd Annual Meeting of the American Association of Physicists in Medicine (AAPM), 48.
• Bilgin, A., Karellas, A., Vedantham, S., Tseng, H. W., & Fu, Z. (2020, Summer). Dedicated Breast CT: Comparative evaluation of multi-scale residual dense network and residual encoder-decoder network for deep learning-driven sparse-view reconstruction. In Annual Meeting of the American Association of Physicists in Medicine.
• Vedantham, S., & Karellas, A. (2017, September). A framework for optimizing micro-CT in dual-modality micro-CT/XFCT small-animal imaging system.. In Proc. SPIE 10393, Radiation Detectors in Medicine, Industry, and National Security XVIII, 103930R (2017/09/07); doi: 10.1117/12.2279351, XVIII, 103930R (2017/09/07).
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  Srinivasan Vedantham; Suman Shrestha; Andrew Karellas; Sang Hyun Cho;
• Vedantham, S., Shi, L., & Karellas, A. (2017, September). Scintillator performance considerations for dedicated breast computed tomography. In Proc. SPIE 10393, Radiation Detectors in Medicine, Industry, and National Security XVIII, 103930M (14 September 2017); doi: 10.1117/12.2279225, XVIII, 103930M.

Presentations

• Bilgin, A., Karellas, A., Vedantham, S., Tseng, H., & Fu, Z. (2020, July). Dedicated Breast CT: Comparative Evaluation of Multi-Scale Residual Dense Network and Residual Encoder-Decoder Network for Deep Learning-Driven Sparse-View Reconstruction. American Association of Physicists in Medicine (AAPM) Annual Meeting. Vancouver, Canada (Virtual): American Association of Physicists in Medicine.
• Karellas, A., Vedantham, S., & Tseng, H. (2020, July). Upright Dedicated Cone-Beam Breast CT: Short-Scan, Non-Uniform, Sparse-View Angular Sampling for Radiation Dose Reduction. American Association of Physicists in Medicine (AAPM) Annual Meeting. Vancouver, Canada (Virtual): American Association of Physicists in Medicine (AAPM).
• Karellas, A., Vedantham, S., & Tseng, H. (2020, November). Short-scan, non-uniform, sparse-view angular sampling for radiation dose reduction in upright dedicated breast CT. University of Arizona Cancer Center (UACC) Retreat. Tucson, AZ: University of Arizona Cancer Center (UACC).
• Bilgin, A., Karellas, A., Vedantham, S., Tseng, H., & Fu, Z. (2019, Dec/Fall). Deep Learning-Driven Sparse-View Reconstruction for Radiation Dose Reduction in Dedicated Breast CT: Quantitative Evaluation.. 105th Scientific Assembly and Annual Meeting of the Radiological Society of North America (RSNA), 2019 RSNA Annual Meeting Program, Abstract # SSC13-05.. Chicago, IL: Radiological Society of North America (RSNA).
• Karellas, A., & Vedantham, S. (2019, February). Automated notification: Radiomics of non-contrast CT scans.. 2019 University of Arizona College of Medicine Research Day. Tucson, AZ: University of Arizona College of Medicine.
• Karellas, A., & Vedantham, S. (2019, February). Interventional Radiology: Dual-energy dynamic imaging.. 2019 University of Arizona College of Medicine Research Day. Tucson, AZ: University of Arizona, College of Medicine.
• Karellas, A., & Vedantham, S. (2019, Summer). Will the Role of Mammography Remain the Same in the Next Five years?. UA Medical Imaging Grand Rounds.
• Karellas, A., Cho, S., Vedantham, S., & Tseng, H. (2019, Aug 2019). Expedient System Optimization of X-Ray Fluorescence Computed Tomography (XFCT) Using Analytical Point Spread Function and Model Observer. 61st Annual Meeting of the American Association of Physicists in Medicine (AAPM), MEDICAL PHYSICS 46 (6), E191-E191. San Antonio, TX: American Association of Physicists in Medicine (AAPM).
• Karellas, A., Vedantham, S., & Tseng, H. (2019, February). Radiation dose reduction in dedicated breast computed tomography.. 2019 University of Arizona College of Medicine Research Day. Tucson, AZ: University of Arizona, College of Medicine.
• Karellas, A., Vedantham, S., & Tseng, H. (2019, February). System design in X-ray Fluorescence Computed Tomography (XFCT) using analytical point spread function system matrix.. 2019 University of Arizona College of Medicine Research Day. Tucson, AZ: University of Arizona, College of Medicine.
• Karellas, A., Vedantham, S., Tseng, H., Tseng, H., Vedantham, S., & Karellas, A. (2018, Summer). Dedicated Breast CT: Impact of Short-Scan Source Trajectory and Sparse-View Acquisition on Image Quality. 60th Annual Meeting of the American Association of Physicists in Medicine (AAPM), Medical Physics 45 (6), E479-E480. Nashville, TN: AAPM.
• Tseng, H., Vedantham, S., & Karellas, A. (2018, Summer). Impact of GPU-Accelerated Sparse-View Reconstruction for Radiation Dose Reduction in Dedicated Breast CT. 60th Annual Meeting of the American Association of Physicists in Medicine (AAPM), Medical Physics 45 (6), E555-E555. Nashville, TN: AAPM.

Poster Presentations

• Karellas, A., Vedantham, S., & Tseng, H. (2019, Aug 2019). Impact of Uniform and Nonuniform Angular Sampling in Short-Scan Dedicated Breast Computed Tomography. 61st Annual Meeting of the American Association of Physicists in Medicine (AAPM), MEDICAL PHYSICS 46 (6), E428-E428. San Antonio, TX: American Association of Physicists in Medicine (AAPM).
• Vedantham, S., & Karellas, A. (2017, July). Dedicated breast CT: Numerical evaluation of improvement in x-ray fluence uniformity using 3D beam-shaping x-ray filter. AAPM Annual Meeting, Medical Physics 44-6, 2017 AAPM Annual Meeting Program pp. 3177 (2017).. Cenver, CO: American Association of Physicists in Medicine (AAPM).
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  Vedantham S and Karellas A. Dedicated breast CT: Numerical evaluation of improvement in x-ray fluence uniformity using 3D beam-shaping x-ray filter.

Reviews

• Karellas, A. (2019. Challenges in Dosimetry and Radiation Dose Trends.(pp Feb;294(2):360-361.).
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  This is an invited commentary by the Editor of Radiology on a publication relating to occupational radiation dose in a large population with focus on the dose to those who perform or assist in interventional fluoroscopic procedures. .