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L Santiago Medina

Publications and source records attributed to L Santiago Medina.

At least 19 recordsLinked to original sources
PubMed2007

Role of functional MR in determining language dominance in epilepsy and nonepilepsy populations: a Bayesian analysis.

PURPOSE: To determine the role of functional magnetic resonance (MR) imaging in assessing hemispheric language dominance in epilepsy and nonepilepsy populations. MATERIALS AND METHODS: A Bayesian analysis study was performed. The study was based on data from the published literature; thus, institutional review board approval was not required. The literature was reviewed to obtain pretest probabilities and likelihood ratios, which were analyzed to determine the posttest probability of language dominance by using functional MR imaging. Pretest probabilities of different hand dominances in epilepsy and nonepilepsy populations were obtained from the largest studies available in the literature. Likelihood ratios were derived from the sensitivity and specificity of functional MR imaging by using electrocortical stimulation (ECS) and the Wada test as reference standards. RESULTS: Likelihood ratios for functional MR in determining language dominance were 9.3 and 12.3 with ECS and the Wada test as reference standards, respectively. Use of functional MR increased the final posttest probabilities of hemispheric language dominance in epilepsy and nonepilepsy populations. In the nonepilepsy population, regardless of hand dominance, there was very high posttest probability (>or=96%) of a correlation between functional MR hemisphere activation and definite left-hemisphere language dominance. In the epilepsy population with right-hand dominance or ambidexterity, there was very high posttest probability (>or=95%) of a correlation between functional MR hemisphere activation and definite left-hemisphere language dominance. In the left-handed nonepileptic subjects, there was high posttest probability (81%-83%) of a correlation between functional MR hemisphere activation and definite right-hemisphere language dominance. In the left-handed epilepsy population, there was high posttest probability (80%-97%) of a correlation between functional MR hemisphere activation and definite left-hemisphere language dominance. In the epilepsy population with ambidexterity, there was high posttest probability (80%-87%) of correlations between functional MR hemisphere activation and both definite right-hemisphere and bilateral language dominance. CONCLUSION: Use of functional MR increases importantly the posttest probabilities of hemispheric language dominance in multiple subgroups of individuals with and without epilepsy.

Bayes Theorem↗
PubMed2006

Diagnostic performance of MRI and MR myelography in infants with a brachial plexus birth injury.

BACKGROUND: Detailed evaluation of a brachial plexus birth injury is important for treatment planning. OBJECTIVE: To determine the diagnostic performance of MRI and MR myelography in infants with a brachial plexus birth injury. MATERIALS AND METHODS: Included in the study were 31 children with perinatal brachial plexus injury who underwent surgical intervention. All patients had cervical and brachial plexus MRI. The standard of reference was the combination of intraoperative (1) surgical evaluation and (2) electrophysiological studies (motor evoked potentials, MEP, and somatosensory evoked potentials, SSEP), and (3) the evaluation of histopathological neuronal loss. MRI findings of cord lesion, pseudomeningocele, and post-traumatic neuroma were correlated with the standard of reference. Diagnostic performance characteristics including sensitivity and specificity were determined. RESULTS: From June 2001 to March 2004, 31 children (mean age 7.3 months, standard deviation 1.6 months, range 4.8-12.1 months; 19 male, 12 female) with a brachial plexus birth injury who underwent surgical intervention were enrolled. Sensitivity and specificity of an MRI finding of post-traumatic neuroma were 97% (30/31) and 100% (31/31), respectively, using the contralateral normal brachial plexus as the control. However, MRI could not determine the exact anatomic area (i.e. trunk or division) of the post-traumatic brachial plexus neuroma injury. Sensitivity and specificity for an MRI finding of pseudomeningocele in determining exiting nerve injury were 50% and 100%, respectively, using MEP, and 44% and 80%, respectively, using SSEP as the standard of reference. MRI in infants could not image well the exiting nerve roots to determine consistently the presence or absence of definite avulsion. CONCLUSION: In children younger than 18 months with brachial plexus injury, the MRI finding of pseudomeningocele has a low sensitivity and a high specificity for nerve root avulsion. MRI and MR myelography cannot image well the exiting nerve roots to determine consistently the presence or absence of avulsion of nerve roots. The MRI finding of post-traumatic neuroma has a high sensitivity and specificity in determining the side of the brachial plexus injury but cannot reveal the exact anatomic area (i.e. trunk or division) involved. The information obtained is, however, useful to the surgeon during intraoperative evaluation of spinal nerve integrity for reconstruction.

Birth Injuries↗
PubMed2006

Interrater reliability in assessing quality of diagnostic accuracy studies using the QUADAS tool. A preliminary assessment.

RATIONALE AND OBJECTIVES: Quality Assessment of Diagnostic Accuracy Studies (QUADAS) is a new tool to measure the methodological quality of diagnostic accuracy studies in systematic reviews. We used data from a systematic review of magnetic resonance spectroscopy (MRS) in the characterization of suspected brain tumors to provide a preliminary evaluation of the inter-rater reliability of QUADAS. MATERIALS AND METHODS: A structured literature search identified 19 diagnostic accuracy studies. These publications were distributed randomly to primary and secondary reviewers for dual independent assessment. Reviewers recorded methodological quality by using QUADAS on a custom-designed spreadsheet. We calculated correlation, percentage of agreement, and kappa statistic to assess inter-rater reliability. RESULTS: Most studies in our review were judged to have used an accurate reference standard. Conversely, the MRS literature frequently failed to specify the length of time between index and reference tests or that the clinicians were unaware of the index test findings when reporting the reference standard. There was good correlation (rho = 0.78) between reviewers in assessment of the overall number of quality criteria met. However, mean agreement for individual QUADAS questions was only fair (kappa = 0.22) and ranged from no agreement beyond chance (kappa < 0) to moderate agreement (kappa = 0.58). CONCLUSION: Inter-rater reliability in our study was relatively low. Nevertheless, we believe that QUADAS potentially is a useful tool for highlighting the strengths and weaknesses of existing diagnostic accuracy studies. Low reliability suggests that different reviewers will reach different conclusions if QUADAS is used to exclude "low-quality" articles from meta-analyses. We discuss methods for improving the validity and reliability of QUADAS.

Brain Neoplasms↗
PubMed2005

Seizure disorders: functional MR imaging for diagnostic evaluation and surgical treatment--prospective study.

PURPOSE: To prospectively evaluate effect of functional magnetic resonance (MR) imaging on diagnostic work-up and treatment planning in patients with seizure disorders who are candidates for surgical treatment. MATERIALS AND METHODS: Institutional review board approval was obtained; informed consent was obtained either from the patient or the parent or guardian in all patients. This study was conducted with Health Insurance Portability and Accountability Act compliance. Sixty consecutively enrolled patients (33 males, 27 females; mean age, 15.8 years +/- 8.7 [standard deviation]; range, 6.8-44.2 years) were prospectively examined. Forty-five (75%) patients were right handed, nine (15%) were left handed, and six (10%) had indeterminate hand dominance. Prospective questionnaires were used to evaluate diagnostic work-up, counseling, and treatment plans of the seizure team before and after functional MR imaging. Confidence level scales were used to determine effect of functional MR imaging on diagnostic and therapeutic thinking. Paired t test and 95% confidence interval analyses were performed. RESULTS: In 53 patients, language mapping was performed; in 33, motor mapping; and in seven, visual mapping. The study revealed change in anatomic location or lateralization of language-receptive (Wernicke) (28% of patients) and language-expressive (Broca) (21% of patients) areas. Statistically significant increases were found in confidence levels after functional MR imaging in regard to motor and visual cortical function evaluation. In 35 (58%) of 60 patients, the seizure team thought that functional MR imaging results altered patient and family counseling. In 38 (63%) of 60 patients, functional MR imaging results helped to avoid further studies, including Wada test. In 31 (52%) and 25 (42%) of 60 patients, intraoperative mapping and surgical plans, respectively, were altered because of functional MR imaging results. In five (8%) patients, two-stage surgery with extra-operative direct electrical stimulation mapping was averted, and resection was accomplished in one stage. In four (7%) patients, extent of surgical resection was altered because eloquent areas were identified close to seizure focus. CONCLUSION: Functional MR imaging results influenced diagnostic and therapeutic decision making of the seizure team; results indicated language dominance changed, confidence level in identification of critical brain function areas increased, patient and family counseling were altered, and intraoperative mapping and surgical approach were altered.

Adolescent↗
PubMed2004

Dissecting nonverbal auditory cortex asymmetry: an fMRI study.

The purpose of this study was to find a robust nonverbal paradigm to obtain reliable, reproducible auditory activation and characterize the nonverbal activation of the auditory cortex in regard to the Brodmann regions. The extent of localization and lateralization of activation was investigated utilizing functional magnetic resonance (fMR). Two tasks were used: monotonous repetitive stimuli of "double octaves" (DO) consisting of alternating four A with four C piano notes and a variated string of "sequential notes" (SN), which was a fast nonrepetitive sequence of piano notes. Eleven volunteers were investigated. The activation periods had a duration of 30 s, and presented every 30 s. All subjects demonstrated fMRI signal activity in the superior temporal gyrus (STG) involving the primary and secondary auditory cortex except one subject who showed no activation with the DO stimulus. SN elicited more activation than DO (p =<.03). The bulk activation for SN and DO was slightly greater in the right hemisphere, although the primary auditory area (Brodmann's 41) was better activated on the left p =<.001. Brodmann's area 22 was most frequently right-side dominant (p =.015, p =.017 for DO and SN, respectively). These findings appear to have implications in the examination of preverbal subjects.

Acoustic Stimulation↗
PubMed2004

Functional MR imaging versus Wada test for evaluation of language lateralization: cost analysis.

PURPOSE: To compare the total direct costs (fixed and variable costs) of functional magnetic resonance (MR) imaging and of the Wada test for evaluation of language lateralization. MATERIALS AND METHODS: The direct fixed and variable costs of functional MR imaging (performed in 21 patients with mean age +/- SD of 15.5 years +/- 8.9) and of the Wada test (performed in 18 patients aged 19.2 years +/- 5.4) were determined prospectively with time and motion analyses. The labor of all personnel involved in evaluations of language lateralization was tracked, and involvement times were recorded to the nearest minute. All material items used in the studies were recorded. Costs of labor and of materials were determined from personnel reimbursement data and from vendor pricing, respectively. Direct fixed costs were determined from hospital accounting department records. Means (+/- SDs) were calculated for all direct fixed and variable costs. Total direct costs were determined for each procedure and compared by using the Student t test. RESULTS: The total direct costs of the Wada test (US dollars 1130.01 +/- US dollars 138.40) and of functional MR imaging (US dollars 301.82 +/- US dollars 10.65) were significantly different (P <.001). The cost of the Wada test was 3.7 times higher than that of functional MR imaging. CONCLUSION: Substantial savings are achievable with the use of functional MR imaging instead of the Wada test to evaluate language lateralization.

Adult↗
PubMed2003

Introduction to evidence-based imaging.

Society is increasingly demanding proof that imaging has an impact on patient outcome and questioning its cost on the health care delivery system. Radiologists should provide the following three key components in their research publications: (1) the statistical power and confidence intervals of the results obtained; (2) the diagnostic performance of the tests, including sensitivity, specificity, and ROC curves; and (3) comprehensive decision analysis and cost-effectiveness analysis to determine the impact that imaging has on health outcome, cost, and quality of life. Strict adherence to these evidence-based medicine principles would help advance the field and provide the best health care for patients.

Diagnostic Imaging↗
PubMed2003

Adults and children with headache: evidence-based diagnostic evaluation.

Headache represents one of the most common complaints in the outpatient and emergency room setting [1]. Most causes of headache are benign and do not require emergent imaging or intervention. The authors' review of the diagnostic tests does not offer absolute indications for neuroimaging because most of the evidence is based on studies that are not randomized controlled trials. Imaging guidelines for adults and children, however, have emerged based on the available level 2 and 3 literature. CT imaging remains the initial test of choice for new-onset headache in adults and headache suggestive of SAH. Most of the available literature also recommends performing lumbar puncture when CT is equivocal in ruling out SAH [1]. The sensitivity of MR imaging appears to be less than CT for SAH [1]. Newer MR imaging techniques need to be tested and developed to determine if they have higher sensitivity than CT or lumbar puncture in the detection of SAH. In adults with suspected brain metastatic disease, contrast-enhanced MR imaging is the imaging study of choice [38,39]. Contrast-enhanced MR imaging is the examination of choice for brain metastatic lesions less than 2 cm [39]. CT angiography and MR angiography have sensitivities greater than 85% for brain aneurysms larger than 5 mm [43]. If clinically warranted, aneurysms smaller than 5 mm may require digitally subtracted angiography because of the low sensitivity of MR and CT angiography. In children, the choice of diagnostic test strategy depends on the risk group. In high-risk patients, MR imaging is the test of choice whereas in low-risk patients, close clinical observation with periodic reassessment is the best strategy [44]. Clinical diagnosis will always play a key role in the evaluation of headache disorders; however, for the small subset of patients who present with headache secondary to an intracranial space-occupying lesion, bleeding, or SAH, making the diagnosis is crucial to decreasing morbidity and mortality. CT, MR imaging, and lumbar puncture play important roles in the assessment of headache disorders, but their future roles will continue to evolve as the technology becomes more sophisticated and robust, and physicians become more expert with their use [1].

Adult↗
PubMed2003

Occult spinal dysraphism: evidence-based diagnosis and treatment.

This article reviews the scientific evidence behind the diagnostic tools available for the appropriate workup and management of patients with occult spinal dysraphism (OSD). The diagnostic tools include the use of detailed history and physical examination, plain films, ultrasound, MR imaging, and neurophysiologic tests. In addition, the article discusses the epidemiology of the most common causes of OSD in children, which will allow physicians caring for children to develop a pretest probability of disease and make a more educated decision as to when additional diagnostic testing is required.

Evidence-Based Medicine↗
PubMed2003

Vesicoureteral reflux imaging in children: comparative cost analysis.

RATIONALE AND OBJECTIVES: The purpose of this study was to compare the costs of voiding cystourethrography (VCUG) versus radionuclide cystography (RNC) for evaluation of vesicoureteral reflux in children. MATERIALS AND METHODS: The variable direct costs of performing 25 VCUG and 25 RNC examinations in age- and general health-matched patients suspected of having vesicoureteral reflux was determined by using time and motion analyses. All personnel directly involved in the cases were tracked, and the involvement times were recorded to the nearest minute. All material items used during the procedures were recorded. The cost of labor was determined from personnel reimbursement data, and the cost of materials, from vendor pricing. The fixed direct costs were assessed from hospital accounting records. Mean, standard deviation, and 95% confidence interval (CI) were determined for all direct (fixed and variable) costs. The total costs were determined for each procedure and compared by using the Student t test. RESULTS: There was a significant difference (P < .0001) between the mean total direct cost of VCUG ($112.17 +/- 10.33) and that of RNC ($64.58 +/- 1.91). VCUG examination for vesicoureteral reflux in children cost 1.74 times more than RNC examination (95% CI: 1.28, 2.36). CONCLUSION: When the technique is clinically appropriate, institutions may obtain substantial cost savings by using RNC in place of VCUG for examining children suspected of having vesicoureteral reflux.

Child↗
PubMed2003

Measurement variability and confidence intervals in medicine: why should radiologists care?

In radiology, appropriate diagnoses are often based on quantitative data. However, these data contain inherent variability. Radiologists often see P values in the literature but are less familiar with other ways of reporting statistics. Statistics such as the SD and standard error of the mean (SEM) are commonly used in radiology, whereas the CI is not often used. Because the SEM is smaller than the SD, it is often inappropriately used in order to make the variability of the data look tighter. However, unlike the SD, which quantifies the variability of the actual data for a single sample, the SEM represents the precision for an estimated mean of a general population taken from many sample means. Since readers are usually interested in knowing about the variability of the single sample, the SD often is the preferred statistic. Statistical calculations combine sample size and variability (ie, the SD) to generate a CI for a population proportion or population mean. CIs enable researchers to estimate population values without having data from all members of the population. In most cases, CIs are based on a 95% confidence level. The advantage of CIs over significance tests (P values) is that the CIs shift the interpretation from a qualitative judgment about the role of chance to a quantitative estimation of the biologic measure of effect. Proper understanding and use of these fundamental statistics and their calculations will allow more reliable analysis, interpretation, and communication of clinical information among health care providers and between these providers and their patients.

Confidence Intervals↗
PubMed2002

Establishing a health outcomes and economics center in radiology: strategies and resources required.

PURPOSE: To describe the resources and strategies required to establish a health outcomes and economics center in radiology. METHODS: Human and nonhuman resources required to perform sound outcomes and economics studies in radiology are reviewed. RESULTS: Human resources needed include skilled medical and nonmedical staff. Nonhuman resources required are: (1). communication and information network; (2). education tools and training programs; (3). budgetary strategies; and (4). sources of income. Effective utilization of these resources allows the performance of robust operational and clinical research projects in decision analysis, cost-effectiveness, diagnostic performance (sensitivity, specificity, and ROC curves), and clinical analytical and experimental studies. CONCLUSION: As new radiologic technology and techniques are introduced in medicine, society is increasingly demanding sound clinical studies that will determine the impact of radiologic studies on patient outcome. Health-care funding is scarce, and therefore third-party payers and hospitals are demanding more efficiency and productivity from radiologic service providers. To meet these challenges, radiology departments could establish health outcomes and economics centers to study the clinical effectiveness of imaging and its impact on patient outcome.

Budgets↗
PubMed2002

False lateralization of language cortex on functional MRI after a cluster of focal seizures.

fMRI can define language cortex but its limitations are not yet fully understood. This article describes a child in whom fMRI falsely lateralized language cortex when performed after a cluster of left temporal lobe seizures. Multiple language tasks revealed no activation over the left temporal lobe despite a normal neurologic exam at the time of the study. A second fMRI performed 2 weeks later activated sites predominantly over the left, which were confirmed by extra-operative functional language mapping. fMRI may be unhelpful after frequent seizures.

Adolescent↗
PubMed2002

Molecular studies in pediatric medulloblastomas.

Ten pediatric medulloblastoma patients were analyzed for DNA content, cell cycle, expression of drug resistance, apoptosis, cell proliferation, and N-myc genes to determine their prognostic significance. Medulloblastoma patients with progressive disease had fourth ventricle foraminal extension and larger tumors in the imaging studies. Patients with aneuploid tumors responded well to treatment regimens as compared with those with diploid tumors. Cell cycle analysis showed that the patients with progressive disease had a high S-phase fraction in the tumor cell population as compared with patients with favorable response to treatment. The correlation coefficients between Bcl-2 and MRP, Bcl-2 and Bax, p53 and p21, as well as Ki67 and PCNA were positive and significant, indicating their possible coregulated expression. The relationship between these markers indicates their relative and cumulative effect on cellular drug resistance, apoptosis, and/or cell proliferation in pediatric medulloblastomas.

Adolescent↗
PubMed2002

Children with suspected craniosynostosis: a cost-effectiveness analysis of diagnostic strategies.

OBJECTIVE: Our purpose was to evaluate the clinical and economic impact of three evaluation strategies in children at different risks of craniosynostosis. MATERIALS AND METHODS: A decision-analytic and cost-effectiveness model was constructed to compare three evaluation in strategies in children with suspected synostosis: no imaging, radiography (if abnormal, followed by three-dimensional CT [3D CT]), and 3D CT. Three risk groups were analyzed on the basis of the prevalence (pretest probability) of disease: low (completly healthy children; prevalence, 34/100,000), intermediate (healthy children with head deformity; prevalence, 1/115), and high risk (children with syndromic craniofacial disorders [i.e., Crouzon's syndrome or Apert's syndrome]; prevalence, 9-10/10). Test performance (sensitivity and specificity) of the evaluation strategies was obtained from the literature. Costs (not charge) estimates were obtained from the hospital cost-accounting database and from the Medicaid fee schedule. RESULTS: In the low-risk group, the radiographic and 3D CT strategies resulted in a cost per quality-adjusted life year (QALY) gained of more than $560,000. In the intermediate-risk group, the radiographic strategy resulted in a cost per QALY gained of $54,600. Three-dimensional CT was more effective than the two other strategies but at a higher cost-hence, with a cost per QALY gained of $374,200. In the high-risk group, 3D CT was the most effective strategy with a cost per QALY gained of $33,800. Less experienced radiologists and poor-quality studies increased the evaluation cost per QALY gained for all of the risk groups because of decreased effectiveness. CONCLUSION: Radiologic screening of completely healthy children (low risk) for synostosis is not warranted because of the high cost per QALY gained of the radiographic and 3D CT strategies. In healthy children with head deformity (intermediate risk), the radiographic strategy had a reasonable cost per QALY gained. Three-dimensional CT was more effective but had a high cost per QALY gained. In children with syndromic craniofacial disorders (high risk), 3D CT was the most effective strategy and had a reasonable cost per QALY gained. Selection of children with suspected craniosynostosis based on their risk group and use of the most appropriate evaluation strategy could maximize clinical and economic outcomes for these patients.

Child↗
PubMed1999

Occult lumbosacral dysraphism in children and young adults: diagnostic performance of fast screening and conventional MR imaging.

PURPOSE: To compare fast screening and conventional magnetic resonance (MR) imaging for the detection of occult dysraphic myelodysplasias in children and young adults. MATERIALS AND METHODS: A retrospective case-control study included 101 patients (mean age, 4.9 years; range, 1 day to 26 years) suspected of having occult lumbosacral dysraphism. Sixty case patients had myelodysplastic lesions (19 filar lipoma, 14 syringomyelia, 10 intradural lipoma, eight dermal sinus, five diastematomyelia, five lipomyelomeningocele, two caudal regression syndrome); 41 control patients had no dysraphic lesions; 17 patients had associated renal anomalies. Two neuroradiologists reviewed MR images from conventional and fast screening protocols. Diagnostic performance parameters included sensitivity, specificity, and area under the receiver operating characteristic curve (Az value). RESULTS: The sensitivity of conventional and fast screening MR studies was 97.1% and 98.5%, respectively, the specificity was 90.9% and 84.8%, respectively. The Az value was 0.973 for the fast screening and 0.976 for the conventional MR studies (P = .83). Interobserver agreement was very good for fast screening images (kappa = 0.68) and excellent for conventional images (kappa = 0.75). For renal anomalies, the Az value was 0.786 and 0.853 for fast screening and conventional MR imaging, respectively (P = .28). CONCLUSION: Conventional three-plane lumbosacral MR imaging in children and young adults suspected of having occult dysraphism provides better diagnostic information than does fast screening two-plane MR imaging because of its higher specificity and interobserver agreement.

Adolescent↗