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✓ To better understand the role of myelin-associated water in the differentiation of white and gray matter in magnetic resonance (MR) imaging, changes in MR relaxation processes were studied in rabbits during myelination and after induction of cytotoxic edema with triethyltin (TET). Normal rabbits were killed at various age intervals ranging from premature (28 days' gestation) to adult, and changes in MR relaxation times (T1 and T2) and in water and electrolyte content were determined for various areas of brain and muscle. Similar measurements were made in rabbits of comparable age exposed to TET. Light and electron microscopy and MR imaging were used to follow myelin development and morphological changes induced by TET. During the first 30 postnatal days, both T1 and T2 declined by 50% in normal rabbits, a fall that paralleled the loss in brain water and sodium that occurred during the same period. Exposure to TET prolonged T1 and T2 in white but not gray matter, reflecting the accumulation of sodium and water (edema fluid) in white matter areas. Multiexponential analysis revealed a second, longer component in T2 magnetization decay of TET-exposed white matter, presumably attributable to accumulation of non-ordered water within intramyelinic vacuoles, a supposition consistent with electron microscopic and MR imaging findings. In contrast to reports by others, changes in T1 (but not T2) closely correlated with alterations in brain water (r = 0.93, df = 39). The absence of tissue disruption in the animals in the present study may account for these differences, but further studies will be required both to resolve this question and to fully understand MR images of white matter edema in mature and immature brain.

Experiments were performed to investigate the feasibility of combining laser heating of tissues while controlling the temperature changes by magnetic resonance imaging (MRI). A great potential exists for applications in cancer treatment and in scientific research.

A retrospective analysis of clinical imaging using 2DFT SSFP at 0.14 T is presented. The technique's potential for tissue characterization and its utility for clinical diagnosis were tested by both in vitro measurements of various tissues and in vivo clinical images. Different pulse angles not only influenced image contrast, but also helped characterize lesions, particularly those containing fat. In addition, the pulse angle changed the signal from venous flow perpendicular to the imaged slice. The slow flow sensitivity of the 2DFT SSFP technique was demonstrated in the detection of CSF motion. Rapid SSFP offers flow sensitivity and adequate lesion detecting ability, along with high patient throughput.

Flow void due to pulsatile motion of cerebrospinal fluid (CSF) has recently been demonstrated by a variety of magnetic resonance techniques with sensitivity to slow flow. It has been suggested that within fluid collections not communicating with the physiologic CSF space, there is less signal loss than with the physiologic CSF spaces. Utilizing the SSFP MR technique, which is sensitive to flow as slow as 1 mm/sec, we evaluated three patients with isolated arachnoid cysts. Irregular signal loss consistent with fluid motion was noted within all of the cysts, as well as within the physiologic CSF spaces. Definitive anatomic evaluation of these lesions, though, required ventriculography, an invasive technique.

The magnetic resonance (MR) relaxation rates of protons were compared in the myelinated and nonmyelinated nerves of the garfish. The long, large olfactory nerve of the garfish, as an easily accessible source of nonmyelinated axons, is uniquely suited for such a comparison. The T1 and T2 measurements revealed distinct and consistent differences between nonmyelinated olfactory nerves and myelinated optic and oculomotor nerves. Comparisons between water content, lipid content, and relaxation rates indicated that the differences in MR properties represent complex differences in the distribution and physical environment of the constituent lipid and water protons.

Dural venous sinus thrombosis is an important complication of L-asparaginase chemotherapy. The diagnosis and followup of this condition, using spin echo and fast imaging techniques, is described in three patients. Magnetic Resonance (MR) imaging is a rapid, noninvasive technique for diagnosis and follow-up of this condition. Fast imaging techniques can improve the assessment of these patients.

Computed tomographic (CT) myelography, when used with metrizamide, permits a reliable demonstration of syringohydromyelic cavities in the cervical spinal cord. We report 6 cases of cervical syrinx demonstrated by high-resolution CT 4 h after metrizamide myelography; these cavities, which were not suspected clinically, extended into the thoracic cord. In addition 4 cases were associated with Chiari Type 1 malformation and 1 case was associated with both Chiari Type 1 malformation and infratentorial arachnoid cyst. We recommend that CT evaluation of cervical syringohydromyelia routinely include the thoracic spine, in order to demonstrate possible thoracic extension of the cavity. Scans of the foramen magnum are also recommended, because of the possibility of concomitant lesions, especially Chiari Type 1 malformation.

The relationships between the T1 and T2 relaxation times, tissue water content and extracellular fluid space of two types of skeletal muscle groups were studied in rabbits and rats by means of NMR proton spectroscopy (10 MHz). Although there was no significant difference in the total water content between muscles rich in type I (74.5 +/- .8%; soleus) or type II (75.0 +/- .7%; gastrocnemius) fibers, the respective T1 (521 +/- 25 vs. 486 +/- 16 millisecond; p less than .01) and T2 (39.5 +/- 1.8 vs. 36.5 +/- 1.0 millisecond; p less than .01) relaxation times were consistently prolonged. The longer relaxation times of the soleus as compared with the gastrocnemius muscle were related to a larger extracellular fluid space as measured by (35S) sulfate +34.5%; p less than .01). For this reason, it seems likely selective changes in these spaces will be detectable by NMR proton imaging.

The changes seen in the T1 and T2 relaxation times, water content and size of the extracellular fluid spaces of rat muscle samples following 15 days of denervation were studied by in vitro proton NMR spectrometry (10 MHz). Two different skeletal muscle groups (gastrocnemius and soleus) were studied. Denervation led to longer T1 values: 548 +/- 61 msec vs. 486 +/- 16 msec (P less than .05) for the gastrocnemius and 581 +/- 27 msec vs. 521 +/- 25 msec (P less than .05) for the soleus. Similar increases in T2 were measured. The sizes of the extracellular fluid spaces of denervated muscle were significantly larger despite a minor increase in total water content. Overall, the relaxation times of skeletal muscle correlated better with the size of the extracellular fluid space than with the total water content.

The role of myelin in determining the magnetic resonance (MR) characterization of the central nervous system (CNS) was investigated in unmyelinated brains of normal fetal mice, as well as myelin-deficient adult mutant mice ( shi, qk, mld ) and their age-matched controls. In vitro NMR relaxation time measurements at 10 MHz for whole brains showed consistently longer T 1 (range 558 ± 8 to 580 ± 27 msec) and T 2 (range 81 ± 3 to 89 ± 3 msec) values for the adult myelin-deficient animals than the age-matched controls ( T 1 = 496 ± 31, T 2 = 79 ± 4 msec). The fetal brains exhibited even more prolonged relaxation times ( T 1 = 976 ± 60, T 2 = 158 ± 7 msec). MR images obtained at 81 MHz using spin echo (SE) sequences, which unlike the in vitro approach allowed discrimination between white and gray matter areas, revealed an absence of gray-white matter contrast in the brains of mutant mice, consistent with longer than normal relaxation of the myelin-deficient white matter. While larger tissue water components such as those present in the immature brain and edematous white matter contribute a greater effect, myelin and its associated bound water may still play an important role in the MR characterization of normal gray and white matter.

• When the spinal motoneurons innervating the external sphincter of the urethra cannot be inhibited voluntarily due to lesions of the spinal cord, the normal capacity to relax this physiologic valve during micturition is lost. Even if contractions of the bladder occur, urinary outflow may be completely blocked at the sphincter, leading to distention of the bladder and the risk of urinary infection. A method is described for controllably relaxing the sphincter, which permits free outflow of urine in paraplegic cats. One pudendal nerve is sectioned, paralyzing half of the sphincter, but leaving the experimental animals entirely continent. The motoneurons supplying the other half of the sphincter are inhibited by means of spinal reflexes, eliminating active resistance to urethral flow. The simplicity of this approach suggests that it may prove equally effective in human paraplegia.

In paraplegics and quadriplegics a profound paralysis of skeletal muscles occurs below the level of the spinal lesion. Unexplained in this state is the development of an overactive external urethral sphincter, which interferes with emptying of the bladder and may lead to infection of the urinary tract. Studies of cats show that the discharge of motoneurons causing this contraction has all the characteristics of a flexor reflex.

In this paper we present our experience with an Image Guided Neurosurgery Grid-enabled Software Environment (IGNS-GSE) which integrates real-time acquisition of intraoperative Magnetic Resonance Imaging (IMRI) with the preoperative MRI, fMRI, and DT-MRI data. We describe our distributed implementation of a non-rigid image registration method which can be executed over the Grid. Previously, non-rigid registration algorithms which use landmark tracking across the entire brain volume were considered not practical because of the high computational demands. The IGNS-GSE, for the first time ever in clinical practice, alleviated this restriction. We show that we can compute and present enhanced MR images to neurosurgeons during the tumor resection within minutes after IMRI acquisition. For the last 12 months this software system is used routinely (on average once a month) for clinical studies at Brigham and Women's Hospital in Boston, MA. Based on the analysis of the registration results, we also present future directions which will take advantage of the vast resources of the Grid to improve the accuracy of the method in places of the brain where precision is critical for the neurosurgeons.

Periventricular leukomalacia (PVL), the principal form of brain injury in the premature infant, is characterized by overt focal necrotic lesions in periventricular white matter and less prominent, more diffuse cerebral white matter injury. The early detection of the latter, diffuse component of PVL is not consistently possible with conventional brain imaging techniques. We demonstrate the early detection of the diffuse component of PVL by diffusion-weighted magnetic resonance imaging (DWI). In a premature infant with no definite cerebral abnormality detectable by cranial ultrasonography or conventional magnetic resonance imaging, DWI showed a striking bilateral decrease in water diffusion in cerebral white matter. The DWI abnormality (ie, decreased apparent diffusion coefficient) was similar to that observed with acute cerebral ischemic lesions in adults. At 10 weeks of age, conventional magnetic resonance imaging and ultrasonography showed striking changes consistent with PVL, including the presence of small cysts. The observations indicate the importance of DWI in the early identification of the diffuse component of PVL and also perhaps the role of ischemia in the pathogenesis of the lesion.

Using a rapid Fourier SSFP imaging technique, which is sensitive to slow flow (approximately 1 mm/sec) in the plane of the image, we obtained 135 brain MRI examinations. The CSF flow/motion patterns were mapped by two images with orthogonal in plane flow sensitivity directions. Analysis showed significant deviations from the "normal" pattern in ventricular enlargements because of obstruction (no evidence of CSF flow/motion) or in normal pressure hydrocephalus (complex, intensive flow pattern in lateral ventricles) suggesting a diagnostic potential for this fast imaging technique.

Currently, thermal ablation via transcranial MRI-guided focused ultrasound is restricted to centrally-located regions in the brain. This limitation is the result of skull heating when the focal region is steered to more peripheral regions in the brain, along with other factors such as limitations in beam steering in the currently-available clinical brain focused ultrasound systems. The treatment envelope could be expanded if the time averaged acoustic power needed for ablation could be reduced.

Background MRI produces images that serve as luminal, edema, & scar maps to assist in the Electrophysiological (EP) treatment of ventricular and atrial arrhythmias [1]. Until MR-compatible EP devices are widely available, there will be an eed to perform EP partially in the MRI for imaging, and partially outside the MRI for ablation, puncture & navigation. An MR-conditional voltage-based Electroanatomic Mapping (EAM) system would allow MR-guided EP in MRI & registration-free EP to be performed outside the MRI during X-ray, Intra-Cardiac-Echo (ICE) or EAM guidance. Previously a 1.5T MR-conditional St. Jude Medical EnSite Velocity (Velocity) voltage-based EAM system was presented [2]. The study objective was to conduct a multicatheter registration free EAM (localization & intracardiac Electrogram (EGM) measurement) both in & outside of the MRI. Methods