We present a detailed evaluation of the total semileptonic B meson width in terms of |V cb | and heavy quark parameters (quark masses and the expectation values of local heavy quark operators). Special attention is given to perturbative corrections which can precisely be calculated in a scheme with a hard Wilsonian cutoff at a scale around 1 GeV appropriate for the OPE, and to the potential impact of higher-order power corrections. We point out that the latter require control over possible contributions from four-quark operators containing charm quark fields. Analytical expressions are given which allow evaluating the width with various choices of parameters; ready-to-use expressions showing the dependence on the heavy quark parameters are presented as well. We illustrate these results by commenting on how these parameters can be extracted and what accuracy is likely to be achievable in the near future.

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CT pulmonary angiography (CTPA) is currently considered the imaging standard of care for the diagnosis of pulmonary embolism (PE). Recent advances in contrast-enhanced pulmonary MR angiography (MRA) techniques have led to increased use of this modality for the detection of PE in the proper clinical setting. This review is intended to provide an introduction to the state-of-the-art techniques used in pulmonary MRA for the detection of PE and to discuss possible future directions for this modality. This review discusses the following issues pertinent to MRA for the diagnosis of PE: (1) the diagnostic efficacy and clinical effectiveness for pulmonary MRA relative to CTPA, (2) the different pulmonary MRA techniques used for the detection of PE, (3) guidance for building a clinical service at their institution using MRA and (4) future directions of PE MRA. Our principal aim was to show how pulmonary MRA can be used as a safe, effective modality for the diagnosis of clinically significant PE, particularly for those patients where there are concerns about ionizing radiation or contraindications/allergies to the iodinated contrast material.

Pulmonary embolism (PE) is a leading cause of acute cardiovascular death throughout the world. Although computed tomography angiography (CTA) is the primary imaging study used to diagnose acute PE, pulmonary magnetic resonance angiography (MRA) is increasingly being used in patients with contraindications for CTA. This manuscript reviews the MRA techniques used for the diagnosis of PE and discuss how these techniques can be implemented in routine clinical practice. In addition, the efficacy and effectiveness of these techniques will be compared to other modalities.

Purpose:To develop an alternating focused ultrasound system ͑AFUS͒ for preclinical studies of thermal and acoustic responses of tumors in small animal models. This work was motivated by the need of noninvasively creating relatively small spheroidal thermal lesions in small targets ͑e.g., a murine tumor͒ without damaging the surrounding tissues. Methods: The AFUS consists of two lead zirconate titanate ͑PZT-4͒ spherically curved ultrasound transducers with focal zones crossing each other at a 90°angle. The transducers were independently powered following a programed alternating firing scheme. Before the device design and construction, an acoustic and biothermal model was developed to simulate the ultrasound pressure field and the resulting temperature and thermal dose distributions. A shape factor, sphericity, to quantify the roundness of the lesions was calculated based on the 240 equivalent minutes at 43°C thermal dose contours. A prototype of the AFUS was constructed with two identical transducers of an operating frequency of 2.25 MHz, 38 mm in diameter, and F-number equal to 1.33. To evaluate the performance of the AFUS experimentally, a series of heating in polyacrylamide phantoms, ex vivo porcine liver tissues, and in implanted mouse tumors fibrosarcoma ͑FSaII͒ in vivo was conducted. In these experimental cases, the sphericity was calculated and compared based on the visible lesion ͑a marked change in coloration͒. Results: As shown in the simulations, the lesions induced in polyacrylamide phantoms, ex vivo porcine liver tissues, and in vivo mouse tumors, the sphericities of the lesions yielded by AFUS heating were approximately 50% higher than those of single focused ultrasound heating as long as moderate intensities were used and the duty cycle pulses were distributed equally among the transducers. Conclusions: The AFUS is a device capable of noninvasively creating spheroidal thermal lesions in small targets such as murine tumors.