Posterior leucoencephalopathy syndrome.
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Adult↗
Biomedical subjects
A Oatridge
Publications and source records attributed to A Oatridge.
Effect of profound ischaemia on human muscle: MRI, phosphorus MRS and near-infrared studies.
A pressure cuff was applied to the legs of two human volunteers in order to stop any blood supply for a period of about 30 min. The affected muscle was monitored using proton magnetic resonance imaging (MRI), phosphorus magnetic resonance spectroscopy (MRS) and near infrared (NIR) spectroscopy before, during and after this procedure. The internal temperature of the tissue was also measured. The phase of water protons in muscle showed changes that were not accounted for by the measured temperature, but which correlated with the large increase in deoxyhaemoglobin and deoxymyoglobin observed with NIR as well as the decrease in PCr and increase in Pi observed with MRS. Little or no change was found in proton density or T2*. These results show that in vivo measurements of temperature using the chemical shift method may be confounded by changes in tissue oxygenation. They also show that T2* is an insensitive measure of changes in tissue oxygenation.
Constriction↗
An evaluation of the effects of susceptibility changes on the water chemical shift method of temperature measurement in human peripheral muscle.
Divergencies between chemical shift measurements of temperature and directly measured values using optical sensors have been studied in vivo in human peripheral muscle with the assistance of a variety of experimental and theoretical techniques. These include the modelling of both thermal and susceptibility changes using two- and three-dimensional finite element methods, as well as the use of multi-wavelength near-infrared observations. The conclusion of these studies is that a simple temperature calibration is not accessible, with results affected by the complex response of the tissue itself.
Humans↗
MR imaging and spectroscopy of the basal ganglia in chronic liver disease: correlation of T1-weighted contrast measurements with abnormalities in proton and phosphorus-31 MR spectra.
The purpose of this study was to correlate the hyperintensity in the globus pallidus seen on T1-weighted magnetic resonance imaging (MRI) of the brain in chronic liver disease with changes in metabolite ratios measured from both proton and phosphorus-31 magnetic resonance spectroscopy (MRS) localised to the basal ganglia. T1-weighted spin echo (T1WSE) images were obtained in 21 patients with biopsy-proven cirrhosis (nine Child's grade A, eight Child's grade B and four Child's grade C). Four subjects showed no evidence of neuropsychiatric impairment on clinical, psychometric and electrophysiological testing, four showed evidence of subclinical hepatic encephalopathy and 13 had overt hepatic encephalopathy. Signal intensities of the globus pallidus and adjacent brain parenchyma were measured and contrast calculated, which correlated with the severity of the underlying liver disease, when graded according to the Pugh's score (p < 0.05). Proton MRS of the basal ganglia was performed in 12 patients and 14 healthy volunteers. Peak area ratios of choline (Cho), glutamine and glutamate (Glx) and N-acetylaspartate relative to creatine (Cr) were measured. Significant reductions in mean Cho/Cr and elevations in mean Glx/Cr ratios were observed in the patient population. Phosphorus-31 MRS of the basal ganglia was performed in the remaining nine patients and in 15 healthy volunteers. Peak area ratios of phosphomonoesters (PME), inorganic phosphate, phosphodiesters (PDE) and phosphocreatine relative to beta ATP (ATP) were then measured. Mean values of PME/ATP and PDE/ATP were significantly lower in the patient population. No correlation was found between the T1WSE MRI contrast measurements of the globus pallidus and the abnormalities in the metabolite ratios measured from either proton or phosphorus-31 MR spectra. Our results suggest that pallidal hyperintensity seen on T1WSE MR imaging of patients with chronic liver disease is not related to the functional abnormalities of the brain observed in hepatic encephalopathy.
Adult↗
Use of subvoxel registration and subtraction to improve demonstration of contrast enhancement in MRI of the brain.
To assess the potential of registration of images before and after contrast medium for improving the demonstration of contrast enhancement, we compared conventional 2D T1-weighted spin-echo images with precisely registered 3D volume images and subtraction images derived from them in 2 normal subjects and 30 patients with a variety of brain disease. The volume images were registered to subvoxel accuracy using a rigid body translation and rotation, sinc interpolation and a least-squares fit; subtraction images were obtained from these. Normal contrast enhancement was demonstrated better with positionally registered volume and subtraction images than with conventional images in the meninges, ependyma, diploic veins, scalp, skin, orbit and sinuses. Abnormal enhancement was seen better in meningeal disease, multiple sclerosis and tumours as well as on follow-up studies. Subvoxel registration of images before and after contrast medium may be of considerable value in the recognition of contrast enhancement where there are small changes, or where the changes affect tissues with high or low baseline signal values. The technique also appears likely to be of value in demonstrating contrast enhancement in tissues at interfaces and at other areas of complex anatomy, and in follow-up studies.
Brain↗
MR imaging of the basal ganglia in chronic liver disease: correlation of T1-weighted and magnetisation transfer contrast measurements with liver dysfunction and neuropsychiatric status.
Conventional T1-weighted spin echo (T1WSE) and T1-weighted magnetization transfer (MT) images were obtained in 26 patients with biopsy-proven cirrhosis (nine Child's grade A, 10 Child's grade B and seven Child's grade C). Four subjects showed no evidence of neuropsychiatric impairment on clinical, psychometric and electrophysiological testing, seven showed evidence of subclinical hepatic encephalopathy and 15 were classified as having overt hepatic encephalopathy. Signal intensities of basal ganglia nuclei (head of caudate, putamen, globus pallidus and thalamus) and adjacent brain parenchyma were measured and contrast calculated. On T1WSE imaging, contrast measurements of the globus pallidus were significantly greater in patients with neuropsychiatric dysfunction than in those who were unimpaired (p < 0.05). This was not observed in the other basal ganglia nuclei. Patients with subclinical and overt hepatic encephalopathy could not be distinguished on the basis of contrast measurements of the globus pallidus or of any other nucleus. T1WSE contrast measurements of the globus pallidus were increased with elevations in blood ammonia levels (p < 0.05) and with the severity of liver dysfunction, when graded according to the Pugh's score (p < 0.05) Those patients with the worst liver injury (Child's grade C) had significantly greater T1WSE pallidal contrast measurements (p < 0.05) than those patients with minimal liver injury (Child's grade A). The patients with intermediate liver damage (Child's grade B) could not be distinguished from the other two groups. While MT imaging highlighted the basal ganglia and showed a correlation between globus pallidus contrast and blood ammonia levels (p < 0.05), no other relationship between MT contrast measurements and either the degree of hepatic encephalopathy or the severity of liver dysfunction was found.
Adult↗
Post partum magnetic resonance imaging: lumbar tissue changes are unrelated to epidural analgesia or mode of delivery.
Thirty five women consented post partum to daily lumbar back pain assessments and magnetic resonance imaging (MRI) (0.15 Tesla) within 48 hours of delivery using a T(1) weighted spin echo and a fat suppression sequence (STIR) to identify tissue water. Nine women (26%) had lumbar disc abnormalities on MRI scan. Variable degrees of soft tissue changes in the lumbar region were observed using the STIR sequence in all patients after delivery. Eight women (23%) had mild, 15 (43%) moderate, and 12 (34%) severe changes with an average of 5 segments involved. These changes were reversible and related neither to the mode of delivery, nor to the trauma of epidural cannulation.
Journal Article↗
Magnetic resonance imaging in partial epilepsy: additional abnormalities shown with the fluid attenuated inversion recovery (FLAIR) pulse sequence.
Thirty six patients with a history of partial epilepsy had MRI of the brain performed with conventional T1 and T2 weighted pulse sequences as well as the fluid attenuated inversion recovery (FLAIR) sequence. Abnormalities were found in 20 cases (56%), in whom there were 25 lesions or groups of lesions. Twenty four of these lesions were more conspicuous with the FLAIR sequence than with any of the conventional sequences. In 11 of these 20 cases, lesions thought to be of aetiological importance were only seen with the FLAIR sequence. In eight this was a solitary lesion. In the other three, an additional and apparently significant lesion (or lesions) was only seen with the FLAIR sequence when another lesion had been identified with both conventional and FLAIR sequences. The 11 additional lesions or groups of lesions were seen in the hippocampus, amygdala, cortex, or subcortical and periventricular regions. No lesion was found with any pulse sequence in 16 (44%) of the original group of 36 patients. In the eight cases where a lesion was seen only with the FLAIR sequence, localisation was concordant with the electroclinical features. Two of the eight patients with solitary lesions seen only on the FLAIR sequence underwent surgery, after which there was pathological confirmation of the abnormality identified with imaging. In one patient with a congenital cavernoma, the primary lesion was best seen with a contrast enhanced T1 weighted spin echo sequence. In this selected series, the FLAIR sequence increased the yield of MRI examinations of the brain by 30%.
Adolescent↗
Artifacts due to stimulus correlated motion in functional imaging of the brain.
To assess the effect of stimulus correlated motion on the appearance of functional magnetic resonance images, conventional visual and motor protocols were each performed by four normal volunteers and an image co-registration technique was used to retrospectively monitor subject motion. In three studies synthetic data sets were constructed from single baseline images using the positional information obtained from the co-registration procedure. Cumulative difference images were then created from both the synthetic and functional image sets. Stimulus correlated motion was detected in all eight studies and the synthetic cumulative difference images showed striking similarities to the equivalent functional images in each case.
Adult↗
Further observations on the measurement of tissue T1 to monitor temperature in vivo by MRI.
Previous results for the measurement of T1 as a means of monitoring temperature have demonstrated a linear calibration with a coefficient of the order of 1.5%/degrees C. We have studied the changes in T1 further, and observe that changes in tissue perfusion are substantial contributors to the effects observed, and that the model of what is happening is complex and may not permit a simple temperature calibration.
Body Temperature↗
Modeling and observation of temperature changes in vivo using MRI.
Models have been developed for the signal changes occurring in human peripheral muscle after thermal stress for some methods of measuring temperature in vivo. These include the dependency of T1 on temperature, observed by both direct, and magnetization transfer, experiments, and the temperature sensitivity of the diffusion coefficient and the chemical shift of the water proton line. Results show the relative complexity of the T1-dependent models when there are significant variations in, possibly amongst other things, tissue perfusion, and how the predictions made using them match the behavior of the practical values quite well. Using changes in the diffusion coefficient appears less problematic, although there can still be significant errors in temperature calibrations. The problems with this approach are likely to be due to the consequences of anisotropy in tissue.
Adipose Tissue↗
Brain swelling in first hour after coronary artery bypass surgery.
Six patients undergoing routine coronary artery bypass surgery were examined by magnetic resonance imaging of the brain before surgery, immediately afterwards, and 6-18 days later. Brain swelling was visible in all six patients on the immediate postoperative scan. In five patients who had later scans the swelling had subsided. No major neurological deficits were seen, and the patients were extubated successfully within 3 h of the operation. The mechanism of the cerebral swelling is uncertain, but it may provide insight into the cause of neurophysiological deficits seen after coronary artery surgery.
Aged↗
Imaging of human brain activity at 0.15 T using fluid attenuated inversion recovery (FLAIR) pulse sequences.
A 3-4% change in signal intensity correlated with visual stimulation was observed in the occipital lobes of three normal volunteers examined with MRI at 0.15 T using fluid attenuated inversion recovery pulse sequences. Similar results were observed at 1.0 T. A double difference technique in which difference images are themselves opposed provided an increase in sensitivity.
Brain↗
MRI diffusion-weighted imaging of the brain: contributions to image contrast from CSF signal reduction, use of a long echo time and diffusion effects.
The contributions of CSF signal reduction, use of a long echo time and diffusion weighting to the appearance of pulsed gradient spin echo (PGSE) images are analysed by reference to T2-weighted spin echo and T2-weighted fluid attenuated inversion recovery (FLAIR) pulse sequences. Both PGSE and T2-weighted FLAIR sequences reduce CSF signal and produce very heavy T2 weighting allowing the specific additional contribution produced by the diffusion weighting of PGSE sequences to be recognized. Considerable advantage accrues from CSF suppression with both PGSE and FLAIR sequences through reduction in partial volume effects and artefacts. The very heavy T2 weighting with both these pulse sequences highlights certain white matter tracts and provides high sensitivity to disease. The additional diffusion weighting with PGSE sequences can enhance or reduce white matter tract signals and may enhance or reduce lesion conspicuity relative to the FLAIR sequences. Many of the benefits attributed to the diffusion-weighted PGSE sequence may result from the reduction of the CSF signal and the heavy T2 weighting of the sequence without a contribution from diffusion effects. However, additional anatomical detail, sensitivity to myelination and increased lesion conspicuity may result from the diffusion weighting.
Brain↗
Regions of interest tracking in temporal scans based on statistical analysis of gray scale and edge properties and registration of images.
Precise measurement of T1 is needed for its use in temperature monitoring in vivo. Movement of tissue relative to fixed regions of interest can result in large variations in apparent T1, with consequent substantial errors in the measured temperature. This paper evaluates methods of tracking regions of interest as tissue moves during a study in an effort to minimize errors from this cause. Tracking techniques evaluated are based on maintaining constant gray scale levels, locating nearby edges and maintaining position relative to them, and global image registration.
Algorithms↗
MR imaging of anisotropically restricted diffusion of water in the nervous system: technical, anatomic, and pathologic considerations.
The use of MR imaging to image anisotropically restricted diffusion (ARD) of water in the nervous system is described. The theoretical basis for the use of the pulsed gradient spin echo sequences is outlined, including an estimate of the range of cell dimensions that can be studied with this technique. The importance of restricted diffusion across myelinated white matter fibre tracts is emphasised and the capacity of MR imaging to demonstrate fibre pathways as a function of their direction is illustrated. Technical developments that have been implemented include 256 x 256 spatial resolution, a wider range of diffusion times Td, and an increased range of diffusion sensitivity parameters b. Effects of these are illustrated together with the use of gradient moment nulling methods, oblique sensitisation, and a smaller set of gradient coils that enable shorter values of echo time to be used with the same value of b. The anatomical basis for ARD imaging is analysed, and association, commissural, and projection fibre tracts are demonstrated in different planes. The published literature on variations of the apparent diffusion coefficient from normal is reviewed and examples where diffusion weighted images revealed information that was not necessarily apparent with conventional sequences are illustrated. These include cases of multiple sclerosis, chronic head injury, progressive multifocal leucoencephalopathy, cerebrovascular disease, astrocytoma, and probable metastases to the brain. Imaging of ARD affords a fascinating conjunction between the microscopic movement of water, the properties of myelinated white matter fibres, gross anatomy of the brain, and changes of the diffusion of water in disease.
Adult↗
Design and implementation of magnetization transfer pulse sequences for clinical use.
The transfer of magnetization between a free and a bound pool of spins is described in terms of the respective longitudinal relaxation times and the life times of spins in each pool. The effect of an off resonance radiofrequency (RF) pulse in producing saturation in the bound pool and a consequent decrease in both the available longitudinal magnetization and the T1 of spins in the free pool is described. The effects of increasing duration of the saturating RF pulse on image pixel signal intensity were used to determine values for the decrease in both T1 and the available magnetization in gray and white matter of the brain as well as in muscle, fat, and CSF. At 0.15 T the available magnetization of muscle was reduced by approximately 60% and its T1 was decreased from 350 to 150 ms. The available magnetization of white and gray matter was reduced by 40% and their values of T1 were reduced by 80-110 ms. The reduction in available magnetization was used to increase contrast on proton density weighted or T2-weighted SE pulse sequences. These changes were also used to design inversion recovery (IR) pulse sequences with particular contrast properties. A short inversion time (TI) magnetization transfer (MT) IR (MT-STIR) pulse sequence was used to reduce the signal from normal muscle to zero to produce an angiographic effect in the leg. Increased tissue contrast was observed with a T2-weighted (MT-SE) sequence in a patient with bilateral cerebral infarction and with an MT-IR pulse sequence in a patient who had an intracranial hematoma. Three patients with cerebral tumors showed high lesion contrast with MT-STIR sequences. Components within two tumors were changed to different degrees by MT and in one case change in the brain attributable to recent radiotherapy treatment was only identified with an MT-STIR sequence. Magnetization transfer can be used to manipulate both the available longitudinal magnetization and the T1 of normal and abnormal tissues. The changes in tissue contrast produced by this can be very substantial and are likely to be of importance in clinical imaging.
Adult↗
Use of fluid attenuated inversion recovery (FLAIR) pulse sequences in MRI of the brain.
Fluid attenuated inversion recovery pulse sequences with a long echo time (TE) have been used to image the brain in one volunteer and four patients. The long inversion time used with this sequence suppresses the signal from CSF and the long TE produces very heavy T2 weighting. The marked reduction in flow artefact from CSF and the high T2 weighting enabled anatomical detail to be seen within the brain stem and produced high lesion contrast in areas close to CSF. Lesions were demonstrated with greater conspicuity than with conventional T2-weighted sequences in patients with cerebral infarction, low grade astrocytoma, and diplegia.
Adolescent↗