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Biomedical subjects

R J Hernandez

Publications and source records attributed to R J Hernandez.

At least 37 records · Page 2Linked to original sources
PubMed1996

Development of a gas-phase oxygen biosensor using a blue copper-containing oxidase.

A gas-phase oxygen biosensor based on blue copper-containing oxidases was developed. Blue-oxidase enzymes, including laccase and ascorbate oxidase, have a blue chromophore prosthetic group, type 1 Cu+2, which can be reduced and decolorized with reducing substrates. When the enzyme is reoxidized with molecular oxygen, there is a concomitant return of the blue color. The oxygen biosensor consisted of the Rhus vernicifera laccase and ascorbate as substrate enclosed in pouches of low-density polyethylene under nitrogen gas. Operational stability of the biosensor was established by exposing it to different oxygen/nitrogen gas mixtures at 5 degrees C. Gas-phase oxygen concentrations were measured by keeping it under nitrogen gas and subsequently recording the rate of reappearance of the enzyme blue color, both visually and spectrophotometrically at 610 nm. The oxygen biosensor was able to detect a wide range of oxygen concentrations. The time required to recover the blue color, namely the biosensor response time, at the optimized assay conditions of 5 degrees C and a high-water activity level, was determined. This research describes the development of an oxygen biosensor with adequate activity and stability to measure gas-phase oxygen concentrations at 5 degrees C and high-water activity levels. The oxygen biosensor could be used to indicate oxygen concentrations above acceptable levels in headspace oxygen concentration which could affect the quality and safety of products packaged under initial low levels of oxygen concentration.

Ascorbate Oxidase↗
PubMed1996

Assessment of central pulmonary arteries in patients with obstructive lesions of the right ventricle: comparison of MR imaging and cineangiography.

OBJECTIVE: MR imaging and cineangiography were compared in the evaluation of central pulmonary arteries in patients with obstructive lesions of the right ventricular outflow tract. SUBJECTS AND METHODS: Prospectively, we obtained multiplanar spin-echo cardiac-gated MR images and cineangiograms in 29 patients who had obstructive lesions of the right ventricular outflow tract (31 examinations). Blinded first observers evaluated the presence, size, confluence, and stenoses of the pulmonary artery and the presence of aortopulmonic collaterals. Blinded second observers evaluated the presence and size of the pulmonary artery. RESULTS: Each imaging technique revealed pulmonary arteries that were not shown by the other technique. We measured pulmonary arteries as being smaller on MR images; however, we found good correlation between the two techniques (r value for right pulmonary arteries = .82, r value for left pulmonary arteries = .88). MR imaging revealed five of six stenoses in the left pulmonary artery, but our observers falsely identified five right pulmonary arteries as stenotic from MR images. Interobserver variability and intraobserver variability in estimating size of the pulmonary artery on MR images and cineangiograms were similar and were less than variability when paired estimations in the same patient with both imaging techniques were compared. CONCLUSIONS: MR imaging and cineangiography should be viewed as complementary techniques.

Adolescent↗
PubMed1996

Reduction of radiation dose in pediatric patients using pulsed fluoroscopy.

OBJECTIVE: The purpose of this study was to determine if pulsed fluoroscopy reduces radiation exposure to pediatric patients undergoing conventional fluoroscopy. SUBJECTS AND METHODS: Four hundred one consecutive patients were nonrandomly divided into pulsed fluoroscopy and conventional fluoroscopy study groups. Two control groups were also assembled: 474 patients evaluated with conventional fluoroscopy before the study and 138 patients evaluated with pulsed fluoroscopy after the study. RESULTS: We found no difference in fluoroscopy times across the groups. Although the number of digital spot films was slightly higher for the pulsed fluoroscopy study group than for the conventional fluoroscopy study group, we found no difference in the number of digital spot films for the pulsed fluoroscopy study group and for the conventional fluoroscopy control group. Furthermore, the difference in the number of digital spot films was also insignificant for the pulsed fluoroscopy control group and the conventional fluoroscopy study group. The radiation exposure in the pulsed fluoroscopy study group was 50% lower (mean, 0.6 R) than in the conventional fluoroscopy study group. When using pulsed fluoroscopy in the 7.5 pulses-per-second mode, we were able to reduce radiation exposure by 75% of that from conventional fluoroscopy. CONCLUSION: Pulsed fluoroscopy reduces fluoroscopic radiation exposure to pediatric patients undergoing conventional fluoroscopy. Despite minor image degradation, pulsed fluoroscopy is the technique of choice at our institution.

Arthrography↗
PubMed1996

Cardiovascular MR imaging of children.

The role of MR imaging in the evaluation of congenital heart lesions is described. Emphasis is placed on those indications where MR imaging complements other imaging modalities, i.e., evaluation of the great vessels. Advantages and disadvantages of different MR imaging techniques (i.e., spin echo, segmented k-space acquisition, and gadolinium-enhanced angiography) are illustrated.

Aorta↗
PubMed1995

Neoplasms in a pediatric population: 2-[F-18]-fluoro-2-deoxy-D-glucose PET studies.

PURPOSE: To assess the uptake of 2-[fluorine-18]-fluoro-2-deoxy-D-glucose (FDG) in common and uncommon tumors in children and to develop a method for performing positron emission tomography (PET) studies in children with malignant neoplasms. MATERIALS AND METHODS: Twenty-two pediatric patients with known or suspected malignancies (27 scans) underwent FDG PET. Tumor uptake of FDG was measured on PET scans. RESULTS: Tumor uptake of FDG was detected in 17 of 21 patients with malignant disease. Neuroblastomas and their metastases (including those that did not absorb metaiodobenzylguanidine) intensely accumulated FDG. In a patient with Ewing sarcoma, FDG PET showed two foci of metastatic disease not evident on bone scans. In two patients, PET showed that large areas of the tumor were necrotic. CONCLUSION: FDG PET is feasible, is useful in the study of tumors in children, and may provide unique, clinically important information.

Adolescent↗
PubMed1995

Improved ejection fraction and flow velocity estimates with use of view sharing and uniform repetition time excitation with fast cardiac techniques.

PURPOSE: To improve the accuracy of ventricular volume estimates and effective temporal resolution in fast cardiac acquisitions. MATERIALS AND METHODS: Data sets at intermediate temporal phases were generated by means of sharing of views from two temporally adjacent data sets. A simulated model was used, and studies with patients and volunteers were conducted. View sharing was implemented in both fast gradient-echo and fast phase-contrast cine acquisitions; breath holding was used when possible. RESULTS: Uniform repetition time (TR) radio-frequency (RF) excitation allowed a better assessment of the end-diastolic ventricular volume. In addition, view sharing provided a better estimate of end-systolic ventricular volume in cases in which rapid changes in volume occurred at or about the temporal boundary of the source images. View sharing also provided a much smoother representation of dynamic cardiac motion when viewed in a cine loop. CONCLUSION: View sharing and uniform TR RF excitation improve the accuracy of end-systolic and end-diastolic ventricular volume measurements by improving the effective temporal resolution.

Adult↗
PubMed1994

Radiation dose reduction in CT of the pediatric pelvis.

PURPOSE: To determine whether a lower radiation dose technique can be used for computed tomography (CT) of the pediatric pelvis without significant loss of diagnostic image quality. MATERIALS AND METHODS: Thirty-six pediatric patients underwent CT at 80 mAs (experimental group), and 42 underwent CT at 240 mAs (control group). Anatomic details, image quality, and the degree of confidence in reaching a diagnosis were graded on a scale of 1 (poor) to 4 (excellent). RESULTS: The difference in perceived image quality between the experimental and control groups was not statistically significant. The mean scores for scans evaluated by the first reader were 3.88 for the experimental group and 3.92 for the control group (P = .2804). The mean scores for the second reader were 3.78 and 3.77 for the experimental and control groups, respectively (P = .8131). CONCLUSION: A substantial dose reduction can be achieved if pelvic CT is performed at 80 mAs, without a recognizable deterioration of diagnostic image quality.

Child↗
PubMed1994

Ultrasound diagnosis of neonatal congenital dislocation of the hip. A decision analysis assessment.

Routine ultrasound evaluation of neonates and young infants for congenital dislocation of the hip has been recommended. We have used the methods of decision analysis to determine whether every neonate should be examined by ultrasound or just those at increased risk. We have also studied the reliability and accuracy of ultrasound in following infants during observation and treatment, using published data. We find that ultrasound is not the preferred strategy for the screening of neonates, and that its role in evaluating high-risk patients depends on the point of view. For an individual, when third parties are bearing the cost, ultrasound is useful. For society as a whole, the routine ultrasound evaluation of the high-risk patient is not advantageous. For follow-up, ultrasound using the methods of Graf has a low reliability and there are no adequate data for methods using dynamic assessment.

Costs and Cost Analysis↗
PubMed1993

Renal imaging in children with persistent hypertension.

The role that imaging plays in the evaluation of the child with hypertension depends in large part on the results of thorough historical, physical, and laboratory examinations. How aggressively one searches for an underlying renal parenchymal or renovascular disorder must be individualized in each child. An individualized approach to renal imaging in children with hypertension is presented.

Child↗
PubMed1993

Thoracic cardiovascular anomalies in children: evaluation with a fast gradient-recalled-echo sequence with cardiac-triggered segmented acquisition.

A fast gradient-recalled-echo sequence with cardiac-triggered segmented acquisition (fastcard) was compared with a standard T1-weighted spin-echo sequence with cardiac gating and respiratory compensation in the evaluation of pediatric patients with thoracic cardiovascular anomalies. Twenty patients aged 1 week to 24 years (median age, 9 months) with various abnormalities underwent magnetic resonance (MR) imaging. In 18 patients, MR imaging was performed with both gated spin-echo and fastcard. Two observers rated the clinical utility of each sequence. Fastcard images were superior to spin-echo images in 10 patients, equivalent in seven, and inferior in one. Two additional patients with suspected pulmonary vascular lesions were accurately evaluated with the fastcard technique. The fastcard technique provides superior demonstration of thoracic cardiovascular structures and turbulent flow and enables imaging in multiple phases of the cardiac cycle.

Adolescent↗
PubMed1993

MR imaging in children with dermatomyositis: musculoskeletal findings and correlation with clinical and laboratory findings.

OBJECTIVE: The purpose of this study was to describe the musculoskeletal MR findings in childhood dermatomyositis and to correlate MR findings with indicators of disease activity such as muscle strength and serum levels of muscle enzymes. SUBJECTS AND METHODS: This prospective study included 24 children: 19 children with dermatomyositis and five control subjects. The diagnosis of dermatomyositis was established by clinical findings and serum levels of muscle enzymes in all patients, electromyography in six patients, and biopsy in four patients. At the time of the initial MR evaluation, patients were classified on the basis of clinical findings as having active (n = 15) or inactive (n = 4) disease. A total of 44 MR evaluations of patients with dermatomyositis were included in the study: 19 initial MR examinations and 12 examinations repeated after 4-6 months of therapy in patients with active disease. An additional 13 examinations were performed on five patients. Conventional T1-weighted (SE 600/20) and T2-weighted (SE 2500/80) spin-echo and fat-suppressed MR images were obtained. The T2-weighted images (TE = 80) were used for comparison. In addition to the visual assessment, ratios between the signal intensity of muscles (gluteus, adductors, quadriceps, and hamstrings) and the signal intensity of subcutaneous fat in the same tomographic section were calculated. RESULTS: All patients with clinically active disease (n = 15) had abnormal findings on MR studies, whereas those with inactive disease (n = 4) had normal MR findings. Signal-intensity ratios of patients with active disease were greater than those in control subjects, whereas the ratios in patients with inactive disease were not different from those in control subjects. After 4-6 months of therapy, the average signal-intensity ratios of treated patients with repeated MR evaluations (n = 12) differed from ratios obtained before therapy in the same patients, but were not different from the ratios in control subjects. Other MR findings observed were perimuscular edema, enhancement of the chemical-shift artifact, and inflammatory changes of subcutaneous fat. Fat-suppressed imaging enhanced visualization of abnormalities. Markedly abnormal signal intensities of muscle were associated with marked elevations of serum levels of muscle enzymes; however, abnormal MR findings were visualized with normal serum levels of muscle enzymes. CONCLUSION: Findings of active childhood dermatomyositis on T2-weighted MR images include increased signal intensity in affected muscle, perimuscular edema, enhanced chemical-shift artifact, and increased signal intensity in subcutaneous fat. After therapy, signal intensity of muscle returns to normal. These MR findings are enhanced on fat-suppressed images.(ABSTRACT TRUNCATED AT 400 WORDS)

Adipose Tissue↗
PubMed1992

Fat-suppressed MR imaging of myositis.

A hybrid fat-suppression sequence in magnetic resonance (MR) imaging was used to evaluate inflammatory muscle disorders in seven children: five patients with dermatomyositis, one patient with vasculitis, and one patient with viral myositis. Fat-suppressed multisection axial images obtained with the same repetition and echo times as those used to obtain standard spin-echo (SE) images enabled direct comparison of images, with little variation of T1 and T2 weighting. In six patients, the contrast on images obtained with T2 fat suppression was 15%-20% greater than contrast on conventional T2-weighted SE images. In all seven patients, the subjective judgment was that T2-weighted fat-suppression sequences improved visualization of muscle abnormalities. It is concluded that T2 fat suppression is useful in evaluation of inflammatory muscle disorders in children because it increases contrast and eliminates fat as a cause of muscle abnormality.

Child, Preschool↗
PubMed1992

Diseases of the musculoskeletal system in children: imaging with CT, sonography, and MR.

We reviewed the applications of CT, sonography, and MR imaging in diseases of the musculoskeletal system in children. Unique advantages of each technique are discussed, and common disease entities and practical applications of the three imaging methods are stressed. Evaluation of congenital dysplasia of the hip, hip effusion, and soft-tissue foreign bodies with sonography are emphasized. The role of CT in imaging patients with congenital dysplasia of the hip, tarsal coalition, osteomyelitis, and benign and malignant bone tumors is stressed. Common applications of MR that are emphasized include imaging of osteomyelitis, musculoskeletal tumors, normal bone marrow, and avascular necrosis. Innovations are briefly discussed, including evaluation of dermatomyositis with MR and imaging sternoclavicular dislocation, congenital vertical talus, and fractures and dislocations with sonography.

Child↗
PubMed1991

Serial magnetic resonance imaging in juvenile dermatomyositis.

Magnetic resonance imaging (MRI) was used to follow the course of juvenile dermatomyositis from the onset of disease through resolution of a primary relapse. The signal intensity of the T2-weighted image of involved muscles was elevated during periods of disease activity, and returned to approximately normal levels with effective suppression of disease activity. T1-weighted images of involved muscles remained approximately normal despite disease activity.

Child, Preschool↗
PubMed1991

"Dilatation" of the left renal vein on computed tomography in children: a normal variant.

Compression of the left renal vein (LRV) between the superior mesenteric artery and the aorta is thought to be a cause of hematuria, periureteral and gonadal varices, and varicocele ("Nutcracker phenomenon"). Previous investigators have suggested that this diagnosis can be made on computed tomography when the LRV ratio greater than or equal to 1.5 (the diameter of the LRV proximal to the aorto-mesenteric angle divided by the diameter of the LRV distal to the aorto-mesenteric angle). This study was designed to establish the normal range for the LRV ratio on CT in children. The LRV ratio was measured in thirty-nine consecutive children undergoing intravenously enhanced CT of the abdomen. None of the children had hematuria on urinalysis immediately before or after the CT. Children with any known abnormality involving the kidneys, adrenal glands, IVC, or renal or gonadal veins were excluded. The patients ranged in age from 3.4 to 18.5 years (mean = 10.6 years). LRV ratio ranged from 0.78 to 2.00 (mean = 1.46; S.D. = 0.312). Twenty of the 39 children (51.3%) had a LRV ratio greater than or equal to 1.50. The conclusion is that the normal range for the LRV ration is too wide for it to be useful in diagnosing LRV entrapment and that a LRV ratio greater than or equal to 1.5 on CT is normal in children.

Adolescent↗
PubMed1991

Association of increased cardiothoracic ratio and intrauterine growth retardation.

Clinical observation suggested an association between an increased cardiothoracic ratio (CT) and growth retardation (IUGR) in the premature neonate. To investigate this hypothesis, a case-control study was performed. Study subjects included 23 cases (IUGR) and 55 control (appropriate for gestational age [AGA]) premature infants with birthweights 2000 gm or less; Apgar scores greater than 5 at 5 minutes; no congenital heart disease; no polycythemia; no toxoplasmosis, rubella, cytomegalovirus, or herpes infection. In random order, the first chest radiograph of each infant (less than 24 hours) was reviewed by a single radiologist, unaware of the infant's growth status. The CT ratio was computed after measuring the widest internal width of the bony thorax and the cardiac diameter. Mean birthweight (+/- 1 SD) of the IUGR infants was 1161 +/- 289 g and of AGA infants was 1401 +/- 401 g (p less than 0.002); the mean gestational ages (+/- 1 SD) were 33.2 +/- 2.8 and 30.8 +/- 2.5 weeks (p less than 0.001). Mean CT for IUGR infants was 0.57 +/- 0.07 (+/- 1 SD) versus AGA infants, 0.51 +/- 0.04 (+/- 1 SD), p less than 0.001. When the infants were stratified by growth status and CT ratio, 11 of 23 IUGR and 1 of 55 AGA infants had an increased CT ratio p less than 0.0001. When birthweight and gestational age were covaried, growth status remained the best predictor of CT, p = 0.005. There is a strong association of increased CT and growth retardation in premature infants with birthweights 2000 gm or less.

Birth Weight↗