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Biomedical subjects

G M Bydder

Publications and source records attributed to G M Bydder.

At least 19 recordsLinked to original sources
PubMed1999

Relationship between MR imaging and histopathologic findings of the brain in extremely sick preterm infants.

BACKGROUND AND PURPOSE: MR imaging can now be used safely in extremely preterm infants. The aim of this study was to compare the MR imaging appearance of the immature brain with neuropathologic findings at postmortem examination. METHODS: Seven extremely sick preterm infants, born at a median of 24 weeks' gestation, were studied using T1- and T2-weighted MR sequences. Infants died at a median of 3 days after initial MR imaging, and postmortem examinations were carried out. RESULTS: The cortex and germinal matrix were seen as areas of low signal intensity on T2-weighted images, which corresponded to their highly cellular histologic appearance. The periventricular and subcortical layers of white matter had a high signal intensity, corresponding to high fiber and relatively low cellular density; the intermediate layer of low signal intensity corresponded to a dense band of migrating cells. Regions of acute hemorrhage were seen as low signal intensity and regions of infarction as high signal intensity on T2-weighted images. One infant with mild periventricular leukomalacia had some low signal intensity on T1-weighted images, but no focal changes on T2-weighted images. Regions of neuronal mineralization, seen in association with infarction and capillary proliferation, within the basal ganglia and thalami were characterized by very low signal intensity on T2-weighted images and by very high signal intensity on T1-weighted images. There were no imaging abnormalities detected in regions with more subtle histologic abnormalities, such as increased glial or apoptotic cells. CONCLUSION: MR imaging can be used to observe normal developing brain anatomy in extremely premature infants; it can detect areas of hemorrhage and infarction within the developing brain, but conventional MR imaging may not detect more subtle histologic abnormalities.

Brain↗
PubMed1998

Cerebral swelling after normothermic cardiopulmonary bypass.

BACKGROUND: Marked cerebral swelling visible on magnetic resonance images has been found immediately after hypothermic (28 degrees C) cardiopulmonary bypass. The mechanism is unknown, but indices of cerebral ischemia are seen during rewarming from hypothermic bypass that are not present with normothermic bypass (37 degrees C). METHODS: T1-weighted and fluid-attenuated inversion recovery magnetic resonance images were taken of seven patients undergoing routine coronary artery bypass surgery before, 1 h, and 7 days after the operation using normothermic bypass. RESULTS: Marked cerebral swelling was seen in fluid-attenuated inversion recovery images in five of seven patients 1 h after bypass. Scans in four patients taken 7 days after bypass showed that the cerebral swelling had returned to normal. There was no change in cerebral ventricular size, and all patients had uncomplicated postoperative courses. CONCLUSIONS: Normothermic bypass is followed by acute postoperative cerebral swelling. However, the amount of swelling was similar to that found in a previous study after hypothermic bypass. The mechanism of swelling is still obscure, and its relation to neurologic outcome is unknown.

Aged↗
PubMed1997

Cerebellar infarction and atrophy in infants and children with a history of premature birth.

BACKGROUND AND OBJECTIVE: We wished to determine the pattern of cerebellar disease in children with a history of premature birth and early ultrasound evidence of intraventricular haemorrhage and/or parenchymal lesions of the cerebral hemispheres. MATERIALS AND METHODS: MRI findings for all premature infants examined in a 3-year period (73 patients) were reviewed to determine the nature and frequency of lesions of the cerebellum and the results were correlated with clinical data. RESULTS: Six cases of unilateral cerebellar infarction were identified. These involved the posterior inferior cerebellar territory in each case (as well as other territories in two cases). A case of generalised cerebellar atrophy and three cases of unilateral cerebellar hemisphere atrophy were identified as well. In nine of these ten cases abnormalities were also seen elsewhere in the brain. CONCLUSION: The literature describes cerebellar infarction in infants and children as rare, but this study shows that it is not unusual following perinatal haemorrhagic/ischaemic anoxic injury. It is suggested that cerebellar atrophy may also occur as a result of vascular disease.

Arteries↗
PubMed1997

Does the brain regenerate after perinatal infarction?

We have used registered serial magnetic resonance scans to assess the growth of the brain after perinatal infarction in six infants. The initial scans were performed at ages of 4 days to 8 weeks and follow-up studies were performed from 4 days to 21 weeks later. A three-dimensional volume acquisition was performed on each occasion. Rigid body translations and rotations were used to match the images obtained on each occasion. Subtraction of the first image from the second then provided an assessment of the growth of the brain that had occurred between the two examinations. In the early phase of infarction (up to 2 months) low signal areas with clearly defined margins developed at the site of infarction. In the late phase (2 months onwards) growth was seen in the brain at the margins of the infarct in each case, and the size of the infarcted region showed a marked decrease in size. The rate of growth of the brain into the infarcted area exceeded that of the surrounding brain in some cases and was less in others. Growth of undamaged tissue may provide an important mechanism for recovery of the developing brain.

Brain↗
PubMed1997

Detection of subtle changes in the brains of infants and children via subvoxel registration and subtraction of serial MR images.

PURPOSE: To compare conventional two-dimensional multisection images with registered three-dimensional volume and subtraction images for detecting subtle changes in the brains of infants and children. METHODS: Twenty-six patients (24 with hemorrhagic/ischemic lesions) and one each with perinatal infection and Sturge-Weber disease were examined on two or more occasions with conventional multisection T1- and T2-weighted sequences as well as with 3-D T1-weighted volume sequences. A registration program was used to match the volume images to subvoxel dimensions, and subtracted images (second volume set minus the first) were obtained. The multisection images were compared with the 3-D and subtracted images and graded for detection of changes in a variety of brain structures. RESULTS: In 16% to 33% of comparisons of different structures, the multisection images and the 3-D registered and subtracted images showed changes equally well. The 3-D registered and subtracted images were better than the multisection images in 67% to 84% of comparisons for detection of changes in the cerebral hemispheres, ventricles, brain stem, cerebellum, and in lesions. Statistically significant differences were found between the graded performance of the registered 3-D images and the conventional 2-D images in detecting cerebral infarction and hypoxic ischemic encephalopathy. In the late phase following neonatal cerebral infarction (1 to 11 months), the 3-D registered and subtracted images revealed growth of the brain at the margins of the lesions. CONCLUSION: Subvoxel registration of serial MR images may be of value in detecting subtle changes in the brains of infants and children.

Brain↗
PubMed1996

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↗
PubMed1996

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↗
PubMed1996

Assessment of brain changes with registered MR before and after bone marrow transplantation for chronic myeloid leukemia.

PURPOSE: To determine the frequency and nature of changes to the brain resulting from chemotherapy, radiation therapy, and bone marrow transplantation for chronic myeloid leukemia and to compare the sensitivity of conventional and registered MR scans for detecting these changes. METHODS: In 15 patients, conventional T1-weighted, T2-weighted, and fluid-attenuated inversion recovery MR sequences, as well as T1-weighted radio frequency spoiled 3-D volume MR scans were performed before, 4 to 6 days after, and up to 339 days after transplantation (13 allografts, two autografts). A subvoxel registration program was used to match the volume images precisely so that small changes could be detected after subtraction of scans. Five healthy adult control subjects were also studied on two occasions 1 month apart. RESULTS: Studies performed 4 to 339 days after transplantation showed ventricular enlargement and cortical atrophy in all 13 patients who had allografts. The changes were evident at 4 to 6 days after transplantation and became more obvious during later follow-up examinations. Similar changes were seen in one patient with an autograft but no significant change was seen in the other patient with an autograft or in the five control subjects. Accurately registered volume scans were more sensitive than unregistered conventional scans in detecting early (9/10 versus 0/10), intermediate (12/13 versus 3/12), and late (10/10 versus 4/9) ventricular enlargement on follow-up examinations. The same applied to cortical atrophy (9/10 versus 0/10, 12/13 versus 0/12, and 10/10 versus 0/9). CONCLUSION: The specific cause and clinical significance of these changes are uncertain. Subvoxel registration of serial MR images may reveal changes that are poorly seen or not apparent on conventional scans.

Adolescent↗
PubMed1995

Magnetic resonance imaging: spinal cord imaging with the turbo-fluid attenuated inversion recovery (FLAIR) pulse sequence.

Twelve patients with suspected or proven spinal cord disease were studied with a fluid attenuated repeated echo sequence employing a fast spin-echo data acquisition (Turbo-FLAIR) and the results were compared with those obtained with conventional T1- and T2-weighted spin-echo sequences. The Turbo-FLAIR sequence utilized an unselected 180 degrees pulse to reduce the signal from CSF followed by a spin-echo sequence based on the Rapid Acquisition with Relaxation Enhancement (RARE) pulse sequence for data acquisition. Three and four echo versions were used. Four low signal intensity lesions (cysts or syrinxes) were seen of which three were better seen with the Turbo-FLAIR sequence than with the other sequences. The remaining lesion was equally well seen. Of the seven high signal lesions found, six were better seen with the Turbo-FLAIR sequence and one was equally well seen. The Turbo-FLAIR sequence is more rapid than the T2-weighted spin-echo sequence and compares favourably with the combined results of both the T1- and T2-weighted spin-echo sequences for lesion conspicuity.

Cysts↗
PubMed1995

High resolution magnetic resonance imaging of the anal sphincter using an internal coil.

An internal receiver coil was used to obtain high resolution transverse and oblique coronal magnetic resonance images of the anal sphincter in five normal volunteers and five patients. The internal sphincter had a high signal intensity on T1 weighted, T2 weighted, and STIR sequences whereas the conjoined longitudinal muscle and external sphincter had a low signal intensity. The internal sphincter (but not the external sphincter) showed contrast enhancement after administration of intravenous gadopentetate dimeglumine. The oblique coronal plane was particularly useful for showing the thickness and the relations of the external sphincter. Sphincteric abscesses as well as muscle defects, hypertrophy, and atrophy were clearly shown. The coil was well tolerated by most subjects. It has considerable potential for improving the diagnosis of anorectal disease.

Adult↗
PubMed1995

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↗
PubMed1995

The Mackenzie Davidson Memorial Lecture: detection of small changes to the brain with serial magnetic resonance imaging.

The use of subvoxel registration of serial magnetic resonance images to detect small changes to the brain and its surrounding tissues and fluids is described and the application of this technique to physiological and clinical problems is illustrated. Isotropic T1 weighted volume images were obtained in normal subjects and patients on two or more occasions (including pre- and post-contrast enhancement). The images were segmented and three-dimensional rigid body translation and rotation were used with sinc interpolation to match precisely the images using a chi 2 test and a minimization routine. Accurately registered images produced in this way, as well as subtraction images derived from them, were used to detect change to the brain. A system of image interpretation based on recognition of changes in tissue or fluid signal intensity as well as site, shape and size is described. Changes in position are analysed using a simple model based on the concept of two plateaux of higher and lower signal intensities and a border zone between them. Small changes due to differences in orientation of the head, as well as inhalation of oxygen, carbon dioxide and carbogen were observed in normal subjects. Changes were also observed in patients with head trauma, an astrocytoma and multiple sclerosis. Differences due to contrast enhancement and treatment were seen. In addition, children showed changes due to growth and development.

Brain↗