Peter L Choyke

National Institutes of Health, Maryland, United States

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Publications (575)2529.64 Total impact

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    ABSTRACT: Prostate cancer is a common cancer in men and continues to be a major health problem. Imaging plays an important role in the clinical management of patients with prostate cancer. An important goal for prostate cancer imaging is more accurate disease characterization through the synthesis of anatomic, functional, and molecular imaging information. Positron emission tomography (PET)/computed tomography (CT) in oncology is emerging as an important imaging tool. The most common radiotracer for PET/CT in oncology, (18)F-fluorodeoxyglucose (FDG), is not very useful in the imaging of prostate cancer. However, in recent years other PET tracers have improved the accuracy of PET/CT imaging of prostate cancer. Among these, choline labeled with (18)F or (11)C, (11)C-acetate, and (18)F-fluoride has demonstrated promising results, and other new radiopharmaceuticals are under development and evaluation in preclinical and clinical studies. Large prospective clinical PET/CT trials are needed to establish the role of PET/CT in prostate cancer patients. Because there are only limited available therapeutic options for patients with advanced metastatic prostate cancer, there is an urgent need for the development of more effective treatment modalities that could improve outcome. Prostate cancer represents an attractive target for radioimmunotherapy (RIT) for several reasons, including pattern of metastatic spread (lymph nodes and bone marrow, sites with good access to circulating antibodies) and small volume disease (ideal for antigen access and antibody delivery). Furthermore, prostate cancer is also radiation sensitive. Prostate-specific membrane antigen is expressed by virtually all prostate cancers, and represents an attractive target for RIT. Antiprostate-specific membrane antigen RIT demonstrates antitumor activity and is well tolerated. Clinical trials are underway to further improve upon treatment efficacy and patient selection. This review focuses on the recent advances of clinical PET/CT imaging and RIT of prostate cancer.
    Seminars in nuclear medicine 01/2011; 41(1):29-44. · 3.96 Impact Factor
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    ABSTRACT: Atlas selection and combination are two critical factors affecting the performance of atlas-based segmentation methods. In the existing works, those tasks are completed in the original image space. However, the intrinsic similarity between the images may not be accurately reflected by the Euclidean distance in this high-dimensional space. Thus, the selected atlases may be away from the input image and the generated template by combining those atlases for segmentation can be misleading. In this paper, we propose to select and combine atlases by projecting the images onto a low-dimensional manifold. With this approach, atlases can be selected according to their intrinsic similarity to the patient image. A novel method is also proposed to compute the weights for more efficiently combining the selected atlases to achieve better segmentation performance. The experimental results demonstrated that our proposed method is robust and accurate, especially when the number of training samples becomes large.
    Medical image computing and computer-assisted intervention : MICCAI ... International Conference on Medical Image Computing and Computer-Assisted Intervention. 01/2011; 14(Pt 3):272-9.
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    ABSTRACT: OBJECTIVE To develop a system that documents the location of transrectal ultrasonography (TRUS)-guided prostate biopsies by fusing them to MRI scans obtained prior to biopsy, as the actual location of prostate biopsies is rarely known. PATIENTS AND METHODS Fifty patients (median age 61) with a median prostate-specific antigen (PSA) of 5.8 ng/ml underwent 3T endorectal coil MRI prior to biopsy. 3D TRUS images were obtained just prior to standard TRUS-guided 12-core sextant biopsies wherein an electromagnetic positioning device was attached to the needle guide and TRUS probe in order to track the position of each needle pass. The 3D-TRUS image documenting the location of each biopsy was fused electronically to the T2-weighted MRI. Each biopsy needle track was marked on the TRUS images and these were then transposed onto the MRI. Each biopsy site was classified pathologically as positive or negative for cancer and the Gleason score was determined. RESULTS The location of all (n= 605) needle biopsy tracks was successfully documented on the T2-weighted (T2W) MRI. Among 50 patients, 20 had 56 positive cores. At the sites of biopsy, T2W signal was considered 'positive' for cancer (i.e. low in signal intensity) in 34 of 56 sites. CONCLUSION It is feasible to document the location of TRUS-guided prostate biopsies on pre-procedure MRI by fusing the pre-procedure TRUS to an endorectal coil MRI using electromagnetic needle tracking. This procedure may be useful in documenting the location of prior biopsies, improving quality control and thereby avoiding under-sampling of the prostate as well as directing subsequent biopsies to regions of the prostate not previously sampled.
    BJU International 01/2011; 107(1):53-7. · 3.05 Impact Factor
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    ABSTRACT: Multiple myeloma (MM) is consistently preceded by its pre-malignant states, monoclonal gammopathy of undetermined significance (MGUS) and/or smoldering multiple myeloma (SMM). By definition, precursor conditions do not exhibit end-organ disease (anemia, hypercalcemia, renal failure, skeletal lytic lesions, or a combination of these). However, new imaging methods are demonstrating that some patients in the MGUS or SMM category are exhibiting early signs of MM. Although MGUS/SMM patients are currently defined as low-risk versus high-risk based on clinical markers, we currently lack the ability to predict the individual patient's risk of progression from MGUS/SMM to MM. Given that the presence of gross lytic bone lesions is a hallmark of MM, it is reasonable to believe that less severe bone changes defined by more sensitive imaging may be predictive of MM progression. Indeed, since bone disease is such an essential aspect of MM, imaging techniques directed at the detection of early bone lesions, have the potential to become increasingly more useful in the setting of MGUS/SMM. Current guidelines for the radiological assessment of MM still recommend the traditional skeletal survey, although its limitations are well documented, especially in early phases of the disease when radiographs can significantly underestimate the extent of bone lesions and bone marrow involvement. Newer, more advanced imaging modalities, with higher sensitivities, including whole-body low-dose computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography (PET) are being employed. Also various imaging techniques have been used to provide an assessment of bone involvement and identify extra-osseous disease. This review emphasizes the current state of the art and emerging imaging methods, which may help to better define high-risk versus low-risk MGUS/SMM. Ultimately, improved imaging could allow more tailored clinical management, and, most likely play an important role in the development of future treatment strategies for high-risk precursor disease.
    Seminars in Hematology 01/2011; 48(1):22-31. · 3.36 Impact Factor
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    IEEE Trans. Med. Imaging. 01/2011; 30:2044-2058.
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    ABSTRACT: During transrectal ultrasound (TRUS)-guided prostate biopsies, the actual location of the biopsy site is rarely documented. Here, we demonstrate the capability of TRUS-magnetic resonance imaging (MRI) image fusion to document the biopsy site and correlate biopsy results with multi-parametric MRI findings. Fifty consecutive patients (median age 61 years) with a median prostate-specific antigen (PSA) level of 5.8 ng/ml underwent 12-core TRUS-guided biopsy of the prostate. Pre-procedural T2-weighted magnetic resonance images were fused to TRUS. A disposable needle guide with miniature tracking sensors was attached to the TRUS probe to enable fusion with MRI. Real-time TRUS images during biopsy and the corresponding tracking information were recorded. Each biopsy site was superimposed onto the MRI. Each biopsy site was classified as positive or negative for cancer based on the results of each MRI sequence. Sensitivity, specificity, and receiver operating curve (ROC) area under the curve (AUC) values were calculated for multi-parametric MRI. Gleason scores for each multi-parametric MRI pattern were also evaluated. Six hundred and 5 systemic biopsy cores were analyzed in 50 patients, of whom 20 patients had 56 positive cores. MRI identified 34 of 56 positive cores. Overall, sensitivity, specificity, and ROC area values for multi-parametric MRI were 0.607, 0.727, 0.667, respectively. TRUS-MRI fusion after biopsy can be used to document the location of each biopsy site, which can then be correlated with MRI findings. Based on correlation with tracked biopsies, T2-weighted MRI and apparent diffusion coefficient maps derived from diffusion-weighted MRI are the most sensitive sequences, whereas the addition of delayed contrast enhancement MRI and three-dimensional magnetic resonance spectroscopy demonstrated higher specificity consistent with results obtained using radical prostatectomy specimens.
    Cancer Imaging 01/2011; 11:31-6. · 1.59 Impact Factor
  • Bioinformatics. 01/2011; 27:2607-2609.
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    ABSTRACT: Sorafenib, a multikinase inhibitor targeting Raf and VEGFR, has shown activity in unselected patients with non-small-cell lung cancer (NSCLC). At present there are no validated biomarkers indicative of sorafenib activity. Patients received sorafenib 400 mg BID daily to determine activity and tolerability and to measure its biological effects. KRAS mutation status (N = 34), angiogenesis markers (VEGF, bFGF, FLT-1, PLGF-1) and imaging with DCE-MRI (dynamic contrast enhanced MRI) to determine early changes in tumor vascular characteristics were evaluated. Three parameters K(trans), K(ep), and V(e) were measured by DCE-MRI at baseline and day 14 of cycle 1. Cytokine analysis was done on days 0, 14, 28, and 54. Thirty-seven patients with previously treated stage IV NSCLC were enrolled in this single-center phase II trial. In 34 evaluable patients, 2 had partial responses and 20 had stable disease for 3 to 17 months, a disease control rate of 65%. The median progression-free survival (PFS) was 3.4 months, and median overall survival (OS) was 11.6 months. Toxicity was consistent with the known side effects of sorafenib. KRAS (32%) and EGFR mutations (22%) showed no correlation with response, PFS, or OS. K(ep), was significant in predicting an improvement in OS (P = 0.035) and PFS (P = 0.029). Cytokine analysis demonstrated an improved OS for bFGF day 0 (<6 vs. >6 pg/mL; P = 0.042), whereas a PFS benefit was seen with bFGF at day 28 (<6 vs. >6; P = 0.028). KRAS and EGFR mutational status showed no correlation with response, PFS, or OS. Radiologic and cytokine changes may act as biomarkers indicative of early angiogenesis inhibition.
    Clinical Cancer Research 01/2011; 17(5):1190-9. · 7.84 Impact Factor
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    ABSTRACT: Autofluorescence arising from normal tissues can compromise the sensitivity and specificity of in vivo fluorescence imaging by lowering the target-to-background signal ratio. Since bioluminescence resonance energy transfer quantum dot (BRET-QDot) nano-particles can self-illuminate in near-infrared in the presence of the substrate, coelenterazine, without irradiating excitation lights, imaging using BRET-QDots does not produce any autofluorescence. In this study, we applied this BRET-QDot nano-particle to the in vivo lymphatic imaging in mice in order to compare with BRET, fluorescence or bioluminescence lymphatic imaging. BRET-QDot655, in which QDot655 is contained as a core, was injected at different sites (e.g. chin, ear, forepaws and hind paws) in mice followed by the intravenous coelenterazine injection, and then bioluminescence and fluorescence imaging were serially performed. In all mice, each lymphatic basin was clearly visualized in the BRET imaging with minimal background signals. The BRET signal in the lymph nodes lasted at least 30 min after coelenterazine injections. Furthermore, the BRET signal demonstrated better quantification than the fluorescence signal emitting from QDot655, the core of this BRET particle. These advantages of BRET-QDot allowed us to perform real-time, quantitative lymphatic imaging without image processing. BRET-Qdots have the potential to be a robust nano-material platform for developing optical molecular imaging probes.
    Contrast Media & Molecular Imaging 01/2011; 6(1):55-9. · 2.87 Impact Factor
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    ABSTRACT: Pazopanib is an FDA approved Vascular Endothelial Growth Factor Receptor inhibitor. We previously reported that it also inhibits tumor cell B-Raf activity in an experimental brain metastatic setting. Here, we determine the effects of different B-Raf genotypes on pazopanib efficacy, in terms of primary tumor growth and anti-angiogenesis. A panel of seven human breast cancer and melanoma cell lines harboring different mutations in the Ras-Raf pathway was implanted orthotopically in mice, and tumor growth, ERK1/2, MEK1/2 and AKT activation, and blood vessel density and permeability were analyzed. Pazopanib was significantly inhibitory to xenografts expressing either exon 11 mutations of B-Raf, or HER2 activated wild type B-Raf; no significant inhibition of a xenograft expressing the common V600E B-Raf mutation was observed. Decreased pMEK staining in the responsive tumors confirmed that B-Raf was targeted by pazopanib. Interestingly, pazopanib inhibition of tumor cell B-Raf also correlated with its anti-angiogenic activity, as quantified by vessel density and area. In conclusion, using pazopanib, tumor B-Raf status was identified as a significant determinant of both tumor growth and angiogenesis.
    PLoS ONE 01/2011; 6(10):e25625. · 3.73 Impact Factor
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    Hisataka Kobayashi, Peter L Choyke
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    ABSTRACT: Conventional imaging methods, such as angiography, computed tomography (CT), magnetic resonance imaging (MRI), and radionuclide imaging, rely on contrast agents (iodine, gadolinium, and radioisotopes, for example) that are "always on." Although these indicators have proven clinically useful, their sensitivity is lacking because of inadequate target-to-background signal ratio. A unique aspect of optical imaging is that fluorescence probes can be designed to be activatable, that is, only "turned on" under certain conditions. These probes are engineered to emit signal only after binding a target tissue; this design greatly increases sensitivity and specificity in the detection of disease. Current research focuses on two basic types of activatable fluorescence probes. The first developed were conventional enzymatically activatable probes. These fluorescent molecules exist in the quenched state until activated by enzymatic cleavage, which occurs mostly outside of the cells. However, more recently, researchers have begun designing target-cell-specific activatable probes. These fluorophores exist in the quenched state until activated within targeted cells by endolysosomal processing, which results when the probe binds specific receptors on the cell surface and is subsequently internalized. In this Account, we present a review of the rational design and in vivo applications of target-cell-specific activatable probes. In engineering these probes, researchers have asserted control over a variety of factors, including photochemistry, pharmacological profile, and biological properties. Their progress has recently allowed the rational design and synthesis of target-cell-specific activatable fluorescence imaging probes, which can be conjugated to a wide variety of targeting molecules. Several different photochemical mechanisms have been utilized, each of which offers a unique capability for probe design. These include self-quenching, homo- and hetero-fluorescence resonance energy transfer (FRET), H-dimer formation, and photon-induced electron transfer (PeT). In addition, the repertoire is further expanded by the option for reversibility or irreversibility of the signal emitted through these mechanisms. Given the wide range of photochemical mechanisms and properties, target-cell-specific activatable probes have considerable flexibility and can be adapted to specific diagnostic needs. A multitude of cell surface molecules, such as overexpressed growth factor receptors, are directly related to carcinogenesis and thus provide numerous targets highly specific for cancer. This discussion of the chemical, pharmacological, and biological basis of target-cell-specific activatable imaging probes, and methods for successfully designing them, underscores the systematic, rational basis for further developing in vivo cancer imaging.
    Accounts of Chemical Research 11/2010; 44(2):83-90. · 20.83 Impact Factor
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    ABSTRACT: This study aims to develop and characterize the trafficking of a dual-modal agent that identifies primary draining or sentinel lymph node (LN). Herein, a dual-reporting silica-coated iron oxide nanoparticle (SCION) is developed. Nude mice were imaged by magnetic resonance (MR) and optical imaging and axillary LNs were harvested for histological analysis. Trafficking through lymphatics was observed with intravital and ex vivo confocal microscopy of popliteal LNs in B6-albino, CD11c-EYFP, and lys-EGFP transgenic mice. In vivo, SCION allows visualization of LNs. The particle's size and surface functionality play a role in its passive migration from the intradermal injection site and its minimal uptake by CD11c+ dendritic cells and CD169+ and lys+ macrophages. After injection, SCION passively migrates to LNs without macrophage uptake and then can be used to image LN(s) by MRI and fluorescence. Thus, SCION can potentially be developed for use in sentinel node resections or for intralymphatic drug delivery.
    Molecular imaging and biology: MIB: the official publication of the Academy of Molecular Imaging 11/2010; 13(6):1163-72. · 2.47 Impact Factor
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    ABSTRACT: Target specific small molecules as modulators of drug delivery may play a significant role in the future development of therapeutics. Small molecules can alter the in vivo pharmacokinetics of therapeutic macromolecules leading to more efficient drug delivery with less systemic toxicity. The potential of creating a more effective drug delivery system through glycosylation has led, for instance, to the addition of galactose to increase drug delivery to the liver. However, there are many other monosaccharides with potentially useful targeting properties that require further characterization. Here, we investigate the potential of glycosylation to guide molecular therapies using five different monosaccharides conjugated to human serum albumin (HSA). Additionally, we investigate how the amount of glycosylation may alter the pharmacokinetic profile of HSA. We introduce the use of in vivo near-infrared optical imaging to characterize the effect of differential glycosylation on the pharmacokinetics of macromolecules.
    Bioconjugate Chemistry 10/2010; 21(10):1925-32. · 4.58 Impact Factor
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    ABSTRACT: Quantum dots (QDs) are fluorescent nanoparticles with broad excitation and narrow, wavelength-tunable emission spectra. They are used extensively for in vitro fluorescence imaging studies and more recently for in vivo small animal and pre-clinical studies. To date there has been little concern about the selection of QD size (and thus emission wavelength peak) and excitation wavelengths, as they have little relevance to the results of in vitro studies. In vivo imaging, however, poses additional constraints, such as the scattering and absorption by tissue, which may influence the signal intensity at the body surface. Here, we demonstrate that longer-wavelength excitation and emission yield less quantization error in measured relative fluorescence intensity, using three near-infrared QDs (QD655, QD705 and QD800) applied to in vivo lymphatic imaging, and a range of excitation wavelengths from the blue to the red. Statistically significant differences in quantization error were observed between nearly all pairs of excitation wavelengths (445-490, 503-555, 575-605, 615-665 and 671-705 nm). Similarly, quantization error decreased with longer emission wavelengths (655, 705 and 800 nm). Light absorbance and scattering were demonstrated to be more potent factors than absorbance efficiency of QDs in producing quantization error in the measured fluorescence intensity. As a result, while wavelengths can be adjusted for qualitative experiments, the longest possible wavelengths should be used if quantification is desired during QD imaging experiments.
    Contrast Media & Molecular Imaging 10/2010; 6(3):148-52. · 2.87 Impact Factor
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    ABSTRACT: Clinical translation of novel optical probes requires testing of human specimens ex vivo to ensure efficacy. However, it may be difficult to remove human tissue from the operating room due to regulatory/privacy issues. Therefore, we designed a portable fluorescence camera to test targeted optical imaging probes on human specimens in the operating room. A compact benchtop fluorescence camera was designed and built in-house. A mouse xenograft model of ovarian cancer with an activatable imaging probe based on rhodamine green was used to test the device. Comparison was made to commercially available imaging systems. The prototype camera produced images comparable to images acquired with commercially available, non-portable imaging systems. We demonstrate the feasibility of a specimen-based portable fluorescence camera for use in the operating room. Its small size ensures that tissue excised from patients can be tested promptly for fluorescence within the operating room environment, thus expediting the testing of novel imaging probes.
    Molecular imaging and biology: MIB: the official publication of the Academy of Molecular Imaging 10/2010; 13(5):862-7. · 2.47 Impact Factor
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    ABSTRACT: To identify , within the framework of a current Phase I trial, whether factors related to intraprostatic cancer lesions (IPLs) or individual patients predict the feasibility of high-dose intraprostatic irradiation. Endorectal coil MRI scans of the prostate from 42 men were evaluated for dominant IPLs. The IPLs, prostate, and critical normal tissues were contoured. Intensity-modulated radiotherapy plans were generated with the goal of delivering 75.6 Gy in 1.8-Gy fractions to the prostate, with IPLs receiving a simultaneous integrated boost of 3.6 Gy per fraction to a total dose of 151.2 Gy, 200% of the prescribed dose and the highest dose cohort in our trial. Rectal and bladder dose constraints were consistent with those outlined in current Radiation Therapy Oncology Group protocols. Dominant IPLs were identified in 24 patients (57.1%). Simultaneous integrated boosts (SIB) to 200% of the prescribed dose were achieved in 12 of the 24 patients without violating dose constraints. Both the distance between the IPL and rectum and the hip-to-hip patient width on planning CT scans were associated with the feasibility to plan an SIB (p = 0.002 and p = 0.0137, respectively). On the basis of this small cohort, the distance between an intraprostatic lesion and the rectum most strongly predicted the ability to plan high-dose radiation to a dominant intraprostatic lesion. High-dose SIB planning seems possible for select intraprostatic lesions.
    International journal of radiation oncology, biology, physics 10/2010; 80(2):614-20. · 4.59 Impact Factor
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    ABSTRACT: Imaging of the lymphatic system is critical in preoperative planning of resections of complex lymphatic malformations. However, safe, effective imaging methods with sufficient resolution to identify the lymphatics have been lacking. In this study, we demonstrate the use of gadolinium-labeled dendrimers to image the lymphatics in small and large animal models during magnetic resonance lymphangiography. Polyamidoamine G6-Gd_1B4M_N-hydroxysuccinimide was synthesized and administered intradermally in the extremities of normal mice and pigs at several doses. The lymphatics were well demonstrated in both animal models and there was rapid uptake in the deep lymphatic system, including the thoracic duct. A significant dose reduction was achieved (1 µmol Gd/kg) in the 35-kg pig compared with mice, while still producing excellent results. No toxicity was observed and only minor inflammatory changes were observed at the injection site 30 days later. We demonstrate that a low dose of a macromolecular magnetic resonance contrast agent can provide rapid imaging of the deep lymphatic system in both small and large animals. This data provides a basis to consider a similar agent in clinical trials.
    Nanomedicine 10/2010; 5(8):1183-91. · 5.26 Impact Factor
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    ABSTRACT: Magnetic resonance imaging (MRI) is a powerful imaging modality that can provide an assessment of function or molecular expression in tandem with anatomic detail. Over the last 20-25 years, a number of gadolinium-based MR contrast agents have been developed to enhance signal by altering proton relaxation properties. This review explores a range of these agents from small molecule chelates, such as Gd-DTPA and Gd-DOTA, to macromolecular structures composed of albumin, polylysine, polysaccharides (dextran, inulin, starch), poly(ethylene glycol), copolymers of cystamine and cystine with GD-DTPA, and various dendritic structures based on polyamidoamine and polylysine (Gadomers). The synthesis, structure, biodistribution, and targeting of dendrimer-based MR contrast agents are also discussed.
    Acta Radiologica 09/2010; 51(7):751-67. · 1.33 Impact Factor
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    ABSTRACT: Biomedical optical imaging is rapidly evolving because of its desirable features of rapid frame rates, high sensitivity, low cost, portability and lack of radiation. Quantum dots are attractive as imaging agents owing to their high brightness, and photo- and bio-stability. Here, the current status of in vitro and in vivo real-time optical imaging with quantum dots is reviewed. In addition, we consider related nanocrystals based on solid-state semiconductors, including upconverting nanoparticles and bioluminescence resonance energy transfer quantum dots. These particles can improve the signal-to-background ratio for real-time imaging largely by suppressing background signal. Although toxicity and biodistribution of quantum dots and their close relatives remain prime concerns for translation to human imaging, these agents have many desirable features that should be explored for medical purposes.
    Nanomedicine 07/2010; 5(5):765-76. · 5.26 Impact Factor
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    ABSTRACT: OBJECTIVE: This review is a primer on the technical aspects of performing a high-quality MRI and MR spectroscopic imaging examination of the prostate. CONCLUSION: MRI and MR spectroscopic imaging are useful tools in the localization, staging, and functional assessment of prostate cancer. Performing a high-quality MR spectroscopic examination requires understanding of the technical aspects and limitations of spectral acquisition, postprocessing techniques, and spectral evaluation.
    American Journal of Roentgenology 06/2010; 194(6):1414-26. · 2.90 Impact Factor

Publication Stats

16k Citations
2,529.64 Total Impact Points


  • 1990–2014
    • National Institutes of Health
      • • Center for Cancer Research
      • • Laboratory of Pathology
      • • Center for Interventional Oncology
      • • Branch of Metabolism
      Maryland, United States
  • 1970–2014
    • National Cancer Institute (USA)
      • • Molecular Imaging Program
      • • Laboratory of Pathology
      • • Genetic Epidemiology
      • • Surgery Branch
      Maryland, United States
  • 2013
    • The Jikei University School of Medicine
      • Department of Internal Medicine H
      Tokyo, Tokyo-to, Japan
    • University of Helsinki
      Helsinki, Southern Finland Province, Finland
  • 2001–2013
    • NCI-Frederick
      • Laboratory of Pathology
      Maryland, United States
  • 1998–2013
    • Leidos Biomedical Research
      Maryland, United States
    • University of Pennsylvania
      Philadelphia, Pennsylvania, United States
  • 2012
    • Texas Christian University
      • Department of Chemistry
      Fort Worth, TX, United States
    • Aarhus University Hospital
      • Department of Nuclear Medicine & PET-Centre
      Århus, Central Jutland, Denmark
  • 2004–2012
    • Virginia Polytechnic Institute and State University
      • Department of Electrical and Computer Engineering
      Blacksburg, VA, United States
  • 2011
    • Osaka Prefecture University
      • Nanoscience and Nanotechnology Research Center
      Sakai, Osaka-fu, Japan
    • Conselleria de Sanidade
      La Corogne, Galicia, Spain
    • United States Army
      Washington, West Virginia, United States
  • 2010–2011
    • University of Copenhagen
      • Department of Clinical Biochemistry
      København, Capital Region, Denmark
    • Boston Children's Hospital
      Boston, Massachusetts, United States
  • 2007–2011
    • The University of Tokyo
      • • Faculty & Graduate School of Medicine
      • • Faculty and Graduate School of Pharmaceutical Sciences
      Tokyo, Tokyo-to, Japan
    • Howard Hughes Medical Institute
      Maryland, United States
    • Virginia State University
      Petersburg, Virginia, United States
    • University of South Dakota
      Vermillion, South Dakota, United States
  • 2006–2010
    • National Human Genome Research Institute
      Maryland, United States
  • 2008
    • Roswell Park Cancer Institute
      • Department of Radiation Medicine
      Buffalo, New York, United States
  • 2007–2008
    • Philips
      Eindhoven, North Brabant, Netherlands
  • 2003–2004
    • Robert Wood Johnson University Hospital
      New Brunswick, New Jersey, United States
    • The Ohio State University
      • Department of Radiology
      Columbus, OH, United States
    • CSU Mentor
      Long Beach, California, United States
  • 2000–2004
    • Uniformed Services University of the Health Sciences
      • • Department of Radiology & Radiological Sciences
      • • Department of Radiobiology
      Bethesda, MD, United States
  • 1986–2004
    • Georgetown University
      • Department of Radiology
      Washington, D. C., DC, United States
    • Hospital of the University of Pennsylvania
      • Department of Radiology
      Philadelphia, PA, United States
  • 2002
    • National Eye Institute
      Maryland, United States
    • George Mason University
      • Department of Computational and Data Sciences
      Fairfax, VA, United States
  • 1999–2002
    • GE India Industrial Pvt. Ltd.
      New Dilli, NCT, India
  • 1996
    • University of Alabama in Huntsville
      • Department of Computer Science
      Huntsville, Alabama, United States
  • 1995
    • Henry M Jackson Foundation
      Maryland City, Maryland, United States
  • 1992
    • The National Institute of Diabetes and Digestive and Kidney Diseases
      Maryland, United States