Velocity-space tomography using prior information at MAST.

Velocity-space tomography provides a way of diagnosing fast ions in a fusion plasma by combining measurements from multiple instruments. We use a toroidally viewing and a vertically viewing fast-ion D-alpha diagnostic installed on the mega-amp spherical tokamak (before the upgrade) to perform velocity-space tomography of the fast-ion distribution function. To make up for the scarce amount of data, prior information is included in the inversions. We impose a non-negativity constraint, suppress the distribution in the velocity-space region associated with null-measurements, and encode the belief that the distribution function does not extend to energies significantly higher than those expected neoclassically. This allows us to study the fast-ion velocity distributions and the derived fast-ion densities before and after a sawtooth crash.

Beam-Ion Acceleration during Edge Localized Modes in the ASDEX Upgrade Tokamak.

The acceleration of beam ions during edge localized modes (ELMs) in a tokamak is observed for the first time through direct measurements of fast-ion losses in low collisionality plasmas. The accelerated beam-ion population exhibits well-localized velocity-space structures which are revealed by means of tomographic inversion of the measurement, showing energy gains of the order of tens of keV. This suggests that the ion acceleration results from a resonant interaction between the beam ions and parallel electric fields arising during the ELM. Orbit simulations are carried out to identify the mode-particle resonances responsible for the energy gain in the particle phase space. The observation motivates the incorporation of a kinetic description of fast particles in ELM models and may contribute to a better understanding of the mechanisms responsible for particle acceleration, ubiquitous in astrophysical and space plasmas.

Velocity-space sensitivities of neutron emission spectrometers at the tokamaks JET and ASDEX Upgrade in deuterium plasmas.

Future fusion reactors are foreseen to be heated by the energetic alpha particles produced in fusion reactions. For this to happen, it is important that the energetic ions are sufficiently confined. In present day fusion experiments, energetic ions are primarily produced using external heating systems such as neutral beam injection and ion cyclotron resonance heating. In order to diagnose these fast ions, several different fast-ion diagnostics have been developed and implemented in the various experiments around the world. The velocity-space sensitivities of fast-ion diagnostics are given by so-called weight functions. Here instrument-specific weight functions are derived for neutron emission spectrometry detectors at the tokamaks JET and ASDEX Upgrade for the 2.45 MeV neutrons produced in deuterium-deuterium reactions in deuterium plasmas. Using these, it is possible to directly determine which part of velocity space each detector observes.

Velocity-space sensitivity of the time-of-flight neutron spectrometer at JET.

The velocity-space sensitivities of fast-ion diagnostics are often described by so-called weight functions. Recently, we formulated weight functions showing the velocity-space sensitivity of the often dominant beam-target part of neutron energy spectra. These weight functions for neutron emission spectrometry (NES) are independent of the particular NES diagnostic. Here we apply these NES weight functions to the time-of-flight spectrometer TOFOR at JET. By taking the instrumental response function of TOFOR into account, we calculate time-of-flight NES weight functions that enable us to directly determine the velocity-space sensitivity of a given part of a measured time-of-flight spectrum from TOFOR.

Resolving the bulk ion region of millimeter-wave collective Thomson scattering spectra at ASDEX Upgrade.

Collective Thomson scattering (CTS) measurements provide information about the composition and velocity distribution of confined ion populations in fusion plasmas. The bulk ion part of the CTS spectrum is dominated by scattering off fluctuations driven by the motion of thermalized ion populations. It thus contains information about the ion temperature, rotation velocity, and plasma composition. To resolve the bulk ion region and access this information, we installed a fast acquisition system capable of sampling rates up to 12.5 GS/s in the CTS system at ASDEX Upgrade. CTS spectra with frequency resolution in the range of 1 MHz are then obtained through direct digitization and Fourier analysis of the CTS signal. We here describe the design, calibration, and operation of the fast receiver system and give examples of measured bulk ion CTS spectra showing the effects of changing ion temperature, rotation velocity, and plasma composition.

Polarizer design for millimeter-wave plasma diagnostics.

Radiation from magnetized plasmas is in general elliptically polarized. In order to convert the elliptical polarization to linear polarization, mirrors with grooved surfaces are currently employed in our collective Thomson scattering diagnostic at ASDEX Upgrade. If these mirrors can be substituted by birefringent windows, the microwave receivers can be designed to be more compact at lower cost. Sapphire windows (a-cut) as well as grooved high density polyethylene windows can serve this purpose. The sapphire window can be designed such that the calculated transmission of the wave energy is better than 99%, and that of the high density polyethylene can be better than 97%.

Multiple indomethacin-induced colonic perforations in an adolescent.

Colonic perforation is an uncommon cause of acute abdomen in paediatric patients, and can present a diagnostic enigma as well as management challenge to the paediatric surgeon. An adolescent developed multiple colonic perforations following a short course of oral indomethacin, requiring emergency hemicolectomy. This is the youngest known case of enteral non-steroidal anti-inflammatory drug (NSAID)-mediated large bowel injury. We review current evidence on NSAID-related enteropathy, and postulate potentiating mechanisms that may have accounted for the unusually rapid clinical course of our patient.

Malignant peripheral nerve sheath tumor mimicking carotid body tumor--case report and review.

Malignant peripheral nerve sheath tumor is a rare neurogenic tumor that usually presents in geriatic patients. Typically, it is found in the trunk and extremities and rarely presents in the head and neck region. It may mimic a carotid body tumor when it presents in the neck. We report the first case of malignant peripheral nerve sheath tumor of the vagus nerve in an adolescent boy. He presented with an asymptomatic lateral neck lump that was thought to be a benign schwannoma on preoperative imaging. We describe the diagnostic dilemma and management difficulties in this patient and review the literature.

Persistent sterile pyuria in children? Don't forget tuberculosis!

Genitourinary tuberculosis (GUTB) is exceptionally uncommon among the local paediatric population. A 10-year-old Chinese girl with no risk factors for tuberculosis presented with recurrent sterile pyuria. Despite extensive renal investigations, no apparent cause could be ascertained for her obstructed left drainage system. The diagnosis was eventually confirmed with urine acid-fast bacilli culture, after a computed tomography scan suggested possible renal tuberculosis. Left nephroureterectomy had to be performed owing to deteriorating left kidney function. This report discusses the importance of considering tuberculosis when assessing a local paediatric patient with an atypical urinary tract infection. Early diagnosis of renal tuberculosis can prevent the sequelae of GUTB, including renal impairment.

Antibiotics and postoperative abscesses in complicated appendicitis: is there any association?

INTRODUCTION: Complicated appendicitis has significant infective postoperative morbidity. There is no universally-accepted antibiotic regime, although traditionally, triple antibiotics are recommended. Our complicated appendicitis clinical pathway recommends ceftriaxone and metronidazole. The study aimed to determine if choice of antibiotics influenced the risk of infective complications. METHODS: We reviewed all paediatric appendicectomy patients between January 1, 2005 and December 31, 2005. All patients with intraoperative diagnosis of perforated appendicitis were recruited, excluding infants, immunocompromised patients, and patients allergic to the guideline antibiotics. All operations were performed by registrar/consultant surgeons and were laparoscopic, unless technically not feasible. RESULTS: There were 82 patients with perforated appendicitis. 62 patients (76 percent) followed pathway antibiotics, and 20 patients (24 percent) deviated from the pathway by receiving additional empiric gentamycin. We compared the pathway compliant and deviation groups, and found no significant differences in patient characteristics, clinical presentation, operation, length of stay and infective complications. Overall there was one wound infection and five (six percent) postoperative abscesses. Initial peritoneal cultures and subsequent drainage cultures of patients who developed abscesses were sensitive to treatment antibiotics. CONCLUSION: In complicated appendicitis, empirical perioperative addition of gentamycin to ceftriaxone and metronidazole did not reduce the risk of developing intra-abdominal abscess, compared to changing antibiotics on clinical grounds. Patients developed postoperative abscesses despite initial peritoneal cultures growing organisms sensitive to treatment antibiotics.

Swallowed foreign bodies in children: report of four unusual cases.

INTRODUCTION: Although a majority of ingested foreign bodies (FBs) pass down the gastrointestinal tract spontaneously, those that are sharp, pointed or large in size need removal to avert serious complications. We highlight the urgent need and utility of endoscopic accessories and technical artistry in safe retrieval of FBs in children. CLINICAL PICTURE: Four children had accidentally swallowed a nail, metallic dumbbell, open safety pin and a cushion pin respectively. They were symptom-free and the abdominal plain radiographs revealed foreign body in the stomach in all the cases. TREATMENT: Oesophago-gastro-duodenoscopy (OGD) was done in all the patients and could retrieve the nail, metallic dumbbell and open safety pin successfully using a Dormia basket, a polypectomy snare and a pair of rat-tooth forceps respectively. The cushion pin had migrated to the duodeno-jejunal junction within 4 hours of ingestion and necessitated open duodenotomy and retrieval. OUTCOME: All patients did well after the procedure with no complications. CONCLUSIONS: Swallowed FBs with pointed or sharp ends or large enough to cross the pylorus and duodenal sweep need removal and in the majority of the cases they can be retrieved by OGD. Sharp or pointed FBs that have crossed the second part of the duodenum necessitate urgent laparotomy for retrieval to prevent complications.

Sutureless circumcision: a prospective randomised controlled study.

Our aim was to study the advantages of glue versus sutures for circumcision in children. A randomised prospective controlled study was conducted with 152 boys; glue was used on 80 and sutures on 72. The procedures were quicker and the duration and severity of postoperative pain were significantly less (p < 0.001) in the cases in which glue was used. The tissue glue is a perfectly feasible alternative to sutures for circumcision in children and has potentially significant advantages.

When is a mediastinal mass critical in a child? An analysis of 29 patients.

The aims of this study were to determine the pattern of presentation of childhood mediastinal masses in our community and to identify factors associated with the development of acute airway compromise. The authors retrospectively reviewed the records of 29 consecutive patients with mediastinal masses managed at their institution between January 1995 and December 2001. Demographic data, mass characteristics, clinical presentation, and surgical procedures were recorded. Seven patients (24.1%) were asymptomatic at presentation. Eight (27.6%) were classified as having acute airway compromise at presentation. Respiratory symptoms and signs were the most common mode of presentation (58.6% and 55.2%, respectively). The most common histological diagnosis was neurogenic mass (37.9%), followed by lymphoma (24.1%). Most masses were located in the superior mediastinum (41.1%). Factors associated with the development of acute airway compromise were (1) anterior location of the mediastinal mass (P=0.019), (2) histological diagnosis of lymphoma (P=0.008), (3) symptoms and signs of superior vena cava syndrome (P=0.015 and 0.003, respectively), (4) radiological evidence of vessel compression or displacement (P=0.015), (5) pericardial effusion (P=0.015), and (6) pleural effusion (P=0.033). Clinical presentation of childhood mediastinal masses is often nonspecific or incidental. Yet they have the propensity of developing acute airway compromise, which is closely associated with superior vena cava obstruction. Such patients should be managed as a complex cardiorespiratory syndrome, termed "critical mediastinal mass syndrome", by an experienced multidisciplinary team.

Childhood acute pancreatitis in a children's hospital.

OBJECTIVE: To analyse the cases of acute pancreatitis presented to a children's hospital in Singapore. METHODS: Clinical charts of all children, aged under 18 years, who presented to our hospital for the first time with pancreatitis (ICD search criteria = 577.x) between the period of 1998 and mid-2002 were reviewed. Parameters analysed included presenting features, aetiology of the acute pancreatitis, length of hospital stay, complications, treatment and outcome. RESULTS: There were 12 cases in the review period, and the attributable causes in these cases were, in descending order, trauma, drug-induced, anatomical anomalies, poisoning and idiopathic. Of interest were two patients whose pancreatitis were results of child abuse. The most common symptoms were abdominal pain (n=11) and vomiting (n=7), though only five patients localised the pain to the epigastrium. Abdominal tenderness could be elicited in all the patients. Eleven had evidence of acute pancreatitis from computerised tomography (CT) whilst the twelfth was diagnosed with ultrasonography. The peak amylase levels amongst these patients were not high, with a median of 512.5 U/L. In the acute stage, only one patient required operative intervention whilst the remainder were managed conservatively. The mean length of hospital stay was 12.41 +/- 4.54 days. The complications encountered included pseudocyst formation, ascites, hypocalcaemia, pleural effusion and coagulopathy. CONCLUSIONS: The diagnosis of acute pancreatitis in children can be difficult. This is often due to ambiguous symptoms, signs and laboratory results. CT and ultrasound are essential investigations in the diagnosis and subsequent follow-up.

Comparing wound closure using tissue glue versus subcuticular suture for pediatric surgical incisions: a prospective, randomised trial.

Tissue adhesives have gained favour for quicker and painless closure of lacerations. To compare the tissue adhesive 2-octylcyanoacrylate with our current standard subcuticular suture for closure of surgical incisions in children, looking at outcome measures of time efficiency, cosmesis, and wound complications, a prospective, randomised, controlled trial was conducted at our institution's ambulatory surgery centre. All healthy patients undergoing unilateral or bilateral herniotomies were recruited prospectively with informed consent and randomly allocated to suture or glue. The exclusion criteria were neonates or children with allergy to tissue glue. Time of wound closure was measured from the subcutaneous layer to application of the dressing. An independent, blinded observer assessed cosmesis at 2 to 3 weeks using a validated wound scale ranging from worst (0) to best (6). Parent satisfaction with wound appearance was recorded on a 100-mm visual analogue scale (VAS). A total of 59 patients were recruited into the study with 26 in the glue group and 33 in the suture group. There was no difference in mean time of closure (glue 181 +/- 62 s vs suture 161 +/- 45 s, P = 0.18). Two patients in each group had a suboptimal Hollander wound score of 5 (7.7% glue, 6.1% suture). There was also no difference in parent satisfaction (VAS: glue 78 +/- 19 mm vs suture 81 +/- 15 mm, P = 0.68). No patient reported any rash, wound infection, or dehiscence. Tissue glue is easy to use with no complications and has equivalent cosmetic results, but is not faster than a subcuticular suture.

Clinics in diagnostic imaging (73). Left hydronephrosis due to pelvi-ureteric junction obstruction.

A full-term male infant was antenatally diagnosed to have left hydronephrosis. Post natal ultrasonography (US) and diuretic renography confirmed the diagnosis of left pelvi-ureteric junction obstruction. His clinical course was complicated by one episode of urinary tract infection. Serial US and diuretic renography showed no improvement in the obstruction. The patient underwent an Anderson-Hynes pyeloplasty at nine months of age with no post-operative complications. The diagnosis and management of antenatally-diagnosed hydronephrosis are discussed.

Intussusception: a three-year review.

INTRODUCTION: Intussusception is the commonest cause of intestinal obstruction in infants and young children. MATERIALS AND METHODS: This report reviews the clinical presentation, investigations and outcomes of patients with intussusception treated at the KK Women's and Children's Hospital between 1 May 1997 and 30 April 2000. RESULTS: The study population comprised 160 consecutive patients treated for intussusception at our hospital over this 3-year period. The commonest symptom was vomiting; present in 135 patients (84.4%). A palpable abdominal mass was present in 90 patients (56.3%). The classical features of vomiting, abdominal pain, abdominal mass and rectal bleeding were present together in only 12 patients (7.5%). Abdominal ultrasonography was performed in 155 patients. One hundred and fifty-two patients (98.1%) had the classical target lesion on ultrasonography. Air enema reduction was attempted in all except 6 patients. In the majority of patients (130 or 84.4%), the intussusception was reduced successfully by air enema reduction. There was no association between the duration of symptoms before radiological reduction and the outcome of radiological reduction. CONCLUSIONS: As the four classical features of intussusception were present together in only 7.5% of our patients, a high index of suspicion is necessary when any of the signs and symptoms are present in an infant or young child. Abdominal ultrasonography is the diagnostic investigation of choice. Air enema reduction was successful in 84.4% of patients and the duration of symptoms did not reduce the success rate. Thus, air enema reduction should be attempted in most patients unless they have absolute contraindications.

Laparoscopy in the evaluation of the non-palpable undescended testes.

AIM OF STUDY: To examine the role of laparoscopy in the evaluation of the non-palpable undescended testes in paediatric patients. METHOD: A review of all laparoscopies performed for the evaluation of the non-palpable undescended testes in a children's hospital over a 12-month period was conducted. Special attention was paid to the patients' age, the location of the testes at the time of laparoscopy, the subsequent surgical procedures and the complications. RESULTS: Sixteen boys underwent laparoscopy to localise 20 nonpalpable testes. 12 patients had unilateral disease while 4 had bilateral disease. 15 non-palpable testes were intraabdominal, 3 had inguinal testicular remnants and 2 had 'vanished'. A contralateral inguinal hernia was incidentally found in one patient. A patient with epididymal-gonadal non-union was not apparent at laparoscopy. There were no post-laparoscopic complications in all 16 patients. CONCLUSION: Laparoscopy is safe and accurate in the evaluation of non-palpable testes in children. The accurate localisation of intraabdominal testes facilitates the development of an optimal surgical strategy.