Negative refraction and the spectral filtering of terahertz radiation by a photonic crystal prism.

We demonstrate how micromachined photonic crystals can be used to negatively refract terahertz frequency light. The photonic crystals, which are constructed from conventional dielectric materials, manipulate the incident beam via interaction with their photonic bands. Consequently, we show that different components of a broadband beam incident on the structure may be positively or negatively refracted, depending upon its frequency and that the structure can be used as an effective spectral filter of THz radiation.

Negative refraction can make non-diffracting beams.

We report the results of simulations relating to the illumination of a structure consisting of a slab constructed from a 2-D hexagonal array of metal rods with a terahertz frequency source. As a consequence of negative refraction an essentially non-divergent beam pattern is observed. Although the results presented relate to the terahertz regime they should also be applicable at other frequencies.

Terahertz filter based on refractive properties of metallic photonic crystal.

We propose a new type of pass-band filter, in this case designed to operate in the terahertz frequency regime, possessing two separate passbands utilizing the distinction between positive and negative refraction in a photonic crystal prism. The prism is formed from a two-dimensional hexagonal arrangement of metallic rods. In order to understand the operation of the filter we both consider the photonic bandstructure of the associated infinite photonic structure and carry out simulations of the refraction properties of the prism using finite-difference time-domain software.

Terahertz radiation from a nonlinear slab traversed by an optical pulse.

We report on the theoretical calculations considering collinear electromagnetic radiation at the propagation of an optical pulse through a slab of nonlinear material. Calculated waveforms of the radiated field fit well to the experimental dependencies showing the remarkable similarities between the radiation at nonlinear wave interaction and the radiation phenomena of moving external charges, similarly to discussed in the Tamm Problem and transition radiation of moving external charges.

Where optics meets electronics: recent progress in decreasing the terahertz gap.

The terahertz region of the electromagnetic spectrum offers considerable opportunities for exploitation. Recent advances in source and coherent-detection technology have enabled advances to be made in a wide range of applications. This article reviews the historical development of the field, summarizes the current state of system technology and outlines a number of current system applications, including medical imaging. The limitations of present-day technology are discussed and some future possible applications are considered.

Catalogue of human tissue optical properties at terahertz frequencies.

Recently published studies suggest thatterahertz pulsed imaging will have applications inmedicine and biology, but there iscurrently very little information about the opticalproperties of human tissue at terahertzfrequencies. Such information would be useful forpredicting the feasibility of proposedapplications, optimising acquisition protocols,providing information about variability ofhealthy tissue and supplying data for studies of theinteraction mechanisms. Research ethicscommittee approval was obtained, andmeasurements made from samples of freshlyexcised human tissue, using a broadbandterahertz pulsed imaging system comprisingfrequencies approximately 0.5 to 2.5 THz.Refractive index and linear absorptioncoefficient were found. Reproducibility wasdetermined using blood from one volunteer,which was drawn and measured on consecutivedays. Skin, adipose tissue, striatedmuscle, vein and nerve were measured (to date, from oneindividual). Water had a higher refractiveindex (2.04 ± 0.07) than any tissue.The linear absorption coefficient was higher formuscle than adipose tissue, as expectedfrom the higher hydration of muscle. As these samples camefrom a single subject, there is currentlyinsufficient statistical power to draw firmconclusions, but results suggest that in vivo clinical imaging will be feasible in certainapplications.

Evaluation of image quality in terahertz pulsed imaging using test objects.

As with other imaging modalities, the performance of terahertz (THz) imaging systems is limited by factors of spatial resolution, contrast and noise. The purpose of this paper is to introduce test objects and image analysis methods to evaluate and compare THz image quality in a quantitative and objective way, so that alternative terahertz imaging system configurations and acquisition techniques can be compared, and the range of image parameters can be assessed. Two test objects were designed and manufactured, one to determine the modulation transfer functions (MTF) and the other to derive image signal to noise ratio (SNR) at a range of contrasts. As expected the higher THz frequencies had larger MTFs, and better spatial resolution as determined by the spatial frequency at which the MTF dropped below the 20% threshold. Image SNR was compared for time domain and frequency domain image parameters and time delay based images consistently demonstrated higher SNR than intensity based parameters such as relative transmittance because the latter are more strongly affected by the sources of noise in the THz system such as laser fluctuations and detector shot noise.

An introduction to medical imaging with coherent terahertz frequency radiation.

Methods have recently been developed that make use of electromagnetic radiation at terahertz (THz) frequencies, the region of the spectrum between millimetre wavelengths and the infrared, for imaging purposes. Radiation at these wavelengths is non-ionizing and subject to far less Rayleigh scatter than visible or infrared wavelengths, making it suitable for medical applications. This paper introduces THz pulsed imaging and discusses its potential for in vivo medical applications in comparison with existing modalities.

The interaction between Terahertz radiation and biological tissue.

Terahertz (THz) radiation occupies that region of the electromagnetic (EM) spectrum between approximately 0.3 and 20 THz. Recent advances in methods of producing THz radiation have stimulated interest in studying the interaction between radiation and biological molecules and tissue. Given that the photon energies associated with this region of the spectrum are 2.0 x 10(-22) to 1.3 x 10(-20) J, an analysis of the interactions requires an understanding of the permittivity and conductivity of the medium (which describe the bulk motions of the molecules) and the possible transitions between the molecular energy levels. This paper reviews current understanding of the interactions between THz radiation and biological molecules, cells and tissues. At frequencies below approximately 6 THz. the interaction may be understood as a classical EM wave interaction (using the parameters of permittivity and conductivity), whereas at higher frequencies. transitions between different molecular vibrational and rotational energy levels become increasingly important and are more readily understood using a quantum-mechanical framework. The latter is of particular interest in using THz to probe transitions between different vibrational modes of deoxyribonucleic acid. Much additional experimental work is required in order to fully understand the interactions between THz radiation and biological molecules and tissue.

Resource utilization and contaminated blood cultures in children at risk for occult bacteremia.

OBJECTIVE: To measure the increases in resource utilization and hospital charges associated with the evaluation of contaminated blood cultures obtained from emergency department patients at risk for occult bacteremia. DESIGN: Retrospective medical record review. SETTING: Emergency department of an urban, university-affiliated pediatric referral center. PATIENTS: Children aged 3 to 36 months with blood cultures positive for bacterial growth obtained between January 1994 and October 1996. MAIN OUTCOME MEASURES: Increased resource utilization related to contaminated blood culture follow-up, including telephone contact, return emergency department visits, additional diagnostic tests and therapies performed at reevaluation, and hospital admissions. Hospital charges for these additional services were tabulated. RESULTS: Of 8,306 children who had blood cultures drawn, 491 (5.9%) had positive findings. Four hundred eighty-five (98.8%) of these were available for review. Two hundred seventy-six (57%) of 485 were excluded from final analysis. Of the remaining 209 patients at risk for occult bacteremia, 85 (41%) had cultures that grew contaminants only. Follow-up of these 85 patients generated 106 telephone calls, 49 return visits to the emergency department, 102 additional diagnostic tests, 18 doses of parenteral antibiotics, and 12 hospital admissions with a combined length of stay of 24 days. This resulted in additional charges of $78,904, or an additional $642 per true pathogen recovered. CONCLUSIONS: Contaminated blood cultures obtained from children at risk for occult bacteremia lead to substantial increases in resource utilization and hospital charges. These untoward effects should be accounted for in formal decision analyses regarding the management of occult bacteremia.

A comparison of the initial to the later stream urine in children catheterized to evaluate for a urinary tract infection.

BACKGROUND: To avoid potential contamination, it is recommended that the first few drops of urine be discarded when obtaining a catheterized urine sample from a child being evaluated for a urinary tract infection (UTI). The existing evidence to make such a recommendation is scant. Our goal, therefore, was to determine whether the urinalysis, Gram stain, and culture results were significantly different from the initial and later urine samples collected from catheterized children. METHODS: A prospective diagnostic discrimination between early and later urine samples was conducted on a convenience sample of pediatric patients being evaluated for a UTI in an urban emergency department. Results of the urinalysis, Gram stain, and quantitative culture were compared between the early and later stream urine samples. RESULTS: Data from 86 children were analyzed. Four of 80 patients had a false identification of low colony count bacteruria from the early but not from the later stream. For patients with negative cultures, the early stream was also more likely to falsely identify > or =5 wbc/hpf (P<0.01) or bacteruria (P<0.05) on urinalysis than the later stream. CONCLUSIONS: There is a small but potentially meaningful contamination of the early stream urine compared with the later stream in young children catheterized to evaluate for a urinary tract infection.

Pediatric Milliman and Robertson length-of-stay criteria: are they realistic?

OBJECTIVE: Guidelines for inpatient length of stay (LOS) have been developed by several groups; among the most widely applied are those published by Milliman and Robertson (M&R). Few published reports have examined the relationship of actual practice to such guidelines, none in pediatric populations. This study was designed to compare pediatric practice in a large and defined population to M&R LOS criteria. METHODS: Administrative data from New York State in 1995 were used to examine LOS for discharges corresponding to 16 selected pediatric diagnoses for which M&R publishes guidelines. Outliers, defined as the 2% of discharges with the longest LOS, were eliminated. The distribution of LOS for each diagnosis was compared with M&R LOS guidelines. RESULTS: In New York State during 1995, pediatric LOS was markedly divergent from M&R guidelines. In general, the percentage of discharges in excess of the criterion LOS was less for nonmandatory admissions (croup: 23%, gastroenteritis: 44%, and pneumonia: 48%) than for those requiring surgery (uncomplicated appendectomy: 67%, pyloromyotomy: 62%, and major but noncritical burns: 64%) or prolonged treatment with antibiotics (bacterial meningitis: 91% and osteomyelitis: 86%). CONCLUSIONS: In New York State during 1995, LOS for selected pediatric conditions was generally in excess of published M&R guidelines. This raises concern about the potential effects of such guidelines on both patients and the hospitals caring for them. While endorsing the need for cost-effective practice, we call attention to the methods used to develop and validate guidelines.length of stay, pediatrics, managed health care, administrative data, practice guidelines.

The associations among pediatricians' knowledge, attitudes, and practices regarding emergency contraception.

OBJECTIVES: To quantify practitioner administration of the emergency contraceptive pill (ECP) among adolescent patients, and to determine if such administration is associated with physician knowledge and attitudes regarding efficacy, side effects, and appropriate use. DESIGN: Survey of pediatricians. SETTING: The survey address list was generated from a database of active Fellows of the American Academy of Pediatrics in the District of Columbia metropolitan area. MAIN OUTCOMES MEASURES: Prescription of the ECP in the previous 12 months, or counseling of an adolescent patient about the ECP. RESULTS: Of the 236 questionnaires distributed, 143 (61%) were returned and 121 (51%) were usable. Twenty-four pediatricians (20%) reported prescribing the ECP, and 29 (24%) had counseled adolescent patients about the ECP. Of the practice-related variables surveyed, both the number of adolescents seen per week and the practice setting were significantly associated with these outcomes. Of the knowledge-related variables surveyed, knowledge of the timing and the Food and Drug Administration-labeled status of the ECP were significantly associated with outcomes. None of the attitude-related variables surveyed were associated with outcomes. CONCLUSIONS: This study demonstrates that knowledge deficits, not attitude-related variables, are significantly associated with the low level of ECP administration and counseling among District of Columbia pediatricians. Because knowledge deficits are amenable to educational interventions, our data suggest that informing pediatricians about the ECP may increase its administration among their adolescent patients.emergency contraceptive pill, pediatricians, adolescents.

Injury surveillance in a pediatric emergency department.

In this study we have tried to determine physician success in the collection of injury data during the emergency department visit. Prospective data were collected from all children between the ages of 0 to 18 treated for an injury. Data were collected at the time of the visit and by chart review the next day. At an urban, university-affiliated, children's hospital, data were collected on 2,156 injured children. Fifty-one percent of the data forms were completed by the treating physician. Physician completion rate was lower on the weekends (46%) than on weekdays (52%, P = .02). The most common mechanisms of injury were falls (34%), motor-vehicle crashes or pedestrians struck (13%), and nonintentional struck by blunt object (12%). The most common mechanism of injury in all age groups was falls. Our results demonstrate that emergency physicians are not successful data collectors. However, when physician data collection is combined with next-day review of patient records, virtually 100% of patients are captured. Active emergency department data collection is important because in contrast to studies which use hospital discharge and mortality data, we found that overall falls account for more injuries presenting to the ED than transportation-related causes. An active surveillance system in emergency departments that does not require extra work on the part of the treating physician would be ideal and may give a more comprehensive description of the scope of the injury problem.

A method for assessing emergency department performance using patient outcomes.

OBJECTIVE: To determine the rates of correct patient disposition after an ED evaluation. METHODS: In a university pediatric hospital, a 25% random sample of ED patients for 4 consecutive months was reviewed, after exclusion of minor injuries and patients triaged to the nonurgent clinic. Patients were categorized into one of 4 outcomes on the basis of inpatient resource use: appropriate admission, inappropriate admission, appropriate release, or inappropriate release. A 10% random sample of released patients was contacted by telephone to detect patients who sought care elsewhere after ED release. RESULTS: 642 of 2,682 ED patients (23.9%) were admitted; 159 (24.7%) were inappropriately admitted, and 26 (1.3%) were inappropriately released. The correct identification of the need for hospitalization (sensitivity) was 94.9%, and for release (specificity) 92.7%. Overall, the correct classification rate was 93.1%. Inappropriate admissions were associated with diagnoses of trauma, seizures, and burns. CONCLUSION: Inappropriate admissions occur at a substantial rate and occur more commonly than inappropriate releases. The correct disposition of patients is a practical and meaningful outcome-based measure of the quality of ED care. This methodology is suitable for use in other EDs.

Pediatric risk of admission (PRISA): a measure of severity of illness for assessing the risk of hospitalization from the emergency department.

STUDY OBJECTIVE: The development and validation of a pediatric emergency department severity of illness assessment method, using hospital admission as the primary outcome. METHODS: A random sample of 25% of ED charts from 4 consecutive months in a university-affiliated pediatric hospital was reviewed, after exclusion of children with minor injuries and children triaged to the nonurgent clinic. Sampled data included components of the medical history, physical findings, physiologic variables, diagnoses, and ED therapies. Univariate and multivariate logistic regression analyses, with bootstrapping validation, were performed to develop a bias-corrected model estimating the probability of hospital admission. RESULTS: Of the 2,683 ED patients whose records were reviewed, 643 (24%) were admitted to the hospital. The final model, which yielded a Pediatric Risk of Admission (PRISA) score, included the following: 3 components of the medical history, 3 chronic disease factors, 9 physiologic variables, 2 therapies, and 4 interaction terms. Overall, the number of hospital admissions was well predicted in both the 80% development and 20% validation samples. In the former, 514 admissions were predicted and 514 were observed; in the latter, 126.9 admissions were predicted and 129 were observed. The Hosmer-Lemeshow goodness-of-fit test demonstrated good agreement between observed and expected admissions in consecutive deciles of admission probability; total chi2 was 10.49 (P=.233) for the development sample and 11.85 (P=.222) for the validation sample. The areas under the receiver operating characteristic curves (+/-SE) were .86+/-.011 and .825+/-.024, respectively. As the risk of hospital admission increased, the proportions of patients using unique hospital-based resources and using ICU resources increased, and the proportion of patients dying increased. CONCLUSION: The probability of admission to the hospital can reliably be estimated from data available during the pediatric ED stay. Applications for this method include studies of quality and efficiency of care and measurements of severity of illness.

Streptococcus pneumoniae bacteremia in children infected with HIV: presentation, course, and outcome.

OBJECTIVE: To examine the presentation, course, and outcome of pneumococcal bacteremia in children infected with human immunodeficiency virus (HIV). METHODS: A retrospective series of HIV-infected children less than 18 years of age with Streptococcus pneumoniae bacteremia from four urban, tertiary care hospitals was evaluated. The main outcome measures included persistent bacteremia, the development of a focal infection, and death. RESULTS: Seventy-two episodes of pneumococcal bacteremia were identified in 59 patients. Fifty-four first episodes were included; 26/54 were occult. Mean temperature was 39.8 degrees C. In patients with bacteremia, white blood cells (WBCs) > or = 15,000 and > or = 10,000 had sensitivities of 40% and 75%, respectively. At the time of bacteremia, age >3 years old was associated with a lower mean WBC count compared with episodes occurring in patients <3 years old (11.2 vs 16.1, P < 0.05). Patients with occult bacteremia who were discharged with antibiotics (12 i.m., 7 p.o.) were less likely than patients without antibiotic treatment to have persistent bacteremia at a return visit within 72 hours (0/19 vs 2/5, P < 0.05). No patient with occult bacteremia died, progressed to clinical meningitis, or had other sequelae. Two of fifty-four patients died as a result of their first episode of invasive pneumococcal disease. Both patients who died had meningitis and appeared ill on initial presentation. CONCLUSIONS: Neither a WBC count > or = 15,000 nor > or = 10,000 is a sensitive indicator of pneumococcal bacteremia in HIV-infected children. Empiric antibiotics are useful to decrease the risk of persistent bacteremia. Children infected with HIV who have occult pneumococcal bacteremia appear to do well with appropriate antibiotics. Patients who are afebrile and well appearing on reevaluation may be safely treated as outpatients.

Blood cultures in the evaluation of children with cellulitis.

OBJECTIVE: To evaluate the yield of blood cultures obtained from immunocompetent children admitted for cellulitis in the post-Haemophilus influenzae type b (Hib) vaccine era and to determine whether these cultures are cost-effective. DESIGN: Retrospective case series. SETTING: Urban pediatric emergency department. Study Population. Patients 2 days to 22 years of age admitted with cellulitis from 1994 through 1995. MEASUREMENTS AND RESULTS: Of 381 patients identified, 266 (70%) had blood cultures and 243 of these children were enrolled. Data recorded include demographics, immunization status, initial clinical appearance, antibiotic pretreatment, preexisting illness, location and precipitating cause of cellulitis, white blood cell count, and band-to-neutrophil ratio (BNR). Blood cultures were categorized as positive, negative, or contaminant. Five cultures (2%) were positive, and 13 (5.4%) were contaminants. The positive blood cultures grew streptococcus and staphylococcus organisms, and none of the children were bacteremic with H influenzae. All patients with group A beta-hemolytic streptococcus had active varicella. The mean age was lower (26 vs 75 months) in those with a positive blood culture, and mean BNR was higher (0.32 vs 0.07). Patient management did not change for bacteremic patients with uncomplicated cellulitis. All repeat cultures were negative. The cumulative charge for all blood cultures was $50 986. CONCLUSIONS: Blood cultures are not cost-effective and are more frequently contaminated than positive in the evaluation of a patient with uncomplicated cellulitis. Since introduction of the H influenzae type b vaccine, the most common organisms are streptococci. Using a BNR = 0.20 as a threshold for sending blood cultures, we would have missed one positive culture, but would have avoided blood cultures in 213 patients (88%) with an estimated savings of $42 850.

A prospective, randomized study comparing intramuscular midazolam with intravenous diazepam for the treatment of seizures in children.

OBJECTIVE: To compare treatment of ongoing seizures using intramuscular (IM) midazolam versus intravenous (IV) diazepam. DESIGN: Controlled clinical trial. PATIENTS: Children with motor seizures of at least 10 minutes' duration. MAIN OUTCOME MEASURES: Time to cessation of seizures. RESULTS: Twenty-four patients were enrolled (13 midazolam, 11 diazepam). Initial treatment with either midazolam or diazepam was successful in 22 of the 24 patients. One patient in each group failed therapy and eventually required endotracheal intubation and general anesthesia for convulsive status epilepticus lasting more than one hour. Patients in the midazolam group received medication sooner (3.3 +/- 2.0 vs 7.8 +/- 3.2 minutes, P = 0.001) and had more rapid cessation of their seizures (7.8 +/- 4.1 vs 11.2 +/- 3.6, P = 0.047) than patients randomized to receive diazepam. CONCLUSIONS: IM midazolam is an effective anticonvulsant for children with motor seizures. Compared to IV diazepam, IM midazolam results in more rapid cessation of seizures because of more rapid administration. The IM route of administration may be particularly useful in physicians' offices, in the prehospital setting, and for children with difficult IV access.