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P J McDonald

Publications and source records attributed to P J McDonald.

At least 19 recordsLinked to original sources
PubMed2006

A unilateral NMR magnet for sub-structure analysis in the built environment: the Surface GARField.

A new, portable NMR magnet with a tailored magnetic field profile and a complementary radio frequency sensor have been designed and constructed for the purpose of probing in situ the sub-surface porosity of cement based materials in the built environment. The magnet is a one sided device akin to a large NMR-MOUSE with the additional design specification of planes of constant field strength /B0/ parallel to the surface. There is a strong gradient G in the field strength perpendicular to these planes. As with earlier GARField magnets, the ratio G//:B0/ is a system constant although the method of achieving this condition is substantially different. The new magnet as constructed is able to detect signals 50mm (1H NMR at 3.2 MHz) away from the surface of the magnet and can profile the surface layers of large samples to a depth of 35-40 mm by moving the magnet, and hence the resonant plane of the polarising field, relative to the sample surface. The matching radio frequency excitation/detector coil has been designed to complement the static magnetic field such that the polarising B0 and sensing B1 fields are, in principal, everywhere orthogonal. Preliminary spatially resolved measurements are presented of cement based materials, including two-dimensional T1-T2 relaxation correlation spectra.

Construction Materials↗
PubMed2006

Variations in consenting practice for laparoscopic cholecystectomy.

INTRODUCTION: To compare the variations in consenting practice amongst trainees and consultant surgeons for laparoscopic cholecystectomy with specific reference to the documentation of significant risks of surgery. PATIENTS AND METHODS: A proforma was devised which included significant and/or commonly recognised complications of laparoscopic cholecystectomy. This was then cross-referenced with the consent forms for the 80 patients included in the study and the documented risks explained in each case were noted. RESULTS: The results showed that there is considerable variation between the three grades of clinicians involved in obtaining a patient's consent for laparoscopic cholecystectomy. There was a clear difference in emphasis of the significant complications depending on the seniority of the consenter. Over 80% of the consents in this study were still being obtained by junior staff. CONCLUSIONS: More often than not, patients are not provided with consistent information to make an informed choice. We suggest that a preprinted consent form will provide a more uniform approach to consenting practice for laparoscopic cholecystectomy.

Cholecystectomy, Laparoscopic↗
PubMed2005

Surface relaxation and chemical exchange in hydrating cement pastes: a two-dimensional NMR relaxation study.

We report the first nuclear magnetic resonance (NMR) two-dimensional correlation T(1) - T(2) and T(2) - T(2) measurements of hydrating cement pastes. A small but distinct cross peak in the two-dimensional relaxation spectrum provides the first direct evidence of chemical exchange of water between gel and capillary pores occurring over the first 14 days of hydration. A correlation of features along the line T(1) = 4T(2) provides strong supportive evidence for the surface diffusion model of (1)H nuclear spin relaxation in cements and for a multimodal discrete pore size distribution. Differences in detail of the results are reported for white cement paste and white cement paste with added silica fume. Both the method and the theory presented can be applied more widely to other high surface area materials with other reactive surface areas.

Journal Article↗
PubMed2005

Can pathological complete response in the primary tumour following pre-operative pelvic chemoradiotherapy for T3-T4 rectal cancer predict for sterilisation of pelvic lymph nodes, a low risk of local recurrence and the appropriateness of local excision?

INTRODUCTION: Local excision is considered inappropriate treatment for T3-T4 rectal adenocarcinomas, as it cannot provide prognostic information regarding lymph node involvement and has a high risk of pelvic recurrence. Preoperative chemoradiation (CRT) studies in rectal cancer suggest that a pathological complete response (pCR) in the primary tumour provides an excellent long-term outcome. If downstaging to stage pT0 predicts a tumour response within the perirectal and pelvic lymph nodes, this may allow local excision to be performed without increased risk of pelvic recurrence. This retrospective study aimed to determine the incidence of involved lymph nodes following pCR (ypT0) after preoperative CRT and total mesorectal excision. METHOD: The outcome and treatment details of 211 patients undergoing preoperative CRT for clinically staged T3-T4 unresectable rectal adenocarcinomas between 1993 and 2003 at Mount Vernon Hospital were reviewed. RESULTS: Data were recorded from the 143 patients who completed treatment with a median follow-up of 25 months. Twenty-three patients (18%) were found to have had a pCR. Four out of 23 patients (17%) had involved lymph nodes. No pelvic recurrences developed after a ypCR. Overall survival was similar for patients with ypT0 or residual tumour. CONCLUSION: Pathological complete response in the primary tumour failed to predict a response in the perirectal lymph nodes (p=0.08). The degree of response predicted a lymph node response (p=0.02). The detection of ypCR identified patients with a low rate of pelvic recurrence. This may in the future allow selection of patients for whom local excision can be performed without a higher risk of local relapse.

Adenocarcinoma↗
PubMed2005

Magnetic resonance profiling of human skin in vivo using GARField magnets.

It is shown that one-dimensional magnetic resonance imaging (MRI-profiling) of human forearm and side-of-hand skin in vivo is possible using GARField magnets. Strong profile contrast originating from differing molecular mobility is seen for stratum corneum and viable epidermis. The first in vivo spatially-resolved field-gradient measurements of water self-diffusivity, D, in the stratum corneum (2.0 x 10(-6) cm(2)/s) and viable epidermis (8.5 x 10(-6) cm(2)/s) are reported. Also reported are spatially resolved measurements of the (1)H spin-lattice relaxation time, T(1), the spin-spin relaxation time, T(2). It is further shown that the application of moisturizing agents to the skin noticeably affects the profiles. However, universal behavior is not seen as both signal increases and decreases are observed dependent on agent and volunteer.

Administration, Cutaneous↗
PubMed2004

GARField magnetic resonance profiling of the ingress of model skin-care product ingredients into human skin in vitro.

A preliminary study of the ingress of mineral oil, decanol, and glycerine into samples of human abdominal skin tissue in vitro made using magnetic resonance profiling with a GARField magnet is reported. Two layers, each circa 50 microm thick and attributed to stratum corneum and viable epidermis, are spatially resolved. Clear differences are observed in the magnetic resonance response of these layers arising from the application of the model skin-care product ingredients. In the case of decanol and glycerine, it is suggested that the profiles show evidence for the effects of moisturization, as distinct from hydration. In the case of glycerine, the effective ingress diffusion coefficient is calculated to be 1.3 +/- 0.5 x 10(-9) cm2s(-1).

Epidermis↗
PubMed2004

Retrograde commercial colonic hydrotherapy.

OBJECTIVE: To ascertain the current practice of commercial colonic hydrotherapy in the UK and to collect data on the profiles of both the practitioners and their clients. In addition to understand how colonic hydrotherapy is perceived by those who use it and how much economic benefit it generates for the practitioners. Information as to training and complications was sought. PATIENTS AND METHODS: A questionnaire was sent to all 80 practitioners registered with the Association of Colonic Hydrotherapists (ACH) of the UK. The practitioners who responded were sent 10 questionnaires to be given to a group of consecutive clients. This client questionnaire included an SF-36 self-administered scoring system and a satisfaction survey. To understand the methodology and ritual of the hydrotherapy procedure a field trip was arranged and two of the authors (NJT and PJM) underwent one colonic hydrotherapy session with an experience practitioner. RESULTS: Thirty-eight (48%) of practitioners responded to our practitioner survey and 242 client questionnaires were returned. One third of practitioners reported a previous clinical background and 32 (83%) were single-handed practitioners. The average time in practice was six years and with an average age of the hydrotherapists being 50 years (22-78 years). Estimated number of sessions conducted were 3200 (range 140-10 000). Average annual income before expenses per practitioner was estimated at pound 45 675. The clients' ages ranged was 18 and 82 years of age (mean 44 years) and had undergone an average of 35 hydrotherapy treatments (range 1-2500). Clients had lower SF-36 scores than the UK norm. CONCLUSION: Colonic hydrotherapy is practised widely in the UK with an estimated 5600 procedures carried out by ACH practitioners monthly. It is not known how much activity is carried out by non-ACH members. ACH practitioners appear to be well trained and a proportion have medical backgrounds. Clients, who are often unhappy with orthodox medicine seem satisfied enough with the experience of colonic hydrotherapy to undergo regular purgings. No serious side-effects have been reported to us. Economic factors could be a driving force for the continuation of the practice as the monies earnt are not inconsiderable.

Adolescent↗
PubMed2002

Multidimensional imaging using combined stray field and pulsed gradients.

The paper describes an advance in stray field imaging (STRAFI) whereby images of planar samples can be obtained in the stray field of a superconducting magnet without the need for sample rotation. This is achieved by using the static stray magnetic field gradient in combination with pulsed orthogonal gradients. Results of both two- and three-dimensional implementations of the experiment are presented and discussed. An extension to diffusion-weighted imaging is introduced. The technique is expected to prove particularly useful in experiments where high resolution is required in only one direction while lower resolution is acceptable in the orthogonal directions, such as in studies of the drying and curing of paints and varnishes. Arising from the work, a new method for accurately calibrating the radiofrequency pulse width in stray field is found.

Journal Article↗
PubMed2002

Vertical water distribution during the drying of polymer films cast from aqueous emulsions.

We present a systematic study of the vertical uniformity of water distribution during the drying of waterborne colloidal films, testing the predictions of a Peclet number Pe defined for this system. Pe indicates the relative contributions of water evaporation and Brownian diffusion in determining the concentration profile in the vertical direction ( i.e. normal to the substrate). When Pe < 1, the water concentration in films cast from an alkyd emulsion is found via magnetic-resonance profiling to be uniform with depth, which is consistent with expectations. When Pe > 1, a gradient in the water concentration develops, with less water near the interface with air. The water profiles reveal that the alkyd particles do not coalesce immediately upon contact in close-packing. At later times, a concentrated surface layer develops, but particles are not coalesced in this layer to form a continuous "skin", but rather the structure is likely to be that of a biliquid foam.

Journal Article↗
PubMed2001

The application of magnetic resonance microimaging to the visible light curing of dental resins. 3. Stray-field nuclear magnetic resonance imaging (STRAFI).

OBJECTIVE: To investigate the application of stray-field nuclear magnetic resonance imaging (STRAFI) to the visible light curing of dental restorative materials. STRAFI can overcome peak broadening associated with the conventional magnetic resonance microimaging (MRM) of glassy polymers, and has the potential to image dental restorative resins at both low and high degrees of conversion. METHODS: Cylindrical composite specimens were light-cured from one end to produce some that were fully cured throughout their length and others that were fully cured at one end and uncured at the other. A one-dimensional probe was used to measure the magnetisation in 40 microm thick slices at 100 microm intervals along the length of the specimen. A quadrature pulse sequence was applied and the magnetisation decay recorded in a train of eight echoes. RESULTS: A value for T(2) could be obtained only for the polymer (59+/-16 microms), therefore the echoes were summed to give an approximate indication of the degree of conversion. The echo sum for the monomer was significantly higher than that for the polymer. Differences in composite shade and cure time produced changes in the cure profiles. SIGNIFICANCE: STRAFI produced measurements for both monomer and polymer in all stages of conversion that allowed cure profiles to be produced. Summing the decay echoes produced a qualitative measure of the condition of the material in the selected slice. The same data can be used to calculate T(2), a quantitative parameter. This first investigation has demonstrated that STRAFI is well suited to polymerisation studies.

Algorithms↗
PubMed2001

Peri-operative management of patients having external anal sphincter repairs: temporary prevention of defaecation does not improve outcomes.

OBJECTIVE: To determine whether there was any detectable difference in outcomes of external anal sphincter repair depending on whether patients were managed routinely with a covering stoma, a constipating dietary regimen or a laxative dietary regimen in the early postoperative period. PATIENTS AND METHODS: A consecutive retrospective series of 299 anal sphincter repairs undertaken on 286 patients within a single institution was studied. Patients were divided into three groups depending on the peri-operative regimen followed: routine use of a covering stoma (group 1), routine use of a postoperative constipating dietary regimen (group 2) and routine use of a laxative dietary regimen (group 3). Choice of peri-operative regimen depended on surgeon preference alone. Short-term outcomes (length of stay, complications) and long-term outcomes (functional reported degree of continence, anal ultrasound and physiology test results) were assessed in relation to peri-operative group as well as aetiology of sphincter damage. RESULTS: Short-term results (complications of surgery) were obtainable in all patients; long-term results were available for 89% of patients. Length of stay was similar for all 3 groups (excluding re-admission for stoma closure). Complication rates were not significantly different between the three groups. Functional improvement in continence was reported by 68% of group 1, 69% of group 2 and 79% of group 3 (differences not statistically significant). An anatomical sphincter defect was detected postoperatively in 8% of patients in group 1, 9% in group 2 and 7% of group 3. Poorer outcomes were achieved in older patients and in patients with previous ileo-anal pouch formation. Early faecal impaction and repair breakdown were independently associated with poor long-term outcomes. CONCLUSIONS: Neither routine use of a covering stoma nor a postoperative constipating regimen produced better results following external anal sphincter repair than did the use of a postoperative laxative regimen which encouraged early passage of loose stool without the need for straining.

Journal Article↗
PubMed2000

Antiepileptic efficacy of topiramate: assessment in two in vitro seizure models.

The antiepileptic efficacy of topiramate (TPM) has been demonstrated in both whole animal seizure models and clinical trials; however, there is no consensus concerning its mechanism of action. We determined first whether the antiepileptic effect of TPM generalized to in vitro seizure models. Epileptiform discharges, recorded extracellularly, were evoked by repeated tetanic stimulation of Schaffer collaterals and layer III association fibers in entorhinal cortex/hippocampus and piriform cortex slices, respectively. TPM was applied at concentrations of 20 or 100 microM. Whole cell recordings were made from CA1 pyramidal neurons and the effect of TPM was assessed on a variety of intrinsic membrane properties including resting membrane potential, input resistance and postspike potentials. TPM (20 microM) was without effect in entorhinal cortex/hippocampus (N=6); however, 100 microM TPM decreased significantly the Coastline Burst Index from 358.3+/-65.8 to 225. 5+/-77.1 (N=4), the frequency of spontaneous epileptiform discharges to 44.6+/-21.8 (N=5) and the duration of primary afterdischarge (PAD) to 65.9+/-10.1 (N=10) percent of control. In contrast, phenytoin (50 microM, N=7; 100 microM, N=8) reduced PAD to 96.9+/-14. 8 and 86.5+/-17.3 percent of control, respectively. TPM (100 microM) did not reduce significantly the frequency of spontaneous discharges in piriform cortex (85.4+/-12.3 percent of control; N=5). TPM (100 microM) was without significant effect on intrinsic membrane properties in CA1 pyramidal neurons. Likely candidate mechanisms underlying the antiepileptic effect produced by TPM include enhancement of chloride-mediated GABA(A) currents and reduction of kainate and L-type calcium currents.

Action Potentials↗
PubMed2000

Cefdinir vs. amoxicillin/clavulanic acid in the treatment of suppurative acute otitis media in children.

An investigator-blinded, randomized, multicenter study was conducted to compare the efficacy and safety of cefdinir and amoxicillin/ clavulanate (amoxicillin/CA) in the treatment of pediatric patients with acute suppurative otitis media. Patients 6 months to 12 years of age were randomized in a 1:1:1 ratio to receive cefdinir 14 mg/kg once-daily, cefdinir 7 mg/kg b.i.d., or amoxicillin/CA 13.3 mg/kg t.i.d. Test-of-cure was determined 11 to 16 days posttherapy. Of the 752 patients who entered the study, 665 (88%) completed treatment and 595 (79%) were evaluable. Response rates in the three treatment groups were similar. Overall rates of adverse events were statistically lower in the cefdinir once-daily group than in the amoxicillin/CA group. Diarrhea was the most common adverse event in all treatment groups. Cefdinir given either once-daily or twice-daily is a safe and effective treatment for pediatric patients with acute suppurative otitis media.

Acute Disease↗
PubMed2000

Model for water transport into powdered xanthan combining gel swelling and vapor diffusion.

Water ingress into xanthan powder compressed to various packing densities has been studied using nuclear magnetic resonance stray field imaging (STRAFI). A foot is observed ahead of the main water ingress front which is attributed to vapor transport around the particles. The main development of the reported work is an analytical model which describes the coupling of vapor transport through the pore space and liquid transport through the progressively swelling gel which gradually occludes the vapor path. Good agreement between theory and experiment is found over a wide range of packing densities with the model requiring only one adjustable parameter, the water diffusivity in the gel measured in a constant polymer mass reference frame. It is suggested that the results are of considerable relevance to situations where the polymer is produced at low concentration by bacteria such as in the rhizosphere and aerial bio films.

Biofilms↗
PubMed1999

A novel high-gradient permanent magnet for the profiling of planar films and coatings.

The design and construction of a low-cost, permanent magnet is described. The magnet is intended for applications which require a large static gradient, such as those for which stray field imaging or fringe field diffusometry are conventionally employed. The magnet has been designed using the scalar potential method. Particular features of the magnet include a field profile such that ||B || is constant in the horizontal plane and such that B is horizontal at the midpoint between the poles. There is a vertical, and therefore orthogonal, strong gradient, G, in ||B ||. The ratio G/ ||B || is constant within a large volume and so allows measurements at a range of gradient strengths. It is this ratio which governs the shape of the pole-pieces. The constructed magnet has a typical operating field of 0.8 T, gives a gradient of 20 Tm-1, and has a useable interpole access of 20 mm. Field plot data show values consistent with the theory. In particular ||B || has a curvature of less than +/-5 microm over a 5 x 5 mm area at the target field. The magnet is most suitable for the one-dimensional profiling of thin planar samples. As an example of the magnet's use, a profile of a sandwich structure made of several polymer layers is shown. In addition, a set of one-dimensional profiles of an alkyd coating, recorded during solvent loss and cross-linking, is presented. This example demonstrates quantitative T2 measurements at a resolution of 6.5 microm across a 70-microm-thick film.

Magnetic Resonance Spectroscopy↗
PubMed1999

Carcinoembryonic antigen: its value in the follow-up of patients with colorectal cancer.

We examined the value of carcinoembryonic antigen (CEA) monitoring for detecting treatable recurrence of colorectal carcinoma. CEA assays were undertaken in 193 patients over a 2-year period. The levels in 34 patients were raised in one or more assays above the laboratory-defined upper limit of normal; 31 cases were reviewed retrospectively. In 10% of patients there were Dukes' A lesions at the initial resection, in 39% Dukes' B, and in 52% Dukes' C1 or C2. Tumours were rectal in 61%. Median follow-up was 3 years (range, 16 years-2 months). In 23 of 31 (74%) there were symptoms or signs of recurrent disease prior to or simultaneously with an observed rise in CEA; in 8 the CEA rise preceded the onset of symptoms or the appearance of signs. Of the 31 cases 26 underwent investigation for recurrent disease, but in only 6 of these was the investigation driven by the observed rise in CEA rather than the onset of symptoms or presence of signs. Three of these six were false-positive results (50%), one has been lost to follow-up, and two had confirmed recurrence. Neither of the two with recurrence had operable disease. One of the two had no further treatment, and one underwent laparotomy at which multiple peritoneal seedlings were found. In both of the two cases going to laparotomy, one of which was prompted by a high CEA, widely disseminated disease was found. Over a 2-year period, serial CEA measurement thus yielded no patient benefit.

Carcinoembryonic Antigen↗
PubMed1999

Solid state spatially resolved 1H and 19F nuclear magnetic resonance spectroscopy of dental materials by stray-field imaging.

As part of a program to evaluate the use of stray-field magnetic resonance microimaging (STRAFI) in dental materials research spatially resolved nuclear magnetic resonance (NMR) for solid dental cements has been investigated. By applying a quadrature echo pulse sequence to a specimen positioned in the stray-field of a NMR spectrometer superconducting magnet the magnetic resonance within a thin slice was obtained. The specimen was stepped through the field in 500 microm increments to record 1H and 19F profiles and T2 values at each point. The specimens were fully cured cylinders made from four types of restorative material (glass ionomer, resin modified glass ionomer, compomer, composite). The values for 1H T2 varied with material type and reflected the nature of the matrix structure. For all materials containing 19F in the glass two values were calculated for 19F T2, one short and one long. These were relatively invariant. Solid state magic angle spinning (MAS)-NMR showed that they came from the glass. This suggests that a proportion of the element is relatively mobile (in a glass phase) and the remainder is more tightly bound (in a compound dispersed in the glass). This demonstration, that NMR microimaging of both 1H and 19F in solid dental cements is possible, opens up exciting new possibilities for investigating the distribution of these elements (in particular fluorine) in solid dental materials.

Journal Article↗