Fundamentals of pair diffusion in kinematic simulations of turbulence.

We demonstrate that kinematic simulation (KS) of three-dimensional homogeneous turbulence produces fluid element pair statistics in agreement with the predictions of L F. Richardson [Proc. R. Soc. London, Ser. A 110, 709 (1926)] even though KS lacks explicit modeling of turbulent sweeping of small eddies by large ones. This scaling is most clearly evident in the turbulent diffusivity's dependence on rms pair separation and, to a lesser extent, on the pair's travel time statistics. It is also shown that kinematic simulation generates a probability density function of pair separation which is in good agreement with recent theory [S. Goto and J. C. Vassilicos, New J. Phys. 6, 65 (2004)] and with the scaling of the rms pair separation predicted by L. F. Richardson [Proc. R. Soc. London, Ser. A 110, 709 (1926)]. Finally, the statistical persistence hypothesis (SPH) is formulated mathematically and its validity tested in KS. This formulation introduces the concept of stagnation point velocities and relates these to fluid accelerations. The scaling of accelerations found in kinematic simulation supports the SPH, even though KS does not generate a Kolmogorov scaling for the acceleration variance (except for a specific case and a limited range of outer to inner length-scale ratios). An argument is then presented that suggests that the stagnation points in homogeneous isotropic turbulence are on average long-lived.

Acceleration statistics as measures of statistical persistence of streamlines in isotropic turbulence.

We introduce the velocity Vs of stagnation points as a means to characterize and measure statistical persistence of streamlines. Using theoretical arguments, direct numerical simulations (DNS), and kinematic simulations (KS) of three-dimensional isotropic turbulence for different ratios of inner to outer length scales L/eta of the self-similar range, we show that a frame exists where the average Vs = 0 , that the rms values of acceleration, turbulent fluid velocity, and Vs are related by La'/u'2 approximately (V's/u')(L/eta)(2/3+q) , and that V's/u' approximately (L/eta)q with q = -1/3 in Kolmogorov turbulence, q = -1/6 in current DNS, and q = 0 in our KS. The statistical persistence hypothesis is closely related to the Tennekes sweeping hypothesis.

Role of breast magnetic resonance imaging in difficult diagnostic situations.

In some patients with breast disease, mammography and ultrasonography can provide only limited diagnostic information. Magnetic resonance imaging of the breast has high sensitivity and specificity and can play a significant diagnostic role in problem situations. Patients who are most likely to benefit are those with (i) axillary adenopathy of unknown primary origin, (ii) possible tumour recurrence after surgery or radiotherapy, (iii) lesions overlying implants, or (iv) those requiring staging of lobular or multifocal carcinoma.

Cat-scratch disease with paravertebral mass and osteomyelitis.

The case of a 9-year-old girl with cat-scratch disease (CSD) complicated by development of a paravertebral mass and osteomyelitis is presented. Following multiple scratches and inguinal lymphadenopathy, she developed back pain, and imaging demonstrated a paravertebral mass with evidence of osteomyelitis involving vertebra T9. The diagnosis was made on the basis of detection of Bartonella henselae by use of molecular techniques on an aspirate from the vertebral column and supportive serology for infection with B. henselae. Eleven other cases of this unusual manifestation associated with CSD have been reported in the literature and are reviewed. The patient was treated with gentamicin, followed by rifampicin and trimethoprim-sulfamethoxazole, orally and made a favorable recovery over 7 months. This is comparable with other case reports, regardless of the choice of antibiotic therapy. CSD in immunocompetent hosts is not always self-limiting, and tissues beyond the lymph nodes can be involved.

Determination of ML-1035 enantiomers in plasma by chiral high-performance liquid chromatography.

ML-1035, is a gastroprokinetic agent structurally related to metoclopramide. Because ML-1035 contains an asymmetric chiral sulphoxide moiety, a chiral HPLC method has been developed to separate and quantitate its R- and S-enantiomers in plasma. The ML-1035 enantiomers present in plasma are extracted with dichloroethane under alkaline conditions, the extract evaporated to dryness and reconstituted in the mobile phase. Samples are chromatographed on a Chiralcel OD HPLC column with hexane-absolute ethanol (1% TEA) (1:1, v/v) as the mobile phase. The enantiomers of the unchanged drug are determined by fluorescence measurement (ex: 310 nm, em: 350 nm). The method provides a linear response for both enantiomers over a concentration range of 25 (limit of determination) to 2500 ng ml-1 with correlation coefficients of 0.9987 or greater. The inter-assay precision is 9.5% or less and the accuracy ranges from 93.9 to 103.4% of the theoretical value. The method is used to determine the plasma concentrations of the R- and S-enantiomers following oral and intravenous administration of R- or S-enantiomers to dogs. The method is also adapted to measure enantiomer levels from in vitro reaction mixtures so that the possibility of metabolic inversion may be assessed. The data suggest that no significant level of inversion between the enantiomers occurred either in vivo or in vitro.

Column-switching high-performance liquid chromatographic (HPLC) determination of hydrochlorothiazide in rat, dog, and human plasma.

A fully automated HPLC assay for hydrochlorothiazide in plasma has been developed using a column-switching technique. The method involves direct injection of plasma to the extraction column for sample cleanup followed by switching onto the analytical column. Good precision, accuracy, and linearity were obtained over a range of 25 to 2000 ng/ml in rat, dog, and human plasma. The column-switching method has also been validated by comparison with a conventional HPLC method requiring a cumbersome plasma extraction procedure. Since the method is simple, rapid, and reproducible, it is useful for determination of hydrochlorothiazide levels in animal and human plasma.

Involvement of posterior visual pathways by optic nerve gliomas.

We describe the computed tomographic (CT) findings in seven children with optic nerve gliomas extending posterior to the chiasm. These tumors spread along the optic tracts and in five of seven cases, involved the lateral geniculate bodies and adjacent optic radiations. The propensity for these tumors to extend along both the anterior and posterior visual pathways aids in their diagnosis. An MR scan was obtained in one patient and identified an unexpected site of tumor extension as well as the mass seen by CT.

Computed tomographic analysis of deformity and dimensional changes in the eyeball.

Computed tomography (CT) was performed in 40 patients with a confirmed ophthalmic diagnosis and a change in the dimensions or configuration of the eyeball. Abnormalities studied included coloboma, microphthalmus, buphthalmos, axial myopia, macrophthalmus, phthisis bulbi, trauma, neoplasm, posterior staphyloma, granuloma, pseudotumor, and surgical scleral banding for retinal detachment. CT findings could be grouped into three categories depending upon whether the eye was small, large, or normal in size, with the findings in each group allowing distinction of most disease processes.

Safety of contrast media in cerebral angiography: iopamidol vs. methylglucamine iothalamate.

A randomized double-blind study was performed in 27 patients to compare the clinical safety, incidence of pain and warmth, and film quality produced by iopamidol and Conray-60 in selective cerebral angiography. No complications or adverse reactions occurred in either group. Iopamidol was significantly less painful than was methylglucamine iothalamate for common carotid artery injections and caused significantly less heat in both common carotid and internal carotid artery injections. Film quality and diagnostic accuracy were excellent in both groups. These results, when viewed in conjunction with laboratory data demonstrating the decreased neurotoxicity of nonionic contrast agents, suggest that iopamidol is an important advance in the development of angiographic contrast media.

CT demonstration of hyperdense cerebral vasculature due to bromide therapy.

An increase in the effective atomic number of blood is among the factors allowing or influencing the visualization of the major cerebral vessels on noncontrast CT. Bromine (atomic number, 50) attenuates 70 keV X-rays significantly and was responsible for a striking enhancement of the major cerebral vessels on the noncontrast CT in a child being treated for epilepsy. Although oral bromides are only occasionally used in the treatment of epilepsy, their use causes an increase in blood density and thus bromides need to be considered along with other etiologies (reviewed) that allow visualization of the major cerebral vessels on noncontrast CT.

Examination of the extracranial carotid bifurcation by thin-section dynamic CT: direct visualization of intimal atheroma in man (Part 1).

Because carotid angiography has been shown to have limitations in the detection of intimal disease at the bifurcation, a new method of examination of the extracranial carotid artery has been developed using thin-section dynamic computed tomographic (CT) scanning. Carotid atheroma and thrombi can be imaged directly on these sections. The intimal lesions are uniformly hypodense with respect to the carotid arterial wall. Radiologic-pathologic correlation studies using human carotid arteries in a neck phantom confirm that these hypodense lesions are atheromas or thrombi. There is good correlation between CT cross-sectional images and cross-sectional postmortem artery sections. While a number of new computer-based methods of reformation of the carotid artery have been developed, consecutive thin slices through the carotid bifurcation display the pathologic lesions satisfactorily.

Role of computed tomography in the radiological evaluation of painful radiculopathy after negative myelography: foraminal neural entrapment.

Thirty-five patients with an unremarkable or a negative water-soluble contrast myelogram and a diagnosis of foraminal neural entrapment made or more firmly established by computed tomography (CT) were detected in evaluating 950 patients presenting for myelography. The CT criterion of foraminal neural entrapment was the presence of a mass displacing epidural fat and encroaching on the neural intervertebral foramen or lateral recess so as to compromise an emerging nerve root. The entrapment (confirmed operatively) was due to a laterally prolapsed disc (16 cases), superior articular hypertrophy (4 cases), lateral recess stenosis (3 cases), posterolateral vertebral bone lipping (2 cases), tumors (6 cases), postoperative scarring (2 cases), spondylolisthesis (1 case), and synovial cysts that encroached on the neural foramina (1 case). CT is an important additional investigation in patients with a painful radiculopathy and a negative or equivocal water-soluble contrast myelogram.

Suprasellar papillary squamous epithelioma ("papillary craniopharyngioma").

Six cases of a distinctive suprasellar papillary neoplasm are presented and the features of this lesion are contrasted with those of the classical adamantinomatous craniopharyngioma. Characteristics distinguishing the former from the latter include a predominate, and perhaps exclusive, occurrence in adulthood; frequent radiologic solidity and absence of calcification; macroscopic papillary nature; and, microscopically, a well-differentiated papillary squamous epithelium without calcification, palisaded cells, or keratoid nodules. We suggest that this papillary lesion is a clinicopathologic entity distinct from the classical adamantinomatous craniopharyngioma.

Craniocerebral trauma in the child abuse syndrome: radiological observations.

Experience with craniocerebral trauma in 712 physically abused children is reviewed. Ninety-three (13%) had evidence of head trauma (cranial and/or intracranial). Seventy-seven of these patients had computed tomography (CT) of the head, and 47 had CT evidence of intracranial injury. Extracerebral fluid collections, predominantly convexity subdural hemorrhage, were the most common acute intracranial lesions. Concurrent intracranial and skeletal trauma (cranial and/or extracranial) was present in 33 of the 47 patients (70%) with intracranial injury. A high incidence of skull fractures (45%) in those children with intracranial lesions suggest a significant role for impact head injuries ("battering") in the pathogenesis of craniocerebral trauma in the child abuse syndrome. Greater emphasis on CT examination in evaluation of the abuse infant and child is recommended.

Craniocerebral trauma in the child abuse syndrome.

Craniocerebral trauma, and more specifically intracranial injury, is the most devastating consequence of child abuse. Cranial computed tomography provides a sensitive method for evaluation of the abused child for craniocerebral injury. CT may be particularly useful for demonstrating intracranial lesions that might not be immediately evident from clinical examination. The CT findings may also clarify the nature of the trauma, both cranial and intracranial, with detail not otherwise possible. It is therefore surprising that an expanded role for CT in evaluation of child abuse has not received wider general consideration or acceptance. Discussions of child abuse either fail to note CT in evaluation of the abused child or give the subject only cursory attention. Caffey's initial admonition that the presence of unexplained fractures in the long bones warrants investigation for subdural hematoma has gone largely unheeded. A high index of suspicion for abuse, especially in the young infant, should be sufficient reason to request cranial CT. In some cases of abuse without acute neurologic abnormality chronic sequelae, otherwise unsuspected, may be demonstrated by follow-up CT.

Single photon emission computed tomography and its application in the lung.

SPECT systems should affect nuclear medicine because of their ability to eliminate overlying and underlying radionuclide activity, their capacity for total volume imaging, and the increased contrast for lesions, compared with conventional planar imaging and their quantitative potential. The authors offer a preview of the uses of this developing technology in the delineation of perfusion abnormalities.