Biomedical subjects

Joseph V Hajnal

Publications and source records attributed to Joseph V Hajnal.

At least 19 recordsLinked to original sources

PubMed2006

Thalamo-cortical connectivity in children born preterm mapped using probabilistic magnetic resonance tractography.

Our aim was to investigate the feasibility of studying white matter tracts and connections between the thalamus and the cortex in 2-year-old infants who were born preterm by probabilistic magnetic resonance (MR) tractography. Using this approach, we were able to visualize and quantify connectivity distributions in a number of white matter tracts, including the corticospinal tracts, optic radiations, fibers of the genu and splenium of the corpus callosum, superior longitudinal fasciculus and inferior fronto-occipital fasciculus, and to map the distribution within thalamus of fibers connecting to specific cortical regions. In eleven infants with no MR evidence of focal cerebral lesions and appropriate neurodevelopment as shown by general quotient (GQ) scores above 100, we mapped cortical connections to the thalamus that appeared similar to those reported in adults. However, in a proof-of-principle experiment, we examined one further child with marked white matter abnormalities and found that the volume and pattern of thalamo-cortical connections were severely disrupted. This technique promises to be a useful tool for assessing connectivity in the developing brain and in infants with lesions.

Cerebral Cortex↗

PubMed2006

Detection of vascular expression of E-selectin in vivo with MR imaging.

PURPOSE: To develop a contrast agent for targeting E-selectin expressed on activated vascular endothelium and to evaluate detection of the agent with magnetic resonance (MR) imaging in an in vivo mouse model of inflammation. MATERIALS AND METHODS: All animal experiments were approved according to animal welfare and local ethics committee regulations. An anti-murine E-selectin F(ab')2 monoclonal antibody, MES-1, was conjugated with ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles. Flow cytometry, Perl Prussian blue staining for iron, and MR imaging were performed by using Chinese hamster ovary (CHO) cells expressing mouse E-selectin to detect binding of the conjugate in vitro, and a mouse model of contact hypersensitivity to oxazolone in the ear was used to investigate the in vivo characteristics of the MES-1-USPIO. Serial imaging was performed by using a 9.4-T MR imaging system with a custom receive-only coil. Tissue slices were stained to define distribution of E-selectin expression and localization of the MES-1-USPIO conjugate. RESULTS: MES-1-USPIO was shown to bind to CHO cells expressing mouse E-selectin in vitro. After injection of MES-1-USPIO in vivo, distinct changes in R2 relaxation rate (1/T2) characteristics were detected in inflamed ears when they were compared with control ears. Histologic analysis confirmed the vascular endothelial distribution of MES-1-USPIO. CONCLUSION: E-selectin expression in vivo can be selectively and directly imaged noninvasively with MR. This has the potential to be useful in the study of inflammatory disease.

Animals↗

PubMed2006

Automatic anatomical brain MRI segmentation combining label propagation and decision fusion.

Regions in three-dimensional magnetic resonance (MR) brain images can be classified using protocols for manually segmenting and labeling structures. For large cohorts, time and expertise requirements make this approach impractical. To achieve automation, an individual segmentation can be propagated to another individual using an anatomical correspondence estimate relating the atlas image to the target image. The accuracy of the resulting target labeling has been limited but can potentially be improved by combining multiple segmentations using decision fusion. We studied segmentation propagation and decision fusion on 30 normal brain MR images, which had been manually segmented into 67 structures. Correspondence estimates were established by nonrigid registration using free-form deformations. Both direct label propagation and an indirect approach were tested. Individual propagations showed an average similarity index (SI) of 0.754+/-0.016 against manual segmentations. Decision fusion using 29 input segmentations increased SI to 0.836+/-0.009. For indirect propagation of a single source via 27 intermediate images, SI was 0.779+/-0.013. We also studied the effect of the decision fusion procedure using a numerical simulation with synthetic input data. The results helped to formulate a model that predicts the quality improvement of fused brain segmentations based on the number of individual propagated segmentations combined. We demonstrate a practicable procedure that exceeds the accuracy of previous automatic methods and can compete with manual delineations.

Adult↗

PubMed2006

Variations due to analysis technique in intracellular pH measurements in simulated and in vivo 31P MR spectra of the human brain.

PURPOSE: To investigate variation in pH generated by different analysis techniques and to find the most robust method, 31P MR brain spectra were acquired in vivo. Three different methods were used to measure the chemical shift of inorganic phosphate (Pi) relative to phosphocreatine (PCr). MATERIALS AND METHODS: Eight healthy volunteers were scanned four times, and manual measurement of the chemical shift in a frequency domain spectrum using the manufacturer's software was compared with values produced by a frequency-domain analysis method (NMR1) and a prior-knowledge-based time-domain technique (MRUI). To explain the in vivo data, simulations of brain spectra, modified in ways typical of real variations in vivo, were produced and the pH was measured using manual measurement and MRUI. RESULTS: Different measurement techniques produced systematically different pH values, with manual measurement producing the lowest variability (manual measurement: pH = 6.999, CoV = 0.297; NMR1: pH = 7.042, CoV = 0.501; MRUI: pH = 7.036, CoV = 0.606). While MRUI more accurately measured the pH of unaltered simulations, it was systematically affected by altering the simulated spectra. Manual measurement was unaffected. CONCLUSION: Manual measurement produces the most consistent pH value, and there is no benefit in using more complex automated spectral fitting methods to measure the pH.

Adult↗

PubMed2006

x-f Choice: reconstruction of undersampled dynamic MRI by data-driven alias rejection applied to contrast-enhanced angiography.

A technique for reconstructing dynamic undersampled MRI data, termed "x-f choice," was developed and applied to dynamic contrast-enhanced MR angiography (DCE-MRA). Regular undersampling in k-t space (a hybrid of k-space and time) creates aliasing in the conjugate x-f space that must be resolved. When regions in the object containing fast dynamic change are sparse, as in DCE-MRA, signal overlap caused by aliasing is often much less than the undersample factor would imply. x-f Choice reconstruction identifies overlapping signals using a model of the full non-aliased x-f space that is automatically generated from the undersampled data, and applies parallel imaging (PI) to separate them. No extra reference scans are required to generate either the model or the coil sensitivity maps. At each location in the reconstructed images, g-factor noise amplification is compared with predicted reconstruction errors to obtain an optimized solution. Acceleration factors greater than the number of receiver coils are possible, but are limited by the sparseness of the dynamic content and the signal-to-noise ratio (SNR) (in DCE-MRA the latter is dominant). Temporal fidelity was validated for up to a factor 10 speed-up using retrospectively undersampled data from a six-coil array. The method was tested on volunteers using fivefold prospective undersampling.

Blood Flow Velocity↗

PubMed2006

Nonlinear phase correction of navigated multi-coil diffusion images.

Cardiac pulsatility causes a nonrigid motion of the brain. In multi-shot diffusion imaging this leads to spatially varying phase changes that must be corrected. A conjugate gradient based reconstruction is presented that includes phase changes measured using two-dimensional navigator echoes, coil sensitivity information, navigator-determined weightings, and data from multiple coils and averages.A multi-shot echo planar sequence was used to image brain regions where pulsatile motion is not uniform. Reduced susceptibility artifacts were observed compared to a clinical single-shot sequence. In a higher slice, fiber directions derived from single-shot data show distortions from anatomical scans by as much as 7 mm compared to less than 2 mm for our multi-shot reconstructions. The reduced distortions imply that phase encoding can be applied in the shorter left-right direction, enabling time savings through the use of a rectangular field of view. Higher resolution diffusion imaging in the spine permits visualization of a nerve root.

Algorithms↗

PubMed2006

Investigating the nonlinear microbubble response to chirp encoded, multipulse sequences.

A modified Rayleigh-Plesset model was used to investigate the nonlinear acoustic response of ultrasound contrast microbubbles to multipulse phase and amplitude modulated, chirp encoded sequences. Trade-offs between the signal-to-noise ratio (SNR) and axial resolution were quantified for differing chirp time-bandwidth products and methods for minimising the artifacts formed in the postprocessing stages were developed. It was found that the chirp length can be increased and bandwidth reduced to improve SNR, though resolution is sacrificed. Results from the simulated chirp, pulse inverted, amplitude modulated (chirp PIAM) sequences were also compared with equivalent short pulse PIAM sequences and it was found that the chirp sequences preserve their extra energy after scattering, which translates to an improved SNR after processing. Compression artifacts were reduced by using chirps with a centre frequency and bandwidth tuned to the frequency response of the microbubble and reversing the frequency sweep of one chirp in the sequence.

Artifacts↗

PubMed2006

Automatic quantification of changes in bone in serial MR images of joints.

Recent innovations in drug therapies have made it highly desirable to obtain sensitive biomarkers of disease progression that can be used to quantify the performance of candidate disease modifying drugs. In order to measure potential image-based biomarkers of disease progression in an experimental model of rheumatoid arthritis (RA), we present two different methods to automatically quantify changes in a bone in in-vivo serial magnetic resonance (MR) images from the model. Both methods are based on rigid and nonrigid image registration to perform the analysis. The first method uses segmentation propagation to delineate a bone from the serial MR images giving a global measure of temporal changes in bone volume. The second method uses rigid body registration to determine intensity change within a bone, and then maps these into a reference coordinate system using nonrigid registration. This gives a local measure of temporal changes in bone lesion volume. We detected significant temporal changes in local bone lesion volume in five out of eight identified candidate bone lesion regions, and significant difference in local bone lesion volume between male and female subjects in three out of eight candidate bone lesion regions. But the global bone volume was found to be fluctuating over time. Finally, we compare our findings with histology of the subjects and the manual segmentation of bone lesions.

Algorithms↗

PubMed2006

Axial and radial diffusivity in preterm infants who have diffuse white matter changes on magnetic resonance imaging at term-equivalent age.

OBJECTIVE: Diffuse excessive high signal intensity (DEHSI) is observed in the majority of preterm infants at term-equivalent age on conventional MRI, and diffusion-weighted imaging has shown that apparent diffusion coefficient values are elevated in the white matter (WM) in DEHSI. Our aim was to obtain diffusion tensor imaging on preterm infants at term-equivalent age and term control infants to test the hypothesis that radial diffusivity was significantly different in the WM in preterm infants with DEHSI compared with both preterm infants with normal-appearing WM on conventional MRI and term control infants. METHODS: Diffusion tensor imaging was obtained on 38 preterm infants at term-equivalent age and 8 term control infants. Values for axial (lambda1) and radial [(lambda2 + lambda3)/2] diffusivity were calculated in regions of interest positioned in the central WM at the level of the centrum semiovale, frontal WM, posterior periventricular WM, occipital WM, anterior and posterior portions of the posterior limb of the internal capsule, and the genu and splenium of the corpus callosum. RESULTS: Radial diffusivity was elevated significantly in the posterior portion of the posterior limb of the internal capsule and the splenium of the corpus callosum, and both axial and radial diffusivity were elevated significantly in the WM at the level of the centrum semiovale, the frontal WM, the periventricular WM, and the occipital WM in preterm infants with DEHSI compared with preterm infants with normal-appearing WM and term control infants. There was no significant difference between term control infants and preterm infants with normal-appearing WM in any region studied. CONCLUSIONS: These findings suggest that DEHSI represents an oligodendrocyte and/or axonal abnormality that is widespread throughout the cerebral WM.

Brain↗

PubMed2006

Designing for e-Health: recurring scenarios in developing grid-based medical imaging systems.

The paper draws on a number of Grid projects, particularly on the experience of NeuroGrid, a UK project in the Neurosciences tasked with developing a Grid-based collaborative research environment to support the sharing of digital images and patient data across multiple distributed sites. It outlines recurrent socio-technical issues, highlighting the challenges of scaling up technological networks in advance of the regulatory networks which normally regulate their use in practice.

Biomedical Research↗

PubMed2005

Padé methods for reconstruction and feature extraction in magnetic resonance imaging.

Methods utilizing Padé approximants are investigated for implementation with magnetic resonance imaging data and are presented both for direct image reconstruction and for feature extraction. Padé approximants are a numerical tool that can be used to accelerate the convergence of a slowly converging sequence by estimating the fully converged sequence values from early data points. Padé approximants can be calculated directly from k-space data by solving a set of linear matrix equations to produce signal values for any desired location in the image domain. This gives an estimate of the fully converged signal intensity at each pixel location in the image, raising the possibility of reconstructing a better estimate of the object from a reduced data set. These methods have been tested on phantom and human data both for image reconstruction and for feature extraction. In image reconstruction, considerable convergence acceleration can be achieved, with steep intensity boundaries reproduced in keeping with higher resolution reconstructions and oscillatory truncation artifact characteristic of Fourier reconstruction removed. The convergence acceleration is variable and there is the possibility of fine detail suppression when insufficient data are included. The use of Padé methods as a tool for feature extraction has shown good agreement with extraction from high-resolution reference data. In this approach the edge information comes intrinsically from Padé reconstruction.

Algorithms↗

PubMed2004

Coil-based artifact reduction.

Multiple MRI receiver coils provide extra information and can enable the reconstruction of multiple images using data from different combinations of coils. Comparison of these images shows that artifacts due to motion or flowing blood appear with different intensities due to the differing coil sensitivities. Typically, the artifact appears amplified in regions of low coil sensitivity. An optimization routine was developed to correct for the artifact by comparing reconstructions from various coil combinations and favoring a self-consistent solution. It is demonstrated that images artifacted by blood flowing in the aorta, or translational motion of the head, can be improved.

Algorithms↗

PubMed2004

Correction of high-order eddy current induced geometric distortion in diffusion-weighted echo-planar images.

Diffusion-weighted images acquired with the echo-planar imaging technique are highly sensitive to eddy current induced geometric distortions that vary with the magnitude and direction of the diffusion sensitizing gradients. Such distortions cause misalignment of images acquired with different diffusion strengths and orientations. This in turn can result in errors when calculating maps of the apparent diffusion coefficient and diffusion tensor. Previous correction methods either require separate calibration data or only deal with low-order errors. In this study, we demonstrate a method that can correct for higher-order errors. The method relies on collecting pairs of images with diffusion sensitizing gradients reversed. This paired data are first corrected for shifts and linear distortion and then combined to cancel higher-order errors. All acquired data contribute to the final results. The method has been tested by simulation, on phantoms, on adult volunteers, and on neonatal brain examinations.

Adult↗

PubMed2004

Increased lung water and tissue damage in bronchopulmonary dysplasia.

OBJECTIVES: To test the hypothesis that high and asymmetrical water content persists in infants with bronchopulmonary dysplasia (BPD) and that this is associated with nonuniform lung damage. STUDY DESIGN: Magnetic resonance imaging was used to assess lung water content in 20 infants and tissue injury in 35 infants of 23 to 33 weeks' gestational age (15 with severe BPD, 13 with mild BPD, and 7 without BPD). Relative proton density provided an index of water content and distribution. The location and extent of focal densities and cyst-like appearances indicating lung damage were defined. RESULTS: Proton density was significantly higher in dependent regions. Average proton density, proton density gradient, and severity of lung damage were greater in infants with severe BPD. Indicators of damage were greatest in dorsal lung regions. BPD was associated with a higher lung water burden and gravity-dependent atelectasis and/or alveolar flooding. Lesions were more common in dorsal lung regions in infants with severe lung damage. CONCLUSIONS: Infants with BPD have increased lung water and are susceptible to gravity-induced collapse and/or alveolar flooding in the dependent lung. Focal tissue damage appears to be distributed inhomogenously.

Bronchopulmonary Dysplasia↗

PubMed2003

Prior knowledge for time domain quantification of in vivo brain or liver 31P MR spectra.

Prior knowledge is required when quantifying in vivo (31)P magnetic resonance spectra from the brain or liver. The prior knowledge system we have used models both the phosphomonoester and phosphodiester resonances as two peaks of equal linewidth and fixed relative chemical shift. The analysis of the data is carried out in the time domain, which allows the broad component of the spectra to be modelled. This prior knowledge method has been tested for analysis of in vivo (31)P MR spectra from the liver and brain and gives results consistent with other methods that are also used to analyse the spectra, but with reduced variability. This technique may be utilized for studies requiring serial MR spectroscopy examinations, before and after patient treatment.

Algorithms↗

PubMed2003

The relationship of in vivo 31P MR spectroscopy to histology in chronic hepatitis C.

Liver biopsy remains the gold standard for characterizing diffuse liver disease and is associated with significant morbidity and, rarely, mortality. Our aim was to investigate whether a noninvasive technique, in vivo phosphorus 31 ((31)P)-magnetic resonance spectroscopy (MRS), could be used to assess the severity of hepatitis C virus (HCV)-related liver disease. Fifteen healthy controls and 48 patients with biopsy-proven HCV-related liver disease were studied prospectively. Based on their histologic fibrosis (F) and necroinflammatory (NI) scores, patients were divided into mild hepatitis (F or= 4/18), and cirrhosis (F = 6/6). Hepatic (31)P MR spectra were obtained using a 1.5-T spectroscopy system. Quantitation of the (31)P signals was performed in the time domain using the Advanced MAgnetic RESonance algorithm. There was a monotonic increase in the mean +/- 1 standard error phosphomonoester (PME) to phosphodiester (PDE) ratios for the control, mild disease, moderate disease, and cirrhosis groups: 0.15 +/- 0.01, 0.18 +/- 0.02, 0.25 +/- 0.02, 0.38 +/- 0.04, respectively (ANOVA, P <.001). An 80% sensitivity and specificity was achieved when using a PME/PDE ratio less than or equal to 0.2 to denote mild hepatitis and a corresponding ratio greater than or equal to 0.3 to denote cirrhosis. No other significant spectral changes were observed. In conclusion, (31)P MRS can separate mild from moderate disease and these 2 groups from cirrhosis. The ability to differentiate these populations of patients has therapeutic implications and (31)P MRS, in some situations, would not only complement a liver biopsy but could replace it and be of particular value in assessing disease progression.

Adult↗

PubMed2003

Diffusion-weighted imaging of the brain in preterm infants with focal and diffuse white matter abnormality.

OBJECTIVE: The most common finding on magnetic resonance imaging (MRI) of the brain in preterm infants at term-equivalent age is diffuse excessive high signal intensity (DEHSI) in the white matter. It is unclear whether DEHSI represents a biological abnormality. This study used diffusion-weighted imaging (DWI) to compare apparent diffusion coefficient (ADC) values in DEHSI with infants with normal imaging and those with overt brain damage to determine whether DEHSI shows the diffusion characteristics of normal or abnormal tissue. METHODS: MRI, using conventional and diffusion-weighted imaging (DWI), was performed in 50 preterm infants at term-equivalent age using a 1.5 Tesla MR scanner. The infants were divided into 3 groups on the basis of their MRI results: 1) normal white matter, 2) DEHSI, or 3) overt white matter pathology. ADC values were measured in the frontal, central, and posterior white matter at the level of the centrum semiovale. ADC values in the 3 groups of preterm infants were compared using a 1-way analysis of variance with a Bonferroni test for multiple comparisons. RESULTS: ADC values were significantly higher in infants with DEHSI and infants with overt white matter pathology than in infants with normal white matter. There was no significant difference between ADC values in infants with DEHSI and those with overt white matter pathology. CONCLUSIONS: This study provides objective evidence that DEHSI represents diffuse white matter abnormality.

Body Water↗

PubMed2003

T2 relaxation values in the developing preterm brain.

BACKGROUND AND PURPOSE: MR imaging is increasingly used to assess maturation and disease in the preterm brain. Knowledge of the changes in T2 values with increasing postmenstrual age (PMA) will aid image interpretation and help in the objective assessment of maturation and disease of the brain in infants. The aim of this study was to obtain T2 values in the preterm brain from 25 weeks' gestational age (GA) until term-equivalent age in infants who had normal neurodevelopmental findings at a minimum corrected age of 1 year. METHODS: The study group consisted of 18 preterm infants, born at 33 weeks' GA or sooner. The median GA of the infants at birth was 27 weeks (range, 23-33 weeks), and the median PMA at imaging was 31 weeks (range, 25-41 weeks). T2 measurements were obtained using a 1.0-T MR system and a four-echo pulse sequence (TR/TE, 2500/ 30, 60, 110, and 600). T2 values were measured in the thalami, lentiform nuclei, frontal white matter, occipital white matter, and central white matter at the level of the centrum semiovale. RESULTS: A significant negative linear correlation between T2 values and PMA was demonstrated in the lentiform nuclei (P =.003), frontal white matter (P <.0001), occipital white matter (P <.0001), and central white matter at the level of the centrum semiovale (P <.0001). T2 values were not significantly reduced with increasing PMA in the thalami (P =.06). CONCLUSION: T2 values decrease with increasing PMA in the preterm brain.

Birth Weight↗