Bio
Dr. Timothy Chang is a Clinical Assistant Professor of Urology at Stanford University. He graduated with High Honors from Princeton University and received a Master of Science from Massachusetts Institute of Technology. He then obtained his medical degree and urology residency training from Stanford University School of Medicine. Dr. Chang has experience in a broad range of adult general urologic care, with a particular focus on kidney stone treatment for which he completed specialized fellowship training at Stanford. He received multiple research awards and authored or co-authored numerous academic publications. With his experience in both the engineering and medical fields, he has particular interest in developing technological medical advancements.
Clinical Focus
- Urology
Honors & Awards
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First prize, Basic Science Research, Annual Fellow Essay Contest, Endourological Society (2020)
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AUA Best Video Award in Bladder Cancer and Urinary Diversion session, American Urological Association Annual Conference (2020)
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Best Basic Science Annual Research Award, Stanford Department of Urology (2018)
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AUA Best Video Award in Bladder Oncology and Diversion session, American Urological Association Annual Conference (2017)
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Winner of Miley B. Wesson Essay Contest, Western Section AUA (2017)
Professional Education
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Board Certification: American Board of Urology, Urology (2022)
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Residency: Stanford University Dept of General Surgery (2015) CA
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Residency: Stanford University Dept of Urology (2019) CA
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Fellowship: Stanford Hospital and Clinics - Dept of Urology (2020) CA
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Medical Education: Stanford University School of Medicine (2013) CA
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Fellowship, Stanford University Department of Urology, Endourology (2020)
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Residency, Stanford University Department of Urology (2019)
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Internship, Stanford University General Surgery (2014)
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S.M., Massachusetts Institute of Technology (2005)
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B.S.E., Princeton University (2002)
All Publications
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Evaluation of Patient Treatment Preferences for 15-20mm Kidney Stones: A Conjoint Analysis.
Journal of endourology
2020
Abstract
INTRODUCTION AND OBJECTIVE: Ureteroscopy (URS) and percutaneous nephrolithotomy (PCNL) are standard surgical treatments for intermediate-size (15-20mm) kidney stones but differ in their postoperative recovery, stone-free rates, and complication risks. We aimed to evaluate what affects patient treatment preferences.METHODS: Patients with urinary stone disease completed a choice-based conjoint analysis exercise assessing four treatment attributes associated with URS and PCNL. A sensitivity analysis using a market simulator was performed and the relative importance of each attribute was calculated. Differences in treatment preferences by demographic subgroup were assessed.RESULTS: A total of 58 patients completed the conjoint analysis exercise. Stone-free rate was the most important treatment attribute while length of hospital stay and cosmesis were less important. Overall, sensitivity analysis based on market simulation scenarios predicted almost equal preference for URS (52.4%) compared to PCNL (47.6%) for treatment of an intermediate-size stone. Older patients (>65 yo) expressed stronger preferences for lower infection rates and shorter hospital stays, and were more likely to prefer URS (67.2%, 95% CI: 52 - 82.5%) compared to younger patients (20-34 yo) (20.3%, 95% CI: 0 - 41.5%) who preferred higher procedure success rates and fewer repeat procedures.CONCLUSION: Conjoint analysis predicts nearly equal patient preference for URS or PCNL for the treatment of intermediate-size kidney stones. Older patients prefer the lower UTI risk and shorter hospital stay associated with URS, while younger patients prefer higher stone-free rates associated with PCNL. These results can help guide urologists in counseling patients and improve the shared decision-making process.
View details for DOI 10.1089/end.2020.0370
View details for PubMedID 32867549
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Ultra-low-dose CT: An Effective Follow-up Imaging Modality for Ureterolithiasis.
Journal of endourology
2019
Abstract
BACKGROUND AND PURPOSE: Classically, abdominal X-ray (KUB), ultrasound or a combination of both have been routinely used for ureteral stone surveillance after initial diagnosis. More recently, ultra-low-dose CT (ULD CT) has emerged as a CT technique that reduces radiation dose while maintaining high sensitivity and specificity for urinary stone detection. We aim to evaluate our initial experience with ULD CT for patients with ureterolithiasis, measuring real-world radiation doses and stone detection performance.METHODS: We reviewed all ULD CT scans performed at the Veterans Affairs Palo Alto Health Care System between 2016 and 2018. We included patients with ureteral stones and calculated the mean effective radiation dose per scan. We determined stone location and size, if the stone was visible on the associated KUB or CT scout film, and if hydronephrosis was present. We performed logistic regression to identify variables associated with visibility on KUB or CT scout film and hydronephrosis.RESULTS: One-hundred and eighteen ULD scans were reviewed, of which 50 detected ureteral stones. The mean effective radiation dose was 1.04 ± 0.41 mSv. Of the ULD CTs that detected ureterolithiasis, 38% lacked visibility on KUB/CT scout film and had no associated hydronephrosis, suggesting they would be missed with a combination of KUB and ultrasound. Larger stones (OR: 1.40, 95% CI: 1.08-1.96 for every 1mm increase in stone size) were more likely to be detected by KUB/CT scout or ultrasound, while stones in the distal ureter (OR: 0.18, 95% CI: 0.03-0.81) were more likely to be missed by KUB/CT scout or hydronephrosis.CONCLUSION: Based on our institutions' initial experience with ULD CT, ULD CT detects small and distal ureteral stones that would likely be missed by KUB or ultrasound, while maintaining a low effective radiation dose. An ULD CT protocol should be considered when re-imaging for ureteral stones is necessary.
View details for DOI 10.1089/end.2019.0574
View details for PubMedID 31663371
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Optical biopsy of penile cancer with in vivo confocal laser endomicroscopy.
Urologic oncology
2019
Abstract
Surgical management of penile cancer depends on accurate margin assessment and staging. Advanced optical imaging technologies may improve penile biopsy and organ-sparing treatment. We evaluated the feasibility of confocal laser endomicroscopy for intraoperative assessment of benign and malignant penile tissue.With institutional review board approval, 11 patients were recruited, 9 with suspected penile cancer, and 2 healthy controls. Confocal laser endomicroscopy using a 2.6-mm fiber-optic probe was performed at 1 or 2 procedures on all subjects, for 13 imaging procedures. Fluorescein was administered intravenously approximately 3 minutes prior to imaging for contrast. Video sequences from in vivo (n = 12) and ex vivo (n = 6) imaging were obtained of normal glans, suspicious lesions, and surgical margins. Images were processed, annotated, characterized, and correlated with standard hematoxylin and eosin histopathology.No adverse events related to imaging were reported. Distinguishing features of benign and malignant penile tissue could be identified by confocal laser endomicroscopy. Normal skin had cells of uniform size and shape, with distinct cytoplasmic membranes consistent with squamous epithelium. Malignant lesions were characterized by disorganized, crowded cells of various size and shape, lack of distinct cytoplasmic membranes, and hazy, moth-eaten appearance. The transition from normal to abnormal squamous epithelium could be identified.We report the initial feasibility of intraoperative confocal laser endomicroscopy for penile cancer optical biopsy. Pending further evaluation, confocal laser endomicroscopy could serve as an adjunct or replacement to conventional frozen section pathology for management of penile cancer.
View details for DOI 10.1016/j.urolonc.2019.08.018
View details for PubMedID 31537485
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Augmented Bladder Tumor Detection Using Deep Learning.
European urology
2019
Abstract
Adequate tumor detection is critical in complete transurethral resection of bladder tumor (TURBT) to reduce cancer recurrence, but up to 20% of bladder tumors are missed by standard white light cystoscopy. Deep learning augmented cystoscopy may improve tumor localization, intraoperative navigation, and surgical resection of bladder cancer. We aimed to develop a deep learning algorithm for augmented cystoscopic detection of bladder cancer. Patients undergoing cystoscopy/TURBT were recruited and white light videos were recorded. Video frames containing histologically confirmed papillary urothelial carcinoma were selected and manually annotated. We constructed CystoNet, an image analysis platform based on convolutional neural networks, for automated bladder tumor detection using a development dataset of 95 patients for algorithm training and five patients for testing. Diagnostic performance of CystoNet was validated prospectively in an additional 54 patients. In the validation dataset, per-frame sensitivity and specificity were 90.9% (95% confidence interval [CI], 90.3-91.6%) and 98.6% (95% CI, 98.5-98.8%), respectively. Per-tumor sensitivity was 90.9% (95% CI, 90.3-91.6%). CystoNet detected 39 of 41 papillary and three of three flat bladder cancers. With high sensitivity and specificity, CystoNet may improve the diagnostic yield of cystoscopy and efficacy of TURBT. PATIENT SUMMARY: Conventional cystoscopy has recognized shortcomings in bladder cancer detection, with implications for recurrence. Cystoscopy augmented with artificial intelligence may improve cancer detection and resection.
View details for DOI 10.1016/j.eururo.2019.08.032
View details for PubMedID 31537407
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Image-Guided Transurethral Resection of Bladder Tumors - Current Practice and Future Outlooks.
Bladder cancer (Amsterdam, Netherlands)
2017; 3 (3): 149–59
Abstract
Transurethral resection of bladder tumor (TURBT) under white light cystoscopy (WLC) is the cornerstone for the diagnosis, removal and local staging of non-muscle invasive bladder cancer (NMIBC). Despite technological improvements over the decades, significant shortcomings remain with WLC for tumor detection, thereby impacting the surgical quality and contributing to tumor recurrence and progression. Enhanced cystoscopy modalities such as blue light cystoscopy (BLC) and narrow band imaging (NBI) aid resections by highlighting tumors that might be missed on WLC. Optical biopsy technologies such as confocal laser endomicroscopy (CLE) and optical coherence tomography (OCT) characterize tissue in real-time to ensure a more thorough resection. New resection techniques, particularly en bloc resection, are actively under investigation to improve the overall quality of resections and aid pathologic interpretation. Moreover, new image processing computer algorithms may improve perioperative planning and longitudinal follow-up. Clinical translation of molecular imaging agents is also on the horizon to improve optical diagnosis of bladder cancer. This review focuses on emerging technologies that can impact the quality of TURBT to improve the overall management of NMIBC.
View details for PubMedID 28824942
View details for PubMedCentralID PMC5545914
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In vivo biodistribution and toxicity of intravesical administration of quantum dots for optical molecular imaging of bladder cancer.
Scientific reports
2017; 7 (1): 9309
Abstract
Optical molecular imaging holds the potential to improve cancer diagnosis. Fluorescent nanoparticles such as quantum dots (QD) offer superior optical characteristics compared to organic dyes, but their in vivo application is limited by potential toxicity from systemic administration. Topical administration provides an attractive route for targeted nanoparticles with the possibility of minimizing exposure and reduced dose. Previously, we demonstrated successful ex vivo endoscopic imaging of human bladder cancer by topical (i.e. intravesical) administration of QD-conjugated anti-CD47. Herein we investigate in vivo biodistribution and toxicity of intravesically instilled free QD and anti-CD47-QD in mice. In vivo biodistribution of anti-CD47-QD was assessed with inductively coupled plasma mass spectrometry. Local and systemic toxicity was assessed using blood tests, organ weights, and histology. On average, there was no significant accumulation of QD outside of the bladder, although in some mice we detected extravesical biodistribution of QD suggesting a route for systemic exposure under some conditions. There were no indications of acute toxicity up to 7 days after instillation. Intravesical administration of targeted nanoparticles can reduce systemic exposure, but for clinical use, nanoparticles with established biosafety profiles should be used to decrease long-term toxicity in cases where systemic exposure occurs.
View details for PubMedID 28839158
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Optical Biopsy of Bladder Cancer Using Crowd-Sourced Assessment.
JAMA surgery
2016; 151 (1): 90-93
View details for DOI 10.1001/jamasurg.2015.3121
View details for PubMedID 26422334
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Endoscopic molecular imaging of human bladder cancer using a CD47 antibody
SCIENCE TRANSLATIONAL MEDICINE
2014; 6 (260)
Abstract
A combination of optical imaging technologies with cancer-specific molecular imaging agents is a potentially powerful strategy to improve cancer detection and enable image-guided surgery. Bladder cancer is primarily managed endoscopically by white light cystoscopy with suboptimal diagnostic accuracy. Emerging optical imaging technologies hold great potential for improved diagnostic accuracy but lack imaging agents for molecular specificity. Using fluorescently labeled CD47 antibody (anti-CD47) as molecular imaging agent, we demonstrated consistent identification of bladder cancer with clinical grade fluorescence imaging systems, confocal endomicroscopy, and blue light cystoscopy in fresh surgically removed human bladders. With blue light cystoscopy, the sensitivity and specificity for CD47-targeted imaging were 82.9 and 90.5%, respectively. We detected variants of bladder cancers, which are diagnostic challenges, including carcinoma in situ, residual carcinoma in tumor resection bed, recurrent carcinoma following prior intravesical immunotherapy with Bacillus Calmette-Guérin (BCG), and excluded cancer from benign but suspicious-appearing mucosa. CD47-targeted molecular imaging could improve diagnosis and resection thoroughness for bladder cancer.
View details for DOI 10.1126/scitranslmed.3009457
View details for Web of Science ID 000343920500006
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Endoscopic molecular imaging of human bladder cancer using a CD47 antibody.
Science translational medicine
2014; 6 (260): 260ra148-?
Abstract
A combination of optical imaging technologies with cancer-specific molecular imaging agents is a potentially powerful strategy to improve cancer detection and enable image-guided surgery. Bladder cancer is primarily managed endoscopically by white light cystoscopy with suboptimal diagnostic accuracy. Emerging optical imaging technologies hold great potential for improved diagnostic accuracy but lack imaging agents for molecular specificity. Using fluorescently labeled CD47 antibody (anti-CD47) as molecular imaging agent, we demonstrated consistent identification of bladder cancer with clinical grade fluorescence imaging systems, confocal endomicroscopy, and blue light cystoscopy in fresh surgically removed human bladders. With blue light cystoscopy, the sensitivity and specificity for CD47-targeted imaging were 82.9 and 90.5%, respectively. We detected variants of bladder cancers, which are diagnostic challenges, including carcinoma in situ, residual carcinoma in tumor resection bed, recurrent carcinoma following prior intravesical immunotherapy with Bacillus Calmette-Guérin (BCG), and excluded cancer from benign but suspicious-appearing mucosa. CD47-targeted molecular imaging could improve diagnosis and resection thoroughness for bladder cancer.
View details for DOI 10.1126/scitranslmed.3009457
View details for PubMedID 25355698
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A small molecule p75(NTR) ligand prevents cognitive deficits and neurite degeneration in an Alzheimer's mouse model.
Neurobiology of aging
2013; 34 (8): 2052-2063
Abstract
The p75 neurotrophin receptor (p75(NTR)) is associated with multiple mechanisms linked to Alzheimer's disease (AD); hence, modulating its function might confer therapeutic effects. In previous in vitro work, we developed small molecule p75(NTR) ligands that inhibited amyloid-β-induced degenerative signaling and prevented neurite degeneration. In the present study, a prototype p75(NTR) ligand, LM11A-31, was administered orally to the Thy-1 hAPP(Lond/Swe) (APP(L/S)) AD mouse model. LM11A-31 reached brain concentrations known to inhibit degenerative signaling without toxicity or induction of hyperalgesia. It prevented deficits in novel object recognition after 2.5 months and, in a separate cohort, deficits in Y-maze performance after 3 months of treatment. Stereology studies found that the number and size of basal forebrain cholinergic neurons, which are normal in APP(L/S) mice, were unaffected. Neuritic dystrophy, however, was readily apparent in the basal forebrain, hippocampus and cortex, and was significantly reduced by LM11A-31, with no effect on amyloid levels. These studies reveal that p75(NTR) is an important and tractable in vivo drug target for AD, with LM11A-31 representing a novel class of therapeutic candidates.
View details for DOI 10.1016/j.neurobiolaging.2013.02.015
View details for PubMedID 23545424
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Interobserver agreement of confocal laser endomicroscopy for bladder cancer.
Journal of endourology
2013; 27 (5): 598-603
Abstract
Emerging optical imaging technologies such as confocal laser endomicroscopy (CLE) hold promise in improving bladder cancer diagnosis. The purpose of this study was to determine the interobserver agreement of image interpretation using CLE for bladder cancer.Experienced CLE urologists (n=2), novice CLE urologists (n=6), pathologists (n=4), and nonclinical researchers (n=5) were recruited to participate in a 2-hour computer-based training consisting of a teaching and validation set of intraoperative white light cystoscopy (WLC) and CLE video sequences from patients undergoing transurethral resection of bladder tumor. Interobserver agreement was determined using the κ statistic.Of the 31 bladder regions analyzed, 19 were cancer and 12 were benign. For cancer diagnosis, experienced CLE urologists had substantial agreement for both CLE and WLC+CLE (90%, κ 0.80) compared with moderate agreement for WLC alone (74%, κ 0.46), while novice CLE urologists had moderate agreement for CLE (77%, κ 0.55), WLC (78%, κ 0.54), and WLC+CLE (80%, κ 0.59). Pathologists had substantial agreement for CLE (81%, κ 0.61), and nonclinical researchers had moderate agreement (77%, κ 0.49) in cancer diagnosis. For cancer grading, experienced CLE urologists had fair to moderate agreement for CLE (68%, κ 0.64), WLC (74%, κ 0.67), and WLC+CLE (53%, κ 0.33), as did novice CLE urologists for CLE (53%, κ 0.39), WLC (66%, κ 0.50), and WLC+CLE (61%, κ 0.49). Pathologists (65%, κ 0.55) and nonclinical researchers (61%, κ 0.56) both had moderate agreement for CLE in cancer grading.CLE is an adoptable technology for cancer diagnosis in novice CLE observers after a short training with moderate interobserver agreement and diagnostic accuracy similar to WLC alone. Experienced CLE observers may be capable of achieving substantial levels of agreement for cancer diagnosis that is higher than with WLC alone.
View details for DOI 10.1089/end.2012.0549
View details for PubMedID 23072435
View details for PubMedCentralID PMC3643225
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Probe-based Confocal Laser Endomicroscopy of the Urinary Tract: The Technique
JOVE-JOURNAL OF VISUALIZED EXPERIMENTS
2013
Abstract
Probe-based confocal laser endomicroscopy (CLE) is an emerging optical imaging technology that enables real-time in vivo microscopy of mucosal surfaces during standard endoscopy. With applications currently in the respiratory and gastrointestinal tracts, CLE has also been explored in the urinary tract for bladder cancer diagnosis. Cellular morphology and tissue microarchitecture can be resolved with micron scale resolution in real time, in addition to dynamic imaging of the normal and pathological vasculature. The probe-based CLE system (Cellvizio, Mauna Kea Technologies, France) consists of a reusable fiberoptic imaging probe coupled to a 488 nm laser scanning unit. The imaging probe is inserted in the working channels of standard flexible and rigid endoscopes. An endoscope-based CLE system (Optiscan, Australia), in which the confocal endomicroscopy functionality is integrated onto the endoscope, is also used in the gastrointestinal tract. Given the larger scope diameter, however, application in the urinary tract is currently limited to ex vivo use. Confocal image acquisition is done through direct contact of the imaging probe with the target tissue and recorded as video sequences. As in the gastrointestinal tract, endomicroscopy of the urinary tract requires an exogenenous contrast agent-most commonly fluorescein, which can be administered intravenously or intravesically. Intravesical administration is a well-established method to introduce pharmacological agents locally with minimal systemic toxicity that is unique to the urinary tract. Fluorescein rapidly stains the extracellular matrix and has an established safety profile. Imaging probes of various diameters enable compatibility with different caliber endoscopes. To date, 1.4 and 2.6 mm probes have been evaluated with flexible and rigid cystoscopy. Recent availability of a < 1 mm imaging probe opens up the possibility of CLE in the upper urinary tract during ureteroscopy. Fluorescence cystoscopy (i.e. photodynamic diagnosis) and narrow band imaging are additional endoscope-based optical imaging modalities that can be combined with CLE to achieve multimodal imaging of the urinary tract. In the future, CLE may be coupled with molecular contrast agents such as fluorescently labeled peptides and antibodies for endoscopic imaging of disease processes with molecular specificity.
View details for DOI 10.3791/4409
View details for Web of Science ID 000209226200018
View details for PubMedCentralID PMC3582651
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Probe-based confocal laser endomicroscopy of the urinary tract: the technique.
Journal of visualized experiments : JoVE
2013: e4409-?
Abstract
Probe-based confocal laser endomicroscopy (CLE) is an emerging optical imaging technology that enables real-time in vivo microscopy of mucosal surfaces during standard endoscopy. With applications currently in the respiratory and gastrointestinal tracts, CLE has also been explored in the urinary tract for bladder cancer diagnosis. Cellular morphology and tissue microarchitecture can be resolved with micron scale resolution in real time, in addition to dynamic imaging of the normal and pathological vasculature. The probe-based CLE system (Cellvizio, Mauna Kea Technologies, France) consists of a reusable fiberoptic imaging probe coupled to a 488 nm laser scanning unit. The imaging probe is inserted in the working channels of standard flexible and rigid endoscopes. An endoscope-based CLE system (Optiscan, Australia), in which the confocal endomicroscopy functionality is integrated onto the endoscope, is also used in the gastrointestinal tract. Given the larger scope diameter, however, application in the urinary tract is currently limited to ex vivo use. Confocal image acquisition is done through direct contact of the imaging probe with the target tissue and recorded as video sequences. As in the gastrointestinal tract, endomicroscopy of the urinary tract requires an exogenenous contrast agent-most commonly fluorescein, which can be administered intravenously or intravesically. Intravesical administration is a well-established method to introduce pharmacological agents locally with minimal systemic toxicity that is unique to the urinary tract. Fluorescein rapidly stains the extracellular matrix and has an established safety profile. Imaging probes of various diameters enable compatibility with different caliber endoscopes. To date, 1.4 and 2.6 mm probes have been evaluated with flexible and rigid cystoscopy. Recent availability of a < 1 mm imaging probe opens up the possibility of CLE in the upper urinary tract during ureteroscopy. Fluorescence cystoscopy (i.e. photodynamic diagnosis) and narrow band imaging are additional endoscope-based optical imaging modalities that can be combined with CLE to achieve multimodal imaging of the urinary tract. In the future, CLE may be coupled with molecular contrast agents such as fluorescently labeled peptides and antibodies for endoscopic imaging of disease processes with molecular specificity.
View details for DOI 10.3791/4409
View details for PubMedID 23354133
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Molecular imaging of urothelial cancer using EGFR-binding peptides
AMER ASSOC CANCER RESEARCH. 2012
View details for DOI 10.1158/1538-7445.AM2012-4595
View details for Web of Science ID 000209701601273
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INTEROBSERVER AGREEMENT AND ACCURACY OF CONFOCAL LASER ENDOMICROSCOPY FOR IN VIVO DIAGNOSIS OF BLADDER CANCER
ELSEVIER SCIENCE INC. 2012: E716
View details for DOI 10.1016/j.juro.2012.02.1791
View details for Web of Science ID 000302912503070
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Next generation of optical diagnostics for bladder cancer using probe-based confocal laser endomicroscopy
Conference on Photonic Therapeutics and Diagnostics VIII
SPIE-INT SOC OPTICAL ENGINEERING. 2012
View details for DOI 10.1117/12.907623
View details for Web of Science ID 000302580900030
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Small Molecule, Non-Peptide p75(NTR) Ligands Inhibit A beta-Induced Neurodegeneration and Synaptic Impairment
PLOS ONE
2008; 3 (11)
Abstract
The p75 neurotrophin receptor (p75(NTR)) is expressed by neurons particularly vulnerable in Alzheimer's disease (AD). We tested the hypothesis that non-peptide, small molecule p75(NTR) ligands found to promote survival signaling might prevent Abeta-induced degeneration and synaptic dysfunction. These ligands inhibited Abeta-induced neuritic dystrophy, death of cultured neurons and Abeta-induced death of pyramidal neurons in hippocampal slice cultures. Moreover, ligands inhibited Abeta-induced activation of molecules involved in AD pathology including calpain/cdk5, GSK3beta and c-Jun, and tau phosphorylation, and prevented Abeta-induced inactivation of AKT and CREB. Finally, a p75(NTR) ligand blocked Abeta-induced hippocampal LTP impairment. These studies support an extensive intersection between p75(NTR) signaling and Abeta pathogenic mechanisms, and introduce a class of specific small molecule ligands with the unique ability to block multiple fundamental AD-related signaling pathways, reverse synaptic impairment and inhibit Abeta-induced neuronal dystrophy and death.
View details for DOI 10.1371/journal.pone.0003604
View details for Web of Science ID 000265134200003
View details for PubMedID 18978948
View details for PubMedCentralID PMC2575383