Biomedical subjects

D J Collins

Publications and source records attributed to D J Collins.

At least 19 recordsLinked to original sources

PubMed2006

Reproducibility of reference tissue quantification of dynamic contrast-enhanced data: comparison with a fixed vascular input function.

Reference tissues are currently used to analyse dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) data. The assessment of tumour response to treatment with anti-cancer drugs is a particularly important application of this type of analysis and requires a measure of reproducibility to define a level above which a significant change due to therapy can be inferred. This study compares the reproducibility of such quantification strategies with that found using a published, group-averaged uptake curve. It is shown that reference tissue quantification gives poorer reproducibility for most parameters than that found using a group-averaged plasma curve (a change in K(trans) of greater than 41.8% and 16.4% would be considered significant in the two approaches, respectively), but successfully incorporates some of the variability observed in plasma kinetics between visits and provides vascular input functions that, across the group, are comparable with the group-averaged curve. This study therefore provides an indirect validation of the methodology.

Antineoplastic Agents↗

PubMed2006

Evaluation of response to treatment using DCE-MRI: the relationship between initial area under the gadolinium curve (IAUGC) and quantitative pharmacokinetic analysis.

The initial area under the gadolinium curve (IAUGC) is often used in addition to or as an alternative to parameters derived from pharmacokinetic modelling of T1-weighted dynamic contrast-enhanced (DCE) MRI data in the assessment of response to treatment of cancer. However, the physiological meaning of the IAUGC has not been rigorously defined with respect to model-based parameters. Here, simulations of DCE-MRI data were used to investigate the relationship between IAUGC and the parameters K(trans) (transfer constant), v(e) (fractional extravascular extracellular volume) and v(p) (fractional plasma volume), using two vascular input functions. It is shown that IAUGC is a mixed parameter that can display correlation with K(trans), v(e) and v(p) and ultimately has an intractable relationship with all three. Furthermore, it is demonstrated that the range over which IAUGC is taken and the nature of the vascular input function do not significantly affect this relationship.

Contrast Media↗

PubMed2006

Colorectal hepatic metastases: quantitative measurements using single-shot echo-planar diffusion-weighted MR imaging.

The purpose of this study was to obtain quantitative measurements of the apparent diffusion coefficient (ADC1), flow insensitive apparent diffusion coefficient (ADC2) and perfusion fraction (F) of colorectal hepatic metastases using DWI and to compare these measurements with those obtained in liver parenchyma. Forty patients with 66 hepatic metastases from colorectal carcinoma were prospectively evaluated using DWI with three b values. Quantitative maps of the ADC1 (using b = 0, 150, 500 s/mm2 images), ADC2 (using b = 150, 500 s/mm2 images) and fractional variation (F) between ADC1 and ADC2, which reflects perfusion fraction, were calculated. The ADC1, ADC2 and F derived from metastases and liver parenchyma were compared. The mean ADC1 values of liver parenchyma and metastases were significantly higher than the mean ADC2 values (P < 0.0001, paired t-test). Colorectal metastases were found to have higher mean ADC1 and ADC2 values compared with liver (P < 0.0001, Mann-Whitney test). However, the estimated F was found to be lower in metastases compared to liver (P = 0.03, Mann-Whitney test). Colorectal hepatic metastases were characterised by higher ADC1 and ADC2 values, but lower F values compared to liver.

Adult↗

PubMed2006

Dynamic contrast-enhanced magnetic resonance imaging is a poor measure of rectal cancer angiogenesis.

BACKGROUND: The aim of this study was to investigate the use of magnetic resonance imaging (MRI) for non-invasive measurement of rectal cancer angiogenesis and hypoxia. METHODS: Fifteen patients with rectal adenocarcinoma underwent preoperative dynamic contrast-enhanced (DCE) and blood oxygenation level-dependent (BOLD) MRI. Microvessel density (CD31 level), and expression of vascular endothelial growth factor (VEGF) and carbonic anhydrase (CA) 9 were measured immunohistochemically in histological tumour sections from 12 patients. Serum VEGF levels were also measured in 14 patients. Correlations between quantitative imaging indices and immunohistochemical variables were examined. RESULTS: There was good correlation between circulating VEGF and CD31 expression (r(S) = 0.88, P < 0.001). CD31 expression did not correlate with any dynamic MRI parameter, except transfer constant, with which it correlated inversely (r(S) = -0.65, P = 0.022). Tissue and circulating VEGF levels did not correlate, and neither correlated with any tumour DCE MRI parameter. No relationship was seen between BOLD MRI and CA-9 expression. CONCLUSION: The negative correlation between transfer constant (reflecting tumour blood flow and microvessel permeability) with CD31 expression is paradoxical. DCE MRI methods for assessing tissue vascularity correlate poorly with histological markers of angiogenesis and hypoxia, suggesting that DCE MRI does not simply reflect static histological vascular properties in patients with rectal cancer.

Adenocarcinoma↗

PubMed2005

Dual-contrast echo planar imaging with keyhole: application to dynamic contrast-enhanced perfusion studies.

A new EPI-based method is presented which features optimized sampling of k-space enabling the integrated acquisition of two gradient echo images. The first of these images is predominantly T1 weighted and the second is T*2 weighted. The new method combines echo sharing of sparsely acquired high spatial frequency components with the keyhole technique and half-Fourier image reconstruction. The feasibility of acquiring high spatial and temporal resolution in vivo images for perfusion mapping is demonstrated. In contrast to most current perfusion methods, which acquire the T1- and T*2-weighted images in separate acquisitions, the need for image co-registration here is obviated since both sets of images are EPI-based and are acquired within the same measurement.

Brain↗

PubMed2003

Sliding window dual gradient echo (SW-dGRE): T1 and proton resonance frequency (PRF) calibration for temperature imaging in polyacrylamide gel.

The aim of the work is to evaluate a magnetic resonance imaging (MRI) thermometry sequence suitable for targeting of focused ultrasound (FUS) when used in vascular occlusion studies. A sliding window dual gradient echo (SW-dGRE) sequence was used. This sequence has the capability of monitoring both T1 relaxation and phase changes, which vary with temperature. Preliminary work involved quantification of the changes in T1 relaxation time with temperature and obtaining the PRF shift coefficient in polyacrylamide gel as it underwent an exothermic reaction during polymerization (avoiding the use of an external heat source). Temperature changes were visualized using thermal maps acquired with the sequence. For FUS guidance a thermal imaging technique is required with a temporal resolution <5 s, a spatial resolution of approximately 1 mm and a temperature resolution of approximately 5 degrees C. The sequence was optimized to improve the CNR (contrast to noise ratio) and SNR (signal to noise ratio) in the phase and magnitude images respectively. The PRF coefficient obtained for the polyacrylamide gel was -9.98 +/- 0.24 ppb degrees C(-1), whilst deltaT1 and temperature change were related by a proportionality factor, the T1 temperature coefficient, of 102.3 +/- 2.9 ms degrees C(-1). The sequence produces an image at every 1.4 s interval. In both magnitude and phase data, the in-plane resolution is +/- 1.2 mm and the temperature resolution is approximately 2 degrees C. The advantage of this sequence is that the temperature obtained from the magnitude data can be confirmed independently using the phase data and vice versa. Thus the sequence can essentially be crosschecked.

Acrylic Resins↗

PubMed2003

Non-invasive study of human gall bladder bile in vivo using (1)H-MR spectroscopy.

The sampling of gall bladder bile for analytical studies remains an invasive procedure. We demonstrate the application of the non-invasive methodology of (1)H-MR spectroscopy to the qualitative and quantitative assessment of human gall bladder bile in vivo. Spectral profiles in vivo are shown in relation to model and porcine gall bladder bile and the quantitation in man of the trimethylamine (choline) and lecithin concentrations were estimated to range from 25.9 mM to 48.4 mM (mean: 35.8 mM, standard deviation: 9.8). The composition of human gall bladder bile together with the quantitation of various constituents can be studied non-invasively in vivo.

Adult↗

PubMed2002

A model to assess SAR for surface coil magnetic resonance spectroscopy measurements.

Surface coils are widely used in magnetic resonance (MR) studies due to their superior signal to noise properties. Application of excessive power levels to transmit surface coils may result in local tissue damage. A homogeneous muscle tissue model for the conservative prediction of surface coil specific absorption rate (SAR) is introduced. Based on this model, sequence parameters can be limited to provide operational levels within safety guidelines. It is demonstrated that this model provides worst-case SAR estimates at MR frequencies of 25.75 MHz and 63.6 MHz. The dependence of SAR on model structure and geometry is analysed and conclusions on the relationship between SAR levels and local anatomy are drawn. By making a worst-case assumption for the tissue parameters the model provides safe operational levels for all tissue types. Power-demanding proton-decoupled 31P magnetic resonance spectroscopy experiments are possible based on the SAR estimates provided. To date SAR values are calculated for 1 g of tissue. Changes in regulations to calculate SAR values for 10 g tissue masses, and the according averaging of local SAR over a larger volume, have been proposed by the International Electrotechnical Commission. A comparative study shows that up to 100% more energy may be applied to surface coils if SAR values are determined for 10 g tissue masses rather than 1 g tissue masses.

Algorithms↗

PubMed2002

An algorithm for the optimum combination of data from arbitrary magnetic resonance phased array probes.

When summing the spectra acquired with phased array coils, signals with low signal-to-noise ratio or wrongly corrected phase may degrade the overall signal-to-noise ratio (SNR). Here we present a mathematical expression predicting the dependence of combined SNR on the signal-to-noise ratios and errors in phase correction of composite signals. Based on this equation, signals that do not lead to an overall increase in signal-to-noise ratio can be identified and excluded from the weighted sum of signals. This tool is particularly useful for the combination of large numbers of signals. Additionally, a simple and robust algorithm for calculating the complex weighting factors necessary for the signal-to-noise weighted combination of spectroscopic data is presented. Errors in the calculation and correction of relative phase differences between composite spectra are analysed. The errors have a negligible effect on the overall spectral SNR for typical clinical magnetic resonance spectroscopy (MRS). The signal combination routine developed here has been applied to the first in vivo MRS study of human rectal adenocarcinomas at 1.5 T (Dzik-Jurasz A S K, Murphy P S, George M, Prock T, Collins D J, Swift I and Leach M O 2001 Magn. Reson. Med. at press), showing improvements of combined spectral SNR of up to 34% over the maximum SNR from a single element.

Adenocarcinoma↗

PubMed2002

Human rectal adenocarcinoma: demonstration of 1H-MR spectra in vivo at 1.5 T.

This study was designed to determine whether 1H-MR spectra of locally advanced human rectal adenocarcinoma could be acquired in vivo at 1.5 T. Despite the relatively large size of these neoplasms, only six out of 21 tumors accommodated a voxel size of 8 cm3. This was due to air pockets within the tumor mass, which limited voxel positioning. Localized proton spectra were acquired at short (20 ms) and long (135 ms) echo times (TEs) using a single-voxel technique. The most commonly detected metabolites were choline and lipid.

Adenocarcinoma↗

PubMed2002

Applications of sliding window reconstruction with cartesian sampling for dynamic contrast enhanced MRI.

Applications of dynamic contrast enhanced MR imaging are increasing and require both high spatial resolution and high temporal resolution. Perfusion studies using susceptibility contrast in particular require very high temporal resolution. The sliding window reconstruction is a technique for increasing temporal resolution. It has previously been applied to radial and spiral sampling, but these schemes require extensive correction and interpolation during image reconstruction. Fourier raw data can be reconstructed simply and quickly using the fast fourier transform (FFT). This paper presents a new Fourier-based sampling scheme and sliding window reconstruction that facilitates fast scanning without needing correction or interpolation. This technique can be used on virtually any MR scanner since it requires no specialized hardware. It is implemented here as a dual gradient echo sequence providing simultaneous T(1)- and T(2)*-weighted images with a time resolution of 1.1 s.

Humans↗

PubMed2002

Early in vivo detection of metabolic response: a pilot study of 1H MR spectroscopy in extracranial lymphoma and germ cell tumours.

Monitoring therapeutic efficacy is essential in oncological practice. We have investigated the feasibility of using proton (1)H MR spectroscopy (MRS), localized to malignant lymphoma and germ cell lesions outside the cranial cavity, to monitor tumour metabolism in vivo during chemotherapy treatment. (1)H single voxel MRS, (stimulated echo acquisition mode, repetition time/echo time=2000/20 ms) was performed prior to treatment in patients with lymphoma or germ cell tumours, and during the first cycle of chemotherapy. Patient response was assessed by independent clinical follow-up at a median of 57 days (range 44-93 days) post-treatment. All 12 non-cystic lesions scanned showed a signal assigned to choline-containing metabolites (tCho); 9 were scanned both pre- and post-treatment. Changes in the tCho:water ratio following treatment were found to predict subsequent patient response. In seven of these nine patients, the tCho:water ratio decreased in the first post-treatment scan, and all subsequently achieved a partial response to treatment. In the remaining two patients, both of whom progressed on treatment, the tCho:water ratio did not change significantly. Normalized to pre-treatment values, the non-responder group values (1.07 and 0.97) were clearly distinct from the responder group, whose values ranged from 0.43 to below detection level. To our knowledge, this is the first report of (1)H MR spectra from these tumour types and sites. These preliminary results indicate that metabolite signals can be detected using (1)H MRS in these tumour types and locations, as has already been established in the brain, breast and prostate. Moreover, the differential changes observed in the tCho region of the spectrum suggest that (1)H MRS could provide an early and sensitive indicator of metabolic response to chemotherapy.

Adolescent↗

PubMed2001

Radio-frequency probe for 1H decoupled 31P MRS of the head and neck region.

For optimal performance of 31P MRS at 1.5 Tesla, the use of a double resonant probe is essential to enable the application of 1H decoupling and Nuclear Overhauser Enhancement. This note describes the design, evaluation and safety validation of a versatile and compact probe optimized for 1H decoupled 31P MRS studies of tumors close to the surface of the body, in particular the head and neck region.

Equipment Design↗

PubMed2001

The quantitative 19F-imaging of albumin at 1.5 T: a potential in-vivo tool.

19F-MR-imaging has been used to quantitate albumin concentration in a phantom at 1.5 T. The experimentally derived relationship between albumin concentration and the T1 relaxation time of a fluorinated marker, tetrafluorosuccinic acid (TFSA) was used to calculate the albumin concentration from a quantitative 19F T1 map acquired using a gradient echo sequence. There was close correlation between calculated and actual BSA concentrations (r = 0.99, SE = 0.15). The potentially interfering effect of paramagnetic species on T1 relaxation times was also investigated. Relaxivity data show that albumin concentration measurements should be performed prior to any contrast agent administration.

Albumins↗

PubMed2001

A test of processing efficiency theory in a team sport context.

In this study, we tested some key postulates of Eysenck and Calvo's processing efficiency theory in a team sport. The participants were 12 elite male volleyball players who were followed throughout the course of a competitive season. Self-report measures of pre-match and in-game cognitive anxiety and mental effort were collected in groups of players high and low in dispositional anxiety. Player performance was determined from the statistical analysis of match-play. Sets were classified according to the point spread separating the two teams into one of three levels of criticality. Game momentum was also analysed to determine its influence on in-game state anxiety. Significant differences in in-game cognitive anxiety were apparent between high and low trait anxiety groups. An interaction between anxiety grouping and momentum condition was also evident in cognitive anxiety. Differences in set criticality were reflected in significant elevations in mental effort, an effect more pronounced in dispositionally high anxious performers. Consistent with the predictions of processing efficiency theory, mental effort ratings were higher in high trait-anxious players in settings where their performance was equivalent to that of low trait-anxious performers. The usefulness of processing efficiency theory as an explanatory framework in sport anxiety research is discussed in the light of these findings.

Adult↗

PubMed2001

Numerical evaluation of shaped surface coil sensitivity at 63 MHz.

Surface coils are widely used in magnetic resonance studies due to their superior signal to noise (SNR) properties. When shaping planar coils to cylindrical surfaces, the region with maximum sensitivity migrates from the coil plane towards the centre of the shaping radius. The influence of the coil current, the probe and tissue dimensions, the electrical tissue properties and the operating frequency on the B1 field strength of a coil has been studied using statistical methods. This analysis allows the dependence of the axial SNR distribution of circular and square surface coils on shaping radius and coil dimensions to be evaluated quantitatively using 3D finite element methods. An empirically derived equation describing the dependence of the SNR distributions on coil geometry and depth allows the optimum coil dimensions to be predicted for a given shaping radius and desired optimized depth of sensitivity. Simulations are validated experimentally using both B1 and SNR mapping techniques. A comparison between the axial SNR of circular and square coils demonstrated equal SNR distributions of coils with equivalent area at depth.

Magnetic Resonance Imaging↗

PubMed2000

1H decoupling for in vivo (19)F MRS studies using the time-share modulation method on a clinical 1.5 T NMR system.

Time-share modulation has been implemented successfully on a clinical 1.5 T nuclear magnetic resonance (NMR) system to perform in vivo (19)F[-(1)H] decoupling. It uses commercially available radiofrequency (RF) filters, a transistor-transistor logic (TTL)-controlled attenuator, and a double-resonant RF surface coil suitable for (19)F magnetic resonance spectroscopy (MRS) studies in vivo. This decoupling scheme gives a threefold improvement in signal-to-noise ratio performance compared with the conventional WALTZ-4 decoupling scheme, when significant interaction exists between the decoupler and the receiver. It can also eliminate receiver saturation (i.e., saturation due to coupling of the strong proton decoupling pulse to the (19)F coil) without the need for a high-isolation coil system, thus allowing flexibility in coil geometry. This method has been demonstrated in vivo in patients receiving 5-fluorouracil chemotherapy. Magn Reson Med 44:5-9, 2000.

Antimetabolites, Antineoplastic↗

PubMed2000

Gallbladder localization of (19)F MRS catabolite signals in patients receiving bolus and protracted venous infusional 5-fluorouracil.

The hepatobiliary distribution of 5-fluorouracil (5FU) catabolites was investigated in nine patients. Using fluorine 3D-chemical shift imaging, four patients receiving protracted venous infusion of 5FU demonstrated catabolite localized to the gallbladder. No hepatobiliary fluorine signals were detected in three patients whose gallbladders were absent or abnormal. Signals from the gallbladder showed a 2.2-2.4 ppm high-frequency shift from alpha-fluoro-beta-alanine, suggesting the presence of alpha-fluoro-beta-alanine-bile-acid conjugates. 3D-chemical shift imaging of two patients receiving bolus 5FU revealed alpha-fluoro-beta-alanine to be localized to the liver within 1 hr of administration. In one patient examined 4 hr after bolus administration, catabolite signal was detected only in the gallbladder.

Aged↗