Intracranial circulation: pulse-sequence considerations in three- dimensional (volume) MR angiography

The technique and feasibility of magnetic resonance (MR) angiography of intracranial vessels were studied in 35 healthy volunteers. Variations in image orientation, repetition time (TR), and flip angle were evaluated to determine their effects on flow-related enhancement. Gradient modifications--including echo time (TE), motion compensation, bandwidth, and field of view--were also studied in an effort to reduce motion-induced phase shifts. Results indicated that a FISP (fast imaging with steady precession) sequence with a TR of 50 msec, TE of 15 msec, velocity compensation in the read and section-select directions, acceleration compensation in the read direction, anisotropic volume, and a 1.25-mm partition thickness produced three-dimensional angiographic MR images that were accurate and reproducible in the depiction of the major intracranial vessels. Difficulties with field of view, persistent signal void secondary to higher-order motion, and spatial resolution remain major problems requiring additional study.     

Paediatric dacryocystorhinostomy

Of 258 cases of dacryocystorhinostomy performed on children in the period September 1981 to September 1991, 130 were for simple, unresolved congenital nasolacrimal duct obstruction. Other indications for surgery included punctal agenesis, lacrimal fistula, post-traumatic and post-inflammatory canalicular obstruction. Of 177 children without canalicular pathology, 171 (96%) were relieved of symptoms with one operation, without canalicular intubation. Of 81 cases with canalicular disease, 55 of 70 (79%) who underwent DCR plus canalicular intubation, and 10 of 11 who underwent DCR plus Lester-Jones tube, were substantially improved with one operation. No child required peroperative or postoperative blood transfusion. Dacryocystorhinostomy in childhood, in experienced surgical hands, is a safe procedure, achieving relief of symptoms in most cases, particularly in the absence of canalicular disease.     

Predominance of null mutations in ataxia-telangiectasia

Ataxia-telangiectasia (A-T) is an autosomal recessive disorder involving cerebellar degeneration, immunodeficiency, chromosomal instability, radiosensitivity and cancer predisposition. The responsible gene, ATM, was recently identified by positional cloning and found to encode a putative 350 kDa protein with a Pl 3-kinase-like domain, presumably involved in mediating cell cycle arrest in response to radiation-induced DNA damage. The nature and location of A-T mutations should provide insight into the function of the ATM protein and the molecular basis of this pleiotropic disease. Of 44 A-T mutations identified by us to date, 39 (89%) are expected to inactivate the ATM protein by truncating it, by abolishing correct initiation or termination of translation, or by deleting large segments. Additional mutations are four smaller in-frame deletions and insertions, and one substitution of a highly conserved amino acid at the Pl 3-kinase domain. The emerging profile of mutations causing A-T is thus dominated by those expected to completely inactivate the ATM protein. ATM mutations with milder effects may result in phenotypes related, but not identical, to A-T.      

The effect of methodology on the determination of nasal resistance

Confusion and controversy continue to characterize scientific understanding of the role that respiration plays in modifying growth. Identification of specific methods to provide valid measurement of nasorespiratory function can help clinicians to (1) make an informed judgment regarding postulated relationships between respiration and growth, (2) test the validity of a diagnosis of impaired nasal respiration or "mouth breathing," and (3) evaluate the efficacy of treatment for nasal obstruction. A method that has been frequently used to quantify nasorespiratory function is nasal resistance measurement or rhinomanometry. This investigation used a common form of this method, studying 25 adult subjects to examine the effect of a number of variables in methodology on nasal airway resistance values. Results indicate that resistance to nasally inspired air was not significantly different from resistance to nasally expired air. However, a significant difference in estimating resistance was found between airflow rates of 0.25 and 0.5 L/sec, with nasal resistance increasing at the higher flow rate. Determination of the method error indicated that the technique was reliable and accurate for the sample studied. It was found that both expansion of the anterior nares and use of a nasal decongestant spray produced a decrease in mean nasal resistance. The study emphasizes the need to standardize the method of determining nasal resistance in order to permit comparisons among studies, to obtain a more reliable estimate of resistance, and to identify the location of maximum constriction in the nasal airway.     

Effects of Mercury on Health and First-Year Survival of Free-Ranging Great Egrets (Ardea albus) from Southern Florida

The objectives of this study were to determine whether elevated mercury (Hg) concentrations have a negative impact on the health and survival of nestling and juvenile free-ranging great egrets (Ardea albus) from southern Florida. During 1994, when health and survival was monitored in a cohort of young birds with naturally variable concentrations of Hg, packed cell volume was positively correlated with blood Hg concentrations, and high Hg concentration in blood was not related to the probability of surviving during the first 10.5 months of life. During 1995, 70 first-hatched great egret chicks were included in a Hg field-dosing experiment to compare the effects of elevated Hg on health and survival. Birds were dosed while in the nest orally every 2.5 days for 15 days with 0.5 mg of methyl mercury chloride (MeHgCl) for an estimated intake of 1.54 mg MeHgCl/kg food intake. These birds were compared with controls, which received an estimated 0.41 mg MeHgCl/kg food. No differences were observed in health parameters or in the probability of surviving during the first 8 months of age between egrets that were dosed with Hg and those that were not. A likely explanation for the lack of any effects on health and survival between both groups could be that chicks at this age were eliminating most of the dietary Hg through the production of new feathers. Received: 10 November 1998/Accepted: 8 April 1999