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Biomedical subjects

D J Collins

Publications and source records attributed to D J Collins.

At least 37 records · Page 2Linked to original sources
PubMed2000

SAR and tissue heating with a clinical (31)P MRS protocol using surface coils, adiabatic pulses, and proton-decoupling.

In MRS studies using surface transmit coils, accurate assessment of local SAR and RF heating represents a difficult problem involving the coil geometry and electromagnetic and geometric tissue properties. Methodologies to determine the optimum operating parameters for dual-resonant surface coil measurements are presented, based on a standardized coil and protocol used in a multicenter (31)P MRS clinical trial, using adiabatic pulses and bilevel proton decoupling. Spatial distributions of absorbed radiation in human calf and in a tissue-equivalent gel phantom were modeled using finite-element simulations and realistic conductivity and permittivity values. Local SAR in worst-case 1 cm(3) volumes of interest (VOIs) in calf is predicted to be below international guidelines, and the temperature at the skin surface was found to increase due to the RF by less than 2 degrees C and remain below 37 degrees C. The heating rate and maximum temperature in the gel, at positions guided by the simulations, were within guideline values for both extremities and trunk and in reasonable agreement with that predicted.

Adult↗
PubMed2000

Electrochemical signaling in green plants: effects of 2,4-dinitrophenol on variation and action potentials in soybean.

Nerve cells in animals and phloem cells in plants share one fundamental property: they possess excitable membranes by which electrical excitations in the form of action potentials can propagate. Action potentials in green plants can be as fast as the action potentials in axons of nervous cells. The presence of the pesticide 2,4-dinitrophenol (DNP) in soil is a most serious environmental problem and has an impact on agriculture and human health. In the present work we show that DNP induces fast action potentials and decreases the variation potential in a soybean. The speed of the propagation of action potentials is up to 2 m/s, and the duration time of single action potentials is typically 20 ms. The automatic measurement of the electrical potential difference can be effectively used in environmental plant physiology, as well as for studying molecular mechanisms of transport processes and the influence of external stimuli on plants.

2,4-Dinitrophenol↗
PubMed1998

Measurements of human breast cancer using magnetic resonance spectroscopy: a review of clinical measurements and a report of localized 31P measurements of response to treatment.

A review of the literature has shown that in human breast tumours, large signals from phosphomonoesters (PME) and phosphodiesters (PDE) are evident. In serial measurements in 19 patients with breast cancer, a decrease in PME was significantly associated with a stable or responding disease (p = 0.017), and an increase in PME was associated with disease progression. Extract studies have shown PME to comprise of phosphoethanolamine (PEth) and phosphocholine (PCho), with the PEth to PCho ratio ranging from 1.3 to 12. The PCho content of high grade tumours was found to be higher than low grade tumours. In some animal models, changes in PCho have been shown to correlate with indices of cellular proliferation, and spheroid studies have shown a decrease in PCho content in spheroids with smaller growth fractions. A serial study of 25 patients with advanced primary breast tumours undergoing hormone, chemotherapy or radiotherapy treatments, showed that in this heterogenous group there were significant changes in metabolites that were seen during the first 3 weeks (range 2-4 weeks) of treatment, that correlated with volume change over this period, employed here as a measure of response. Changes in PME (p = 0.003), total phosphate (TP) (p = 0.008) and total nucleoside tri-phosphate (TNTP) (p = 0.02) over 3 (+/-1) weeks were significantly associated with response, as were the levels of PME (p<0.001), PDE (p = 0.01), TP (p = 0.001) and TNTP (p = 0.007) at week 3 (+/-1). PME at week 3 (+/-1) was also significantly associated with the best volume response to treatment (p = 0.03). A reproducibility analysis of results from the observation of normal breast metabolism in four volunteers showed a mean coefficient of variation of 25%, after correcting for changes resulting from the menstrual cycle. Reproducibility studies in four patients with breast cancer showed a mean coefficient of variation of 33%, with the reproducibility being better in patients measured on different days (difference in TP was -6%) compared with those measured on the same day (difference in TP was -29%).

Adult↗
PubMed1998

Absolute metabolite quantification by in vivo NMR spectroscopy: II. A multicentre trial of protocols for in vivo localised proton studies of human brain.

We have performed a multicentre trial to assess the performance of three techniques for absolute quantification of cerebral metabolites using in vivo proton nuclear magnetic resonance (NMR). The techniques included were 1) an internal water standard method, 2) an external standard method based on phantom replacement, and 3) a more sophisticated method incorporating elements of both the internal and external standard approaches, together with compartmental analysis of brain water. Only the internal water standard technique could be readily implemented at all participating sites and gave acceptable precision and interlaboratory reproducibility. This method was insensitive to many of the experimental factors affecting the performance of the alternative techniques, including effects related to loading, standing waves and B1 inhomogeneities; and practical issues of phantom positioning, user expertise and examination duration. However, the internal water standard method assumes a value for the concentration of NMR-visible water within the spectroscopic volume of interest. In general, it is necessary to modify this assumed concentration on the basis of the grey matter, white matter and cerebrospinal fluid (CSF) content of the volume, and the NMR-visible water content of the grey and white matter fractions. Combining data from 11 sites, the concentrations of the principal NMR-visible metabolites in the brains of healthy subjects (age range 20-35 years) determined using the internal water standard method were (mean+/-SD): [NAA]=10.0+/-3.4 mM (n=53), [tCho]=1.9+/-1.0 mM (n=51), [Cr + PCr]=6.5+/-3.7 mM (n=51). Evidence of system instability and other sources of error at some participating sites reinforces the need for rigorous quality assurance in quantitative spectroscopy.

Adult↗
PubMed1998

Muscular development motives for exercise participation: the missing variable in current questionnaire analysis?

Motivation questionnaires that are currently validated do not account for muscular development motives in exercise populations, and have rarely been used to examine resistance training populations. Resistance training is a popular and widely available exercise, so the lack of such motivational information is a cause for concern. The aim of this study was to assess the need for considering motives for muscular development. This was achieved by the development of a simple scale that matched the format and style of the Exercise Motivations Inventory. The muscular development scale was combined with the 'weight management' and 'appearance' items of the Exercise Motivations Inventory to form a 13-item test questionnaire. This was administered to four groups of experienced exercisers: resistance training males (n = 40), resistance training females (n = 36), males training in a variety of sports (n = 27) and aerobic training females (n = 40). Factor analysis with varimax rotation revealed a relatively distinct muscular development factor, but with cross-loading on weight management. Muscular development was shown to be the most effective discriminator for the four groups. A multivariate analysis of variance and additional discriminant analysis revealed a series of significant differences between groups, which suggests that motive-based differences are more powerful than sex factors in determining choice of exercise modality. Although the interrelated nature of muscular development and weight management needs to be recognized and accounted for, there is a clear need for considering muscular development motives in future investigations, especially those that intend to examine motives for 'ideal' physical appearance.

Adolescent↗
PubMed1997

Quantification of phosphorus metabolites in human calf muscle and soft-tissue tumours from localized MR spectra acquired using surface coils.

Metabolite concentrations determined from MR spectra provide more specific information than peak area ratios. This paper presents a method of quantification that allows metabolite concentrations to be determined from in vivo 31P MR spectra acquired using a surface coil and ISIS localization. Corrections for the effects of B1 field inhomogeneity produced by surface coils are based on a measured and calibrated spatial sensitivity field map for the coil. Account is taken of imperfections in pulse performance, coil loading effects and relaxation effects, the latter making use of published metabolite relaxation times. The technique is demonstrated on model solutions. The concentrations of the main 31P metabolites in normal human calf muscle measured using this method are [PCr] = 26.9 +/- 4.1 mM; [Pi] = 3.6 +/- 1.2 mM; [NTP] = 6.8 +/- 1.8 mM. Quantification of spectra acquired from soft-tissue tumours in patients both pre- and post-treatment showed that changes in metabolite concentrations are more sensitive to metabolic changes than changes in peak area ratios.

Adenosine Triphosphate↗
PubMed1997

MRI study of hepatic tumours following high intensity focused ultrasound surgery.

High intensity, focused ultrasound has considerable potential as a non-invasive surgical technique, with applications which include the treatment of benign prostatic hyperplasia and the elimination of metastatic disease in the liver. In this study, the use of MRI for treatment planning and subsequent monitoring of ultrasound therapy in the liver has been evaluated. In an experimental model both tumour bearing and normal liver lobes were treated invasively with high intensity focused beam ultrasound surgery. Subsequent changes in the tissue properties were investigated using MRI, in combination with the intravenous contrast agent, Gd-DTPA. The repair of ultrasound damaged tissue was followed until 8 weeks after treatment. The appearance of the MR images was compared with histological sections prepared from parallel experiments. Imaging and histology results showed excellent agreement, illustrating that MRI is well suited to the non-invasive observation of the effects of high intensity focused ultrasound therapy on tissue. Thus, as the clinical potential of ultrasound surgery is realized, MRI, together with the use of contrast agents, will be invaluable both in treatment planning and in monitoring the progress of a treated tumour.

Animals↗
PubMed1996

Measurement of plasma 5-fluorouracil by high-performance liquid chromatography with comparison of results to tissue drug levels observed using in vivo 19F magnetic resonance spectroscopy in patients on a protracted venous infusion with or without interferon-alpha.

PURPOSE: To measure plasma 5-fluorouracil (5-FU) levels using high-performance liquid chromatography (HPLC) and compare the findings to the tissue metabolism of 5-FU evaluated using 19F magnetic resonance spectroscopy (MRS), during a protracted venous infusion (PVI) with or without interferon-alpha. METHODS: Patients receiving PVI 5-FU (300 mg/m2/day) with or without interferon-alpha (5 x 10(6) units 3 times per week), had 2 weekly plasma 5-FU levels evaluated using reverse-phase ion-pairing HPLC. These samples were drawn just prior to the patient undergoing MRS using a 1.5T Siemens Magnetom whole body magnetic resonance system with a 16 cm surface coil placed over normal liver or metastatic tumour. Semi-quantitated MRS values were compared with the plasma 5-FU levels using linear regression analysis. Data were available from patients given interferon-alpha with PVI 5-FU from day 1 or at the point of 5-FU refractory disease. RESULTS: A total of 30 patients were studied. Plasma 5-FU concentrations while on a protracted venous infusion varied from <25 ng/ml (0.192 mu M) to 25,000 ng/ml (192 mu M). A high plasma 5-FU concentration was associated with an increase in patient toxicity. Patients given interferon-alpha with 5-FU had higher median plasma 5-FU levels higher than patients on 5-FU alone (6138 vs. 218 ng/ml; p = 0.03). There was no correlation between the plasma 5-FU concentration and tumour response. A comparison of the plasma 5-FU data to the MRS studies in normal liver revealed a positive correlation between plasma 5-FU and liver catabolite signal (r = 0.68; p = 0.016) but a negative correlation with the log plasma 5-FU concentration and 5-FU liver signal (r = -0.63; p = 0.022). The patients experiencing toxicity, in addition to having a higher plasma 5-FU concentration did not exhibit a liver 5-FU signal, while the reverse was true for those having no toxicity. CONCLUSIONS: Plasma 5-FU levels may show greater interpatient variation when given as a protracted venous infusion. Levels of 5-FU correlated with treatment toxicity but not with anti-tumour activity. The addition of interferon-alpha to 5-FU increases plasma 5-FU levels. MRS findings suggest patients with low plasma 5-FU levels have higher 5-FU levels in normal liver tissue than in those with higher plasma levels.

Antimetabolites, Antineoplastic↗
PubMed1995

Quality assessment in in vivo NMR spectroscopy: III. Clinical test objects: design, construction, and solutions.

Based on the requirements of test protocols developed to evaluate clinical MRS single slice and volume localisation sequences, two clinical test objects, STO1 and STO2 have been developed. The properties of a range of potential construction materials have been assessed, demonstrating that the water/Perspex interface produced minimum susceptibility effects. The design of the objects has been evaluated in trials on different magnetic resonance instruments, with size and loading being adjusted to allow use on currently available equipment. Appropriate test solutions for 31P and 1H measurements have been developed and their properties evaluated.

Magnetic Resonance Spectroscopy↗
PubMed1995

Quality assessment in in vivo NMR spectroscopy: IV. A multicentre trial of test objects and protocols for performance assessment in clinical NMR spectroscopy.

A multicentre trial of test objects and protocols for performance assessment in single volume and slice selective magnetic resonance spectroscopy (MRS) was conducted by the European Community Concerted Action on MRI and MRS. The trial assessed phosphorus and proton localisation techniques implemented on commercially available MR systems at ten sites in Europe. At each site, a number of parameters devised by the Concerted Action were measured using prototype test objects. Some of these parameters related to the quality of localisation and others to the overall performance of the spectrometer. Results were obtained for the ISIS, DRESS, STEAM, and PRESS sequences with a range of acquisition parameters, allowing evaluation of the assessment methodology and comparison of the efficacy of various implementations of these localisation techniques. The results of this trial have been important in the development of the Concerted Action's final recommendations for MRS performance assessment, and demonstrate that such assessment provides valuable information in the comparison of spectroscopy data from different sites and in the development of new localisation sequences, and provides a means of quality assurance in MRS.

Magnetic Resonance Spectroscopy↗
PubMed1995

Quantification of signal selection efficiency, extra volume suppression and contamination for ISIS, STEAM and PRESS localized 1H NMR spectroscopy using an EEC localization test object.

The three most widely used single-volume NMR localization techniques (ISIS, STEAM and PRESS) are assessed quantitatively for 1H spectroscopy using an EEC localization test object. Signal selection efficiency, suppression of outer volume signals and contamination are measured on a 1.5 T whole-body Siemens GBS1 system. The ISIS signal selection efficiency (volume of interest (VOI), 1-125 cm3) ranged from 90% to 95%, with T1 relaxation during the sequence shown to account for the observed 5-10% signal loss. Contamination for ISIS was found to be higher for smaller VOIS and ranged from approximately 45% (VOI = 1 cm3) to approximately 9% (VOI = 125 cm3). For PRESS, contamination ranged from 7% to 12% and it was between 3% and 8% for STEAM. However, the maximum signal selection efficiency for the latter two techniques (echo time, 270 ms) was relatively low (10-17%), and limited by T2 losses and the non-rectangular slice profiles of sinc pulses.

Humans↗
PubMed1993

The non-invasive monitoring of low dose, infusional 5-fluorouracil and its modulation by interferon-alpha using in vivo 19F magnetic resonance spectroscopy in patients with colorectal cancer: a pilot study.

BACKGROUND: 5-Fluorouracil (5-FU) is the most widely used cytotoxic drug in oncology and the only one useful in the management of colorectal cancer - a leading cause of cancer death worldwide. Recent studies of 5-FU have focused on increasing efficacy and reducing toxicity by varying the delivery schedule and combining it with modulators. With the development of whole body magnetic resonance systems it is now possible to examine the metabolism of 5-FU in vivo by exploiting the magnetic properties of the fluorine atom which is an integral component of the drug. PATIENTS AND METHODS: Magnetic Resonance Spectroscopy (MRS) was used to non-invasively monitor the metabolism of 5-FU in the liver metastases of colorectal cancer patients. The patients were treated with a continuous low dose intravenous infusion of 5-FU until the point of refractory disease, at which time interferon-alpha was added with the objective of modulating 5-FU activity. MRS was performed at specific phases of the treatment. RESULTS: Twenty-six patients were treated with 5-FU, 11 (42%) achieving partial response. Of the 15 given interferon when disease became refractory to 5-FU, 4 showed signs of further response. In patients observed by MRS during the first 8 weeks of 5-FU treatment, those with a visible 5-FU signal were likely to respond to treatment (p = 0.017). At the time of interferon-alpha addition, MRS showed that 7 patients developed new or increased 5-FU signals, and 4 patients showed a signal from the active metabolites of 5-FU. The patients who exhibited a new or increased 5-FU signal were more likely to show further response to interferon-alpha (p = 0.007). CONCLUSIONS: MRS is a powerful technique for monitoring intratumoural metabolism and modulation of 5-FU enabling prediction of tumour outcome. Direct metabolic information may facilitate the rapid development of optimal clinical schedules for 5-FU and its modulators, thus maximising antitumour effect and minimising toxicity to the patient. This technique may be applied to other areas of clinical medicine where knowledge of the tissue metabolism of a fluorinated drug is of interest.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1992

Magnetic resonance behaviour of lipiodol.

Lipiodol is a frequently used contrast agent for lymphangiography and more recently has been used in the investigation of hepatoma. We describe the magnetic resonance characteristics of lipiodol using a Siemens 1.5 T Magnetom with reference to the appearance and behaviour of lipiodol in abdominal lymphadenopathy. The characteristics described differ from previously published reports.

Adult↗
PubMed1992

Drug abuse economics: cost estimates and policy implications.

This paper presents a brief summary of the results of a study estimating the economic costs of drug abuse in Australia and commentary on these results. It proceeds to draw some conclusions about the extent of the potential benefits of drug harm minimization programmes and of the types of programmes which might yield high rates of return. It applies some standard analyses normally used in the areas of industry and taxation economics to draw conclusions in regard to tobacco advertising, competition between federal and state governments in drug policies and the hypothecation (earmarking) of taxes to drug programmes.

Journal Article↗
PubMed1991

The water resonance as an alternative pH reference: relevance to in vivo 31P NMR localized spectroscopy studies.

pH measurements require a suitable pH reference within the 31P NMR spectrum with respect to which the chemical shift of Pi, and hence pH, may be calculated. In muscle spectra PCr is prominent and provides a reference frequency. However, recent localized tumor studies have reported the absence of PCr, for example, in breast tumors. The use of the alpha-, beta-, and gamma-ATP peaks as suitable references has been suggested, but the position of the beta- and gamma-ATP peaks is dependent upon the intracellular Mg2+ concentration. The alpha-ATP is not affected by ionic concentrations; however, it contains UDPG and NAD+, the presence of which can lead to peak-shape distortion. This paper considers the use of the H2O resonance from the proton spectrum used for shimming as a suitable pH reference, provided this is also localized to the same region of interest, using a sequence giving rise to eddy current effects comparable to those of the 31P NMR sequence. Localized in vivo measurements in the muscle and brain of volunteers indicate good agreement between the proton and phosphorus chemical shifts, allowing the PCr position to be predicted to within 0.01 ppm in all cases.

Body Water↗
PubMed1991

A quantitative analysis of the accuracy of in vivo pH measurements with 31P NMR spectroscopy: assessment of pH measurement methodology.

31P NMR spectroscopy provides a means of monitoring intracellular pH (pHi). In order to determine the significance of observed pH changes, an assessment of the measurement uncertainty is required. This paper considers the possible sources of error involved, firstly in chemical shift assignment and, secondly, in relating chemical shift to pH. A statistical analysis of these errors is presented and an expression for the accuracy of pH measurements obtained using in vivo 31P NMR spectroscopy is derived. Computer simulations and clinical measurements are considered to determine the likely error in clinical measurements. A comparison of pH measurement methodology using a centre-of-gravity calculation, Gaussian and Lorentzian fitting is also presented and discussed.

Humans↗