Cardiogenic and septic shock associated with aortic and mitral valve infective endocarditis caused by Abiotrophia Defectiva from a urinary tract infection.

Abiotrophia defectiva, also known as nutritionally variant streptococcus, is part of the normal flora of the oral cavity and urogenital and intestinal tracts and is a rare cause of infective endocarditis. It is fastidious or difficult to culture and associated with high rates of septic embolization, treatment failure and mortality. We describe an unusual presentation of infective endocarditis with severe mitral valve regurgitation due to Abiotrophia defectiva in an immunocompetent patient. After a complicated hospital course, surgical replacement of both the mitral and aortic valves was performed. We suggest that this patient likely had subacute infective endocarditis before diagnosis and treatment of her urinary tract infection, and following treatment failure, she developed life-threatening infective endocarditis. This case report highlights that patients with Abiotrophia defectiva infections are at high risk for infective endocarditis and that the clinical progression from this infection can be slow, with difficulty isolating the pathogen, which can significantly impact patient outcome.

Maximum-Likelihood Estimation of Scintillation Pulse Timing.

Including time-of-flight information in positron emission tomography (PET) reconstruction increases the signal-to-noise ratio if the timing information is sufficiently accurate. We estimate timing information by analyzing sampled waveforms, where the sampling frequency and number of samples acquired affect the accuracy of timing estimation. An efficient data-acquisition system acquires the minimum number of samples that contains the most timing information for a desired resolution. We describe a maximum-likelihood (ML) estimation algorithm to assign a time stamp to digital pulses. The method is based on a contracting-grid search algorithm that can be implemented in a field-programmable gate array and in graphics processing units. The Fisher-information (FI) matrix quantifies the amount of timing information that can be extracted from the waveforms. FI analyses on different segments of the waveform allow us to determine the smallest amount of data that we need to acquire in order to obtain a desired timing resolution. We describe the model and the procedure used to simulate waveforms for ML estimation and FI analysis, the ML-estimation algorithm and the timing resolution obtained from experimental data using a LaBr3:Ce crystal and two photomultiplier tubes. The results show that for lengthening segments of the pulse, timing resolution approaches a limit. We explored the method as a function of sampling frequency and compared the results to other digital time pickoff methods. This information will be used to build an efficient data-acquisition system with reduced complexity and cost that nonetheless preserves full timing performance.

Takotsubo cardiomyopathy complicating thoracoabdominal aortic aneurysm repair.

We describe the management of a patient with symptomatic spinal cord hypoperfusion after thoracoabdominal aortic aneurysm repair, where the neurological insult and associated emotional stress precipitated Takotsubo cardiomyopathy. Transthoracic Echocardiography showed akinetic mid and apical left ventricular segments, while basal segments were spared. Emergent coronary angiography ruled out acute coronary syndrome. Excess catecholamines have been postulated as a contributing mechanism to the disease, therefore, catecholamines were avoided to prevent further myocardial injury. Takotsubo cardiomyopathy is associated with serious morbidity and mortality, which highlights the importance of early recognition and proper management for complete recovery of both cardiac and neurologic functions.

Estimation of Fano factor in inorganic scintillators.

The Fano factor of an integer-valued random variable is defined as the ratio of its variance to its mean. Correlation between the outputs of two photomultiplier tubes on opposite faces of a scintillation crystal was used to estimate the Fano factor of photoelectrons and scintillation photons. Correlations between the integrals of the detector outputs were used to estimate the photoelectron and photon Fano factor for YAP:Ce, SrI2:Eu and CsI:Na scintillator crystals. At 662 keV, SrI2:Eu was found to be sub-Poisson, while CsI:Na and YAP:Ce were found to be super-Poisson. An experiment setup inspired from the Hanbury Brown and Twiss experiment was used to measure the correlations as a function of time between the outputs of two photomultiplier tubes looking at the same scintillation event. A model of the scintillation and the detection processes was used to generate simulated detector outputs as a function of time for different values of Fano factor. The simulated outputs from the model for different Fano factors was compared to the experimentally measured detector outputs to estimate the Fano factor of the scintillation photons for YAP:Ce, LaBr3:Ce scintillator crystals. At 662 keV, LaBr3:Ce was found to be sub-Poisson, while YAP:Ce was found to be close to Poisson.

Impact of the Fano Factor on Position and Energy Estimation in Scintillation Detectors.

The Fano factor for an integer-valued random variable is defined as the ratio of its variance to its mean. Light from various scintillation crystals have been reported to have Fano factors from sub-Poisson (Fano factor < 1) to super-Poisson (Fano factor > 1). For a given mean, a smaller Fano factor implies a smaller variance and thus less noise. We investigated if lower noise in the scintillation light will result in better spatial and energy resolutions. The impact of Fano factor on the estimation of position of interaction and energy deposited in simple gamma-camera geometries is estimated by two methods - calculating the Cramér-Rao bound and estimating the variance of a maximum likelihood estimator. The methods are consistent with each other and indicate that when estimating the position of interaction and energy deposited by a gamma-ray photon, the Fano factor of a scintillator does not affect the spatial resolution. A smaller Fano factor results in a better energy resolution.

Photoelectron anticorrelations and sub-Poisson statistics in scintillation detectors.

The performance of scintillation detectors for x rays and gamma rays is limited fundamentally by the statistics of the scintillation light and the resulting photoelectrons. This paper presents a new experimental approach to studying these statistics by observing correlations in the signals from two photodetectors. It is shown that the Fano factors (ratios of variance to mean), both for the number the photoelectrons produced on the photocathode of the photomultiplier and for the underlying number of scintillation photons, can be deduced from these correlations. For LaBr(3)(Ce) and 662 keV gamma rays, the photopeak signals obtained by photomultipliers on opposite faces of a thin sample are negatively correlated, and the Fano factor for the photoelectrons is significantly less than one. The inferred Fano factor for the optical photons is very small, indistinguishable from zero within experimental error.