Charles Hyde

Clinical correlates of high-intensity transient signals detected on transcranial Doppler sonography in patients with cerebrovascular disease.

Background and Purpose High-intensity transient signals detected by transcranial Doppler sonography have been associated with particulate cerebral emboli. Their clinical correlates are poorly understood. This study was undertaken to assess their relation to cerebral ischemia and to determine whether the severity of cerebral arterial stenosis has an impact on their occurrence. Methods We studied 96 arteries in 75 consecutive patients with extracranial or intracranial arterial lesions or potential cardiac sources of cerebral embolism. Sixty patients had histories of cerebral or retinal transient ischemic attacks or infarcts, and 15 were asymptomatic. The diagnosis of ischemia was based on the clinical presentation and was supported by extensive laboratory testing. A transcranial Doppler sonography unit equipped with special software for emboli detection was used. Signals were selected based on criteria established a priori. Results Signals were detected in the territories of 28.3% of symptomatic and 11.6% of asymptomatic arteries. The difference was significant (P=.045). When patients with suspected cardiac embolic sources were excluded, the difference between symptomatic (27.9%) and asymptomatic (2.9%) arteries remained significant (P=.003), and signals were more frequent distal to arteries with more than 50% area stenosis (23.5%) than arteries with stenoses equal to or less than 50% (3.7%) (P=.028). In patients with only extracranial internal carotid artery stenoses, the difference between these degrees of stenosis remained significant (P=.043). Conclusions We conclude that high-intensity transient signals are significantly more common in the territories of symptomatic arteries and distal to lesions causing more than 50% stenosis. These findings may have diagnostic and therapeutic applications.

Cerebral Microembolism and Early Recurrent Cerebral or Retinal Ischemic Events

BACKGROUND AND PURPOSE We investigated whether cerebral microembolism as detected by transcranial Doppler ultrasonography (TCD) identifies patients at an increased risk for early, recurrent cerebral or retinal ischemic events. METHODS Records of consecutive patients examined during a 40-month period in the Neurovascular Laboratory were reviewed for the presence of cerebral microembolism. Of the original 302 patients, 229 with 310 arteries met inclusionary criteria. Follow-up information was obtained from the laboratorys database as well as the hospital records. Microembolus detection studies were performed on TC-2000 or TC-2020 instruments equipped with special software, and criteria established a priori were used for microembolus selection. TCD testing was performed a median interval of 9 days after the initial symptoms of cerebral ischemia. Severity of arterial stenosis was determined by cerebral angiography or noninvasive methods. RESULTS Microembolic signals were detected more frequently in symptomatic (40/140; 28.6%) than asymptomatic (21/170; 12.4%) arteries (P < .001). Ten recurrent ischemic events occurred during a median follow-up of 8 days after TCD examination, all in the territories of symptomatic arteries. Nine events occurred in the territories of microembolic signal positive arteries (9/61; 14.8%) and one in the territory of a microembolic signal-negative artery (1/249; 0.4%) (P < .00). No association was detected in the subgroup with known cardiac lesions. Microembolic signals were more frequent in arteries with lesions causing 70% or more stenosis or occlusion (26/99; 26.3%) than in those with a degree of stenosis less than 70% (17/126; 13.5%) (P = .016). CONCLUSIONS In this retrospective study, microembolic signals were more common in the territories of symptomatic arteries and particularly those with severely stenotic lesions. During a short follow-up, recurrent ischemic events were more common along the territories of arteries with TCD-detected microembolism and previous symptoms of cerebral or retinal ischemia.

Effect of Time and Cerebrovascular Symptoms on the Prevalence of Microembolic Signals in Patients With Cervical Carotid Stenosis

BACKGROUND AND PURPOSE High-intensity transient signals (HITS) detect ed by transcranial Doppler ultrasonography correspond to microemboli in intracranial arteries. The aim of this study was to determine the time course of cerebral microembolism in patients with symptomatic internal carotid artery stenosis and to assess its relation to specific symptoms of cerebral ischemia. METHODS On the basis of criteria established a priori, 69 middle cerebral arteries were selected from a series of consecutive studies obtained at our neurovascular laboratory. All patients had radiological evidence of cervical internal carotid artery disease and had corresponding symptoms. A TC-2000 instrument equipped with special software for microembolus detection was used. Accepted signals were unidirectional from baseline, had a chirping sound, were 9 dB higher than the surrounding blood, and lasted 25 milliseconds or more. RESULTS HITS were identified in 20 of 69 (29%) arteries. The median interval between onset of symptoms and time of testing was 4 days for HITS-positive arteries and 12 days for those that were HITS negative (P=.0046). Fourteen of 32 (44%) arteries with transient ischemic attacks and 6 of 37 (16%) arteries with cerebral infarction were HITS positive (P=.012). CONCLUSIONS In patients with symptomatic carotid stenosis, HITS are detected more frequently when patients are tested soon after symptoms of cerebral ischemia. HITS are also more prevalent in the territories of arteries with transient ischemic attacks rather than cerebral infarction. These findings may have diagnostic and therapeutic implications.

Cerebral Microembolism in Patients With Retinal Ischemia

BACKGROUND AND PURPOSE We investigated the frequency of cerebral microembolism detected by transcranial Doppler ultrasonography in patients with clinical evidence of retinal ischemia, including transient monocular blindness, central and branch retinal artery infarction, and ischemic oculopathy, and assessed its correlation with carotid artery stenosis. METHODS Records of 331 consecutive patients examined during a 47-month period at the Neurovascular Laboratory were reviewed. Of the original 453 intracranial arteries, 186 middle cerebral arteries (MCAs) satisfied qualifying criteria that excluded patients with cardiac embolic sources. Forty-five MCAs ipsilateral to the symptomatic eye constituted the study group. The control group consisted of 141 asymptomatic MCAs. Microembolus detection studies were performed on transcranial Doppler instruments equipped with special software, and the degree of carotid artery stenosis was measured by cerebral or MR angiography or by color duplex studies. RESULTS Microembolism was detected in 40.0% of study MCAs and 9.2% of controls (P < 0.001). In the study group, microembolic signals were detected in 61.9% of MCAs tested within a week of symptom onset and 20.8% of those tested afterward (P < 0.001). Severe (> or = 70%) carotid stenosis or occlusion was more frequent in the study group (P < 0.001). Microembolic signals were detected in 25.3% and 11.2%, respectively, of MCAs distal to carotid arteries with 70% to 100% and 0% to 69% stenosis (P = 0.013). CONCLUSIONS In patients without cardiac embolic sources, cerebral microembolism is frequently present on the side of retinal ischemia, particularly during the week after onset of symptoms. It is often associated with severe stenosis or occlusion of the ipsilateral carotid artery.

General competencies in radiology residency training: definitions, skills, education and assessment.

The Accreditation Council for Graduate Medical Education (ACGME) Outcome Project is a long-term initiative by which the ACGME is increasing emphasis on educational outcomes in the accreditation of residency education programs (http://www.acgme.org). The impetus for this project is a system of medical education that relies heavily on public funding and is therefore accountable to the public to meet public needs and prepare well-qualified new physicians as cost effectively as possible. The current model of accreditation focuses on the potential of a residency program to educate residents (ie, whether the program complies with the requirements, has established objectives and an organized curriculum, and evaluates the residents and itself). Examining structure and process, however, is not a direct way to measure the quality of a program’s educational outcomes. In future, accreditation will focus on a program’s actual accomplishments, through assessment of program outcomes (ie, whether residents achieve the stated learning objectives, whether the program provides evidence of this achievement, and whether it demonstrates continuous improvement in its educational process). The ACGME Outcome Project Advisory Committee identified six general competencies that were subsequently endorsed by the ACGME in February 1999: patient care, medical knowledge, practice-based learning and improvement, interpersonal and communication skills, professionalism, and systems-based practice. By July 2002 all Residency Review Committees (RRCs) must include minimum language regarding the general competencies and evaluation processes in their respective program requirements. A major activity of the Outcome Project was the identification and development of measurement tools for programs to use as part of an overall evaluation system. The ACGME and the American Board of Medical Specialties (ABMS) collaborated on developing a “Toolbox of Assessment Methods” (version 1.1, September 2000; ACGME/ABMS; http://www.acgme.org/outcome/assess /toolbox.asp). The Toolbox includes descriptions of instruments recommended for use by programs assessing the outcomes of their educational efforts, as well as information pertaining to the use, the psychometric qualities, and the feasibility and practicality of different assessment methods. A radiology “quadrad,” made up of representatives from the radiology RRC (including a resident member of the RRC), the American Board of Radiology (ABR), and the Association of Program Directors in Radiology (APDR), was formed in the spring of 2000 to interpret the six competencies as they relate to radiology. The Acad Radiol 2002; 9:721–726

The significance of early postoperative duplex studies following carotid endarterectomy

This study was conducted to evaluate the significance of duplex ultrasound performed soon after carotid endarterectomy. The records of patients with 150 carotid endarterectomies and postoperative duplex ultrasound within 24 h were reviewed. Eleven (7.3%) had abnormal studies with > or =50% stenosis. Two patients with abnormal studies sustained a perioperative stroke and three patients underwent reoperation for persistent lesions (P<0.0001). Preoperative and postoperative cerebral imaging studies (computed tomography (CT) or magnetic resonance imaging (MRI)) were performed on 114 patients. Seven of these demonstrated areas of infarction and all seven had abnormal duplex ultrasound studies. Twenty-six CT scans were performed with two positive for cerebral infarction in the two patients with clinical stroke. In the 88 MRI studies, five demonstrated small, subcortical focal areas of ischemia, which were clinically silent. The relationship of infarction on postoperative cerebral studies and abnormal postoperative duplex ultrasound was significant (P<0.0001). It was concluded that early postoperative duplex ultrasound studies of > or =50% stenosis demonstrate significant association with postoperative stroke or reoperation, as well as with ischemic changes on brain imaging studies. Earlier detection with intraoperative duplex would probably be more advantageous than postoperative duplex ultrasound.

The adoption of coke-smelting by the British iron industry, 1709–1790

The application of coal to the production of pig iron was one of the important innovations af the British Industrial Revolution of the eighteenth century. Coal (in the form of coke) was first used to make pig iron at the Coalbrookdale furnace of Abraham Darby around 1709 and was in continuous use there after that date.’ Other ironmasters did not adopt the new technique until the early 1750s and actually increased their charcoal-smeiting capacity in the interim, constructing at least twenty-two new charcoal furnaces during the period 1720-1755.2 The standard interpretation of the iron industry’s failure to adopt coke-smelting before mid-century was first advanced by T. S. Ashton in his classic history of the iron industry3 and has gone largely unchallenged by other scholars.4 Ashton argued that the technical limitations of coke-smelting, particularly the poor quality of the product, prevented its adoption for nearly a haIf-century.’

The adoption of the hot blast by the British iron industry: A reinterpretation

The use of a heated blast of air in the furnace, patented by James Beaumont Neilson in 1828, is commonly recognized as one of the key innovations in ironmaking made in the nineteenth century. Economic historians, however, have largely misunderstood the economic impact of the hot blast on the Scottish iron industry, as well as the subsequent adoption of the new technique in the other ironmaking districts of Britain. This article will reassess the traditional interpretation of the impact of the hot blast on the British iron industry.

Technological Change and the British Iron Industry, 1700-1870.

The Description for this book, Technological Change and the British Iron Industry, 1700-1870, will be forthcoming.