PubMed · 11976537
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J-M Bonnetblanc. 2002. [Cutaneous hydration].. https://pubmed.ncbi.nlm.nih.gov/11976537/
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Water diffusion within the brain is studied numerically for various clinical conditions. The numerical procedure used in this work is based on the Galerkin weighted residual method of finite-element formulation. A wide range of pertinent parameters such as Lewis number, cell volume, and the buoyancy ratio are considered in the present study. Comparisons with previously published work show excellent agreement. The results show that the diffusion coefficient, cell volume, and the buoyancy ratio play significant roles on the characterization of the mass and heat transfer mechanisms within the cell. Concentration maps are developed for various clinical conditions. Pertinent results for the streamlines, isotherms and the mass and heat transfer rates in terms of the average Sherwood and Nusselt numbers are presented and discussed for different parametric values. Experimental tests are also conducted to produce an 8 Tesla image which is compared with our numerical simulation. The present study provides essential maps for brain disorders classified based on several pertinent clinical attributes.
Diabetes insipidus is a heterogeneous condition characterized by polyuria and polydipsia caused by a lack of secretion of vasopressin, its physiological suppression following excessive water intake, or kidney resistance to its action. In many patients, it is caused by the destruction or degeneration of the neurons that originate in the supraoptic and paraventricular nuclei of the hypothalamus. Known causes of these lesions include: germinoma or craniopharyngioma; Langerhans cell histiocytosis and sarcoidosis of the central nervous system; local inflammatory, autoimmune or vascular diseases; trauma following surgery or accident; and, rarely, genetic defects in vasopressin biosynthesis inherited as autosomal dominant or X-linked recessive traits. Thirty to fifty percent of cases are considered idiopathic. Magnetic resonance imaging (MRI) allows identification of the posterior pituitary hyperintensity and of hypothalamic-pituitary abnormalities. Thickening of the pituitary stalk is the second most common finding on MRI scans in several local inflammatory pathologies and autoimmune diseases or germinoma, but it is not specific to any single subtype. A progressive increase in the size of the anterior pituitary gland should alert physicians to the possibility that a germinoma is present, whereas a decrease can suggest the presence of an inflammatory or autoimmune process. Most children with acquired central diabetes insipidus and a thickened pituitary stalk have anterior pituitary hormone deficiencies during follow-up. Biopsy of enlarged pituitary stalk should be reserved for patients with a hypothalamic-pituitary mass and progressive thickening of the pituitary stalk, since spontaneous recovery may occur.
A high-resolution spin-echo imaging method is presented (called CP-LASER) which exploits the spin refocusing capability of an adiabatic Carr-Purcell (CP) pulse sequence to measure apparent 1H2O transverse relaxation (T2+) and generate contrast based on microscopic tissue susceptibility. High-resolution CP-LASER images of the human occipital lobe were acquired at four different echo times from six subjects at 4T and eight subjects at 7T to investigate the effect of magnetic field strength (B(0)) and the CP interpulse time (tau(cp)) on T2+. Susceptibility contrast was identified and T2+ was quantified for long tau(cp) (>10 ms) and short tau(cp) (7 ms at 4T and 6 ms at 7T) in gray matter, white matter, and cerebral spinal fluid. The 1H2O relaxation rate constants (1/T2+) of gray and white matter each increased approximately linearly with field strength and T2+ was inversely related to tau(cp). The average T2+ value of gray matter was 19% and 9% smaller than that of white matter at 4T and 7T, respectively. These results are consistent with higher levels of compartmentalized ferritin and increased blood volume in gray matter compared to white matter in this region of the brain.