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Search Results: 1 - 10 of 411984 matches for " Christopher M. Collins "
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Analysis of Conservative and Magnetically Induced Electric Fields in a Low-Frequency Birdcage Coil  [PDF]
Bu S. Park, Sunder S. Rajan, Christopher M. Collins, Leonardo M. Angelone
Journal of Electromagnetic Analysis and Applications (JEMAA) , 2013, DOI: 10.4236/jemaa.2013.57043

Numerical methods are used to evaluate variations of the electromagnetic fields generated by a head-sized birdcage coil as a function of load (“loading effect”). The loading effect was analyzed for the cases of a coil loaded with a conductive cylindrical sample, a dielectric cylindrical sample, and an anatomically precise head model. Maxwell equations were solved by means of finite difference time domain (FDTD) method conducted at 12.8, 64, and 128 MHz. Simulation results indicate that at 12.8 MHz the conservative electric field (Ec) caused by the scalar electric potentials between the coil and the load or within the load was significantly higher than the magnetically-induced electric field (Ei) and was the major component of the total electric field (Etotal). The amplitudes of Ec and Etotal are seen to be lower within a sample than at a corresponding location in an empty coil, but approximately 65% higher in the space between coil and sample than at a corresponding location in an empty coil. This is due to polarization effects generating an additional scalar potential parallel to the original field. The increased electric field between coil and sample may cause increased power deposition at the surface of the sample and may affect the RF-induced currents in external leads used for physiological recording, i.e. ECG, during MRI scanning.

Periurethral Smooth Muscle Tumor of Undetermined Malignant Potential
Jessica Hsieh,Sarah Collins,Christopher M. Morosky
Case Reports in Obstetrics and Gynecology , 2012, DOI: 10.1155/2012/546852
Abstract: Smooth muscle tumors of undermined malignant potential (STUMP) are atypical smooth muscle tumors. The majority of these tumors are of uterine origin. We report the first known periurethral STUMP. Complete surgical resection is recommended for all cases of STUMP. They can recur in the form of STUMP or leiomyosarcoma.
Tracking Murine Gammaherpesvirus 68 Infection of Germinal Center B Cells In Vivo
Christopher M. Collins, Samuel H. Speck
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0033230
Abstract: Infection of mice with murine gammaherpesvirus 68 (MHV68) provides a tractable small animal model to study various aspects of persistent gammaherpesvirus infection. We have previously utilized a transgenic MHV68 that expresses enhanced yellow fluorescent protein (EYFP) to identify infected cells. While this recombinant MHV68 has been useful for identifying infected cell populations by flow cytometry, it has been suboptimal for identification of infected cells in tissue sections due to the high solubility of EYFP. Efficient detection of EYFP expressed from the MHV68 genome in tissue sections requires fixation of whole organs prior to sectioning, which frequently leads to over-fixation of some cellular antigens precluding their detection. To circumvent this issue, we describe the generation and characterization of a transgenic MHV68 harboring a fusion gene composed of the EYFP coding sequence fused to the histone H2B open reading frame. Because the H2bYFP fusion protein is tightly bound in nucleosomes in the nucleus it does not freely diffuse out of unfixed tissue sections, and thus eliminates the need for tissue fixation. We have used the MHV68-H2bYFP recombinant virus to assess the location and distribution of virus infected B cells in germinal centers during the peak of MHV68 latency in vivo. These analyses show that the physical location of distinct populations of infected germinal center B cells correlates well with their surface phenotype. Furthermore, analysis of the distribution of virus infection within germinal center B cell populations revealed that ca. 70% of MHV68 infected GC B cells are rapidly dividing centroblasts, while ca. 20% have a clear centrocyte phenotype. Finally, we have shown that marking of infected cells with MHV68-H2bYFP is extended long after the onset of latency – which should facilitate studies to track MHV68 latently infected cells at late times post-infection.
Expansion of Murine Gammaherpesvirus Latently Infected B Cells Requires T Follicular Help
Christopher M. Collins,Samuel H. Speck
PLOS Pathogens , 2014, DOI: doi/10.1371/journal.ppat.1004106
Abstract: X linked lymphoproliferative disease (XLP) is an inherited immunodeficiency resulting from mutations in the gene encoding the slam associated protein (SAP). One of the defining characteristics of XLP is extreme susceptibility to infection with Epstein-Barr virus (EBV), a gammaherpesvirus belonging to the genus Lymphocryptovirus, often resulting in fatal infectious mononucleosis (FIM). However, infection of SAP deficient mice with the related Murine gammaherpesvirus 68 (MHV68), a gammaherpesvirus in the genus Rhadinovirus, does not recapitulate XLP. Here we show that MHV68 inefficiently establishes latency in B cells in SAP deficient mice due to insufficient CD4 T cell help during the germinal center response. Although MHV68 infected B cells can be found in SAP-deficient mice, significantly fewer of these cells had a germinal center phenotype compared to SAP-sufficient mice. Furthermore, we show that infected germinal center B cells in SAP-deficient mice fail to proliferate. This failure to proliferate resulted in significantly lower viral loads, and likely accounts for the inability of MHV68 to induce a FIM-like syndrome. Finally, inhibiting differentiation of T follicular helper (TFH) cells in SAP-sufficient C57Bl/6 mice resulted in decreased B cell latency, and the magnitude of the TFH response directly correlated with the level of infection in B cells. This requirement for CD4 T cell help during the germinal center reaction by MHV68 is in contrast with EBV, which is thought to be capable of bypassing this requirement by expressing viral proteins that mimic signals provided by TFH cells. In conclusion, the outcome of MHV68 infection in mice in the setting of loss of SAP function is distinct from that observed in SAP-deficient patients infected with EBV, and may identify a fundamental difference between the strategies employed by the rhadinoviruses and lymphocryptoviruses to expand B cell latency during the early phase of infection.
Periurethral Smooth Muscle Tumor of Undetermined Malignant Potential
Jessica Hsieh,Sarah Collins,Christopher M. Morosky
Case Reports in Obstetrics and Gynecology , 2012, DOI: 10.1155/2012/546852
Abstract: Smooth muscle tumors of undermined malignant potential (STUMP) are atypical smooth muscle tumors. The majority of these tumors are of uterine origin. We report the first known periurethral STUMP. Complete surgical resection is recommended for all cases of STUMP. They can recur in the form of STUMP or leiomyosarcoma. 1. Introduction Smooth muscle tumors of undetermined malignant potential (STUMP) are rare smooth muscle tumors that are not definitively benign or malignant on histologic evaluation [1]. The majority of STUMPs are of uterine origin. In this paper, we present the first known case of a periurethral STUMP that was treated by surgical excision. 2. Case Report A 37-year-old nulligravid female presented to our clinic for an annual gynecologic examination. There were no abnormal findings noted on pelvic exam and a screening Pap smear was performed. Four weeks later, the patient returned for a colposcopic examination for findings of low-grade squamous intraepithelial lesion on her Pap smear. She was without complaint at this follow-up visit. However, her cervix was obstructed from view by a new anterior vaginal wall mass. The patient was sent for voiding cystourethrogram (VCUG), which did not demonstrate a urethral diverticulum. Subsequently, the patient was sent for magnetic resonance imaging (MRI). The MRI characterized a centimeter mass located within the anterior vaginal wall with mild homogeneous enhancement (Figure 1). After consultation with a urogynecology specialist, the patient was taken to the operating theater for excision of the mass via the vaginal approach. A transverse incision was made along the anterior vaginal wall epithelium overlying the periurethral mass. Two solid individual masses were then carefully dissected away from the urethra. The periurethral tissues were closed in layers using a pants-over-suit technique. Figure 1: T2-weighted MRI of the pelvic characterized a centimeter mass located within the anterior vaginal wall with mild homogeneous enhancement. A gross inspection by the surgeons revealed two soft, tan, smooth masses with no evidence of necrosis upon cross-section. They were felt to be periurethral leiomyomas and were sent to pathology for permanent section. The dimensions of the masses were centimeters and centimeters. Final histopathology revealed smooth muscle tumors with diffuse moderate atypia, absent necrosis, and less than 2 mitotic figures (MFs) per 10 high powered fields (HPFs) (Figure 2). The final diagnosis was STUMP. A second, independent pathologist was consulted and agreed. Figure 2: Hematoxylin and
Interleukin 21 Signaling in B Cells Is Required for Efficient Establishment of Murine Gammaherpesvirus Latency
Christopher M. Collins,Samuel H. Speck
PLOS Pathogens , 2015, DOI: 10.1371/journal.ppat.1004831
Abstract: The human gammaherpesviruses take advantage of normal B cell differentiation pathways to establish life-long infection in memory B cells. Murine gammaherpesvirus 68 (MHV68) infection of laboratory strains of mice also leads to life-long infection in memory B cells. To gain access to the memory B cell population, MHV68 infected B cells pass through the germinal center reaction during the onset of latency and require signals from T follicular helper (TFH) cells for proliferation. Interleukin 21 (IL-21), one of the secreted factors produced by TFH cells, plays an important role in both the maintenance of the germinal center response as well as in the generation of long-lived plasma cells. Using IL-21R deficient mice, we show that IL-21 signaling is required for efficient establishment of MHV68 infection. In the absence of IL-21 signaling, fewer infected splenocytes are able to gain access to either the germinal center B cell population or the plasma cell population – the latter being a major site of MHV68 reactivation. Furthermore, the germinal center B cell population in IL-21R-/- mice is skewed towards the non-proliferating centrocyte phenotype, resulting in reduced expansion of infected B cells. Additionally, the reduced frequency of infected plasma cells results in a significant reduction in the frequency of splenocytes capable of reactivating virus. This defect in establishment of MHV68 infection is intrinsic to B cells, as MHV68 preferentially establishes infection in IL-21R sufficient B cells in mixed bone marrow chimeric mice. Taken together, these data indicate that IL-21 signaling plays multiple roles during establishment of MHV68 infection, and identify IL-21 as a critical TFH cell-derived factor for efficient establishment of gammaherpesvirus B cell latency.
Slice-Selective Transmit Array Pulses for Improvement in Excitation Uniformity and Reduction of SAR  [PDF]
BuSik Park, Kyunghyun Sung, John McGarrity, Suk-hoon Oh, Zhipeng Cao, Zhangwei Wang, Christopher M. Collins
Journal of Electromagnetic Analysis and Applications (JEMAA) , 2013, DOI: 10.4236/jemaa.2013.55033
Abstract: To overcome challenges of inhomogeneous transmit B1 distribution and high specific energy absorption rate (SAR) in MRI, we compare slice-selective array-optimized composite pulse and RF shimming designed to both improve B1 uniformity and reduce SAR using an 8-channel transmit head array loaded with a head model at various RF pulse excitation times, and compare results with standard quadrature voltage distribution at 3T (128 MHz) and 7T (300 MHz). The excitation uniformity was estimated throughout the 3D brain region and SAR was calculated for the whole head. The optimized composite pulse could produce significantly better homogeneity and significantly better homogeneity when SAR was not constrained, and both significantly better homogeneity and lower SAR when the pulse duration was allowed to be twice that of the quadrature or RF shimmed pulse. When the total pulse durations were constrained to the same length, the relative advantages of the optimized composite pulse for producing better homogeneity and lower SAR simultaneously were diminished. Using the optimization results, the slice-selective composite pulse sequence was implemented on a 3D MRI simulator currently under development, and showed both effective slice selection and improvement in excitation uniformity compared to a conventional quadrature driving method.

Characterization of Omental Immune Aggregates during Establishment of a Latent Gammaherpesvirus Infection
Kathleen S. Gray, Christopher M. Collins, Samuel H. Speck
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0043196
Abstract: Herpesviruses are characterized by their ability to establish lifelong latent infection. The gammaherpesvirus subfamily is distinguished by lymphotropism, establishing and maintaining latent infection predominantly in B lymphocytes. Consequently, gammaherpesvirus pathogenesis is closely linked to normal B cell physiology. Murine gammaherpesvirus 68 (MHV68) pathogenesis in laboratory mice has been extensively studied as a model system to gain insights into the nature of gammaherpesvirus infection in B cells and their associated lymphoid compartments. In addition to B cells, MHV68 infection of macrophages contributes significantly to the frequency of viral genome-positive cells in the peritoneal cavity throughout latency. The omentum, a sheet of richly-vascularized adipose tissue, resides in the peritoneal cavity and contains clusters of immune cell aggregates termed milky spots. Although the value of the omentum in surgical wound-healing has long been appreciated, the unique properties of this tissue and its contribution to both innate and adaptive immunity have only recently been recognized. To determine whether the omentum plays a role in gammaherpesvirus pathogenesis we examined this site during early MHV68 infection and long-term latency. Following intraperitoneal infection, immune aggregates within the omentum expanded in size and number and contained virus-infected cells. Notably, a germinal-center B cell population appeared in the omentum of infected animals with earlier kinetics and greater magnitude than that observed in the spleen. Furthermore, the omentum harbored a stable frequency of viral genome-positive cells through early and into long-term latency, while removal of the omentum prior to infection resulted in a slight decrease in the establishment of splenic latency following intraperitoneal infection. These data provide the first evidence that the omentum is a site of chronic MHV68 infection that may contribute to the maintenance of chronic infection.
The Human Body and Millimeter-Wave Wireless Communication Systems: Interactions and Implications
Ting Wu,Theodore S. Rappaport,Christopher M. Collins
Computer Science , 2015,
Abstract: With increasing interest in millimeter wave wireless communications, investigations on interactions between the human body and millimeter wave devices are becoming important. This paper gives examples of current regulatory requirements, and provides an example for a 60 GHz transceiver. Also, the propagation characteristics of millimeter-waves in the presence of the human body are studied, and four models representing different body parts are considered to evaluate thermal effects of millimeter-wave radiation on the body. Simulation results show that about 34% to 42% of the incident power is reflected at the skin surface at 60 GHz. This paper shows that power density is not suitable to determine exposure compliance when millimeter wave devices are used very close to the body. A temperature-based technique for the evaluation of safety compliance is proposed in this paper.
MR thermometry characterization of a hyperthermia ultrasound array designed using the k-space computational method
Osama M Al-Bataineh, Christopher M Collins, Eun-Joo Park, Hotaik Lee, Nadine Smith
BioMedical Engineering OnLine , 2006, DOI: 10.1186/1475-925x-5-56
Abstract: A 3D acoustical prostate model was created using photographic data from the Visible Human Project?. The k-space computational method was used on this coarse grid and inhomogeneous tissue model to simulate the steady state pressure wavefield of the designed phased array using the linear acoustic wave equation. To ensure the uniformity and spread of the pressure in the length of the array, and the focusing capability in the width of the array, the equally-sized elements of the 4 × 20 elements phased array were 1 × 14 mm. A probe was constructed according to the design in simulation using lead zerconate titanate (PZT-8) ceramic and a Delrin? plastic housing. Noninvasive MRI thermometry and a switching feedback controller were used to accomplish ex vivo and in vivo hyperthermia evaluations of the probe.Both exposimetry and k-space simulation results demonstrated acceptable agreement within 9%. With a desired temperature plateau of 43.0°C, ex vivo and in vivo controlled hyperthermia experiments showed that the MRI temperature at the steady state was 42.9 ± 0.38°C and 43.1 ± 0.80°C, respectively, for 20 minutes of heating.Unlike conventional computational methods, the k-space method provides a powerful tool to predict pressure wavefield in large scale, 3D, inhomogeneous and coarse grid tissue models. Noninvasive MRI thermometry supports the efficacy of this probe and the feedback controller in an in vivo hyperthermia treatment of canine prostate.Prostate cancer causes approximately 30,000 deaths among Americans every year with more than 230,000 new patients in 2004 [1]. Most of the patients are elderly and often can not withstand invasive surgical procedures to eradicate the tumor in its early stages [2]. Radiation and hormone therapies are still the treatment of choice for these patients [3]. Thermal treatment has shown to be effective in therapy for different kinds of tumors including prostate cancer [4-8]. Hyperthermia therapy raises the temperature of the tumor and a
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