An SVD Investigation of Modeling Scatter in Multiple Energy Windows for Improved SPECT Images.

In this work singular value decomposition (SVD) techniques are used to investigate how the use of low energy photons and multiple energy windows affects the noise properties of Tc-99m SPECT imaging. We have previously shown that, when modeling scatter in the projector and backprojector of iterative reconstruction algorithms, simultaneous reconstruction from multiple energy window data can result in very different noise characteristics. Further, the properties depend upon the width and number of energy windows used.

The AAPM/RSNA physics tutorial for residents. Physics of SPECT.

Single-photon emission computed tomography (SPECT) provides three-dimensional (3D) image information about the distribution of a radiopharmaceutical injected into the patient for diagnostic purposes. By combining conventional scintigraphic and computed tomographic methods, SPECT images present 3D functional information about the patient in more detail and higher contrast than found in planar scintigrams. A typical SPECT system consists of one or more scintillation cameras that acquire multiple two-dimensional planar projection images around the patient.

Attenuation compensation for cardiac single-photon emission computed tomographic imaging: Part 2. Attenuation compensation algorithms.

Attenuation is believed to be one of the major causes of false-positive cardiac single-photon emission computed tomographic perfusion images. This article provides an introduction to the approaches used to correct for nonuniform attenuation once a patient-specific attenuation map is available. Comparison is made of specific attenuation-correction algorithms from each of three major categories of compensation methods that are or will be available commercially.

A Monte Carlo investigation of artifacts caused by liver uptake in single-photon emission computed tomography perfusion imaging with technetium 99m-labeled agents.

Background: Significant hepatobiliary accumulation of technetium 99m-labeled cardiac perfusion agents has been shown to cause alterations in the apparent localization of the agents in the cardiac walls. A Monte Carlo study was conducted to investigate the hypothesis that the cardiac count changes are due to the inconsistencies in the projection data input to reconstruction, and that correction of the causes of these inconsistencies before reconstruction, or including knowledge of the physics underlying them in the reconstruction algorithm, would virtually eliminate these artifacts.

Methods And Results: The SIMIND Monte Carlo package was used to simulate 64 x 64 pixel projection images at 128 angles of the three-dimensional mathematical cardiac-torso (MCAT) phantom.

Attenuation compensation for cardiac single-photon emission computed tomographic imaging: Part 1. Impact of attenuation and methods of estimating attenuation maps.

Attenuation is believed to be one of the major causes of false-positive cardiac single-photon emission computed tomographic (SPECT) perfusion images. This article reviews the physics of attenuation, the artifacts produced by attenuation, and the need for scatter correction in combination with attenuation correction. The review continues with a comparison of the various configurations for transmission imaging that could be used to estimate patient specific attenuation maps, and an overview of how these are being developed for use on multiheaded SPECT systems, including discussions of truncation, noise, and spatial resolution of the estimated attenuation maps.

Quantitative SPECT imaging: a review and recommendations by the Focus Committee of the Society of Nuclear Medicine Computer and Instrumentation Council.

This article is a review of the physics principles, instrumentation and reconstruction methods behind SPECT imaging. Particular attention is paid to the mechanisms that can significantly affect the accuracy of a SPECT image. We describe instrumentation advances and reconstruction methods used to correct images to improve image quality and produce quantitative images.

A fast and stable maximum a posteriori conjugate gradient reconstruction algorithm.

We have derived a maximum a posteriori (MAP) approach for iterative reconstruction based on a weighted least-squares conjugate gradient (WLS-CG) algorithm. The WLS-CG algorithm has been shown to have initial convergence rates up to 10x faster than the maximum-likelihood expectation maximization (ML-EM) algorithm, but WLS-CG suffers from rapidly increasing image noise at higher iteration numbers. In our MAP-CG algorithm, the increasing noise is controlled by a Gibbs smoothing prior, resulting in stable, convergent solutions.

Assessment of arylamine N-acetyltransferase (NAT1) activity in mononuclear leukocytes of cystic fibrosis patients.

The clearance of sulphamethoxazole (SMX), a compound metabolised primarily by the N-acetyltransferase NAT1, is increased in cystic fibrosis (CF) patients. We assessed the activity and kinetic properties of NAT1 in lysates of peripheral blood mononuclear leukocytes (MNL) from CF (n = 17) and control (n = 22) subjects using SMX and p-aminobenzoic acid (PABA) as test substrates. The Km and Vmax values of both substrates in MNL from CF patients and control subjects were not significantly different.

Pharmacokinetics and metabolism of diltiazem in rats following a single intra-arterial or single oral dose.

Diltiazem (DTZ) 20 mg/kg was given to male Sprague-Dawley rats either orally (p.o.) or intra-arterially (i.

A filtering technique to compensate for detector response in converging-beam SPECT reconstruction.

In this study a non-stationary filtering technique was developed to compensate for spatially variant detector response in fan- and cone-beam SPECT. First the frequency-distance relation for fan- and cone-beam geometries was derived from their parallel-beam counterpart, and then used to compute the Fourier transform of the detector response that was used as the MTF of a Metz filter. The filter was applied to the blurred data before reconstruction.

Improving the convergence of iterative filtered backprojection algorithms.

Several authors have proposed variations of the iterative filtered backprojection (IFBP) reconstruction algorithms claiming fast initial convergence rates. We have found that these algorithms are trying to minimize an unusual squared-error criterion in a suboptimal way. As a result, existing IFBP algorithms are inefficient in the minimization of the criterion, and may become unstable at higher iteration numbers.

Acetylator phenotyping: the urinary caffeine metabolite ratio in slow acetylators correlates with a marker of systemic NAT1 activity.

Eighteen healthy Caucasians were evaluated for the systemic acetylation of a caffeine metabolite using the urinary caffeine metabolite ratio 5-acetylamino-6-formylamino-3-methyluracil (AFMU) to 1-methylaxanthine (1X) and for N-acetyltransferase activity in peripheral blood mononuclear leukocytes (MNL) using p-aminobenzoic acid (PABA). These are markers for systemic NAT2 and NAT1 N-acetyltransferase activities, respectively. Fourteen slow acetylators and four fast acetylators (the NAT2 polymorphism) were identified by the caffeine metabolite ratio.

Noise properties of the EM algorithm: II. Monte Carlo simulations.

In an earlier paper we derived a theoretical formulation for estimating the statistical properties of images reconstructed using the iterative ML-EM algorithm. To gain insight into this complex problem, two levels of approximation were considered in the theory. These techniques revealed the dependence of the variance and covariance of the reconstructed image noise on the source distribution, imaging system transfer function, and iteration number.

Noise properties of the EM algorithm: I. Theory.

The expectation-maximization (EM) algorithm is an important tool for maximum-likelihood (ML) estimation and image reconstruction, especially in medical imaging. It is a non-linear iterative algorithm that attempts to find the ML estimate of the object that produced a data set. The convergence of the algorithm and other deterministic properties are well established, but relatively little is known about how noise in the data influences noise in the final reconstructed image.

Optimal imaging techniques for locating leaflets after escape from prosthetic heart valves.

The authors report two cases of leaflets escaping from an Edwards-Duromedics bileaflet prosthetic heart valve (Baxter-Edwards Division, Baxter Healthcare Corp., Irvine, Calif.).

The importance and implementation of accurate 3D compensation methods for quantitative SPECT.

The purpose of this study was to investigate the importance of 2D versus 3D compensation methods in SPECT. The compensation methods included in the study addressed two important degrading factors, namely attenuating and collimator-detector response in SPET. They can be divided into two general categories.

An analytical reconstruction algorithm for multifocal converging-beam SPECT.

Multifocal converging-beam collimation has been suggested for cardiac SPECT imaging to increase sensitivity over the heart without truncation of the activity distribution in the chest. In this study, an analytical reconstruction algorithm is derived for multifocal fan-beam and multifocal cone-beam tomography. In the algorithm, the projection data are differently weighted and filtered, depending on the distance from the detector.

Quantitative single-photon emission computed tomography: basics and clinical considerations.

Although quantitative single-photon emission computed tomography (SPECT) has been the goal of much research effort for a number of years, only recently has it received wide interest, especially for clinical applications. It has been increasingly recognized that the achievement of quantitative SPECT will increase the accuracy of measurements, such as dimensions of specific regions of interest, absolute amount of radioactivity, and dosimetry calculations, and substantially reduce reconstruction image artifacts and distortions, thus, greatly improving clinical diagnosis. This article provides a review of the definition of terms, major factors affecting SPECT quantitation and their degrading effects on SPECT image quality, and methods to compensate for these effects.

Evaluation of cardiac cone-beam single photon emission computed tomography using observer performance experiments and receiver operating characteristic analysis.

Rationale And Objectives: Single photon emission computed tomography (SPECT) with a cone-beam collimator improves the trade-off between detection efficiency and spatial resolution for cardiac imaging. However, acquisitions using orbits where the focus remains in a plane do not provide sufficient data for exact reconstruction. In the current study the authors evaluate the clinical utility of planar-orbit cone-beam SPECT in detecting a simple myocardial defect.

A generalized Gibbs prior for maximum a posteriori reconstruction in SPECT.

In this paper, we introduce a Gibbs prior for use in MAP (maximum a posteriori) reconstruction in SPECT. This new prior, with three parameters, is able to approximate the results of previously-proposed priors with two parameters, as well as a continuum of others. Also, it allows the user increased flexibility in selecting the properties to be emphasized in the final reconstructed image estimate.

Direct cone beam SPECT reconstruction with camera tilt.

A filtered backprojection (FBP) algorithm is derived to perform cone beam (CB) single-photon emission computed tomography (SPECT) reconstruction with camera tilt using circular orbits. This algorithm reconstructs the tilted angle CB projection data directly by incorporating the tilt angle into it. When the tilt angle becomes zero, this algorithm reduces to that of Feldkamp.

Simultaneous acquisition of emission and transmission data for improved thallium-201 cardiac SPECT imaging using a technetium-99m transmission source.

Transmission computed tomography (TCT) data provides useful complementary information to single-photon emission computed tomography (SPECT) reconstructions, especially for cardiac studies. In particular, TCT data has been used to correct for nonuniform attenuation in the chest. Typically the transmission data are acquired in a separate acquisition, but simultaneous acquisition is preferable both to save time and to avoid difficulties involved with registration.

Performance characteristics of transmission imaging using a uniform sheet source with parallel-hole collimation.

Transmission imaging is receiving increasing attention in SPECT due to the need to compensate for nonuniform attenuation in cardiac-chest SPECT. The quality of a transmission image has an important effect on the measured attenuation distribution. To improve image quality, knowledge of the performance characteristics of a transmission imaging system is essential.

An evaluation of maximum likelihood-expectation maximization reconstruction for SPECT by ROC analysis.

A ROC study was performed in order to evaluate whether the maximum likelihood expectation maximization (ML-EM) reconstruction algorithm improves diagnostic performance compared to the conventional filtered backprojection method in SPECT. Several implementations of the algorithm were tested including 25 and 50 iteration stopping points, with and without nonuniform attenuation compensation, and with and without Metz filtering. Filtered backprojection was with Metz filter and without attenuation compensation.