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P M White

Publications and source records attributed to P M White.

At least 19 recordsLinked to original sources
PubMed2004

The endovascular management of pericallosal artery aneurysms.

AIM: to describe our experience with a series of 18 patients with pericallosal artery aneurysms, in whom endovascular coil insertion was attempted. METHOD: the CT and angiographic appearances, coiling techniques and patient outcomes are discussed. RESULTS: we encountered a higher than expected level of technical difficulty and procedure related complication than when coiling aneurysms in more common locations. In particular the distal position of the aneurysms lead to poorer control over the microcatheter position. Procedure related rupture occurred in three cases. Coiling was not possible in one case only. An association between an angulated bifurcation of the anterior cerebral artery and a sidewall aneurysm configuration was noted. CONCLUSION: despite the technical difficulties and high procedure related rupture rate, coiling of pericallosal aneurysms is feasible and has good outcome.

Adult↗
PubMed2003

Influence of organic and inorganic soil amendments on plant growth in crude oil-contaminated soil.

Phytoremediation can be a viable alternative to traditional, more costly remediation techniques. Three greenhouse studies were conducted to evaluate plant growth with different soil amendments in crude oil-contaminated soil. Growth of alfalfa (Medicago sativa L., cultivar: Riley), bermudagrass (Cynodon dactylon L., cultivar: Common), crabgrass (Digitaria sanguinalis, cultivar: Large), fescue (Lolium arundinaceum Schreb., cultivar: Kentucky 31), and ryegrass (Lolium multiflorum Lam., cultivar: Marshall) was determined in crude oil-contaminated soil amended with either inorganic fertilizer, hardwood sawdust, papermill sludge, broiler litter or unamended (control). In the first study, the addition of broiler litter reduced seed germination for ryegrass, fescue, and alfalfa. In the second study, bermudagrass grown in broiler litter-amended soil produced the most shoot biomass, bermudagrass produced the most root biomass, and crabgrass and bermudagrass produced the most root length. In the third study, soil amended with broiler litter resulted in the greatest reduction in gravimetric total petroleum hydrocarbon (TPH) levels across the six plant treatments following the 14-wk study. Ryegrass produced more root biomass than any other species when grown in inorganic fertilizer- or hardwood sawdust + inorganic fertilizer-amended soil. The studies demonstrated that soil amendments and plant species selection were important considerations for phytoremediation of crude oil-contaminated soil.

Cynodon↗
PubMed2003

Unruptured intracranial aneurysms.

Between 3.6 and 6% of the population harbour an unruptured intracranial aneurysm. Risk of rupture is related to aneurysm site and size and whether or not the patient has already had a subarachnoid haemorrhage (SAH) from another aneurysm. In ISUIA 2, the rupture rate for anterior circulation aneurysms<7mm was 0% per year in patients with no prior SAH, and 0.3% per year in patients with previous SAH; 7-12mm aneurysms, 0.5% per year (both groups); 13-24mm aneurysms, 3% per year; and giant aneurysms 8% per year. Rupture rate for posterior circulation aneurysms is higher at all sizes:<7mm was 0.5% per year in subjects with no prior SAH, 0.7% in those with prior SAH; 7-12mm, 3% per year; 13-24mm, 3.7% per year; and giant aneurysms, 10% per year. Non-invasive tests like contrast enhanced magnetic resonance angiography (MRA) and multislice computed tomographic angiography (CTA) are alternatives to intra-arterial digital subtraction angiography (IADSA) to detect aneurysms. Although these are promising techniques, the quality of data testing their accuracy remains limited and single slice CTA and time-of-flight MRA are poorer at detecting aneurysms<5mm diameter, which account for up to 1/3 of unruptured aneurysms. For ruptured aneurysms, the only large scale randomised controlled trial comparing surgical and endovascular treatment (ISAT) by coiling, resulted in an absolute 8.8% reduction (updated figure as of June 2003 for 1888 patients) in death or dependency at 1 year compared with surgical clipping. For unruptured aneurysms, the best available data so far comparing coiling and clipping is from the prospective (but non-randomised) arm of ISUIA. Elective surgical clipping had combined morbidity and mortality at 1 year of 12.2% versus 9.5% for coiling, although the groups were not matched with more high risk patients in the endovascular treatment cohort. Nevertheless these data are encouraging for future randomised trials of elective coiling versus clipping for asymptomatic aneurysms, in particular as the unproven long-term durability of coiling treatment and the fact that complete aneurysm occlusion is not always achieved remain obstacles to its wider use in unruptured aneurysms. There is an increased risk of SAH in relatives of patients with SAH (highest in those with two or more first degree relatives affected), but most SAH is sporadic and therefore the balance of available evidence indicates that mass screening for aneurysms is not cost effective. There may be a limited role for investigation of high-risk subgroups and ideally such screening should be tested in a randomised trial. The avoidance and active management of vascular risk factors should also be part of the management of at risk subjects.

Aneurysm, Ruptured↗
PubMed2001

Neural crest stem cells undergo cell-intrinsic developmental changes in sensitivity to instructive differentiation signals.

Rat neural crest stem cells (NCSCs) prospectively isolated from uncultured E14.5 sciatic nerve and transplanted into chick embryos generate fewer neurons than do NCSCs isolated from E10.5 neural tube explants. In addition, they differentiate primarily to cholinergic parasympathetic neurons, although in culture they can also generate noradrenergic sympathetic neurons. This in vivo behavior can be explained, at least in part, by a reduced sensitivity of sciatic nerve-derived NCSCs to the neurogenic signal BMP2 and by the observation that cholinergic neurons differentiate at a lower BMP2 concentration than do noradrenergic neurons in vitro. These results demonstrate that neural stem cells can undergo cell-intrinsic changes in their sensitivity to instructive signals, while maintaining multipotency and self-renewal capacity. They also suggest that the choice between sympathetic and parasympathetic fates may be determined by the local concentration of BMP2.

Acetylcholine↗
PubMed2001

Experimental modification of P50 suppression.

White and Yee (1997) found that normal suppression of the P50 component of the event-related potential was disrupted during a paired-click paradigm when nonpsychiatric subjects performed mental arithmetic (MA) problems aloud, concurrently with the presentation of auditory stimuli. In fact, the degree of disruption reflected in the P50 suppression ratio fell within the range that is typically observed in schizophrenia patients. The present study was conducted to clarify the processes that might underlie the apparent disruption of P50 suppression during performance of an oral MA task. Participants completed a series of tasks designed to examine the impact of competing cognitive activity, competing auditory stimulation, muscle activity, and acute psychological stress on P50 amplitude and P50 suppression. Results suggested that psychological stress and heightened facial muscle activity may exert modulatory effects on P50 suppression.

Acoustic Stimulation↗
PubMed2001

Magnetic resonance imaging as the primary imaging modality in children presenting with acute non-traumatic hip pain.

The role of magnetic resonance imaging (MRI) in children presenting with acute non-traumatic hip pain was evaluated prospectively. Hip MRI was performed in addition to standard investigations (arthrosonography +/- hip radiographs) in 50 children presenting to the accident and emergency department of a paediatric hospital. MRI was performed on an open 0.23T system and comprised gradient echo T1 weighted coronal, fast spin echo T2 weighted coronal and inversion recovery spin echo (IRSE) axial sequences. Diagnostic quality MRI examinations were obtained in 94% of children. The IRSE sequence was the most reliable at determining underlying disorder (p<0.002). Interobserver agreement on the MRI examinations was very good with unweighted kappa value of 0.89, 95% confidence intervals 0.79, 0.99. Sensitivity of MRI was 0.79 (0.68, 0.90, specificity 1.00 (0.89, 1.00), accuracy 0.81 (0.70, 0.92), PPV 1.00 (0.89, 1), NPV 0.36 (0.25, 0.47). Sensitivity of standard imaging was 0.70 (0.54-0.86), specificity 0.57 (0.41, 0.73), accuracy 0.72 (0.56, 0.88), PPV 0.91 (0.75, 1.00), NPV 0.24 (0.08, 0.40). MRI correctly identified all seven children with serious underlying disorder whereas conventional imaging correctly diagnosed only two. Pelvic musculoskeletal infection was associated with the combination of marked alteration in signal in tissues adjacent to a symptomatic hip and an erythrocyte sedimentation rate of >20 mm 1st h (p<0.0001). In conclusion, MRI is a practical, well accepted and accurate non-invasive imaging technique in children presenting with acute non-traumatic hip pain. Combined with inflammatory markers MRI can be used to determine those children who require aggressive management. Where it is available, MRI is the imaging modality of choice in this condition.

Adolescent↗
PubMed2001

What is the most sensitive non-invasive imaging strategy for the diagnosis of intracranial aneurysms?

OBJECTIVES: To determine whether combining non-invasive tests for intracranial aneurysms together would significantly improve aneurysm detection over individual tests. METHODS: 114 patients undergoing intra-arterial digital subtraction angiography to confirm or exclude an intracranial aneurysm were also examined by CT angiography, MR angiography, and transcranial power Doppler ultrasound. The reviewers and ultrasonographers were blinded to the angiogram result, other imaging results and all clinical information. RESULTS: The combination of non-invasive tests did improve diagnostic performance on a per patient basis. The combination of power Doppler and CT angiography had the greatest sensitivity for aneurysm detection (0.83; 05% confidence interval (95% CI) 0.66-0.93) and the level of agreement for this strategy with the reference angiographic standard was excellent (kappa 0.84; 95% CI 0.72-0.95). The improvement in sensitivity of adding power Doppler to CT angiography was not significant (p=0.55) but the improvement in the level of agreement with the reference standard was substantial. However, even the most sensitive combination strategy performed poorly in the detection of small (3-5 mm) and very small (<3 mm) aneurysms with a sensitivity of 0.43 (95% CI 0.23-0.66) and 0.00 (95% CI 0.00-0.31) respectively. CONCLUSIONS: The addition of transcranial power Doppler ultrasound to either CT angiography or MR angiography does improve diagnostic performance on a per patient basis but aneurysms of 5 mm or smaller can still not be reliably identified by current standard clinical non-invasive imaging modalities.

Adult↗
PubMed2001

Intracranial aneurysms: CT angiography and MR angiography for detection prospective blinded comparison in a large patient cohort.

PURPOSE: To compare computed tomographic (CT) angiography and magnetic resonance (MR) angiography with intraarterial digital subtraction angiography (DSA) in the detection of intracranial aneurysms. MATERIALS AND METHODS: One hundred forty-two patients underwent intraarterial DSA to detect aneurysms. CT angiography, three-dimensional time-of-flight MR angiography, and intraarterial DSA were performed contemporaneously. Film hard-copy images and maximum intensity projection reconstructions of the CT angiograms and MR angiograms were reviewed at different times. RESULTS: The accuracy per patient for the best observer was 0.87 at CT angiography and 0.85 at MR angiography. The accuracy per aneurysm for the best observer was 0.73 at CT angiography and 0.67 at MR angiography. Differences between readers and modalities were not significant. Interobserver agreement was good: kappa value of 0.73 for CT angiography and of 0.74 for MR angiography. The sensitivity for detection of aneurysms smaller than 5 mm was 0.57 for CT angiography and 0.35 for MR angiography compared with 0.94 and 0.86, respectively, for detection of aneurysms 5 mm or larger. The accuracy of both CT angiography and MR angiography was lower for detection of internal carotid artery aneurysms compared with that at other sites. With low observer confidence, the likelihood of correct interpretation was significantly poorer. CONCLUSION: CT angiography and MR angiography have limited sensitivity in the detection of small aneurysms but good interobserver agreement. There is no significant difference in diagnostic performance between the noninvasive modalities.

Adult↗
PubMed2001

Power transcranial Doppler ultrasound in the detection of intracranial aneurysms.

BACKGROUND AND PURPOSE: We sought to perform a large, prospective, multicenter, blinded study comparing power transcranial color duplex sonography (power TCDS) with intra-arterial digital subtraction angiography (IADSA) in the detection of intracranial aneurysms. METHODS: Contemporaneous TCDS and IADSA examinations were performed in 171 subjects with suspected intracranial aneurysm. Via the temporal bone window, a 2-dimensional hand-held noncontrast transcranial duplex ultrasound imaging system was used operating in power and spectral modes. Sonographers were blinded to clinical history and results of brain CT and IADSA. RESULTS: We found that 157 subjects (92%) had an adequate bone window. Sensitivity per patient was 0.78 (95% CI, 0.66 to 0.87) and 0.46 (95% CI, 0.36 to 0.56) for any anterior circulation aneurysms. Sensitivity was 0.35 (95% CI, 0.24 to 0.46) for aneurysms </=5 mm and 0.81 (95% CI, 0.62 to 0.94) for aneurysms >5 mm. Accuracy was lower for aneurysms on the cavernous and terminal internal carotid arteries, including posterior communicating artery origin (0.71; 95% CI, 0.63 to 0.79), than for those on the anterior (0.82; 95% CI, 0.74 to 0.89) or the middle cerebral arteries (0.79; 95% CI, 0.71 to 0.86). CONCLUSIONS: Power TCDS is a promising, inexpensive, noninvasive test for anterior circulation intracranial aneurysms but is less sensitive per aneurysm than alternatives such as CT angiography or MR angiography. Sensitivity is poor for aneurysms </=5 mm in diameter. The internal carotid artery is the most difficult segment to interpret.

Adult↗
PubMed2000

Left temporal deficit of P300 in patients with schizophrenia: effects of task.

P300 is often, but not always, observed to be more reduced over left than right temporal lobes in patients with schizophrenia. The possibility that task differences contribute to the inconsistency in the literature was explored in this study. ERPs were collected from 17 right-handed men with schizophrenia (DSM-IIIR) and 11 right-handed healthy male community controls, performing three auditory oddball tasks - respond to a target tone by: (1) counting; (2) pressing a response button with the right index finger; or (3) pressing a response button with the left index finger. Although patients with schizophrenia had smaller and later P300 amplitudes than controls, they did not have smaller P300s over the left temporal scalp (T3) than over the right (T4). P300 recorded over the left (C3) and right (C4) motor cortices indicated sensitivity to responding hand, with greater negativity being associated with contralateral button pressing. Failure to find P300 asymmetry is not related to the presence or absence of a button pressing task, or the hand used for button pressing. Rather, P300 asymmetry may be related to structural neuroanatomical asymmetries.

Adult↗
PubMed2000

The detection and management of unruptured intracranial aneurysms.

The incidence of subarachnoid haemorrhage (SAH) is 6-8 per 100 000 person years, peaking in the sixth decade. SAH, mostly due to rupture of an intracranial aneurysm, accounts for a quarter of cerebrovascular deaths. Aneurysms increase in frequency with age beyond the third decade, are 1.6 times more common in women and are associated with a number of genetic conditions. Prospective autopsy and angiographic studies indicate that between 3.6 and 6% of the population harbour an intracranial aneurysm. Studies have found an increased rate of SAH in first degree relatives of SAH patients (relative risk 3.7-6.6). In affected families, the most frequent relationship between sufferers is sibling to sibling. The rupture rate of asymptomatic aneurysms was thought to be 1-2% per annum, but the recent International Study of Unruptured Intracranial Aneurysms found that the rupture rate of small aneurysms was only 0.05% per annum in patients with no prior SAH, and 0.5% per annum for large (>10 mm diameter) aneurysms and for all aneurysms in patients with previous SAH. Non-invasive tests such as magnetic resonance angiography (MRA), computed tomographic angiography (CTA) and transcranial Doppler (TCD) have been advocated as alternatives to intra-arterial digital subtraction angiography to screen for aneurysms. Although all are promising techniques, the quality of data testing their accuracy is limited. Overall reported sensitivity for CTA and MRA (TCD is poorer) was 76-98% and specificity was 85-100%, but many subjects had an aneurysm or recent SAH, which could overestimate accuracy. CTA and MRA are much poorer methods for the detection of aneurysms <5 mm diameter, which account for up to one-third of unruptured aneurysms. Elective surgical clipping of asymptomatic aneurysms has a morbidity of 10.9% and mortality of 3. 8%. Treatment of aneurysms by Guglielmi coils, for which there is less long-term follow-up available, has a 4% morbidity and 1% mortality, but only achieves complete aneurysm occlusion in 52-78% of cases. There has been interest in screening for aneurysms, but the indication for, and cost effectiveness of screening are unclear because aneurysm prevalence varies, rupture rate is low, non-invasive imaging tests are not yet accurate enough to exclude small aneurysms and the morbidity and mortality for elective surgical treatment of unruptured aneurysms is high. There may be a limited role for investigation of high risk subgroups. Ideally, screening in such subgroups should be tested in a randomized trial. The avoidance of risk factors for aneurysms such as smoking, hypertension and hypercholesterolaemia should be part of the management of at-risk subjects.

Adult↗
PubMed2000

Can noninvasive imaging accurately depict intracranial aneurysms? A systematic review.

PURPOSE: To perform a systematic review to determine the accuracy of computed tomographic (CT) angiography, magnetic resonance (MR) angiography, and transcranial Doppler ultrasonography (US) in depicting intracranial aneurysms. MATERIALS AND METHODS: A 1988-1998 literature search for studies with 10 or more subjects in which noninvasive imaging was compared with angiography was undertaken. Studies meeting initial criteria were evaluated by using intrinsically weighted standardized assessment to determine suitability for inclusion. Studies scoring greater than 50% were included. RESULTS: Of 103 studies that met initial criteria, 38 scored greater than 50%. CT angiography and MR angiography had accuracies per aneurysm of 89% (95% CI: 87%, 91%) and 90% (95% CI: 87%, 92%), respectively. For US, data were scanty and accuracy was lower, although the CIs overlapped those of CT angiography and MR angiography. Sensitivity was greater for detection of aneurysms larger than 3 mm than for detection of aneurysms 3 mm or smaller-for CT angiography, 96% (95% CI: 94%, 98%) versus 61% (95% CI: 51%, 70%), and for MR angiography, 94% (95% CI: 90%, 97%) versus 38% (95% CI: 25%, 53%). Diagnostic accuracy was similar for anterior and posterior circulation aneurysms. CONCLUSION: CT angiography and MR angiography depicted aneurysms with an accuracy of about 90%. Most studies were performed in populations with high aneurysm prevalence, which may have introduced bias toward noninvasive examinations.

Cerebral Angiography↗
PubMed1999

Prospective identification, isolation by flow cytometry, and in vivo self-renewal of multipotent mammalian neural crest stem cells.

Multipotent and self-renewing neural stem cells have been isolated in culture, but equivalent cells have not yet been prospectively identified in neural tissue. Using cell surface markers and flow cytometry, we have isolated neural crest stem cells (NCSCs) from mammalian fetal peripheral nerve. These cells are phenotypically and functionally indistinguishable from NCSCs previously isolated by culturing embryonic neural tube explants. Moreover, in vivo BrdU labeling indicates that these stem cells self-renew in vivo. NCSCs freshly isolated from nerve tissue can be directly transplanted in vivo, where they generate both neurons and glia. These data indicate that neural stem cells persist in peripheral nerve into late gestation by undergoing self-renewal. Such persistence may explain the origins of some PNS tumors in humans.

Animals↗
PubMed1999

Imaging of the thorax in the management of germ cell testicular tumours.

AIM: To evaluate role of chest computed tomography (CTC) and chest radiography (CXR) in management of patients with testicular germ cell tumours (GCT). PATIENTS AND METHODS: An analysis was undertaken of staging and re-assessment CTC and CXR examinations performed on patients with GCT over a 4.5-year period. Data were obtained on clinical presentation, tumour histology, tumour marker levels and clinical course. Consensus review interpretation was combined with these data to obtain a 'standard of reference'. Sensitivity, specificity and predictive values were derived by comparison of original imaging reports to 'standard of reference'. RESULTS: Six hundred and twenty-three CTC examinations on 207 patients with GCT were included. Intrathoracic metastases were identified in 1% of seminoma patients compared with 20% of non-seminoma (NSGCT) patients. CTC was more accurate than CXR in the detection of intrathoracic metastases at 0.97, 0.96-0.98 (95% CI) compared with 0.91, 0.89-0.93. The agreement between imaging techniques and the standard of reference (determined by Kappa statistic) was respectively 0.96 for CTC and 0.65 for CXR. In GCT patients undergoing re-assessment with both CXR and CTC, CXR never detected unknown intrathoracic metastatic disease. Abdominopelvic lymphadenopathy was associated with intrathoracic metastases (P < 0.001), however re-assessment CTC did identify intrathoracic metastases in 27 cases without concurrent abdominopelvic disease. CXR was negative in 19 of these. CONCLUSION: Routine interval CXRs are unnecessary in NSGCT patients undergoing regular re-assessment CTC due to the low additional yield and limited effect on management. Re-assessment should still include CTC. In low risk, pure seminoma patients (abdominal CT and marker negative) re-assessment CTC can be safely avoided. Baseline CTC is advocated with CXR alone for re-assessment.

False Negative Reactions↗
PubMed1999

Mutational analysis of acylphosphatase suggests the importance of topology and contact order in protein folding.

Muscle acylphosphatase (AcP) is a small protein that folds very slowly with two-state behavior. The conformational stability and the rates of folding and unfolding have been determined for a number of mutants of AcP in order to characterize the structure of the folding transition state. The results show that the transition state is an expanded version of the native protein, where most of the native interactions are partially established. The transition state of AcP turns out to be remarkably similar in structure to that of the activation domain of procarboxypeptidase A2 (ADA2h), a protein having the same overall topology but sharing only 13% sequence identity with AcP. This suggests that transition states are conserved between proteins with the same native fold. Comparison of the rates of folding of AcP and four other proteins with the same topology, including ADA2h, supports the concept that the average distance in sequence between interacting residues (that is, the contact order) is an important determinant of the rate of protein folding.

Acid Anhydride Hydrolases↗