New source of MeV negative ion and neutral atom beams.

The scenario of "electron-capture and -loss" was recently proposed for the formation of negative ion and neutral atom beams with MeV kinetic energies. However, it does not explain why the formation of negative ions in a liquid spray is much more efficient than with an isolated atom. The role of atomic excited states in the charge-exchange processes is considered, and it is shown that it cannot account for the observed phenomena. The processes are more complex than the single electron-capture and -loss approach. It is suggested that the shell effects in the electronic structure of the projectile ion and/or target atoms may influence the capture/loss probabilities.

Pair creation in collision of γ-ray beams produced with high-intensity lasers.

Direct production of electron-positron pairs in two-photon collisions, the Breit-Wheeler process, is one of the basic processes in the universe. However, it has never been directly observed in the laboratory because of the absence of the intense γ-ray sources. Laser-induced synchrotron sources emission may open a way to observe this process. The feasibility of an experimental setup using a MeV photon source is studied in this paper. We compare several γ-ray sources and estimate the expected number of electron-positron pairs and competing processes by using numerical simulations including quantum electrodynamic effects.

Human gastrocnemius medialis pennation angle as a function of age: from newborn to the elderly.

The aim of the present study was to quantify changes in human skeletal muscle pennation angle (F theta) values during growth and adult life. The human gastrocnemius medialis muscle of 162 subjects (96 males and 66 females) in the age range 0-70 years was scanned with ultrasonography. The subjects were laying prone, at rest, with the ankle maintained at 90 degrees with all muscles relaxed. F theta increased monotonically starting from birth (0 years) and reached a stable value after the adolescent growth spurt. There was a significant (p < 0.05) linear relationship between F theta and muscle thickness (TK). F theta = 0.84 (+/- 0.09) * TK + 3.15 (+/- 1.13). Human gastrocnemius medialis F theta and TK data found in the literature seem to fit the F theta-TK plot in a coherent manner, independent of the physiological or anatomical characteristics of the subject. The present findings indicate that F theta is not a constant parameter but evolves, as is the case for bone length and height, as a function of age.

Doppler waveform of hepatic veins in healthy children.

OBJECTIVE: This study intends to document the presence or absence of triphasic waveforms in hepatic veins in healthy children. Does absence of triphasic hepatic vein flow indicate hepatic abnormality? SUBJECTS AND METHODS: One hundred children without a known hepatic or intrathoracic abnormality underwent Doppler sonography of their hepatic veins. Fifty girls and 50 boys were divided into five age groups. RESULTS: Forty-two children had triphasic flow in all three hepatic veins. Veins approaching an angle of 90 degrees with the inferior vena cava could not be assessed or had the least flow modulations despite angle correction. Neonates had the highest percentage of monophasic flow (seven of 21) in all three hepatic veins and none had triphasic flow in all three veins. CONCLUSION: Not all healthy children have a triphasic flow pattern in all hepatic veins. Before suspecting hepatic abnormality with abnormal parenchymal compliance (cirrhosis, graft rejection) by virtue of lack of triphasic hepatic vein flow, a normal variant of the flow should be considered. Only the change of a previously documented triphasic flow to monophasic flow in a given vein should be assessed as a sign of possible abnormality.

Sonographic nomogram of the leptomeninges (pia-glial plate) and its usefulness for evaluating bacterial meningitis in infants.

BACKGROUND AND PURPOSE: To our knowledge, the upper limits of the thickness of normal meninges on neurosonograms are not known. We therefore established a nomogram for sonographic measurements of the leptomeninges (pia-glial plate) and assessed its usefulness in neurosonographic examinations of children with bacterial meningitis. METHODS: The pia mater-cortical glia limitans complex on the surface of the brain and in the sulcus of a frontal gyrus was measured on neurosonograms in 100 infants without meningeal disease in order to establish a nomogram of the thickness of this pia-glial plate, referred to as the leptomeninx. Effects of prematurity, age, sex, and single-layer (surface) versus double-layer (sulcus) measurements were analyzed. Meningeal thicknesses derived from a retrospective analysis of the neurosonograms of 33 patients with purulent meningitis and a prospective study of 22 patients with bacterial meningitis were compared with the nomograms. Clinical outcomes of children with meningeal thickening were compared with those of affected children with normal meninges. RESULTS: The distribution of sulci measurements was significantly asymmetrical around the mean. Statistical data showed no influence of prematurity and sex, but showed surface measurements to be more consistent than sulcal measurements. Older chronological age was related to slightly larger sulci, but did not influence the surface measurements. In children with bacterial meningitis, the surface meninges were less frequently thickened than were the sulci. Sulcal enlargement occurred often in combination with echogenic deposits in the sub-arachnoid space. CONCLUSION: Leptomeninges are best measured on the surface of a gyrus rather than in a sulcus, as the normal thickness of the sulci shows much more variability. Clinical outcome of bacterial meningitis cannot be predicted by presence or absence of meningeal thickening as the only sonographic abnormality.

Nephrogenic adenoma of the bladder: ultrasound demonstration. A case report.

A 4-year-old girl developed a space-occupying lesion in the bladder. This was demonstrated by US after resection of a huge ureterocoele and bilateral re-implantation of ureters at 3 months of age and after three episodes of urinary tract infection. The mass developed outside the field of surgery and was removed endoscopically. Histology revealed a nephrogenic adenoma. US findings have not been emphasised previously. US should be useful in the detection of such lesions and for surveillance of recurrence.

Acute childhood pyelonephritis: predictive value of positive sonographic findings in regard to later parenchymal scarring.

RATIONALE AND OBJECTIVES: The authors evaluated the importance of positive sonographic findings in acute childhood pyelonephritis. MATERIALS AND METHODS: A total of 290 children (91 boys, 199 girls, aged 4 days to 15 years [median, 394 days]) with clinically suspected acute pyelonephritis underwent initial renal gray-scale ultrasound (US) and dimercaptosuccinate scintigraphic examination within 3 days of onset. A total of 173 patients underwent color or energy US examination. One hundred fifteen children with normal scintigraphic or pathologic findings (other than acute pyelonephritis) were excluded from further study; 170 patients with abnormal scintigraphic findings underwent follow-up scintigraphic scanning 60-90 days later. RESULTS: When pathologic structures other than acute pyelonephritis were not considered, the diagnostic value of gray-scale US was poor, with a sensitivity of 45.5%, a specificity of 86.6%, a positive predictive value of 88.8%, and a negative predictive value of only 40.6%. In regard to future renal scarring, gray-scale US had a positive predictive value of 67.7%, a negative predictive value of 40%, and a likelihood ratio of 1.16. Abnormal Doppler findings helped predict future scarring with a positive predictive value of 85.7%, a negative predictive value of 37.2%, a very low sensitivity of 26.9%, a high specificity of 90.6%, and a likelihood ratio of 2.87. CONCLUSION: Positive US Doppler findings in children with clinically suspected acute pyelonephritis indicate the need for immediate treatment. A positive initial gray-scale US examination does not predict future renal scarring, but a positive Doppler examination indicates a high probability of scarring. Negative gray-scale or Doppler US does not exclude a diagnosis of acute pyelonephritis and it cannot predict an absence of future scarring.

Appendicitis in children and young adults: Doppler sonographic-pathologic correlation.

OBJECTIVE: The purpose of this study was to determine the following: whether the arterial supply of a normal appendix is visible with Doppler sonography; whether the physiologic vasodilatation that accompanies childhood appendicitis is visible; what Doppler patterns appear once necrosis of the appendix has occurred; what Doppler shifts are visible with chronic, recurrent appendicitis; and whether other conditions in the right lower quadrant can mimic the Doppler sonographic patterns of appendicitis. MATERIALS AND METHODS: Twenty-five fasting patients without abdominal pain or intestinal disease and 45 patients (1-25 years old; mean, 8 years old) with right lower quadrant pain and suspected appendicitis were examined sonographically, using 5- and 7-MHz linear, color, and pulsed Doppler transducers. Arterial signals were sought within the appendix and neighboring tissues, counted, and classified as sparse (1-2), moderate (3-4), or abundant (>4). The resistive index (RI) was measured. Thirty patients who underwent surgery were retained for surgical and pathologic correlation, and only they formed the appendicitis study. RESULTS: A normal appendix was found in 10 patients. Doppler shifts were sparse, and diastolic flow was low or absent (RI, 0.85-1). Acute uncomplicated appendicitis was found in 13 patients, who had abundant color Doppler signals throughout most of the appendix, with high diastolic flow (RI, 0.40-0.77; mean, 0.54). Acute necrotic appendicitis with perforation was found in 11 children, eight of whom showed no signals in the necrotic area at the tip. Few or no signals were seen in the remainder of the appendix (RI, 0.33-0.90; mean, 0.54). In two patients, signals were abundant in the tissues surrounding the appendix. Recurrent or chronic appendicitis was found in three patients, previously diagnosed as having Crohn's disease, psychosomatic illness, or nonspecific abdominal pain. The appendix had Doppler signals confined to the tip (RI, 0.63-0.83; mean, 0.75). Other diagnoses were found in three patients, in whom the appendix was not seen. There were abundant color signals in the intestinal wall and adjacent tissues in the right lower quadrant. Two patients had Crohn's disease, and the third had an unsuspected early pregnancy. The appendix was normal in all. CONCLUSION: Acute appendicitis is accompanied by inflammatory hypervascularity reflected as an increased number of color signals and higher diastolic Doppler shifts as compared with those found in normal persons. No Doppler shifts are identified in areas of appendiceal ischemia. Other acute inflammation in the right lower quadrant also produces numerous Doppler shifts with high diastolic flow, as does ovulation. Care must be taken to identify the source of these Doppler signals. The changing vascularity of healing, recurrent, and chronic appendicitis promises to further our understanding of the pathogenesis and evolution of this disease.

Ultrasonography of jejunal intussusception in children.

OBJECTIVE: To describe the ultrasonographic findings in different forms of jejunal intussusception in three children. PATIENTS AND METHOD: Two children with hamartomatous polyps of the jejunum acting as lead points for antegrade jejunoileocolic intussusception and retrograde jejunoduodenogastric intussusception respectively and one child with idiopathic postoperative intussusception were examined by ultrasonography. RESULTS: The findings of the US studies were abnormal and different in each case, depending on the underlying condition and the direction (antegrade or retrograde) of the intussusception. The hamartomatous polyps were seen as hyperechoic solid masses but could not be diagnosed more specifically with US. A target lesion was found in the case of idiopathic postoperative intussusception. The US results prompted the next imaging procedure, air enema in the one patient in whom the intussusception had reached the colon and preoperative barium meal in all of the patients. Surgery was performed without the delay that usually occurs with jejunal intussusception. CONCLUSION: In the appropriate clinical setting, US should be used to look for jejunal intussusception, so that suitable diagnostic gastrointestinal studies can be performed and delay in diagnosis avoided.

Testicular torsion in infants and children: diagnosis with Doppler sonography.

The accuracy of Doppler sonography in the evaluation of testicular torsion was tested in 65 boys (aged 0-18 years) with acute scrotal pain or swelling. All patients underwent pulsed Doppler sonography of both testes, followed by scintigraphy (n = 16) and/or surgery (n = 34) and a close clinical follow-up for 4-8 months (n = 31). Color Doppler sonography was performed in 29 patients. The testicular artery was deemed patent if Doppler shifts from branches within the parenchyma could be found. Surgery revealed 19 cases of testicular torsion, 17 of which were diagnosed with Doppler sonography. There were six technical failures, in which no signals could be found on either side. In four boys, no color signals were obtained in either testis but subsequent examination with a mechanical sector scanner and pulsed Doppler sonography yielded arterial signals. Doppler sonography was successful in 59 of 65 boys (91%) and yielded a sensitivity of 89% and specificity of 100%. Pulsed Doppler sonography with mechanical sector scanners was more sensitive than color Doppler sonography. Intermittent torsion was missed both with Doppler sonography and scintigraphy.

Duplex Doppler sonographic examinations of the testis in prepubertal boys.

This retrospective study of 143 pediatric patients with unilateral acute scrotal disease was done to assess the value of duplex Doppler sonographic examination prior to puberty (110 patients) in comparison to a pubertal group (33 patients) in a pediatric hospital, where the examinations are done by staff radiologists and radiology residents of varying degrees of expertise and experience with Doppler technique. All patients seen during an 18 month period were included. The unaffected side was examined in most patients and served as control. The normal Doppler shift in the center of the prepubertal testis was found to be 0.2 to 0.5 kHz, when using a 5 MHz duplex Doppler probe. With puberty, the Doppler shift increased to 0.5 to 1 kHz. Of 18 patients (10 prepubertal) with testicular torsion, five (three prepubertal) had false-positive Doppler shift. In four of these five cases, faulty placement of the Doppler sample volume cursor was probably the cause. Using a multi-way frequency analysis, puberty was found to have no significant influence on results of Doppler signal (chi square = 0.1346; P = 0.7137). Duplex Doppler sonographic examination is as useful to rule out testicular torsion in prepubertal boys as it is after puberty. Meticulous technique is essential. The opposite side should be examined first and serves as control for the affected one. Results showing no flow in the center of the diseased testis with positive flow in the unaffected one should lead to further clinical action (scintigraphy or surgery).