George S. K. Fung's research while affiliated with Johns Hopkins University and other places

Publications (78)

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Purpose: In this work, we explore the potential of region-of-interest (ROI) imaging in x-ray computed tomography (CT). Using two dynamic beam attenuator (DBA) concepts for fluence field modulation (FFM) previously developed, we investigate and evaluate the potential dose savings in comparison with current FFM technology. Methods: ROI imaging is...
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Purpose: We present a new concept for dynamic fluence field modulation (FFM) in x-ray computed tomography (CT). The so-called z-aligned sheet-based dynamic beam attenuator (z-sbDBA) is developed to dynamically compensate variations in patient attenuation across the fan beam and the projection angle. The goal is to enhance image quality and to redu...
Article
Purpose: It has been a long-standing wish in computed tomography (CT) to compensate the emitted x-ray beam intensity for the patient's changing attenuation during the rotation of a CT data acquisition. The patient attenuation changes both spatially, along the fan beam angle, and temporally, between different projections. By modifying the pre-patie...
Article
Objective: The aim of this study was to compare the effects of combined virtual monoenergetic extrapolation (VME) of dual-energy computed tomography data and iterative metal artifact reduction (iMAR) at higher photon energies on low- and high-density metal artifacts and overall image quality of the ankle arthroplasty implants with iMAR, weighted f...
Article
Optimal treatment planning for radioembolization of hepatic cancers produces sufficient dose to tumors for control and dose to normal liver parenchyma that is below the threshold for toxicity. The non-uniform distribution of particles in liver microanatomy complicates the planning process as different functional regions receive different doses. Hav...
Article
Objective Technetium-99m (99mTc)-sestamibi single-photon emission computed tomography/computed tomography (SPECT/CT) has previously been shown to allow for the accurate differentiation of benign renal oncocytomas and hybrid oncocytic/chromophobe tumors (HOCTs) apart from other malignant renal tumor histologies, with oncocytomas/HOCTs showing high u...
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The new PET tracer, ¹⁸F-flurpiridaz, with high myocardial extraction allows quantitative myocardial blood flow (MBF) estimation from dynamic PET data and tracer kinetic modeling. The goal of this study is to determine the optimal imaging protocols and parameters using a realistic simulation study. The time activity curves (TACs) of different tissue...
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The four dimensional (4D) eXtended CArdiac-Torso (XCAT) series of phantoms was developed to provide accurate computerized models of the human anatomy and physiology. The XCAT series encompasses a vast population of phantoms of varying ages from newborn to adult, each including parameterized models for the cardiac and respiratory motions. With great...
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Purpose: This work concerns computed tomography (CT)-based cardiac functional analysis (CFA) with a reduced radiation dose. As CT-CFA requires images over the entire heartbeat, the scans are often performed at 10-20% of the tube current settings that are typically used for coronary CT angiography. A large image noise then degrades the accuracy of...
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Purpose: Analytical phantoms have closed form Fourier transform expressions and are used to simulate MRI acquisitions. Existing three-dimensional (3D) analytical phantoms are unable to accurately model shapes of biomedical interest. The goal of this study was to demonstrate that polyhedral analytical phantoms have closed form Fourier transform exp...
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Newly developed spectral computed tomography (CT) such as photon counting detector CT enables more accurate tissue-type identification through material decomposition technique. Many iterative reconstruction methods, including those developed for spectral CT, however, employ a regularization term whose penalty transition is designed using pixel valu...
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Iterative reconstruction (IR) methods for x-ray CT is a promising approach to improve image quality or reduce radiation dose to patients. The goal of this work was to use task based image quality measures and the channelized Hotelling observer (CHO) to evaluate both analytic and IR methods for clinical x-ray CT applications. We performed realistic...
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The value of Tc-99m MIBI parathyroid SPECT for localizing parathyroid hyperplasia in chronic renal failure patients remains inconclusive due to limited image quality. Advanced reconstruction methods to improve image quality have been developed but require optimization and evaluation. The goal of this study was to optimize and evaluate compensation...
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This paper describes the process in which complex lesion geometries (specified by computer generated perfusion defects) are incorporated in the description of nonlinear FE mechanical models used for specifying the motion of the left ventricle (LV) in the 4D XCAT phantom to simulate gated cardiac image data. An image interrogation process was develo...
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The purpose was to determine the effect of bilateral superior laryngeal nerve (SLN) lesion on swallowing threshold volume and the occurrence of aspiration, using a novel measurement technique for videofluoroscopic swallowing studies (VFSS) in infant pigs. We used a novel radiographic phantom to assess volume of the milk containing barium from fluor...
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Digital phantoms and Monte Carlo (MC) simulations have become important tools for optimizing and evaluating instrumentation, acquisition and processing methods for myocardial perfusion SPECT (MPS). In this work, we designed a new adult digital phantom population and generated corresponding Tc-99m and Tl-201 projections for use in MPS research. The...
Conference Paper
In recent years, iterative algorithms have become popular in diagnostic CT imaging to reduce noise or radiation dose to the patient. The non-linear nature of these algorithms leads to non-linearities in the imaging chain. However, the methods to assess the performance of CT imaging systems were developed assuming the linear process of filtered back...
Conference Paper
Objectives: Partial volume effects (PVEs) caused by the limited spatial resolution reduce quantitative accuracy of cardiac PET. We have previously developed a partial volume compensation (PVC) method that uses CT defined region-of-interest (ROI) maps and a shift-invariant uniform Gaussian resolution model to improve both the image quality and the q...
Article
Purpose: To develop an easily-implemented technique with free publicly-available analysis software to measure the modulation transfer function (MTF) and noise-power spectrum (NPS) of a clinical computed tomography (CT) system from images acquired using a widely-available and standardized American College of Radiology (ACR) CT accreditation phantom...
Conference Paper
One of the major obstacles toward photon counting detector (PCD)-based clinical x-ray CT systems is the large count rates, because when operated under too intense x-rays, pulse pileup effects (PPEs) due to coincident photons distort the spectrum recorded by PCDs. In this paper we discuss a strategy using a hybrid detector, which consists of PCDs fo...
Conference Paper
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This research aims to develop a new feature guided motion estimation method for the left ventricular wall in gated cardiac imaging. The guiding feature is the “footprint” of one of the papillary muscles, which is the attachment of the papillary muscle on the endocardium. Myocardial perfusion (MP) PET images simulated from the 4-D XCAT phantom, whic...
Article
Partial Volume Effect (PVE), the image blurring caused by the finite spatial resolution of PET imaging system, can cause incorrect quantification of radioactivity especially for small objects. High-resolution small animal PET system has been developed for rodents, but sizes of rodent hearts are still close to the spatial resolution, that might caus...
Conference Paper
Accurate estimation of cardiac motion from clinical medical images especially motion components parallel to edges has been found to be difficult using the intensity based optical flow algorithm without any prior information. This research aims to develop a new feature guided cardiac motion estimation method for gated myocardial perfusion (MP) PET i...
Conference Paper
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PURPOSE Dysphagia, the inability to swallow correctly, is a significant but overlooked problem that can result in aspiration pneumonia. The gold standard for quantifying the kinematics of swallowing is x-ray fluoroscopy of barium (Ba) swallows, a 2D technique. One critical measurement is the fluid remaining in the oropharynx after a swallow, the re...
Conference Paper
PURPOSE The ultimate goal of this research is to develop a novel cardiac computed tomography (CT) imaging method to obtain the following triple cardiac information from single CT scan: vulnerable coronary plaques or CT angiography (CTA), myocardial perfusion imaging (MPI), and cardiac function/motion analysis (CFA). The purpose of this work is to d...
Conference Paper
PURPOSE To compare the detectability of vulnerable coronary plaque using photon-counting detectors with and without compensation for spectral distortions versus conventional energy integrating detectors. METHOD AND MATERIALS Simulation studies for the detectability of atherosclerotic plaque were performed using a realistic computer phantom, a phot...
Conference Paper
PURPOSE Descriptions of computed tomography (CT) resolution and noise are often limited to simple measurements using bar patterns and standard deviation, respectively. More sophisticated metrics of modulation transfer function (MTF) for resolution and noise-power spectrum (NPS) for noise exist but are rarely measured due to the complexity of measur...
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Background: Partial volume effects (PVEs) in PET imaging result in incorrect regional activity estimates due to both spill-out and spill-in from activity in neighboring regions. It is important to compensate for both effects to achieve accurate quantification. In this study, an image-based partial volume compensation (PVC) method was developed and...
Article
The aim of this in vitro study was to examine the capability of three protocols of dual-energy CT imaging in distinguishing calcium oxalate, calcium phosphate, and uric acid kidney stones. A total of 48 calcium oxalate, calcium phosphate, and uric acid human kidney stone samples were placed in individual containers inside a cylindric water phantom...
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The x-ray spectrum recorded by a photon-counting x-ray detector (PCXD) is distorted due to the following physical effects which are independent of the count rate: finite energy-resolution, Compton scattering, charge-sharing, and Kescape. If left uncompensated, the spectral response (SR) of a PCXD due to the above effects will result in image artifa...
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In clinical computed tomography (CT), images from patient examinations taken with conventional scanners exhibit noise characteristics governed by electronics noise, when scanning strongly attenuating obese patients or with an ultra-low X-ray dose. Unlike CT systems based on energy integrating detectors, a system with a quantum counting detector doe...
Conference Paper
PURPOSE To evaluate the image quality of the IRIS and SAFIRE iterative reconstruction methods using a combination of patient data and simulated liver lesions of different sizes, contrasts, and locations. METHOD AND MATERIALS Projection data of abdominal patient CT scans were downloaded from a Flash CT scanner.The same data acquisition parameters w...
Conference Paper
PURPOSE To optimize the dual-energy CT (DECT) imaging protocols of a dual-source CT (DSCT) system for maximum kidney stone differentiation at different patient sizes using a realistic CT/human-model simulation package. METHOD AND MATERIALS A newly developed XCAT/DRASIM simulation package, an integration of an anatomic realistic phantom and an inst...
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Coronary artery disease and its related cardiac disorders represent the most common cause of death in the USA and Western world. Despite advancements in treatment and accompanying improvements in outcome with current diagnostic and therapeutic modalities, it is the correct assignment of these diagnostic techniques and treatment options which are cr...
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Contrary to conventional energy integrating detectors, electronics noise in quantum counting detectors (also frequently referred to as photon counting detectors) mainly affects the spectral resolution of the detector. There is almost no impact on the counting signal itself. This promises improved image quality due to image noise reduction in scans...
Conference Paper
The goal is to generate and evaluate a simulated 4D Rb-82 PET dataset that realistically models simultaneous respiratory and cardiac motions for use to study the effects of the motions and their compensation using various gating schemes. Normal cardiac and respiratory (C&R) motions were simulated separately using the realistic 4D XCAT phantoms. The...
Conference Paper
The goal is to develop a 4D digital perfusion cardiac-torso (PCAT) phantom, a tracer kinetic extension of the XCAT phantom, by modeling the time activity curves (TACs) of individual organ regions in the phantom for dynamic perfusion PET and SPECT simulation studies. The PCAT phantom is based on a generalized compartmental model, which accepts the b...
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A detailed three-dimensional (3D) model of the coronary artery tree with cardiac motion has great potential for applications in a wide variety of medical imaging research areas. In this work, we first developed a computer-generated 3D model of the coronary arterial tree for the heart in the extended cardiac-torso (XCAT) phantom, thereby creating a...
Conference Paper
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The 4D NCAT and XCAT phantoms have been found useful in the simulation of medical image data especially SPECT, PET, CT and more recently MRI. The phantoms provide realistic models of the anatomical structures and respiratory and cardiac motions of humans. When combined with accurate models of the physics and instrumentation involved in the imaging...
Article
The aim of this research is to develop a complete CT/human-model simulation package by integrating the 4D eXtended CArdiac-Torso (XCAT) phantom, a computer generated NURBS surface based phantom that provides a realistic model of human anatomy and respiratory and cardiac motions, and the DRASIM (Siemens Healthcare) CT-data simulation program. Unlike...
Conference Paper
The current 3D XCAT phantom allows users to manually define the regional myocardial perfusion defect (MPD) as a simple pie-shaped wedge region with reduced activity level in the myocardium of left ventricle. To more accurately and realistically model the MPD, we have developed a new regional MPD model for the 3D XCAT phantom for myocardial perfusio...
Conference Paper
PURPOSE To evaluate the accuracy of CT numbers of the renal parenchyma, masses and stones on virtual noncontrast (VNC) CT created from contrast-enhanced dual-energy (DE) CT datasets with tube voltage sets at 80 kVp and 140 kVp (80/140 kVp) with a 1st generation scanner, and at 100 kVp and 140 kVp with a tin filtration (100/140 kVp with Sn) with a 2...
Conference Paper
PURPOSE To evaluate which temporal resolution index best predicts the strength of motion artifacts in cardiac CT images. METHOD AND MATERIALS Three candidate indices were evaluated: full-width-at-half-maximum (FWHM), full-width-at-tenth-maximum (FWTM), and full-width-at-base (FWB) of the temporal gating window. A digital chest phantom with 60 hear...
Article
A realistic 3D coronary arterial tree (CAT) has been developed for the heart model of the computer generated 3D XCAT phantom. The CAT allows generation of a realistic model of the location, size and shape of the associated regional ischemia or infarction for a given coronary arterial stenosis or occlusion. This in turn can be used in medical imagin...
Article
Color constancy is one of the most amazing features of the human visual system. When we look at objects under different illuminations, their colors stay relatively constant. This helps humans to identify objects conveniently. While the precise physiological mechanism is not fully known, it has been postulated that the eyes are responsible for captu...
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Significant stent graft remodeling commonly occurs after endovascular repair of thoracic aortic dissections because of continuing expansion of the true lumen. A suboptimal proximal landing zone, minimal oversizing, and lack of a healthy distal attachment site are unique factors affecting long-term stent graft stability. We used computational fluid...
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Endovascular aortic stent-graft is a new, minimally invasive procedure for treating thoracic aortic diseases, and has quickly evolved to be one of the standard treatments subject to anatomic constraints. This procedure involves the placement of a self-expanding stent-graft system in a high-flow thoracic aorta. Stent-graft deployment in the thoracic...
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In treating thoracic aortic diseases, endovascular repair involves the placement of a self-expanding stent-graft system across the diseased thoracic aorta. Computational fluid dynamic techniques are applied to model the blood flow by numerically solving the three-dimensional continuity equation and the time-dependent Navier-Stokes equations for an...
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The direct Fourier transform method is a straightforward solution with high accuracy for reconstructing magnetic resonance (MR) images from nonuniformly sampled k-space data, given that the optimal density compensation function is selected and the underlying magnetic field is sufficiently uniform. The computation however is very time-consuming, mak...
Article
A load signature is an electrical expression that a load device or appliance distinctly possesses. Load signatures can be applied to produce many useful services and products, such as, determining the energy usage of individual appliances, monitoring the health of critical equipment, monitoring power quality, and developing facility management tool...
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Multi-slice Computed Tomography (MSCT) is an important medical imaging tool that provides dynamic three-dimensional (3D) volume data of the heart for diagnosis of various cardiac diseases. Due to the huge amount of data in MSCT, manual identification, segmentation and tracking of various parts of the heart are very labor intensive and inefficient....
Article
Endovascular aortic stent-graft is a new, minimally invasive procedure for treating thoracic aortic diseases, and has quickly evolved to be one of the standard treatments subject to anatomic constraints. Stent-graft deployment in the thoracic aorta, especially close to the aortic arch, normally experiences a significant drag force which might lead...
Conference Paper
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Recently, the authors introduced least square quantization table (LSQT) method to accelerate the direct Fourier transform to reconstruct magnetic resonance images acquired using a spiral trajectory. In this paper, we will discuss the LSQT further in its adaptability, reusability and choice of the number of groups. The experimental results show tha...
Conference Paper
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The least squares quantization table (LSQT) method is proposed to accelerate the direct Fourier transform for reconstructing images from nonuniformly sampled data, similar to the look-up table (LUT) and equal-phase-line (EPL) methods published recently. First, it classifies all the image pixels into several groups using the Lloyd-Max quantization s...
Conference Paper
With the recent advancement of C-arm angiographic techniques in acquiring the 3D rotational angiography, the system has the ability to reconstruct the CT-like transaxial slices of the scan volume, but at lower image quality compared to those reconstructed from standard CT system. For liver imaging, the scan time can range from 5 to 10 seconds to co...
Conference Paper
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Multi-slice CT (MSCT) provides dy- namic three-dimensional (3D) volumetric data of the whole heart, and is an important medical imaging tool for diagnosis of cardiac diseases. Due to the large size of the dynamic data, manual identification, segmentation and track- ing of various parts of the heart will be very labor intensive and inefficient. Alte...
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Coronary artery imaging with multi-slice helical computed tomography is a promising noninvasive imaging technique. The current major issues include the insufficient temporal resolution and large patient dose. We propose an image reconstruction method which provides a solution to both of the problems. The method uses an iterative approach repeating...
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A detailed four-dimensional model of the coronary artery tree has great potential in a wide variety of applications especially in biomedical imaging. We developed a computer generated three-dimensional model for the coronary arterial tree based on two datasets: (1) gated multi-slice computed tomography (MSCT) angiographic data obtained from a norma...
Article
Recent research in transform-based image denoising has focused on the wavelet transform due to its superior performance over other transform. Performance is often measured solely in terms of PSNR and denoising algorithms are optimized for this quantitative metric. The performance in terms of subjective quality is typically not evaluated. Moreover,...
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Three-dimensional computer vision techniques have been ac- tively studied for the purpose of visual traffic surveillance. To determine the 3-D environment, camera calibration is a crucial step to resolve the relationship between the 3-D world coordinates and their corresponding image coordinates. A novel camera calibration using the geometry prop-...
Article
A novel approach to compute the discrete Hartley transform (DHT) is proposed. By using a modular mapping, DHT is approximated by the sum of a finite sequence of discrete moments. This enables the computational techniques developed for computing moments to be employed in computing DHT efficiently. We demonstrate this by applying our earlier systolic...
Article
For an accurate scene analysis using monocular color traffic image sequences, a robust segmentation of moving vehicles from the stationary background is generally required. However, the presence of moving cast shadow may lead to an inaccurate vehicle segmentation, and as a result, may lead to further erroneous scene analysis. We pro- pose an effect...
Conference Paper
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For an accurate scene analysis in monocular image sequences, a robust segmentation of a moving object from the static background is generally required. However, the existence of moving cast shadow may lead to an inaccurate object segmentation, and as a result, lead to further erroneous scene analysis. An effective detection of moving cast shadow in...
Conference Paper
This paper presents a visual-based dimension estimation method for vehicle type classification. Our method extracts moving vehicles from traffic image sequences and fits them with a simple deformable vehicle model. Using a set of coordination mapping functions derived from a calibrated camera model and relying on a shadow removal method, vehicle's...
Conference Paper
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In this paper, a vehicle shape approximation method based on the vehicle motion in a typical traffic image sequence is proposed. In the proposed method, instead of using the 2D image data directly, the intrinsic 3D data is estimated in a monocular image sequence. Given the binary vehicle mask and the camera parameters, the vehicle shape is estimate...
Conference Paper
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In this paper, an effective method for the detection of moving cast shadow for visual traffic surveillance is proposed. Based on the cast shadow observations in luminance, chrominance, gradient density and geometry domains, a combined probability map, called the shadow confidence score, of the region belonging to the shadow is deduced. The object r...