Pectoralis major muscle flap use in a modern head and neck free flap practice.

PURPOSE: Pectoralis major muscle flaps (PMMF) are a commonly used reconstructive modality to repair head and neck defects. As the use of free flap reconstruction is increasingly practiced in the head and neck, the role of the PMMF may be changing as well. This study sought to analyze indications and outcomes for PMMF following head and neck resections from one surgeon's experience. MATERIALS AND METHODS: Retrospective review from December 1, 2013 through September 30, 2017 at a tertiary care academic medical center. Indications for the PMMF were examined as well as surgical outcomes. Basic demographic data, patient head and neck cancer history, history of radiation and/or chemotherapy, and history of previous reconstructive procedures were obtained and compared across all subjects. RESULTS: Forty patients underwent a PMMF within the designated time frame. The majority of patients were male (83%) and the average age was 65 years (range 55.4-74.6 years). Of the 40 cases, 9 of the PMMFs were performed as primary reconstruction of the defect. In the remaining 31 cases, these flaps were utilized as a secondary reconstructive option following fistula formation (13), dehiscence (6), need for an additional flap for recurrent disease (6) infection (4), or major bleeding (2). In every case that it was utilized, the PMMF was the definitive reconstruction. Within the same time frame, 429 free flaps were performed by the same surgeon, with an average of 125 free flaps performed yearly. The rate of total flap failure overall was 3.9%. The other failed free flap reconstructive options used besides a PMMF were secondary free flaps (11), local wound care (4), or obturator placement (2). The secondary pectoralis flaps occurred following 7.2% of free flaps with total or partial failure that were performed within the same time range. The indications for the PMMF did not change or evolve during the time frame of the study. CONCLUSIONS: Although free flaps were performed with far greater frequency than PMMFs at our institution, the PMMF demonstrated continued utility as a secondary reconstructive option. For a surgeon who performs a high volume of free flaps, preservation of the pectoralis muscle and associated vasculature for possible later secondary reconstruction should be considered due to its strong efficacy.

Interior tomography with curvelet-based regularization.

The interior problem, i.e. reconstruction from local truncated projections in computed tomography (CT), is common in practical applications. However, its solution is non-unique in a general unconstrained setting. To solve the interior problem uniquely and stably, in recent years both the prior knowledge- and compressive sensing (CS)-based methods have been developed. Those theoretically exact solutions for the interior problem are called interior tomography. Along this direction, we propose here a new CS-based method for the interior problem based on the curvelet transform. A curvelet is localized in both radial and angular directions in the frequency domain. A two-dimensional (2D) image can be represented in a curvelet frame. We employ the curvelet transform coefficients to regularize the interior problem and obtain a curvelet frame based regularization method (CFRM) for interior tomography. The curvelet coefficients of the reconstructed image are split into two sets according to their visibility from the interior data, and different regularization parameters are used for these two sets. We also presents the results of numerical experiments, which demonstrate the feasibility of the proposed approach.

In situ Structure of Rotavirus VP1 RNA-Dependent RNA Polymerase.

Rotaviruses, like other non-enveloped, double-strand RNA viruses, package an RNA-dependent RNA polymerase (RdRp) with each duplex of their segmented genomes. Rotavirus cell entry results in loss of an outer protein layer and delivery into the cytosol of an intact, inner capsid particle (the "double-layer particle," or DLP). The RdRp, designated VP1, is active inside the DLP; each VP1 achieves many rounds of mRNA transcription from its associated genome segment. Previous work has shown that one VP1 molecule lies close to each 5-fold axis of the icosahedrally symmetric DLP, just beneath the inner surface of its protein shell, embedded in tightly packed RNA. We have determined a high-resolution structure for the rotavirus VP1 RdRp in situ, by local reconstruction of density around individual 5-fold positions. We have analyzed intact virions ("triple-layer particles"), non-transcribing DLPs and transcribing DLPs. Outer layer dissociation enables the DLP to synthesize RNA, in vitro as well as in vivo, but appears not to induce any detectable structural change in the RdRp. Addition of NTPs, Mg2+, and S-adenosylmethionine, which allows active transcription, results in conformational rearrangements, in both VP1 and the DLP capsid shell protein, that allow a transcript to exit the polymerase and the particle. The position of VP1 (among the five symmetrically related alternatives) at one vertex does not correlate with its position at other vertices. This stochastic distribution of site occupancies limits long-range order in the 11-segment, double-strand RNA genome.

Particle segmentation algorithm for flexible single particle reconstruction.

As single particle cryo-electron microscopy has evolved to a new era of atomic resolution, sample heterogeneity still imposes a major limit to the resolution of many macromolecular complexes, especially those with continuous conformational flexibility. Here, we describe a particle segmentation algorithm towards solving structures of molecules composed of several parts that are relatively flexible with each other. In this algorithm, the different parts of a target molecule are segmented from raw images according to their alignment information obtained from a preliminary 3D reconstruction and are subjected to single particle processing in an iterative manner. This algorithm was tested on both simulated and experimental data and showed improvement of 3D reconstruction resolution of each segmented part of the molecule than that of the entire molecule.

lop-DWI: A Novel Scheme for Pre-Processing of Diffusion-Weighted Images in the Gradient Direction Domain.

We describe and evaluate a pre-processing method based on a periodic spiral sampling of diffusion-gradient directions for high angular resolution diffusion magnetic resonance imaging. Our pre-processing method incorporates prior knowledge about the acquired diffusion-weighted signal, facilitating noise reduction. Periodic spiral sampling of gradient direction encodings results in an acquired signal in each voxel that is pseudo-periodic with characteristics that allow separation of low-frequency signal from high frequency noise. Consequently, it enhances local reconstruction of the orientation distribution function used to define fiber tracks in the brain. Denoising with periodic spiral sampling was tested using synthetic data and in vivo human brain images. The level of improvement in signal-to-noise ratio and in the accuracy of local reconstruction of fiber tracks was significantly improved using our method.