Biomedical subjects
Publications and source records attributed to G M Bydder.
Fourteen patients with disease of the spinal cord were imaged with fluid-attenuated inversion-recovery (FLAIR) sequences in which the inversion time was chosen to substantially reduce or null the signal from CSF. Lesions were seen with greater conspicuity than with conventional contrast-enhanced and -unenhanced T1- and T2-weighted sequences in 11 cases.
Magnetic resonance (MR) imaging continues to develop at a rapid rate. Major new innovations include functional neuroimaging, fast spin-echo, magnetization transfer, the fluid attenuated inversion recovery sequence, MR angiography and measurement of cerebrospinal fluid (CSF) flow. Further developments of functional imaging and interventional techniques are expected.
Soluble and insoluble polysaccharides were derivatized with diethylenetriaminepentaacetic acid (DTPA) and/or spin-labeled with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO). Polysaccharides derivatized with DTPA were prepared via cyanogen bromide activation, coupling to a diamine linker, and to DTPA anhydride. Spin-labeled polysaccharides were also prepared via cyanogen bromide activation. The extent of derivatization for dextran (18 kDa) was about 120 glucose units per DTPA, and for cellulose and starch about 15-30 units per DTPA. For spin-labeled polysaccharides, the average loading ranged from 1 nitroxide per 16 glucose units for starch to 181 for dextran (82 kDa). These derivatized paramagnetic polysaccharides were shown to be more effective relaxants than the small paramagnetic molecules alone. Both soluble and insoluble polysaccharide-linker-DTPA-Gd(III) complexes were effectively cleared from the body (rats) after oral administration. After intravenous administration, the biodistribution of dextran-linker-DTPA-Gd(III) complexes differed significantly from that of GdDTPA. Reduction of the nitroxide by ascorbic acid was retarded in the polysaccharide derivatives, particularly in starch derivatized with both nitroxide and linker-DTPA-Cu(II). These agents showed contrast enhancement in the gastrointestinal tract of rabbits.
Although parenteral contrast agents are now widely used in the central nervous system, progress in the development of applications in the remainder of the body has been slow. Both intravenous Gd-DTPA and magnetic iron oxide particles have many potential applications but the former will probably require faster imaging techniques and the latter will require reformulation to produce a less toxic preparation. In spite of these problems methods have been developed for the diagnosis of myocardial infarction, breast carcinoma, and musculoskeletal tumors. Interesting preliminary results are available for other applications of contrast agents in the body and many of these are likely to become routine over the next 5 years.
The use of magnetic resonance imaging to detect normal and pathological problems of perfusion and diffusion is reviewed. Motion sensitised spin-echo images can be used to detect changes in slow flow velocity within a voxel (intravoxel coherent motion (IVCM)) as well as intravoxel incoherent motion (IVIM) effects attributable to both diffusion and perfusion. Changes have been identified in a variety of brain diseases in the absence of changes in conventional images but the techniques are very vulnerable to motion artefact of all types. More rapid and more sensitive approaches using steady state free precision and echo-planer imaging are being investigated. Anisotropic diffusion imaging enables white matter tracts to be demonstrated within the brain and spinal cord as a function of their direction because diffusion of water across axons is much more restricted than it is along them. This technique provides a unique method for localisation of lesions and displays obvious changes in disease in which diffusion becomes less restricted.
Two types of contrast media are now used in clinical magnetic resonance imaging (MRI). Intravenous gadolinium-DTPA serves as a marker of blood-brain barrier disruption while intravenous magnetic iron oxide particles are of value in imaging the liver and spleen. The efficacy of MRI is improved with these agents but the examination is prolonged.
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This communication describes the use of a binomial pulse sequence designed from solvent suppression in proton spectroscopy to convert the small frequency changes associated with field variations into significant amplitude changes in magnetic resonance images. This technique can be used to demonstrate tissue susceptibility change.
The measurement of the velocity of perfused flow in tissue in vivo is complicated by the presence of stationary as well as moving spins and by a variety of dephasing phenomena which affect signal amplitudes. This paper describes a technique by which, using flow-sensitized spin-echo sequences with a set of very long TE times, the velocity of the moving component can be assessed.
Attempts at saturation by nonselective rf pulses, followed by gradient spoiler pulses, are sometimes used as the basis of a method of measuring T1 in magnetic resonance imaging, because a method of this type is perceived as being less affected by slice shape artifact than partial saturation methods. This note suggests that, unless care is taken, this assumption can be quite erroneous.
Artifacts due to localized susceptibility effects, variations in the spin-lattice relaxation time constants of signals and a mixing of signals arising from tissue motions can contaminate otherwise credible results. The sources and magnitude of some of these are discussed and their likely impact assessed, so that the necessity of incorporating additional measurements in an individual study can be demonstrated.
A prospective magnetic resonance imaging (MRI) study was carried out in 13 patients (19 examinations) with primary bone tumours to assess the relative value of each of four pulse sequences in showing the extent and nature of the lesion. The four pulse sequences used were a T1-weighted spin-echo (SE544/44), a T2-weighted spin echo (SE1500/80), a short TI inversion recovery (STIR) (IR500/100/44), and a partial saturation (PS) (PS500/22) with field echo data collection. For soft tissue disease the combination of PS and STIR gave better definition of the boundary of the tumour than the more conventional T1 and T2-weighted spin echo sequences. For the demonstration of bone cortex, periosteal change and calcification, T1 and T2-weighted spin echo sequences were better. However, for calcified tissues, plain radiographs were better than either MRI combination. On the assumption that plain films will be available in all cases, PS and STIR sequences could therefore be substituted for T1 and T2-weighted spin echo sequences allowing an increase in soft tissue detectability for lesions in both red and yellow marrow.
Cranial ultrasound (US) was used in 14 neonates to define three categories of extensive cystic leucomalacia, namely periventricular, mixed, and subcortical. The initial US findings were compared with serial magnetic resonance imaging (MRI) and the neurodevelopmental outcome of the children. In the infants with periventricular leucomalacia, MRI showed a decrease in the size of the cystic areas with age. Six of these seven children showed an increase in the level of myelination upon follow-up examination, although white matter development was slower in the vicinity of the cysts. The lateral ventricles of these children were slightly enlarged and the occipital horns showed an irregular angular outline. In the infants with mixed leucomalacia, MRI showed cystic areas which remained obvious at the final examination. Myelination was grossly delayed in these patients. The lateral ventricles were enlarged and remained unchanged, with the exception of one infant whose ventricles collapsed after shunt revision. In the three children with subcortical leucomalacia, MRI confirmed shrinkage of the cysts in two of the three infants upon the first follow-up examination but thereafter the cysts remained unchanged. No supratentorial myelination was demonstrated in these patients. The ventricles were enlarged and the cortical sulci were prominent in all these infants. A strong correlation was shown between the MRI appearances and the clinical outcome in these children. MRI may be most useful for making the diagnosis of cystic leucomalacia in children not submitted to US examination as neonates or in whom only some of the classical US features have been identified.
A range of cerebral structures was assessed in a series of 172 CT scans of groups of psychiatric patients (including 101 in-patients with chronic schizophrenia) and related to assessments of clinical state and psychological function. Ventricular indices were increased in patients with schizophrenia by comparison with patients with other psychiatric disorders: brain area, which is modestly positively correlated with ventricular indices, was significantly (P less than 0.01) reduced in patients with schizophrenia. Among in-patients with chronic schizophrenia, measures of increased ventricular size were significantly associated with impaired social behaviour and with movement disorder. Memory for famous names in the distant past (a test of remote memory) was the only psychological test which showed significant associations with indices of ventricular size; this suggests that ventricular enlargement and its psychological sequelae occur relatively early in the disease process. Dichotomization of the sample of schizophrenic patients around the mean age of onset revealed that a range of clinical and psychological functions are significantly more abnormal in those with an early age of onset than in those in whom the onset was later. Early onset cases also perform less well academically and occupationally before illness onset. Within the early onset group some significant correlations between cognitive function and brain area were seen. The findings suggest that: (i) some at least of the structural changes in schizophrenia arise at a time when the brain is still developing; and (ii) age of onset is an important determinant of social and intellectual impairment and is relevant to the relationship between brain structure and cognitive deficits.
Some features of the design and implementation of NMR probes for insertion into peripheral orifices of the body are described. In particular, the possibilities of using parasitic coils without direct connections in conjunction with conventional whole body coils are examined. The use of windings around the NMR probe carrying gradient pulses as a means of eliminating the very high signals from tissue immediately adjacent to the coil windings is also evaluated. These approaches are, in practice, difficult to combine, and hence need to be viewed almost as alternative possibilities. Practical results of experimental investigations are presented using both phantoms and volunteers.
This communication describes the design and application of a receiver coil operating at liquid nitrogen temperature and intended as a surface coil in a whole-body imager. Its particular application is seen as the external receiver for parasitic internal or implanted detectors.
The use of a phase mapping technique for detection of brain perfusion is described. The method was used in a patient with epilepsia partialis continua and displayed an area of abnormal perfusion in the frontal lobe during the ictal phase. Following improved treatment the perfusion pattern was near normal 12 weeks later.