Browse Health
Radiologist
8 years of experience
Accepting new patients

Education ?

Medical School Score Rankings
Harvard University (2002)
  • Currently 4 of 4 apples
Top 25%

Awards & Distinctions ?

Associations
American Board of Radiology

Affiliations ?

Dr. Stewart is affiliated with 12 hospitals.

Hospital Affilations

Score

Rankings

  • U Mass Memorial Med Ctr - Memorial Campus
    119 Belmont St, Worcester, MA 01605
    • Currently 4 of 4 crosses
    Top 25%
  • NSMC - Salem Hospital
    81 Highland Ave, Salem, MA 01970
    • Currently 4 of 4 crosses
    Top 25%
  • Massachusetts General Hospital
    55 Fruit St, Boston, MA 02114
    • Currently 4 of 4 crosses
    Top 25%
  • Lowell General Hospital
    295 Varnum Ave, Lowell, MA 01854
    • Currently 3 of 4 crosses
    Top 50%
  • Caritas Norwood Hospital
    800 Washington St, Norwood, MA 02062
    • Currently 2 of 4 crosses
  • North Shore Medical Center - Union Hospital
    500 Lynnfield St, Lynn, MA 01904
    • Currently 2 of 4 crosses
  • Saints Memorial Medical Center Inc
    1 Hospital Dr, Lowell, MA 01852
    • Currently 2 of 4 crosses
  • Martha's Vineyard Hospital
    PO Box 1477, Oak Bluffs, MA 02557
    • Currently 1 of 4 crosses
  • North Shore Children's Hospital
    57 Highland Ave, Salem, MA 01970
  • Merrimack Valley MRI
  • North Shore Magnetic Imaging Center
  • U-Mass Memorial Medical Center
  • Publications & Research

    Dr. Stewart has contributed to 11 publications.
    Title Multimodality Imaging of Peripheral Neuropathies of the Upper Limb and Brachial Plexus.
    Date January 2011
    Journal Radiographics : a Review Publication of the Radiological Society of North America, Inc
    Excerpt

    The peripheral nerves of the upper limb are affected by a number of entrapment and compression neuropathies. These discrete syndromes involve the brachial plexus as well as the musculocutaneous, axillary, suprascapular, ulnar, radial, and median nerves. Clinical examination and electrophysiologic studies are the traditional mainstay of diagnostic work-up; however, ultrasonography and magnetic resonance imaging provide spatial information regarding the affected nerve and its surroundings, often assisting in narrowing the differential diagnosis and guiding treatment. Imaging is particularly valuable in complex cases with discrepant nerve function test results. Familiarity with the clinical features of various peripheral neuropathies of the upper extremity, the relevant anatomy, and the most common sites and causes of nerve entrapment assists in diagnosis and treatment.

    Title Imaging and Percutaneous Treatment of Secondarily Infected Hepatic Infarctions.
    Date April 2008
    Journal Ajr. American Journal of Roentgenology
    Excerpt

    OBJECTIVE: The objective of our study was to describe the imaging features and success rate of percutaneously treated infected hepatic infarctions. MATERIALS AND METHODS: Three hundred ninety-two patients had percutaneous liver abscess aspiration and drainage or aspiration and intraoperative d├ębridement at our institution between 1990 and 2003. One hundred fifty-one of these patients underwent CT at least 2 days before the drainage procedure and immediately before the procedure. Retrospective review of the imaging and medical records identified 13 patients with microbiologically documented liver abscesses who had liver lesions consistent with hepatic infarction on the baseline CT. RESULTS: Twenty-one hepatic infarctions in 13 patients were documented on baseline CT, 15 of which became secondarily infected. Ten of 15 patients with infected infarctions had undergone either hepatic transplantation or the Whipple procedure. Although the left lobe was slightly more commonly infarcted than the right lobe (54% vs 46%, respectively), right lobe infarctions were more commonly superinfected than left lobe infarctions (61% vs 39%); however, neither of these distinctions was statistically significant. Twelve of 13 patients underwent percutaneous drainage. The duration of catheter drainage was significantly longer in patients in whom catheter drainage was complicated by biliary communication than those without biliary communication (61 vs 19 days, respectively). Eleven of 12 patients (92%) responded to drainage such that they survived to discharge from the hospital. CONCLUSION: Patients with hepatic infarctions are at risk for secondary infection, particularly those patients having undergone surgery involving the porta hepatis. Percutaneous abscess drainage can be performed safely with excellent technical and clinical outcomes in this complex patient population.

    Title Is the Screening Portable Pelvis Film Clinically Useful in Multiple Trauma Patients Who Will Be Examined by Abdominopelvic Ct? Experience with 397 Patients.
    Date February 2005
    Journal Emergency Radiology
    Excerpt

    The multiple trauma patient is usually initially imaged with a portable "trauma series" consisting of a lateral cervical spine film, a portable chest film, and a portable pelvis film (PPF). An investigation was performed to determine whether the screening PPF could be eliminated for multiple trauma patients being examined by abdominopelvic CT scan (APCT). A retrospective investigation analyzed all patients evaluated in our level I trauma center from 1 January to 31 December 2000 who were examined with a "trauma series" followed by an APCT scan within 8 h. The numbers and types of fractures diagnosed by PPF and by APCT were compared and correlated with clinical follow-up. Of 397 patients imaged by both PPF and APCT, 43 patients were diagnosed with 109 individual fractures by CT scan. The PPF did not detect 51 of the 109 individual fractures (47%) and failed to diagnose 9 of the 43 patients (21%) with a pelvic fracture. The PPF most often failed to detect sacral and iliac fractures. The four cases in which the PPF reported a fracture not listed in the APCT report were due to reporting errors or film artifacts. No soft tissue injuries were seen by PPF that were not also seen by APCT. We conclude that the screening PPF appears to be an unnecessary exam in multiple trauma patients about to be imaged by APCT scan.

    Title Body-weight-support Treadmill Training Improves Blood Glucose Regulation in Persons with Incomplete Spinal Cord Injury.
    Date January 2005
    Journal Journal of Applied Physiology (bethesda, Md. : 1985)
    Excerpt

    The impact of a 6-mo body-weight-supported treadmill training program on glucose homeostasis and muscle metabolic characteristics was investigated. Nine individuals (31 +/- 3 yr, 8.1 +/- 2.5 yr postinjury; means +/- SE) with incomplete spinal cord injury trained three times weekly for a total of 6 mo. Training session duration and intensity (velocity) increased by 54 +/- 10% (P < 0.01) and 135 +/- 20%, respectively. Muscle biopsies and a modified glucose tolerance test (100 g glucose with [U-(13)C]glucose) were performed before (Pre) and after training (Post). Training resulted in a reduction in area under the curve of glucose x time (-15 +/- 4%) and insulin x time (-33 +/- 8%; both P < 0.05). Oxidation of exogenous (ingested) glucose increased as a result of training (Pre = 4.4 +/- 0.7 g/h, Post = 7.4 +/- 0.6 g/h; P < 0.05), as did oxidation of endogenous (liver) glucose (Pre = 3.8 +/- 0.3 g/h, Post = 5.2 +/- 0.3 g/h; P < 0.05). Training resulted in increased muscle glycogen (80 +/- 23%; P < 0.05) and GLUT-4 content and hexokinase II enzyme activity (126 +/- 34 and 49 +/- 4%, respectively, both P < 0.01). Resting muscle phosphocreatine content also increased after training (Pre = 62.1 +/- 4.3, Post = 78.7 +/- 3.8, both mmol/kg dry wt and P < 0.05). Six months of thrice-weekly body-weight-supported treadmill training in persons with an incomplete spinal cord injury improved blood glucose regulation by increasing oxidation and storage of an oral glucose load. Increases in the capacity for transport and phosphorylation glucose in skeletal muscle likely play a role in these adaptations.

    Title Treadmill Training-induced Adaptations in Muscle Phenotype in Persons with Incomplete Spinal Cord Injury.
    Date August 2004
    Journal Muscle & Nerve
    Excerpt

    Body weight-supported treadmill (BWST) training has been shown to improve ambulatory capacity in persons with a spinal cord injury (SCI); however, the effect that BWST training has on skeletal muscle phenotype is unknown. We aimed to determine whether 6 months (three sessions/week) of BWST training in neurologically stable persons with a traumatic spinal cord injury (ASIA C) alters skeletal muscle phenotype, ambulatory capacity, and blood lipid profile. Externally supported body weight decreased, and walking velocity and duration of the training sessions increased (all P < 0.05) as a result of training. Muscle biopsies revealed increases in the mean muscle-fiber area of type I and IIa fibers. Training induced a reduction in type IIax/IIx fibers, as well as a decrease in IIX myosin heavy chain, and an increase in type IIa fibers. Maximal citrate synthase and 3-hydroxy-acyl-CoA dehydrogenase activity also increased following training. BWST training brought about reductions in plasma total (-11%) and low-density lipoprotein (-13%) cholesterol. We conclude that, in patients with a spinal cord injury, BWST training is able to induce an increase in muscle fiber size and bring about increases in muscle oxidative capacity. In addition, BWST training can bring about improvements in ambulatory capacity and antiatherogenic changes in blood lipid profile.

    Title Bcl-2 Expression Decreases Cadherin-mediated Cell-cell Adhesion.
    Date May 2004
    Journal Journal of Cell Science
    Excerpt

    Bcl-2, a member of the apoptosis-regulating family of proteins confers a survival advantage on cells by inhibiting apoptosis. Bcl-2 expression is estrogen-responsive and high in various tumors. Overexpression of Bcl-2 has been associated with the loss of contact inhibition, unregulated growth and foci formation in culture. In this study, we have examined the effects of bcl-2 overexpression and expression on cell-cell adhesion in MCF-7 and MDCK epithelial cell lines respectively. Overexpression of Bcl-2 in estrogen receptor-positive MCF-7 mammary carcinoma cells led to decreased cell surface E-cadherin and the disruption of junctional complexes concurrent with intracellular redistribution of their components. Particularly noticeable, was the partial nuclear localization of the tight junction-associated protein ZO-1 which coincided with upregulation of ErbB2. The expression of this EGF co-receptor is regulated by the ZO-1-associated transcription factor ZONAB. Growth in estrogen-depleted media led to downregulation of Bcl-2 expression and upregulation and membrane localization of all junctional proteins. Similar disruption in junctions, accompanied by decreased transepithelial resistance, was observed when Bcl-2 was expressed in MDCK cells. These results strongly suggest that Bcl-2 expression decreases the level of functional E-cadherin thereby interfering with junction formation. The inhibition of junction formation decreases cell-cell adhesion leading to the loss of contact inhibition, which, in vivo, can lead to unregulated growth and tumorigenesis.

    Title Potentiating the Benefit of Vascular-supplied Glutamine During Small Bowel Storage: Importance of Buffering Agent.
    Date February 2002
    Journal Transplantation
    Excerpt

    BACKGROUND: Glutamine (gln)-supplemented University of Wisconsin (UW) solution improves overall small bowel (SB) preservation. Sustained gln metabolism in a system devoid of hepatic detoxification will necessarily result in the accumulation of pH active end products leading to nonphysiologic pH shifts. We hypothesized that simultaneous addition of N,N-bis[2-hydroxyethyl]-2-aminoethane sulfonic acid (BES), a known buffering agent, would potentiate the beneficial effect of gln supplementation by addressing the fundamental metabolic principle of pH homeostasis. METHODS: Sprague-Dawley SB rats were administered a vascular flush with one of four solutions: UW; UW+90 mM BES (UWB); UW+2% gln (UWG); or UW+2% gln+90 mM BES (UWBG). Indices of energetics, barrier function, gln catabolism, and histology (light and electron microscopy) were assessed over a 10-hr cold storage time course. RESULTS: Superior gln utilization in the UWBG group was indicated by elevated levels of key catabolites (glutamate, aspartate, glycine, ammonia). The addition of BES and gln resulted in significantly higher levels of all energetic parameters (ATP, total adenylates) at 10 hr compared with UW, UWB, and/or UWG. Barrier function was markedly improved after 10 hr storage in the UWBG group; mannitol permeability was 169 nmol/cm2/hr versus 572 and 445 nmol/cm(2)/hr (for UW and UWG, respectively). Histologic injury at 10 hr was 5.5, 7.5, and 8 (Park's grade) for UWBG, UWG, and UW. Ultrastructural damage was markedly reduced with UWBG, as assessed by grade of mitochondria damage. CONCLUSION: This study strongly supports that the beneficial effects of gln-enriched UW solution can be amplified when combined with an effective buffering agent such as BES.

    Title Directed Evolution of Toluene Dioxygenase from Pseudomonas Putida for Improved Selectivity Toward Cis-indandiol During Indene Bioconversion.
    Date February 2001
    Journal Metabolic Engineering
    Excerpt

    Toluene dioxygenase (TDO) from Pseudomonas putida F1 converts indene to a mixture of cis-indandiol (racemic), 1-indenol, and 1-indanone. The desired product, cis-(1S,2R)-indandiol, is a potential key intermediate in the chemical synthesis of indinavir sulfate (Crixivan), Merck's HIV-1 protease inhibitor for the treatment of AIDS. To reduce the undesirable byproducts 1-indenol and 1-indanone formed during indene bioconversion, the recombinant TDO expressed in Escherichia coli was evolved by directed evolution using the error-prone polymerase chain reaction (epPCR) method. High-throughput fluorometric and spectrophotometric assays were developed for rapid screening of the mutant libraries in a 96-well format. Mutants with reduced 1-indenol by-product formation were identified, and the individual indene bioconversion product profiles of the selected mutants were confirmed by HPLC. Changes in the amino acid sequence of the mutant enzymes were identified by analyzing the nucleotide sequence of the genes. A mutant with the most desirable product profile from each library, defined as the most reduced 1-indenol concentration and with the highest cis-(1S,2R)-indandiol enantiomeric excess, was used to perform each subsequent round of mutagenesis. After three rounds of mutagenesis and screening, mutant 1C4-3G was identified to have a threefold reduction in 1-indenol formation over the wild type (20% vs 60% of total products) and a 40% increase of product (cis-indandiol) yield.

    Title The Two Forms of Karyogamy Transcription Factor Kar4p Are Regulated by Differential Initiation of Transcription, Translation, and Protein Turnover.
    Date February 1999
    Journal Molecular and Cellular Biology
    Excerpt

    Kar4p is a transcription factor in Saccharomyces cerevisiae that is required for the expression of karyogamy-specific genes during mating, for the efficient transit from G1 during mitosis, and for essential functions during meiosis. Kar4p exists in two forms: a constitutive slower-migrating form, which predominates during vegetative growth, and a faster-migrating form, which is highly induced by mating pheromone. Transcript mapping of KAR4 revealed that the constitutive mRNA was initiated upstream of two in-frame ATG initiation codons, while the major inducible mRNA originated between them. Thus, the two forms of Kar4p are derived from the translation of alternative transcripts, which possess different AUG initiation codons. Site-directed mutations were constructed to inactivate one or the other of the initiation codons, allowing the expression of the two Kar4p forms separately. At normal levels of expression, the constitutive form of Kar4p did not support wild-type levels of mating. However, the two forms of Kar4p could also be expressed separately from the regulatable GAL1 promoter, and no functional difference was detected when they were expressed at equivalent levels. Pulse-chase experiments showed that the induced form of Kar4p was highly expressed and stable during mating but rapidly turned over in vegetative cells. In contrast, the constitutively expressed longer form showed the same rate of turnover regardless of the growth condition. Furthermore, overexpression of either form of Kar4p in vegetative cells was toxic. Thus, the elaborate regulation of the two forms of Kar4p at the levels of transcription, translation, and protein turnover reflects the requirement for high levels of the protein during mating and for low levels during the subsequent phases of the cell cycle.

    Title Kar4p, a Karyogamy-specific Component of the Yeast Pheromone Response Pathway.
    Date September 1996
    Journal Molecular and Cellular Biology
    Excerpt

    Karyogamy is the process whereby two haploid nuclei fuse to form a diploid nucleus during mating in Saccharomyces cerevisiae. Here, we describe the characterization of the KAR4 gene, previously identified in a screen for new nuclear fusion-defective mutants. During mating, kar4 mutants were defective for the microtubule-dependent movement of nuclei, a phenotype identical to that of mutations in KAR3 and CIK1. Consistent with its mutant phenotype, we found that the kar4 mutation resulted in failure to induce KAR3 and CIK1 mRNA during mating. Expression of KAR3 and CIK1 under independent regulatory control suppressed the kar4 defect, indicating that KAR4 is required primarily for the induction of KAR3 and CIK1. KAR4 was also required for meiosis, during which it may regulate KAR3; however, mitotic expression of KAR3 and CIK1 during S/G2 phase was independent of KAR4. A 30-bp region upstream of KAR3 conferred both KAR4- and STE12-dependent induction by mating pheromone. This region contained one moderate and two weak matches to the consensus pheromone response element to which the Ste12p transcriptional activator binds and five repeats of the sequence CAAA(A). Overproduction of Ste12p suppressed the kar4 defect in KAR3 induction and nuclear fusion. In contrast, Ste12p-independent expression of Kar4p did not alleviate the requirement for Ste12p during KAR3 induction. We propose that Kar4p assists Ste12p in the pheromone-dependent expression of KAR3 and CIK1. KAR4 defines a novel level of regulation for the pheromone response pathway, acting at a subset of Stel2p-inducible genes required for karyogamy.

    Title "respite." Paper Given at National Multiple Sclerosis Society; Sydney, 13-15 October 1978.
    Date April 1979
    Journal The Australasian Nurses Journal

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