Andrew Karellas

• PhD
• Managing Director at University of Massachusetts Chan Medical School

Purpose: We aim to determine the combination of X-ray spectrum and detector scintillator thickness that maximizes the detectability of microcalcification clusters in dedicated cone-beam breast CT. Approach: A cascaded linear system analysis was implemented in the spatial frequency domain and was used to determine the detectability index using nu...

Background Dedicated cone‐beam breast computed tomography (CBBCT) using short‐scan acquisition is being actively investigated to potentially reduce the radiation dose to the breast. This would require determining the optimal x‐ray source trajectory for such short‐scan acquisition. Purpose To quantify the projection angle‐dependent normalized gland...

Objective: A dedicated cone-beam breast computed tomography (BCT) using a high-resolution, low-noise detector operating in offset-detector geometry has been developed. This study investigates the effects of varying detector offsets and image reconstruction algorithms to determine the appropriate combination of detector offset and reconstruction al...

Purpose A clinical‐prototype, dedicated, cone‐beam breast computed tomography (CBBCT) system with offset detector is undergoing clinical evaluation at our institution. This study is to estimate the normalized glandular dose coefficients (DgNCT) that provide air kerma‐to‐mean glandular dose conversion factors using Monte Carlo simulations. Material...

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 wo...

The purpose of this study is to quantify the impact of sparse-view acquisition in short-scan trajectories, compared to 360-degrees full-scan acquisition, on image quality measures in dedicated cone-beam breast computed tomography (BCT). Projection data from 30 full-scan (360-degrees; 300 views) BCT exams with calcified lesions were selected from an...

Mammography started as a diagnostic imaging modality and it was practiced largely in women who were symptomatic of a breast abnormality. The potential of digital mammography was envisioned on the basis of physical principles and computations, which predicted that this technology would increase tissue contrast and it would enable improved detection...

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 red...

Background: 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. Ob...

Objective: 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. Methods: Single pinhole (SPH) collimator and three types of multi-pinhole (MPH) collimators were evaluated. MPH collimators...

Objective: 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. Methods: Cone-beam CT scans were performed using an experimental benchto...

Purpose: Dedicated cone beam breast CT (CBBCT) suffers from x-ray scatter contamination. We aim to identify the source of the significant difference between the scatter distributions estimated by two recent methods proposed by our group and to investigate its effect on CBBCT image quality. Method: We recently proposed two novel methods of scatte...

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 s...

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 deve...

Purpose: The quality of dedicated cone-beam breast CT (CBBCT) imaging is fundamentally limited by x-ray scatter contamination due to the large irradiation volume. In this paper, we propose a scatter correction method for CBBCT using a novel forward-projection model with high correction efficacy and reliability. Method: We first coarsely segment...

In digital breast tomosynthesis and digital mammography, the x-ray beam filter material and thickness vary between systems. Replacing K-edge filters with Al was investigated with the intent to reduce exposure duration and to simplify system design. Tungsten target x-ray spectra were simulated with K-edge filters (50��m Rh; 50��m Ag) and Al filters...

Background and purpose: Advancements in medical device and imaging technology as well as accruing clinical evidence have accelerated the growth of the endovascular treatment of cerebrovascular diseases. However, the augmented role of these procedures raises concerns about the radiation dose to patients and operators. We evaluated patient doses fro...

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...

Purpose: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 l...

Purpose: In digital breast tomosynthesis (DBT) systems capable of digital mammography (DM), Al filters are used during DBT and K-edge filters during DM. The potential for standardizing the x-ray filters with Al, instead of K-edge filters, was investigated with intent to reduce exposure duration and to promote a simpler system design. Methods: Anal...

Purpose: In Contrast Enhanced Spectral Mammography (CESM), Rh filter is often used during low-energy image acquisition. The potential for using Ag, In and Sn filters, which exhibit K-edge closer to, and just below that of Iodine, instead of the Rh filter, was investigated for the low-energy image acquisition. Methods: Analytical computations of th...

Purpose:The image quality of dedicated cone-beam breast CT (CBBCT) is fundamentally limited by substantial x-ray 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...

Purpose:Scatter contamination is detrimental to image quality in dedicated cone-beam breast CT (CBBCT), resulting in cupping artifacts and loss of contrast in reconstructed images. Such effects impede visualization of breast lesions and the quantitative accuracy. Previously, we proposed a library-based software approach to suppress scatter on CBBCT...

Purpose:To optimize the cesium iodide (CsI:Tl) scintillator thickness in a complimentary metal-oxide semiconductor (CMOS)-based detector for use in dedicated cone-beam breast CT. Methods:The imaging task considered was the detection of a microcalcification cluster comprising six 220µm diameter calcium carbonate spheres, arranged in the form of a re...

Purpose 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...

Purpose: Scatter errors are detrimental to cone-beam breast CT (CBBCT) accuracy and obscure the visibility of calcifications and soft-tissue lesions. In this work, we propose practical yet effective scatter correction for CBBCT using a library-based method and investigate its feasibility via small-group patient studies. Method: Based on a simplifie...

The ability to discern malignant from benign tissue in excised human breast specimens in Breast Conservation Surgery (BCS) was evaluated using a prototype single frequency terahertz radiation. Terahertz (THz) images of the specimens in reflection mode were obtained by employing a gas laser source and mechanical scanning. The images were correlated...

Purpose: 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 multil...

Small intestine is the longest organ in the gastrointestinal tract where much of the digestion and the food absorption take place. Wireless video capsule endoscope (VCE) is the first device taking 2-D pictures from the lesions and the abnormalities in the entire length of the small intestine. Since precise localization and mapping inside the small...

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 observatio...

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...

A multimodality system combining a clinical prototype digital breast tomosynthesis with its imaging geometry modified to facilitate near-infrared spectroscopic imaging has been developed. The accuracy of parameters recovered from near-infrared spectroscopy (NIRS) is dependent on fibroglandular tissue content. Hence, in this study, volumetric estima...

This updated edition of the leading text on the imaging of child abuse and its imitators combines radiographic images with pathologic correlates of inflicted injuries. Presented in full color for the first time, it contains many new photomicrographs and clinical images of bone scintigraphy, CT, MRI and sonography. Presenting radiologic findings in...

Over the past decade, annually for women 50 years of age or older, the breast cancer incidence rate in the United States has ranged from 400 to 500 per 100 000 women and the breast cancer mortality rate has ranged from 60 to 80 per 100 000 women. Though there has been a decline in the breast cancer mortality in the past decade it continues to be th...

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 dosi...

Purpose: 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. Methods: Experiments were designed to optimize the detector’s x-ray response and find the best parameter comb...

Detectors with hexagonal pixels require resampling to square pixels for distortion-free display of acquired images. In this work, the presampling modulation transfer function (MTF) of a hexagonal pixel array photon-counting CdTe detector for region-of-interest fluoroscopy was measured and the optimal square pixel size for resampling was determined....

To determine the spatial distribution of x-ray scatter and scatter-to-primary ratio (SPR) in projections during cone-beam breast CT (CBBCT) with laterally-shifted detector that results in coronal (fan-angle) truncation. We hypothesized that CBBCT with coronal truncation would lower SPR due to reduction in irradiated breast volume, and that the loca...

To design a 3 -D beam-shaping filter for cone-beam breast CT for equalizing x-ray photon fluence incident on the detector along both fan and cone angle directions. The 3-D beam-shaping filter was designed as the sum of two filters: a bow-tie filter assuming cylindrical breast and a 3D difference filter equivalent to the difference in projected thic...

Breast imaging technology is advancing on several fronts. In digital mammography, the major technological trend has been on optimization of approaches for performing combined mammography and tomosynthesis using the same system. In parallel, photon‐counting slot‐scan mammography is now in clinical use and more efforts are directed towards further de...

Purpose: Several commercial and non-commercial software and techniques are available for determining breast density from mammograms. However, where mandated by law the breast density information communicated to the subject/patient is based on radiologist’s interpretation of breast density from mammograms. Several studies have reported on the conco...

Breast imaging technology is advancing on several fronts. In digital mammography, the major technological trend has been on optimization of approaches for performing combined mammography and tomosynthesis using the same system. In parallel, photon-counting slot-scan mammography is now in clinical use and more efforts are directed towards further de...

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...

In this chapter certain fundamental aspects of radiologic image formation and technologies that are important for understanding the role of each imaging modality on the evaluation of suspected child abuse are described. The emphasis will be on x-ray imaging including digital radiography (DR), fluoroscopy, and computed tomography (CT), but the techn...

In this prospective pilot study, the feasibility of non-contrast dedicated breast computed tomography (bCT) to determine primary tumor volume and monitor its changes during neoadjuvant chemotherapy (NAC) treatment was investigated. Eleven women who underwent NAC were imaged with a clinical prototype dedicated bCT system at three time points - pre-,...

Monte Carlo simulations were used to investigate large-angle x-ray scatter at design energy of 25 keV during small field of view (9.6 cm × 5 cm) differential phase contrast imaging of the breast using Talbot–Lau interferometry. Homogenous, adipose and fibroglandular breasts of uniform thickness ranging from 2 to 8 cm encompassing the field of view...

A novel technique is presented for obtaining a single in-vivo image containing both functional and anatomical information in a small animal model such as a mouse. This technique, which incorporates appropriate image neutron-scatter rejection and uses a neutron opaque contrast agent, is based on neutron radiographic technology and was demonstrated t...

Mammography is the gold standard in routine screening for the detection of breast cancer in the general population. However, limitations in sensitivity, particularly in dense breasts, has motivated the development of alternative imaging techniques such as digital breast tomosynthesis, whole breast ultrasound, breast-specific gamma imaging, and more...

Systems and methods for providing radiographic, stereoscopic and tomographic images of an object of interest. Examples of objects of interest are body parts of living beings, such as the human breast and the human chest. The apparatus includes a high-fluence rate x-ray source and a plurality of satellite x-ray sources operating at lower fluence rat...

Purpose To fabricate and test nanometric organic photovoltaic (OPV) cells made of various active‐layer/electrode thicknesses and sizes; to determine the optimal material combinations and geometries suitable for dose measurements in clinical kilovoltage x‐ray beams. Methods The OPV consisted of P3HT:PCBM photoactive materials sandwiched between alu...

Purpose: To measure the volumetric breast density (VBD) from digital breast tomosynthesis (DBT) reconstructions and compare with estimates from mammography. Methods: A kernel-based fuzzy c-means algorithm developed to segment DBT reconstructed slices to provide anatomic priors for near-infrared spectroscopy (NIRS) in a multimodality NIRS/DBT clinic...

Medical Physics 2.0 is a bold vision for an existential transition of clinical imaging physics in face of the new realities of value-based and evidencebased medicine, comparative effectiveness, and meaningful use. It speaks to how clinical imaging physics can expand beyond traditional insular models of inspection and acceptance testing, oriented to...

Wireless video capsule endoscopy allows the noninvasive visualization of the small intestine. Currently, capsules do not provide localization information while traversing the GI tract. To report on the radiological validation of 3-dimensional localization software incorporated in a newly developed capsule. By using radiofrequency transmission, the...

This study retrospectively analyzed the mean glandular dose (MGD) to 133 breasts from 132 subjects, all women, who participated in a clinical trial evaluating dedicated breast CT in a diagnostic population. The clinical trial was conducted in adherence to a protocol approved by institutional review boards and the study participants provided written...

The ability to discern malignant from benign tissue in excised human breast specimens in Breast Conservation Surgery (BCS) was evaluated using single frequency terahertz radiation. Terahertz (THz) images of the specimens in reflection mode were obtained by employing a gas laser source and mechanical scanning. The images were correlated with optical...

Learning objectives: 1. Understand the principles and differences between breast tomosynthesis and breast CT, and the technical advantages and limitations of each. 2. Understand potential roles of nuclear medicine/PET in lesion detection, diagnosis, and therapy monitoring. 3. Identify at least three new MR techniques used to image/characterize bre...

Purpose: To determine the x-ray scatter content in differential phase-contrast imaging of the breast using a gratings-based interferometer. Methods: X-ray scatter during small field-of-view (9.6×5-cm) differential phase-contrast breast imaging with a gratings-based interferometer (25-keV design) was determined using GEANT4 Monte Carlo (MC) toolk...

Purpose: To investigate the radiation dose reduction and the effect of weighting schemes on image quality in cone-beam dedicated breast CT acquired with coronal truncated projections that is similar in concept as extended field-of-view imaging with laterally-shifted flat-panel detectors. Methods: Three pre-weighting schemes were implemented in c...

Writing and Reviewing Papers for Medical Physics There is an art to writing a scientific paper so that it communicates accurately, succinctly, and comprehensively. Developing this art comes with experience, and sharing that experience with younger physicists is an obligation of senior scientists, especially those with editorial responsibilities for...

An Institutional Review Board-approved protocol was used to quantify breast tissue inclusion in 52 women, under conditions simulating both craniocaudal (CC) and mediolateral oblique (MLO) views in mammography, dedicated breast CT in the upright subject position, and dedicated breast CT in the prone subject position. Using skin as a surrogate for th...

Purpose: Phase contrast imaging, particularly of the breast, is being actively investigated. The purpose of this work is to investigate the x-ray phase contrast properties of breast tissues and commonly used breast tissue substitutes or phantom materials with an aim of determining the phantom materials best representative of breast tissues. Metho...

Purpose: To determine the mean and range of location-averaged breast skin thickness using high-resolution dedicated breast CT for use in Monte Carlo-based estimation of normalized glandular dose coefficients. Methods: This study retrospectively analyzed image data from a clinical study investigating dedicated breast CT. An algorithm similar to t...

Purpose: To determine the x-ray photon energy dependence of the anatomic power spectrum of the breast when imaged with dedicated breast computed tomography (CT). Methods: A theoretical framework for scaling the empirically determined anatomic power spectrum at one x-ray photon energy to that at any given x-ray photon energy when imaged with dedi...

STUDY DESIGN: Observational. OBJECTIVE: To estimate the radiation dose imparted to patients during typical thoracolumbar spinal surgical scenarios. SUMMARY OF BACKGROUND DATA: Minimally invasive techniques continue to become more common in spine surgery. Computer-assisted navigation systems coupled with intraoperative cone-beam computed tomography...

Purpose: To determine the mean and range of volumetric glandular fraction (VGF) of the breast in a diagnostic population using a high-resolution flat-panel cone-beam dedicated breast CT system. This information is important for Monte Carlo-based estimation of normalized glandular dose coefficients and for investigating the dependence of VGF on bre...

RF localization science and technology started with the global positioning systems for outdoor areas, and it then transformed into wireless indoor geolocation. The next step in the evolution of this science is the transformation into RF localization inside the human body. The first major application for this technology is the localization of the wi...

URL's http://www.imp.uni-erlangen.de/RSNA2012/ Sub-Events

LEARNING OBJECTIVES 1) New trends in X-ray generation, X-ray target, filtration and spectra for digital mammography. 2) Appreciate the impact of X-ray spectral changes on parameters such as exposure time, contrast, and average glandular dose. 3) Review of new trends in X-ray detectors for mammography, their impact on dose reduction, and their poten...

PURPOSE: To compare stereoscopic digital mammography (DM) with standard DM for the rate of patient recall and the detection of cancer in a screening population at elevated risk for breast cancer. MATERIALS AND METHODS: Starting in September 2004 and ending in December 2007, this prospective HIPAA-compliant, institutional review board-approved scree...

This report presents the first experimental demonstration, to our knowledge, of benchtop polychromatic cone-beam x-ray fluorescence computed tomography (XFCT) for a simultaneous determination of the spatial distribution and amount of gold nanoparticles (GNPs) within small-animal-sized objects. The current benchtop experimental setup successfully pr...

Comment on: Comparison of radiologist performance with photon-counting full-field digital mammography to conventional full-field digital mammography. [Acad Radiol. 2012]

Purpose: Phase contrast breast imaging has the potential to improve visualization of anatomic structures. While the physics is well-understood, there are several choices for implementation. In order to evaluate these choices, it is essential to design a phantom for phase contrast imaging with appropriate breast-equivalent materials. Methods: Phanto...

Purpose: To test the hypothesis that the mean skin thickness determined using cone-beam dedicated breast CT varied between breasts with malignant, hyperplasia and benign pathology, and to determine the appropriate skin thickness for Monte Carlo based estimation of normalized glandular dose coefficients. Methods: Breast skin thickness was estimated...

There is an art to writing a scientific paper so that it communicates accurately, succinctly, and comprehensively. Developing this art comes with experience, and sharing that experience with younger physicists is an obligation of senior scientists, especially those with editorial responsibilities for the journal. In this workshop, the preparation o...

Purpose: To determine the spatial distribution and amount of gold nanoparticles (GNPs) within small-animal-sized objects using polychromatic cone-beam x-ray fluorescence computed tomography (XFCT) under realistic constraints on x-ray dose, scan time, and image resolution. Methods: 6-mm-diameter cylindrical tubes containing saline solution and 0.5-2...

Dedicated breast CT prototypes used in clinical investigations utilize single circular source trajectory and cone-beam geometry with flat-panel detectors that do not satisfy data-sufficiency conditions and could lead to cone beam artifacts. Hence, this work investigated the glandular dose characteristics of a circle-plus-line trajectory that fulfil...

In breast conservation surgery, surgeons attempt to remove malignant tissue along with a surrounding margin of healthy tissue. Subsequent pathological analysis determines if those margins are clear of malignant tissue, a process that typically requires at least one day. Only then can it be determined whether a follow-up surgery is necessary. This p...

LEARNING OBJECTIVES Sub-Events

LEARNING OBJECTIVES 1) New trends in X-ray generation, X-ray target, filtration and spectra for digital mammography. 2) Appreciate the impact of X-ray spectral changes on parameters such as exposure time, contrast, and average glandular dose. 3) Review of new trends in X-ray detectors for mammography, their impact on dose reduction, and their poten...

Digital breast tomosynthesis (DBT) is a limited-angle tomographic x-ray imaging technique that reduces the effect of tissue superposition observed in planar mammography. An integrated imaging platform that combines DBT with near infrared spectroscopy (NIRS) to provide co-registered anatomical and functional imaging is under development. Incorporati...

Purpose: Current approaches for ensuring adequate visualization of neuroendovascular devices that are implanted under fluoroscopic guidance, such as stents and flow diverters, are based on ad hoc methods and measures. Lack of specific standards makes it difficult to determine the adequacy of device contrast under clinical conditions. Inadequate dev...

Purpose: Cone‐beam CT with circular trajectory is susceptible to cone‐angle related artifacts that affect quantitative imaging. These artifacts were quantified under conditions relevant to dedicated breast CT for full and short‐scans. Methods: Three sets of numerical phantoms (0.2‐mm voxels) were used: (1) cylindrical Defrise phantom of 14‐cm diame...

There is an art to writing a scientific paper so that it communicates accurately, succinctly, and comprehensively. Developing this art comes with experience, and sharing that experience with younger physicists is an obligation of senior scientists, especially those with editorial responsibilities for the journal. In this workshop, the preparation o...