Biomedical subjects

D J Tozer

Publications and source records attributed to D J Tozer.

10 recordsLinked to original sources

PubMed2006

Sources of variation in multi-centre brain MTR histogram studies: body-coil transmission eliminates inter-centre differences.

OBJECT: 1. Identify sources of variation affecting Magnetisation Transfer Ratio (MTR) histogram reproducibility between-centres. 2. Demonstrate complete elimination of inter-centre difference. MATERIALS AND METHODS: Six principle sources of variation were summarised and analysed. These are: the imager coil used for radiofrequency (RF) transmission, imager stability, the shape and other parameters describing the Magnetisation Transfer (MT) pulse, the MT sequence used (including its parameters), the image segmentation methodology, and the histogram generation technique. Transmit field nonuniformity and B1 errors are often the largest factors. PLUMB (Peak Location Uniformity in MTR histograms of the Brain) plots are a convenient way of visualising differences. Five multi-centres studies were undertaken to investigate and minimise differences. RESULTS: Transmission using a body coil, with a close-fitting array of surface coils for reception, gave the best uniformity. Differences between two centres, having MR imagers from different manufacturers, were completely eliminated by using body coil excitation, making a small adjustment to the MT pulse flip angle, and carrying out segmentation at a single centre. Histograms and their peak location and height values were indistinguishable. CONCLUSIONS: Body coil excitation is preferred for multi-centre studies. Analysis (segmentation and histogram generation) should ideally be carried out at a single site.

Artifacts↗

PubMed2006

Neoadjuvant chemotherapy in breast cancer: early response prediction with quantitative MR imaging and spectroscopy.

A prospective study was undertaken in women undergoing neoadjuvant chemotherapy for locally advanced breast cancer in order to determine the ability of quantitative magnetic resonance imaging (MRI) and proton spectroscopy (MRS) to predict ultimate tumour response (percentage decrease in volume) or to detect early response. Magnetic resonance imaging and MRS were carried out before treatment and after the second of six treatment cycles. Pharmacokinetic parameters were derived from T1-weighted dynamic contrast-enhanced MRI, water apparent diffusion coefficient (ADC) was measured, and tissue water:fat peak area ratios and water T2 were measured using unsuppressed one-dimensional proton spectroscopic imaging (30 and 135 ms echo times). Pharmacokinetic parameters and ADC did not detect early response; however, early changes in water:fat ratios and water T2 (after cycle two) demonstrated substantial prognostic efficacy. Larger decreases in water T2 accurately predicted final volume response in 69% of cases (11/16) while maintaining 100% specificity and positive predictive value. Small/absent decreases in water:fat ratios accurately predicted final volume non-response in 50% of cases (3/6) while maintaining 100% sensitivity and negative predictive value. This level of accuracy might permit clinical application where early, accurate prediction of non-response would permit an early change to second-line treatment, thus sparing patients unnecessary toxicity, psychological morbidity and delay of initiation of effective treatment.

Adult↗

PubMed2005

Magnetization transfer histograms in clinically isolated syndromes suggestive of multiple sclerosis.

In established multiple sclerosis, magnetization transfer ratio (MTR) histograms reveal abnormalities of normal-appearing white matter (NAWM) and grey matter (NAGM). The aim of this study was to investigate for such abnormalities in a large cohort of patients presenting with clinically isolated syndromes suggestive of multiple sclerosis. Magnetization transfer imaging was performed on 100 patients (67 women, 33 men, median age 32 years) a mean of 19 weeks (SD 3.8, range 12-33 weeks) after symptom onset with a clinically isolated syndrome and in 50 healthy controls (34 women, 16 men, median age 32.5 years). SPM99 software was used to generate segmented NAWM and NAGM MTR maps. The volumes of T2 lesions, white matter and grey matter were calculated. Eighty-one patients were followed up clinically and with conventional MRI after 3 years (n = 61) or until they developed multiple sclerosis if this occurred sooner (n = 20). Multiple regression analysis was used to investigate differences between patients and controls with age, gender and volume measures as covariates to control for potential confounding effects. The MTR histograms for both NAWM and NAGM showed a reduction in the mean (NAWM, 38.14 versus 38.33, P = 0.001; NAGM 32.29 versus 32.50, P = 0.009; units in pu) and peak location, with a left shift in the histogram. Mean NAWM and NAGM MTR were also reduced in the patients who developed clinically definite multiple sclerosis and multiple sclerosis according to the McDonald criteria but not in the 24 patients with normal T2-weighted brain magnetic resonance imaging (MRI). MTR abnormalities occur in the NAWM and NAGM at the earliest clinical stages of multiple sclerosis.

Adult↗

PubMed2005

Correlation of apparent myelin measures obtained in multiple sclerosis patients and controls from magnetization transfer and multicompartmental T2 analysis.

Two relatively new techniques purport to give measures of the myelin content of brain tissue. These measures are the myelin water fraction from multicompartmental T(2) analysis, and the semisolid proton fraction from analysis of magnetization transfer (MT). The myelin water fraction is the fraction of signal with a T(2) of less than 50 ms measured from a 32-echo sequence. It is believed to originate from water trapped between the myelin bilayers. The semisolid proton fraction is thought to include protons within phospholipid bilayers and macromolecular protons, and may also be a measure of myelin content. Multicompartmental T(2) and MT imaging were carried out on controls and patients with multiple sclerosis (MS), and estimates of the semisolid proton and myelin water fractions were obtained from white matter (WM), gray matter (GM), and MS lesions. These were then correlated for each tissue and subject group. Positive correlations were seen for MS lesions (r approximately 0.2) and in WM in patients (r = 0.6). A negative correlation (r approximately -0.3) was seen for GM. These results indicate that the two techniques measure, to some extent, the same thing (most likely myelin content), but that other factors, such as inflammation, mean they may provide complementary information.

Adult↗

PubMed2004

Estimation of the macromolecular proton fraction and bound pool T2 in multiple sclerosis.

This study used a model for magnetization transfer (MT) to estimate two underlying parameters: the macromolecular proton fraction (f) and the bound pool T2 (T2b) in patients with multiple sclerosis (MS). Sixty patients with clinically definite MS and 27 healthy controls were imaged using: (1) a dual echo fast spin echo sequence, (2) a MT sequence (with ten MT power and offset frequency combinations) and (3) proton density and T1 weighted sequences (for T1 relaxation time estimation). Fourteen normal-appearing white matter (NAWM) regions of interest (ROI) and six normal-appearing gray matter (NAGM) ROIs were outlined in all subjects. Lesions were also contoured in subjects affected by MS. The model was fitted to the data leading to estimates of T2b and f. Results showed that T2b was increased in lesions whereas f was reduced. In NAWM, f was decreased while T2b was only increased in secondary progressive MS. NAWM f correlated modestly with disability. Further studies are needed to investigate the pathological basis of the abnormalities observed.

Adult↗

PubMed2003

Preliminary magnetic resonance study of the macromolecular proton fraction in white matter: a potential marker of myelin?

We report on a new quantitative magnetization transfer (MT) technique that allows for the in vivo estimation of the macromolecular proton fraction (f) and the bound pool T2 relaxation time (T2b), whilst permitting whole brain coverage. In this pilot study, five subjects with multiple sclerosis (MS) and five healthy controls were studied. Both f and T2b were significantly different between MS lesions and normal control white matter (WM). Relationships between f and T1 relaxation time [Spearmans rank correlation coefficient (r(s)) = -0.97, P < 0.001] and f and the magnetization transfer ratio (MTR; r(s) = 0.80, P < 0.001) were observed. Compared with MTR, f and T2b have the potential advantage of relative independence from MT acquisition protocol while offering more pathologically specific information. In particular, f may provide a more direct indication of myelin content in WM.

Adult↗

PubMed2001

Experimental assessment of lanthanide ion donor preference: spectroscopic and theoretical dissection of static charge and dynamic polarisation contributions to axial ligation in a C4-symmetric chiral europium complex.

Measurements of the equilibrium constants for ligand exchange (MeCN, 295 K) involving the axial donor in a C4-symmetric, mono-capped, square antiprismatic cationic Eu complex, supported by calculations based on an electrostatic perturbation model, have been interpreted in terms of a predominant ligand polarisation interaction defined by observation of the hypersensitive delta J = 2 normalised emission intensity, in association with measurements correlating delta J = 1 band splitting and 1H NMR dipolar shifts that vindicate Bleaney's theory of magnetic anisotropy.

Journal Article↗

PubMed2001

Comparison of quantitative T2 mapping and diffusion-weighted imaging in the normal and pathologic prostate.

In this study, diffusion-weighted images of the human prostate were successfully obtained, enabling quantification of apparent diffusion coefficients (ADCs) in normal and pathologic regions. A dual acquisition fast spin-echo sequence was used for accurate T2 calculation. T2 values were significantly higher in the peripheral zone than the central gland (P = 0.015). No significant correlations were found in either normal or pathologic tissue between ADC values and relaxation rates for all three gradient directions and the orientationally averaged water diffusion coefficient. Evidence suggesting that diffusional anisotropy is present in normal prostatic tissue is also detailed, with significant differences noted between the z-component and both the x- and y-components of the ADC for peripheral zone (P < 0.040) and central gland (P < 0.001).

Adult↗

PubMed2000

Bilateral open breast coil and compatible intervention device.

Dynamic contrast-enhanced breast MRI is an extremely sensitive method for breast lesion detection. For MR-only detected lesions it is essential that needle biopsy or localization prior to surgery is carried out under MR guidance. This work describes a bilateral open breast coil and prototype intervention device, which may be used in these situations. Results demonstrate that the open coil provides images superior to those obtained with a conventional closed breast coil. Initial phantom tests with the intervention device indicate a potential for this system to be used in the MR-guided localization of breast lesions. J. Magn. Reson. Imaging 2000;12:984-990.

Biopsy, Needle↗

PubMed1999

A simple and realistic tissue-equivalent breast phantom for MRI.

A simple and inexpensive breast phantom is described for use in magnetic resonance imaging. The work demonstrates the similarity of the phantom materials to in vivo breast tissue in terms of T(1) relaxation times. The phantom is also qualitatively compared with images acquired from a patient with a primary breast lesion.J. Magn. Reson. Imaging 10:968-971, 1999.

Adipose Tissue↗