Frank Wübbeling

List Mode–Driven Cardiac and Respiratory Gating in PET

Gating methods acquiring biosignals (such as electrocardiography [ECG] and respiration) during PET enable one to reduce motion effects that potentially lead to image blurring and artifacts. This study evaluated different cardiac and respiratory gating methods: one based on ECG signals for cardiac gating and video signals for respiratory gating; 2 others based on measured inherent list mode events. Methods: Twenty-nine patients with coronary artery disease underwent a 20-min ECG-gated single-bed list mode PET scan of the heart. Of these, 17 were monitored by a video camera registering a marker on the patients abdomen, thus capturing the respiratory motion for PET gating (video method). Additionally, respiratory and cardiac gating information was deduced without auxiliary measurements by dividing the list mode stream in 50-ms frames and then either determining the number of coincidences (sensitivity method) or computing the axial center of mass and SD of the measured counting rates in the same frames (center-of-mass method). The gated datasets (respiratory and cardiac gating) were reconstructed without attenuation correction. Measured wall thicknesses, maximum displacement of the left ventricular wall, and ejection fraction served as measures of the exactness of gating. Results: All methods successfully captured respiratory motion and significantly decreased motion-induced blurring in the gated images. The center-of-mass method resulted in significantly larger left ventricular wall displacements than did the sensitivity method (P < 0.02); other differences were nonsignificant. List mode–based cardiac gating was found to work well for patients with high 18F-FDG uptake when the center-of-mass method was used, leading to an ejection fraction correlation coefficient of r = 0.95 as compared with ECG-based gating. However, the sensitivity method did not always result in valid cardiac gating information, even in patients with high 18F-FDG uptake. Conclusion: Our study demonstrated that valid gating signals during PET scans cannot be obtained only by tracking the external motion or applying an ECG but also by simply analyzing the PET list mode stream on a frame-by-frame basis.

Oxidative DNA damage in human sperm can be detected by Raman microspectroscopy

OBJECTIVE To determine whether Raman microspectroscopy can identify different levels of oxidative sperm nDNA damage and to corroborate the findings using an established method and an alternative but complementary spectroscopic technique. DESIGN Three-way comparison of Raman profiles, Fourier transform infrared spectroscopy (FTIR) spectra, and flow-cytometric assessments of sperm nDNA damage. SETTING University-based research laboratory. PATIENT(S) Thirty-eight men attending the infertility clinic at the Centre of Reproductive Medicine and Andrology. INTERVENTION(S) Induction of oxidative damage by Fentons reaction on semen samples. MAIN OUTCOME MEASURE(S) Raman profiles, FTIR spectra, and flow-cytometric analysis of DNA fragmentation. RESULT(S) Raman and FTIR spectra contained distinctive differences between untreated and fragmented nDNA sperm that were indicative of oxidative attack. The changes in Raman profiles were similar to those previously seen and corresponded to the DNA backbone. The peak attributions were corroborated by the FTIR spectra. Principal component analysis of the entire Raman spectra distinguished samples with varying degrees of damage. After determination of a cutoff value (0.63), estimation of the percentage of sperm with nDNA damage using the intensity ratio of Raman peaks (1,050/1,095 cm(-1)) correlated linearly to the flow-cytometric assessment. CONCLUSION(S) Raman microspectroscopy still requires further validation but may potentially provide a means of assessing the nDNA status of a living sperm.

Accurate EM-TV algorithm in PET with low SNR

PET measurements of tracers with a lower dose rate or short radioactive half life suffer from extremely low SNRs. In these cases standard reconstruction methods (OSEM, EM, filtered backprojection) deliver unsatisfactory and noisy results. Here, we propose to introduce nonlinear variational methods into the reconstruction process to make an efficient use of a-priori information and to attain improved imaging results. We illustrate our technique by evaluating cardiac H215O measurements. The general approach can also be used for other specific goals allowing to incorporate a-priori information about the solution with Poisson distributed data.

EMRECON: An expectation maximization based image reconstruction framework for emission tomography data

We present a flexible image reconstruction framework for emission tomography data called EMRECON. The software includes multiple expectation maximization based reconstruction algorithms as well as support for several scanner geometries. In order to implement novel reconstruction techniques (e.g. TV-based regularization or combined reconstruction and motion correction) or scanner models, full access to every stage of the reconstruction pipeline is vital. EMrecon is fully open and well-documented, thus permits testing without the need to care about data formats or standard reconstruction and data correction algorithms. Due to the GATE-like syntax new scanner geometries, including an exact definition of each single crystal, can be added easily. The parallel (multi-core) C implementation was successfully tested on several Linux distributions. This makes EMRECON a useful tool for the development of new reconstruction algorithms and also serves as a platform for testing different scanner geometries.

EM-TV Methods for Inverse Problems with Poisson Noise

We address the task of reconstructing images corrupted by Poisson noise, which is important in various applications such as fluorescence microscopy (Dey et al., 3D microscopy deconvolution using Richardson-Lucy algorithm with total variation regularization, 2004), positron emission tomography (PET; Vardi et al., J Am Stat Assoc 80:8–20, 1985), or astronomical imaging (Lanteri and Theys, EURASIP J Appl Signal Processing 15:2500–2513, 2005). Here we focus on reconstruction strategies combining the expectation-maximization (EM) algorithm and total variation (TV) based regularization, and present a detailed analysis as well as numerical results. Recently extensions of the well known EM/Richardson-Lucy algorithm received increasing attention for inverse problems with Poisson data (Dey et al., 3D microscopy deconvolution using Richardson-Lucy algorithm with total variation regularization, 2004; Jonsson et al., Total variation regularization in positron emission tomography, 1998; Panin et al., IEEE Trans Nucl Sci 46(6):2202–2210, 1999). However, most of these algorithms for regularizations like TV lead to convergence problems for large regularization parameters, cannot guarantee positivity, and rely on additional approximations (like smoothed TV). The goal of this lecture is to provide accurate, robust and fast EM-TV based methods for computing cartoon reconstructions facilitating post-segmentation and providing a basis for quantification techniques. We illustrate also the performance of the proposed algorithms and confirm the analytical concepts by 2D and 3D synthetic and real-world results in optical nanoscopy and PET.

Marching schemes for inverse acoustic scattering problems

SummaryFor the numerical solution of inverse Helmholtz problems the boundary value problem for a Helmholtz equation with spatially variable wave number has to be solved repeatedly. For large wave numbers this is a challenge. In the paper we reformulate the inverse problem as an initial value problem, and describe a marching scheme for the numerical computation that needs only n2 log n operations on an n × n grid. We derive stability and error estimates for the marching scheme. We show that the marching solution is close to the low-pass filtered true solution. We present numerical examples that demonstrate the efficacy of the marching scheme.

Structural and Functional Integrity of Spermatozoa Is Compromised as a Consequence of Acute Uropathogenic E. coli-Associated Epididymitis

ABSTRACT Uropathogenic Escherichia coli (UPEC)-associated epididymitis is commonly diagnosed in outpatient settings. Although the infection can be successfully cleared using antimicrobial medications, 40% of patients unexplainably show persistent impaired semen parameters even after treatment. Our aim was to investigate whether pathogenic UPEC and its associated virulence factor hemolysin (hlyA) perturb the structural and functional integrity of both the epididymis and sperm, actions that may be responsible for the observed impairment and possibly a reduction of fertilization capabilities. Semen collected from patients diagnosed with E. coli-only related epididymitis showed that sperm counts were low 14 days postantimicrobial treatment regardless of hlyA status. At Day 84 following treatment, hlyA production correlated with approximately 4-fold lower sperm concentrations than in men with hlyA-negative strains. In vivo experiments with the hlyA-producing UPEC CFT073 strain in a murine epididymitis model showed that just 3 days postinfection, structural damage to the epididymis (epithelial damage, leukocyte infiltration, and edema formation) was present. This was more severe in UPEC CFT073 compared to nonpathogenic E. coli (NPEC 470) infection. Moreover, pathogenic UPEC strains prematurely activated the acrosome in vivo and in vitro. Raman microspectroscopy revealed that UPEC CFT073 undermined sperm integrity by inducing nuclear DNA damage. Consistent with these observations, the in vitro fertilization capability of hlyA-treated mouse sperm was completely abolished, although sperm were motile. These findings provide new insights into understanding the possible processes underlying clinical manifestations of acute epididymitis.

Motion Correction in Respiratory Gated Cardiac PET/CT Using Multi-scale Optical Flow

Respiratory motion is a source of degradation in positron emission tomography. As the patients cannot hold breath during the PET acquisition, spatial blurring and motion artifacts are unavoidable which may lead to wrong quantification of the data. A solution based on respiratory-gating and optical flow based correction of the PET data is proposed. This includes deformation of the CT data for accurate attenuation and listmode based reconstruction. All methods are applied to real patient data and are evaluated with respect to three criteria.

Parallel medical image reconstruction: from graphics processing units (GPU) to Grids

We present and compare a variety of parallelization approaches for a real-world case study on modern parallel and distributed computer architectures. Our case study is a production-quality, time-intensive algorithm for medical image reconstruction used in computer tomography (PET). We parallelize this algorithm for the main kinds of contemporary parallel architectures: shared-memory multiprocessors, distributed-memory clusters, graphics processing units (GPU) using the CUDA framework, the Cell processor and, finally, how various architectures can be accessed in a distributed Grid environment. The main contribution of the paper, besides the parallelization approaches, is their systematic comparison regarding four important criteria: performance, programming comfort, accessibility, and cost-effectiveness. We report results of experiments on particular parallel machines of different architectures that confirm the findings of our systematic comparison.

A nonlinear variational method for improved quantification of myocardial blood flow using dynamic H 2 15 O PET

H215O as a PET-tracer offers the opportunity to examine perfusion of blood into tissue non-invasively (cf. [1]). It features a short radioactive half-life (≈ 2 min.) and therefore adds a smaller radiation exposure to the patient in comparison to other tracers. The disadvantages arising from the short radioactive half-life are noisy, low-resolution reconstructions. Previous algorithms first reconstruct images from each dynamic H215O dataset independently, e.g. via the standard EM-algorithm (cf. [2]) or FBP. Hence, temporal correlation is neglected. The myocardial blood flow (MBF) and other important parameters, like tissue fraction, arterial and venous spillover effects are computed subsequently from these reconstructed images. Our new method interprets the direct computation of parameters as a nonlinear inverse problem. This implies the need for inversion of a nonlinear operator G(p) (with p denoting the parameters to compute), but allows to skip the process of generating noisy images. The process is schematically described in Figure 1. Therefore, our method takes into account the temporal correlation between the datasets, and not the correlation between noisy, low resolution images. The problem is transferred to a nonlinear parameter identification problem. Furthermore, regularization can be added to each parameter independently, assuring meaningful results.